Observations on the Free Volatile Acids in Milk1

1764

JOURNAL OF DAII~Y SCIENCE OBSERVATIONS

ON THE

FREE

VOLATILE

Small a m o u n t s of f r e e volatile f a t t y acids in r a w nfilk h a v e been r e p o r t e d p r e v i o u s l y (1,2). This s t u d y was u n d e r t a k e n to d e t e r m i n e the different f r e e f a t t y acids p r e s e n t in milk a n d t h e i r possible r e l a t i o n s h i p to flavor of the milk. F o r t y - o n e f r e s h h e r d milks, collected a t the time of milking, were studied. A p r o t i o n of each s a m p l e was l a b o r a t o r y p a s t e u r i z e d at 145 ° F . - 30 rain., cooled, a n d e x a m i n e d f o r flavor. The r e m a i n d e r was i m m e d i a t e l y a n a l y z e d f o r volatile acids. The acids were e x t r a c t e d f r o m t h e m i l k by ether and the extracts were then subjected to gas c h r o m a t o g r a p h i c a n a l y s i s (1). U s u a l l y , t h e acids w e r e identified b y c o m p a r i n g t h e i r t h r e s h o l d v o l m n e s w i t h t h o s e of k n o w n acids.

ACIDS

IN MILK

1

H o w e v e r , c o n f i r m a t i o n of i d e n t i f i c a t i o n w a s o b t a i n e d b)f i n f r a r e d a n a l y s i s of f a t t y acids o b t a i n e d f r o m t h r e e milks. F o r t h e s e s a m p l e s , a n aliquot was a n a l y z e d b y gas chromatogr a p h y to establish the r e t e n t i o n volume of t h e v a r i o u s acids. T h e n , f r a c t i o n s c o r r e s p o n d ing' to t h e r e t e n t i o n v a l u e of each acid were o b t a i n e d f r o m a second a l i q u o t b y t r a p p i n g t h e gas s a m p l e s of each f r a c t i o n i n l i q u i d n i t r o g e n . T h e s e s a m p l e s were dissolved in carbon tetrachloride and analyzed with the Beckman IR-5 Infra-Red Spectrometer, using c a r b o n t e t r a c h l o r i d e as r e f e r e n c e . The r e s u l t s were c o m p a r e d w i t h k n o w n a u t h e n t i c v o l a t i l e acids. F o r m i c , acetic, b u t y r i c , valeric, caproic, a n d c a p r y l i c acids were identified i n all t h r e e of t h e m i l k samples. Results for both the fatty acids and the m i l k flavors f o r t h e 41 s a m p l e s a r e p r e s e n t e d in T a b l e 1. I n all, s e v e n f r e e f a t t y acids were identified as b e i n g i n a t l e a s t some of t h e s a m p l e s : f o r m i c , acetic, cap~Tlic , eaproic, val-

Technical P a p e r 361. The Department of Dairy Technology, The Ohio Agricultural Experiment Station. Ohio Agricultural Experiment Station Journal Article 7461. Supported by IIatch Ftmds from the U. S. Department of Agriculture.

TABLE 1 Free volatile acids in fresh raw milk of varying flavor quality ~M/50 ml. milk a Good (13 samples)

Free volatile acid Formic Acetic Propionic Butyric Valerie Caproie Caprylic

Feed ( 15 samples )

Oxidized (6 samples)

Rancid (7 s,amples)

Range

Av.

l~ange

Av.

Range

Av.

Range

Av.

9.8-43.1 2.6-20.5 0-1.5 0.1-1.9 0-1.9 2.3-4.6 4.8-7.4

19.6 9.0 0.3 0.4 0.7 3.0 6.7

23.5-47.0 6.4-17.9 0-1.9 0.3-1.8 0.1-1.3 1.7-4.6 5.9-14.8

31.3 10.2 0.6 0.8 0.6 3.0 8.9

25.4-50.9 5.1-14.1 0-0.4 0-.7 0-0.9 1.9-40 4.6-6.4

37.2 9.0 0.2 0.3 0.4 2.9 5.3

25.5-54.9 12.8-28.1 0-1.5 4-10.9 0.9~1.7 5.7-8.0 7.2-12.5

47.0 16.6 0.5 7.6 1.2 6.9 9.6

'~ Values corrected to 100% recovery. TABLE 2 Changes in free volatile free f a t t y acids in eight fresh and stored pasteurized milks t~M/50 ml. milk a Stored at ~0 ° F. Fresh Analysis Flavor score b B a c t e r i a l c o u n t × 108 Free vol. acids Formic Acetic Propionic Butyric Valerie Caproie Caprylie

Range 37.5~38.5 7-46

7 Days Av.

38 23

Range 37.5-3.8 21-76

21 Days

14 Days Av.

Range

Av.

38 47

36-38 56-3,300

37 238

3.3-23.5

15.9

:L.9-27.6'

12.9

4.3-46.2

17.7

2.6-7.7 0.1-0.6 0.7-1.2 0-0.4 0.3-13.6 0.6-1.6

6.8 0.2 0.9 0.1 0.7 0.8

2.8 7.6 0.1-0.4 0.6-1.1 0.1-0.5 0.3-14.7 0.6-1.4

5.7 0.2 0.8 0.2 0.8 0.8

2.6-22.6 0.1-0.5 0.8-2.4 0.1-0.6 0.4-17.6 0.6-1.7

9.6 0:2 1.2 0.3 1.0 0.8

Range

Av.

Samples Spoiled 2)600~- 23,400 66,500 103-380 160 11-199 0.7-2.7 2.4-9.6 0'.7-2.7 2.2-8.9 0.8-10.6

9.5 0.5 5.6 1.5 6.0 5.6

" Values corrected to 100% recovery. All values based on increase in concentration as compare¢t to fresh raw milk. b Averages computed to nearest whole number.

TECHNICAL NOTES

eric, butyric, and propionie. Only the first four acids were found in all milks. F o r goodflavored milk, the relative concentrations of the acids were in the order in which they are listed. Of the 41 milks, 13 were considered free of off-flavors, 15 had feed flavors, six were oxidized, and seven were rancid. Milk with feed flavors usualy contained relatively higher average concentrations of formic, butyric, and caprylic acids; whereas, for rancid-flavored milk, butyric, caproic, caprylic, formic, and acetic acids were present in comparatively high levels. The milk with oxidized flavor was not characterized by a characteristic f a t t y acid pattern. I n an additional experiment, eight paired lots of raw and pasteurized milk were obtained from commercial companies. The raw samples were obtained from the system just before the milk passed into the pasteurizer; the pasteurized samples were obtained directly from the bottle filler. Pasteurization temperatures varied from 170 to 180°F. and holding times from 16 to 22 sec. The raw and pasteurized milks were analyzed immediately for flavor, volatile acids, and total bacterial counts. The pasteurized samples were stored at 40°F. and evaluated for flavor, analyzed for f a t t y acids, and standard plate counts made after seven, 14, and 21 days of storage. Table 2 presents the results. The data reveal that commercial pasteurization produced a general increase in the free f a t t y acids, but the increase was significant FURACIN

only for the formic and acetic acids: averaging 16.9 ~M/50 ml. and 6.8 ~M/50 ml., respectively. The heat treatments used generally caused a slight heated flavor. The pasteurized milk showed no significant changes in flavor, bacterial and free f a t t y acid during the first seven days of storage. A f t e r 14 days, bacterial counts had increased and the concentration of free f a t t y acids increased slightly. The sample with the 3.3 million bacterial count contained the highest concentration of all free f a t t y acids. A f t e r 21 days, the samples were spoiled and total bacterial numbers exceeded 2.6 million in all samples. V e r y substantial increases in free f a t t y acids accompanied the spoilage, with formic and acetic acid values increasing about ten times in concentration as compared to the 14-day samples. Approximately fivefold increases were observed for butyric, valeric, caproic, and caprylic acids. W. J. ttARPER I. A. GOULD AND C. L. HANKINSON

Department of Dairy Technology The Ohio Agricultural Experiment Station Columbus I~EFER,ENCES (1) HANKINSON, C. L., ItAI~P]~, W. J., AND MIKOLAJCIK, E. A Gas-Liquid Chromatographic Method for Fatty Acids in Milk.

J. Dairy Sci., 41: 1502. 1958. (2) M o ~ , C. V., HA~PF~z,W. J., AN~ Gouu), I. A. Acids Produced by High Heat Treatment of Milk. J. Dairy Sci., 4.0: 964. 1957.

RESIDUES

Furacin ~ is a preparation for the treatment of bovine mastitis which is available only at the professional level. I t is being used by veterinarians in cases where prior treatment by the milk producer with other mastitis p r e p a r a tions has failed. The manufacturers advise that nlilk from treated quarters of udders should be discarded for 72 hr. after the last treatment if the l%racin preparation also contains penicillin. I t is recommended that the milk from quarters treated with Furacin alone need be discarded for only 24 hr. after the last treatment (1). Furacin is effective against Bacillus subtilis (3), the microorganism commonly used in the disc assay method for the detection of penicillin and other antibiotic residues in milk. Its effect upon growth and scouring in dairy calves has been evaluated (2). This investigation was undertaken for the Technical contribution No. 369, South Carolina Agricultural Experiment Station, Clemson Agricultural College, Clemson, South Carolina. "~Trade name for 5 nitro, 2 furaldehyde semicarbazone, and a product of Eaton Laboratories, Norwich, New York.

1765

IN MILK 1

purpose of determining the minimum level of Furacin detectable in milk using the disc assay (_4) and the period of time the milk should be discarded after the last treatment with Yuracin alone. Samples of raw milk were prepared containing concentrations of Furacin ranging from 0.2 mg/ml to 0.03 ~g/ml. Another set of sampies containing similar Furaein concentrations was prepared in distilled water. Duplicates of all samples in both milk and water were heated to a minimum temperature of 85 ° C. for 5 rain. before assay to avoid the possibility of false readings. Results show that heating Furacin in milk or water did not affect the diameter of the zones produced. Other results, presented in Table 1, show that 0.03 ~g. of Furacin (the lowest level tested) could be detected using the disc assay method. I t should be noted that the zones produced had unifox~dy small diameters, witll little difference between the 0.03 ~g/ml and 25 t~g/ml levels of Furacin. The zone produced by 200 ~g/ml of Furacin was of the same diameter as that produced by 0.1