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Kerala Veterinary and Animal Sciences University, Wayanad

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Subject: Dairy Microbiology × Author: SILPA K RAJ × Thesis Type: M.Tech. ×
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    ThesisItemOpen Access
    STUDY ON POST FERMENTATION ACIDIFICATION BY DAHI STARTER CULTURES
    (VERGHESE KURIEN INSTITUTE OF DAIRY AND FOOD TECHNOLOGY MANNUTHY, THRISSUR, KERALA VETERINARY AND ANIMAL SCIENCES UNIVERSITY, 2023-01-03) SILPA K RAJ; DR. Ligimol James
    One of the main constraints being raised about dahi, a traditional Indian fermented dairy product prepared at households and industrial level is the increase in acidity that occurs during its storage even after ensuring proper cold chain maintenance. This continued development of acidity after the desired fermentation is referred to as post-fermentation acidification (PFA), which is not at all desirable. In the current study, twenty-two dahi cultures were screened for their post acidification potential and only three, namely L. acidophilus 307, L. casei and L. helveticus 53, were found to be low post acidifying i.e., elicited ΔpH48 of ≤0.3 units on extended storage for 48 h at fermentation temperature. Activity profiling of the three low post acidifying cultures and two high post acidifying cultures, namely L. casei 01 and L. rhamnosus 18 during refrigerated storage could distinctly classify the cultures into two different acidification pattern categories agreeing with the results of the post fermentation screening procedure adopted. Effect of thermization at 65oC as well as of microwave treatment at 600W for different periods on post acidification of dahi samples prepared using L. rhamnosus 18 or L. casei 01 upon refrigerated storage was assessed. Regardless of the treatments and the starter culture used, significant (p < 0.01) decrease in pH and increase (p < 0.01) in titratable acidity and lactobacilli count were observed in all of the dahi samples. In general, thermization at 65°C for 30 sec, 60 sec, 2 min and 5min had no inhibitory effect on post-fermentation acidification. However, microwave treatment was found to control PFA during refrigeration though in a culture specific manner. The microwave treatments adopted were found to be effective in controlling PFA during refrigerated storage. The study also explored the possibilities of using UV and mild heat stress exposures to develop low post acidifying cultures. Adopted UV treatments resulted in significant(p<0.01) reduction of ΔpH48 of both the UV treated high post acidifying cultures but could not generate low post acidifying cultures. On the other hand, mild heat stress (460C for 1 h) exposure did not elicit any noticeable impact on the post￾fermentation acidification potential of both the culture. Current study could establish strain wise differences in the post fermentation acidification pattern ofdahi cultures and scientifically assess the impact of different treatments on post fermentation acidification. Outcome of this study calls for further studies to understand the genetic and enzymatic background of the differential post acidification pattern exhibited by the tested isolates.