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A BACTERIOLOGICAL STUDY OF COTTAGE CHEESE WITH PARTICULAR REFERENCE TO ’ PUBLIC HEALTH HAZARD BY PAUL ROBERT LYONS A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MAS TER OF SCIENCE Department of Bacteriology 1953 Tthls u/gz/ffi we DEDICATION This work is dedicated to my mother, my wife, and my four children, Connie Lou, Bobby, Janie, and Joie. Without their patience and forebearance this paper would not have been started, nor could it have been finished. (Eil'QiO ACKNOWLEDGMENTS The author wishes to express his sincere appreciation to Dr. W. L. Mallmann for his valued assistance and guidance. Thanks are extended also to the Lansing, Heatherwood Farms, and Arctic Dairies, without whose generosity much of this work would not have been possible. Appreciation is also expressed to my employers, the Lansing- Ingham County Health Department, for their cooperation during this we rk. INTRODUCTION . . . . STUDY TABLE OF CON TENTS ........................... I. COLIFORM INDEX OF MARKET COTTAGE CHEESE ............................... Introduction ............................ Procedure ..... . ...... . . . ........... Results and Discussion ................... Summary . II. LINE RUNS IN COTTAGE CHEESE , PROCESSING PLANTS .................... Introduction Procedure Summary . . III. SURVIVAL OF SELECTED ORGANISMS IN CO T TAGE CHEESE ........ . .............. Introduction Procedure Results and Discussion .......... . ........ Summary . . LI TERA TURE CITED OOOOOOOOOOOOOOOOOOOOOOOOOOO 401.4: 14 15 15 16 17 19 21 21 23 25 26 32 IN TROD UC TION Few city milk ordinances take into account the sanitary as— pects involved in the production and handling of cottage cheese. In most instances, reference to cottage cheese is one of definition only. In accordance with the various ordinances, careful sanitary inspections are made of milk plants, and, although the inspection covers all phases of milk processing, emphasis is always placed on fluid milk production. In milk processing plants where cottage cheese is also manu- factured and packaged, the sanitary methods used in manufacturing and packaging are in contrast to the methods used in the care and handling of milk. The use of improperly sanitized equipment, hand methods of conveying and packaging, and a general air of laxity are all common errors in the production of cottage cheese. Needless to say, such methods and equipment have not been used for the handling of market milk for many years. It is interesting to note 'that at one time milk was sold in “bulk to retailers for resale to their customers. The retailer would then ladle the milk into the customer's own container. However, as early as 1876, glass containers were used for the delivery of milk to the consumer (2). Since that time recognition of the public health hazards involved in bulk milk sales, as well as other factors, has made it mandatory for milk to be handled in only legally approved containers. Yet, today, thirty-seven years after bulk milk sales were outlawed in Michigan, the sale of bulk cottage cheese is still permitted (3). It is apparent that this 'product was not merely forgotten by the manufacturer and the public health officials, for there must have been some logical reason why it was ignored for so many years. This complacency seems to be founded on the premise that cottage cheese is too acid a product to require more than just casual care in its manufacture. It is true that in the early history of modern dairy production cottage cheese was a more acid product. Incom- plete cooking of the curd, resulting in larger amount of lactose being incorporated within the curd, resulted in a consequent fermentation and an increase in acidity in the finished product. More recent practice, undoubtedly motivated by consumer demand, is for com- pletely cooked curd with thorough rinsing and draining. This re- sults in most of the lactose being expelled with the whey in the draining operation, and checks the rapid production of acid in the finished product. This bland cheese is quite different from the cottage cheese of twenty or thirty years ago, and yet the manufactur- ing methods used are essentially the same. Without the protection of high acidity in the finished product, greater care and stricter sanitary precautions are necessary to produce a safe product. In view of the above facts, this study was undertaken to de- termine if the commonly used methods of cottage cheese production and packaging actually constitute a public health hazard, or if, on the other hand, the product still remains sufficiently acid to warrant its casual handling by the manufacturer and disinterest on the part of the public health official. STUDY I COLIFORM INDEX OF MARKET COTTAGE CHEESE Introduction This study was made using samples obtained from eight dairies, six of which were under public health inspections as re- quired by city ordinances, and two creameries which were without such inspections. Packages of cheese were ~obtained at plant storage points and retail outlets. The samples were collected at intervals over a twelve-month period, and tests were made within twenty-four hours of the time collected. According to Standard Methods for the Examination of Dairy Products (1), the coliform test constitutes by far the most delicate method available for detecting recontamination of dairy products. Inasmuch'as the problem is entirely one of recontamination by handlers and improperly sanitized equipment, the coliform test was chosen as the most exact instrument to obtain the necessary data. Dairy products were tested for the presence of coliforms through the use of 2 per cent brilliant green bile broth tubes or desoxycholate agar in accordance with the standards set up by the A.P.H.A. (1). Both media were used so that comparative counts could be obtained and, if deemed advisable, isolation from the solid media could be accomplished by picking off individual colonies and subjecting them to further study. Every effort was made to obtain samples representative of the production of each plant. Nothing was said or done to persuade the cheese processors to alter in any way their usual methods of handling. Samples were selected at random from the total day's production. Of course, the fact that samplings were being made would tend to make the handlers a little more careful in their methods, but, as will be shown, this does not seem to have made any signifi- cant difference in the final results. Procedure A Waring blendor was sterilized by washing thoroughly with a detergent wetting agent, and soaking for thirty minutes in a 500 ppm sodium hypocblorite solution. After soaking, it was rinsed in running water for about ten minutes. Checks for free chlorine and possible carry-over of alkali from the chlorine solution were made by thiosulphate titration and by checking with the Beckman pH meter. There was no indication that the chlorine solution was carried over after the blendor had been rinsed for ten minutes in running water. One hundred m1 of sterile distilled water was put into the sterile Waring blendor. The machine was run for a few seconds and then one-ml amounts of the water were placed in each of three bril- liant green bile broth tubes. Dilutions of 1-10 and 1-100 were made on desoxycholate agar by putting 0.1 ml of the water into a Petri dish and by putting one ml of the water into a 99 ml dilution blank and transferring one ml of this dilution to a Petri dish. De— soxycholate agar was then added to these Petri dishes and mixed with the water being tested. These two tests constituted a sterility con- trol on the .Waring blendor. Using aseptic precautions, 10 gm of cottage cheese to be sampled was weighed out and added to the 90 m1 of sterile water in the Waring blendor. After rendering the mixture homogeneous, 1.0 m1 amounts were transferred to each of five brilliant green bile fermentation tubes, and dilutions of 1-10 and 1-100 were made into desoxycholate agar by the same methods described above in plating the water used as a sterility control. These samples, as well as all samples in this study, unless specifically stated otherwise, were . incubated at 37 C. A sufficient quantity of the mixture was also removed at this point to determine the pH of the cheese with a Beckman pH meter. Results and Discussion The pH determination on over 150 samples of market cottage cheese revealed that the pH was between 4.7 and 5.5, with over 80 per cent of the samples falling between 5.0 and 5.5. The pH of such cheese consequently was within the range tolerated by the coliform organisms. Counts on the brilliant green bile tubes were taken at twenty- four and forty-eight hours. It was found that about 67 per cent of the samples collected contained coliform in the amount of 220 or- ganisms or more per hundred gm of cheese. The percentage of positive samples collected from each dairy varied from 33 to 100 per cent (Table I). There seemed to be no correlation between the individual dairy plant's ability to produce coliform-free bottle products and its ability to produce coliform-free cottage cheese. Plants with excel- lent records in these respects had rather high percentages of coli- form-contaminated samples at times, and this was variable from plant to plant. TABLE I COTTAGE CHEESE PACKAGED AT PLANT No. of Samples Showing Coli Dairy No. of Colonies on De- Total No. Per .Cent No. Samples soxycholate Agar P051tive P051tive Sample 5 Sample 3 1-10 1- 100 l 16 1 6 7 44 2 18 4 1 5 28 3 25 10 4 14 56 4 12 3 4 7 60 5 l4 6 2 8 57 6 12 4 6 10 83 7 15 6 8 14 87 8 18 8 10 18 100 Totals 131 42 41 83 63 84% of all samples had a pH of 5.0 to 5.6. TAB LE I (Continued) No. of Positive Samples in 5 Tubes of Brilliant Green Bile Broth T013? No. Per Cent P051tive P051t1ve 1/5 ' 2/5 3/5 4/5 5/5 Samples Samples ' ' 7 ‘ Z 9 56 l 1 2 ‘ 2 6 33 4 l 2 .. 8 15 60 3 " - Z 2 7 60 4 2 1 1 l 9 64 2 1 1 Z 4 10 83 " 1 1 Z 10 14 87 ‘ l 1 7- ‘ 14 18 100 l4 7 15 9 43 84 64 10 OOH ea v m N _N - ooz In H_ as N oo o v a a m .. oo o 9 oz a 03; SJ m\m m\v m\m m\~ m\H m. meagmm mvaEmm mofimgdm um .04 Auoym 02m oumaoau>x0m monEmm .oZ o>wxmom o>fizmonm m>flfimom . 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