Optimization of Mixed Fermentation Process of Purple Rice Flour and Its Nutritional Improvement

In order to optimize the nutritional quality of infant supplementary food, purple rice, the raw material used in this paper, was fermented by Rhizopus oryzae and Lactobacillus plantarum in the way of mixed fermentation, and subsequently extruded before it was produced as an instant infant purple rice flour. Based on reducing sugar content, anthocyanin content, sensory evaluation and titratable acidity, the conditions of the purple rice flour mixed fermentation process were optimized. Results showed that, the optimum technological parameters of mixed fermentation of purple rice noodles were 8:1 g/mL inoculation proportion (Rhizopus oryzae:Lactobacillus plantarum), 0.8% inoculation dose, 1:0.8 g/mL solid-liquid ratio, 12 h fermentation time, and 31 ℃ fermentation temperature. Compared with the unfermented purple rice flour as a control, the starch digestibility in vitro of the fermented flour increased from 50.27% to 62.37%, the free phenol content increased from 204.46 mg GAE/100 g DW to 231.44 mg GAE/100 g DW, and phytic acid degraded 25.64%. After fermentation and extruded, the starch digestibility in vitro of the infant purple rice flour reached 84.39%, the free phenol content was 192.73 mg GAE/100 g DW, and the phytic acid degradation rate was 35.58%. The results indicated that fermentation significantly optimized the starch digestibility and phenolic composition of the purple rice flour, and reduced the content of anti-nutrition factor. In summary, the present study provides technical reference for the development of purple rice infant supplementary food with high nutritional value.