The Effects of Pea and Rice Protein Isolates on Structural–Sensory Attributes and Phenolic-Related Antioxidant Properties of Vegan Cookies

In response to growing consumer interest in plant-based and eco-friendly diets, the food industry is seeking to enrich bakery products with functional plant proteins, which are highly nutritious and environmentally beneficial. This study aimed to evaluate the effect of incorporating pea protein isolate (PPI) and rice protein isolate (RPI) at levels of 5% and 15% on the structural and sensory quality and nutritional properties of vegan cookies. The addition of plant-derived proteins significantly influenced the colour and texture of the cookies. The addition of PPI increased lightness (L* up to 70.05 at 5%), whereas the addition of RPI caused pronounced browning (BI = 100.00 at 15%) and structural hardening at higher inclusion levels. Protein content increased with enrichment, reaching 9.49 g/100 g in the P15% sample (a 95.7% increase compared to the control sample). Total phenolic content increased markedly, particularly in the P15% sample, rising by 144%. However, this was not accompanied by a proportional increase in antioxidant activity, as determined by ABTS and DPPH assays. Sensory evaluation revealed that cookies enriched with 5% protein maintained high consumer acceptability (overall scores > 7.0), whereas higher levels of protein incorporation led to a significant reduction in sensory quality. The results indicate a trade-off between nutritional enhancement and sensory acceptability in vegan cookies enriched with pea and rice protein isolates, with 5% incorporation providing the most balanced outcome within the studied formulations.