Optimization Of Phenol Production From Wheat Bran By Mixed Fermentation And Study On Antioxidant Activity Of Phenolic Products

Objective:In order to improve the ability of solid-state co-fermentation of Aspergillus niger and Aspergillus awamori to produce phenols,the co-fermentation conditions were optimized,and the application of fermentation products was preliminarily studied.The total phenol yield of culture medium was the index to evaluate the fermentation effect.Plackett-Burman design and response surface methodology were applied to determine and optimize the co-fermentation parameters.The total phenolic content of the optimized product increased by 37.32%compared with that before optimization,and DPPH radical scavenging rate and total reducing power were also significantly increased（P<0.05,P<0.01）.Studies have confirmed that phenolic products extracted after fermentation have a certain effect on the healing of scalded wounds in rats,which provides a new idea for solid-state co-fermentation of high-yield bioactive substances,and provides a basis for the medicinal value of phenolic substances.Methods:Using wheat bran as raw material,Aspergillus niger and Aspergillus awamori were mixed for solid-state co-fermentation to extract phenols and other antioxidant active substances.Combined with response surface methodology,multi-factor and multi-level optimization was carried out for the reaction conditions which had great influence on fermentation,such as the proportion of bacteria,culture temperature and culture time.Firstly,Plackett-Burman design experiment was used to quickly screen out the significant influencing factors of phenolic products.Then,combined with the Path of steepest ascent method and Box-Behnken response surface method,the corresponding continuous variable curve model was constructed.Finally,through the analysis and screening of significant influencing factors,the results were statistically analyzed to obtain a reaction condition that can achieve the highest total phenol content,and then verified.Then the phenolic products fermented before and after the optimized process were compared,and the changes of antioxidant activity were comprehensively analyzed by measuring DPPH radical scavenging rate and total reducing power.The animal model of scald was established.Phenolic products were dissolved in glycerol and mixed with Jingwanhong ointment at a ratio of 1:1 to prepare sample solutions with concentrations of 10 and 20mg/mL respectively.The effects of phenolic products on scald healing in rats were preliminarily investigated from three aspects:wound healing area,hydroxyproline content,IL-6 and TNF-αcontent in serum.Results:The effects of wheat bran,（NH₄）₂SO₄,KH₂PO₄,the ratio of Aspergillus niger and Aspergillus awamori,inoculum amount,water content,fermentation temperature,fermentation time and other influencing factors were screened.The results showed that inoculum amount,water content and（NH₄）₂SO₄content were the three factors with the highest effects on total phenol content.After multi-factor optimization,the optimal fermentation parameters were determined as follows:5g wheat bran,0.20 g/g for（NH₄）₂SO₄content,0.03 g/g for KH₂PO₄content,79.05%for water content,2:1 for inoculation ratio of Aspergillus niger and Aspergillus awamori,27℃for fermentation temperature and 5 days for fermentation time.Under these optimized conditions,the total phenol content reached 2498.34μg/g,which was 37.32%higher than that before optimization,and the radical scavenging rate and total reducing power were significantly improved.Further studies on the effect of phenolic products on scald healing showed that total phenolic substances extracted from fermentation products,mixed with Jingwanhong ointment at a concentration of 20 mg/mL,could promote wound healing,reduce the levels of inflammatory factors IL-6 and TNF-α,and promote scald healing.Conclusion:This study is devoted to screening strains,updating technology and finding efficient ways to release phenols by wheat bran fermentation.At the same time,the antioxidant activity of phenolic products was analyzed,and the effect of phenolic products on scald healing in rats was preliminarily explored.This study not only proved the medicinal value of phenolic products after wheat bran fermentation,but also helped to alleviate the waste of resources and further improve the value of wheat bran development and utilization.