Technological impact of sub-atmospheric pressure on yogurt fermentation kinetics and gel properties

Sub-atmospheric pressure fermentation is an emerging approach in food processing, but its effects on yogurt manufacture remain poorly understood. This study evaluated the impact of reduced fermentation pressure (20–90 kPa) on acidification kinetics and physicochemical properties of set-type yogurt. UHT milk inoculated with a commercial starter culture ( Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus ) was fermented under atmospheric and sub-atmospheric conditions. Fermentation was monitored by pH, carbohydrate utilization, lactic acid formation, viable cell counts (CFU), and viscosity. Acetaldehyde concentration and syneresis were determined in selected treatments. Fermentation at 20 kPa accelerated acidification, reaching pH 5.0 earlier than all other treatments, while final lactic acid concentrations remained comparable. Yogurt produced at 20 kPa exhibited reduced low-shear viscosity, increased syneresis (+39.2 %), and reduced acetaldehyde concentration (−6.0 %). These findings indicate that 20 kPa may affect texture and flavor-related attributes.