Thermal Processing of Watermeal for High-Protein Gluten-Free Rice Bread: Effects on Functional and Quality Properties

Wolffia spp., commonly known as watermeal, is a nutrient-rich aquatic plant with potential as a sustainable food ingredient; however, its high moisture content (approximately 95%) necessitates effective drying to preserve product quality. This study evaluated hot-air oven and vacuum drying at 60 and 70 °C and subsequently investigated the effects of incorporating 0-20% watermeal powder into gluten-free rice bread as a product innovation. Vacuum drying at 70 °C produced powder with the lowest moisture content and water activity and the highest protein content (26.44 g/100 g), total phenolic content, and solubility. Based on these combined physicochemical and nutritional characteristics, the vacuum-drying-at-70 °C powder was selected for incorporation into gluten-free rice bread. The powder contained all nine essential amino acids, although their concentrations varied among drying treatments. Watermeal powder incorporation increased the viscoelastic moduli of the batter and enhanced its structural resistance and recovery behavior. Incorporating 20% watermeal powder increased the protein and crude fiber contents of the bread from 5.65 to 8.15 g/100 g and from 1.33 to 5.08 g/100 g, respectively, while decreasing the specific volume from 2.64 to 1.83 cm³/g and loaf height from 43.92 to 39.17 mm. Bread staling was evaluated during 3 days of storage at 25 ± 2 °C. Despite these changes, the bread remained sensorially acceptable, with an overall-liking score of 6.0. These findings demonstrate the potential of dried watermeal as a nutrient-rich functional ingredient for gluten-free bread, providing nutritional enhancement while maintaining acceptable product quality.