Impact of Natural Fermentation on Mineral Composition, Resistant and Non-Resistant Starches, Microbial Diversity, and Global Metabolite Profiles in Commercial Poi from Hawai‘i

Background/Objectives: Taro (Colocasia esculenta L.) is a nutritionally rich and historically significant crop widely consumed in tropical and subtropical regions. Poi, a traditional Hawaiian food made from mashed cooked taro corms, is lauded for its digestibility, prebiotic properties, and potential health benefits. The goal of our study was to evaluate the effects of natural fermentation on the nutritional and metabolic profiles of five commercial poi brands from Hawai‘i. Methods: All poi were fermented at 25 °C for 24 h and 48 h. Resistant starch (RS) and non-resistant starch (NRS) were analyzed using Megazyme assay kits, minerals were analyzed by the EPA 3050B method, fermenting bacteria were analyzed by 16S sequencing, and global metabolites were analyzed using a gas chromatography time-of-flight mass spectrometer. Results: RS and NRS significantly increased in fermented poi, while mineral composition remained unaffected. Untargeted global metabolomic analysis revealed fermentation-induced shifts in metabolite profiles, with increased amino acid concentrations but no changes in essential fatty acids, vitamin E, or flavanols. Fermentation increased the dominance of health-promoting lactic acid bacteria (LAB) such as Leuconostoc, Lactococcus, Weissella, and Lactobacillus, known for their health-promoting properties. No significant correlations were identified among the fermenting bacteria and metabolites. This is probably one of the first comprehensive evaluations to identify the impact of fermentation on the starch, mineral, fermenting microbes, and metabolite content of commercial poi and show the presence of 18 amino acids, including nine essential amino acids. Conclusions: Our findings highlight the nutritional and microbiological significance of fermented poi and its potential as a functional food. Further studies are warranted to explore the health benefits and probiotic effects of poi.