STANDARDIZING CONDITIONS FOR PILOT SCALE PRODUCTION AND STORAGE OF WHOLE BUFFALO MILK DAHI USING STREPTOCOCCUS THERMOPHILUS : SOME CHEMICAL ASPECTS
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Date
1990
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AAU, Anand
Abstract
Nine different types of dahi were prepared from whole buffalo milk standardized to 4,5 per cent fat but having three different concentrations of total solids namely 15(TS-l), 18(TS-2) and 21(TS-3) percent.Performance of three strains of Streptococcus thermophilus namely MD2(SC-l), MD8(SC-2) and D3(SC-3) was evaluated using each of the standardized milk adjusted to predetermined total solids level for its dahi making qualities. Condensed Buffalo skim milk (1:3 concentration) was used for the standardization of total solids of raw whole buffalo milk. The steps followed for the dahi making were t Standardization of milk to predetermined fat and total solids level, preheating to 60°C, homogenization in single stage homogenizer (100 kg/cm2 pressure), preheating at 85°C for 10 min, cooling to 40°C, adding cultures at 2 per cent rate, filling in polystyrene cups with lid on, inctabating at 40 + 1°C till 0.75 per cent acidity and finally keeping in the refrigerator (6 ± 1°C) for about 12 h. This was considered the 0 h storage. For assessing the chemical changes in dahi during storage at refrigeration temperature (6 + 1°C) the samples were drawn at intervals of 6 days upto total of 18 days, while during storage at room temperature (37 + 1°C) the samples were drawn at intervals of 12 h upto total of 48 h . All the treatments were replicated four times. The mean values of the chemical constituents of milk and dahi of TS-1, TS-2 and TS-3 treatments showed significant (P<0.05) differences in the levels of total solids , lactose, protein and pi but non significant differences in fat and acidity . Effect due to the use of the type of culture, namely, SC-1, SC-2 and SC-3 was non significant on the t o t a l solids, fat, protein, lactose, acidity and pH values of dahi manufactured from milk of each level of s o l i d s . The three types of starter cultures had significant (P < 0.05) effect on total lactic acid, while non significant effect on citric acid, orotic acid and free fatty acids of dahi. The order of cultxires in the increasing content of lactic acid, orotic acid and free fatty acids in each case was: SC-3 > SC-2 > SC-1, while, the order of cultures in the increasing content of citric acid was: SC-2 > SC-3 > SC-l. The mean values (ppm) of diacetyl and acetaldehyde were: 0.625 and 4.707; 0.773 and 5.458; and 0.882 and 6.817 in TS-1, TS-2 and TS-3 treatments, respectively. The overall increasing order of diacetyl production by different starter cultures was t SC-1>SC-2>SC-3. Whereas the increasing order of acetaldehyde production was SC-1> SC-3 > SC-2 in all the treatments of total solids of dahi. The diacetyl production was influenced significantly (P SC-2 > SC-l as the levels of nonprotein nitrogen and tyrosine value were higher in the order of the cultures, irrespective of the treatment of dahi. The statistical analysis of levels of titratable acidity, free fatty acids, diacetyl, tyrosine value and total lactic acid of dahi during room temperature (37 + 1°C) storage revealed significant (P<0.05) differences in titratable acidities, free fatty acids, diacetyl, tyrosine value and total lactic acid. The maximum levels of titratable acidity, free fatty acids and tyrosine valxoe were observed at 48 h while the maximum levels of diacetyl and total lactic acid were observed at 24 h of storage. During storage at refrigeration temperature, the maximum levels of titratable acidity and total lactic acid were on the 12 d of storage; maximum levels of free fatty acids and tyrosine value were on the 18 d of storage, while the maximum level of diacetyl was on 0 d of storage. Different periods of storage showed significant (P< 0.05) differences in titratable acidity, free fatty acids, diacetyl and tyrosine value but nonsignificant in total lactic acid. Polyacrylamide gel electrophoresis of casein isolated from dahi revealed k-casein was degraded during 0 h of storage and both k- and aseins were degraded during 24 h of storage of dahi at room temperature. Paper chromatographic analysis of carbohydrates revealed the presence of glucose, galactose and lactose during storage of dahi for 24 h at room temperature. The concentration of glucose was lower than galactose at 24 h storage of dahi indicating that glucose is preferentially utilized by the starter cultures. The sensory evaluation of dahi revealed that the dahi of best quality can be prepared from buffalo milk of TS-l treatment (15 per cent total solids and 4,5 per cent fat) using MDQ(SC-2) strain of Streptococcus thermophilus as the starter and with no storage either at refrigeration or room temperature, Dahi from milk of TS-l treatment using Streptococcus thermophilus MD8 as the starter culture had the following average chemical composition : 15.17 per cent total solids; 4.53 per cent fat; 5.23 per cent protein; 3,66 per cent lactose; 1.05 per cent acidity; 4.57 pH; 0.58 per cent total lactic acid; 131.00 (mg/100g) citric acid; 0.90 µeq/g free fatty acids; 17.17µg/g orotic acid; 0.63 ppm diacetyl; 4.52 ppm acetaldehyde and 96.50 (µg/g) tyrosine value. The nitrogen distribution (per cent) in different fractions of dahi were 0.82, total nitrogen; 0.06, non-casein nitrogen;0.03 proteose-peptone nitrogen and 0.03 nonprotein nitrogen. Thus standardized buffalo milk of TS-l treatment, that is , milk having mean values of 15.33 per cent total solids, 4.65 per cent fat, 4.86 per cent protein, 5.70 per cent lactose, 0.19 per cent titratable acidity and 6.84 pH, is recommended for the commercial production of dahi of best quality under the standardized conditions as described and using 2 per cent of Streptococcus thennophilus MD8 as the starter culture.
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Keywords
DAIRY CHEMISTRY, A STUDY