Effect of Some Preservatives on Babcock Tests and Fat Hydrolysis in Single Milk Samples

Manus, L.J.; Bendixen, H. A.

doi:10.3168/jds.s0022-0302(59)90721-0

Cited by 6 publications

(1 citation statement)

References 3 publications

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“…Some market milk composites, although in excellent condition for sampling at 98-103 °F, gave low Milko-tester readings because of high fat acidities. The effect of holding at 38-40 °F on hydrolysis of milks preserved with mercuric chloride has been noted previously (Manus & Bendixen 1956, 1959McDowell, 1968). Since average increases in fat acidity were smaller at atmospheric temperatures than at 38-40 °F, composite samples might well be kept at 55-60 °F rather than at refrigeration temperatures (McDowell, 1968).…”

Section: (D) Correction Of Milko-tester Readingsmentioning

confidence: 56%

Fat testing of composite Milk samples with the Milko-tester

McDowell¹

1968

Journal of Dairy Research

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SummaryWith 10-day composite milk samples the effect has been investigated of various preservatives, of variations in the method of preparing the composites and of the condition of the composites at sampling on Milko-tester results for fat content.The results for composites preserved with mercuric chloride agreed much more closely with the Werner Schmid results than did those for corresponding composites preserved with potassium dichromate, formaldehyde solution or paraformaldehyde.In composites preserved with mercuric chloride, prepared and held at ambient temperatures at 2 dairy factories, a small proportion contained destabilized fat when sampled at 98–103 °F and gave very low Milko-tester results in comparison with the Werner Schmid and Gerber results. After high-speed mixing of the composites at 115 °F the Milko-tester results were closer to, but still lower than, the Werner Schmid results.The average Milko-tester result for 133 composites free from destabilized fat when sampled at 98–103 °F was 0–099 ± 0.055% lower than the average Werner Schmid result. Results for 133 duplicate samples, which were also free of destabilized fat at 98–103 °F but which had not been swirled after the daily addition of fresh milk, were on average — 0.158 ± 0.076% lower than the Werner Schmid result. The Werner Schmid and Gerber results agreed well. The lowering of the Milko-tester result in the ‘swirled daily’ samples was due (a) to the effect produced by dissolving mercuric chloride in milk, (b) to slight fat hydrolysis, and (c) to some other factor, possibly fat oxidation. The further lowering of the Milko-tester result in the ‘non-swirled’ samples was due mainly to greater hydrolysis of the fat with production of higher fat acidities. Other composites, which were swirled daily but which were held at 38–40 °F gave on the average higher fat acidities and lower Milko-tester results than the ‘swirled daily’ composites held at ambient temperatures.A correction of +0.10% to the Milko-tester readings of all ‘swirled daily’ composites, preserved with mercuric chloride and in suitable condition for sampling at 98–103 °F, brought over 90% of the results to within ± 0.10% of the Werner Schmid results.The Milko-tester (Foss Electric, Hillerød, Denmark) is already in use in a number of countries for the rapid estimation of fat in milk. The fat content is read directly by a photometric measurement of the turbidity due to the fat globules after heating, homogenizing and diluting the sample with a protein-dissolving versene solution. The instrument has been found satisfactory for the routine testing not only of fresh milks but also of milks to which preservative has been added (Černá & Písecký, 1966; Murphy & McGann, 1967). Grubb (1966), however, reported that Milko-tester readings for samples preserved with potassium dichromate were lower after 14 days' storage.In the present paper the results are presented of an investigation into the suitability of the Milko-tester for fat testing of 10-day composite milk samples.

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Section: (D) Correction Of Milko-tester Readingsmentioning

confidence: 56%

Fat testing of composite Milk samples with the Milko-tester

McDowell¹

1968

Journal of Dairy Research

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Errors in fat testing of composite milk samples

McDowell

1968

Journal of Dairy Research

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SummaryAnalyses were made at the Institute chemistry laboratory over 2 dairy seasons of 900 composite milk samples prepared for routine fat testing at 2 dairy factories and held at ambient temperature. The composites, which were preserved with mercuric chloride, frequently had high free fat acidities and high bacterial and mould counts.At one factory, where the composites were sampled at 85−90 °F, the samples contained incompletely dispersed fat. Werner Schmid fat values for 83 milks pipetted immediately after factory sampling were lower on average by 0·084±0·089% than values obtained for the same samples after high-speed mixing at 115°F. At the other factory, where the samples were mixed at 98–103°F, Werner Schmid tests on 56 milks showed a corresponding difference of only 0·033±0·047%.For 273 factory composites, mixed at high speed, results by the Babcock test and by the Gerber test averaged, respectively, 0·015±0·019% and 0·059±0·054% higher than those by the Werner Schmid test.High bacterial and mould counts in factory composites were attributed to contamination from unsterilized bottles and stoppers and to failure of factory staff to mix the contents of each bottle after the daily addition of milk. Low bacterial and mould counts and negligible increases in free fat acidity were found in composites made up from factory milk in the Institute laboratory in sterilized bottles, kept at ambient temperature and swirled daily. Composites made up from fresh farm milks and held at 38–40°F remained in good condition for sampling after warming to 98–103°F but showed wide variation in free fat acidity.Rises in free fat acidity occurred only in composites preserved with mercuric chloride. Other preservatives, however, were less effective in preventing bacterial growth at ambient temperatures.Increases in free fat acidity up to 10 (ml N alkali/100 g fat) had no effect on results in the Babcock tests but caused a slight rise with the Gerber tests. Acidities over 20 caused a decrease in Babcock and a further rise in Gerber values.It is suggested that fat destabilization in composite samples could be minimized by avoiding rises in temperature during transport of fresh daily samples from farm to factory, by holding composites at 55–60°F and by mixing after each daily addition of milk.

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Comparison of Relative Accuracy between Testing Semimonthly Composites or Single Random Samples of Herd Milk for Composition

Manus

Erb

1963

Journal of Dairy Science

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Effect of Some Preservatives on Babcock Tests and Fat Hydrolysis in Single Milk Samples

Cited by 6 publications

References 3 publications

Fat testing of composite Milk samples with the Milko-tester

Fat testing of composite Milk samples with the Milko-tester

Errors in fat testing of composite milk samples

Comparison of Relative Accuracy between Testing Semimonthly Composites or Single Random Samples of Herd Milk for Composition

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