Amaranth Seeds as Lactic Acid Bacteria Fermentation Substrates: Prospects for Metabiotic Foods and Functional Ingredients

Amaranth, a nutritionally dense pseudocereal, is an exceptional substrate for producing functional and metabiotic food products via lactic acid fermentation. This review provides a comprehensive analysis of both ungerminated and germinated amaranth seeds as fermentation matrices, assigning their nutritional profiles, bioactive constituents, and compatibility with microbial transformation. Central to this discussion are the synergistic interactions between amaranth’s native compounds and lactic acid bacteria (LAB), with an emphasis on four key bioconversion mechanisms: protein hydrolysis, polyphenol activation, antinutrient reduction, and the biosynthesis of functional and metabiotic metabolites. Essential fermentation parameters, including substrate preparation, inoculation strategies, pH, temperature, and fermentation time, are systematically reviewed to guide optimization of bioactive compound yields. Post-fermentation processing approaches, such as freeze-drying, controlled drying, and product standardization, are assessed for their capacity to preserve product stability and ensure consistent functional performance. The review further explores the incorporation of fermented amaranth into diverse food systems, such as gluten-free bakery goods, functional beverages, and nutraceutical formulations, as well as its application in animal nutrition, where it supports improved digestibility and gut microbiome health. The review concludes by mapping current challenges, unresolved knowledge gaps, and priority research directions, positioning fermented amaranth systems as versatile, science-backed platforms for developing next-generation functional and metabiotic ingredients.