Investigating the effects of citric acid concentrations on acidification, rheological, and microbial properties of fermented soy protein isolate yogurts.

As consumer awareness grows regarding the environmental and health impacts of animal-based products, plant-based alternatives are gaining popularity in developed countries. Plant-based proteins, like soy protein isolate (SPI), are valued for their sustainability and ability to complement animal proteins. SPI is commonly used in plant-based yogurts due to its high-quality protein, strong gelling capacity, and support for lactic acid bacteria (LAB) growth. Typically, plant-based yogurts use citric acid (CA) as a preservative, but its effect on LAB quality and effects is not fully understood. This study examines how different CA concentrations (0%, 1%, 1.5%, 2%, and 3%) influence the physicochemical, rheological, and microbial properties of fermented SPI yogurts under various temperature conditions over time (0, 15, and 24 h at 45°C and 48 h readings at 4°C). Higher CA concentrations led to lower pH, higher total titratable acidity, a loss modulus (G″) exceeding the storage modulus (G'), and increased viscosity. LAB growth was significant at refrigeration temperatures across all samples, indicating LAB adaptation to produce more lactic acid during storage. The study highlights that fermentation duration, temperature, storage conditions, and CA concentration significantly affect the properties of plant-based yogurts. Yogurts with 1% CA exhibited the best quality attributes while maintaining a pH below 4.6 as a food safety process control. This research provides insights into the preservation, safety, and quality of plant-based yogurts. PRACTICAL APPLICATION: This research aims to help food manufacturers improve the quality and safety of plant-based yogurts by optimizing citric acid levels. By balancing acidity and probiotic content, producers can create healthier, more sustainable yogurt alternatives that appeal to environmentally conscious consumers.