The role of poi as a naturally fermented Hawaiian food in the modulation of gut health

Abstract

Poi, a culturally significant staple food in the Hawaiian diet, is traditionally made from cooked taro and can undergo natural fermentation by lactic acid bacteria (LAB). Previous studies have suggested potential health benefits of poi, such as its prebiotic, probiotic, and anti-cancer properties. However, the specific health advantages and the underlying mechanisms related to the probiotic nature of poi remain unclear. The gut microbiota plays crucial roles in various physiological functions, and communication within this microbial community is facilitated by the production of metabolites such as short-chain fatty acids (SCFAs). Probiotics and probiotic foods can help replenish beneficial bacteria in the gut and reduce chronic inflammation in the intestines associated with gastrointestinal disorders. Poi, as a naturally fermented food, has the potential to deliver beneficial bacteria and improve gut homeostasis. This dissertation aimed to investigate the probiotic properties of poi, its anti-inflammatory effects, its regulation of lipid metabolism, and its impact on gut microbiota.Six commercially available poi brands were subjected to simulated gastrointestinal digestion, and LAB surviving the process were isolated and identified. The analysis revealed changes in bacterial abundance and diversity in poi after digestion, identifying 13 different LAB species, including the most prevalent species: Leuconostoc lactis, Leuconostoc mesenteroides, Enterococcus lactis, Leuconostoc pseudomesenteroides, and Lactiplantibacillus plantarum. Some LAB isolates demonstrated antimicrobial activities against Listeria monocytogenes and/or Salmonella enterica serotype Typhimurium, as well as bile salt hydrolase activities and cholesterol assimilation. The adhesion abilities to human intestinal epithelial cells (Caco-2) varied among the LAB isolates. Furthermore, extracts from both fresh and fermented poi were tested on Caco-2 cells to evaluate their effects on bacterial infection, inflammation, oxidative stress, and lipid metabolism. The extracts inhibited the adhesion and invasion of L. monocytogenes and S. Typhimurium, suppressed the expression of pro-inflammatory genes, promoted the expression of anti-inflammatory genes, and upregulated tight junction proteins essential for gut barrier integrity. The poi extracts also influenced gene expressions related to lipid metabolism, favoring lipid oxidation and gastrointestinal immunoregulation, including PPARs, FIAF, and SREBP-2. Finally, the impact of fresh and fermented poi on human gut microbiota was assessed using in vitro fecal fermentations. Fermented poi significantly increased microbial diversity. Both fresh and fermented poi altered microbial community structure and promoted the production of SCFAs, including butyrate, valerate, isobutyrate, and isovalerate. Poi affected the abundances of various bacterial phyla and genera, increasing beneficial genera such as Bacteroides, Bifidobacterium, and Roseburia, while decreasing potentially harmful genera such as Fusobacterium and Klebsiella. The fermented poi group exhibited more pronounced effects on gut microbiota and predicted metabolic pathways compared to the fresh poi group. In conclusion, this study has illuminated the potential probiotic properties of poi, especially fermented poi, as demonstrated by the presence of probiotic LAB, inhibition of pathogenic bacteria, modulation of inflammatory responses, enhancement of gut barrier function, and influence on gut microbiota composition and SCFA production. Further research is needed to elucidate the contribution of specific bioactive compounds in poi to its health-promoting attributes. The findings presented in this dissertation may contribute to the development of preventive strategies against inflammatory bowel diseases and metabolic syndromes.