Effect of Different Pretreatment Methods of Water Extracts of Polygonatum sibiricum on the Quality of Yogurt in Cold Storage

In order to investigate the effects of water extracts from Polygonatum sibiricum prepared using different pretreatment methods on yogurt quality, this study was conducted to provide a theoretical basis for the development of Polygonatum sibiricum yogurt. This study investigated the effects of aqueous P. sibiricum extracts prepared using different pretreatment methods (liquid nitrogen freeze-dried, high-temperature vacuum steaming, and nine-steaming-nine-basking) on the storage quality of solidified yogurt. The aqueous P. sibiricum extracts were used to make yoghurt by replacing 5% milk by volume and the changes of the indexes of yoghurt under storage at 4 ℃ for 21 d were measured. Principal component analysis was used for the evaluation to select the best yogurt and correlation analysis was performed to study the correlation between nutrients and yogurt quality. The results showed that the hardness, consistency, cohesion and viscosity indices of Polygonatum sibiricum yogurt initially increased and then decreased during storage, while the water-holding capacity, viable bacteria count and sensory scores showed a consistent decline. All three water extracts of Polygonatum sibiricum significantly improved the water-holding capacity, viscosity, and the number of viable bacteria (P<0.05), hardness, consistency, and cohesion of yogurt, and the gel network structure became tighter, and all of them restrained the post-acidification of yogurt (P<0.05), as compared with control yogurt. There were significant differences (P<0.05) in hardness, consistency, and water-holding capacity of the three Polygonatum sibiricum yogurts during refrigeration. Specifically, the viable bacterial counts, water-holding capacity, hardness, and consistency of ERP (water extracts of liquid nitrogen freeze-dried Polygonatum sibiricum yogurt) were significantly higher than those of EHTP (water extracts of high-temperature vacuum-steamed Polygonatum sibiricum yogurt) and E9P (water extracts of nine-steaming-nine-basking Polygonatum sibiricum yogurt) (P<0.05), with values of 9.95 lg CFU/g, 71.10%, 215.87 g, and 1612.88 g·s, respectively. The comprehensive evaluation based on principal component analysis illustrated that ERP was better, showing that water extracts of liquid nitrogen freeze-dried Polygonatum sibiricum had the most significant effect on the improvement of yogurt. The results of correlation analysis showed that the polysaccharide and protein contents were significantly and positively correlated with a number of quality indexes of yogurt (P<0.05).