Stale-Flavor Components in Dried Whole Milk. II. The Extraction of Stale Butter Oil from Stale Dried Whole Milk by Organic Solvents

Stale-Flavor Components in Dried Whole Milk. II. The Extraction of Stale Butter Oil from Stale Dried Whole Milk by Organic Solvents

S T A L E - F L A V O R COMPONENTS IN DRIED W H O L E MILK. II. THE EXTRACTION OF STALE BUTTER OIL FROM STALE DRIED W H O L E M I L K BY ORGANIC SOLVE...

683KB Sizes 0 Downloads 48 Views

S T A L E - F L A V O R COMPONENTS IN DRIED W H O L E MILK. II. THE EXTRACTION OF STALE BUTTER OIL FROM STALE DRIED W H O L E M I L K BY ORGANIC SOLVENTS R. I~[cL. W H I T N E Y AND P. H. TRACY

Department of Food Teohno~ogy, University of I~linois, Urbana

In a previous paper (4), it was reported that the stale-flavor components which develop in spray-dried whole milk during storage were found to be concentrated in the butter oil when prepared according to the usual method. However, due to unavoidable homogenization in the spray-drying process, the recovery of butter oil from the dried whole milk, and hence the removal of the stale-flavor components was very inefficient (approximately 35 per cent). Consequently, the possibility of obtaining stale butter oil directly from the whole milk powder by extraction with organic solvents was investigated. For such a method to be applicable, the recovery of the butter oil must be reasonably high, the stale-flavor components must be extracted with the butter oil and the solvent must not interfere in any way with the flavor judgments of the products. THE

EFFICIENCY OF THE

EXTRACTION

PROCEDURE

Preliminary work indicated that the stale-flavor component could be extracted with the butter oil from stale, spray-dried whole milk by organic solvents. However, suitable techniques would be needed to improve the efficiency of the extraction procedure and to prevent the interference of solvent flavors with the judgment of the product. In order to improve the efficiency of extraction of the butter oil from the spray-dried whole milk, several modifications involving the type of whole milk powder extracted, the pretreatment of the powder before extraction and the extracting solvents were investigated. Manufacture and storage of dried whole milk. Two types of dried whole milk were prepared in a pilot-size experimental spray drier. Powder no. 104 was manufactured from condensed whole milk without previous homogenization, while powder no. 105a was made from uncondensed, unhomogenized milk. The conditions of manufacture and storage are indicated in table 1. General experimental methods. In all experiments, a weighed sample of the milk powder of known fat content, as measured by the Mojonnier method, was pretreated in the manner specified and extracted in a Soxhlet apparatus with a measured volume of solvent. The solvent was maintained at the boiling point by immersing the flask in a constant-temperature water bath. After the specified number of trips of the syphon, the solution was removed from the Soxhlet apparatus and the solvent evaporated from the butter oil under reduced pressure. The extracted butter oil was weighed to determine the efficiency of the method. The anhydrous ethyl ether used was prepared by redistilling U.S.P. grade Received for publication September 12, 1949. 5O

51

STALE-FLAVOR COMPONENTS IN DRIED WHOLE MILK

ethyl ether over metallic sodium. The petroleum ether was distilled over solid KOH and the fraction boiling between 30 and 41 ° C. collected. Experimental results. While a considerable number of extractions were performed, only typical examples of the various procedures are reported in table 2. In experiments i and 2, powder no. 104, was extracted with anhydrous ethyl ether and with petroleum ether, respectively, without pretreatment. Poor recoveries were obtained with both solvents. TABLE 1 Manufacturing

d a t a f o r d r i e d whole railk Batch no. 104

R a w milk: Source ........................................................................ F a t content ( % ) .......................................

U n i v e r s i t y herd 4.3

Preheat treatment: Temp. ( ° C.) ............................................................ Time (rain.) ...............................................................

77-79 21

Condensing: Temp. ( ° C.) ......................................................... V a c u u m (rata. o f H g ) .................................... Time (hr.) ................................................................. Total solids ( % ) .................................................... F a t content ( % ) ...................................................

46-71 49-64 1.2 35.24 11.37

Cooling & s t o r a g e : F i n a l temp. (° G.) ............................................. Method ........................................................................... S t o r a g e time (hr.) ............................................. S t o r a g e temp. ( ° C.) .......................................

12-15 s u r f a c e cooler 22.5 ~7

Drying: S p r a y i n g temp. (° C.) .................................... S p r a y i n g p r e s s u r e (lb./in.2) ................... S p r a y nozzle size ................................................... I n l e t temp. (° C.) ................................................ Outlet temp. ( ° C . ) ............................................ F a t content ( % ) ............................................... Moisture content ( % ) .................................. Solubility index ......................................................

54-61 450-550 63-17 135-154 85-97 31.60 2.07 0.6

Powder storage: Time of s t o r a g e (rao.) ................................ ~ 8 Temp. of storage (° C.) .............................. 7

105a U n i v e r s i t y herd 3.9 71 30

none

55-61 450-600 69-20 121-149 82-107 29.56 2.33

0.1

~ 1 ~ 7

Since Holm et al. (2) had reported that the fat is more readily extracted by carbon tetrachloride from a powder prepared from uncondensed, unhomogenized milk, powder no. 105a was extracted without pretreatment in experiments 3 and 4. Satisfactory recoveries were obtained with both solvents. However, this powder developed a tallowy flavor quickly, which made it unsatisfactory for the investigation of the stale flavor~ Lampitt and Bushill (3) had observed that the amount of fat that could be extracted by organic solvents from dried whole milk prepared by the usual spraydrying process was increased by hydrating the powder to approximately 8 per

52

R. MCL. WHITNEY AND P. H. TRACY

c e n t m o i s t u r e . I n e x p e r i m e n t 5, d r i e d whole m i l k no. 104 was stored i n e v a p o r a t i n g dishes a n d p l a c e d i n desiccators over w a t e r at room t e m p e r a t u r e . After storage f o r 44.25 hr. u n d e r these c o n d i t i o n s , the m o i s t u r e c o n t e n t of the powder, as d e t e r m i n e d b y the t o l u e n e - d i s t i l l a t i o n m e t h o d , was 7.87 p e r cent. E x t r a c t i o n of this p o w d e r w i t h a n h y d r o u s e t h y l e t h e r y i e l d e d s a t i s f a c t o r y recoveries. However, the t i m e r e q u i r e d to h y d r a t e the p o w d e r b y this m e t h o d was l o n g e r t h a n desirable. The d y n a m i c m e t h o d s u g g e s t e d b y W i l s o n (5) was e m p l o y e d i n e x p e r i m e n t 6. A i r was d r a w n b y m e a n s of a h i g h - v a c u u m p u m p t h r o u g h the f o l l o w i n g succesTABLE 2 T y p i c a l results o f various m e t h o d s f o r the solvent extraction o f b u t t e r oil f r o m dried whole mil~

Expt. no. 1

2

3

4

5

6

7

Powder no............... 104 104 105a 105a 104 104 104 Moisture content ( % ) ........................ 2.07 2.07 2.33 2.33 2.07 2.07 2.07 Special static dynamic alcohol pretreatment ... none none none none hydration hydration treatment Moisture content after pretreatment (%) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7;87 9.20 ............ Wt. of powder (g.) ..................... 40.00 40.03 40.00 40.00 176.8 40.01 402.1 Fat content of powder (%) ...... 31.60 31.60 29.56 29.56 29.73 29.30 31.60 anhydrous petroleum anhydrous petroleum anhydrous petroleum petroleum Solvent ........................ ethyl ether ethyl ether ethyl ether ether ether b.p. ether b.p. ether b.p. b.p. 41"C. ~41"C. ~ 4 1 ° C. ~ 4 1 °C. Vol. of solvent (ml.) ........................ 400 300 400 500 750 340 2620 Temp. of extraction (°C.) ......... 43 49 43 49 40 43-49 47-48 Time of extraction (hr.) ......... 4.5~ 3.5 6 3.25 3 4.25 5.5 11.0 4.25 No. of trips of 18a s y p h o n . . ............................

Wt. of extracted butter oil (g.) Recovery of butter oil (%)

1.00 7.9

18

4.31 34.1

.....................

11.50 97.5

9.30 78.5

19

19

19

51.2

11.11

20 115.5

97.5

94.6

90.9

a The powder was divided equally between extraction thimbles. The variations in time of extraction are due to different periods for tripping of the syphon caused by differences in construction of the extraction apparatus used. s i r e s t a g e s : a c h a r c o a l a d s o r p t i o n tube, a w a s h i n g bottle filled w i t h w a t e r m a i n t a i n e d a t room t e m p e r a t u r e b y i m m e r s i o n i n a w a t e r b a t h , a modified R e g n a u l t dew p o i n t h y g r o m e t e r , a t u b e c o n t a i n i n g 600 g. of d r i e d whole m i l k no. 104 a n d a second h y g r o m e t e r . A t 1-hr. i n t e r v a l s , the absolute h u m i d i t y of the a i r on both the i n l e t a n d o u t l e t sides of the p o w d e r was d e t e r m i n e d . T h r o u g h o u t the h y d r a t i o n p e r i o d , the a i r i n the i n l e t side was m a i n t a i n e d a t as n e a r s a t u r a t i o n as possible b y r e g u l a t i n g the flow of a i r w i t h a stopcock at the p u m p . The absolute

STALE-FLAVOR COMPONENTS

IN

DRIED W H O L E

~'ILK

53

humidity was 22.8 to 24.3 ram. of m e r c u r y on the inlet side and 2.4 to 9.5 ram. of m e r c u r y on the outlet side, while the air temperature was 24.0 to 25.8 ° C. A f t e r 25 hr. of treatment, the moisture content of the dried whole milk was determined by the toluene-distillation method and a weighed sample extracted with petroleum ether in the usual manner. Satisfactory recoveries of butter oil were obtained. To f u r t h e r reduce the time required for p r e t r e a t m e n t of the dried whole milk, the possible application of an observation of L a m p i t t and Bushill (3) was studied. These investigators had noticed that, in freeing the fat for extraction by hydration of the milk powder to a moisture content of approximately 8 per cent, the lactose was crystallized. They also f o u n d that the lactose crystallized when the powder was dispersed in 95 per cent ethyl alcohol. To test whether p r e t r e a t m e n t of the powder with alcohol also would free the fat for extraction and to develop the most satisfactory technique, a variety of experiments were performed. Experiment 7 illustrates the most satisfactory procedure used. A p p r o x i m a t e l y 400 g. of dried whole milk no. 104 was agitated with 3,400 ml. of 95 per cent ethyl alcohol and 25.8 ml. of distilled water for 1 hr. and filtered. The alcoholic filtrate was divided into three portions, each of which was concentrated to approximately 850 ml. by evaporation u n d e r vacuum at room temperature. E i g h t h u n d r e d and fifty ml. each of petroleum ether and distilled water then were added to each portion and the mixture agitated for 2 rain. in a separatory funnel. A f t e r the alcohol-water layer had been discarded, the petroleum-ether layer was used to extract the treated powder. Satisfactory recoveries of fat were obtained. Discussion. In interpreting the results of this study, it must be kept in mind that the purpose was not to explore completely the effect of various factors upon the extraction procedures, but r a t h e r to develop efficient and usable methods for this step in the isolation of the stale flavor component. Therefore, no conclusions are justified with respect to small differences in recovery of b u t t e r oil, but certain general observations are possible. While there were several differences in the methods of m a n u f a c t u r e and storage of the two dried whole milks extracted, the chief difference was the d r y i n g of a condensed (powder no. 104) and an uncondensed (powder no. 105a) milk. The results of the first four experiments, m a y be considered as confirming the observation of Holm et al. (2) that fat is extracted more completely by organic solvents from a powder p r e p a r e d from an uncondensed than from a condensed product. Unfortunately, the powder p r e p a r e d from the uncondensed whole milk was so unstable that it was unsuitable for the study of stale flavor. A reasonable hypothesis for the instability of this product is that the physical condition of the powder which makes the fat more available for solvent extraction also makes it more susceptable to oxidation. The results of the experiments in which the dried whole milk was h y d r a t e d to approximately 8 per cent moisture before extraction confirm the observations of Lampitt and Bushill (3) that the fat was readily extracted by organic solvents from dried whole milk when pretreated in this manner. As was expected, the rate of hydration was more rapid when the dynamic method of Wilson (5) was used.

54

R. ~CL.

WHITNEY

AND

P. H.

TRACY

The experiments employing the alcohol pretreatment indicate that satisfactory recoveries of butter oil can be obtained by agitation for 1 hr. of the dried whole milk with 95 per cent ethyl alcohol to which sufficient water has been added to hydrate the powder to 8 per cent moisture followed by extraction with petroleum ether in the usual manner, provided the fat dissolved in the alcohol used in the pretreatment is recovered. The reaction involved in the freeing of the fat for extraction by the alcohol pretreatment apparently approaches completion in 1 hr. However, shorter periods of treatment were not investigated. Some slight improvement in recovery was indicated by experiments in this series when water was added to the 95% alcohol. However, additional information is needed before any conclusions concerning the optimum amount to be used can be made. Several hypotheses may be suggested for the mechanism of the process whereby the fat is freed by the alcohol pretreatment. The alcohol may serve as a medium by which the water may be brought into more intimate and continuous contact with the lactose in the milk powder, thus speeding the crystallization process. This, in turn, would free the fat for extraction by destroying the continuity of the lactose glass which may entrap the fat. In this case there should exist between the alcohol and the lactose a competition for the water and additional water in the alcohol should shift the equilibrium toward the formation of more crystalline lactose and the consequent freeing of more fat for extraction. However, the evidence is only suggestive and t he other possibilities that the alcohol simply serves as a medium in which the lactose crystals may grow or that the alcohol may effect the other components of the powder so as to make it more porous cannot be eliminated. A M E T H O D FOR T H E REMOVAL OF S O L V E N T FLAVORS FROI~ B U T T E R OIL

When the solvents were removed from the butter oils in the previous study by evaporation under vacuum at approximately 40 ° C., the butter oil, reconstituted with fresh skim milk to the approximate composition of the original milk (3.8 per cent fat), possessed sufficient solvent flavor to interfere with the establishment of its stale-flavor threshold value. Investigation of other common methods of solvent removal did not yield satisfactory results. Hence, a method specifically designed for this purpose was developed. Experimental Method. Briggs (1) had observed that, by the adsorption of gases on activated cocoanut charcoal at liquid-air temperatures from low-pressure systems, higher vacuums could be obtained than by use of high-vacuum pumps alone. Also it is known that organic solvents are adsorbed strongly by charcoal at low temperatures. Therefore, the special tube shown in fig. 1 was constructed. B u tter oil and the solvent to be investigated were added to the pyrex flask A. Cocoanut charcoal (--~31 g.) was placed in the pyrex tube B, which was connected to the flask by means of a ground-glass joint. The flask A and its contents were held at a constant temperature of 40 ° C. in water bath, while the entire apparatus was agitated continuously by a Boerner shaker. The bulk of the solvent was removed with an aspirator through stopcock C, and then a vacuum pump was attached and the pressure reduced to 0.1 ram. of mercury or less. After the sys-

STALE-FLAVOR

COMPONENTS

IN

DRIED

WHOLE

~IILK

55

tern had been evacuated for a sufficient length of time, the charcoal in the tube B was degassed by being heated with a B u n s e n b u r n e r while the p u m p was still in operation. The heating period (usually 15-20 rain.) was complete when no change in the pressure of the system could be noted a f t e r the charcoal h a d been heated f o r a 5-min. period in a closed system. W i t h the stopcock still closed, the charcoal bulb was allowed to cool to room t e m p e r a t u r e , a n d then the pressure of the system was f u r t h e r reduced to 10 -5 ram. of m e r c u r y or less b y immersion of the bulb in liquid air contained in a 1 1. D e w a r flask. A f t e r a sufficient time, the bulb was removed f r o m the liquid air, the stopcock C was opened and the -145ram.

L

E o

E

~B

25ram

I Lii E E

E E

B

A_( _)

t

FIG. 1. Apparatus for removal of solvents 2rein butter oil: A--500 ml. pyrex flask for butter oil and ether. B---Cocoanut charcoal (31 g.). C---Stopcock leading to vacuum pump. D-Ground glass fitting. E--25 ram. pyrex tube. flask containing the b u t t e r oil was disconnected f r o m the bulb. The pressure in the system d u r i n g the process was determined b y m e a n s of a h i g h - v a c u u m arc tester which gives a pale-blue arc at less t h a n 0.1 ram. of m e r c u r y pressure and no discharge at 10 -5 ram. of m e r c u r y pressure or less. While this method for measuring the pressuure m a y seem somewhat qualitative, it was satisfactory for the purpose of this study. Time study. To determine the m i n i m u m time required for evacuation with the h i g h - v a c u u m p u m p a n d f o r the charcoal adsorption f o r the solvents used in this study, the duration of these t r e a t m e n t s was varied a n d the b u t t e r oils obtained, blended with fresh skim milk to 3.8 per cent f a t a n d scored for solvent flavor b y

56

R. MCL. WHITNEY W H I T N E Y AND P. H. H. TRACY

a panel panel of experienced judges. judges. Their observations are recorded in table 3. Discussion. In In the development of o£ this this procedure no attempt attempt was made to determine the effect of changes changes in in such variables variables as weight and and type of charcoal, design of apparatus, apparatus, or amount· amount' of bbutter u t t e r oil, since a satisfactory method was deTABLE TABLE 3 solvent Effect of time of evacuation evacuation and time of charcoal adsorption adsorption upon the completeness completeness of solvent removal removal from butter butter oil Judging Judging 0

~

.....

;:l <0

p. IS ol ~

1:1<0

,::; 0o

W.

W.

........0 C::$ ~]

.....

..,

o ~ ,....;~

0-

>~

0 e.j..j~ Ool


.§ ~

E-<
~Ol

00

eg~~ <0 ... ,.<:1

.§ ~0

~

'"

E-
.....obi) lll o'"§

~...

.., ~

0o

Z·....

0

2+ 2+ 222+ 2+ 222+ 2+ 222+ 2+ 221+ 1+ 331+ 31 -+ 31+ 1+ 33-

(g.) (g.)

(mi.) (m~.)

..._. (hr.) (hr.)

...... (hr.) (hr.)

1

ethyl ethyl ether ether

40

400

21.8

......... .........

4

2

ethyl ethyl ether ether

40

400

21.8

1.0

4

3

ethyl e t h y l ether ether

40

400

21.8

3.0

44:

4

ethyl e t h y l ether ether

40

400

21.8

24.0

4

5

ethyl ethyl ether ether

40

400

......... .........

3.0

4

6

ethyl e t h y l ether ether

40

400

4.1

3.0

4

7

ethyl ethyl ether ether

40

400

1.0

3.0

4

'<:l~

..,a'lS' ~... ol
E-<17l

4+ 4+ 4+ 4+ 44444+ 4+ 4+ 4+ 4+ 4+

8

ethyl ethyl ether ether

40

400

24.0

3.0

4

1+ 1+ 33-

9

ethyl ethyl ether ether

40

400

16.0 16.0

5.0

2

22-

10

ethyl ethyl ether ether

40

400

8.25

10.6

3

33-

11 12 13 14 15

ethyl e t h y l ether ether ethyl ethyl ether ether ethyl e t h y l ether ether ethyl ethyl ethQr ether methyl m e t h y l alcohol & pet. pet. ether ether (1/1) (1/1) methyl m e t h y l alcohol & pet. pet. ether ether (1/1) (1/1) methyl m e t h y l alcohol & pet. ether & pet. ether (1/1) (1/1)

40 40 40 150 150 150

400 400 400 250 500

8.0 4.0 4.0 4.0 4.0

8.0 3.0 2.0 2.0 2.0

3 2 3 3 4

3322333344-

2+ 2+ 1<') 1 (~) 111+ 1 1 +(~) 1 (f) 1 (f) (~) 22332233334+ 4+

150

500

4.0

4.0

2

22-

22-

150 150

500 500

4.0 4.0

3.0 3.0

33

33-

1+ 1+ 22-

16 17

•a (+) presence of (+) indicates i n d i c a t e s presence of solvent s o l v e n t flavor. Apparently, A p p a r e n t l y , in in the t h e initial i n i t i a l experiments e x p e r i m e n t s some of of the t h e jjudges u d g e s had h a d difficulty in in recognizing r e c o g n i z i n g the t h e solvent s o l v e n t flavor since solvent s o l v e n t flavor was sometimes sometimes reported r e p o r t e d in i n the t h e fresh f r e s h control. control. Results R e s u l t s are are included i n c l u d e d only only to add a d d weight w e i g h t to to the t h e results r e s u l t s of of the the later l a t e r experiments. experiments.

veloped by by controlling the time of evacuation and and the time of adsorption adsorption on cocoanut n u t charcoal charcoal at liquid-air liquid-air temperature. temperature. Although Although there are some inconsistencies

STALE-FLAVOR COMPONENTS IN DRIED WHOLE MILK

57

in the results reported in table 3, subsequent use has confirmed the conclusions reached in the time study that satisfactory removal of ethyl ether from at least 150 g. of b u t t e r oil was accomplished b y 4-hr. evacuation with the pump at pressures of 0.1 mm. of m e r c u r y or less and 2-hr. adsorption on cocoanut charcoal at liquid-air temperatures, while the mixture of petroleum ether and methyl alcohol required an additional 2-hr. adsorption on the cocoanut charcoal. The results in table 3 indicate that evacuation alone, even for 21.8 hr., is insufficient to reduce the solvent concentration in the butter oil below the threshold value. Apparently, pressures of solvent vapor of the order of 0.1 mm. of merc u r y are in equilibrium with a concentration of solvent in the b u t t e r oil which is above the threshold value. However, as also indicated by the data, some evacuation with the pump is necessary to reduce the total amount of solvent in the system below a certain value before the adsorption on the charcoal can reduce the concentration in the b u t t e r oil below the threshold value. The time of adsorption on charcoal required is a p p a r e n t l y determined by the rates of diffusion of solvent in the various states and the dimensions of the apparatus. T H E REMOVAL OF STALE-FLAVOR COMPONENT W I T H THE BUTTER OIL FROM THE STALE DRIED WHOLE MILK BY SOLVENT EXTRACTION

W i t h the development of a special procedure for eliminating the interferences of solvent flavors with the judgments of the butter oil, a series of experiments was p e r f o r m e d to determine whether the stale-flavor component was removed efficiently from the dried whole milk with the butter oil by solvent extraction. Experimental methods. Three different procedures for p r e t r e a t m e n t of the dried whole milk were employed, all of which-had been f o u n d to yield satisf a c t o r y recoveries of b u t t e r oil on subsequent extraction with organic solvents. The conditions of extraction and solvent removal are supplied in table 4. A f t e r the solvent was removed from the extracted butter oils, they were blended with fresh skim milk to the composition of the original whole milk (4.3 per cent fat) and their stale-flavor threshold values were determined by the procedure described in our previous publication (4). Samples of the dried whole milk before pretreatment were reconstituted with distilled water to the same composition and their threshold values determined. These results also are recorded in table 4. Discussion. Consideration of these results indicates that by all methods investigated the threshold value of the stale extracted butter oil is approximately the same as the percentage of fat from the stale reconstituted whole milk present at its threshold value. 1 Thus, it is indicated that the amount of the stale-flavor component per unit weight of fat is approximately the same for both the extracted b u t t e r oil and the dried whole milk from which it was extracted. Therefore, it can be concluded that, within the limits of experimental error, the efficiency of extraction of the stale-flavor component is proportional to the efficiency of extraction of the b u t t e r oil and that 90 per cent or more of the stale-flavor component is removed along with the butter-oil by the procedures used. I n the 1 Calculated by the following f o r m u l a : The p e r cent f a t is reconstituted whole milk times the threshold value of stale reconstituted whole milk.

58

R. 1VICL. W H I T N E Y

first experiment,

the presence

AND P.

H.

TRACY

of an off-flavor which was considered

ferent from that of ethyl ether and which could not be removed removal technique

indicated the possible formation

to be dif-

by the solvent-

of flavored reaction products

TABLE 4

Effect of pretreatment and solvent extraction q~pon the efficiency of removal of stale-flavor vomponen~ ~rom dried whole milk Expt. no.

Powder no. Pretreatment

l~[oisture content a f t e r pretreatment ( % ) Wt. of powder (g.) F a t content of powder ( % ) Solvent Vol. of solvent (ml.) Temp. of extraction (°C.) Time of extraction (hr.) No. of trips of syphon Temp. of solvent removal (°C.) Pressure during evacuation

(ram. of Hg) Time of evacuation (hr.) Time of adsorption on charcoal (hr.) Wt. of extracted butter oil (g.) Recovery of b u t t e r oil ( % ) Threshold value of stale reconstituted whole milk

1

2

3

104

194

104

static hydration as in table 1, expt. 5

dynamic hydration as in table 1, expt. 6

alcohol treatment as in table 1, expt. 7, except time of treatment was 7 hr. .........

7.87 176.8 29.73 anhydrous ethyl ether 750 40 4.25 19 40

9.20 198.5 29.30 pet. ether b.p. ~ 41 °C. 850 43-49 23.75 18 40

205 31.60 pet. ether b.p. ~ 41 °C. 850 47 9.17 a 4.17 18 47

~ 0.1 for 4 hr. ~ 0.1 for 4 hr. 8 2.25

~ 0.1 20.2 4

~ 0.1 for 1 hr. ~ 0.1 for 4 hr. 5 4

51.2

56.0

61.8

97.5 (6) 40 + 9

96.2 (6) 50 + 9

95.4 (8) 50 + 8

1.7 + 0.'4

2.2 +_0.4

2.2 _+0.4

(4) 2.8 _+9.9

(8) 1.8 +_0.5

(6) 1.0 +_0.5

(%)b

F a t from stale reconstituted whole milk at threshold value ( % ) c Threshold value of stale extracted butter oil ( % ) b Comments

Medicinal, Solvent Pyrolysis Product

a The alcohol-treated powder was divided into 2 equal fractions and extracted in 2 different Soxhlet extractors. The difference in time of extraction is due to the design of the apparatus. b The numbers in parenthesis represent the no. of judgments. Rejected judgments are not included. ~.Calculated b y the following formula: % F a t in reconstituted whole m i l k × t h r e s h o l d value of stale reconstituted whole milk.

f r o m t h e e t h y l e t h e r a n d s o m e c o m p o n e n t o f t h e b u t t e r oil. S i n c e t h i s o f f - f l a v o r was not present in the other experiments in which petroleum ether was used as the extracting solvent, it appears to be the more suitable solvent for this study.

STALE-FLAVOR COMPONENTS IN DRIED WHOLE MILK

59

SUMMARY I n this s t u d y of the stale flavor which develops in dried whole milk on storage, it was necessary to develop a more efficient method for obtaining stale butter oil from the dried whole milk. A n investigation of various Soxhlet-type extraction procedures with organic solvents resulted in two suitable procedures which yielded better t h a n 90 per cent recovery of stale butter oil. Difficulties encountered in the removal of solvent from the extracted butter oil necessitated the development of a special technique to reduce the solvent concentration in the butter oil to the point where it did not interfere with the organoleptic j u d g m e n t of the product. The stale-flavor component was extracted with the b u t t e r oil b y these procedures i n approximately the same ratio to the fat as existed in the original dried whole milk and therefore m a y be considered to be better t h a n 90 per cent extracted from the dried whole milk.

ACKNOWLEDGMENTS This paper reports research undertaken in cooperation with the Quartermaster F o o d and Container Institute for the A r m e d Forces and has been assigned No. 269 in the series of papers approved for publication. The views or conclusions contained in this report are those of the authors. They are not to be construed as necessarily reflecting the views or indorsement of the Department of the A r m y . The authors wish to express their appreciation to R. J. lV[cCauley, Rachel 8eitz, Mrs. N o r m a Willard, Katherine Faulson, and Joseph Tobias for aid in p e r f o r m i n g the experiments at various stages of the research. REFERENCES (1) BRIGGS,H. Prehensility: A Factor of Gaseous Adsorption. Proe. Roy. Soc. Edinburgh, 42: 26-33. 1922. (2) HOLM, G. E., GREENBANK,G. 1~., AND DEYSHER, E. F. The Effect of Homogenization, Condensation, and Variation in the Fat Content of a Milk upon the Keeping Quality of its Milk Powder. J. Dairy Sci., 8(6) : 515-522. 1925. (3) LAXFITT, L. H., AND BUSmLL, J. H. The Physicochemieal Constitution of Spray-Drled Milk Powder. J. Hoe. Chem. Ind., 50: 45T-54T. 1931. (4) WHITNEY,R. MCL., AND TRACY,P. H. Stale-Flavor Components in Dried Whole Milk No. I. The Distribution of Stale Flavor between Fractions of Reconstituted Stale Whole Milk Powder. J. Dairy Sci., 32. (5) : 383-390. 1949. (5) WILSON, R. E. Humidity Control by Means of H2SO+Solution with Critical Compilation of Vapor Pressure Data. J. Ind. Eng. Chem., 13: 326-331. 1921.