Effect of processing on the physicochemical properties of extrudates and shortbreads from a pearl-barnyard millet blend and their fortification with epigallocatechin gallate

Millets are climate-resilient, nutritious, and naturally gluten-free grains that serve as sustainable alternatives to conventional cereals. Their high dietary fiber, rich mineral content, fair protein content, and appreciable essential amino acid levels make them suitable for value-added food products, particularly for individuals with gluten intolerance and lifestyle-related disorders. Among the available processing techniques, extrusion (a thermomechanical process) and baking (a thermal process) are widely used to produce ready-to-eat and baked products with desirable texture and consumer acceptability. In this study, a 60:40 blend of pearl millet and barnyard millet was selected due to their balanced nutritional and functional characteristics. Pearl millet contributes higher protein and essential amino acids, while barnyard millet provides dietary fiber, micronutrients, and improved processing behavior. The objective of this study was to develop pearl millet–barnyard millet based extruded and baked products and to evaluate the stability of epigallocatechin gallate (EGCG) in extruded and baked products.Extrusion experiments were designed using a Box–Behnken design to investigate the effects of barrel temperature, screw speed, and feed moisture content on the physicochemical properties of the extrudates. Baking experiments were conducted using a Central Composite Design to evaluate the effects of baking time and temperature on the textural properties of shortbreads. Response Surface Methodology was applied to analyze the influence of processing parameters on the measured responses. The extrudates and shortbreads were compared with commercial reference products, and a weighted scoring system was employed to identify the samples with the most desirable characteristics and determine the corresponding optimized processing conditions.Epigallocatechin gallate (EGCG), a polyphenol with antioxidant and health-promoting properties, is highly susceptible to degradation during food processing. Therefore, its non-covalent complexation with whey protein isolate (WPI) was investigated as a strategy to improve stability. Under the optimized processing conditions, EGCG, in the form of green-tea extract (GTE) was incorporated in the free and WPI–GTE complex form, and its retention was quantified using high-performance liquid chromatography. The results showed that the WPI–GTE complex provided greater protection to EGCG during baking, whereas no significant protective effect was observed during extrusion.Overall, this study demonstrated the potential of a pearl millet–barnyard millet blend for the development of extruded and baked products and highlights the influence of processing conditions on product characteristics and bioactive stability.