Effect of Traditional Dried Starter Culture on Morphological, Chemical and Physicochemical Properties of Sweet Fermented Glutinous Rice Products

Abstract

Sweet glutinous rice products or khao-mak in Thai were prepared by fermenting cooked glutinous rice (RD6 variety) using traditional starter cultures from Samut Sakhon (SSK) and Pathum Thani (PTT) Provinces at room temperature (28±2 °C) for 3 days. Amylolytic activities of microbial excisting in the traditional starter cultures were tested. Meanwhile, types and amounts of microbial growth in fermented rice products were investigated. Both traditional dried starter cultures showed strong amylolytic activity after inoculation for 2 and 3 days in starch agar. Microbiological profiles of rice fermentation were varied in total plate count, yeast and molds over the fermentation period. Different starter cultures resulted in a wide variation of end products with diverse chemical, microbiological and morphology properties; however those changes exhibited similar trends in all treatments. As fermentation time increased, protein content remained unchanged while total soluble solids, pH, acidity, sugar and alcohol content markedly increased compared with unfermented cooked rice. PTT showed products with higher acidity and alcohol content (0.50%, 2.58%) than SSK (0.31%, 1.85%). Morphological examination of rice grains revealed that microbial growth started from the outer surface and then moved inside the rice grains with greater corrosion was observed as fermentation time increased. Pasting and gelatinization properties of the rice flour were also strongly affected by fermentation.