MVSc

In the present investigation, a total of 180 freshly prepared curd samples belonging to 10 batches were collected on the day of production. Two samples from each batch were selected at random and examined on zero day and the remaining samples were stored under refrigeration and duplicate samples examined on day 3, 5, 7, 9, 12, 15, 18 and 21 of storage. A total of 80 curd samples belonging to four brands viz. A, B, C and D were also collected from retail outlets in and around Thrissur Corporation. All samples of curd were tested to evaluate the microbial quality by estimating the total viable count (TVC), coliform count (CC), faecal streptococcal count (FSC), psychrotrophic count (PC) and yeast and mould count (YMC). Isolation and identification of Escherichia coli, Staphylococcus aureus, Salmonellae, Pseudomonas aeruginosa and Bacillus species were also carried out. The organoleptic qualities of curd such as colour and appearance, flavour, body and texture and product acidity and physico-chemical parameters such as pH and titratable acidity were also assessed. Microbial quality assurance of curd during its production and critical control points of microbial contamination in the production line were also evaluated during the study.
Paired‘t’ test of the data revealed that mean TVC of the samples increased at a highly significant (p<0.01) level from zero day to fifth day of storage, after which it decreased gradually. The mean CC of curd samples showed a gradual decreasing trend till the 12th day of storage. Coliforms were not detected in 90 per cent of the fresh curd samples. The mean FSC of curd samples also decreased significantly through out the storage period. On 18th and 21st day, 70 per cent of the samples did not reveal the presence of faecal streptococci. The mean PC decreased subsequently during storage till 12th day, after which it slightly increased. The mean YMC of fresh curd was 3.91 ± 0.11 log10cfu/g and it increased gradually from third day of storage compared to the count of the fresh sample. The count increased by 1.5log10cfu/g on the 12th day of storage and the increase was highly significant (p<0.01). A highly significant (p<0.01) and positive association was observed between the mean TVC and FSC on 21st day of storage. A significant (p<0.05) and negative association was observed between the mean TVC and PC on day nine of storage. A similar association was observed between mean CC and PC of samples on 12th day of storage and mean YMC and PC of samples on 15th day of storage.
E. coli was not detected from any of the fresh and refrigerated samples of curd. Staphylococcus aureus was isolated from 35 per cent of fresh curd samples. On day 3, 5 and 7 of storage, 25, 20 and 10 per cent of the samples revealed the presence of the organism and all isolates were coagulase and TNase positive. None of the curd samples revealed the presence of Salmonellae and Pseudomonas aeruginosa. Bacillus species were present in 70 per cent of the fresh samples and 20 per cent each of the samples tested on day 15 and 18. Bacillus cereus was not detected in any of the curd samples and among the isolates, 55.4 and 25.67 per cent were B. subtilis and B. coagulans.
The mean titratable acidity showed an increase till ninth day of storage and then decreased throughout the storage period. The pH of fresh curd samples decreased on storage and after 15th day, it increased gradually. Analysis revealed that flavour scores decreased during storage. Body and texture score remained almost the same throughout the storage period except a slight decrease on the third day. Colour and appearance score decreased significantly during the storage period and product acidity score also got reduced during storage.
Of the 80 samples collected from the four brands, 42.5, 37.5 and 20 per cent had mean TVC at the level of 109, 108 and 107 cfu/g, respectively. Highly significant (p<0.01) difference was observed in mean CC of the samples of the different brands. Coliforms were not detected in the samples of brand B and 80 and 70 per cent samples of the brands C and D, respectively. A highly significant (p<0.01) difference was observed between the mean FSC count of samples from the four brands. Of the samples, 40 per cent did not reveal the presence of the organism and the count in 50 per cent samples from brand A was at the level of 103cfu/g.
E. coli was not detected in the samples of brands B and D. The organism was isolated from 5 and 15 per cent of samples of brand A and C and the four isolates belonged to the serotype O157, O5, O148 and rough type. None of the samples from the four brands revealed the presence of Salmonellae. Pseudomonas aeruginosa was present in 2.5 per cent of the samples from the four brands. Staphylococcus aureus was detected in two of the curd samples, one (5%) each from brand A and C. Bacillus species was isolated from 62.5 per cent of the samples and among the isolates, 14.14 per cent was B. cereus.
Analysis of variance test revealed a highly significant (p<0.01) difference in the mean titratable acidity and pH of the samples from the various brands. Organoleptic score analysed by Kruskal-Wallis test revealed that the product acidity score of the market curds varied significantly (p<0.01).
Air samples collected from the various areas of curd production revealed highest bacterial count at the area of thermal treatment and lowest at the area of cream separation. The mean YMC was higher at the pasteurisation room. Hand washings of the personnel had the highest mean TVC and CC. E. coli was detected only in hand washings of personnel. Samples collected from the cream separator had the highest mean TVC and least in packaging material. Faecal streptococci were detected in all the samples tested and highest count was observed in the case of storage can. Samples from the double jacketed vat had the highest CC. Coliforms were not detected in the washings of the packaging material.
Heat treated skim milk was free of coliforms and the mean FSC was significantly (p<0.05) lower than that of starter inoculated milk after one and six h of incubation. Yeast and moulds were not detected in heat treated skim milk, but present in starter inoculated one and six h milk samples. The mean pH of fresh curd samples was significantly (p<0.01) lower than that of heat treated skim milk. The starter culture was free of coliforms and faecal streptococci.
The present study reflects the importance of quality assurance during every step of production and storage of curd to avoid early spoilage and to safeguard consumer health. Presence of pathogenic organisms in curd is of great public health significance as it is consumed as such paving way to food poisoning.