DECEMBER,

1963

WILTON TABLE

Fat [-I m a r i n e oil 4 0 / 4 2 [-I m a r i n e oil 4 0 / 4 2 [-I m a r i n e oil 3 8 / 4 0 ~I. cottonseed oil 3 6 / 3 8 [-I. cottonseed oil 3 6 / 3 8 P ahn oil r a l l o w ............. Shea b u t t e r ...........

1) 2) 3) 4)

AND \u

CRYSTALLIZATION

III

M1)a ~

OTcmp~

Ta min

TMin - To

34.5 36.5 33 26.5 28 28 35 24

34 35.5 32.5 25.5 27.3 26 33.5 23

0.5 10 3 0 0 4 2 100

17 42 22 3 4.5 7 30

formation time (T a) in Table I I I are set = 0, the time has been less t h a n 30 sec and could not be determined with accuracy. The t r a n s f o r m a t i o n time seems to be correlated to the time interval on the cooling curve between the time for the first deviation f r o m the liquid oil curve and the m i n i m u m for the f a t (TMIx-To). Due to their empirical nature, the methods described above give only a p p r o x i m a t e values for the crysetallization course of fats. They have been devised in order to provide, in a quick and simple manner, an idea of how

BEHAVIOR

711

OF FATS

the crystallization proceeds during cooling processes. I n the m a n u f a c t u r e of m a r g a r i n e the crystallization of the f a t takes place u n d e r vigorous agitation, which certainly promotes the formation of the fl'-form. D u r i n g the cooling process in the f a c t o r y the transformation time f r o m a- to fl'-form seems to be much shorter than the cooling curve and microscopic technique indicate. The methods, however, have proved to be of value in assessing the various factors which m a y have influence on the consistency of the margarine. REFERENCES i. Zeitschr. Angew. Chem., 563 (1899). 2. Milchw. Forsch., 2, 24 (1925). 3. Quimby, O. T., R. L. Wille, and E. S. Lntton, JAOC~S, 30, 186 (1953). 4. Sachsse, ~I., J. R o s e n s t c i n , F.u.S., 55, 26 ( 1 9 5 3 ) . 5. Jacobson, G. A., P. J . T i e m s t r a , W . B. Pohle, J A O C S , 88, 399 (1961). 6. L u d d y , F. E., S. G. M o r r i s , P . M a g i d m a n , R. "vV. R i e n m n s c h n e i d e r , Ibid., 32, 522 ( 1 9 5 5 ) . [Received

July

6, 1 9 6 2 - - A c c e p t e d

June

5, ] 9 6 3 ]

A Method for the Determination of the Extent of Polymerization m Frying Fats and in Fats Extracted from Fried Foods M. R. SAHASRABUDHE and V. R. BHALERAO, 1 Food and Drug Directorate, Ottawa, Canada Abstract

Experimental

A method is described for the isolation of polymerized products in f r y i n g fats as a urea non-inclusion fraction ( N A F ) . Analysis of fats used in commercial f r y i n g operations and of fats extracted f r o m some fried foods is reported. A m o u n t of N A F obtained by the method appears to be in direct relation to the duration of heating. Oils heated at 200C for 24 hr yield 15-18% of N A F having molecular weights of 500-550. Some of the fats extracted f r o m fried foods yielded up to 2.5% of the polymeric f a t t y acids.

Introduction OMMERCIALLY FRIED FOOD p r o d u c t s represent a significant portion of foods consumed in North America. D u r i n g f r y i n g the fats are exposed to elevated t e m p e r a t u r e s and other conditions for a considerable length of time. Thermal degradation of oils at these t e m p e r a t u r e s has been extensively studied (1-6). Thermal oxidation of fats proceeds in two stages. The first is a c c o m p a n i e d . b y a decrease in the iodine value (I.V.) of the f a t and a r a p i d increase in the carbonyl value. I n the second, the rate of decrease in I.V. is considerably slower while the viscosity increases rapidly. Although I.V. and viscosity determination will indicate the advanced stages of polymerization, these criteria are not of significant value in the earlier s t a g e s . The purpose of this p a p e r is to describe a simple method for the isolation and estimation of the amount of the p o l y m e r i z e d material in saponified f r y i n g fats and fats extracted f r o m fried foods.

C

1 :Present a d d r e s s :

Dairy Research Institute, Karnal,

India.

Control Samples. A commercial b r a n d of winterized corn oil, and a hydrogenated vegetable shortening, were used in the study. One hundred g samples of f a t were heated in stainless steel beakers to 200r for 8, 16, a n d 24 hr. The f a t was continuously agitated during heating. A t the end of the experimental period the fats were t r a n s f e r r e d to glass stoppered conical flasks and stored under nitrogen in a freezer at - 1 0 C . A 100 g sample of corn oil was also heated intermittently at 200C for 4 hr periods each day for 6 days. One ml of distilled w a t e r was stirred into the flask each day p r i o r to heating, to p a r t l y simulate the moisture added in f r y i n g fresh potato chips. Commercial Samples. F o r comparison 4 b r a n d s each of potato chips and frozen french fried potatoes were obtained f r o m the local market. Ten samples of fats used for deep f r y i n g in the r e s t a u r a n t s in the Ottawa and Toronto area were also obtained. These oils were p r i m a r i l y used for f r y i n g potato chips. All samples were stored u n d e r nitrogen in the freezer. The fried potato products were ground with pestle and m o r t a r and extracted with petroleum ether (4060C) containing 10% ethyl ether. The extract was washed with water and dried with sodium sulfate, followed by evaporation of the solvent under reduced pressure. Sapo~ificc~tion. Twenty-five g of the f a t was saponifled by refluxing w i t h 125 ml of 5% alcoholic potassium hydroxide for 2 hr. On cooling, 10,0 ml water was added and the saponification mixture was acidified with dilute hydrochloric acid (1:1). The f a t t y acids were extracted with two 100 ml portions of ethyl ether. The combined extracts were washed with water to remove all mineral acid and dried over so-

7]2

THE

JOURNAL

OF THE

AMERICAN

OIL

CHEMISTS'

TABLE I

TABLE

A n a l y t i c a l d a t a on C o r n Oil a n d V e g e t a b l e S h o r t e n i n g h e a t e d a t 2 0 0 C Fat

Time in hr at 200C

I.V. 123.7 118.7 115.9 111.3 112.0 110.8 74.7 71.0 68.1 65.8

16 24 24 24 8 ] 24

C o r n oil h e a t e d i n t e r m i t t e n t l y ..............

%

mol w t

0.5 3.5 8.0 17.5 18.0 16.8 0.5 5.0 12.0 15.0

30 2 483 537 54 3 53 9 549 294 454 502 53 0

4,5

386

a N o n - a d d u c t f o r m i n g fatty a c i d f r a c t i o n .

dium sulfate. The solvent was then removed by evaporation under reduced pressure. Urea inclusion. Twenty g of the f a t t y acids was weighed into a 500 nfl flask and dissolved in 200 m l of methanol containing 80 g urea. The flask was heated until a clear solution was obtained and then stored overnight in a refrigerator. The contents were then filtered through a Buchner funnel and the precipitate was washed with 50 ml portions of cold ethyl ether. The filtrate was evaporated to dryness on a flash evaporator. This fraction was called the non-adduet f o r m i n g fraction ( N A F ) . To the precipitate, 100 ml water and 1 0 g sodium chloride were added. The f a t t y acids were released by heating and then extracted with ethyl ether. The resulting f a t t y acids were again treated with urea and methanol ( 5 g urea and 10 ml methanol for each g of f a t t y acids). The f a t t y acids were then recovered from the u r e a inclusion products as described earlier. Molecular weights were determined by the eryoseopic method using wet benzene (7). I.V. was determined b y the conventional W i j ' s method, AOCS Official Method Cd 1-25. Results and Discussion Distributions of the total f a t t y acids f r o m the adduct and the non-adduct f o r m i n g f a t t y acid fraction ( N A F ) , along with the molecular weights are shown in Table I. Reproducibility of the N A F determination was tested b y heating three 100 g samples for 24 hr. The amount of N A F in fresh fat, is ca. 0.5%. The yield of N A F was found to increase with the duration of heating. Molecular weights also show a remarkable increase, as would be expected of polymerized material. The molecular weights of f a t t y acids obtained as urea inclusion products are comparable to those of the original oil and were in the range of 291-296. The percentage of N A P material T A B L E II M o l e c u l a r w e i g h t s a n d p e r c e n t a g e of n o n - a d d u c t f o r m i n g f a t t y a c i d f r a c t i o n ohtMned f r o m c.ommercial sa mple s of f r y i n g oils b e f o r e a n d a f t e r u s e in a deep ~ryer Fresh Fat S a m p l e No.

% NAF

1 ..................................... 2 3 4 5 6 7 8 9 10

...................................... b ...................................... b ..................................... ....................................... ...................................... ....................................... .................................... ..................................... b .....

0.52 0.45 0.48 0.50 0.48 0.50 0.52 0.56 0.35 0.35

Percentage

III

a n d molecular w e i g h t s of n o n - a d d u c t f o r m i n g f r a c t i o n ( N A F ) obtained in fried foods

fatty

acid

NAF

Corn oil ............................... C o r n oil ............................. C o r n oil .............................. C o r n oil .............................. C o r n oil .............................. C o r n oil ............................... S h o r t e n i n g .......................... S h o r t e n i n g ........................ S h o r t e n i n g ......................... S h o r t e n i n g ..........................

VoL. 40

SOCIETY

reel w t 272.7 280.2 294.6 284.0 300.3 324.3 292.4 318.2 279.3 270.7

A f t e r use i n deep f r y e r

Product

P o t a t o Chip .........................

Frozen french f r ie d p o t a t o e s .................

Sample No.

%

NAF reel w t

1 2 3 4

0.60 0.56 0.52 0.48

278.7 283.4 280.0 271.5

1 2 3 4

2.5 1.5 1.2 2,0

366.0 385.3 436.5 427.2

formed between 16-24 hr increased over 10,0% with no significant increase in the molecular weight. This p r e s u m a b l y is due to other degradation products. The sample of corn oil heated intermittently showed an appreciably lower percentage of polymerized f a t t y acids and lower molecular weight of the N A F than did the f a t heated continuously for 24 hr. The data on N A F obtained with commercial samples of fat, before and a f t e r use in the deep fryer, are shown i n Table [I. No record was available as to how long these fats had been in use. Three of the samples, a f t e r use in the deep fryer, were highly viscous and the molecular weights of the N A F were found to be in excess of 500. I n the other fats, after use in the deep fryer, the molecular weights of the N A F were f o u n d to range 287.8-386.2. The results of the analysis of fats extracted from potato chips a n d frozen french fried potatoes are shown in Table I I I . The molecular weights, of the N A F obtained for the fats from potato chips were found to be similar to those obtained for fresh fats; however, the molecular weights of the N A F for the fats extracted f r o m the frozen french fries were considcrably higher. The rate of f a t turnover, the effect of steam distillation due to added moisture, and the presence of food particles and other factors m a y alter the rate of formation of polymers. I n the laboratory the fats were heated at t e m p e r a t u r e s similar to those used in f r y i n g operations; however, the two systems should not be compared without consideration of other factors involved in deep frying. The intermittent heating with added moisture a p p e a r s to simulate the deep f r y i n g operation resulting in lower yields of polymer~ ized material as compared to continuous heating for the same period. V e r y little information is available on other methods for the estimation of polymerization in heated oils. F r a n k e l et al. (3) reported a liquid partition chromatographic method for dimeric and polymeric products in oxidized oils. The present method is believed to be simple enough for routine analyses of eomnlereial f r y i n g fats. ACKNOWLFDG MEET

Helpful Director,

evaluation

of this m a n u s c r i p t by 1%. A. C h a p m a n , Scientific Services, Food and D r u g Directorate.

Assistant

N•F

tool w t

1%EFERENCES

0.50

295.8 314.7 529.5 550.0 348.6 386.2 358.6 358.9 287.8 552.6

1. B e n n i o n , M., a n d F . H a n n i n g , F o o d T e c h n o l. , 10, 2 2 9 - 2 3 2 ( 1 9 5 6 ) . 2. C a r l i n , G. T . , 1%. P . H o p p e r , a n d B. N. R o c k w o o d , Ibid., 8, 1 6 1 165 (1954). 3. F r a n k e l , E . N., C. D. E v a n s , I t . E . Moser, D . G. M e C o n n e l , and J . C. Cowan, J A O C S , 38, 1 3 0 - 1 3 4 ( 1 9 6 1 ) . 4. J o h n s o n , O. C., a n d F. A. K u m m e r o w , Ibid., 84, 4 0 7 - ~ t 1 0 ( 1 9 5 7 ) . 5. P e r k i n s , E . G., a n d F. A. K t t m m e r o w , Ibid., 36, 3 7 1 - 3 7 5 ( 1 9 5 9 ) . 6. S a h a s r a b u d h e , M. R., a n d I. G. F a r n , Ibid., ( i n p r e s s ) . 7. Smith, W. T., a n d 1%. L. S h r i n e r , E x a m i n a t i o n of N e w O r g a n i c Compounds, J o h n W a e y a n d Sons, I n c . , N e w Y o r k ( 1 9 5 6 ) .

0.81 4.82 5.25 0.87 0.58 0.52 0.71 0.63 4.52

a NO r e c o r d is a v a i l a b l e as to how l o n g the se f a t s h a d b e e n used in t h e deep f r y e r s . S a m p l e s Nos. 3, 4, a n d 10 w e r e h i g h l y viscous.

[Received November 15, ]962--Accepted June 11, 1963]