Density Ranges of Plastic Beads for Milk Density Measurement

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JOUI~NAL

OF

DAII~Y

SCIENCE

ACKNO~VLEDGI~ENT

This investigation was supported in part by Public Health Service l~esearch Grant EF 00099 from the Division of Environmental Engiueering and Food Protection.

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I{EFERENCES

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(1) BOLDINOH, J., AND TAYLOI%, R. J. 1958. Process of Flavoring and Product. U.S. Pat.

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SCALE

FIG. 2. Mass spectrum of ~-caprolactone. F r a c t i o n s of both the synthetic S-eaprolactone and the corresponding component in the heated milk f a t were collected f r o m the gas chromatograph and i n f r a r e d spectra obtained. These spectra are reproduced in F i g u r e 1. Both compounds show the characteristic lactone absorptions at 1,740 cm ~ and 935 cm -~ (2). The mass spectrum of the isolated component is shown in F i g u r e 2; this is identical to that of the synthetic compound. This spectTum follows the general p a t t e r n of the Cs to C~ 3-1actones reported by M c F a d d e n et al. (6). I t is estimated f r o m recovery studies that ~-eaprolactone is present in heated milk fat at a concentration of about 2 ppm. THOMAS H. P A R L I M E N T "~ WASSEI~ W. NAWAR IRVING S. FAGERSON D e p a r t m e n t of Food Science and Technology University of Massachusetts, Amherst 2 National Defense Graduate Fellow.

DENSITY

RANGES

2,819,169, issued Jan. 7. (2) BOLnlNGH, J., ~N]) TAYLOR, R. J. 1962. Trace Constituents of Butterfat. Nature, 194: 909. (3) DE BRUYN, J., AND SCHOGT, J. C. M. 1961. Isolation of Volatile Constituents from Fats and Oils by Vacuum Degassing. J. Am. Oil Chemists' Soc., 38: 40. (4) EDWAI%DS) R. A., AND FAOERSON, I. S. 1965. Unpublished results. University of Massachusetts. (5) KEENEY, P. G., AND PATTON, S. 1956. The Coconu~dike Defect of Milk Fat. I. Isolation of the Flavor Compound from Butteroil and Its Identification as ~-Decalactone. J. Dairy Sci., 39: 1104. (6) MCFADDEN, W. H., DAY, E. A., AN]) DIAMOND, M. J. 1965. Correlations and Anomalies in Mass Spectra. Lactones. Anal. Chem., 37 : 89. (7) NAWAI%, W. W., CANCEL, h. E., AND FAGEI%SON, I. S. 1962. Heat-Induced Changes in Milk Fat. 5. Dairy Sci., 45: 1172. (8) R.OBINSON, R., AND SMITH, L. H. 1937. The Oxidation of Cyclo-Hexanone and Suberone by Means of Caro's Acid. J. Chem. Soc. (London), 371. (9) THARP, B. W., AND PATTON, S. 1960. Coconut-like Flavor Defect of Milk Fat. IV. Demons%ration of ~-Dodeealactone in the Steam Distillate from Milk Fat. J. Dairy Sci., 43: 475.

OF PLASTIC

DENSITY

BEADS

FOR MILK

MEASUREMENT

Investigators have questioned the accuracy of graded density (Golding) plastic beads as a measure of the n o n f a t solids in milk. An examination was made of over 6,000 beads by placing them in a series of NaC1 solutions of known density, to determine their accuracy. Twenty-one solutions, 500 ml each, ranging f r o m 1.0246 to 1.0346 g / m l at .0005 intervals, ± .0001, were p r e p a r e d by blending calculated amounts of 1.0200 and 1.0400 g / m l NaC1 solutions, each with 0.1 ml wetting agent (50% alkyl dimethyl benzyl a m m o n i u m chloride) p e r liter. A glass plummet, loaded with glass beads, displacing 27.1553 ml distilled water at 20--+ 0.1 C and a Mettler balance, were used to deter-

mine solution densities each day that examinations were made. Solutions were kept at all times in 16-oz glass vegetable j a r s (70 mm opening, with a screw cap), both for density determinations and for bead examinations. All work was done in a room thermostatically controlled at just under 20 C. Beads were tempered overnight or longer at 20 C before examination. The density of a bead was taken as that of' the solution in which it would just sink to the bottom. I n routine examinations, beads were t r a n s f e r r e d f r o m heavie~ solutions to lighter ones, a f t e r r e m o v i n g free solution by touching them to cheese cloth. Table 1 summarizes the distribution of beads

TECHNICAL NOTES

617

TABLE 1 All beads In range, -.0004 to +.0001 S1. light, --.0004 to --.0009 S1. heavy, +.0001 to +.0006 Too light, --.0009 to --.0014 Too heavy, +.0006 to +.0011 Total

Age of beads 1-2 yr

About 2 yr

4,893

(%) 79.11

],383

339

8.55

5

.30

3

756

12.22

255

15.51

4

.06

1

3 6,185

.05

0 1,644

in the arbitrary classes according to the solutions in which they just sank. According to this distribution, the older beads are more dense than the newer ones. However, the older beads have the highest percentage in the in-range classification. Furthermore, most of the new beads were from one shipment, which may imply a manufacturing variable rather than an age variable. Other workers have observed a shrinking of beads with age, which has raised some question as to the reliability of bead density readings. However, if one does not expect extreme precision from this method it should be acceptable for certain investigations. I t does seem remarkable that they can be as accurate as they are. There are other points that warrant attenVACUUM INSIDE

THE

(%) 84.12

1 yr or less 853

(%) 71.86

.09

521

27.89

501

15.83

0

0

.06

0

0

3

.25

0

3 3,164

.09

0 1,377

0

2,657

(%) 83.98

tion, such as a) agitate mildly while heating the milk to dislodge attached small air bubble~. b) avoid bead sorting, since colors are not always distinguishable and wrong beads may be placed in the jars, and e) control the temperature of milk at time of reading as closely as possible to 20 C. D. J . HA:NKINSON

Department of Food Science and Technology AND

S. N. G A u ~ Department of Veterinary and Animal Sciences University of Massachusetts Amherst

COW'S TEAT AT END OF MACHINE

The main conclusions of the very valuable contribution by Witzel and McDonald (1) on pressures in the teat and udder sinuses during milking are that both these pressures remain near atmospheric until milk flow ceases, after which the teat sinus shows pressure fluctuations similar to and in phase with those in the pulsation chamber of the teatcup assembly but the pressure in the udder remains unaltered. The authors "believe that the gland sinus does not exhibit marked pressure changes because of annular ring closure at the end of milk flow." They also found that after milk flow ceased the pressure inside the teat fell during each cycle almost to the full vacuum attained in the pulsation chamber but did not return to atmospheric pressure when the pulsation chamber did so. In some experiments the streak canal was occluded by suturing at the end of milking, and the teatcup replaced. Again, teat sinus pressure changes were similar to those in the pulsation chamber, but there was no residual vacuum and the total pressure change was less than at the end of milking. These differences led the authors to the conclusion that vacuum changes in the teat sinus are partly

MILKING

due to pressure change in the pulsation chamber and partly to extension of the milking vacuum through the streak canal when the liner is open. I t was thought that residual teat sinus vacuum at the end of milking might be relieved after teateups are removed either through equilibration with the gland sinus or through the teat canal, although definite experinmntal evidence of the mechanism was not obtained. We think that a clearer interpretation of the experimental data emerges if it is accepted that both the gland sinus and the teat sinus collapse completely under external air pressure as the last of the available milk is extracted. I t might be argued that this is self-evident. Nevertheless, we have measured the volume of teats occluded at the proximal end and related the reduction in volume when stripped of milk by hand to the amount of milk obtained. It was also shown that occluded teats which had been emptied did not contain either milk or gas a nfinute later. A group of five cows was used: three British Friesians in first lactation (207, 219, 204 in Figure 1); a Friesian in seventh lactation (910); and an Ayrshire in