MVSc

In the present study 296 milk samples were collected from dairy farm, processing plant and retail shops and analysed for the microbial quality by estimating various microbial counts and assessing the presence of certain bacteria of public health importance. The microbial, physico-chemical and organoleptic qualities of pasteurized milk samples stored under refrigeration were evaluated. The critical points of bacterial contamination of milk at various stages of production, pasteurization, packaging and storage were also assessed during the investigation.
Out of 60 samples of raw milk from individual animal, pooled milk and chilled milk analysed, 46.7 and 36.6 per cent samples were graded as very good and good based on BIS (IS 1977). However only 25 per cent samples were only considered satisfactory based on coliform count with none of the pooled milk samples meeting the standards. Pooled milk samples revealed maximum contamination with highly significant (p0.01) difference between mean TVC and CC and significant (p0.05) difference between mean PC and FSC of milk from individual animal. However mean E.coli count was more in individual animal milk sample when compared with pooled milk. The pooled milk sample was kept under chilled condition for 17 hours. The chilled milk had higher mean TVC, ECC and PC however the increase was not statistically significant.
Pasteurization of milk was effective in reducing the microbial population of raw milk and there was highly significant (p0.01) reduction in TVC, CC, PC, FSC and YMC. From the sample of milk collected immediately after heating, after pasteurization and after packaging the mean TVC was high in packaged milk sample (4.76±0.15 log10 cfu/ml). Coliform was absent in cent percent of heated milk. However, 60 per cent of packaged milk had the organism with the mean count of 0.98±0.36 log10 cfu/ml. Only 40 per cent of packaged milk was graded satisfactory based on coliform standards prescribed by BIS (Indian Standards, 1992). E.coli could not be detected from milk collected after heating section and immediately after pasteurization. Maximum microbial contamination was seen in packaged milk. This indicates that contamination of milk occur in the storage tank or packaging section. Hence proper cleaning and sanitation of storage tank and packaging machine will reduce the microbial contamination to a considerable extent.
The microbial analysis of the retail milk sample (56) of the brands A, B, C and D revealed that the samples of the brand B had highest mean TVC (5.91 ± 0.01 log10 cfu/ml) and FSC (1.52 ± 0.22 log10 cfu/ml). The highest mean coliform (3.08 ± 0.29 log10 cfu/ml), E. coli, (2.35 ± 0.38 log10 cfu/ml), psychrotrophic counts (5.68 ± 0.25 log10 cfu/ml) were seen in the samples of brand C. Brand A had highest mean YMC (1.21 ± 0.22 log10 cfu/ml). Only 23.2 and 26.8 per cent retail samples met the TVC and CC standards prescribed by BIS (IS-1992). However, 57.14 per cent of the samples of the brand A met the standard. On comparison of freshly packed milk obtained from dairy plant with the retail brands revealed that freshly packed milk sample had highly significant (p0.01) difference and lesser TVC, CC and PC in comparison with the brands B, C and D. Thus the microbial quality of retail milk available in the locality varied among different brands hence strict hygienic measures should be adopted to minimize microbial contamination.
Pasteurized milk stored under refrigeration (4±1°C) showed an increase in TVC, CC, ECC, PC, FSC and YMC throughout the storage period. However, the initial growth rate of microorganism was slow due to sub lethal injury of microorganism during pasteurization and storage of milk under refrigerated condition. The increase in TVC, CC, ECC, PC, FSC and YMC between zero day and 12th day was 3.96, 1.76, 0.16, 3.76 and 2.37 log10 cfu/ml, respectively. The increase in the count of organism during storage may present the problem of shelf life deterioration of milk.
The public health impact on the consumers was assessed by isolation and identification of E.coli, S. aureus and L. monocytogenes, the organisms of public health importance. Escherichia coli contamination of milk occurs through unhygienic handling of milk. The organism was detected in four samples (20 per cent) of the samples of raw pooled milk and was of serotypes 05 (2 samples), 0141 and 0172. Ten per cent of freshly packaged and refrigerated milk samples revealed the presence of the organism and all isolates were of serotypes 0148. A total of 38 E.coli isolates were obtained from retail milk samples. S. aureus was isolated from 60, 5, 12.5 per cent of the samples of raw, freshly pasteurized and retail milk, respectively. The organism was isolated from 5 per cent of the samples stored on sixth day and from 10 per cent samples stored on the eight day. L. monocytogenes was not isolated from milk samples.
Sensory analysis of refrigerated milk samples showed an overall reduction in the score of colour and appearance, flavour, odour and body as the storage period increased. Development of off odour, salty or stale flavour and presence of clotted particles indicated the sensory spoilage and the maximum shelf life obtained was eight days. There was reduction in mean pH value throughout the storage period. All the samples showed positive to clot on boiling test on the day 12 of storage but the sample showed sensory unacceptability earlier.
The various critical points of bacterial contamination of milk was evaluated by collecting samples of air, water, rinse samples from utensils, equipments, hand washing of milker/personnel in the processing line, strainer and packaging material and were subjected to estimation of various bacterial counts. The mean total viable count and yeast and mold count of air samples were found to increase after the milking process or processing. Among the water samples, coliform and E. coli was detected more in the samples obtained from dairy farm. High microbial count was recorded for milk pail, milkers hand washings and package machine wash indicating an important sources of contamination. Strict hygienic practices followed by health education will minimize the microbial contamination to a considerable extent.