Millets belong to a nutritionally significant group of cereals widely cultivated in semi-arid regions. Although they are well known for their nutritional potential, their use in diets is often limited because of the presence of antinutritional factors such as phytic acid, tannins, oxalates and protease inhibitors. These compounds interact with grain components, thereby lowering mineral bioavailability, protein digestibility and starch utilization. Therefore, this study aims to critically summarize the soaking-induced modifications in millets with emphasis on reduction of antinutritional factors, improvement in nutrient bioavailability and changes in dough rheology and functional properties.
A wide variety of recent publications were identified through electronic databases including ScienceDirect, PubMed, SpringerLink, Google Scholar, Scopus and ResearchGate using different keywords such as millets, soaking, hydration, antinutrients, phytic acid reduction, nutrient bioavailability, digestibility, dough rheology and millet processing. Relevant research and review articles published during the past five years were critically screened and analyzed to understand the effect of soaking treatments on nutritional and rheological properties of different millet varieties.
Soaking is one of the simplest and most widely used preprocessing methods for millets. It induces structural modifications, dissolution of soluble compounds into the soaking medium and activation of endogenous enzymes, collectively improving millet quality. In this context, modification refers to not only leaching but also hydration-mediated softening, endogenous enzyme activation and structural changes in the protein-starch matrix. Soaking conditions can reduce phytic acid, lower trypsin inhibitor activity and improve in vitro protein digestibility. Enzymatic degradation of phytate decreases Phy:Fe and Phy:Zn molar ratios, thereby improving the bioavailability of iron, zinc and calcium. It improves the water absorption, pasting behavior and viscoelastic characteristics of millet flour, which support the application of millet flour in gluten-free and functional food products.
This review comprehensively discusses soaking-induced modifications in millets by integrating their effects on antinutritional reduction, nutrient bioavailability and dough rheology. The compiled information provides useful insights for researchers and food industries regarding the use of soaking as an effective, low-cost processing strategy for improving millet quality and functionality.
