Slow digestible colored rice flour as wall material for microencapsulation: Its impacts on gut bacterial population and metabolic activities.

Black waxy and red jasmine rice flour (6.5% and 18.7% amylose content, respectively) were modified using pullulanase followed by heat-moisture treatment (Hydrolyzed-HMT) to produce microcapsules that entrapped L. plantarum TISTR 1465. Hydrolyzed-HMT of colored rice flours showed restricted pasting properties, lower breakdown and higher thermal properties than native flour (p<0.05). Hydrolysis treatment was able to promote a low molecular weight starch that easily formed a crystalline structure after HMT. As a consequence, a significant increase in slowly digestible starch was observed (from 23.7% to 37.0% in waxy type and 22.2% to 34.6% non-waxy type). The survival of L. plantarum TISTR 1465 after simulated gastric fluid (90min) and simulated intestinal fluid (120min) of the Hydrolyzed 36h-HMT black waxy rice was higher (8.07±0.13logCFU/g and 7.48±0.12logCFU/g) than gum arabic (6.12±0.11 and 4.72±0.28logCFU/g) and no carrier (3.34±0.23 and 0.43±0.75logCFU/g) respectively. Moreover, these microcapsules also obtained the highest survival (8.67±0.20logCFU/g) after storage for 90days at 4°C. Under scanning electron microscopy, starch granules of the hydrolyzed 36h-HMT were seen as polyhedral shapes in the spherical aggregates that carried the microorganisms and reduced their injury and mortality. Short-chain fatty acids of the hydrolyzed 36h-HMT were much higher than positive control at every fermentation time (p<0.01). The fluorescence in situ hybridization result showed that the prebiotic property of hydrolyzed 36h-HMT black waxy rice can better aid the beneficial probiotic Lactobacillus spp. growth after 24h fermentation than the negative control (from 8.40±0.48 to 7.03±0.21logCFU/g, p<0.05) and commercial prebiotic Orafti®Synergy1 (8.40±0.48 to 7.47±0.08logCFU/g, p<0.01). Microencapsulation of hydrolyzed black waxy rice flour followed by HMT is proposed as a synbiotic ingredient to apply in synbiotic foods.