Impact of Heat on Microbial Survival and Physicochemical Characteristics of Coconut Neera

Coconut Neera (Cocos nucifera L.) is a sweet and nutritious drink by the presence of sucrose and minerals. The high sucrose content in neera makes it highly prone to spontaneous fermentation, leading to rapid deterioration of its physicochemical and sensory attributes. In this study, the efficacy of mild heat as single-stage and double-stage (tyndallization) treatment at 50°C, 55°C, and 60°C were assessed for 5 and 10 min treatment time. The decimal reduction time and microbial log reduction for single-stage and double-stage treated neera were determined in the storage period (4°C ± 1°C). The physiochemical and sensory properties of stored neera were evaluated up to 21 days. Among the treatment methods, the double-stage heat treatment at 60°C–10 min exhibited the least number of microbial survival (6.68 ± 0.02 log CFU/mL) and shortest D_t values (3.50 ± 0.04) after treatment. The microbial log reduction was extended up to the storage period of 21 days with the result of 1.16 ± 0.01—total viable count, 1.06 ± 0.01—Bacillus, 0.27 ± 0.01—lactic acid bacteria, and 0.86 ± 0.03—yeast in double-stage treatment at 60°C–10 min. Moreover, TEM images of this treatment confirmed the lethal effect against the microorganisms. Therefore, the double-stage treatment at 60°C–10 min depicted non-significant physicochemical changes and sensory attribute up to 21 days. Finally, the results conclude that the method of tyndallization at 60°C–10 min could be an effective temperature against microbes includes spore former of Bacillus in neera.