Process optimization for lactic acid bacteria fermentation to reduce cadmium in rice

Abstract: A kind of rice noodle fermentation broth from Changde provides strains to remove the heavy metal cadmium in rice. And the main microbial flora in this fermented liquid is plant lactobacillus. Plant lactobacillus can break down the rice protein to make cadmium free from combining state and then move out from rice. The bacterial cell membrane can also remove cadmium from rice by the effect of adsorption. Plackett-Burman design (PBD), Steepest ascent experiment (SAE), and Box-Behnken design (BBD) were used to optimize the process of this experiment. The results showed that, main factors which obviously affected the rates of cadmium removal in rice screened by PBD were the additive quantity of water, the amount of strengthening bacteria and the fermentation temperature. We also adopted the response surface design of experiment to find the optimum fermentation conditions by using SAE that is a high efficient screening experiment method. The scopes of 3 main factors were respectively that, the additive quantity of water was from 110%-130%, the amount of strengthening bacteria was from 0.5‰ to 0.9‰ and the fermentation temperature was from 30℃ to 34℃. The optimum fermentation conditions were obtained, which were the additive quantity of water of 120%, the amount of strengthening bacteria of 0.8‰, and the fermentation temperature of 32℃. It also included the other fermentation conditions just like the additive amount of liquid yeast of 2%, the additive amount of salt of 0.8%, and the time fermentation period of 22-26 h. Under this optimal condition, the removal rate of cadmium was 79.24%. Heavy metal cadmium in rice was determined by Graphite Furnace atomic absorption spectrometry. Finally, this method was verified on its effects on 3 different batches of cadmium rice. The research results showed that this method could be used in different batches of early rice. Full rice grain was used to ferment in this experiment. And after completion of fermentation, the rice grain was still intact, which retained the comprehensive processing suitability of rice. This method which used microbial fermentation to remove the cadmium from rice was simple and convenient. It was also suitable for the industrial large-scale processing. Although the rice material after dealing with cadmium removal through fermentation could not be used in the food processing industry, it completely reached the requirements of food processing or other industry processing. Therefore, the results of this research have great significance in improving the status quo of cadmium rice in some regions.