Effect of cocoa powder on the physicochemical, microbial, and sensory properties of synbiotic freeze-dried yogurt

Abstract

Cocoa has been demonstrated to support the growth of beneficial gut bacteria. This study aimed to investigate the effect of cocoa powder on the physicochemical, microbial, and sensory characteristics of synbiotic freeze-dried yogurt. Various concentrations of cocoa powder were added to yogurt before freeze-drying. Four formulations of freeze-dried yogurt were developed by varying treatments: 7 % (w/w) inulin (control) and 7 % (w/w) inulin with 1 %, 2 % and 3 % cocoa powder (w/w), respectively. No significant difference was found in water activity and pH of all samples. However, total phenolic content and antioxidant properties were found to increase with increasing of cocoa powder. Scanning electron microscopy images revealed that the cocoa powder-fortified samples exhibited smoother, denser surfaces with lower porosity compared to the control sample. The final abundance of Lactobacillus spp. in all samples was higher than the recommended concentration for probiotic food at 106–107 CFU g−1. After 12 weeks of storage, the survival rates of all samples maintained probiotic levels above 7.51 log CFU g−1 but there were not significantly different (p > 0.05) across all sample. The survival rates of probiotics during intestinal phase of in vitro INFOGEST digestion significantly differed between the control and the cocoa powder-fortified freeze-dried yogurt (p ≤ 0.05). Furthermore, sensory test indicated that freeze-dried yogurt fortified with 2 % (w/w) cocoa powder scored the highest overall acceptability with the mean score of 7.20. Our results suggested that the developed freeze-dried yogurt could be served as alternative snack with synbiotic benefits.

Keywords

• Lactobacillus spp.
• Cocoa powder
• Freeze-drying
• Synbiotic
• Sensory properties