Abstract:
This study investigated the effects of stem presence and freezing rate on the freezing quality of
Lycium barbarum, nitogen (N
2) and air were employed as heat transfer medium for quick freezing (NF
−30 ℃, NF
−50 ℃, NF
−70 ℃, NF
−90 ℃, NF
−100 ℃) and freezer quick freezing (AF
−40 ℃, AF
−20 ℃). The freezing characteristics and quality changes of
Lycium barbarum with and without stems were analyzed and compared. The results indicated that the weight loss rate for the air group and the N
2 group with stems were 20% to 22% and 8% to 17% lower respectively, than those without stems. Additionally, the nutrient retention rates increased by 8% to 23% and 6% to 53%, respectively. Notably, the difference in weight loss rates between
Lycium barbarum with stems and those without was significant when the freezing rate was below 1.58 °C/min. The freezing rate in the N
2 group (1.58~5.09 ℃/min) was approximately 2~24 times greater than that of the air group (0.21~0.78 ℃/min). The quality retention effect could be ranked as NF
−90 ℃≥NF
−100 ℃>NF-
70℃>NF
−50 ℃>NF
−30 ℃>AF
−40 ℃>AF
−20 ℃. Under a freezing rate of 3.94 °C/min (NF
−90 °C treatment group), a higher the freezing rate, resulted in better quality preservation. The nutritional quality of
Lycium barbarum with stems in the NF
−90 ℃ treatment group maintained more than 75% of the fresh wolfberry quality, with the color closely resembling fresh wolfberry, and a weight loss rate of only 0.93%. Pearson and cluster analyses further confirmed that the optimal freezing mode of
Lycium barbarum was NF
−90 ℃ with stems. The results indicated that when the freezing rate was below 1.58 ℃/min, the protective effect of wolfberry stems on fruit freezing characteristics was more pronounced, and the impact of heat transfer medium on quality was greater than that of freezing temperature. The freezing rate was the decisive factor for quality when
Lycium barbarum was frozen with stems. The factors affecting the freezing quality of
Lycium barbarum could be ranked as follows:
Lycium barbarum stems>freezing rate>heat transfer medium>freezing temperature. This study provides a theoretical basis and technical guidance for the freezing processing of
Lycium barbarum.