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THE RELATION BETWEEN CARBOHYDRATE
CONTENT AND THE COOKING
IIUALITIES OF MICHIGAN

POTATOES

THESIS FOR THE DEGREE OF M. S.
jennie D. Fisher
1931

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THE RJLATION BJTLAJN
CARBOHYDRATE CONTLKT AKD THE COOKING

QUALITIJS or LZICILIGAN POTATOLS.

n ihesis Submitted to
the Facultj of
Michigan State College in
Partial Fulfillment of the
Requirements for the Degree
of Lester of Science.

by
Jennie D. Fisher

Department of Food and Nutrition
Division of Kome Economics

1931.

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Acknowledgements.

The writer wishes to express to Dr. Marie Dye
and Hrs. Amy Hewberg her sincere appreciation of
the helpful suggestions and criticisms given during
this study.

She is, also, eSpecially grateful to Kiss
Elizabeth Whittaker, Miss Beatrice Grant, hiss
Flora Hanning, and Miss Sylvia hedsker for their

splendid co-cperation as judges.

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. ..

Table of Contents.

I. Object of Study - - - - - - - I.
II. Previous Investigations - - - - 2.
III.Proceedure- - - - - - - - - 14.

1. Description of Samples - - - l4.

2. Methods of Analysis

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5. Cooking Tests - - - - - - 13.
IV. Discussion of Results - - - - - 21.
'V. Summary- - - - - ~ - - - - 50.

v1. Bibliography - - - - - - - - 32.

THE RELATION BETWEEN
CARBOHYDRATE CONTENT AND THE COOKING
QUALITIES OF MICHIGAN POTATOES.

Object of the study.

The potato, because of its high nutritive
value and relatively low cost, is one of the most
widely used vegetable foods. Since 1920 there have
been from $20,458,000 to 465,350,000 bushels of
potatoes per year raised in the United States. The
bulk of this crop is used for food. In spite of
the fact that it occupies such an important place
in the dietaries of the majority of American people
the factors affecting its culinary qualities have
not been made the subject of much investigation.
Very poor lots of potatoes are frequently encounter-
ed but little or no information can be gleaned from
literature as to the cause of poor cooking qualities.

Because this very important question has not
been satisfactorily answered, and also because the
potato crop in Michigan is an important one, the
present investigation was begun. The purpose was
to discover what relations exist between the sugar,
dextrin, starch and fiber content of Michigan pota-
toes and the cooking qualities of the tubers.

v.5 o4}

-2-
Previous Investigations.

The factors most commonly taken into account
in former investigations have been; the different
methods of potato culture; the relative value of
different fertilizers and their effects on the
composition of the potato; the methods of increas-
ing the yield; the comparitive merits of different
varieties with special reference to appearance,
keeping qualities, and yield.

The composition of the potato has been deter-
mined by many workers but the relation of composi-
tion to culinary quality has been considered in
very few of these cases.

In 1897, Frisby and Bryant (7) made a study
of the composition of different parts of the potato
and the loss of nutrients during cooking. The water,
nitrogen, fat, ash, and carbohydrate (by difference)
were determined in the skin, cortex, external medulla
and internal medulla and the composition of the whole
tuber was computed. It was found that there was an
unusually large percentage of water in the variety
tested. In his study of the loss of nutrients he
found that the greatest losses were in nitrogenous
matter and minerals. These losses were very slight

when the tubers were boiled in their skins.

-5-

Snyder (17) also carried on a series of ex-
periments concerning the effect of cooking on the
composition of potatoes. He, also, found that
the losses in cooking unpared potatoes was so small
that it was not worth considering. He used lime
water, salted water, and distilled water and found
that minerals were extracted to greater extent when
potatoes were soaked previous to cooking and were
started in cold distilled water. Lime water seemed
to cause an increased extraction of nitrogenous
matter.

In 1897 Condon and Bussard (4) published an im-
portant paper upon the relation existing between cu-
linary qualities and composition of potatoes. In
their study they found that the composition of the
potato varied with the part considered. The cortex
or outer layer was in all cases found to contain a
greater percentage of dry matter, therefore more
starch and relatively more albuminoid though less

tota1_nitrogen than the medulla. The outer medulla
was richer in dry matter than the inner medulla.
They stated that there was no definite relation
existing between starch and quality although gener-
ally very good potatoes contained less starch than

those of poor quality. They found that mealiness

-4-

generally accompanied a high starch content but
since it was not invariably true, no definite con-

clusions could be drawn. However they considered

 

that the ratio, albuminoid matter x 100, bore a

' starch
distinct relation to mealincss. For the non-mealy
potatoes the ratio ranged between 8.5 to 14; for
the slightly mealy potatoes the ratio ranged between
6.6 to 8.4; for the very mealy potatoes the ratio
was from 4.5 to 6.6.

The nitrogen content of different varieties was
subject to very irregular variations and therefore
could not be used as a basis for judging quality.
However when the ratio, total nitrogenous matter x100,

starch
was taken the potatoes could be classed in order df
merit. The ratio of very good potatoes ranged from
21 to 25 and the very poor below 16.

"Peterman in his study of potatoes found that
their criterion of quality the ratio,
total nitrogenous matter x 100, was not wholly

starch
trustworthy but he substantially confirmed the con-
clusion that the ratio, albuminoids x 100, was of
starch
value as a criterion of mealiness" (3).

One should remember that Condon and Bussard

judged cooking qualities of potatoes according to

the French Standards which differ widely from the

American Standards. French Standards of excellence

.L..'— (\-

demand a tuber which when cooked will hold its
shape. A good potato must be waxy and therefore
higher in nitrogen and relatively lower in starch.

In our country and in England the chief test
for excellence in a potato is its degree of meali-
ness, which according to Langworthy (13) means that
when cooked it should form a light crystalline-like
mass with almost distinct glistening particles of
starch. He says that this quality depends largely
upon the proportion of starch present. If the
starch is abundant and evenly distributed through-
out the tuber then the cells will burst open in
cooking and form a light flaky crystalline mass,
but if the starch is not uniformly distributed
there is likely to be spots where water will settle,
causing sogginess. Young potatoes or potatoes
stored at a low temperature contain less starch
than fresh mature tubers and consequently are less
mealy.

Butler and Bell (5) disagree with Langworthy
(15) as to the cause of mealiness. They believe
that mealiness is caused by separation of the cells
during the cooking process and not by bursting of
the cells. Butler states that there seems to be no

relation between dry matter and mealiness or between

.5-

starch and mealiness. He tested only one variety,
the dry matter of which ranged from 19.7 to 24.5 per
cent. There was very little difference in the dry
matter content of mealy and non-mealy, but consider-
ing the fact that he used only one variety of pctaoes
his results seem to indicate some correlation between
dry matter and mealiness. Especially does this seem
true since it was found that the cortex is always
more mealy than the medulla, the difference corre-
sponding to a well marked higher dry matter content.
He found that there was no relation to meali-
ness in potatoes and the amount of sugar present but
the relation between sweetness to taste and degree
of mealiness was well marked. In no case was a
potato that was judged sweet to the taste found to
be mealy. The temperature at which potatoes are
stored affects the amount of sugar present. Sugar
is formed from the starch of the tuber therefore
decreasing the amount of starch. Low temperature
favors the development of sugar. In experiments
concerning storage of potatoes Butler et a1 (5)
found that potatoes stored at a temperature of 1°
to 5° C. were markedly inferior to those stored at
8° to 11° 0. Those stored at 20° 0. were better
than tubers stored at 8° to 11°C., but storage for

-7-

more than twenty days at this high temperature re-
sults in germination with marked deterioration. He
concluded therefore that 8° to 11° C. was the best
temperature for storing potatoes.

Appleman (2) in a study of the changes in pota-
toes during storage found that the rate of accumu-
lation of sugar is most rapid when the storage temp-
erature is from 29° to 52° F. or 00 to 2° C. The
maximum of three to four percent of sugar is reached
in four to six weeks of storage. If potatoes which
have accumulated sugar are stored for a week or long-
er at a temperature of 21° to 24° C. threefourths
of the sugar will be converted back to starch and
the remainder will be lost through respiration.
Storage at too high temperature results in changes
due to germination and loss in weight due to evapora-
tion and respired carbon dioxide. The optimum.temp-
erature for storage of potatoes to be used for culin-
any purposes is between 8° to 11° C.

In a very recent article Sweetman(l7) reports
that the amount of sugar in the tuber definitely
affects the color cf the potato chips produced.
Potatoes stored at or below 38° F or 0° 0. contained
more sugar and produced darker colored chips than

those stored at higher temperatures. She, also,

3‘1]:

-8-

found that if potatoes which had been stored at low
temperatures were kept for several days at room
temperature the amount of sugar in the tuber decreas-
ed. Potatoes which were dug at an early date and
were therefore somewhat immature also gave chips

of darker color than those of mature tubers.

In 1905 Gilmore (8) of Cornell Agricultural
Experiment Station, made an investigation of the
factors affecting culinary quality in potatoes. His
conclusion was that the culinary qualities of pota-
toes depend not so much upon the chemical composition
of the tuber as upon its anatomical and perhaps its
physiological structure, and upon the arrangement
and distribution of water areas. The structural
characteristics in turn are affected in the main by
the following factors: " The daily range of tempera-
ture of soil and atmoSphere during the growth period;
the degree of ripeness of the tuber when the plant
dies; the physical condition and type of soil in
which the plant is grown. "

Gilmore (8) says that in general when the cor-
tical layer is thick and dense the tuber is of poor
quality. A thin more translucent and less differen-
tiated cortical layer and a uniform external medul-

lary area indicates an even distribution of starch

-9-
cells and starch grains in the cells which are in-
dications of superior quality. A large branching,
highly differentiated inner medullary ares indicates
that there is a large proportion of potato substance
which does not contain enough starch grains to rup-
ture the cell walls when the tuber is cooked, hence
sogginess will result.

He says that if the starch content is not less
than 17 per cent and if it is evenly distributed then
the potato will meet our culinary standards. He found
that variations in nitrogen content do not seem to
have any noticeable effect on quality although there
is slight indication that extremely high nitrogen
content may make the flavor more pronounced.

East (6) in his study of the improvement of the
potato reaches conclusions that are in agreement
with Gilmore. He states that tubers containing less
than 18 per cent dry matter cannot be of good quality.
However, he thinks that when dry matter is above
that level that the quality is not directly affected
by variations in starch or dry matter content.

In 1925 Sister nary B. Lies (14), of the Uni-
versity of hinnesota, made a study of the relations
existing among composition, shape and cooking quali-

ties in potatoes. She found no indication that the

texture and sluffing bear any definite relation to
shape in any of the varieties studied. She agrees
with East (6) that there is no relation existing be-
tween mealiness and dry matter unless one considers
only samples of exceptionally low dry matter. She
did find however that samphes showing the worst
sluffing were also mealy and concluded that these
two factors are probably the results of the same
group of properties of the tuber.

Within the standard varieties used the shape
ratios did not very enough to materially affect the
composition of the tuber. However there was a ten-
dency for the percent of dry matter to become less
as the tubers became relatively shorter. The shape
of the tubers varied more widely among the Rural
Russet samples than any other variety.

In the Rurals and Cobblers there was an in-
crease in nitrogen, both on the fresh and dry basis
as the dry matter decreased. This is probably due
to the fact that among the zones of the tuber the
nitrogen and dry matter vary inversely. She agrees
with Butler et al (3) that mealiness depends upon
the separation of cells and not on the disintegra-

tion of the starch cells.

-11..

H.E. Goldwaite (ll) conducted an intensive
study of the composition of Colorado potatoes.
Several hundred analyses, including the determina-
tion of moisture, dry matter, starch, nitrogen and
ash, were made. Individual tubers were used for
these analyses and no two potatoes of identical com-
position were found even though analyses were made
on tubers taken from the same hill at the same time.
"The variations when calculated as numerical differ-
ences only are eSpecially striking in percentage of
water, dry matter and total carbohydrates; but when
calculated as percentage differences they are frequent-
ly more striking in the percentage of nitrogenous mat-
ter and ash." In agreement with other workers Gold-
waite (11) found that the percentage of water increas-
es from cortex to core. The potato proteins and min-
erals are also greater in cortex than core.

The effects of irrigation on composition of pota-
toes was also studied and it was found that there
was no indication of any relation existing between
the amount of water received by the plant and the
amount of moisture in the potato. This was in agree-
ment with the findings of Richman (16) who studied
effects of irrigation on water content of plants.
The total average of percentage of water in dryland

and irrigated potatoes was almost identical.

.Jsru.

-12-

In the work on composition of cooked potatoes
Goldwaite (11) found that the steamed halves of
potatoes showed less water c ngcn than the corres-
ponding rav halves, and consequently greater content
of dry matter, starch total carbohydrates and nitro-
genous matter and ash. Boiled halves of potatoes
cooled unpeeled showed nearly the same content of
water, dry matter, starch and total carbohydrates
as their correSponding raw halves, but a less con-
tent of nitrogenous matter and ash; peeled hot and
then cooled they showed a lower percen'age of water
and corresponding high content of starch, nitrogen-
ous matter and ash. Analyses of whole boiled and
baked potatoes were unsatisfactory because they could
only be compared with analyses of other tubers, and
were unsatisfactory. ho two tubers were found to have
the same chemical composition.

Child and Willaman (5) made a study of the cul-

.0

inary qualities cl potatoes using fifteen lots of
tubers. Their conclusions were that higher dry mat-
ter tends to be accompanied by better texture and
flavor w'thin the group studied, which was rather
low in dry matter.

huch variation of opinion exists concerning the
relation of dry matter and carbohydrate content to

the cooking qualities of potatoes. Child and Uillaman

(5), and Butler, Lorrison, and Boll (5) are of the

-13-

of the Opinion that better texture is accompanied
by a higher level of dry matter. Lies (14), East
(6), and Gilmore (8), say that the quality of the
tuber is not affected by any difference in the per-
centage of dry matter if it is above the level of
17 to 18 percent. There has been very little in-
vestigation concerning sugar content of potatoes
but workers seem to agree that a high percentage of
sugar is detrimental to quality. All investigators
except Goldwaite (11) agree that there is no positive
correlation between percent of starch and quality.
However, they do say that higher starch content is

often accompanied by better texture.

"II--

I

 

-14-
Proceedure.
Description of Samples.

The original plan was to use only Michigan
grown potatoes for this study. However, since
there were no striking relations shown between the
carbohydrate content and culinary quality within this
variety, it was thought wise to use some other
potatoes for comparison.

The ten samples in series A were of the Rural
Russet variety, which were grown on the experimental
farms at Hichigan State College. Series B consisted
of two lots of Idaho Bakers which were purchased on
the market at East Lansing. Series C consisted
of two samples of new potatoes of the Early Hose
variety, which were also purchased on the open mar-
ket.

Ten sound tubers of approximately the same size
and shape were chosen for each sample. They were
peeled as thinly and quickly as possible and one length-
wise half was dropped into cold water to be reserved
for cooking tests. The other halves were thinly slic-
ed, weighed and covered with 95 percent alcohol and
dried in a Freas electric oven at a temperature of
550 C. for approximately 72 hours or until the weight

remained constant. The low temperature and treatment

.4

-15-

with alcohol, according to Goldwaite (11) prevents
dextrinization and discoloration of sample. The
dried samples were ground on a fine food chopper,
then pulverized in a mortar and stored in glass

stoppered containers.
Hethods of.Analys°s.

The drying of the sample leads simultaneously
to the determination of both water and total solids.
The percentage was calculated from the difference
in weight between the fresh and dried sample.

For the determination of sugar the solution
was prepared according to method 18 p. 118 of the
Official and Tentative hethod of analysis of the
Association of Official Agricultural Chemists,

Second Bdition. A suitable aliquot was taken and
method Ho. 55 p. 190 of the Official and Tentative
Method of Analysis of Association of Official
Agricultural Chemists was used for the precipitation
of cuprous oxide. The reduced copper was then deter-
mined by the volumetric thiosulfate method.

For the determination of dextrin the residue
left after filtering off the sugar solution was treat-
ed with 200 cc of water and let stand, with frequent
shaking at room temperature for three hours. The

mixture was then filtered and the residue reserved.

The filtrate was made 2% percent acid with Sulfuric
acid and was then hydrolyzed for l%-hours. The
solution was cooled, nearly neutralized with sodium
hydroxide and made to volume. The reducing sugar
was determined as above.

The starch was determined by method 21 p. 119
of the Official and Tentative Methods of Analysis
of the Association of Official Agricultural Chemists,
Second Edition.

For the determination of crude fiber the follow-
ing modification of Ho. 17 p. 118 of hethods of Analysis
in the Official and Tentative Methods of Analysis of the
Association of Official Agricultural Chemists, Second
Edition was used. Since there is less than one tenth
of one percent of fat in potatoes it was considered
unnecessary to carry out the ether extraction. About
two grams cf dried sample were weighed and transferred
to a one liter beaker without lip. 200 cc of hot 0.255
E. sulfuric acid was added and the beaker covered with
a round bottom flask which was filled with distilled
water for washing. This flask served as a reflex con-
denser. The contents of the beaker was brought to
boiling within one minute and boiling continued for
exactly thirty minutes. 100 cc of hot 1.45 N. sodium

hydroxide was then added and boiling continued for

-17-

‘

thirty minutes longer. Tnis amount of sodium hydr-
oxide is calculated to neutralize the sulfuric acid
and bring the solution to the prOper concentration
(.125 grams of sodium hydroxide per 100 00.).

Care was taken at all times to prevent any ma-
terial from creeping up on the sides of the beaker
Where it would not be properly digested. The mix-
ture was filtered immediately thru a properly pre-
pared asbestos mat in a good crucible. It was wash-
ed thoroughly with hot water and finally with 95%
alcohol and dried at 1100 C. until the weight was
constant. The crucible and contents were then in-
cinerated and the loss in :eight reported as crude

fiber.

Cooking Tests.

All cooking tests were made as soon as possible
after they were pared. The time required for caring
for the samples for analysis was never more than ten
minutes. The halves of potatoes reserved for cooking
were again divided into halves, one section being
used for boiling and the other for steaming.

For boiled potatoes the quarters were put into
an enamel sauce pan and covered with one liter of
boiling, unsalted distilled water. The pan was co-
vered and the water kept boiling without vigorous
bubbling. The potatoes were considered done when,
pierced by a fork, they were found to be tender.

The time of cooking varied from 17 to 21 minutes
depending somewhat on the size of the tubers.

The portions of potato reserved for the steam-
ing tests were placed on waxed paper an wire racks
in the steamer and were steamed until they were
tender. The length of time for steaming was from
21 to 25 minutes.

The potatoes were judged immediately upon re-
moval from the fire because it was found.upon cool-
ing and exposure to the air caused a change. Five

members of the Home Economics faculty acted as judges.

-19..

Each value for cooking qualities represents an av-
erage of the results of the five judges.

After studying the score cards of Lies (14),
Child and Williams (5) and Butler et a1 (5) the
following one was devised for use in the present

study. See score card on page 20.

choom Hmpoe

I'll,

.ma mmopepom dmammpm How ohoom poomnmm

om mmopwpom umafion How onoom pwmmhom

mmopmpom uoafiop op mane mofiHmmw mane

III!

I

I I

 

 

 

 

 

 

 

 

 

 

 

 

 

dmpmam oopwnm dopmswmp copwhm
-mpcflmue -opnenfle snag Inflmee ma -mpnamae
macpcfimaoo sons umpwnodos mapgmfiam nowmonooo
conflwnm
ammom ammom doqflwnm easy
hfipgwfiam mwws ouhfloo mawma
hawoa mum» ondpwoe
hnpnwo mnohpm pway woman pawmwmfim
awaken Ho>nah
mamas Mowap
Spas BoHHmm Boaaom mpfigs
smfimcnm nmfimwnm Boaaoz haaono means Hafioo
emaempm emflaom H m r, m er, 1. m mmapfiaeea
. “open tit; . = r: r. r: .02 pomh

 

.mMomwaom mo mmHaHgdba meMooo wszmbh Mom ammo mmOom

F

 

-21-

Discussion of Results.

Huch difficulty was experienced in defining a
standard for cooking tests since all testing was n
necessarily subjective. Until some more objective
means of judging and comparing mealiness, color,
and flavor is devised, it will be difficlut to draw
definite conclusions. It may be said, however, that
the personnel of the judging team remained relative-
ly constant throughout the experiment and that the
individual findings of the judges were generally in
very close agreement.

In practically all cases the steamed potatoes
received relatively lower scores than the boiled
ones. In no instance was the color of the steamed
potatoes considered as good as that of the ones
which had been boiled. Poorer flavor in steamed
potatoes was also indicated by the fact that in only
two instances was the score of the steamed potatoes
equal to that of the boiled ones. The difference
in scores for texture was not quite so marked as
for color and flavor, but it also indicates that
the steamed product was not found to be quite so
mealy as the boiled ones.

The results obtained in this investigation
were not studied statistically since the number of

samples was so small that the coefficient of cor-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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mwfl ms; eé .m out we saw last. eel 06H! 55m} ...MF
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ms mew was can we emw Te 1m; roe as; Ed .mvi
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F a
orgasms semen. earn: 35¢me emflem seems eflom sense? lewflomaflwpm eflcm 3.2.5
mohoom Hepoe msflmmnam canvass seesaw} Hmwoo
.mmaoom mcaoSn Mo ommnmpw I.Iluwmosom smohmm

 

 

.mMoHMBom mo mmHBH

(Fer

meMoQo OB mnmwmm mo mum mmeedu Wmm mo ZOHBdAmm

A.mofismm Scam we mnepacu Hensflpfide Mo nomflhcmaoov

.H gamma

 

 

 

-22-

relation would hardly be justified.

In table I the results of analyses for starch
and dry matter of the individual samples of each
series are given together with the corresponding
scores for cooking qualities. An examination of
the data presented in this table shows very clearly
that there is no correlation between the dry mat-
ter or starch in the individual samples within a
given variety and the cooking qualities of the
potatoes.

In table II the average percent of starch in
each of the three varieties and the average of the
judges for each variety is given. From this data
we would conclude that there is no relation between
the amount of starch and either color or flavor of
the potatoes. The scores for texture, however, do
indicate that there is a correlation between the
amount of starch and the degree of mealiness. The
scores for steamed potatoes bring this fact out
more clearly than do the scores for boiled potatoes.
The difference in scores for boiled potatoes is only
.3 while for steamed potatoes it is 1.7. The above
results also indicate that there is relation between
the amount of starch and the degree of sluffing. The

variety containing the smallest amount of starch shows

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

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r Ir %0
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323 .22.: 38: ”as $93 03.3 1 I ll Jmofoe

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89mg $.93 magnified, mammal! $3M! 1!!!! passages
.EE was .52 was! r! I: lllll I

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A .cawmmfim use nocnoo Scam»
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-23-

very little sluffing, the score being 4.8 out of a
possible 5 points, while the sample having the great-
est percentage of starch shows much sluffing, the
score in this case being 5.2 out of a possible 5. Ho
definite conclusion can be drawn concerning quality
as a whole and the amount of starch because the scores
for quality as a whole do not increase regularly with
the increase in starch. However, the score for both
boiled and steamed potatoes is highest for the variety
containing the most starch.

These results are only partially in agreement
with the conclusions of other workers. Condon and
Bussard (4) showed that the amounts of starch in
potatoes was not a relaible guide to the quality as
a whole or of mealiness in particular. However,
their study included 34 varieties of tubers and the
present only 3 varieties. Their results are summa-
rized in table III.

Harcourt, also, concludes that there is no rel-
ation between the percent of starch and quality as
a whole or between the percent of starch and meali-
ness. Table IV presents the data gathered by him.

In a study of relation between mealiness in
potatoes and the amount of potash in the fertilizer

Neil and Whittemore (15) found that there was a

 

 

 

 

 

 

 

 

 

 

 

 

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NO.OH es.Om ow - OO N0.0H OH.Om OOH . OO
.Qflu .ssm .pomwsom, .sflu .msm I. .poemsemr
mpeaom oe mpcwoe OOH
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I, 'll

 

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m HEHHdmfi 9mm WBHHNDG OB mommem mo ZQHqumm

A.phsoohsm aonmv

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l

 

 

positive relation between the amount of starch and
mealiness in only one third of their eXperiments.
Therefore they concluded that the percentage of
starch has no direct influence on the degree of
mealiness in potatoes.

In his study of culinary quality of potatoes
Butler (3), also, concludes that the percentage of
starch has no direct influence on the degree of
mealiness in potatoes. Table IV presents his re-
sults.

In the present investigation the conclusion,
that there is a positive relation between the a-
mount of starch and the mealiness of the potato, is
in agreement with Goldwaite's (10) statement that,
"The higher the percentage of starch the mealier the
petato."

East (6) states that the paucity of stardh in
the inner medullary layers causes the cells to be
only partially ruptured, hence the water may settle
causing sogginess. On the other hand, in the corti-
cal layer where the starch is more abundant, it
swells on cooking, the cells becoming ruptured and
mealiness resulting. In agreement with this state-
ment Butler et a1 (3) also, found that the cortical

layer is always more mealy than the medulla, the dif-

 

.
flat
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Emma sIHIEmHHm 3.3 on mommoHd Ham
flees HOJH I I no I I IIIMOImmfiIgHm
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©.HH m.>H m.¢ m.m ©.& ¢.¢ b.¢ ¢.¢ w.¢ mm.mm o
m.m m.©H N.¢ m.m m.& H.& N.¢ O.n 0.6. f&.mm 4
Pemewfim OmHHom Omeom omega emHHom Ommefim OmHmo ngwpm made .85. 32mm
amiss
mmaoom Hopes mede waspsme Mopeds HOHoo - ham
II II II. %o
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.mMo94eom mo mMHBHHflDd GZHMQQO OB mmeamfi wmm Mo BQHB¢AMM mme

 

«Ma

r.

-25..

ference corresponding to a well marked, higher dry
matter content.

The data showing the relation of dry matter to
cooking qualities of the potato is presented in
table VI.

In his study of the improvement of the pota-
toes East (6) states that there is a lower limit of
18 percent dry matter below which the tuber cannot
be of good quality. He says, however, that when the
dry matter is above that level the quality is not
seemingly affected by any differences in dry matter.

In all of the samples analyzed during the pre-
sent study the dry matter content was well above the
limit of East, the range being from 21.46 percent
to 25.95 percent. Examination of the data presented
in table II shows that the dry matter content of the
individual samples within a given variety does not
bear any relation to the quality of the potato. How-
ever, it can be seen from the data presented in table
VI that there is an indication that a positive cor-
relation exists between the amount of dry matter and
the quality as a Whole. The scores for color, flavor,
texture, and sluffing do not indicate that there is
any relation between these factors and the amount of

dry matter.

I) II [If

 

m.m 0.0H m.¢ &.m n.m H.n N.¢ o.m m.¢ fbm.o

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.4
m .3“ 0 .3“ m .m m J m .m H .H. o .m _ HJ w 3v ”van .9 .m
I l I II I
o.HH m.nH m.¢ m.m m.n ¢.¢ a b.¢ ¢.¢ m.¢ wbH.o o
esteem H520 Omflom 233m emHHom seesaw eoHaom smegma. Oonmm II fiwflmm
I I .995.
mpoom H.309 sauna—“m — musesoa II Hopsflm I .330 .335.
- . II I II I. Mo
monoom memes... Ho swayed; :soohmm

 

 

 

 

.mmoedeom ho mmHBqubd 025800 on. emmpfioo mabm .mo ZOHBTHMM
HHP mafia

 

-25-

Child and Willaman (5) state that higher dry
matter tends to be accompanied by better texture
within the group studied, which was rather low in
dry matter. The maximum amount of dry matter in
tubers analyzed by them was 19.0 percent and the
maximum was 13.1 percent. Condon and Bussard (4)
concludes that as a rule mealiness is greater when
the water content is relatively low. In agreement
with Butler et a1 (3) says that potatoes high in
water content are less mealy than those relatively
low in water. Since the influence of dry matter is
the converse of that of water the conclusion, from
the present investigation, that higher dry matter
seems to be correlated with better quality, is in
agreement with these workers. All data presented
in the literature studied seems to uphold this
theory.

Data presented in table VII seems to indicate
that there is a correlation between the amount of
sugar and the color of the tuber, since in both the
steamed and the boiled potatoes the variety contain-
ing the least amount of sugar received the highest
score for color. This difference is more significant
in the steamed potatoes. There does not seem to be

any relation between the sugar content and any of

 

 

1“.( (I II 1'

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_
O.HH O.sH O.e O.m O.m e.e s.e e.e O.e new. O
m.m O.OH m.s O.m O.n H.O m.e O.O O.e ems. a
m.mH O.wH m.m m.e O.m H.e O.O H.e O.e mmH. m
.Omesmpm OmHHom OmHaom Owesesm OmHaom .eeemw OmeHHom Omeempm OmHHmn I. II.ommem
I, II. .hobd
mmhoom Hmpoe 4 wasam wasp we b Hobsam no 00 _nfihpsmm
.I I. I. no
.mmaoom wowusa Mo omwhcbd _pnmosmm

 

 

 

.mflommmom Mo mmHBHHdbm wzHMooo OB sz Nmn mo HOHBdAmm
.HHH> Mmmde

-27-

the other factors or the quality as a whole. These
results are in agreement that there is no relation
between the mealiness or quality as a whole and the
sugar content. He does say, however, that a potato
which is sweet to the taste is never of good quality.
Little work has been done on the relation of
sugar to quality except with reference to the desir-
ability of the potato for use in making potato chips
for frying. It is well known that the carmelization
of sugar gives a darker color therefore tubers which
are to be cooked at this high temperature must be
low in sugar if light colored uniform chips are to
be produced. Sweetman (16) studied the effect of
storage on accumulation of sugar in tubers and its
effect on the color of potato chips. She concluded
that high sugar content was detrimental to quality.
The data in table VIII seems to indicate that
there is a positive correlation between the amount
of dextrin and the texture of the potato. The vari-
ety containing the least dextrin received the high-
est score for mealiness. This difference is more
marked in the steamed potatoes than in the boiled
ones. The scores for sluffing shows a correlation
between the amount of dextrin and the degree of
sluffing. The sample containing the least dextrin

showed the most sluffing. No definite conclusion

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I BI a

O.HH OsH OJ Oh es 1 ed .3. ed

m.m.m 0.3” win mé. m5 HJ o.m Haw

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a
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I I I I named
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- m8
.mohoom momma. Mo amassed psoosmm
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.NH mange

 

 

-28-

can be drawn concerning the relation between the
amount of dextrin and the quality as a whole but
the sample containing the least dextrin received t
the highest score.

There is no study reported in which the dextrin
has been determined. Carbohydrates are, in the major-
ity of cases, determined by difference.

The scores for color indicate that there may
be a correlation between the amount of fiber and the
color. The samples containing the most fiber were
least acceptable in color. The scores for steamed
potatoes show more of a significant difference than
the boiled ones show. The data also indicates that
there is a corredation between fiber content and
flavor. Again the scores for steamed potatoes seem,
to be more significant than the boiled ones. There
does not seem to be any correlation between the
amount of fiber and the texture, sluffing or quality
as a whole. There is no record in literature of a
study of the relation of fiber to the cooking quali-
ties of the tuber.

According to Frisby and Bryant (7) the average
of all American analysis for fiber was 0.3 percent
and the average for European analysis was 0.7 percent.
Charles D. Woods (19) reports the average of all

American analysis to be 0.4 percent and the average

 

ll . I. '1' I lI l. I ." “(Tlllu'l I.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(I (I I II (I (WIIHIIIIII( (“Hill
m.mH 0.0H m.O O.e m.n H.e 0.0 H.¢ O.e Oe.Om m
0.0 0.0H m.e O.m O.& H.& m.e O.m O.e sm.OH 4
O.HH O.aH O.e O.m O.m e.¢ s.e e.e O.e «H.OH O
.OoEempm OoHHom OoHHomwmseopm OOHHom geeopm Ommaom IeI..pm eMHHdm Iuamee mHmmO
I.I. II. O m O
.mmaoom Haves uswde_ osspwoa Hogwam Hoaoo proe
I. II. he
. . mnoom mowdsh Mo umssobd II;I ammommm

 

.mfloafleom mo mmHBHQdflw azHMooo OB mMammnwmodeo H4809 mo ZOHamflmm

.M mnm4a

 

for Kaine potatoes analyzed by him to be 0.6 percent.
In the present study it was found that hichigan
potatoes contained the greatest amount of fiber and
the new potatoes the smallest amount.

Table X presents percent of total carbohydrates
and the corresponding scores for cooking qualities.
The scores for texture indicate that there is a posi-
tive correlation between the amount of carbohydrates
present and the mealiness of thepotato. The sample
having the largest percent of carbohydrate shows the
most sluffing. There is a great difference of Opin-
ion concerning the cause of good quality in potatoes.
The present investigation presents some results con-
cerning factors not hitherto studied but no definite
conclusions could be drawn because of the subjective
method of judging and the small number of samples
studied. The effect of the percentage of the differ-
ent carbohydrates on the individual factors of cock-
ing qualities was studied as well as the effect on
cooking qiality as a whole. There has been no former
study made of the relation of dextrin and fiber to

culinary qualities in potatoes. In general the re-
sults of this investigation agree with the majority
of workers but there is so much difference of opinion
that it seems desirable that more work be done. con-

cerning factors which affect culinary quality.

Summary

1. Steamed potatoes received relatively lower
scores for cooking qualities than the boiled ones.
The differences in the scores for the three varie-
ties were more significant than the differences

in the scores for boiled potatoes.

2. hichigan potatoes, of the Rural Russet variety,
received a lower score for cooking qualities than

the Idaho Baker or Early Rose potatoes.

3. Within a given variety the cooking qualities
of the potatoes, which were both boiled and steamed,
do not seem to be affected by the difference in

amounts of various carbohydrates present.

4. There is no correlation between color, flavor
or quality as a whole and the percent of starch in
potatoes. There seems to be a positive correlation
between the amount of starch and mealiness and sluf-

fing.

5. Higher dry matter seems to be accompanied by bet-

ter texture and quality as a whole.

6. There seems to be an inverse relation between the

amount of sugar and color of potatoes.

“l
-../-

7. There seems to be a positive correlation be-
tween the percent of dextrin in potatoes and the
texture. However, there seems to be an inverse
relation between the amount of dextrin and the de-

gree of s uffing.

8. There seems to be an inverse relation between
the amount of fiber and color and between the amount

of fiber and flavor in the potatoes studied.

9. Higher total carbohydrate content seems to be
accompanied by better texture within the group studied.
Samples having the largest per cent of total carbo-

d

hydrates shows the greatest amount of sluffing.

1.

6.

7.

Bibliography.

13.811132], 80F. ,

A Study of Factors Affecting the Quality
and Composition of Potatoes.

Journ. of Agr. Sci I 1905-05.

1.
I

Changes in the Irish Pota.o During 3t

0
.'
f.)
on
(D
.

La. Agr. :xwt. Sta. Bull. 157 p. 527-554.

Butler, 0., Lorrison, P.B., Boll, 9.3.,

Studies on Factors Affecting Culinary
Qualities of Potatoes.

Journ. of Amer. Soc. Agron 5, p. 1-55

Condon, H., Bussard, L.,

Researches sur la Pomme de Terre Alimintaire

Amer Sci Agron. Ho 2 p. 250-291.

Child, Alice, and Willaman, J.J.,

ulinary Quality of Potatoes.

PC:
KO
0

Amer. Potato Journ. vol VI Sept. 19

A Study of the Factors Influencing Improve-
ment of the Potato.

111. Exp. Sta. Rept. 127 p. 375-455.

Frisby, A.J., and Bryant, A.P.,

Composition of Different Parts of the Potato
and Loss of Hutrients in Boiling.

7T0 30 DOA. "OOEI So 3111].. 4:50

8. Gilmore , F. TI. ,
A Study of Quality in Potatoes.
(‘V 0':

l TTniv. Agr. 131:0. eta. 3111. no

.L

9. Gwen , lie ta ,

‘\

Points to Keep in Lind When nuying and
Cooking Potatoes.

Home Economist Vol.VI.P. 514.

10. Gol,waite, E.E.,
Potatoes from the Housekeepers Standpoint.

Colorado Exp. Sta. Bull. 296.

110 Goldi'laite, H.130,
Variations of Composition of Colorado Potatoes.

Colorado Esp. Sta. Bull 297.

12. Harcourt, R.
Composition and Cooking Qualities of Potatoes.

Farmer's Inst of Ont. 12th Eept., 1907.

15. Longworthy, C.F.,
Potatoes and Other Root Creps TTsed for Food.

U.S.D.A. Farmer's Bull. 29..

14. Lies, Sister Lary 3.,

Relations Existing Among Composition, Shape
and Cooking Qualities of Potatoes.

Unpublished Thesis, Vniversity of Linn.

15.

16.

17.

18.

19.

-a4-

Neil, B. and Whittemore, 1.,

Relation Between K aliness in Potatoes and
Amount of Potash in Eertliner.

Amer. Potato Journ. Vol VII . Ho. 10

Richman, H.

Effect of Irrigation TTpon Water Content of
Plants.

Wtah Exp. Sta. Bull. 5, 1891.

Snyder, H.,

The Composition of Different Parts of the
Potato and Loss of Nutrients During Boiling.

TTOSODOA. 00E. S. Bull]. 43.

Sweetman, E.D.,

Chips as Influenced by

Color of Potato
en erature of Tubers and Other

Storage T ;p
Factors.

Journ. of Agr. Research vol. 41 Ho. 6.

EstrOOdS, Che-So Do,
Potato Studies.

Kaine 2X10 Sta. Bull. 277.

jun 29 40 1% u’m.t10n (Opt.

Jun. “441‘.
M744

Feb 20 ’58

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