PERFORMANCE EVALUATION OF STREPTOCOCCUS THERMOPHILUS STRAINS IN SKIM MILK DAHl MANUFACTURE WITH REFERENCE TO ITS MICROBIOLOGICAL AND KEEPING QUALITY

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dc.contributor.advisorSannabhadti, S. S.
dc.contributor.authorSaxena, Alok
dc.date.accessioned2018-05-21T06:55:50Z
dc.date.available2018-05-21T06:55:50Z
dc.date.issued1990
dc.description.abstractThis study was planned and conducted to evaluate the comparative performance of three promising strains of Streptococcus thermophiius, naraely D-3(C1), MD-2(C2) and MD-8(C.j) isolated from market samples of aahi, and to assess their feasibility for commercial manufacture of dahi from standardized buffalo skim milk adjusted to three levels of total solids. These strains grown in skim milk were also examined for their antibacterial ability against Escherichia coli, Staphylococcus aureus. Salmonella typhosa. Bacillus cereus and Pseudomonas aeruginosa. For studying different attributes, dahi was manufactured on pilot scale from buffalo skim milk adjusted to 1O.O(T1), 12.5(T2) and IS.OCT^) per cent total solids by addina condensed buffalo skim milk. After standardization of these three lots of milk, they were heat treated to 90 C for 10 min and then cooled to 40 C, The standardized milk, having individual level of milk solids, was divided further into three equal parts. To each of these, D-3,MD-2 and MD-8 strains were added as inoculum individually at the rate of 2 per cent. The inoculated milk sanples were filled in polystyrene cups having lids and then inoculated at 40 + 1 C.For assessing microbiological changes during incubation, a set of cups from each lot of milk were drawn at 0,2,4 and 6 hour periods. For analysis of skim milk dahi during storage, samples were transferred to a refrigerator (5 - 7 C) when the curd sanples attained an acidity of 0.75 per cent and kept overnight. End of this period was considered as 0 hour/day for storage studies. After this storage, half of the total samples of curd were retained in the refrigerator and remaining half were transferred to an incubator(37 + 1C), For assessing microbial changes in dahi at ambient temperature storage (37 4; 1 C), samples were drawn at 0, 12, 24 and 48h of storage and at 0, 6, 12 and 18 days in case of refrigerated storage (5 - 7 C), T, (15 per cent T.S.) level of total solids gave significant (P^O.GS) result than other level of total solids with respect to change in titratable acidity, shift in pH, extent of lactose degradation, change in lactic count and /B-galactosidase content during incubation with all the three strains, c2 and C3 showed higher acid production throughout the incubation period than C1 which took nearly 5.5h to form the product. Dahi with desired level of titratable acidity was produced with C and C3 cultures within 4.5 hours of incubation.During ambient and refrigerated temperature storage also, T- showed significant result (P 4 0,05) with respect to change in titratable acidity, shift in pH, change in lactic count, extent of lactose degradation, B-galactosidase content and standard plate count. Dahi showed a shelf life of 12 days at refrigerated temperature and only 24 h at ambient temperature Coliform count was found within prescribed BIS limit of Max, 10/g throughout the storage period while yeast and mold count was within prescribed limit of Max, 100/g, only upto 24 h in case of room temperature storage and 12 days at refrigerated storage, with dahi showing high count at 46 h and IC days at which period the product was unacceptable organoleptically. In the in-vitro study on antibacterial activity of the product, MD-2 culture showed maximal antibacterial activity among the three strains against Escherichia coli. Bacillus cereus. Staphylococcus aurevis cind Pseudomonas aeruginosa which was followed by MD-8. D-3 showed the least antibacterial activity and it was found to be mainly due to lactic acid. Antibacterial activity against Salmonella typhosa, however, was the highest with MD-8 followed by MD-ยป2 and D-3, From these observations it can be stated that in MD-2 and MD-8, the components other than lactic acid arealso involved in antibacterial activity. From the observations on uniform rate of acid production, lactose utilization, increase in lactic count, B-galactosidase to activity, etc., it is possible recommend all the three iv strains of S-, thermophilus for the manufacture of dahi using buffalo skim milk standardized between 10 and 15 per cent TS. Among the three strains, although all of them were capable of producing acceptable product within about 5,5 of incubation, MD-2 and MD-8 strains of S, thermophiluaverefound superior to D-3 strain as they could set the gel within 4.5h and have better antibacterial activity against pathogenic and spoilage organisms. The results of the study on B-galactosidase activity in the product made with the three strains show that the enzyme level was much higher in MD-2 and MD-8 cultures than D-3 culture. The concentration of this enzyme in D-3 culture was less than half of that observed with MD-2 or MD-8. However, looking to the high lactic count and almost similar Jactose degradation in D-3 culture it is thought that in this strain, the pathway adopted for lactose degradation was somewhat different than MD-2 and MD-8, In which permease system seems to be operative. -temperature. The product stored at ambient/was spoiled within 24 h while refrigerated storage kept the product for 12 days, so for better storage stability of the product, refrigerated storage is recommended Hence hi oh yeast and mold counts seem to be the cause for spoilage of the product, avoiding their entry and restricting their growth in the product is essential, for further enhancing the shelf life of the product.en_US
dc.identifier.urihttp://krishikosh.egranth.ac.in/handle/1/5810046870
dc.keywordsPERFORMANCE EVALUATION OF STREPTOCOCCUS THERMOPHILUS STRAINS, SKIM MILK DAHl MANUFACTURE, REFERENCE TO ITS MICROBIOLOGICAL AND KEEPING QUALITYen_US
dc.language.isoenen_US
dc.publisherAAU, Ananden_US
dc.research.problemPERFORMANCE EVALUATION OF STREPTOCOCCUS THERMOPHILUS STRAINS IN SKIM MILK DAHl MANUFACTURE WITH REFERENCE TO ITS MICROBIOLOGICAL AND KEEPING QUALITYen_US
dc.subDairy Microbiologyen_US
dc.subjectDAIRY MICROBIOLOGY, DAIRYINGen_US
dc.subjectEVALUATIONen_US
dc.themePERFORMANCE EVALUATION OF STREPTOCOCCUS THERMOPHILUS STRAINS IN SKIM MILK DAHl MANUFACTUREen_US
dc.these.typeM.Scen_US
dc.titlePERFORMANCE EVALUATION OF STREPTOCOCCUS THERMOPHILUS STRAINS IN SKIM MILK DAHl MANUFACTURE WITH REFERENCE TO ITS MICROBIOLOGICAL AND KEEPING QUALITYen_US
dc.typeThesisen_US
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