Tests of Milkofix, A New Preservative Substance for Milk Samples Used for the Purposes of An Infrared-Analysis of Basic Milk-Composition .1. Checks of Bacteriostatic and Bactericidal Abilities and Interferential Effect

Veterinarni Medicina 37, 1992, 21-31

Hygienic, ecological and health problems of sample preservation for an analysis of basic milk components make us continually to develop a safer chemical preservative substance which will preserve the original sample composition for the time required and which will not influence the analyses. T r z i c k y (1990) proposed Milkofix (M), a preservative substance on the basis of silver compound. The author reports on minimum risks of the use of this preparation, in comparison with traditional preservatives. Preservative efficiency of Milkofix was compared with other preservatives: K2Cr2O7 (C), NaN3 (A) and bronopol (B). The following concentrations were used: A - 0.0085 g NaN3 and 0.0630 g NaCl, B - 0.0050 g bronopol and 0.0500 g NaCl, C - 0.0330 g K2Cr2O7 and 0.0670 g KCl in tablet, M - 0.1250 g of the mixture, all amounts are per 25 ml milk. The observed antibacterial efficiency of M could be seen in a slower decrease in actual acidity, and/or in an increase in titratable acidity in M-treated samples unlike untreated ones (N). From the starting value pH 6.3 (Fig. 1), the value of N treatment dropped to 3.8 after two days, the values of M and A treatments dropped to 4.9 after nine days and to 5.7 after twelve days, respectively. As for SH, the values increased within the same interval from 6.5 (2.5 mmol/l) to 28.6 in N, and to 22.3 in M and 9.4 in A (Fig. 3). There was a similar trend when the milk samples were stored at a temperature of 4-degrees-C, but the differences between the preservation methods were not so clear in comparison with storage at a temperature of 20-degrees-C (Figs. 1 and 3). The standardized SH value of 9.0 (2.5 mmol) for infraanalyzer measurements was exceeded after 24 hours in N samples, after four days in M samples and after 12 days in A samples at a temperature of 20-degrees-C. The observation of the growth of microorganism counts (CPM) showed that this growth was slower in M than in N, but faster in the samples of C treatment (Fig. 5). The generative time of CPM in N made 1.6 hours, in M 2.4 hours and in C 7.9 hours. The lag phase of these mixed cultures was 24 hours in M, 60 hours in C and in N treatment the lag phase was zero. The demonstrated antibacterial effects of Milkofix were weaker than those of A, bronopol and C

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