A Study On Co-Fermentation Of Spirulina And Its Effect On Metabolic Associated Fatty Liver Disease

Spirulina is the highest quality natural protein food source ever discovered and has been recognized as a"future super-nutrient food"by the World Health Organization.However,the current market of Spirulina is mainly focused on primary products,and the undesirable flavorof Spirulina products has reduced the willingness of consumers to accept,implying the severe development problems.of the Spirulina industry.The application of probiotic fermentation technology in the processing of Spirulina can not only simply combine probiotics with Spirulina,but also further enhance its functional activity and improve the odor,which is of great significance for promoting the upgrading of the Spirulina industry structure.This article focuses on a series of studies on the fermentation of Spirulina with probiotics.Firstly,probiotic strains and combinations suitable for Spirulina fermentation were selected based on indicators such as bacterial quantity,active ingredients,and antioxidant capacity,and their fermentation characteristics were also analyzed.Moreover,,the Spirulina fermentation process was further optimized using single-factor and response surface experiments,with bacterial quantity and antioxidant capacity as evaluation indicators.LC-MS and GC-IMS were used to clarify the changes in nutrient and flavor components before and after Spirulina fermentation.Finally,the effects of Spirulina fermentation product on metabolic-associated fatty liver disease（MAFLD）were comprehensively evaluated through physiological and biochemical indicators,tissue morphology.In addition,liver metabolomics and 16S r RNA sequencing technology were used to preliminarily explore the mechanism of its action from the aspects of liver metabolites and intestinal flora.Results showed that the selected high quality LAB and yeast strains and their combinations have good cholesterol-lowering and gastroentestinal tolerance ability.By comparing and analyzing the fermentation characteristics of Spirulina at different times with different strains,the optimal fermentation combination of strains was finally determined as Lactobacillus acidophilus and Kluyveromyces marxianus with a fermentation time of 24 hours.Key fermentation factors were selected through single-factor experiments and optimized using response surface design with FRAP value as the evaluation index.The optimal fermentation conditions were found to be an inoculum volume of 4.7%,a ratio of LAB to yeast of 1:2,and a fermentation temperature of 30.5°C,achieving FRAP value of 206.96μmol·L^-1.Metabolomics data indicated that dual-strain fermentation could significantly increase the content of amino acids and other nutrients in Spirulina,and sensory analysis showed that dual-strain fermentation greatly improved the flavor of Spirulina,thereby enhancing its nutritional quality,functional properties,and bioavailability,which could provide a reference for large-scale production.Animal experiments showed that gavage administration of fermented Spirulina could alleviate liver fat accumulation,protect liver cells,and relieve oxidative stress under high-fat diet（HFD）.Analysis of liver metabolites and intestinal microorganisms in mice showed that fermented Spirulina significantly altered the composition of liver metabolites and intestinal microbiota,indicating that fermented Spirulina could restore the normal function of the liver in MAFLD model mice and markedly improve the dysbiosis of intestinal microbiota caused by a high-fat diet.In conclusion,Lactobacillus acidophilus and Kluyveromyces marxianus are the optimal bacterial strains for fermenting Spirulina.The fermentation of Spirulina by these two strains can significantly enhance its nutritional functional components,significantly improve its unfavorable taste,and alleviate liver damage caused by HFD through liver metablism and intestinal microbiota regulation.The research conclusion provides a theoretical reference for the deep processing of Spirulina by probiotic fermentation technology and provides technical support for riching the diversity of Spirulina products,which will promote the rapid and efficient development of the Spirulina industry.