Optimization of Germination Enhances Nutritional Composition and In vitro Enzyme Inhibitory Properties of Selected Millets

Abstract

Germination is an effective bioprocessing technique that improves the nutritional quality and functional characteristics of cereal grains by activating endogenous enzymes and modifying the biochemical composition of seeds. Millets are recognised as nutrient-dense cereals with low glycaemic potential; however, comparative information on how germination affects their nutrient composition and enzyme inhibitory properties remains limited. This study evaluated the effects of germination on the nutritional composition of Pennisetum glaucum (pearl millet), Panicum miliaceum (proso millet),
Panicum sumatrense (little millet), and Echinochloa frumentacea (barnyard millet), as well as their in vitro inhibitory activities against α-amylase, α-glucosidase, and acetylcholinesterase. The mode of enzyme inhibition was characterised through kinetic analysis, and germination conditions were optimised using response surface methodology.
Germinated millet flours were analysed for carbohydrate, reducing sugar, protein, and dietary fibre content using standard analytical procedures. Enzyme inhibitory activity against α-amylase, α-glucosidase, and acetylcholinesterase was evaluated using established in vitro assays, and inhibitory potency was estimated by IC₅₀ determination. Lineweaver–Burk plots were used to determine the mode of enzyme inhibition. Central Composite Design coupled with Response Surface Methodology was applied to optimise soaking and germination conditions for maximum enzyme inhibitory activity. Germination enhanced the nutritional attributes of the selected millets: pearl millet showed the highest protein and reducing sugar content, while little millet showed the highest dietary fibre content. All germinated samples showed concentration-dependent inhibitory activity against the three enzymes evaluated, with little millet the most potent α-amylase inhibitor (IC₅₀ = 4.95 ± 0.20 μg mL⁻¹). Kinetic analysis indicated competitive inhibition of α-amylase and α-glucosidase, and non-competitive inhibition of acetylcholinesterase. Response surface optimisation identified 12 h of soaking followed by 6 h of germination as the optimum processing conditions for maximising enzyme inhibitory activity. Germination improved the nutritional quality and in vitro enzyme inhibitory properties of the millets investigated, highlighting their potential as ingredients for functional cereal-based foods. The biological activities reported are, however, based exclusively on in vitro assays; further phytochemical characterisation together with animal and clinical studies are needed to establish their physiological relevance and health benefits.