Utilization of the enzyme pullulanase and Lactobacillus acidophilus as to produce synbiotic rice yogurt cakes

This study developed a synbiotic rice yogurt cake with a medium glycemic index by combining resistant starch-enhanced rice with Lactobacillus acidophilus. The effects of substrate concentration (20-40%), pullulanase enzyme activity (20-40 U/g), and hydrolysis time (4-8 hr) on resistant starch content were investigated. At a substrate concentration of 30%, an enzyme activity of 30 U/g, and a hydrolysis time of 6 hr, the optimal resistant starch content was 14.54 ± 0.96%. After being treated to enhance its resistant starch content, IR504 rice was mixed with milk and processed to produce rice milk. The rice milk was fermented for 12 hr at 37°C with a 3% inoculum ratio, yielding the highest L. acidophilus count of 5.62 × 10⁷ CFU/g. After freeze-drying, the synbiotic rice yogurt cake contained 3.8 × 10⁷ CFU/g L. acidophilus and 3.55 g/100 g resistant starch. Nutritional analysis showed 82.4 g carbohydrates, 6.78 g lipids, 8.90 g proteins, and 1.05% moisture per 100 g. This product achieved a lower estimated glycemic index of 69.32 ± 0.534 compared with non-resistant starch (77.74 ± 0.369). Microbiological tests confirmed safety standards were met, with undetectable Enterobacteriaceae (<10 CFU/g), Listeria monocytogenes (undetectable/25 g), and undetectable total mold. The predicted shelf life of the synbiotic rice yogurt cake was approximately 198 days under typical storage conditions at 30°C and L. acidophilus count of 4.8 × 10⁶ CFU/g. Therefore, the synbiotic rice yogurt cake can be used as a product supporting glycemic control while simultaneously providing a substrate for beneficial gut bacteria.