Study on optimization of removing cadmium by lactobacillus fermentation and its effect on physicochemical and quality properties of rice noodles

In recent years, cadmium (Cd) contaminated rice has aroused widespread concerns about the safety of rice or its products, and microbial fermentation has been proved to be a promising method for reducing Cd. The fermented rice flour can be applied as the main ingredient of rice noodles, a traditional breakfast staple in southern China. This study is aimed to screen out the optimum conditions for reducing Cd in rice noodles by mixed-Lactobacillus (LAB) fermentation, and to study its effect on the physicochemical and quality properties of rice noodles. The results revealed that the best condition of wet digestion for Cd detection in 0.5 g fermented rice noodles was following: digestive agent of 7 ml nitric acid (GR) + 3 ml perchloric acid (GR) +1 ml hydrogen peroxide (30% GR), digestion at 90 °C, 150 °C and 250 °C for 30 min, 60 min and 120 min, respectively. The optimized fermentation condition for decreasing the Cd concentration in rice flour was fermented by 8% (v/v) of mixed-LAB at 35 °C for 28 h, with the reduction of 87.6%. The mixed-LAB fermentation in rice flour was found to increase the concentrations of amylose and reducing sugar, improve its swelling power and gel properties, and produce lactic acid with the maximum amount of 612.1386 mg/L; while its rheological characteristics were significantly affected. Moreover, the quality properties of rice noodles made by the above fermented rice flour had also been improved, with higher hardness and chewiness, shorter rehydration duration, higher rehydration rate, less cooking loss and broken rate. These results showed that the fermentation by mixed-LAB can efficiently reduce excess concentration of Cd in rice flour, improve its physicochemical properties, and promote the quality property improvement of rice noodles made by it.