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A STUDY OF CERTAIN FACTORS
INFLUENCING THE CULINARY QUALITY

OF POTATOES. WITH SPECIAL REFERENCE
TO THE COLOR OF BOILED POTATOES

THESIS FOR THE DEGREE OF M. 3.
Arthur Ward GIidden
1932

 

 

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.

E DATE DUE DATE DUE DATE DUE

6/ IS Kz/Prol/Acc&Pres/CIRC/DateDueForms_20|5.Indd - pg]

 

A STUDY OF CERTAIN ACTORS IITE'LUFEJCII-TG THE
CULINARY gUALITY OF POTATOES, 11TH SPECIAL FETIRTEJCE
TO THE COLOR OF BOILED POTMOBS

THESIS

 

 

AC BS'IOIF.’LEDGEIZEI T

The author wishes to express his appreciation
to Professor H. C. Meore and Dr. E. J. Miller for
their guidance and helpful criticism given this work;
to the manbers of the Experiment Station Chemistry
staff who assisted in the scoring of the potatoes;
and to all others who from time to time have given

the author their COOpGration.

96413

A STUDY OF CELTAIII FACT RS I--i_ol CIZ'G I'IIFZ CULINARY

U

001.011 OF BOILED POT ATOES

OUTLILE

I. . II‘ITRODUCTION
II. PEVKITI 1‘ LITERATURE

A. Factors Influencing the General Culinary
Kalil]. ity o i‘ Pot a toes

3. Factors Relative to the Color of Cooked
Potatoes

III. nifl‘TI—‘IIIZ’I i
A. General LIothodsof Procedure
1. Lletl od of Determining; ulinar y Quality
2. Method of Scoring
3. Liethod of Cooking;

B. Part I. Factors Influencing the Ce enera l
C‘O‘Ilir‘ar;r Quality of Potatoes

1. Proccc‘ture and Results

a. Comparison of he Culin ary Cuality of
Certain Varieties fro"; Various Sources

b. The Influence of Maturity upon
Culinary quality

(a) Tests with mate rial i'I‘O’Z. IDate of
Planting; Plo us

(‘0) Tests t’i th material from Greenhouse
Flots

UALIT'I 0? P01". JOBS ‘IIITII .SE'ECIAL FER'IR'LTIICE '30 THE

10
ll

(‘3
CO

PO
to

Page
c. Influence of Fertilizer Analysis and
-ate of Application upon Culinvry Quality
of irrigated and nor-irrigated plots 55
2. Discussion
a. Influence of Varieties and their Source
upon Culinary wuality 55
b. Influence of Katurity upon Culinary
unality 36
C. Part II. Factors Influencing: the Color of
Boiled Iotataes 37
1. Procedure and Results
a. Effect of Poor Aeration of nature Russet
Rurals upon Color 40
b. Effect of Door Aeration of I: ature
Russet Rurals upon Color 40
0. Effect of Poor Aeration of 1952 Winter
crop of Florida Spaulding Rose and Bliss
Triumph potatoes upon Color QC
2. Discussion 47

IV. S 1.3 ARY AID CCII’JLUSIOIIS 49

A STUDY OF CERTAIN FACTORS IIIZELTIIICIIZTG TIE CULINARY
QUALITY OF POTATOES, BITE-I SPECIAL R'EFIJRJEICE TO THE
COLOR OF BOIIED POTATOES

A Thesis Prepared by
ARTHUR WARD {EDEN
in partial fulfillment of
the requirements for the
Degree of Master of Science

Department of Farm Crops

IIZICHIGAN STATE COLLEGE OF AGRICULZURE AIID APPLIED SC

1932

-1'r' "t
A'JA'CJIJ

RTRODUCTION

Uith the exception of the potatoes used for seed
purposes, practically all of the potatoes produced in the
United States are used.ibr human consumption. Consequently
quality is an important factor in potato production and
marke ting-5, .

finality in potatoes is dependent upon two component
factors, namely, market quality and culinary quality. Iarket
quality of potatoes is determined by the general appearance
of the tubers, attention being given to the size, type and
unifornity of the potatoes as well as freedom from surface
diseases and mechanical injuries. Culinary quality refers to
the quality of the potatoes when prepared for table use.
Culinary quality is determined by the cohesion of flesh or
sluffing of the cortical layer, the color, tie texture and the
flavor of the potatoes when cooked.'

In recent years the culinary Quality of Lichigan
potatoes has been severely criticized. This criticism is no
doubt at least partially reSponsible for the range in price
between Iichigan potatoes and potatoes produced in some other
states. The price of Kichigan potatoes on the Detroit market
during the first week of Decenber 1951 was 49 cents per bushel,
compared with 31.10 per bushel for Idaho potatoes and 67 cents
per bushel fer potatoes produced in Kaine. It is impossible

to determine accurately the exact percentage of this difference

which is due to poor quality, but it would be reasonable
to conclude that the profitableness of the potato crOp in
Michigan calld be greatly increased by improving the quality
of the crop.

The experiments reported in this paper are all more
or.less of a preliminary nature. An attempt has been made
to determine in what manner Midaigan potatoes differ in culinary
quality from potatoes grown in Idaho, Kaine and Florida. A
study of maturity'and certain cultural practices was also made
in an attempt to ascertain the practices which are inducive to
good culinary quality. Since the darkening after cooking is
often a serious factor inhidiigan potatoes, a shady was

made to determine the cause of this condition.

REVIEW OF LITERATURE
FACTORS INFLUENCING THE GENIRAL CULINARY QUALITY OF POTAZOES

Gilmore (1905) working with the Doe's Pride variety
found.that tubers produced on clay loam were poor in quality,
being firm and soggy after boiling, while tubers produced on
sandy loam were excellent in quality. The same investigator
also reported that immature tubers were less mealy andxnore
soggy than mature tubers. .

Ashby (1906) woniing in England, summarized his
investigations as follows: "Indications seem.to point to
physical causes as exercising the greatest influence on quality,
eSpeciaily temperature and water supply. Loamy soils give
unifOrm warmth and water supply and,therefore, produce the
best quality."

East (1908) reported that to give good culinary quality
the starCh content of the tuber should be high enough to fill
the cells of the cooked tuber to the bursting point. Potatoes
with a starch content above a certain point, approximately 18%,
would easily fall to pieces, or if the cell walls were strong
enough to hold together’under pressure they would necessarily
be tough.and woody.

Butler, Horrison and Boll (1913) concluded from

their investigations that:

1. As the relative quality of the potatoes in-
creased there was a decrease in the differentiation of the
inner medulla.

2. The percentage of starch'had no direct influence
upon the mealiness of the potato.

5. ifealiness is modified by tire water content,
potatoes having a relatively high water content being less mealy

than potataes of low water content.

Headen (1927) reported that the results of 68 tests
showed.that the application of nitrates produced potatoes of
poor duality.

Findlay (1928) made an investigation of the quality
of potatoes in Scotland. A brief summary of his work is here
given:

1. A better quality of potatoes was produced on
sandy soil.than was produced on clay or peat soils.

2. Dry conditions favored good quality, whereas, wet
conditions were apt to cause poor quality.

3. Regardless of wet or dry seasons early plantings
gave extremely dry, mealy potatoes, while late plantings gave
wet, soapy potatoes.

4. Excessive use of nitrogen and poorly balanced
fertilizers resulted in poor quality.

5. The quality of the potatoes Was lowered by the

omission of phosphorous from the fertilizer mixture.

6. The omission of potash caused many of the
varieties to turn black after cooking.

7. Quality was impaired by line and the continued
use of manure.

8. mosaic affected plants showed no difference in
quality, but plants affected with leafroll tended to produce

poor quality potatoes.

Child and Williman (1929) feund that potatoes with
a high percentage Of dry matter tend to be accanpanied by better
texture and flavor than potatoes with a low percentage of dry
matter.

The work of heil.and Whittimore (1950) on.the relation
of;mealiness in potatoes and the amount of potash in the
fertilizer shows that boiled, baked and mashed potatoes are
more mealy when fertilized with a high rather than a low
quantity of potash. No correhation between starch content and
mealiness was found.

Peacock, Wright, Whitaman and Fuller (1930) made a
study of the influence of storage temperatures upon the quality
of potatoes. Their investigations showed that the cooking
quality becomes better as the storage temperature increased
from 32° F. to 60° F. The maximum culinary quality was found
.in the tubers stored at 60° F. The tubers stored at the lower
temperatures were poorest in quality due to the sweet flavor

caused by the accumulation of sugars.

6.

FACTORS RELATIVE T0 1 3 ODLOR OF COOKED POTATOES

Several investigations have been made to determine
the cause of the blackening of raw potatoes. Since there may
be a relationship between this type of blackening and the
blackening of potatoes after cooking it seems advisable to
review some of the outstanding and more recent works. Reference
will first be made to the oxidation enzymes of the potato in
order to make the resume of these investigations more understand-
able.

Onslow (1931) classifies the potato as a plant giving
oxygenase and tyrosinase reactions as well as peroxidase re-
actions. Associated.with these enzymes are certain aromatic
compounds with the ortho-dihydroxy grouping characteristic of
catechol. Oxygenase (Onslow, 1951) catalyses the autoxidation
of this group of aromatic substances. This reaction gives an
organic peroxide, catechol peroxide, which is subsequently
decomposed in the presence of water, giving hydrogen peroxide.
The enzyme tyrosinase (Onslow, 1931) is closely associated with
oxygenase, as no plant so far studied gives the tyrosinase
reactions without also giving oxygenase reactions. Tyrosinase
has the power to catalyze the oxidation of the amino acid,
tyrosine, producing a pink coloration rhich gradually deepens
to red.and finally to black. The black compounds thus formed
are known as melanins. Peroxidase (Onslow, 1951) in the presence
of hydrogen peroxide will oxidize a number of phenolic

substances of different composition such as pyrogallol, catechol,

x

‘

quinol, benzidine, guaiacum, guaiacol, p-cresol aid others.
The nature of the actual oxidations associated pith peroxidase
in the plant iS‘unkuown. uuen1m3mul.res iration is tdfihm;
place in the iotats tuber the reactions of these three enzymes

are held in a delicate balance and no bad effects are produced.

Und:r conditions of abnormal resgiration certain of
these enzymes catalyze reactions detrimental to the pot to tuber.

Evidence of this is the blackening of raw potato tissue which
may be b'oucht about by various causes.

Khan a raw potato tuber is injured mechanically
blackenin takes place. Cnslow (1931) reports this blackening
as being typical of all plants containing oxygenase and a
catechol compound. Th; discoloration is the result 01 tie
oxidation of the aromatic substrate by oxy;2 enase and in addition
the probagle secondary oxidation of other aromatic substances.

Bartholomew (1913), Stewart and :ix (1917), Bartholomew
and Bennett (1924) and others ‘1 ave shown that black heart
develops when potatoes are stored where the oxygen supgly is not
ample. According to Bartholomew (1913) an excess of oxygen
accumulates in fine tubers when they are again placed in an ample
atr losphere of oxygen. As a result, the en zylne tyrosina se
catalyzes the oxidation of the amino acid tyrosine which has
accumulated in a free Donn. As a final result, the tissue
ultimately becomes black.

While working with potato enzymes Onslow (1931)

obs enved<nuaner°tvre of dDuOP::LIMHMViOTo ThiSIWQJalso have

f4

 

some bearing upon the blackeniig of potaaaes after cooking.

In making enzyme preparations from normal potatoes this investi-
gator faind that it was possible to wash away the aromatic
compound, catechol, with alcohol leaving a colloidal surface
bearing only traces of oxidized products of this substance.

Such a preparation will give a negative test with guaiacum,
since no peroxide will be harmed by the action of the oxygenase
present. As a result the enzyme peroxidase, which is also
present and acts as a catalyst only in the pIesence of a perdxide,
cannot catalyze the oxidation of the guaiacum. However, if

the potato tissue is allowed to oxidize considerably before

it is treated with alcohol it is inpossible, even by the most
careful methods, to wash the colloidal surface free from the
oxidation products of catechol. The combination of oxygenase
and.the oxidation products of catechol present in such a
preparation is called a laccase. A laccase will always give a
positive test with guaiacum.

Tinkler (1931) states that the actual blacnening of
potatoes after sacking is probably due to oxidation. However,
enzyme oxidation is out of the question as any enzymes present
would be killed by the boiling process which is at least
twenty minutes in duration.

Tinkler makes no mention of the possibility that
oxidation products formed previous to the time of cooking
Kay'have an important bearing upon the extent of blackening of

cooked potatoes. However, the findings of Onslow, Bartholomew

(5)

Stewart and xix, Bartholomew and Bennett, and others, indicate

that such a condition is probable.

10.

EXP? RI: SITTE‘L

Gene ral Method 3

 

The method of determining the culinary quali ty, the
method of scoring and the method of cooking the potatoes was
the same throughout all of the emaeriments. An explanation of

these methods is given in the following. general procedure.

Method of Determining Culinary 'uual ity

The culinary quality of the potatoes co oked in the
experiments reported in this paper was determined by the color,
texture, cohesion of flesh, and flavor of the cooked tubers.
Perhaps the most important of these factors is the color of
flesh after cooking. The most desirable color for boiled,
baked or mashed potatoes is a creamy rhi te. A yellowish- White
tinge is rather common, and although it is not preferred it is
more desirable than a dark grayish or black color. Texture
is a second factor which determines culinary quality. A tuber
which is mealy or somewhat granular in structure is preferred
to one Whi ch is soggy, waxy or tough. Sluffing of the cortical
layer and cohesion of the flesh is a third factor in-
fluencing culinary quality. This applies chiefly to boiled
potatoes. The general preference is in favor of a potato which
is not firm after boiling and is still held together enough

to prevent a sluffing and consequent loss of the cortical layer.

ll.

Flavor is the fourth factor used in determining the culinary
quality of potatoes. Usually a potato is not seriously
discriminated ag dnst unless it is either bitter or sweet to

the taste.

Method.of Scoring

The score card used in judging the culinary Quality
of the potatoes in these experihients \as a simplified form
of a score card submitted by Dr. C. F. Clark, Office of
Horticultural Crops and Diseases, Bursa; of Plant Industry,
United States Den pa mt 2.ent of Agriculture. The original score
card su gested by Dr. Cla L was rather c mplicated, as it
involved many factors and even included the degree of intensity
of these factors. The individual interpretation of dais score
card by members of the “xperiment Station staff vas so varied
that it was believed the final results mould be very in-
consistent if such a scoring system were used. The folloring

simplified score card Las devised to overcore this discrepancy.

SCOi? CARD FOR BOILBD POTATOES

 

 

 

 

 

 

 

 

 

Cohesion Slightly Moderately Firm much Completely
of disinte- disinte- disinte- disinte-
flesh grated grated . grated . grated
Score 5 Score 4 Score 3 Score 2 Score 1
Color Creamy YellowiSh Grayish Yellow Cortex or
of white White Basal end
flesh blackish
Score 5 Score 4 Score 3 Score 2 Score 1
Texture Mealy Kealy Waxy Soggy
Coarse Fine
Grained Grained
Score 4 Score 3 Score 2 Score 1
Flavor Normal Flat Earthy Sweet
of Pleasant
flesh Score 4 Score 3 Score 2 Score 1

 

 

 

 

 

Figures l,2,3,4,5 illustrate the five degrees of cohesion

of flesh given on the above score card.

I.

I‘D

 

13.

Effectiveness of the Score Card Used

The score card used in determining the culinary
quality of potatoes in these experiments was, in most cases,
satisfactory. in occasional lot of potatoes was found, however,
which was difficult to score. Such lots were always tough
and hard after they had been cooked. Experience with these
lots has suggested the advisability of adding to the score card

a factor pertaining to the tenderness of the cooked potato.

l4.

 

Figure l. A Cooked Potato Tuber Slightly Disintegrated

15.

 

Figure 2. A Cooked Potato which is Moderately
Disintegrated

 

Figure 5. A Cooked Potato Tuber which is Firm

l7.

 

Figure 4. A Cooked Potato Tuber which is LIuch
Disintegrated

l8.

 

Figure 5. A Cooked Potato Tuber Completely Disi ntegrated

kethod of Cooking

In.tte cooking tests the potatoes were boiled.
Preliiinary observations indicated fiia t this method emphasized
the factors which go to make up culinary quality better than
baking or mash ing. These observations were similar to the
results obta ned by Child and 'Jilliman (1929) who found that
potatoes Which show high quality for boiling will also show it
for baking, providing the tendency to sluff is ignored. Boiling
also has certain advantages over baking as a method of determining
the culinary giality of potatoes. First, it requires less tire
to com plete the test. Second, in boiling potatoes the sluf fing
of the cortical layer becomes an additional factor by which the
culina y quality can be judged.

The potatoes r. ere boiled in four-miart alulninum
kettles. TaCh kettle was provided with a galvanize ed wire baslm t
which was suspended in the kettle so that the bottom of the
basket was one a-d one-half to two inches from fine bottom.of
the kettle. The tubers were placed in the basket for boiling.
This method facilitated the removal of the potatoes when cooked
and prevented burning. A hole was made in the cover of each
kettle so that a thermometer could be inserted in one of the
tubers. iiis apparatus is shown in Figure 6.

Peacock, Wright, Whit eman and Fuller (1950) found that
potatoes were thoroughly cooked when fine temperature inside

the tubers reached 95° C. Preliminary tests showed this

(b
r.) .

temperature to be very'satisfactory for these exleriments.
When this temperature was reached the potatoes were removed
and placed on porous plates. After allowing feur minutes to

cool the potatoes were scored.

 

 

Figure 6. The Apparatus used in the Cooking, Experiments

T 3
{“9

Two phases of eXperimental work are here presented.
Part I deals with factors influencing the general culinary
quality of potatoes. Part II deals with factors influencing.
the color oi‘boiled potataes.

PART I

FACTORS INFLUTLCIKC THE GENTP£L CULIIAnY gUALITY OF POTATOES

Procedure ani Results

 

Comparison of th e Culinez ry uality of Certain Varieties of
Potatoes from Various Sources

In this er periment co 1parisons were made between
the culinary quality of the 1931 crop of Idaho Russet Burbanks,
Maine Green mountains, Iflcldgan U} 8. $1 Russet Rurals, Lichigan
Kew Standard Potato Club Russet Rurals and the 1932 crop of
Winter potatoes of the Spaulding Rose and Bliss Triumph varieties
from Florida.

q

The Few standard Potato Club is an organization of
ifichigan potato growers under the direct supervision of the
idchigan Crop Improvement Association. Potatoes marketed as Pew
Standard Club stock have been grot'n under soil ani cultural

conditions which tend to pqoduce a product of good culinary

quality. The niles regulating the grading and sorting of this

25,

stock are very strict. The potatoes must be graded to a 2%
inch minim . All mechanically injured, scabby and off-type
hibers must be removed to eliminate waste in paring. All
potatoes marketed as New Standard Club potatoes bear the tag of
the Ljichigan Crop Improvement Association stati n5 that the
above conditions have been fulfilled.

Ten lots of Idaho Russet Burbanks and the U. S..#l
ljchigan Russet Rurals were purchased from time to time from
grocery stores in Lansing and East lensing. Ten lots of the 1952
winter crop of the Spaulding Rose and Bliss Triumph varieties
from Florida were obtained fron.produce terminals in Detroit
through the Eichigan State Department of Agriculture. Only sevai
lots of‘haine Green heuntains could conveniently be obtained.
Two of these lots were purchased from grocery stores in Lansing.
The remaining five lots were obtained from produce terminals
and grocery stores in Detroit. Twenty-five lots of Lhchigan
New Standard Potato Club Russet Rurals were used in this
experiment. Two of these lots were purchased in Karch 1952
from grocery stores in Lansing. The remaining twenty-three lots
were obtained directly from.the growers during November 1931.

The general method of‘saapling for the boiling tests
vas as follows. Three samples of five tubers of uniform size
were taken from each lot and boiled in separate kettles. Each
sample was scored by three judges. The same individuals
acted as judges throughout the entire experiment. The data

presented are the average score of all judges for all three

24.

samples. Two exceptions were made in this procedure. Only

one sample was taken from.the twenty-three lots of New

Standard Potato Club Russet Rurals obtained from the growers.

It is felt that the relatively large number of lots helps to
offset this discrepancy. The second exception was made with

the Spaulding Rose and Bliss Triumph potatces from Florida.
'These lots were a) small that only two samples could be used for
the cooking tests. However, little variation was observed in
the tubers from.any one of these lots and it is believed that the
culinary quality of eadh lot was accurately determined by the

two samples.

Calculations

In making the comparisons between the varieties the
mean total score was used. The probable error was calculated by
multiplying the standard deviation by 0.6745 and dividing by

he square root of the nunber of lots. Ez'pressed by formula

this method is

P. E. 3 S. D. X 0.6745

mean
Q N

When comparisons were made between varieties which

 

were represented by an unequal number of lots the smaller

number of lots was taken as the value of N.

The mean scores of the varieties and their differences
wifii their respective probable errors are given in Table I.

An additional comparison was made to show the manner
in which the varieties differed from.each other. These data
are given in Table II. Each factor upon which the culinary
quality was determined is listed in column 1 opposite the
varieties in column 2. The number of times each variety received
a certain score for each factor on the score card is given in
column 3. In order to make the comparisons more apparent, the
figures given are all on the basis of 100 times scored. The
actual number of times scored is given in column 4. The weirnted
average score for each variety for each factor is given in
column 5. As calculated, the weighted average score for any
factor is the sum.of the products of the number of times each
score was given, multiplied by the number corresponding to
that score, divided by 100. For example, on the basis of 100
times scored the cohesion of flesh for the Idaho Russet
Burbanks was scored 20 times as 5, 23 times as 4, 19 times as
3, 28 times as 2, and 10 times as l. The weighted average

score for cohesion of flesh for this variety consequently is,

(20 x 5)T(23 x 4)+Ll9 x 3)+(28 x 21+(10 x 11, : 3,15
100

26.

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The Influence of Maturity Upon Culinary Quality

In recent years early planting of potatoes has been
strongly recommended in Iiichi gan. An experiment was conducted
to determine whether or not the increased maturity obtained by
early planting had any influence upon culinary quality. The
potatoes used for this study were Russet Rurals obtained from the
1951 Date of Planting Demonstration Plots and from greenhouse

plOtSo

Tests with Russet Rurals from 1931 Date of
Planting Demonstration Plots

The Date of Plan ting Demonstration Plots were grown
under the supervision of Mr. .T. 3‘. Bird, Extension Specialist
in Fam CropS. These plots were planted on three dates, the
first planting being on May 15, the second on June 1, and the
final planting on June 15. At the time of harvesting in the
latter part of September and the first part of October,a sample
was taken from each date of planting.

Material was collected from one plot in each of the
following counties, Emmet, Otsego, Tuscola, Oakland and Lenawee.
The June 15 planting was not harvested in Tuscola county due
to a very poor stand.

Previous to the time the cooking tests were made,

which was during the first week in December, the samples were

stored in a cold storage plant at 40° F.

Five tubers were selected from each sample and cooked
to determine the culinary quality. Each sample was scored by
flaree judges. Tie data given in Table III are averages of the

scores of all judges.

Table III. Average score for culinary quality of potatoes
Iflanted on three dates

 

 

 

Date of Planting Average Score Given
Cohesion Color Texture Flavor Total
of flesh Score
May 15 4.46 3.94 2.80 3.40 14.60
JUne l 4.40 3.40 2.80 3.13 13.73
Inna 15 4.60 2.60 2.60 2.80 12.60

 

Tests with Russet Rurals from Greenhouse Plots

Eighty hills of PMsset Rural potatoes were planted in
theggreenhouse on.January l, 1932. The plots were planted with
certified seed which had been treated with ethylene chlorhydrin
to break the rest period.

The entire planting was divided into three blocks
for harvesting. Block I was haIwested on Rarch 28, 88 days
after planting, block II was harvested on April 7, 98 days after
painting, and block III was harvested on April 18, 109 days

after planting. Figure 7 shows the greenhouse plots at the time

block II was dug. Blocks I and II were.¢iven the same treatment.

.1

Sir bills in block III were given an excess oi‘tater daily for
six days previous to di5”ing. An attempt was made to hasten the
maturity of the remainder of block III by not watering it 1
seven days previous to dig;ing. However, the potatoes aarvestea
from this block were still immature at tine of harvesting.

In general the tubers produced in all blocks were of
good type. An exception was faind, however, '1 the six hills
in block III which.were excessively watered for six ays previous
to digging. A few of the tubers from these hills had deveIOped
considerable second growth. Figure 8 shows some of the off-type
tubers from these hills in comparison with typical Russet Rural
tubers from.the portion of block III which had not been watered
ibr seven days pnavimis to digging.

The cooking: tests were r.:ade the same day the potatoes
were harvested. Five hibers were selected from each block for
the cooking tests. There was a marked unifamuity in the culinary
quality of the individual tubers from all the greenhouse plots.
In every case the three judges, work'nf independently, scored
the tubers from ead: block exactly the same. For this reason
it is believed that the five tubers cooked gave an accurate

criterion of the culinary quality of the block which they

represented.

"\Q.--‘ ‘ .

if r‘ 'n era‘s . \9
x ‘ “\fi*~?~-~“\

,- «'<
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‘9. ‘ 9* .i'1p3:§§C\ an
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he Q

 

Figure 7. Greenhouse plots at the tine of harvest of
Block II, April 7, 1932, 98 days after planting

 

52.

 

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Figure 8. The three tubers at the left were produced in
Block III and were not watered for seven days
previous to digging. The tubers at the right
were also produced in Block III, but were given
an excess of water daily for 6 days previous to
digging.

m1 f" 1 ~43 ‘5‘ .— ‘- -. --. , n J" {i J“ ~.'z V», + "- ‘r‘ .~
rue results or the cooking tests bade on tie notatoes

from the greenhouse nlots are iiven in Table IV.

 

 

Table IV. Score for Culinary Quality of Potatoes from Greenhouse
Ilots
Days Average score riven
C-I‘O‘ffing 1 ‘ FT 1 . r71, 4. '1
Eeriod Cones1on Color ierture Ilavor ioiui
of flesn score

 

Block I 88 4 5 16

Block II 98 12

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Bloc}: III dry 109

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Block III wet 109 2

Influence of Fertilizer Analysis and Rate of
Application upon Culinary duality of Irr'gated and ion-
Irrigated Ilots

The material used for this experiment was obtained
from the 1931 fertilizer and irriration plots at ;ast Lansing.
Fertilizers of the fella ing anal
0-8-16 and 0-16-0. Applications were made at the ‘ate of 1,000 and
2,000 pounds per acre. Each plot was divided into three blocks
for;irriration. The first block was not irrigated, the second

block mas irrigated from July 16 to September 3 at the rate of

d-
(D
Q;

2.08 inches of water per week, and.the third block was irriga

a the rate 0 ,-r week from August 27 to

as
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September 3. A check plot was also included under the t
irrigation. Theioverhead sprinkling type of irrigation was used. \
These plots were not replicated.

One sample was taken from each plot for cooking
purposes. Five tubers were cooked from each s nple and scored by
three Judges.

It is believed that the results obtained in this
experiment are not worthy of detailed study, as the data do not
show any outstanding differences between any of the treatments.
Furthermore, since the plots were not replicated comparisons made

between them wiuld not be reliable.

DISCUSSION

The Influence of Varieties and Their Source upon Culinar;r :1,uality

The data obtained in the comparison of the culinary
qaality of Ilichi {an New Standard Potato Club Russet Rurals, Idaho
Russet Burbanks, Florida Spaulding Rose and Bliss Triumph potatoes, ‘
Kaine Green Mountains and iiicl‘igan U. S. 3341 Russet Rurals are
given in Tables I and II.

Table I gives a comparison of the average total score
of each variety. The differences between the Elichigan New
Standard Russet Rurals and the two lowest scoring varieties, the
Kaine Green I'Iountains and the I‘Ticirigan ms. :21 Russet Rurals,
are great enough to indicate that the variation in culinary
quality is die to factors other than chance. The same is also
true regarding the Idaho Russet Burbanks and the two lowest
scoring varieties.

The average score of each variety for each factor
on the score card is given in Table II. The I-.Iichi gan I‘Tew
Standard Russet Rurals scored relatively high for all factors,

and were considered outstanding from the standpoint of flavor.

The Idaho Russet Burbanks were exceptionally good in color and
texture. The flavor of this variety was frequently flat and

a few lots were distinctly bitter. The Idaho potatoes showed a
decided tendency to sluff when boiled. If sluffing and the
cohesion of flesh were not a factor, as is the case when potatoes
are baked, the Idaho Russet Burbanks would have been of excellent
culinary quality. The potatoes from Florida were poor in texture
in comparison to The Idaho Russet Burbanlzs and the Ilichigan liew
Standard Russet Rurals. Otherui se, the Florida varieties tested
were of good culinary quality. The Ifaine Green liountains and
the. I'Zic‘rigan U.S. #1 Russet Rurals very frequently turned {grayish
or black after boiling. These varieties were also inferior

in texture and flavor.

3

I»

are Influence of liaturity upon Culinary vuality

H

The Influence of Date of Planting upon
Culinary Quality

Potatoes were collected from five Date of Planting;
Plots to determine the influence of early planting upon
culinary quality. Although probable errors are not given in
Table III a comparison of the differences of the average total
scores in respect to their pmbable errors was made. No

significant differences were found between any of the average

t013511 scores. The number of plots represented is not large
enough to warrant definite conclusions. However, the data
presented in Table III indicate that culintrv quality may be

‘1

irproved by early'planting.

Influence of Time of Harvesting upon Culinary Quality

of Potatoes from.Greenhouse Plots

Table IV gives the culinary Quality scores of potatoes
aflotn.in_the greenhouse and harvested at regular intervals.
The average total scores were nearly the sane for the lots
harvested 98 and 109 days after planting. The total score for
the lot harvested 88 days after planting is considerably higher
than the otter'scores. No satisfactory explanation can be
rade for this result. The texture was apparently improved
then.the potatoes were given the longest growing period and no
water was applied for seven days previous to harvesting. An
excessive application of water for six days previous to di;ging

caused potatoes given the longest growing period to be soggy.

PART II

FACTORS INFLUEKCIN THE COLOR OF BOILED POTAQIES

While making the cooking tests previously described

it was noted that certain lots of potatoes showed a tendency to

turn gray or black after cooking. This blackening usually
occured in the cortical area at or near the stem end of the tuber.
The tendency to blacken after cooking was more pronounced in the
lots of Kichigan U. S. #1 Russet Rurals and the Maine Green
mountains than in the otheI'samples cooked. For this reason
studies were made in an attenpt to determine the cause of the

blackening of potatces after cooking.

The Influence of Poor Aeration in Storage upon the Color
of Boiled potatoes

A series of experiments were conducted in an attempt
to produce the blackening of potatoes after cooking by inter-
fering with the nonnal respiration of the potato tubers. In
these experiments six to eight tubers were sealed in air tight
glass jars and kept in a room.where the temperature was approxi-
mately 700 F. Figure 9 shows tubers sealed in one of the jars
used in these experiments. The tubers were kept in the sealed
jars for varying lengths of time. When the jars were opened
half of the tubers were cooked immediately. The remaining
tubers were placed in thin white muslin sacks and stored in a
room at 70° F. for several days before being cooked. nature and
immature Russet Rurals and Florida Spaulding Rose and Bliss

Triumph potatoes were used in these experiments.

39.

 

Figure 9. This photograph shows the type of jar used
to produce conditions of poor aeration.

40.

Experiment with Kature Russet Rural Potatoes

The potatoes used in this experiment were Russet
Rurals grown in Emmet county. The tubers were all of good type
and varied from.7 to 10 ounces in weight. This lot of potatoes
was selected for the experiment because cooking tests showed
them to be free from.blackening after cooking. Previous to the
beginning of the experirent on larch 7, 1952 the tubers were
stored at 400 F.

Ten jars were used in this experiment. The first jar
was opened four days after it had been sealed. One of the
remaining jars was Opened eaCh day thereafter until the tenth
jar'had been opened. As previously stated, half of the tubers
were cooked immediately'after the jars were Opened. With the
exception of the tubers from jars 9 and 10, which were sealed 12
and 15 days respectively, the portion of the sample which was
stored at 700 F. was not cooked until 7 days after removal from
the jars. This exception was made because the tubers stored
in jars 9 and 10 were so badly decayed when the jars were opened
that it was believed they would not keep longer than one or

two days. The results of this experiment are given in Table V.

I.
An

Experiment with Immahire Russet Rural Potatoes

An experiment similar to the one just described was

conducted with some of the potatoes which were-grown in the

Table V. The Effect of Deficient Oxygen Supply upon the Color
of Russet Rural Potatoes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Jar Days Days Color of ° Condition of
Number sealed stored cooked tubers at time
in jar in sacks tubers _-of cggking
Check 0 0 White Normal
1 4 0 Black Normal
1 4 7 Black Iformal
2 5 0 3711 i t e IT 0 I'UE l
2 5 7 Bleak Button rot and
slight black heart
3 6 0 White Normal
3 6 7 Black Black heart
4 7 O Bleak Normal.
4 7 7 Black Black heart
5 8 O Uhi t e Ii orma l
5 8 7 Black Black heart
6 9 O Tddte Nermal
6 9 7 Bkmk Bkmkhmmt
7 10 0 White Nbrmal
7 10 7 Black Black heart
8 ll 0 White Normal
8 ll 7 Black Black.heart and
Button rot
9 12 0 White Wet curdy rot
9 l2 2 Black serious Black
heart and Button
rot —
10 13 0 White - Wet curdy rot
10 13 1 Black Serious Black

heart and Button
rot

greenhouse for the maturity studies. The potatoes used in this
experiment were obtained from block I which was dug, on Liarch

28, 88 days after planting. As would be expected these potatoes
were very immature. The tubers were sealed in five jars. The
first jar was opened three days after sealing. One of the
remaining fOur jars was opened every other day thereafter. Two
check lots were used in this experirmnt. The first check was
cooked at the time the jars were sealed. The second lot of
Check tubers was stored in thin white muslin sacks at 700 F.
This lot was cooked when the experiment was completed. The

results Of this experiment are given in Table VI.
Experiment with 1932 Winter Crop Of Florida Potatces

Six lots Of the 1952 winter crop Of Florida potatoes
were used in a third experiment to detennine the effect of poor
aeration upon the color of boiled potatoes. The lots used in
this experiment were selected frOm.the lots used in the variety
comparison. Five of the six lots were Spaulding Rose, the
remaining lot was Bliss Triumph. With.the exception of one lot
there was a sufficient number Of tubers in the lots to place in
two jars. One jar was Opened seven days after sealing, the
other eleven days after sealing. The single lot which was placed
in one jar was Opened eleven days after it was sealed. In all

cases two sets Of check tubers were used. One set was cooked

45.

the day the jars were sealed and the other when the experimnt
was completed. The results of this experiment are given in

Table VII.

44.

Table VI. The Effect of a Deficient Oxygen Supply upon the
Color of Immature Russet Rural potatoes. The potatoes
used were grown in the Greenhouse and dug 88 days

after planting

 

 

 

 

 

 

 

 

Jar Days Days Color of Condition of
Number sealed stored cooked tubers at time
in jar in sacks tubers of cooking
Che ck {f1 0 0 Win: te Normal
" f2 0 17 White Slightly wilted
l 3 0 ‘..-'hi te Normal
1 3 8 White Wilted
2 5 O ‘an it 9 Normal
2 5 9 White wilted
3 '7 0 27111 te N or ma 1
5 7 9 Ihite Jilted
4- 9 O ' White Slight curdy
rot
4 9 9 Gray Soft and
flabby
ll 0 White Pronounced
curdy rot
5 ll 3 Gray Button rot, no

'31-‘2—‘-
slack heart

 

 

 

 

 

 

 

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7 .
DI scuss I on

The data presaited ir Tables V, VI and VII were
obtained in three experiments unich were canducted to determine
the influence of poor aeration in store e upon the color of
boiled potatoes.

The results of these ei,erimeits show that the black-
ening after cooking was more frequent in the tubers which had
been sealed in jars and later stored in cloth sacns. The length
of the storage period in the sealed jars that was necessary to
produce this condition varied with the different lots of potatqzs
used. Ho relationship was apparent between the blackening of
cooked potatoes and black heart.

The changes tithin the potato tuber which are
reSpo:sible fer the blackening after cooking are not definitely
known. However, it is possible that these dianges are in some
nanner associated with the reactions studied by Onslow,
Bartholomew, etc., to which reference has previously been made.
The results of the investigations of these experimentors help to
form a basis for the following discussion of the blackenin: of
potatoes after cooking.

The normal respiration of the potato tuber is in-
terfered with by poor aeration in storage. Under these conditions
the amount of oxygen decreases very rapidly until it is either
very small or entirely consumed. As the oxygen concentration

decreases the carbon dioxide concentration increases. then the

tubers are subsequently stored in a well ventilated place they

48.

absorb oxygen rapidly. It is believed that associated Ydth this
oxygen absorption there is an oxidation of some of the aromatic
compounds present in the potato tuber. The fact diet potatoes
which blacken after cooking appear normal before cooking is taken
as evidence to indicate that this oxidation is inhibited before
it is complete and that only intermediate products are fbrmed.
Upon eXposure to air after cooking these intermediate products
are auto-oxidized and the resultant black color is formed.

It will be noted by a study of Tables V, VI and VII
that the procedure followed did not produce blackening in certain
lots after cooking. Koreover, certain inconsistencies occur in
the lots which did blacken after cooking. These differences nay
be due to inhibiting factors, or perhaps factors oflier than poor
aeration have an influence upon the blackening of potatoes after
cooking. The data su gest that maturity or the stage of the
rest period or both may be such factors. Furthermore, the in-

“’1

crease or carbon dioxide under conditions of poor aeration
cannot be ignored, for it may also play a role in the blackening
of potatoes.

The data given in this paper are of’a preliminary
nature. A more complete and thorough investiggati on is necessary

before definite conclusions can be made concerning the cause of

the blackening;of cooked potatoes.

l.

5.

4.

49.

UlIZARY :l‘TD COITCLUSIGZTS

U)

A comparison of the culinary quality of Kichigan New
Standard Potato Club Russet Rurals, Iiichigan U. s. #1
Russet Rurals, Idaho Russet Burbanks, Kaine Green Hountains,
and the 1952 winter crop of Florida Spaulding Rose and

Bliss Triumph potatoes has been made.

The results of this comparison indicate that the Kichigan
New Standard Potato Club Russet Rurals and the Idaho
Russet Burbanks were superior in culinary quality to the
ifaine Green I-Eountains and the liichican U.S. 331 Russet
Rurals. The Spaulding Rose and Bliss Triumph potatoes
from Florida were intermediate in culinary quality, being
superior to the Kaine Green Hountains and the Xichigan

U. S. #1 Russet Rurals, but inferior to hichigan New

Standard Russet Rurals and the Idaho Russet Burbanks.

The results of an experiment to determine the influence of
the date of planting of Russet Rural potatoes upon culinary
quality indicate that early planting may improve the

culinary quality.

Cooking tests made on potatoes grown in the greenhouse
indicate that a.heavy application of water for a few days
previous to harvesting causes the potatoes to be so: y in

texture nhen cooked.

5.

6.

Experimental evidence was obtained mhich indicates that
poor aeration in potato storafe may be one factor which
causes potatoes to turn black When cooked. Bartholomew
and other investigators produced bled: heart in similar

experirents, but made no reference to the effect of poor

aeration upon the color of the cooked potatoes.

Black heart was pnbmiced in the'potatxas in the experiments
which were stored under conditions of poor aeration.
ho relationship was found, however, between black heart and

the blackening of cooked potatoes.

51.

LIERAIURE CITED

Ashby, S. F.
1906 A contribution to the Study of Factors Affecting
the duality and compostion of Potatoes. Jour.
Agr. Sci. (England) 1:347-557.

Bartholomew, E. T.
1913 Black heart of Potatoes. Phytopath 5:180-182.

and Bennett, J. P.

#1924_’ The Respiration of Potato Tubers in Relation of
the Occurence of Black heart. Univ. Calif.
Tech. Paper 14: 1-55.

 

Butler, 0, Morrison, F. B., and Boll, F. E.
1913 Studies of the Factors Affecting the Culinary
Quality of Potatoes. Am. Soc. of Aaron. 5:1-55.

Bast, Edward W.
1908 A Study of the Factors Influencing the Improve-
ment of the Potato. 111. Agr. Exp. Sta. Bul.
127: 575-456.

Findlay, U. M.
1928 ,uality in Potatoes. Scot. Jour. Agr. 11:559-544.

Gilmore, John V.
1905 ,uality in Potatoes. Cornell Univ. Agr. Exp.
3138. Bill. 250: 503-525. .

Headden, William P. _ _
1924 The Effects of Nitrates on the Composition of
the Potato. Colo. Exp. Sta. Bul. 291:1-97.

Neil, Bernice and Uhittemore, Kargaret
1930 The Relation Between Healiness in Potatoes and,
the Amount of Potash.in tie Fertilizer.
Am. Potato Jour. 7: 275-285.

Onslow, Iuriel W.
1951 The Principles of Plant Biochemistry. Part I.
Cambridge Univ. Press p. 123-172.

Peacock, X. M., Wright, R. C., Uhiteman, T.E., and Fuller,Zlizabeth
1950 Differences in the Cooking Quality of Potatoes
Due to Storage Temperatures. Proc. 17th Ann.
fleeting of Potato Assoc. of Amer. 109:116.

U1
PO

Stewart, F. C., and Iix, A. J.
1917 Black heart and the Aeration of Potatoes in Storage.
B. Y. Geneva Apr. Exp. Sta. Bul. 456: 521-562.

Tinkler, Charles K.
1951 The Blackening of Potatoes after Cooking. biochem.
Jour. (England) 25: 775-777.

Manna use (mu.
993.124; '36
Dec 10 48

E 93.5.