t I t 3% ““2" 3, "I! ‘. . Kr, 5—- I P '- ut (r - :3 a!“ z: w..- '4‘ U 14; f :2» V o 3;: ".2 1&1 1 ., a IOU." U... 3..“ ... fa JV .4: tn 2!: In In “’1. 'J V o .- KI? v“... 5 Lg ‘. ‘13.’~ , ‘, .0 L3 3 \( .1 b. Agnew 34... J4‘..& EFFECT OF SELECTED TREATMENTS ON QUALITY AND STORAGE STABILITY OF FROZEN MUSHROOMS By \ { ‘-.. 3"}. x - \' Joseph E? Skwara A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Food Science 1970 ABSTRACT EFFECT OF SELECTED TREATMENTS ON QUALITY AND STORAGE STABILITY OF FROZEN MUSHROOMS by Joseph E. Skwara Whole and sliced mushrooms were frozen after being treated with various chemicals or by blanching to prevent quality deterioration, especially discoloration, in storage. Treatments, consisting of exposing the mushrooms to $02 gas, followed by dips in chemical solutions containing either sodium chloride, ascorbic acid or a combination of sodium acid pyrophosphate and disodium ethylenediaminetetraacetate provided better colored mush- rooms than those involving blanching or treatment with 802 alone. Dip treatments, alone, were unsuccessful in preventing dis- coloration during frozen storage. Sodium bisulfite, ascorbic acid, citric acid, sodium chloride, sodium acid pyrophosphate, sodium tri- polyphosphate, disodium ethylenediaminetetraacetate and histidine and combinations of these chemicals were tested. Vacuum impregnation with chemical solutions prior to freezing and also dehydrofreezing were unsuccessful. Methods for analyzing for 802 and for determining color were developed. ii ACKNOWLEDGEMENTS The author is appreciative of the assistance and suggestions of his major professor, Dr. Theodore Wishnetsky during the course of this work. The author also wishes to acknowledge the assistance of Professor Clifford L. Bedford and Professor Robert C. Herner in this project. Many others in the Michigan State University Food Science Department gave freely of their time and assistance. The author wishes to express appreciation to all those who assisted. iii TABLE OF CONTENTS ABSTRACT . . . . . . . . . . . . . . . . . ACKNOWLEDGEMENTS . . . . . . . . . . . . . LIST OF TABLES . . . . . . . . . . . . . . LIST OF FIGURES . . . . . . . . . . . . INTRODUCTION . . . . . . . . . . . . . . REVIEW OF LITERATURE . . . . . . . . . . . METHODS AND MATERIALS . . . . . . . . . . Mushrooms . . . . . . . . . . . . . . . Processing Procedures and Equipment . . Test Series I . . . . . . . . . . . . Test Series II . . . . . . . . . . . . Test Series III . . . . . . . . . . . Test Series IV . . . . . . . . . . . . Test Series V . . . . . . . . . . . . Test Series VI . . . . . . . . . . . . Physical and Chemical Evaluation . . . . Sensory Evaluation . . . . . . . . . . Statistical Analysis of Test Results . RESULTS AND DISCUSSION . . . . . . . . . . Analytical Procedures . . . . . . . . . Test Series I . . . . . . . . . . . . Test Series II . . . . . . . . . . . . Test Series III . . . . . . . . . . . Test Series IV . . . . . . . . . . . . Test Series V . . . . . . . . . . . . Test Series VI . . . . . . . . . . . . iv Page ii iii vi ix 0‘ mJ-‘KDOONG FJFJ 19 22 24 26 26 30 32 36 37 44 59 TABLE OF CONTENTS (CON'T.) Page SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . 63 APPENDIX 0 O 0 O 0 O O O 0 I 0 O I O O O O O 0 O O O O O 66 REFERENCES 0 O O O O O O O O I O O I O O O O O O O O O O O 67 LIST OF TABLES Table Page 1. Chemical Dip and Spray Treatments Used to Inhibit Discoloration in Frozen Mushrooms . . . . . lO 2. Effect of Mushroom Size and Sample Position on Hunter Color Measurements . . . . . . . . . . . . . 27 3. Comparison of Hunter Color Values of Standard Tiles Measured With and Without Mushroom Plate and TrYCite C I O C C O O O I O O O O O O O O 28 4. Mean Hedonic Score of Color Panel and Corresponding Hunter Color Values for Frozen Whole Mushrooms . . 29 5. Test to Determine PrOper Amount of Buffer for Use in SO2 Determination . . . . . . . . . . . 31 6. Determination of Accuracy of Modified Ponting Method for $02 Determination . . . . . . . . . . . 31 7. Test Series I. Chemical Dip Treatments Used to Inhibit Discoloration in Frozen Mushrooms. Color Rank and Quality Observations After One Week at "LT" Storage . . . . . . . . . . . . . . . 33 8. Test Series II. Color Evaluation of Dip and Spray Treated Frozen Mushrooms After Two and Eight Weeks of "LT" Storage . . . . . . . . . . . . . . . 35 9. Test Series III. Effect of Vacuum Impregnation Procedure on Weight Gain in Mushrooms . . . . . . . 38 10. Test Series IV. Treatment of Mushrooms with Sulfur Dioxide. Test Variables and Residual Sulfur Dioxide in Frozen Mushrooms . . . . . . . . 39 11. Test Series IV. Taste Panel Results. Preference Tests Between Samples With and Without Added 802 o o o ‘0 o o o o o o o o o o o o o o o o o o o o 41 12. Test Series IV. Hunter Color Measurements and Color Rating of Mushrooms Stored 16 Days Under "HT" Conditions After Pre-Freezing Treatments with Sulfur Dioxide in Conjunction with Various Chemical Dips . . . . . . . . . . . . . . . 42 vi LIST OF TABLES (CONT.) Table Page 13. Comparison of 802 Levels in Frozen and Sauteed Whole Mushrooms . . . . . . . . . . . . . . 43 14. Test Series V. Hedonic Color Scores for Frozen Sliced Mushrooms After Storage Intervals of 15, 35, and 61 Days Under Both "LT" and "HT" Storage Conditions . . . . . . . . . 45 15. Test Series V. Hedonic Color Score Equivalents After Various Storage Intervals for Mushrooms PaCked 3-5-70 and 3—17-70 0 o o o o o o o o o o o o 46 16. Test Series V. Significance of Differences in Color Panel Hedonic Ratings of Whole Mushrooms . . 47 17. Test Series V. Hunter Color Values After Various Storage Intervals for Whole MUShrOOUlS PaCked 3-5-70 0 o o o o o o o o o o o_ o o 48 18. Test Series V. Hunter Color Values After Various Storage Intervals for Whole Mushrooms Packed 3-17-70 . . . . . . . . . . . . . 49 19. Test Series V. 802 Residue (ppm) in Frozen Whole Mushrooms After Various Storage Intervals C O O O O O O O C O O O C O O O O O O O I 52 20. Test Series V. 802 Residue (ppm) in Frozen Sliced Mushrooms After Various Storage Intervals . . . . . 53 21. Test Series V. Texture Preference Tests for Blanched vs. Unblanched Mushrooms and for "Freon" 12 vs. Air Blast Frozen Mushrooms Packed 3-5-70 . . . . . . . . . . . . . . . . . . . 55 22. Test Series V. Hedonic Flavor Scores for Whole Mushrooms Packed March 5, 1970 and Held Under "LT" Storage Conditions . . . . . . . . . . . . . . 56 23. Test Series V. Hedonic Flavor Scores for Frozen Sliced Mushrooms After 15 and 61 Days Storage Under "LT" Conditions . . . . . . . . . . . . . . . 56 vii LIST OF TABLES (CONT.) Table Page 24. Test Series V. Weight Change in Whole Mushrooms Frozen in "Freon" 12 and in air . . . . . . . . . . 57 25. Test Series V. Weight Change in Sliced, "Freon" 12 - Frozen Mushrooms . . . . . . . . . . . . . . . 58 26. Test Series V. pH Values for Frozen Whole Mushrooms After Various Storage Intervals . . . . . 6O 27. Test Series V. pH Values for Frozen Sliced Mushrooms After Various Storage Intervals (Values Represent Data from Individual Samples . . . . . . . . . . . . . . . . . . . . . . 61 28. Test Series VI. Rehydration Rates for Dehydro- frozen Mushrooms . . . . . . . . . . . . . . . . . 61 viii LIST OF FIGURES Figure l DuPont Laboratory Scale "Freon" Food Freezant System . . . . . . . . . . . . . . . 2 Plate and Setup for Hunter Color Measurements of Frozen Mushrooms . . . . . . . . . 3 Whole Frozen Mushrooms (Packed 3—5-70) after 100 Days Storage at -10 F . . . . . . 4 Whole Frozen Mushrooms (Packed 3-17-70) after 88 Days Storage at -10 F . . . . . . . . . . . ix INTRODUCTION Fresh mushrooms are an extremely perishable commodity. They retain prime quality for only five days at 32 F, three days at 40 F, or one day at 50 F according to Handbook 66 of the U.S. Department of Agriculture (Wright, 1966). Tomkins (1966) reported that mushrooms held in cold storage must be handled with special care, and even so could often be identified as having been cold stored because of the con— spicuousness of bruises when brought out and held at warmer temperatures. Mushroom surfaces darken during storage, especially if handled roughly; caps open and gills become dark brown. If held dry, mushrooms wilt with consequent moisture and weight loss. If held under damp conditions, mushrooms become slimy. Because of the short shelf life of fresh mush- rooms, high quality frozen mushrooms could provide significant benefits in terms of reduced spoilage losses, greater convenience, and more consistent quality. The purpose of this research was to determine the effects of selected treatments on color and other quality factors in frozen mush- rooms and to determine the relative effectiveness of the various treatments in retarding quality loss during frozen storage. REVIEW OF LITERATURE Mushrooms frozen without blanching or other enzyme-inhibiting treatment retain their color for about one month, after which the tissue becomes very dark (Lambert, 1963). Factors such as storage temperature and packaging could cause the rate of color degradation to vary. Poly- phenolase is the enzyme primarily responsible for the discoloration (Reed, 1966). It catalyzes the oxidation of O-dihydroxy phenolic compounds such as catechol and caffeic acid, which are present in plant tissue in trace amounts. Ortho quinones are formed which in turn are oxidized and polymerize to form pigmented melanins. Normal procedure for the prevention of enzymatic activity in fruits and vegetables is to blanch them in either steam or hot water prior to freezing. Minimum steam blanch to inactivate enzymes com- pletely in mushrooms ranges from four minutes for small mushrooms to five and one-half minutes for large ones (McArdle and Curwen, 1962) with resultant shrinkage of 20 to 25 percent because of the loss of moisture and some soluble solids. This shrinkage data is consistent with that of other researchers. Feinberg, g£_§1,, (1968) report losses of up to 30% by weight and Hale and Tressler (1969) state that weight loss caused by blanching ranges from 15 to 35 percent. An alternative to blanching is the inhibition of enzyme catalyzed discoloration by the use of chemical additives. Various types of chemical agents have been shown to have an effect on polyphenolase. Knapp (1965) inhibited extracted eggplant polyphenolase, which is a copper-containing enzyme, with copper-chelating agents l-phenyl 2-thiourea or diethyldithiocarbamate and to a lesser extent with chloride ions using sodium or potassium chloride. Embs and Markakis (1965) found that sulfur dioxide reduces the ability of mushroom polyphenolase to cause browning by combining with ortho-quinones and preventing their polymerization to melanins. Sulfur dioxide has been used in food preservation since ancient times (Joslyn and Braverman, 1954) as a chemical preservative to prevent spoilage by micro-organisms, as an antioxidant and as an inhibitor of enzyme- catalyzed browning and non-enzymatic browning. Ascorbic acid has been used widely as an antioxidant to inhibit browning (Johnson and Guadagni, 1949; Sutton and Lauck, 1967). Ascorbic acid is oxidized by ortho quinones and in turn reduces them to ortho dihydroxyphenols. Bedrosian, g£_§1,, (1959, 1960) found that borate forms a complex with the substrate, preventing oxidation, and also that borate acts synergistically with disodium phosphate, sodium chloride and sulfur dioxide to inhibit discoloration. Smith and Davis (1961), working with potatoes, and Hoover (1964) with sweet potatoes, used sodium acid pyrophosphate (SAPP) to prevent discoloration caused by the reaction of O-dihydroxyphenols with ferrous iron. Ethylenediaminetetraacetic acid (EDTA) has also been widely used to prevent discoloration in foods (Furia, 1964). Techniques for the application of chemical additives to food pro- ducts for the prevention of discoloration have been studied extensively. Guadagni (1949) prevented the browning of fruits by adding sugar syrup with ascorbic acid to the fruit by a vacuum-impregnation process and found that the flavor and texture were better than when blanched or sulfite dipped. Makower and Schwimmer (1956) patented a process for inhibiting browning of plant tissue by adding adenosine triphosphate solution and then subjecting the product and solution to a vacuum to draw out gasses and facilitate penetration of the solution. Bedrosian, .EE.§£-’ (1959) used a vacuum impregnation technique for the addition of borates and other chemicals to apples. Colby (1966) inhibited enzyme activity in fruits which would subsequently be canned by evacuating oxygen from the fruit in a vacuum and infusing the cavities with liquid. Sodium chloride, citric acid and tartaric acid were claimed to be helpful in preventing browning. Working with products in aqueous alkaline solutions, both in vacuum and under atmospheric pressure, Finkle (1964) applied the enzyme o-methyltransferase to convert ortho-hydroxyl groups to methoxy groups and thus prevent reaction with polyphenolase. Duggan and Byrne (1967), Molsberry (1966) and Hale and Tressler (1969) have patents dealing specifically with the preservation of color in frozen mushrooms. Duggan and Byrne's procedure consists of dipping mushrooms in a solution containing sodium bisulfite, citric acid and salt together with a partial blanch before freezing. They claimed a weight loss of only 10 percent by this method. Molsberry treated sliced mushrooms with a "sealer" solution containing sodium sulfate, disodium phosphate and sodium metabisulfite and then with a "bleaching" solution containing sodium sulfate, sodium chloride and sodium metabisulfite. He claimed a weight increase of 15 to 20 percent during processing. Hale and Tressler applied gaseous mixtures containing sulfur dioxide to mushrooms, either in a closed container at atmospheric pressure or under a slight vacuum. Another approach to freezing preservation which has been applied successfully to various fruits and vegetables including apples, peas, potatoes, pimentos, cherries and apricots is dehydrofreezing (Lazar, 1968). This process, which is a combination of dehydration and freezing has several advantages over freezing in that volume and weight can be reduced to 50% or less of normal frozen food with minimal loss of "frozen food" quality. Quality loss is held to a minimum because the product is only partially dried. Drying normally takes part in two cycles. In the "rapid cycle" 90% of water normally removed in dehydration is evaporated rapidly. Advantage is taken of this in dehydrofreezing. Drying is stOpped before it enters the second or slow cycle where most deteriorative reactions occur during drying. Except for the drying step, products are treated in the same manner as for freezing which includes enzyme inactivation by blanching or with additives such as 802. Most dehydrofrozen products are presently used in the institutional and remanufacturing trades. METHODS AND MATERIALS Mushrooms The mushrooms used for these experiments comprised a white strain of Agaricus bisporus. Field-run, fresh mushrooms were ob- tained from the Great Lakes Mushroom Co-operative, Warren, Michigan. They were either delivered to Michigan State University Stores or obtained directly from Great Lakes Mushroom Co-operative's storage facilities in Warren on the day they were to be processed. Processing Procedures and Equipment Test Series I.—-Treatment of mushrooms with chemical dips prior to freezing to inhibit enzymatic discoloration. Field run mushrooms were used for this experiment without size grading. However, broken and otherwise defective mushrooms were re- moved. The treatments in Test Series I consisted basically of five steps. 1. A two pound batch of mushrooms was washed in cold tap water (approximately 60 F0 with slight hand agitation for one minute to remove surface dirt and any other extraneous material. 2. It was dipped in one of the solutions listed in Table 7 for the indicated length of time. Additional details con- cerning the treatments, most of which were deveIOped em- pirically, are listed in Table 7. 6 3. The batch was drained for 10 minutes on a 12 x 24 inch, perforated stainless steel tray. 4. The mushrooms were Individually Quick Frozen (IQF) on the same trays for 45 minutes in a Puffer—Hubbard (Model No. SSA.F.15.1.SC) circulating air freezer set at ~30 F. 5. The frozen mushrooms were packaged in one pound portions in Saran bags for color evaluation after one and five weeks storage. The storage facility, which was also the primary storage facility for later test series, was a Chrysler and Koppin Walk-in air blast freezer. The temperature in this freezer gradually and cyclically fluctuated between -9 F and -15 F (32 minutes from -9 to —15 F and 20 minutes back to —9 F). This storage condition will hereafter be designated as "LT" (for Lower Temperature). "HT" (Higher Temperature) storage, also used for subsequent test series, comprised a Puffer-Hubbard circulating air freezer (Model No. F.235.1.P) at O F. The automatic defrosting system in this unit twice daily brought the temperature to a peak of about 15 F approximately ten minutes after the start of the defrost cycle after which it took an hour to return to 0 F. This freezer was also used for storage of non—mushroom test materials which resulted in frequent door openings and consequently, greater temperature fluctuations then indicated above. Test Series II.--Treatment of mushrooms to inhibit discoloration with chemical dips prior to freezing and chemical glazes after freezing. Mushrooms used for test series II were not size graded but had broken and defective pieces removed. One-pound batches were washed and dipped in the same manner as test series I. The treatments are listed in Table 1. To glaze samples after freezing, when this was done, a solution, propelled by dichlorodifluoromethane in a Crown Spra- Tool Power Pak container, was sprayed for 10 seconds over the mushroom surfaces before packaging in Saran bags. Freezing for this experiment was done in an Air Products and Chemicals Cryo-Test Chamber (Model No. CT—l818 -12 F) set at ~100 F with a fan speed setting of "30". Freezing was accomplished by holding the mushrooms in the chamber on a wire mesh screen for approximately 10 minutes under the above conditions of exposure to liquid nitrogen vapors. Test Series III.--Inhibition of color changes in frozen mush— rooms through vacuum impregnation with chemical solutions prior to freezing. Mushrooms with diameters ranging from 1-1/4 to 1-1/2 inches were used for this study. They were washed in tap water for thirty seconds to remove dirt and other extraneous material and then washed for two minutes in a solution of 0.7% sodium bisulfite, 0.5% citric acid and 0.5% ascorbic acid. Approximately one-half pound samples were placed under a ceramic plate in a desiccator (250 mm.i.d., Arthur H. Thomas no. 4440) and held under a 26 to 29 inch vacuum for 30 minutes. The vacuum equipment consisted of a Cenco Pressurevac 4 Pump powered by a 1/3 H.P. electric motor attached to the desiccator. Six tests were performed and the vacuum was released in each test with one of the solutions listed below. Solution: 1 Distilled Water (Control) 2 1% Sodium Chloride 3 2% II II 4 0.2% citric acid, 0.2% ascorbic acid, 0.05% sodium bisulfite 5 0.5% sodium acid perphosphate 6 0.2% H II II The mushrooms were held in solution for ten additional minutes and then drained for two minutes on an 8-mesh screen before freezing. A DuPont Laboratory Freezer which is depicted in Figure l was used to freeze the mushrooms for these tests. "Freon" ll (trichloromonofluoromethane) and dry ice in the outer jacket provided refrigeration to keep the "Freon" 12 (Food-grade dichlorodiflouromethane) in the central chamber at approximately -108 F. Temperature of the "Freon" 12 could be adjusted between -22 F and -108 F by immersing a container of heated water directly into the "Freon" 12. The samples were frozen at -108 F in the initial vacuum im- pregnation tests. Because of this extreme temperature, a technique of dipping the mushrooms in and out for ten second intervals for a total of 60 seconds of immersion time was used rather than uninterrupted immersion. It must be noted that the mushrooms cracked badly even using this technique. This cracking also occurred in later tests with sol- ution-impregnated mushrooms when the "Freon" temperature was brought up to —30 F- After freezing, the mushrooms were packaged in polyethylene bags and held in "LT" storage conditions for examination in 30 days. Test Series IV.--Su1fur dioxide treatment of mushrooms prior to freezing. um. (I). N Table 1 Test Series 11. Chemical Dip and Spray Treatments Used to Inhibit Discoloration in Frozen Mushrooms Chemicals Solution Concentration (%) No. Dip Spray Chemical 1 0.18 0.36 SOdium bisulfite 2 3.0 6.0 Sodium chloride 3 0.5 1.0 Citric acid 4 0.3 0.6 Ascorbic acid 5 0.2 0.4 Disodium ethylenediaminetetraacetate(EDTA- -Na 2) 6 3.0 6.0 Sodium tripolyphosphate (STPP) 7 3.0 6.0 Sodium aCid pyrophosphate(SAPP) Treatment No. Dip Solution Spray Solution 1 Control --- --— 2 1 ——— 3 1,2 --- 4 1,2,4 ___ 5 1,3,4 --- 6 l,2,3,4 --- 7 1,3 4 8 1,2 4 9 1,2,3 4 10 1,5 --- 11 1,6 5 12 l 6 13 1,5 6 l4 1,5,6 --- 15 1,5,7 --- 16 1,4,5 --- 17 1,4 5 l8 1,4,6 ——- 19 1,4,7 —-- 20 1,4 2,5 6 21 1,4 --- 22 1,7 --- 10 -o ." A?" — — - — — -..- I w 0 Q a. ..‘-.‘-..="~:: v' Eur,.. Entire Freezer Freezing Chamber Freezer Basket FREEZING CHAMBER (contains "Freon" 12) OUTER JACKET (contains "Freon" 11 and dry ice) INSULATION .3: {-2‘ - . 4' . o , . 0. , g o O-0 ‘ l -- I mens ons *-~- “ Di 1 ’. 0"va V’Q4 ‘h’d’i'44‘P‘F‘QbN‘5“ Height Diameter A‘Ag‘,... ‘ 31" 23" FREEZER BASKET 24" 13" 4" 11" Figure l DuPont Laboratory Scale "Freon" Food Freezant System (Not to Scale) 11 12 The initial test in this test Series was designed to determine if sulfur dioxide could be effectively applied to mushrooms and if it would be of practical value in inhibiting discoloration. Field-run mushrooms were divided into three lots after having first been washed in tap water at approximately 60 F for two minutes to remove debris and dirt. These lots were to be subjected to a vacuum broken with sulfur dioxide after having been given one of the following treatments: 1. Control. No treatment. 2. One and one-half minute soak with slight agitation in a solution containing 0.18% sodium bisulfite and 1% sodium chloride (Goodman, 1967). 3. One and one-half minute soak with agitation in a solution containing 0.18% sodium bisulfite and 0.5% citric acid. For the sulfur dioxide treatments, lOO-gram batches were vacuum- impregnated with the same equipment used in test series III. Sulfur dioxide was introduced into the desiccator, by weight, from a one pound lecture bottle of anhydrous sulfur dioxide mounted in a Mettler balance. Treatments, listed in Table 10 ranged from 28 inches of vacuum broken with 60 grams of sulfur dioxide to no vacuum with the addition of one gram of sulfur dioxide. These mushrooms were all frozen by immersion in "Freon” 12 at approximately -30 F for 90 seconds as recommended by Armstrong (1967). This same freezing procedure was used for the second and third groups of tests in this test series. The mushrooms were held in "HT" storage in Saran bags and tested for sulfur dioxide content within a few days after processing. 13 A second group of tests was conducted to determine if any of the chemicals used previously in conjunction with sodium bisulfite would react synergistically with sulfur dioxide and thereby allow lower concentrations of sulfur dioxide to be used. For these treatments, 100 gram samples of mushrooms in a desiccator at atmospheric pressure were subjected to one gram of sulfur dioxide and held for two minutes. The samples were then immersed, with slight agitation, in chemical solutions prior to being frozen in "Freon" 12. The solutions contained sodium chloride, SAPP, EDTA-Naz, ascorbic acid, citric acid and histidine. Combinations used are listed in Table 12. The tests were repeated with the dip treatment preceding the gas treatment. A third group of tests in test series IV was conducted to ascertain the approximate level of SO2 gas that would be feasible from a standpoint of flavor acceptability. For this test, SO gas was 2 weighed into a 65-1iter, closed, Nalgene (polyethylene) container holding two pounds of mushrooms. Mushrooms within the container were held in approximately two inch layers on each of two screens (one pound per screen) to allow for circulation of the sulfur dioxide. Four lots were processed. They consisted of a control without 802 and lots with 1, 1-1/2, and 2 grams of 802, respectively. Mushrooms were held in the 802 atmosphere three minutes, immersed in water for one minute and frozen in "Freon" 12. A flavor panel was conducted after 12 days of "LT" storage comparing the control and the lot to which one gram of 802 had been added. The other lots had levels of $02 which were obviously too high and were not flavor tested. 14 Test Series V.—-Storage stability of sliced and whole mushrooms treated with sulfur dioxide and other chemicals. A test consisting of three lots of sliced mushrooms and duplicate tests, each consisting of nine lots of whole mushrooms, were conducted so that the effects of storage could be observed on the quality of mushrooms treated with sulfur dioxide. Field-run mushrooms (not size-graded) were used for this test series. Sliced mushrooms, designated lots 1, 2 and 3 were treated on February 26, 1970 as follows: Lot 1. 25 lbs. of mushrooms in 2-lb. lots were immersed in tap water with agitation for 2 minutes, sliced by hand and immersed in "Freon" 12 at approximately - 30 F for 45 seconds. The entire 25 lbs. in a large Saran bag were stored in a freezer ("LT") overnight. Lot 2. This lot, also consisting of 25 lbs. of mushrooms, was treated in two pound portions according to the method described in Molsberry's patent (1967). l. Mushrooms were dipped in a "sealer" solution and left in the solution for one-and-one-half minutes. The solution consisted of a mixture of anhydrous sodium sulfate (27.5 parts by weight), anhydrous disodium phosphate (25.8 parts by weight) and sodium metabisulfite (45.7 parts by weight) diluted at a ratio of 1-1/2 ounces to 6 gallons of water. 2. They were then dipped in a "bleaching" solution and held in the solution four minutes. The "bleaching" 15 solution contained a mixture of anhydrous sodium sulfate (27.3 parts by weight), sodium chloride (29.0 parts by weight) and sodium metabisulfite (41.7 parts by weight), diluted at a ratio of 3 ounces per 6 gallons of water. 3. The mushrooms were sliced by hand. (Approximately 1/8 to 3/16 inch thick slices) 4. The dip in "sealer" solution was repeated with the sliced mushrooms. 5. The dip in "bleaching" solution was repeated. 6. The sliced mushrooms were frozen and packaged in the same manner as Lot 1. Lot 3. Twenty five pounds of mushrooms in two-pound portions in a closed, Nalgene container at atmospheric pressure were exposed to air containing 0.5% sulfur dioxide by volume (1 gram SO2 per 65 liters air) for three minutes, sliced, immersed for four minutes in a solution con- taining 0.5% sodium chloride and 0.09% sodium bisulfite, and then frozen and packaged as described for Lot 1. All three lots were weighed before being treated and after being frozen. The following day all of the mushrooms in Lots 1, 2 and 3 were vacuum packed in half-pound portions in 7 x 8 inch pouches of Mylar-Saran- polyethylene laminate (IKD All-Vac #13). Vacuum was drawn for ten seconds and the bags were heat sealed with a Kenfield, Model C-l4, l6 Vacuum Sealer. Samples of each lot were stored under "LT" storage conditions for periodic color, flavor, 802 and pH checks and also under "HT" storage conditions for periodic color checks. Whole mushrooms, designated lots A, B, C, D, E, F, G, H, and J, were treated on March 5, 1970 in two pound portions, as follows: Lot A, the control was washed in water for two minutes, drained two to five minutes and frozen for 90 seconds in "Freon" 12 at approxi- mately -30 F. Lots B through J were also frozen by this same method. Lot B was washed two minutes, steam blanched for three minutes, cooled with a water spray one minute and frozen. Lot C was treated by the method of Duggan's patent (1966). The mushrooms were washed in water for two minutes and then dipped for two minutes in a solution containing 0.75% sodium bisulfite, 4.4% sodium chloride and 0.75% citric acid. This was followed by steam blanching for 2-1/2 minutes, cooling with a water spray for one minute, dipping in the aforementioned solution for two minutes, draining for 15 minutes on a perforated tray and freezing. Lot D in a closed Nalgene container at atmospheric pressure was subjected to air containing 0.5% (by volume) of 802 for three minutes, washed two minutes with water, drained two to five minutes, and frozen. Lots E and F were essentially similar to D except that they were washed in 2% sodium chloride solution rather than water. Lot F was individually quick frozen in the Chrysler and Koppin walk-in freezer at -10 F to check differences between air and "Freon" 12 freezing methods. G, H, and J were also essentially like D, except for variations in the composition of the wash solution. C was washed in 0.5% ascorbic acid 17 solution, H in a mixture of 0.5% ascorbic acid and 2% sodium chloride solution and J in a mixture of 0.2% EDTA-Na2 and 0.5% SAPP solution. The SO2 concentration was increased to 0.75% for G, H and J because of the observation that treatments D, E and F were not being adequately bleached.' These processing variables are summarized in Table 15. Most mushrooms in this test series were packaged in one pound portions in Saran bags and stored under "LT" conditions for flavor, texture, and pH tests. Enough samples of 1 to 1-1/4 inch diameter mushrooms for periodic color tests and SO determinations were vacuum packaged 2 (nine mushrooms per package) as described for the sliced mushrooms in this experiment. Mushrooms were weighed before the start of each treatment and after freezing. Because of the necessity of changing sulfur dioxide level midway through this test a second set of samples was processed twelve - days later (March 17, 1970) for color, 802 and pH tests. Lots D through J were subjected to air containing 0.5% (by volume) of sulfur dioxide for three minutes. These were vacuum packed in the manner previously described for sliced mushrooms. All of the whole mushrooms in this test series (both dates of pack) were originally stored under "LT" conditions. Twenty-seven days after the first pack (15 days after the second) a portion of all of the samples packed for color tests were moved to "HT" storage conditions for further comparisons. These are referred to as "LT-HT" stored samples. 18 Test Series VI.--Dehydrofreezing mushrooms. The mushrooms for this experiment were divided for processing into two lots on the basis of visual estimates of size ("large" and "small"). Twenty-five mushrooms of each lot were measured for cap diameter (in l/l6” increments) with the following results. Small Large Diameter(inches) _No. Diameter NO 1-7/16 1 1-15/16 1 1-6/16 4 1-14/16 0 1-5/16 3 1-13/16 l 1-4/16 5 1-12/16 2 1-3/16 2 1-11/16 l 1-2/16 l 1-10/16 3 1+1/16 2 1- 9/16 4 1 3 1- 8/16 4 15/16 2 1- 7/16 6 14/16 _35_ 1- 6/16 _;3_ Avg. diameter 1-3/16 in. 1- 9/16 in. Avg. weight 0.29 oz. 0.55 oz. The large and small mushrooms were each divided into two portions. One of the two portions was washed for five minutes in a solution con- taining 0.9% sodium bisulfite. The second portion of each was blanched for three minutes in steam. The samples were placed on 19 x 30 inch perforated stainless steel trays and dried in a Proctor and Schwartz Cabinet Dehydrator at 150 F. The trays were removed every ten minutes for weighing and rotating in the dehydrator. The mushrooms were dried until they had lost approximately 50 percent of their original weight. After two days of storage at ~10 F rehydration studies were made on the dehydrofrozen mushrooms by immersing 100 to 200 gram samples in approximately one liter of 70 F to 150 F water for from 1 to 12 hours. 19 Physical and Chemical Evaluagion pH: pH determinations were made with a Beckman Zeromatic pH meter. The mushrooms were blended with distilled water (2 parts mushrooms to 1 part water) for approximately two minutes in a Waring Blendor. The blended material was filtered through a milk filter disc and pH measurements were made on the filtrate. This procedure was necessitated by the difficulty in blending mushrooms without the use of water. Color: Color of the frozen whole mushrooms was determined objectively with a Hunterlab D-25 L Color Difference Meter and corre— lated with subjective ratings of a panel of judges. Frozen sliced mushrooms were rated subjectively only. For color measurements, a metal plate consisting of nine 7/8 -inch-diameter holes to accommodate nine mushrooms, was placed over the Color Difference Meter aperture (Figure 2). This plate served to standardize the surface area being measured. Mushrooms were positioned over the holes of the plate. Because of the possibility of moisture from the frozen mushrooms dripping into the aperture, a two-mil-thick sheet of clear Trycite (polystyrene) was stretched across and taped over the aperture before the plate was placed over it. The recessed underside of a second adjoining plate between the mushroom plate and Trycite prevented the protruding mushrooms from coming into contact with the Trycite. The plate and sample were covered to negate the possible effects of extraneous light. After L, a, and b measurements were made, the plate was rotated horizontally 1800 and a second set of measurements were made. TOP VIEW 0 9‘0”““T It“ G G- l 1/16" thick with 9-7/8" Dia Holes. inn. 0 -— - ----- OO Masonite Plate l/8" thick with one 4" hole in center. . - .w SIDE VIEW r A! III. ! o.-. H r ! Hagu’ I it 1/16 Thick Metal Plate .1 : ---- 1/8 Thick Masonite Plate Clear Trycite Sheet 4" APERTURE. Color Difference Meter Wall 9 ( ———————— . - Light Source Figure 2 Plate and Setup for Hunter Color Measurements of Frozen Mushrooms (Not to Scale) 20 21 Test results obtained during develOpment of analytical tech- niques are discussed under "Results and Discussion". Sulfur dioxide content: The method of Ponting and Johnson (1945) was modified and used for the determination of sulfur dioxide. This method, originally developed for fruits is essentially as follows: 1. Blend in a Waring Blendor for five minutes: a. 100 grams of sample b. 10 ml of 0.5 M tartrate buffer at pH 4.5 (tartaric acid and sodium hydroxide) c. 490 ml of aqueous sodium chloride solution (20% by weight) 2. Filter through cotton milk filter disc 3. Pipette a 50 ml portion of filtrate into each of two 125-ml Erlenmeyer flasks. 4. Add 2 ml of l N sodium hydroxide to each 5. After approximately 30 sec., acidify each with 2 ml. of 6 N hydrochloric acid 6. Add 1 ml of 1% starch solution to one sample as an indicator for titration 7. Titrate one sample with standard 0.02 N iodine 8. Add 1 m1 of 40% formaldehyde to the second sample; hold for 10 minutes; add 1 ml Of 1% starch solution and titrate as above. This is a blank. Modifications in this original method were that 100 m1 of buffer éirnd 400 m1 of sodium chloride solution (25% by weight) were used for 22 blending to maintain the pH between 4 and 5. 0.005 N iodine solution was used instead of 0.02 N because of the low level of $02 present and 10 ml. of 1% starch was used in place of 1 ml to obtain a sharper endpoint. SO2 content (ppm) was calculated as follows: = (g, liquid in sample + 500) Total SO2 (ppm) (ml 12) x (N 12) x (640) x ( g sample ) Mushrooms were considered to have 90% moisture (Watt and Merrill, 1963), except when sauteed. Moisture content was then calculated on the basis of weight loss during cooking. SensorygEvaluation Sensory panels were conducted for the determination of accept- able SO2 levels in cooked mushrooms and their relationship to SO2 levels in the product before cooking, to determine the effects of frozen storage on flavor of sliced and whole frozen mushrooms, and to ascertain the effects of processing variables on textural quality. Color panels were conducted for the determination of the effects of storage and processing and storage variables on color of frozen sliced and whole mushrooms. Panels consisted of approximately twenty randomly-selected and untrained persons from the Food Science Department. Flavor and texture panels: Whole mushrooms (one pound samples) were placed in a very lightly buttered sauce pan (7-1/2 inch diameter x 3 inch height) and heated for five minutes, covered, using the "high" heat setting on a General Electric, Model P 7 electric range. Liquid 23 was drained off and the mushrooms were sauteed over medium heat with four tablespoons of butter for ten minutes. The mushrooms were stirred frequently and the saucepans were shifted between burners for uniformity of heating. Sliced mushrooms were prepared in the same manner as the whole mushrooms but were sauteed for only six to seven minutes. Samples were served warm by portioning them out as required for each panelist. Remaining mushrooms were kept over "low" heat until portioned out. Samples for flavor and texture evaluations were presented on round plates with both the plates and scorecards coded in random order. Red light was used in the taste panel room to partially offset the effects of color differences. For the one panel session conducted to determine the accept~ ability of a particular 502 level the panelists were presented with two samples, one treated with 802 and one that had not been. They were asked to state their flavor preference, after which they were asked if any off flavors were detected in either sample. To check the effect of storage on flavor, panelists were given either three samples of sliced mushrooms or four samples of whole mush- rooms at a session. They were requested to score each sample hedonically on a nine point scale with the following descriptions. Description Score Like extremely Like very much Like moderately Like slightly Neither like nor dislike Dislike slightly Dislike moderately Dislike very much Dislike extremely HNLAJ—I—‘MC‘NGDKO Comments were always solicited. 24 For texture preference panels, two samples were presented to each panelist and he was requested to state his preference. Color panels: Six samples of sliced frozen mushrooms or eighteen samples of whole frozen mushrooms were presented in random order to the panelists at a given session. Samples were set up in the following manner to prevent thawing. A one inch layer of crushed dry ice was placed in a stainless steel pan and covered with a sheet of pale grey cardboard. The frozen mushroom samples were transferred from the bags used for storage into 5-1/2 x 5-1/2-inch translucent plastic trays (Spectrum Weight Boats), which were placed on the cardboard. Six trays were placed in each pan. The pans were placed on a table in the center of the Food Science Department taste panel room (room 101). Normal fluorescent lights were used for illumination. The same hedonic rating scale used for flavor was used to evaluate color. Individual samples consisted of about 100 grams of sliced mushrooms or, in the case of whole mushrooms, nine stemmed whole mushrooms positioned with cap facing up. Hunter color measure- ments were made on the whole mushrooms immediately after the color panel evaluation was completed. Statistical Analysis of Test Results Significance of differences in scores of hedonically-rated samples were determined by analysis of variance of a randomized complete-block design with samples and judges as factors (Amerine, g£_§13, 1965) and by Duncan's Multiple Range Test (1965) wherever differences at the 5% level were found. 25 Chi2 values (Amerine, _£__1., 1965) were obtained to determine significance of preference test results. Simple linear regression equations and correlation coefficients (Amerine, g£_§i,, 1965) were determined to compare hedonic color ratings with Hunter L measurements and also in developing the Hunter color measurement procedure. Multiple linear regression and correlation coefficient analyses among hedonic color ratings and Hunter L, a and b measurements were made with a Mathatron 4280 desk tOp digital computer using the Banachiewicz-Cholesky-Crout method for solving simultaneous equations. (Mathatronic 4280 TD Tape Set Instructions). RESULTS AND DISCUSSION Analytical Procedures Color Measurement.--When the color of one—inch and one-and- three-quarter inch mushrooms from the same lot was measured, com- parable readings were obtained. There was no evidence that "pillowing" or the protrusion of mushrooms toward the aperture affected the readings as reported by Clydesdale and Francis (1969). Rotating the plate 1800 also did not significantly change the L, a and b values (Table 2). L, a and b values of standard tiles were significantly lower when placed on the mushroom plate over a sheet of Trycite (Table 3). There were high degrees of correlation between the readings and therefore the readings with the mushroom plate and Trycite can be corrected to compensate for their effects by the following equations, L' = 2.15 L - 16.6; a' = 2.32 a + 0.79; b' = 2.00 b + 0.39 where L, a and b denote readings with the plate and Trycite. Tristimulus values of the Hunter instrument showed a highly significant correlation with Hedonic color scores (Table 4). Test results indicate that practically all of the observable differences in mushroom color were covered by a measurement with the L scale. The b values contribute slightly to the color evaluation and the a 26 Table 2 Effect of Mushroom Size and Sample Position on Hunter Color Measurements Measurements First Second* Mushroom Mushroom Sub- Condition Diameter Sample L a b L a b Not frozen- 1ight color 1" 1 44.8 2.8 8.7 44.6 2.7 8.8 2 44.7 2.8 8.7 44 8 2.7 8.6 1-3/4" 1 44.5 2.8 8 8 44.8 2.6 8.7 2 44.5 2.6 8 6 44.7 2.7 8.6 Frozen- light color 1" 43.5 0.0 9.4 43.8 -0.1 9.3 1-3/4" 43 6 -001 9 5 4306 -001 903 dark color 1" 38.0 3.2 9.6 38.3 3.0 9.6 1—3/4" 38.2 3.2 9.5 38.3 3.3 9.6 * Second measurement was made after rotating plate 180°. 27 Table 3 Comparison of Hunter Color Values of Standard Tiles Measured With and Without Mushroom Plate and Trycite Hunter Color Values Without Plate and With Plate and Trycite Trycite Tile Color L' a' b' L a b White 94.8 -0.7 2.7 52.7 -O.3 1.5 Yellow 83.0 -3.7 26.4 46.4 -2.1 13.6 Pink 75.2 12.4 9.1 42.5 6.5 4.6 Blue 66.6 -5.1 -ll.7 37.9 -2.7 -5.8 Green 60.5 -l6.3 7.2 35.0 -8.0 3.5 Grey 22.6 -l.3 -l.0 18.6 -0.4 -0.5 Red 24.8 26.2 13.0 19.4 9.3 4.2 Black* 20.9 0.0 0.0 17.8 —0.1 0.2 Regression Correlation Standard Error Equation Coefficient of Estimate L' = 2.15L - 16.6 .999 1.52 a' = 2.32a + 0.79 .986 2.31 b' = 2.00b + 0.39 .988 1.85 * This was a metal disc painted the same black color as the perforated plate. 28 Table 4 Mean Hedonic Score of Color Panel and Corresponding Hunter Color Values for Frozen Whole Mushrooms ' Mean Hunter Values Date of Storage Date of Hedonic Pack Conditions Examination Score (H) L a b 3-5-70 LT 4-2-70 2.5 35.4 3.3 8.35 " " " 2.6 36.35 1.25 8.9 " " " 4.7 41.15 0.4 9.6 " " " 4.5 40.85 0.25 9.4 " " " 5.4 40.95 0.4 9.45 " " " 3.7 39.25 0.45 11.8 " " " 6.4 42.9 0.0 8.5 " " " 6.7 43.0 0.3 8.15 " " " 6.9 44.3 -0.1 8.8 3—17-70 LT 4-2-70 2.5 35.9 3.2 9.35 " " " 3.5 38.75 1.0 7.7 " " " 5.3 42.7 0.1 8.9 " " " 5.0 43.25 -0.4 8.4 " " " 6.9 45.3 -0.4 8.2 " " " 7.4 44.95 -0.4 7.9 " " " 7.2 44.2 -0.75 7.95 " " " 7.3 44.45 -0.55 7.7 " " " 6.6 45.6 —0.5 7.9 3-17-70 HT 5-8-70 8.1 46.1 -0.6 8.0 " " " 4.8 41.45 -0.1 10.0 " " " 7.6 44.5 -0.25 7.75 " " " 6.7 42.95 —0.75 8.15 " " " 7.9 44.1 -0.1 6.95 ” " " 3.3 41.15 -0.15 8.95 " " " 5.9 41.55 -0.1 8.85 " ” " 3.6 38.5 -0.35 8.05 " " " 2.0 33.25 3.2 9.15 3-5-70 HT 5—8-70 4.1 40.45 -0.3 10.15 " " " 5.6 42.9 -0.5 9.2 " " " 5.7 43.5 -0.5 8.9 Correlation Factors Correlated Coefficient Regression Equation Hedonic (H) and L .924 H = 0.5975 L - 19.54 H and L plus b .940 H = 0.474 L - 0.334 b - 11.479 H and L plus a plus b .945 H = 0.564 + 0.228 a 29 -0.280b - 15.7849 30 values are of little importance. If it is assumed that the color panel used for these tests is reasonably representative of the average consumer, then the regression equation H (hedonic color score equivalent) = 0.474 L - 0.334 b - 11.479 can be used as a guide for predicting color preferences in whole frozen mushrooms. Sulfur Dioxide Determination.--Initia1 studies using the Ponting and Johnson (1945) method with known amounts of $02 blended into "untreated" samples gave poor recovery and progressively greater losses of S02 with greater time lapse-from start of blending. pH determinations on the blended material indicated a pH of 6.5. In- creasing the amount of buffer to 100 ml resulted in a pH level between 4 and 5 (Table 5). With this amount of buffer, the re- covery of added 802 was 90 to 100% (Table 6) and a time lapse of ten minutes between the start of blending and determination of 802 did not result in any 502 loss. Following the method of Ross and Treadway (1960), 10 m1 of 1% starch solution was used as an indicator. This gave a more readily perceivable end point which was considered to be the first medium blue color to persist for at least 20 seconds. Titrations were always done rapidly to provide a sharper and more accurate end point. Accord- ing to Ross and Treadway, rapid titration is necessary "to prevent less rapid side reactions from becoming significant". Test Series I: Treatment of mushrooms with chemical dips prior to freezing to inhibit enzymatic discoloration. Table 5 Test to Determine Proper Amount of Buffer for Use in 802 Determination Test 1 2 3 4 Mushrooms (g) 100 100 100 100 Buffer (ml) -—- 10 50 100 NaCl Solution (ml) a. 20% 500 490 --- —-- b. 22% -—- --- 450 -—- c. 25% ——- --- -—- 400 BE Buffer + NaCl solution 3.25 3.55 3.75 3.90 Blended product 6.50 6.40 5.55 4.60 Table 6 Determination of Accuracy of Modified Ponting Method for 802 Determination Blending time (min) 5 2 2 2 2 $02 (ppm) added 106 110 100 200 200 SO2 (ppm) recovered Time 1apse* 5 minutes -—— 95 101 194 198 10 " 100 100 94 200 -l96 20 " 96 90 88 192 189 25 " 90 _-_ _-_ --_ -_- 30 " 82 --- _-- -_- _-_ 40 " 83 __- -__ -__ _—_ * From start of blending to start of titration 31 32 Because of the screening nature of this experiment, little data was obtained other than a subjective cuality evaluation by two panelists after one- and five-week periods of frozen storage. The results and Observations reported after one week's storage are tabulated in Table 7. No differences were noted between the one- and five-week storage samples. None of the dip treatments were particularly effective. Bruising that occurred during the treatments adversely affected the appearance of all samples where bisulfite was not part of the treat- ment. STPP and EDTA both seemed to inhibit surface darkening somewhat_ but STPP caused the mushrooms to turn yellow. SAPP used alone actually increased discoloration and in addition caused the uncooked, thawed mushrooms to have a slight acid flavor. STPP and EDTA did not affect the flavor of the mushrooms. The sample treated in the manner of Duggan's patent had good color but harsh flavor. Also a 16% weight loss occurred during the blanching phase of Duggan's process. The high color ranking obtained in this preliminary study by both samples of bisulfite-treated mushrooms (samples no. 2 and 3 in Table 7) suggested that subsequent studies should include sodium bi- sulfite. It was also decided to explore the use of coatings to inhibit discoloration, which would be accomplished by glazing frozen mushrooms with various chemical solutions using a spray technique. Test Series 11: Treatment of mushrooms to inhibit discoloration with chemical dips prior to freezing and chemical glazes after freezing. Frozen samples of each treatment were rated subjectively for color, while in the frozen state, by two panelists after two weeks and Test Series I. Table 7 in Frozen Mushrooms. Chemical Dip Treatments Used to Inhibit Discoloration Color Rank and Quality Observations After One Week at "LT" Storage Dip time Color Treatment Chemical Treatment (minutes) Rank Observations l. Control-no treatment 13 Dark brown 2. Sodium bisulfite (900 ppm 802) and sodium chloride (1%) 1-1/2* 2 Good color 3. Sodium bisulfite (400 ppm 802), sodium chloride (4.4%) and citric acid (0.75%) 2 ** 1 Chalky white 4. Sodium acid pyrophosphate (SAPP) (1%) 2 13 Dark brown 5. SAPP (1%) 5 13 Dark brown 6. SAPP (1%) *** 3 Good cOlor 7. SAPP (3%) 2 13 Dark brown 8. SAPP (3%) 5 13 Dark brown 9. Sodium tripolyphosphate (STPP) (1%) 5 4 Slight yellow 10. STPP (1%), and sodium chloride (1%) 5 5 Slight yellow 11. STPP (1%), sodium chloride (1%) and citric acid (1%) 5 12 Brown 12. STPP (3%) 2 6 Yellow 13. STPP (3%) and sodium chloride (1%) 5 7. Yellow 14. STPP (3%), sodium chloride (1%) and citric acid (1%) 2 ll Brown-orange 15. STPP (3%), sodium chloride (1%) and citric acid (1%) 5 10 Yellow 16. Disodiumethylenediaminetetraacetate (EDTA-Naz) (0.1%) 2 9 Tan 17. EDTA—Na2 (0.1%) ' 4 8 Tan * . of Missouri recommended treatment for fresh mushrooms (Goodman, 1957). ** *** Blanched 2 min. 3'? in 1% SAPP solution at 200 F. Duggan patented process (1966), consisted of 2 min. dip, 2-1/2 min. steam blanch and a second 2 min. dip in same solution as previous dip. 34 again after two months storage under ”LT" storage conditions. These observations are summarized in Table 8. fied in Table 1. Sample treatments are identi- Sam les rated " ood" in color after two weeks storage had the P 3 following treatments: Sample No. 21 22 l6 17 ll 10 9 Ascorbic acid SAPP Dip* Ascorbic acid, EDTA-Na2 -—- Ascorbic acid STPP EDTA-Na EDTA-N82 EDTA-N82 Sodium chloride, citric acid Ascorbic acid * Sodium bisulfite was included in all dips in Test Series 11. Those rated good after two months had the following treatments: Sample No. 20 7 21 19 22 The chemicals in the following list were Dip Ascorbic acid Citric acid Ascorbic acid Ascorbic acid, SAPP SAPP Spray Sodium chloride, EDTA-Naz, STPP Ascorbic acid treatment components in the "good" colored samples (either singly or in combination). The list includes the number of samples rated good and in parentheses the number of samples treated with the particular chemical. Chemical component Sodium bisulfite Sodium chloride Citric acid Ascorbic acid EDTA-N32 STPP SAPP 2 7 2 1 4 4 0 1 weeks (21) (6) (4) (12) (8) (6) (3) 2 months 5 n:sas4n~sas‘ Test Series II. Table 8 Color Evaluation of Dip and Spray Treated Frozen Mushrooms After Two and Eight Weeks of "LT" Storage Two Weeks Storage Eight Weeks Storage Rank* Sample No. ** Color Sample No. ** Color 1 21 Good 20 Good 2 22 H 7 H 3 l6 " 21 " 4 l7 " l9 " 5 11 " 22 " 6 10 " 10 Fairly good 7 9 II 16 I! H 8 15 Fairly 17 " " 9 8 H 9 H H 10 7 " 2 Fair 11 12 " 15 " 12 2O " Balance were all 13 19 Fair very poor 14 14 " 15 13 " 16 18 " l7 2 Poor l8 3 " 19 4 " 20 5 " 21 6 " 22 l " * ** Average of rankings for color by two panelists. Comments apply to relative color within each group of storage samples and should not be used for comparison between the two groups. Sample numbers refer to treatments described in Table 1. 35 36 Although the results of this test series did not provide readily discernible overall patterns of effectiveness for the various additives, some of the results seemed fairly conclusive. For example, samples 7, 8 and 9, in which the ascorbic acid was applied as a spray, were each rated higher than their counterparts (samples 5, 4 and 6 re- spectively), in which ascorbic acid was one of the components of the dip solution. Four of the five samples that were color-rated "good" after two months of "LT" storage had been treated with sodium bisulfite plus ascorbic acid, either as a 2-component system or in combination with other additives. The fifth sample in the "good'' color category after two months of storage had been treated with SAPP plus sodium bisulfite. Test Series III. Inhibition of color changes in frozen mushrooms through vacuum impregnation with chemical solutions prior to freezing. Mushrooms samples which were vacuum-impregnated with chemical solutions were examined in the frozen state fOr color after 30 days "LT" storage with the following results: Treatment Color 1. Control-distilled water Good-white 2. 1% NaCl Very yellow 3. 2% NaCl Very yellow 4. 0.2% citric acid, 0.2% ascorbic acid, 0.04% NaHSO3 Good~white 5. 0.5% SAPP Very yellow 6. 0.2% SAPP Very yellow When thawed, either in air or in hot water (approximately 100 F) while still in bags and tasted in the uncooked state by the author all samples were very insipid in flavor and had very mushy texture . 37 Because of this poor taste in the finished product, it was concluded that this would not be an acceptable process for IQF frozen mushrooms. The process may be adaptable to a specialty type mushroom product, (e.g. a flavored mushroom with its own gravy or sauce) if the texture can be improved. Table 9 contains weight gain data from the aforementioned tests (samples 1 to 6) and from subsequent tests (samples 7 to 10) in which complete or partial vacuum was drawn. Test Series IV: Sulfur dioxide treatment of mushrooms prior to freezing. Test results for sulfur dioxide¥treated mushrooms, applied both with and without the use of vacuum, are shown in Table 10. Sulfur dioxide applied to mushrooms in a closed container at atmospheric pressure provided ”good” colored frozen mushrooms. A simple test using catechol (Ponting, 1945) was performed on mushroom samples immediately after exposure to sulfur dioxide. No enzyme activity was evident in the mushrooms exposed to sulfur dioxide while under vacuum. However, the high sulfur dioxide level in these mushrooms rendered them inedible. The seven lots of mushrooms which had no vacuum treatment but were exposed to one gram of sulfur dioxide (per 100 g. sample) had no enzyme activity to a depth of approximately 1/16 inch below the surface. These mushrooms, with 162 to 315 ppm 802, did not have an objectionable flavor when tasted in the uncooked state by the author. Table 9 Test Series 111. Effect of Vacuum Impregnation Procedure on Weight Gain in Mushrooms Time held in solution Vacuum After release Weight * Sample Vacuum (time held) of vacuum gain inches min. min. % 1 26-29 30 10 61 2 H II I! 50 3 II M H 67 4 H H II 73 5 H II N 76 6 H H H 70 7 H H H 70 8 H II S 68 9 10 " " 32.5 10 10 10 " 20.5 * % Weight gain = final Wt' x 100 -100 original wt. 38 Table 10 Test Series IV. Treatment of Mushrooms with Sulfur Dioxide. Test Variables and Residual Sulful Dioxide in Frozen Mushrooms 802 Treatment Size of Pre- Vacuum $02 Residual Mushrooms Treatment Added 802* Rested inches g ppm Water 28 60 Not tested --- . Water 28 10 " " --- Water 20 l 5200 mixed Water None 1 212 " Water " 1 198 " NaHSO3 and NaCl " l 183 " " " " " l 172 1-1/2" dia. H H H II 1 315 1" diao NaHSO3 and citric acid " l 162 1-1/2" dia. " " " " l 283 1" dia. * Test results for individual samples. 39 40 The mushrooms used in this test were held overnight at approxi- mately 35 F after having been washed in pretreatment solutions listed in Table 10. Those treated with sodium bisulfite and citric acid, although initially as white as the other pretreated lots, turned dark yellow during this holding period. The color of the other lots did not change noticeably during the holding period. Hunter color measurements and subjective color ratings summarized in Table 12 are for mushrooms treated with various dip solutions to test for synergistic effects when used with sulfur dioxide. Samples immersed in sodium chloride, a mixture of EDTA and SAPP, ascorbic acid or citric acid, after having been exposed to sulfur dioxide, were rated "good" and were all much better (whiter) than mushrooms treated with sulfur dioxide alone. Mushrooms treated with dip solutions before the $02 gave comparable results as when the same dips were applied after exposure to $02. Whole mushrooms containing 184 ppm 802 in the frozen state and 50 ppm 802 after being sliced and sauteed were found not to be signifi- cantly different in flavor from untreated control samples and, in fact, tended to be preferred (Table 11). This level of 802, which was obtained by applying one gram of $02 to mushroom samples in a closed container with a capacity of 65 liters, was used in subsequent tests. The relationship between 802 levels in frozen and sauteed mushrooms, which was obtained from samples processed for the above- mentioned taste panel tests, is shown in Table 13. Samples 1, 2 and 3 in this table were treated with 0.5, 0.75, and 1% (by volume) atmos- pheres of 802 gas respectively (1 gram, 1-1/2 grams, 2 grams 802 per 65 liters of air). Sixty—one percent to 85 percent of the residual Table 11 Test Series IV. Taste Panel Results. Preference Tests Between Samples With and Without Added 802 Sample Total Control Treated With Trials 802* Significance No. Preferred 30 12 18 N.S. Off Flavor Comments** Burned Sweet Flat Unpleasant Fishy Strong Metallic Bitter * The treated sample had 184 ppm 802 when frozen and 50 ppm SO2 after being sliced and sauteed. ** Each comment listed appeared only once. Comments apply to the sample in the column heading. 41 Table 12 Test Series IV. Hunter Color Measurements and Color Rating of Mushrooms Stored 16 Days Under "HT" Conditions After Pre- Freezing Treatments with Sulfur Dioxide in Conjunction With Various Chemical Dips Hunter Values* L a b Hedonic Color Subjective Score Color Chemical dips Equivalent** Rating*** NaCl (1%) 43.8 0.0 8.5 6.4 Good SAPP (3%) 43.7 -O.4 9.3 6.1 Fair EDTA-Naz (0.2%) 42.1 -0.9 9.6 5.3 Fair EDTA-N82 (0 . 27a) and SAPP (0.3%) 43.9 -0.5 8.0 6.6 Good Ascorbic acid (0.3%) 43.9 -0.6 8.7 6.4 Good Ascorbic acid (0.3%) and EDTA-Na2 (0.2%) 43.5 -0.8 9.6 5.9 Fair Ascorbic acid (0.3%) and SAPP (0.3%) 43.3 -0.4 9.5 5.9 Fair Citric acid (0.5%) 43.2 -0.5 9.7 5.8 Good Sodium bisulfite (0.18%) 41.6 0.0 9.0 5.3 Poor Water 41.0 -O.l 9.9 4.7 Poor EDTA-Na2 (0.2%) and histidine (0.2%) 41.4 -O.4 9.3 5.0 Poor * Average Hunter value for all samples immediately after freezing was L - 44.2, a = .0.3, b = 8.3. ** Hedonic color score equivalent 8 0.474L - 0.334b - 11.479. Average hedonic color score equivalent was 6.7 immediately after freezing. *** As rated by two panelists. 42 Table 13 Comparison of $02 Levels in Frozen and Sauteed Mushrooms Sample 1 2 3 ppm 802 Raw (whole)* 184 474 541 Sauteed (whole)* 50 317 501 Sauteed (sliced)** 51 274 273 Loss of SOZ*** per cent Sauteed (whole) 85 66 61 Sauteed (sliced) 86 70 76 * Raw 8 mean of two samples ** Sauteed = individual samples *** Calculated as follows: ppm in fresh -(ppm in sauteed) (Sauteed wt.) 7. loss . LfreSh Wt') x 100 ppm in fresh 43 44 802 was dissipated during sauteeing of whole mushrooms. When the mushrooms were sliced and sauteed 70 to 86 percent was dissipated. Test Series V: Storage stability of sliced and whole mushrooms treated with sulfur dioxide and other chemicals. In general, no appreciable color deterioration was evidenced in either sliced or whole mushrooms, controls or treated samples, when stored under "LT" conditions for the periods of time involved in these storage tests (approximately three months). However, when held under "LT-HT" storage conditions for these same periods of time the color of all samples, except for those that had been blanched, deteriorated (Table 15). In the sliced mushroom color tests reported in Table 14, treatments 2 and 3 had a similar color which was highly acceptable when rated by panel members. Samples of treatments 2 and 3, stored both under "LT" and "HT" conditions, were given a significant level of preference over control samples that were held at the same temperature for 15, 35 and 61 days. Color panel hedonic rating and Hunter color values of whole mush- rooms after approximately one and two months storage (Table 16) were used to calculate the regression equation H = 0.474L -0.334b -ll.479. This was used to calculate hedonic color score equivalents (Table 15) using Hunter color values obtained after various storage intervals (Tables 17 and 18). Treatments E, F, G, H and J all of which were treated with both sulfur dioxide and a chemical dip, rated, with two exceptions, Table 14 Test Series V. Hedonic Color Scores for Frozen Sliced Mushrooms After Storage Intervals of 15, 35, and 61 Days Under Both "LT” and "HT" Storage Conditions Treatment Statistical Sig. Storage 1 2 3 of differences Time No. of Control Molsberry 802 + NaCl between mean (days) Trials "LT" "HT" "LT" "HT" "LT" "HT" scores** 15 17 5.3 5.1 7.8 6.9 7.5 6.9 1 l 2 3 3 2 H L H H L L 5% 1% 35 21 5 2 2 7 7.8 6 8 7 7 5 9 l 1 3 2 3 2 H L H H L L 5°. ‘=-:_:__ 1% -—:;_. 61 18 5.8 4.6 7.2 6.0 7.5 6.3 1 l 2 3 2 3 H L H H L L 5% -:;_. 1% * H - "HT" L = "LT" ** Sample treatments not connected by underscored line are significantly different at the level noted. 45 .m>mp NH umuwm mom HA um pmuoum muo3 animaln pmxoma moose qw>Mp mm umufim wow 94 um voyeum ouoa onlmlm poxoma mmHaEMm Hmleq «ss .Nom Nmk.o empHmumu .cho o~-n-m mo scan .4 can a .o «« .NH :cowum: :« conouw who: muwsuo Ham .uwm :H cououm « 46 o H H H q.m ~.s HeusH am sac Nm.o he a m o o.H m.m w.m smusH .uHom UHHtoumm m H n.k ~.k N.s s.o s.s o.e o.o HH Nm.o EH chm: >H emaoHHom Now AwesHo> any Nm.o «A u o s ~.H a.H a.~ se-sH m a H.o ~.~ s.o a.~ a.m m.m m.m 9H .Homz Na cH swat an tmaoHHoH New HmeaHo> sac Hm.o * a A s H.k o.m s.m He-HH a t s.o m.k H.o w.m m.q w.a k.m 9H .Hotz NH cH 5mm; an chaoHHoH Now HuasHo> sac Hm.o m m a o.m w.~ s.m Hm-sH N o H.m ~.o H.o H.m ~.m a.s o.m EH .Hmta that: so soaoHHou Now HmasHo> any Hm.o a .nucman umuwm paw muomwa .cwa N pwum uwuuau Nmn.o paw H m N.m m.m o.q HHIHH OGHLOHeu saHeom NS.< .muHLHsmHH saHeom NmH.o o q m.m m.n o.m m.e 0.4 m.q m.s 9H :H tuaaHu .uosoamHH steam .mmmuoua ammmsn o o s o.q H.~ H.m 9:-9H A a m.s m.s m.s m.~ a.N m.~ m.m AH .E NHN um mauscHs m .tuamHH steam m o H ~.H o.H o.H HeusH o N s.~ q.~ H.m H.~ s.~ m.~ H.~ AH .waHntth «touts sHao amt: Loam: Hotuaoo < m Hm mH o ooH no AN H *«Amwwtoum utmeumous «too whom mmmp okuanm Ho Home oknmum Ho Homa Asse.HHn Hemm.u Hess. u uoHou 0Haovw= "coHumsom conmwueom scum vouaHonao mmaHm>v .osnsHum use caumum smegma maoounmaz Lou mam>uuuam owmuoum msofiua> swuw< wuaoao>wsvm whoom uoaoo vasomom .> mowuom amps ma vague Table 16 Test Series V. Significance of Differences in Color Panel Hedonic Ratings of Whole Mushrooms Examination Date 4-2-70 5-8-70 Storage Conditions g LT-HT* No. of Trials 21 20 Mean Mean Pack** Hedonic Signif. Pack Hedonic Signif. Code Date Value 5% 1% Code Date Value 5% 1% A 3-5 2.5 A 3-17 2.0 A 3-17 2.5 | D 3-17 3.3 B 3-5 2.6 B 3—17 3.6 l a 3-17 3.5 H 3-5 4.1 I F 3-5 3.7 l H 3-17 4.8 D 3-5 4.5 G 3-5 5.6 C 3-5 4.7 J 3—5 5.7 I D 3-17 5.0 c 3—17 5.9 l C 3-17 5.3 F 3-17 6.7 l E 3-5 5.4 ' G 3—17 7.6 G 3-5 6.4 E 3-17 7.9 l J 3-17 6.6 J 3-17 8.1 H 3-5 6.7 E 3-17 6.9 J 3-5 6.9 G 3-17 7.2 H 3-17 7.3 F 3-17 7.4 * ** Remaining codes in "LT-HT" storage had poor color and were not presented to panel for hedonic rating. "LT-HT" samples packed 3-5-70 were stored at "LT" for first 27 days. Those packed 3-17-70 were stored at "LT" for first 12 days. Pack Date Examination date Days ippstoragg 3-5-70 4-2-70 27 3-5-70 5-8-70 63 3-17-70 4-2-70 15 3-17-70 5-8-70 51 47 Amoaeawm 03u «0 some use mo=Hm> wwwuoum zap moo uoooxo madcamm Happw>wpcu Eouw dump usomouewu monum> Hamv .myop hm umuwu you HA um payoum who: moaasmm Haiku «e .NH :sowum: ca museum mums mumsuo HH< .uww aw cowoum a 48 NF" 00 NN m me o.¢¢ m.w H.0I m.c¢ m.o o.n¢ 0.0 m.o ¢.o m.o m.H m.n n.c< c.<¢ m.Nq n.mm H.mm ¢.Hq m.o¢ 0.5m w.qn 82184 HA HZIHA HA 9:194 HA HEIHA HA BEIHA HA HmIHA HA HmlHq BA HEIHA HA Hmlha HA .mm haw mh.o .Humz NN.o van vaum ownuoomu Nm.o :H can; he poaonaow Now Aoa=Ho> sac mh.o .UflUQ Uflfiuoumfl Nmoo cw sums up poaoHHom New Amasao> Nu as can: an pmaoaaom Now Awasao> NN as now: ma pwaoaaom Now Amesao> .cmma noun: xp pozoaaom New Auaado> .gucwan uuuuw tan .aHs N eHuu OHLHHU Nn5.o can aaHuom no.4 .ouHHHsmHn asHvom “av mh.o .Homz may Nm.o - .Hoaz >nv mm.o may um.o and whom ovHuoHeu "ms.o cH wear saws comma; aowum .umououn awwwsn .m NHN um mouscwa m .noaman Emwum .waNwmuu wuomon mace 5mm: umumz Houucoo m.oc o.mq N.m m.~v N.¢e m.w 0.5m o.wm m.oH n.wm n.0e m.o m.mm N.H< H.m N.mm a.o< c.m n.0m c.om $.w o.mn «.mm e.w A n m OOH me 5N pump a« mafia oMWHOum **WWWHOUW unweumoua chlmln vuxumm msoounmsz 0H053 you mHm>uOuGH owmuoum msowuo> umum< mosam> uoaou Hausa: .> mowumm amok NH macaw ovoo .Ammaaamm 03» up some one mosam> omwucum Hop 0 umcu uaooxm measam Hmapw>upcw Baum sump uaumounmu mo=Hm> Hamv .HH um wrap ~H umuum Hem papaya mum: MOHaEmw H: to .NH :cooum: cu amuouu one: mumcuo HH< .uHm ca emuoum « 49 m.Hc «.mq w.~q m.~¢ .w>< 0.0: H.e¢ HmlHq .mm an um.o H H.0I m.H< H=IHH .Huaz N~.o pad vuua ownuoomw um.o :H n.ou o.¢c 5.5 o.ou n. How Nn.c : m.ou n.¢¢ H=IHA .vuuu oaauoumo um.o 6% m.OI o.mc 0.5 w.ou N.qc «.5 m.c o.q¢ HA cum: Ha poaoaaom New Ams=Ho> Haw um.o o 0.? 93 HTS . .Hoaz NH 5 N.OI n.¢e m.5 «.9: o.m¢ m.w H.OI m.cq HA new? >3 vOROHH0m New AoEsHo> Hay um.o « m H.OI H.Q¢ HIIHA .Humz NN aw NS- “.3 «S to- The ma o5 mi 5 is. .3 88:01. Now 3533 h: "To m «5: «.3 :75 - . . not: m.on m.~e q.w «.0: m.me o.w H.o w.~< HA usums >a vasoHH0u New noesao> >nv Nm.° a oLUGQH£ Hfluwfl VG” UHOWOD .GHE N vans ouuuuo Nm5.o van ovuuoanu anvom H.01 o.ae H=IHA Ne.e .0uwmaauwn seamen Nn5.o cw onwv o.o N.a¢ ¢.m H.o 5.~c 5.5 m.o c.Hq HA saw: sounds Human .mwmuoua comma: 0 «.ol n.wm HmlHA o.H m.wm 5.5 o.H m.wm m.5 w.o o.wm HA .m NAN um neuscws m .sucmHn amoum m ~.m n.mm HmlHq N.m <.om q.m N.m a.nm c.w 5.~ w.om HA .wawuwoum mucumn HHao new: head: Houucoo < a A n o A a a A «ammoHOuw ucoaummuH opou Hm ma 0 mmmm,aw mad» mwmmmwm 05I5HIn poxoam waooucmsz macs: new mHa>uouau omoHOum upouuu> uouu< moaao> uoHou nouns: .> oawuum umOH we 0H£MH 50 significantly better in color after one month of "LT" storage than the control sample, A, the blanched sample, B, the sample pre- pared according to Duggan's patent, C, and the sample treated with sulfur dioxide alone, D (Table 16). Figures 3 and 4 depict samples of each treatment of whole mushrooms after approximately three months of "LT" storage. Hedonic color score equivalents for these mushrooms appear in Table 15 (pack of 3-5-70, 100 days storage; pack of 3-17-70, 88 days storage). These can be considered to be representative of the panel ratings of 4-2-70 since the Hunter color values changed very little in the ensuing storage. As shown in the "LT-HT" color ratings of 5-8-70 (Table 16) 0 F storage temperature caused a considerable amount of color deterior- ation. The relative ranking of samples within the "LT-HT" group was essentially similar to color ranking in "LT” groups with the notable exception that treatment H (SO2 and a dip in a sodium chloride-ascorbic acid mixture) became yellow and consequently was rated much lower than the remaining 802 treated samples. As has been noted, yellowing was evidenced in frozen storage in the various Test Series after several types of treatments with no apparent pattern. Residual sulfur dioxide levels for stored frozen mushrooms are shown in Tables 19 (for whole mushrooms) and 20 (for sliced mushrooms). Even where the level was very low or undetectable, as in C, D, E, F and J for the pack of 3-5-70, color panel hedonic ratings (Table 16) were significantly better than those of the control samples. There does not appear to be an appreciable change in sulfur dioxide level in frozen storage of treated mushrooms even where color deterioration is occurring but data were insufficient to draw a firm conclusion on this point. Figure 3. A B C D E F G H J Whole frozen mushrooms (packed 3-5-70) after 100 days storage at -10 F. Left to right: Samples A, B, C, D, E, F, G, H, J. (See Table 15 for treatment description.) Figure 4. A B C D E F G B J Whole frozen mushrooms (packed 3-17-70) after 88 days storage at -10 F. Left to right: Samples A, B, C, D, E, F, G, H, J. (See Table 15 for treatment description.) 51 52 .Amoaaeom Hospfi>wvaa HoOHOAaou sumo Aocuo HH< .mzmv ma umqu Aom HA um mums moaasom O515H1m .mouoofiaosv mo osam> coma Hammouoou sump How A poo oV .Nom AHA.o HH>HHHHA .AHao oAumum Co Home .s was A .u «Ht .NH :COOHE: CH .mAHH AN HHLHH tom AH Ha HHHH sonouw mum: ouozuo HH< .AA< GA oououm «a ouoa 05Im|m mo xuoa Eouw moaosom HmlHH « HASH Ana HON mAH HAH HAH AH NA NA AH Ham AH Am.o «t« s .Huaz N~.o can oqm AHA HAN AHA AoH oAH NoH NHH HHHH uHHLoumH Am.o :H Hams AH HoaoHHoA Now oasHo> AH um.o ««« = cos AHA HAN HAH om NH NOH AA .HHHH HHHAooha Am.c HH Ham: AH wasoHHoA New masHo> AH Am.o «A; o AmH «AH AHH HAH o o o A .Homz AN :H Hams AH HmaoHHoA Now oasHo> AH Am.o «« A NHN as“ HoN oHN o o o m .Hosz AN HH Hana AH HtaoHHoA Now ossHo> AH Am.o m AHH NAH AHH HHH H AM H An .HmHa Hausa AH HuonHoH Now weaHo> AH NA.o a .socwfin nouuo poo ouowoa .owa N kuo uwuuwo AAA.o was oeHAoHHu asHHoH NH.H .oHHAHHHHH ssHeoH o o HH 0 o o c H AAA.o :H HAHH .HHHHHH swoon .mmououa amwwaa o paummu uoo pause» uoo .m NAN um Housewa m .nocoan Eoouw m cuumou uoo vaumoH Ho: .uouuooum ouowon Haco 5mm: Adam: Houuooo < N and om mcoauwvooo uaoaumouH ovou «AHIAH AH AH AH «AmnAH AH AH AH ammuoum mm mm «H o ooH no AN H AHAHHV ammuoum 05|5HIm mo xoom O5Inlm «0 xumm mHo>Aouou owMAOHm msoauo> Aouu< mascunmaz macs: :ououm a“ Assay ospwmom N ma UHAMH om .> maHuom HHHA Table 20 Test Series V. 302 Residue (ppm) in Frozen Sliced Mushrooms After Various Storage Intervals Treatment Storage 1 2 3 Time Storage Control Molsberry 802 and (Days) Conditions Patent NaCl JPN - 0 LT Not Tested 180 145 15 LT " " 165 135 35 LT " " 95 115 71 LT " " 143 86 35 HT " " 86 115 0 Day Values Represent Means of Three Samples. Data From Individual Samples. 53 Other Values Represent 54 Some of the variations in measured sulfur dioxide levels may have resulted from uneven penetration during treatment, caused by vari- ations in size as well as other variations in the physical and physiological conditions of individual mushrooms. 5 The texture of unblanched mushrooms was preferred to that of blanched mushrooms (Table 21). Tests to determine preference be- tween texture of mushrooms frozen in "Freon" 12 or in air blast showed no significant differences. Unblanched mushrooms (treatment A) scored higher in flavor than did the blanched samples (treatment B) but the difference was not statistically significant. Samples in which the pre-freezing treatment included sodium chloride (C, E and H) tended to be preferred over those where sodium chloride was not part of the treatment. In the hedonic flavor tests, samples treated with sulfur dioxide or sodium bisulfite (with or without other additives) almost invariably scored higher than did corresponding control samples (Table 22 and 23). No apparent flavor deterioration was observed during frozen storage of either the controls or treated samples. Data in Table 24 and 25 show the weight relationships between ‘ fresh mushrooms (prior to treatment) and frozen mushrooms as well as the effects of blanching on product weight. As expected, there was a sub- stantial weight loss during blanching. Weight gain in mushrooms frozen - in "Freon" 12 was probably caused in part by water adhering to mushroom surfaces and possibly also to absorption of.solution during the washing process. The apparent weight gain in samples B and C between blanching and freezing cannot readily be explained and may have resulted from Table 21 Test Series V. Texture Preference Tests for Blanched vs. Unblanched Mushrooms and for "Freon" 12 vs. Air Blast Frozen Mushrooms Packed 3-5-70 mm Blanched vs. unblanched Storage Treatment time Total A (unblanched) B (blanched) (days) Trials No. preferred ' 41 20 16* 4 61 18 15** 3 "Freon" 12 vs. air blast freezing Storage ' Treatment time. Total E ("Freon" 12) F (air blast) (days) Trials No. preferred 41 21 11 10 61 18 ll 7 * Denotes significance at 5% level. ** Denotes significance at 1% level. 55 Test Series V. Table 22 Hedonic Flavor Scores for Whole Mushrooms Packed March 5, 1970 and Held Under "LT" Storage Conditions Statistical Significance Storage Treatment Code* of Differences Time Total Between Mean (days) Trials A B C E G H J Scores 32 20 6.0 5.8 5.8 6.8 N.S. 33 17 6.9 6.8 6.5 6.1 N.S. 63 20 6.3 5.7 6.9 7.4 B A C E 500 '—=—— 64 21 7.2 6.1 7.3 6.6 G J H E 5% -——- *1 Treatments are identified in Table 17. Table 23 Test Series V. Hedonic Flavor Scores for FroZen Sliced Mushrooms After 15 and 61 Days Storage Under "LT" Conditions Statistical Treatment Significance 1 2 . 3 of Differences Storage Total Control Molsberry $02 and Between Mean Trials Patent NaCl Scores 15 days 30 6.0 7.4 6.8 l 3 2 ' 5% -—- 1% -—-=.—..... 61 days 20 6.3 7.1 7.5 l 2 3 5% -:;__ 56 Table 24 Test Series V. Weight Change in Whole Mushrooms Frozen in "Freon" 12 and in air Total % weight % weight change change caused by from fresh Code Treatment blanching*** to frozen*** A Control water wash only before freezing. --- +6.9 B Steam blanch, 3 minutes at 212 F. -24.8 -21.0 C Duggan process. Steam blanch with dips into .75% sodium bi- sulfite, 4.4% sodium chloride and 0.75% citric acid 2 min. before and after blanch. -15.9 -10.5 D 0.5% by volume 802 followed by water wash. --- +12.6 E 0.5% by volume S02 followed by wash in 2% NaCl. --- +8.2 F * 0.5% by volume 802 followed by wash in 2% NaCl. --- -5.8 G ** 0.5% by volume 802 followed by wash in 0.5% ascorbic acid. --- +12.7 H ** 0.5% by volume 802 followed by wash in 0.5% ascorbic acid and 0.2% NaCl. --— +10.4 J ** 0.5% by volume 802 followed by wash in 0.2% EDTA and 0.5% SAPP. ' --- +10.l 3- Frozen in air. All others were frozen in "Freon" 12. ** G, H and J, pack of 3-5-70 only, received 0.75% 802. *** Based on initial weight of raw material before start of treatments. 57 Table 25 Test Series V. Weight Change* in Sliced, "Freon" 12 - Frozen Mushrooms Treatment 1 2 33 Control, Molsberry Patent 802 and NaCl Water Wash Procedure percent +16.7 +27.4 +24.6 * Based on initial weight of raw material before start of treatments 58 59 weighing errors. The higher weight gains in sliced mushrooms compared to whole mushrooms is probably due to their greater surface area. The weight loss that occurred when mushrooms were frozen in air (sample F) was presumably due to dehydration. Water adhesion could account for the 15 to 20% weight gain claimed by Molsberry to be achieved by his patented method. It should be noted that during taste panel prepar- ations of both whole and sliced mushrooms, a substantial amount of liquid had to be drained from the thawed mushrooms so they could be sauteed properly. pH measurements taken throughout the storage study are shown in Tables 26 and 27. There is no indication from this study that pH is related to color deterioration in frozen mushrooms. Test Series VI: Dehydrofreezing mushrooms. Dehydrofrozen mushrooms increased in weight from 2 to 10% of the mushrooms weight in the dehydrofrozen state (Table 28). These results compare unfavorably with Lazar's (1968) results in which he found that pie apples during soaking, baking and cooling often absorb 110 to 120% of the weight of the dehydrofrozen slices. Besides the disappointing rehydration data, the quality of the dehydrofrozen mushrooms, as determined subjectively, was poor. Both the SOz-treated samples and the blanched samples were badly shrivelled. The blanched samples had a poor, dark grey color while the former had a slight, distinctly yellow off-color. When sauteed in butter (about four tablespoons per pound of mushrooms) for approximately ten minutes after rehydration S02 treated samples were fairly good in color, texture, and Test Series V. Table 26 After Various Storage Intervals pH Values for Frozen Whole Mushrooms Pack of 3-5-70 Pack of 3—17-70 Storage (days) 1 27 63 100 100 0 15 88 88 LT LT LT LT HT* LT LT LT HT* Treatment** pH A 6.50 6.45 6.55 6.60 6.60 6.60 6.55 6.50 6.50 B 6.50 6.55 6.50 6.50 6.60 6.50 6.60 6.60 6.60 c 6.10 6.55 6.50 6.50 6.60 6.50 6.60 6.60 6.60 n 6.60 6.60 6.65 6.60 6.60 6.50 6.55 6.60 6.45 E 6.65 6.60 6.60 6.50 6.60 6.60 6.45 6.65 6.55 F 6.65 6.60 6.60 6.50 6.60 6.60 6.60 6.55 6.60 0 6.45 6.50 6.60 6.50 6.50 6.40 6.60 6.60 6.50 H 6.40 6.50 6.60 6.50 6.50 6.35 6.50 6.40 6.45 J 6.40 6.60 6.55 6.40 6.40 6.50 6.50 6.50 6.50 (all data represents individual samples) * HT samples from pack of 3-5-70 were held at LT for 3-17-70 samples were at LT for first 15 days. ** See Table 15 for test descriptions 60 first 27 days. Table 27 Test Series V. pH Values for Frozen Sliced Mushrooms After Various Storage Intervals (Values Represent Data From Individual Samples m Treatment Storage 1 2 3 Time Storage Control Molsberry $02 and NaCl (days) Conditions Patent pH 0 LT 6.60 6.50 6.60 15 ' LT 6.55 6.50 6.60 35 LT 6.60 6.60 6.60 71 LT 6.60 6.50 6.60 35 HT 6.60 6.55 6.55 Table 28 Test Series VI. Rehydration Rates for Dehydrofrozen Mushrooms m ’— Treatment ' SQZ_Hash, Blanch Size ' Sm Sm Sm Lg Sm Sm Sm Lg Rehydration 1 3 12 12 1 '3 12 12 time (hours) Water temp 150 70 7O 70 150 70 70 70 (° F) Wt. gain (Z) 2 10 3 O 3 12 4 3 61 62 flavor but remained shrivelled. The blanched samples had good flavor but were dark, tough, and shrivelled. Because of these initial poor results no further tests in dehydrofreezing were carried out. SUMMARY AND CONCLUSIONS The effectiveness of sulfur dioxide gas, alone, and in con- junction with various chemical dips, in preventing color changes in stored, frozen mushrooms was evaluated. Chemical dips alone, vacuum impregnation with chemical solutions, dehydrofreezing, and "Freon" 12 immersion versus conventional air blast freezing were also studied. An objective method for measuring color using a Hunter Lab Color Difference Meter was developed and shown to give high correlation with subjective color measurements by a panel composed of Food Science Department personnel. A procedure to determine 802 inmushrooms, based on modifications of Ponting's method for fruits, also was developed. Dips or dip and spray treatments of whole mushrooms with empirically developed combinations of chemicals were only slightly successful in preventing discoloration. The chemicals tested, sodium bisulfite, citric acid, ascorbic acid, sodium chloride, SAPP, STPP, EDTA-Naz, and histidine were relatively ineffective in producing color comparable to fresh mushrooms. This was attributed to lack of effective penetration of the chemicals in the dip solutions. Molsberry (1967) has determined that dip treatments could be successful in freezing sliced mushrooms. "Good" colored frozen sliced mushrooms were produced here following his patented method. Sulfur dioxide gas was found to be an effective means of ob- training penetration of the amount_of chemical necessary to inhibit 63 64 enzymatic discoloration to the extent believed to be necessary for commercial application. When whole mushrooms were treated with 0.5% by volume of $02 for three minutes and then dipped in solutions containing 2% sodium chloride or 0.5% ascorbic acid or a combination of 0.2% EDTA-Naz and 0.5% SAPP "good" colored frozen mushrooms were produced. Color was better than that attained by $02 alone, or by blanching or by Duggan and Byrne's (1966) patented method which consisted of a combination of blanch and chemical dip treatments. The level of S02, necessary, under 200 ppm, was found to be undetectable by taste panels. Samples treated with $02 tended to be preferred in flavor to controls which had not been treated. Blanching had an adverse effect on texture, when compared by taste panel with unblanched mushrooms after frozen storage. Texture panel preference appeared to be unaffected by freezing rate. No color, flavor or texture comparisons were made between fresh and frozen product during the course of this study. Treatment of sliced mushrooms with 802 followed by a dip in 2% NaCl solution produced mushrooms comparable in color and flavor to those with Molsberry's method. Freezing with "Freon" 12 produced weight gains in frozen mush- rooms while weight loss was experienced when an air blast technique was used. The gain is probably due to water adhesion while the loss in the latter method is undoubtedly due to dehydration. The weight gain could be an economic advantage but also could cause problems be- cause of drainage during food preparation. In limited testing, no significant texture differences were found in mushrooms frozen by 65 these two methods. Color seemed to be slightly better in "Freon" frozen mushrooms but the data is inconclusive. In three months of storage at -10 F very little quality de- terioration was noted in either control or treated samples in this study. At 0 F quality deteriorated appreciably in all samples that were not blanched. Vacuum impregnation, as a method of introducing discoloration- inhibiting chemicals was unsuccessful, principally, because of the mushy texture of the thawed product. Dehydrofreezing was also considered to be unsuccessful with either blanched or bisulfite treated mushrooms. The mushrooms shrivelled badly and could not be properly rehydrated. ‘ No relationship between pH and discoloration in frozen storage was found. 10. 11. 12. 13.- 14. 15. 16. 17. APPENDIX Chemicals used in Mushroom Treatments and Analyses Ascorbic Acid, U.S.P., Pfizer, C024486G1. Citric Acid, Reagent Grade, J. T. Baker, 0110. Disodium Ethylenediaminetetraacetate, Certified A.C.S., Fisher, S—311. Iodine, Reagent Grade, J.T. Baker, 2208. Potassium Iodide, Reagent Grade, J.T. Baker, 3164. Silver Nitrate, Analytical Reagent, Mallinckrodt, 2169. Sodium Acid Pyrophosphate, Commercial Grade, Calgon. Sodium Bisulfite, Analytical Reagent, Mallinckrodt, 7448. Sodium Chloride, Analytical Reagent, Mallinckrodt, 7581. Sodium Hydroxide, Reagent Grade, J.T. Baker, 3722. Sodium Metabisulfite, Analytical Reagent, Mallinckrodt. Sodium Sulfate, Reagent Grade, J.T. Baker, 3824. Sodium Sulfate, Reagent Grade, J.T. Baker, 3891. Sodium Tripolyphosphate, Commercial Grade, Calgon. Starch, Reagent Grade, J.T. Baker, 5006. Sulfur Dioxide, Anhydrous, Matheson. Tartaric Acid, Analytical Reagent, Mallinckrodt, 2312. 66 REFERENCES Amerine, M.A., R.M. Pangborn and E.B. Roessler. 1965. Principles of sensory evaluation of food. Academic Press. New York. Armstrong, T.D. 1967. 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