Effects of Sunflower, Pumpkin, and Hemp Seed Proteins on the Quality Attributes of Yogurt

The growing demand for protein-enriched foods has increased interest in incorporating plant proteins into fermented dairy products. This study investigated the effects of sunflower, pumpkin, and hemp seed protein preparations, added in amounts adjusted according to their protein content to provide an additional 5% or 10% protein (w/v), on the physicochemical, nutritional, and microbiological properties of yogurts. The obtained products exhibited improved nutritional properties, with protein and dry matter contents reaching up to (16.14 ± 1.03) and (24.01 ± 1.24) g/100 g, respectively. Protein enrichment resulted in higher pH values, whereas total lactic acid production remained comparable to the control. More than 96% of the lactic acid produced was present as the L-(+) isomer, indicating proper starter culture activity and efficient fermentation. Microbial viability was influenced by both ingredient type and supplementation level. A 5% addition improved the viability of Streptococcus thermophilus and Lactobacillus spp. during refrigerated storage, whereas increasing it to 10% decreased total bacterial counts. Although freshly prepared enriched yogurts exhibited higher syneresis, whey separation stabilized or slightly decreased during storage. Protein preparations were also associated with larger growth inhibition zones against selected food-relevant strains. These findings indicate that oilseed-derived protein preparations are promising functional components for developing hybrid dairy–plant yogurts. However, their effects on acidification and bacterial viability should be considered when optimizing product formulations.