Structural Characteristics, Nutritional Significance and Processing Techniques of Various Millets: A Comprehensive Review

Abstract

Millets are a taxonomically heterogeneous group of small-grained cereals whose renewed prominence rests on claims that they are simultaneously climate-resilient and nutritionally superior to refined staple foods. The evidence underpinning the second claim is substantially weaker than the first, and much of it is derived from compositional analyses rather than from demonstrations of physiological benefit of farm produce. This review evaluates the literature connecting the structural organisation of the millet caryopsis to its nutritional value and to the outcomes of processing, and asks how far that connection has actually been established. Peer-reviewed publications retrieved from openly accessible scholarly indexes were appraised for methodological adequacy, consistency and relevance, and were synthesised thematically rather than catalogued. Three findings emerged. First, the structural features that distinguish millets from wheat and rice, namely a thin adherent pericarp, a pigmented testa in several species, a continuous protein matrix surrounding small polygonal starch granules, and heavily lignified peripheral cell walls, are the same features that constrain nutrient release, so that gains in one nutritional dimension are frequently obtained at the cost of another. Second, processing operations are routinely evaluated against compositional endpoints that have limited predictive value for absorption or glycemic index outcome, and the small number of controlled human studies has produced results considerably more modest than the in-vitro literature. Third, methodological heterogeneity in cultivar selection, processing intensity and analytical protocol is severe enough to account for many apparent contradictions between studies, and this heterogeneity is rarely acknowledged. Confidence is highest for the effects of decortication and germination on anti-nutrient content and for the post-harvest losses of pearl millet flour perhaps during processing storage, and lowest for claims of clinically meaningful metabolic benefit. Priorities include standardised processing descriptors, cultivar-resolved reporting, and adequately powered human trials that test defined processed matrices rather than millet as an undifferentiated category.