ASSESSING THE FEASIBILITY OF MANUFACTURE OF CONCENTRATED DAHI USING SELECTED STARTER CULTURES OF Streptococcus thermophilus AND Lactococcus lactis
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Date
1997
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AAU, Anand
Abstract
This study was planned and conducted to assess the feasibility of promising strains oi Streptococcus thermophihts, namely D-3 (C1) and MD-8 (C2) and Lactococcus lactis subsp. lactis strain C-10 (C3) in the manufacture of concentrated dahi from standardized milk adjusted to three different levels of total solids. For studying different attributes, concentrated cfahi was manufactured on pilot scale from standardized milk adjusted to 20.00(T1), 24.00(T2) and 28(T3) per cent total solids by fortification with skim milk powder. After standardization of these three lots of milk, they were heat treated to 90°C for 10 minutes and then cooled to room temperature. Starter culture was added as inoculum in each lot at the rate of 10 per cent based on preliminary studies. The inoculated milk of each lot was filled in polystyrene cups(100 ml capacity) having aluminium foil lids and then incubated at a temperature of 40±2°C in case of S/replococciis ihennophilus strains and 30+1 °C in case of Lactococcus lactis subsp. lactis strain. For assessing, chemical and microbiological changes during incubation, a set of cups from each lot of milk was drawn at 0, 4 and 8 hours interval. When the product attained an acidity of about 0.75-0.80 per cent lactic acid, a set of cups was transferred to the refrigerator and kept overnight. Next day product was subjected to the sensory evaluation by a panel of judges. Another set of cups was transferred to low temperature incubator maintained at a temperature of 10°C and the product was stored for 7 days at this temperature to know the acceptability of the product. T2 (24.00 per cent TS) level of total solids gave significant results than other level of total solids with respect to change in titratable acidity, extent of the lactose degradation, change in lactic count and utilization of soluble nitrogen during incubation with all the three strains. Among the cultures used, culture C1 showed higher acid production throughout the incubation period than C2 and C3, Dahi with desired level of titratable acidity was produced with C1 and C2 cultures within 4.0 hours of incubation. While it needed 8 hours with C3 culture. After storage of the product for 7 days at 10°C, C3, showed significant results with respect to change in titratable acidity, shift in pH, extent of lactose degradation, change in free fatty acids, changes in the soluble nitrogen and changes in lactic count indicating continued activity of culture even during refrigerated storage. Concentrated dahi was found veiy much acceptable even after 7 days of storage at al! levels of total solids with cultures C1 and C2. However, C3 produced bitterness in the product after 7 days of storage in T3 level of total solids and the product was unacceptable. Coliform count was found within prescribed BIS. limits of max. 10/g at the end of storage period. Same was also true with that of yeast and mold count which was within prescribed limit of max.100/g From the observations on uniform rate of acid production, lactose utilization and stability to higher concentration of total solids, it is possible to recommend all the three strains for the manufacture of concentrated dahi using standardized milk between 20 and 28 per cent total solids (TMS), Among the three strains, although all of them were capable of producing acceptable product within 6 hours of incubation, D-3 and MD-8 strains of Streptococcus thermophilus were found superior to C-10 strain of Lactococciis laciis as they could set the product within 4 hours and had better acceptability score even after 7 days storage at 10°C.
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DAIRY MICROBIOLOGY, DAIRYING, A STUDY