Dr. J. B. PrajapatiGEETA CHAUDHARY2018-01-042018-01-042016http://krishikosh.egranth.ac.in/handle/1/5810038779The present study was carried out to investigate the changes in physicochemical, texture and sensory properties of milk fermented with different strains of lactic acid bacteria. Recently the consumers’ requirements for the quality of the fermented milk products are increasing. Rheology and sensory attributes are very important factors governing quality of Dahi. Different cultures procured from market and the Department of Dairy Microbiology, were used to prepare Dahi. All the curd samples were prepared from cow milk standardized to 3.5 % fat and 14 % TS. Standardized milk was f e r m e n t e d a t t e m p e r a t u r e o f 3 9 ̊ C till the pH reached u p t o 4 . 6 f o l l o w e d b y t r a n s f e r o f s a m p l e s t o r e f r i g e r a t o r ( 5 ± 2 ̊ C) for overnight. Textural and sensory analyses were carried out next day morning. In screening phase, fifteen lactic cultures of Lactoccoccus lactis, Streptococcus thermophiles and lactobacilli nomenclatured from A to M were analysed for texture as well as sensory analysis. The textural analysis was carried out using TAHD plus texture analyser, which analysed various properties like fracturability, hardness, cohesiveness, gumminess, springiness, chewiness, resilience and adhesiveness etc. Results of fracturability revealed that cultures B (370.28 g) and K (354.26 g) were showing higher value, while Culture C, E, H, I and M had fracturability in the range of 278 to 295 g, which was at par. Cultures C (586.58 g), D (509.57 g) and B (491.23 g) were best with respect to hardness. Higher cohesiveness value was reported for cultures J (0.41) and M (0.42). Cultures C (231.95 g), D (193.49 g) and B (188.98 g) were observed to possess better results for gumminess. Cultures H, J, K, L and N were also at par in terms of gumminess. Culture J and M reported high value for springiness, chewiness and resilience. The springiness value of cultures A, B, C, D, E, F, G, H, I, K, L and N (around 1 mm) were at par. Cultures J (1823.98 g.sec), M (1719.07 g.sec) and N (1622.25 g.sec) were best with respect to adhesiveness. The results for sensory attributes revealed that cultures B (8.25), D (8.00), K (8.09) and L (8.07) were better in terms of overall acceptability. Total eleven culture combinations were made on the basis of screening phase to obtain a better quality Dahi. Different combinations were A2 (B + E), B2 (B + I), C2 (D + E), D2 (D + I), E2 (J + L) and F2 (M + K) in a ratio of 50:50, while G2 (B + E), H2 (B + I), I2 (D + E) and J2 (D + I) in a ratio of 75:25.Cultures B2, C2, E2 and G2 had fracturability in the range of 300 to 311 g, which was at par. Cultures A2 (435.05 g), B2 (421.35 g) and D2 (421.77 g) possessed good hardness while lowest value of hardness was reported for EPS producing cultures E2 (372.923 g) and F2 (357.22 g). For cohesiveness, B2, C2, D2, I2 and J2 were at par (0.387 to 0.398). Cultures G2 (181.97 G), H2 (186.02 g) and I2 (178.67 g) gave better results for gumminess. Culture E2 and F2 reported higher value for springiness, chewiness and resilience. Cultures E2 (1317.75 g.sec) and F2 (1329.71 g.sec) were good with respect to adhesiveness. The Dahi prepared with cultures E2 (8.00), F2 (7.95), I2 (8.21) and J2 (8.35) showed maximum acceptability as reflected by highest scores for different parameters during sensory evaluation. The best culture combinations (E2, F2, I2 and J2) were analyzed for the shelf-life at 5 ± 2 ̊C . During storage, fracturability did not show any significant change, while the hardness was significantly increasing. After 21 days of storage, the hardness was found to be the highest for culture I2 (522.03 g). There was a nonsignificant difference in the value of cohesiveness with storage time. With storage, the value of gumminess was significantly increasing and was observed maximum in Dahi prepared with culture I2 (187.31 g). Springiness value was increasing for EPS producing cultures during storage period and was highest for culture I2 (2.55 mm). With the days of storage, the value of chewiness was increasing in all the cultures but the values of resilience showed non-significant difference up-to 14th day. Adhesiveness was observed to decrease for non-EPS producing cultures. All the samples were having the initial lactic count of 109 cfu/g, which reduced marginally but still remained nearly 107 to 108 cfu/g throughout the refrigerated storage period of three weeks. Strict sanitary conditions followed during preparation and storage of samples resulted in absence of coliform in 1 g and yeast and mold count was less than 10 cfu/g for fresh as well as stored samples. The acidity increased gradually in all treatments during storage of the Dahi. Fresh samples were having acidity around 0.71 to 0.72 %LA. At the end of storage culture I2 had least increase in the acidity. The initial pH value at 0 day was around 4.62 to 4.66. During storage the pH value was decreasing. Sample I2 had least decrease in pH. From the sensory analysis on 9-point hedonic scale, it was clear that all the parameters (flavour, body, acidity, color & appearance and overall acceptability) for cultures I2 and E2 were superior from other cultures when they were fresh and even at the end of the storage. Mean flavour score was higher for culture I2 (7.13) followed by E2 (7.1) and J2 (6.94). Body score was higher for culture I2 and followed by E2. Overall score was also higher for culture I2 (7.24) and E2 (7.22). All the four Dahi samples (I2, J2, E2, and F2) were acceptable throughout the re f r i g e r a t e d s t o r a g e ( 5 ± 2 ̊C ) of three weeks, along with viable count of 7-8 log cfu/g. Cultures I2 and E2 scored higher for sensory attributes as compared to J2 and F2. Present study entailed to conclude that better quality Dahi, with respect to texture and sensory qualities can be prepared by using cultures I2(D + E) (75 : 25) and E2 (J + L) (50 : 50).endairy science, dairy microbiologyEvaluationThesis