Neutrons and Food 8 at MLZ

Plant-based milk alternatives are valued for their nutritional benefits; however, off-flavors such as green and grassy notes limit the application of plant proteins in fermented dairy systems. This study investigated key volatile off-flavor compounds in fermented dairy beverages enriched with hazelnut and pea proteins and fermented with Lactobacillus acidophilus. Formulations were developed using response surface methodology by varying hazelnut-to-pea protein ratios (0–100%) and total protein concentration (1–4 g/100 mL). Volatile compounds were analyzed by solid-phase microextraction gas chromatography–mass spectrometry. Hexanal, hexanol, and pentanol were identified as major off-flavor contributors. Benzaldehyde was detected only in the hazelnut-based formulation at the highest concentration, whereas 3,5-octadienone was observed exclusively in the pea-protein beverage. Hexanal levels increased with hazelnut protein content, while hexanol and pentanol were more closely associated with pea protein. Hexanal peaked at 267.5 ppm in the 100:0 formulation (4 g/100 mL), whereas hexanol was highest (205.3 ppm) in the 50:50 mixture at the same concentration. Pentanol reached its maximum level (156.1 ppm) in the 0:100 pea beverage at 1 g/100 mL. These results highlight the role of protein source and concentration in off-flavor development and provide guidance for improving the sensory quality of plant-protein–enriched fermented dairy beverages.