Green efficient preparation and on-line monitoring: Hybrid effect of okra pectin and controlled-temperature ultrasound on physicochemical properties of low-fat yogurt.

Pectin replaces fat as a stabilizer in making green low-fat yogurt. Controlled-temperature ultrasonic-assisted fermentation (CTUAF) was used, and its acoustic field was monitored in time-frequency domains during the fermentation. Meanwhile, the effect of the addition of okra pectin (OP) on the acoustic field intensity in the yogurt was discussed. Furthermore, the synergistic effect of ultrasound and OP on the physicochemical and structural properties of yogurt was studied, including post processing operations and storage of yogurt. Results showed that adding OP increased the intensity of acoustic field and improved the efficiency of yogurt fermentation. 0.1% OP, ultrasound and hybrid of both shortened the fermentation time of yogurt by 0.75 h, 0.5 h and 1.0 h, respectively. Ultrasound and OP reduced syneresis and optimized hardness, rheological properties and processing quality of yogurt. The cross-linking of OP with casein increased and filled casein cavities, and ultrasound enhanced this interaction. The hybrid of OP and CTUAF also improved the survival rate of probiotics. • Both ultrasound and okra pectin (OP) shortened fermentation time by 1 h maximally. • Ultrasound and OP were conducive to a more stable protein network structure. • In post processing operations, both ultrasound and OP stabilized yogurt texture. [ABSTRACT FROM AUTHOR]