Grape Leaf Powder as a Green Fortifier in Bread: Effects on Nutritional and Technological Quality

This study explored the impact of grape leaf powder (GLP) incorporation (0%-6%) on the quality characteristics of bread. Increasing GLP levels significantly (p < 0.05) affected crust and crumb color values, decreasing lightness (crust L*: 53.14 → 42.75; crumb L*: 75.85 → 44.05) and intensifying green color tones (a*: -1.86 in crust and -5.15 in crumb at 6% GLP). At high GLP utilization ratios, bread volume and specific volume markedly decreased, indicating a denser bread structure. Textural properties of dough and bread were significantly (p < 0.05) influenced by GLP addition. Fresh dough hardness increased from 2080.73 g (control) to 8077.93 g (6% GLP), while fermented dough springiness decreased from 0.88 to 0.11. When GLP levels exceeded 3%, the baked bread crumb firmness (on Day 3) increased significantly (p < 0.05) and reached up to 13,636.34 g at the highest GLP levels. SEM analysis revealed a more compact and disrupted starch-protein matrix with increasing GLP substitution. Nutritional composition, as ash (0.76 up to 1.23 g/100 g), protein (12.47 up to 13.74 g/100 g), and fat contents (1.10 up to 1.56 g/100 g) improved with GLP utilization. Functional properties were markedly enhanced: total chlorophyll content reached up to 262.80 mg/kg at 6% GLP, while antioxidant activity increased substantially, with DPPH values rising from 34.73 to 26,147.19 mg TE/kg and total phenolic content from 5429.81 to 8948.77 mg GAE/kg (p < 0.05). In conclusion, moderate GLP incorporation (≤ 3%) enhanced the nutritional and functional properties of bread without severely compromising bread texture and appearance, highlighting GLP as a promising ingredient for green fortification of wheat-based bakery products. PRACTICAL APPLICATIONS: Incorporating small amounts (2%-3%) of GLP into bread formulations can naturally enhance antioxidant capacity and mineral content, without compromising key technological properties. This clean-label approach offers bakeries and food manufacturers a sustainable way to upcycle grapevine by-products into functional ingredients, supporting both product innovation and environmental sustainability.