THE DETERMINATION OF CARBOHYDRATES IN VEGETABLE ...

THE DETERMINATION OF CARBOHYDRATES IN VEGETABLE FOODS.

BY VICTOR C. MYERS AND HILDA M. CROLL.

(From the Laboratory of Pathologial Chemistry, New York Post-Graduate Medical School and Hospital, New York.)

(Received for publication, March 24, 1921.)

Our present knowledge of the carbohydrate content of vegetables is based largely upon data collected by Atwater and Bryant.1 Their figures for total carbohydrate include “fiber,” which is not digested by the human body. In some instances they record the percentage of fiber alone. The total carbohydrate has been determined generally by difference, thus causing the combined errors of all other analyses to fall upon this constituent. Olmsted2 has determined the total available carbohydrate of certain raw and thrice boiled vegetables by two methods: first, starch hydrolysis by diastase and dilute hydrochloric acid, with estimation of reducing sugar by Bertrand’s titration method; second, the determination of the sugar excreted by phlorhizinized dogs which were fed certain of the vegetables. His results agree rather closely with earlier recorded figures.

The form in which the available carbohydrate exists in foods is of significance in any attempt to develop satisfactory methods of cooking, aiming either to conserve as much as possible of the foDd value, or to remove most of the carbohydrate, as is desirable in the feeding of diabetic patients. Little is recorded in the litera- ture concerning the form of available carbohydrate in vegetables. Atwater and Bryant’ have recorded analyses of a few vegetables and fruits in which the percentage of sugar is given, in addition to the t,otal carbohydrate. They report that one sample of carrots contained 3.6 per cent cane-sugar and 3 per cent fruit-sugar.

1 Atwater, W. O., and Bryant, A. P., Chemical composition of American food materials, U. S. Dept. Agric., Bull. 28, revised 1906.

2 Olmsted, W. H., J. Biol. Chem., 1920, xli, 45.

537

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538 Carbohydrates in Vegetable Foods

One sample of boiled white potatoes contained 9.2 per cent cane- sugar, 0.2 per cent glucose, and 17.4 per cent starch. The edible portion of twenty-six samples of raw sweet potatoes contained an average of 2.5 per cent cane-sugar and 3.4 per cent invert sugar. One sample of turnips contained 4.4 per cent sugar. Of the fruits of which the percentages of sugar are recorded, sugars form a large proportion of the total carbohydrate. Thus the edible portion of one sample of apple contained 6.4 per cent glucose, 6 per cent cane-sugar, and 1.2 per cent starch, acids, etc. The edible portion of one sample of apricot contained 11.9 per cent sugar, as against 13.4 per cent total carbohydrate on an average of eleven samples. Eight samples of oranges contained an average of 9 per cent sugar. Lemon juice contained’ 2.3 per cent sugar and 7.5 per cent citric acid, making up 9.8 per cent of total carbohydrate. WardalP states that among the vegetables which she studied, artichokes, celery, spinach, .rhubarb, kale, carrots, asparagus, endive, cauliflower, mushrooms, beets, and parsnips, only cauliflower, parsnips, cabbage, and carrots showed the presence of even a very small amount of starch, the others apparently containing the carbohydrate in the form of soluble sugars. Most of the carbohydrate of the carrot was found to be in the form of soluble reducing substance, while sucrose appeared to be the chief form of carbohydrate in beets. Wardall emphasizes the fact t,hat “information concerning the nature and physiolog- ic significance of the carbohydrate will lead to a rational method of procedure in the preparation of the foods.” Street and Bailey4 in a study of the carbohydrates of the soy bean used the method of analysis by which the soluble reducing sugars and sucrose were extracted with boiling 95 per cent alcohol, the dextrins and soluble starch then extracted with water, and the insoluble starch hydrolyzed with malt extract. The final determination of the sugars was made by reduction of Fehling’s solution before and after acid hydrolysis of these extracts.

The present study was undertaken to work out a relatively simple method for the determination of available carbohydrate in vegetable foods; by the use of this method to determine the amount and form of such carbohydrate in those vegetables and

3 Wardall, R. A., J. Am. Med. Awn., 1917, Ixix, 1859. 4 Street, J. P., and Bailey, E. M., J. Ind. and Eng. Chem., 1915, vii, 853.


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V. C. Myers and H. M. Croll

fruits most used in feeding diabetic patients; and t,o observe the effect of different factors in cooking on the removal of carbohydrate from vegetables.

Studies concerning the carbohydrate content of various foods have been in progress in this laboratory for several years. At the suggestion of one of us, Bernhard5 in 1915 employed a colori- metric procedure for the determination of free reducing sugars and total carbohydrate in miscellaneous food materials. This method depends on the extraction with water of the reducing sugars and their determination by the well known color reaction with sodium picrate.6s7 The total carbohydrates were determined by direct hydrolysis after heating the food with approximately normal hydrochloric acid on a reflux condenser for 24 to 3 hours, and subsequent calorimetric determination of the reducing sugar formed. Bernhard published the results of the analysis of various fruits and vegetables for free reducing sugars, and of various other food materials for free reducing sugars and total carbohydrates. Myers and Rose* employed a similar colori- metric method for a study of the carbohydrate changes in the ripening of bananas. In the preceding paper, Rose9 has described a very simple method for the inversion and determination of cane- sugar, which depends upon the hydrolysis of the sucrose by boiling for 10 minutes with picric acid solution and the subsequent determination of the reducing sugar by reduction of sodium picrate.

Method.

The method here described makes use of the following prin- ciples. The free soluble sugars are extracted with water from the ground vegetable and are determined by reduction of sodium picrate to sodium picramate, both before and after hydrolysis of the non-reducing sugar with picric acid.g In the determination of total available carbohydrate, however, the method of direct acid hydrolysis is open to question, since some of the indigestible

5 Bernhard, A., Sugar, 1915, xvii, 41. 6 Lewis, R. C., and Benedict, S. R., J. Biol. Chem., 1915, xx, 61. 7 Myers, V. C., and Bailey, C. V., J. Biol. Chem., 1916, xxiv, 147. *Myers, V. C., and Rose, A. R., J. Am. Med. Assn., 1917, lxviii, 1022. 9 Rose, A. R., J. Biol. Chem., 1921, xlvi, 529.


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Carbohydrates in Vegetable Foods

“fiber” and hemicelluloses may be hydrolyzed, and fructose and maltose partly decomposed. Accordingly, an attempt was made to hydrolyze this starch with LLtaka-diastase,“lo and it was found that when the preliminary hydrolysis is completed by gentle acid hydrolysis of the dextrins and maltose with approximately 0.6 N

HCI for 1 to 2 hours in a water bath, satisfactory results are obtained. The reducing sugar is then determined by the reduction of sodium picrate.

The determination of free soluble sugars is carried out in the following manner: The edible portion of the vegetable or fruit is ground up finely in a food chopper and the material is thoroughly mixed. Two or more samples” are accurately weighed into beakers, transferred to a mortar and thoroughly ground with sand, and finally with a measured volume of water, until all of the soluble carbohydrate has been extracted. A portion of this (cool) mixture is then saturated with dry picric acid, purified according to

Halverson and Bergeim,12 and filtered. The estimation is now carried out without delay essentially as described by Myers and Bailey7 for blood sugar. 3 cc. of the clear filtrate are accurately measured into each of two tall glass test-tubes graduated to 3, 4, 10, 15, and 20 cc. (sugar tubes). To the first tube is added 1 cc. of 22 per cent sodium carbonate solution, both tubes are immersed in a boiling water bath and after 10 minutes 1 cc. of 22 per cent sodium carbonate is added to the second tube. Both tubes are now heated for 20 minutes, cooled, and diluted to 10, 15, or 20 cc. (or more) to match approximately the standard and compared in the Bock- Benedict calorimeter with the standard. A 0.02 per cent solution of pure glucose in saturated picric acid solution is used as a standard. 3 cc. of this mixt,ure are heated in a sugar tube with 1 cc. of 22 per cent sodium carbonate for 20 minutes in a boiling water bath. This is cooled, diluted to 10 cc., and set at 15 mm. in the calorimeter. If there is an increase in the percentage of reducing sugar after hydrolysis of the filtrate with picric acid, this represents the non-reducing soluble sugar (sucrose) present. Calculation :

X g = per cent of sugar in vegetable.

Dz = Dilution of unknown tube.

10 The “taka-diastase,” manufactured by Parke, Davis and Co., De- troit, was employed.

11 The following proportions of vegetable and water were found con- venient according to the amount of carbohydrate recorded as present. 1 to 5 per cent of carbohydrate; 6 to 3 gm. samples of food; 100 cc. of water. 6 to 10 per cent of carbohydrate; 3 to 2 gm. samples of food; 200 cc. of water. 15 or more per cent carbohydrate; 3 gm. samples of food; 100 cc. of water, with dilution of filtrate 1 to 5, or 10 if necessary.

I2 Halverson, J. O., and Bergeim, O., J. Bid. Chem., 1917, xxxii, 164.


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V. C. Myers and H. M. Croll 541

& = Reading in calorimeter of unknown tube. R, = Reading in calorimeter of standard. D, = Dilution of standard. 0.0006 = gm. of glucose in 3 cc. standard solution. 3 cc. = volume of unknown filtrate used. V = Volume of water added to vegetable sample plus volume of water

contained in the sample itself. In some cases moisture determinations were made on the vegetable; in others the average recorded values for moisture content were used.

W = Weight of the sample of vegetable. The determination of the total available carbohydrate is carried out

according to the following procedure. SamplesI of the ground vegetable are weighed accurately into a small necked Florence flask of 250 to 300 cc. capacity, calibrated to a mark on the neck. About 100 cc. of water are added, and the material is boiled with a reflux condenser for about 13 hours. The vegetable is then ground to a paste in a mortar and rinsed back quan- titatively into the flask with the mother liquor and with water until the volume is about 150 to 200 cc. The flask is stoppered with cotton and the contents are heated to boiling, then cooled to about 40°C. ; 5 cc. of a 1 per cent solution of “taka-diastase” and a few cubic centimeters of toluene are added. The contents are shaken and the flask is again stoppered with cotton and allowed to stand for 18 to 20 hours in the incubator at 35-37°C. The liquid is then allowed to cool and the volume is made up with cold water to a mark on the neck of the flask. The flask is thoroughly shaken and a portion of the liquid is filtered off. 20 cc. of this filtrate (or 10 cc. of filtrate plus 10 cc. of water, if the percentage of carbohydrate is above 10 per cent) are pipetted into a large test-tube calibrated to a 25 cc. mark, 1.4 cc. of concentrated hydrochloric acid (34 per cent) are added to make the acid concentration about 0.6 N; a small funnel is inserted into the top of the test-tube as condenser, and the tube is heated in a boiling water bath for 1 to 2 hours. The dextrin and maltose formed from the starch by the diastase are thus changed to simple reducing sugar. The cooled liquid is then almost neutralized with strong sodium hydroxide, made up with water to the 25 cc. mark, and saturated with dry picric acid. 3 cc. portions are measured into sugar tubes and the color is developed on heating with 1 cc. of 22 per cent sodium carbonate solution before and after hydrolysis by heating for 10 minutes with picric acid. Comparison is made in the colo- rimeter with the standard glucose solution, and the percentage of reducing sugar found represents the total available carbohydrate in the vegetable. In the calculation, allowance must be made for the reducing sugar in the

13 For total carbohydrate the following proportions of vegetable and water were found suitable, according to the amount of carbohydrate recorded as present. 1 to 5 per cent carbohydrate; 15 to 5 gm. samples of food; about 300 cc. of water (up to graduation mark). 6 to 10 per cent carbohydrate; 5 to 2 gm. samples of food; about 300 cc. of water. 15 or more per cent carbohydrate; 5 to 4 gm. samples of food; about 300 cc. of water.


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“taka-diastase,” which is determine& separately in the above manner for eqch 1 per cent solution prepared. After acid hydrolysis for 1 hour this has been found to be about 0.5 to 0.7 per cent reducing sugar in the 1 per cent diastase solution. A solution may be kept active for at least a week, if preserved with toluene in the refrigerator.

This method has been tested and found to give accurate check determinations on the same vegetable. Glucose, sucrose, and starch added to the vegetable have been recovered quantita- tively. The method for total carbohydrate has been tried on starch alone, and 100 per cent recovery has been obtained when the final hydrolysis with 0.6 N hydrochloric acid has been carried on for 2 hours. When the total carbohydrate was determined on vegetables low’in starch content, .higher results were obtained at the end of 1 hour acid hydrolysis than at the end of 2 hours, suggesting the loss of a small percentage of the sugar by prolonged heating with hydrochloric acid. We are aware of certain criti- cisms which have been directed against the determination of sugar by the calorimetric picrate method, but we believe that the results are quite as accurate as those obtained with some of the more standard methods, and may be secured in a small fraction of the time.

DISCUSSION.

Determinations of free soluble sugars were made on a variety of raw and cooked vegetables and fruits and in many cases on the water drained from the vegetables after boiling; determinations of total available carbohydrate were made on certain of these vegetables. The samples of fruits and vegetables were obtained through the cooperation of the dietary department of the hospital. The vegetables which were boiled once were prepared in the manner generally employed in the household, the vegetables being cut into medium-sized pieces and boiled until the vegetables were soft in a small amount of water, generally suffi- cient to cover the vegetable. The “boiling water,” remaining after the boiling process, was drained off at once, and the volume was measured. In the thrice boiling process the vegetables were cut into smaller pieces and the time of boiling and volume of “boiling water” were greater than for the other process. The results are tabulated in Tables I, II, and III. When classified


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Aspa

ragu

s.

Lima

bean

s.

Cann

ed.

0.17

1.

38

1.55

13

.4

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ry.

Outsi

de

porti

on.

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ts.

Lettu

ce.

Gree

n le

aves

. W

hite

le

aves

. M

ixed

head

.

Caul

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r.

TABL

E I.

Free

Su

gars

in Ve

geta

bles

Expr

esse

d in

Term

s of

Glu

cose

.

FCZU

l.

Raw.

1

X bo

iled.

I ‘B

1

w

um

1.20

0.

57

67 t

en

0.01

0.

24

ar

Lwzl

pe

r ce

nt

1.21

2.

5 0.

81

1.4

Raw.

0.

54

0.02

0.

56

3.3

(Inclu

des

1 i<

boile

d.

0.28

0.

15

0.43

fib

er).

Raw.

1.

70

0.24

1.

94

3.3

Raw.

0.

82

0.12

0.

94

“ 1.

42

9.25

1.

67

“ 2.

01

0.20

2.

21

2.2

‘1 1.

84

0.20

2.

04

1 X

boile

d.

1.07

0.

13

1.20

Ra

w.

1.74

0.

42

2.16

1

X bo

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0.

90

0.15

1;

05

Rang

e 2.

4 to

5.

0 ,(r

aw).

j B ;i 8 1 c er te

n

‘95.3

93.2

95.0

91.9

95

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4r

con,

94.0

91.6

79.5

94.5

94.7

92.3

92.3

35

25

60

75 -

: j I : F -- -

1:O.f

1:l 1:2

1:3.

L

er c

ent

67

77

59

49

Rem

arks


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TABL

E I-&

mchd

ed.

Vege

table.

Caul

iflowe

r.

Cucu

mbe

r. M

inim

um.

Max

imum

. Av

erag

e.

Radi

shes

, M

inim

um.

Max

imum

. Av

erag

e.

Strin

g be

ans.

Gree

n.

Tom

ato.

Form

.

Raw.

1 X

boile

d Ra

w.

1 X

boile

d.

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1

X bo

iled.

Raw.

“ “

Raw.

3.

22

‘I 3.

02

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12

Raw.

1

X bo

iled.

Raw.

1

X bo

iled.

Ca

nned

.

ii .“4

3

I?7 te

n

2.05

1.

50

2.02

1.

39

2.66

1.

45

1.59

3.

40

2.50

2.66

1.

17

3.39

2.

21

2.91

c f f cli

0.2

2 er te

n 0.

29

0.23

0.

50

0.27

0.

30

0.24

3 & ST te

n,

2.34

1.73

2.

52

1.66

2.

90

1.69

per

cent

Aver

age

3.7.

0.14

1.

73

0.00

3.

40

0.07

2.

57

1.7

3.1

2.4

0.13

3.

35

2.7

0.40

3.

42

7.6

0.27

3.

39

5.1

0.77

0.

34

0.08

0.

33

0.34

3.43

1.

51

3.47

2.

54

3.25

5.5 1.st

3.3 3.5

.-

! ! ( ! ! .!

;i 3 8 B z -- R cen

i 33

.3

k4.5

22

.5

33.9

31

.7

34.0

c: P s 8; $8

5 ET te

n

92.3

92.3

92.3

95.4 91.8

91.4

89

.2

94.6

95

.3

94.3

94.0

30

50

30

90

25

er ce

n1

74

66

58

44

73


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Cabb

age.

Raw

. 3.0

8 0.1

4 3.2

2

1 X

boile

d.

0.89

0.19

1.08

Raw.

3.3

1 0.0

0 3.3

1 1

X bo

iled.

0.6

8 0.0

6 0.7

4

Raw.

‘I

3 X

boile

d.

3.10

0.50

3.60

3.50

0.66

4.16

0.77

0.06

0.83

Squa

sh.

Raw.

4.8

4 0.1

7 5.0

1 1

X bo

iled.

2.4

8 0.4

3 2.9

1 3

X bo

iled.

2.2

6 0.4

0 2.6

6

Gree

n pe

as.

Raw.

0.3

9 5.1

0 5.4

9 15

.2 1

X bo

iled.

0.3

0 2.5

0 2.8

0 8.1

Carro

ts.

Raw.

6.2

0 1

X bo

iled.

3.6

0

Onion

s. Ra

w.

1 X

boile

d.

1.30

0.11

2.90

1.70

7.50

8.2

3.71

5.7t

5.40

4.40

8.30

9.1

87.6

6.10

4.1

91.2

Rang

e 2.9

to

6.4

(raw)

. 2.6

t

2.6t

Aver

age

4.5.

9.8

93.8

96.6

93.3

96.8

93.5

91.1

93.7

94.0

91.5

91.5

91.5

91.5

87.6

74.6

73.8

88.2

35

1:3

60

1:4.1

35

55

40

50

45

40

1:8.3

1:1.:

1:2.c

1:1.:

1:l.i

1:o.t

33.8

22.4

19.9

58

53

51

49.5

73.5

-

;c

Boile

d 15

, 10

, an

d 10

mi

n-

0

utes.

g m

Boile

d 10

, 15

, E

and

15

min-

Q

utes.

.x F

* Un

marke

d re

cord

ed

value

s ar

e fro

m At

water

an

d Br

yant.

1 t

Value

s fro

m Jo

slin

(Josli

n, E.

P.

, Th

e tre

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diabe

tes

mellit

us,

Phila

delph

ia an

d Ne

w Yo

rk,

1916

).


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Carbohydrates in Vegetable Foods

according to the carbohydrate found, the vegetables and fruits in the tables generally fall into the proper groups in the classi- ficat,ion by Joslin14 of foods with 5, 10, 15, and 20 per cent of carbohydrate. It is seen that in those veget,ables studied which belong to the 5 and 10 per cent groups of Joslin and in all the fruits studied, most of the carbohydrate is in the form of soluble sugars and often chiefly free reducing sugars. Small percentages of starch are present in most of those tested for total carbohydrate. The amount of soluble sugars for most of the fruits and vegetables compares well with the amount of total carbohydrate minus fiber in the recorded figures, and this leads to the inference that the percentage of starch is small in fruits and in many of those vegetables not tested for total carbohydrate. On the other hand, potatoes, peas, and lima beans apparently contain a large proportion of starch in comparison with soluble sugars. These findings are similar to those of Falk,15 who studied the form of the carbohydrates in fresh and dehydrated vegetables using the method of Street and Bailey.4 Table IV shows a comparison of the distribution of the available carbohydrate in carrots and in potatoes, as determined by Falk and by the picric acid method described here. Falk reports a distribution of the carbohydrates in cabbage and in turnips similar to that in carrots. Myers and Rose* found a great variation in the relative amount of sugar and starch in the banana, according to the degree of ripeness. Thus a green banana with greenish yellow peel was found to have 1.17 per cent reducing sugar, 4.6 per cent sucrose, and 15.62 per cent starch, all expressed in terms of glucose. A very ripe banana with light brown peel had 7.08 per cent reducing sugar, 11.10 per cent sucrose, and 0.71 per cent starch. A very green banana for which the starch is not recorded, was shown to have 0.55 per cent reducing sugar and 1.20 per cent sucrose.

Since most of the carbohydrate in many of the vegetables and fruits studied appears to be in a soluble form, then theoretically it should be possible to remove practically all of the sugars by extraction with wat,er. The ordinary method of boiling vegetables for a minimum time and with a small amount of water was found (Tables I and III) to remove 23 to 66 per cent

I* Josh, E. P., Am. J. Med. SC., 1915, cl, 485. I5 Falk, K. G., J. Znd. and Eng. Chem., 1919, xi, 1133.


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Lemon juice.

Lemon.

Strawberry (medium ripe).

per cent per cent per@& per cent

0.95 0.46 1.41 (Sugar) 2.3.

1.41 0.56 1.97

3.77 0.33 4.10 Range 3.7 to 10.0. (Glucose) 5.5.

Grapefruit. 7:28 1.35 Cuban grapefruit. 5.23 3.72

Orange juice. 2.70 4.08 FIorids orange. 5.01 4.57

8.63 8.95

6.78 Range 9.58 11.6 to 18.5.

(Sugar) 9.0.

Orange. 4.10 5.70 9.80 California orange. 6.08 8.10 14.18

Winter pear. 10.20 1.70 11.90 11.4

Apple. 11.00 0.10 11.10 Range Baked apple. 11.20 0.80 12.00 7.9 to 19.9. George Washington 9.25 3.45 12.70 Average 13.0.

apple. (Sugars) 12.4. Northern Spy apple. 11.45 2.55 14.00

Tangerine. 4.75 8.90 13.65

Banana.* Very green. 0.55 1.20 1.75 Range Medium ripe. 2.88 12.52 15.40 15.3 to 28.8. Very ripe. 7.08 11.10 18.18 Average 21.0.

Malags grapes. 22.25 0.25 22.50 Average 15.0.

+ The data on banana are taken from Myers and Rose.&

Fruit. TOtd sugar.

V. C. Myers t-md H. M. Croll 547

TABLE II. Free Sugars in Fruits Expressed in Terms ef Glueose.


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Vege

table.

Celer

y. Ou

tside

po

rtion.

Cauli

floae

r.

TABL

E III

.

Free

Su

gars

and

Tota

l Ca

rboh

ydra

te in

Vege

table

s Ex

pres

sed

in Te

rms

of Gl

ucos

e.

Form

.

tP

Raw.

0.4

8 0.0

4 0.5

2 0.5

7 1

X bo

iled.

0.2

1 0.0

6 0.2

7 0.3

6 Ra

w.

1.02

0.22

1.24

1.70

3 X

boile

d.

0.28

0.16

0.44

0.65

Raw.

1.6

9 0.1

3 1.8

2 2.4

8 1

X bo

iled.

0.9

7 0.0

8 1.0

5 1.0

9 3

X bo

iled.

0.5

2 0.0

4 0.5

6 0.5

6

Raw.

. 1.6

5 0.2

8 1.9

3 2.8

9 3

X bo

iled.

0.6

2 0.1

0 0.7

2 CL

79

Raw.

4.3

5 0.5

7 4.9

2 5.8

6 -

T

-

t pe

r ca

nt

3.3

(Inclu

des

fiber

). 3.3

Rang

e 2.4

to

5.0

(raw)

.

Aver

age

4.4.

92.6

95.0

XT

ten

94.5

94.5

92.3

92.3

mr

cell

70

1:3.1

63

45

1:14

.! 38

35

1:2.1

44

35

1:8.3

22.6

45

1:5.4

27

Rema

ds.

Boile

d 15

, 15

, an

d 15

m

in-

utes

.

Boile

d 10

, 15

, an

d 15

m

in-

utes

.

Boile

d 15

, 15

, an

d 15

m

in-

utes

.


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V. C. Myers and H. M. Croll


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of the carbohydrate, leaving 34 to 77 per cent of the carbohydrate of the raw vegetable in the cooked sample. The use of thrice boiled vegetables’in the dietary of diabetic patients advocated by Allen,16 has been developed on the theory that more carbohydrate is lost if the water is changed several times during the boiling process. Examination of the tables shows that 62 to 83 per cent of the carbohydrate is lost, or 11.6 to 38 per cent of the carbohydrate of the raw vegetable is retained in the thrice cooked vegetable, where the proportion of “boiling water” to vegetable is relatively large. In the thrice boiling of squash the proportion of water was low and the percentage of carbohydrate retained is 53 per cent, almost as great as the percentage retained (58 per

TABLE IV.

Comparison of the Distribution of Available Carbohydrate in Carrots and

PC

Per cent of total reducing power due to.

Simple reducing sugars before acid hydrolysis.. . . . . . . . . . . . . . . . . . . . . .

Simple reducing sugars after acid hydrolysis.. . . . . . . . . . . . . . . . . . . . . .

Dextrins and soluble starch.. . . . . . Insoluble starch.. . . . .‘. . . . . . . . . . . . .

7tL -

. -

-

rtoes.

Raw carrota. T per cent per cent

57.1 34.5

92.2 96.5

_- I

_-

-

Raw potatoes.

Falk.

per cent pe? cent

2.5 4.75

4.9 0.5

94.0 ; -

6.0

i 94.0

cent) in the vegetable boiled one time. WardalP shows that in 3, 4, and 5 extractions, respectively, by boiling celery, fresh spinach, and rhubarb, all the reducing substance is removed. 6 extractions are required for carrots, 9 for asparagus, and 16 for cauliflower. CammidgeJ7 reports similar results in finding that celery, spinach, turnips, and carrots are more easily freed from carbohydrate by extraction than are other veget,ables. O’Reilly and McCabe,*8 using a technique similar to that of Olmsted,2 found that if 20 parts of water are used as compared with 10, for each of the three boilings of vegetables, the carbohydrate extraction is more complete. In this way they were able to remove

I6 Allen, F. M., Boston Med. and Surg. J., 1915, clxxii, 241. 1’ Csmmidge, P. J., Lancet, 1919, ii, 1192. 18 O’Reilly, L., and McCabe, E. H., .I. Biol. Chem., 1921, xlvi, 83.


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V. C. Myers and H. M. Croll 551

completely the available carbohydrate from vegetable marrow, lettuce, and celery, and to remove nearly all of the carbohydrate from canned spinach, canned asparagus, turnips, beets, and onions. They found that carrots, cauliflower, canned string beans, pumpkin, and cabbage still retain about 0.5 per cent of available carbohydrate. The use of 0.05 per cent and 0.1 per cent concentrations of sodium bicarbonate in these extractions was found to favor the removal of the carbohydrate from the vegetable. Masters and Garbuttlg and DentonzO show that greater loss of fuel value occurs in vegetables when they are cut into small pieces and when the time of boiling and the volume of the boiling water are increased. The fact is shown clearly in Tables I and III that the greater the proportion of water used in boiling the vegetable and the longer the time of boiling, the greater is the loss of carbohydrate in the boiling process. It is shown also that the greatest loss of carbohydrate occurs in those vegetables in which most of the carbohydrate occurs in a soluble form.

SUMMARY.

1. A relatively simple calorimetric method is described for the determination of the amount and form of the available carbohydrate in vegetable foods.

2. Results are given for analyses of vegetables and fruits such as are used in feeding diabetic patients. It is shown that a large proportion of the available carbohydrate occurs in a soluble form.

3. The effect of different factors in cooking on the removal of carbohydrate from vegetables is discussed. The conclusion is reached that the soluble form of the carbohydrate and the increase in time of boiling and in volume of boiling water, favor the removal of carbohydrate from vegetables.

19 Masters, H., and Garbutt, P., Biochem. J., 1920, xiv, 75. *O Denton, M., J. Home Econ., 1919, xi, 143,200.


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Victor C. Myers and Hilda M. CrollFOODS

CARBOHYDRATES IN VEGETABLE THE DETERMINATION OF

1921, 46:537-551.J. Biol. Chem.

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