组合浸渍和超低温冻融预处理对真空冷冻干燥蓝莓品质的影响

Effects of mixed immersion and ultra-low temperature freeze-thaw pretreatment on the quality of vacuum freeze-drying blueberry

为探究组合浸渍冻干保护剂(海藻糖-CaCl_(2))和超低温冻融预处理对蓝莓活性物质和品质的影响,该研究以直接冷冻干燥为对照组,以普通冻融(-20℃)、超低温快速冻融(-80℃)、超声波辅助冻干保护剂浸渍冻融(-20℃)、(-80℃)预处理后进行真空冷冻干燥为试验组,比较分析蓝莓活性物质(多酚氧化酶和过氧化物酶活性)、营养物质(维生素C、花青素、总酚、类黄酮)、质构特性(硬度、咀嚼性)等指标的变化情况,并在此基础上进行BoxBehnken三因素三水平试验设计。结果表明:单一的冻干保护剂浸渍处理或者超低温处理均不如两者组合效果理想,两者组合浸渍后-80℃冻融处理可以有效维持蓝莓硬度,提高蓝莓营养物质的保留度并减少真空冷冻干燥时间。冻融次数为2次,浸渍时间为3.7 h,单次冷冻时间为4.2 d时蓝莓综合指标最高,营养物质保留度最高。该研究阐述了冻干保护剂浸渍预处理与超低温冻融两者联合处理对真空冷冻干燥蓝莓品质提升的机理,探究了冻融次数、冷冻时间、浸渍时间对品质的影响,得出了真空冷冻干燥预处理的最佳参数,为蓝莓真空冷冻干燥技术的发展提供了新思路。

A series of experiments were carried out to explore the effects of combined immersion freeze-drying protectants(trehalose CaCl_(2))and ultra-low temperature freeze-thaw pretreatment on the active substances and quality of blueberries.Directly dried blueberries were taken as the control group.Three groups were selected as the ordinary freeze-thaw(-20℃),ultra-low temperature rapid freeze-thaw(-80℃),and ultrasound-assisted freeze-drying protectants immersion freeze-thaw(-20℃),and(-80℃).A systematic comparison was implemented to determine various indicators of blueberry,including the active substances(PPO and POD enzyme activity),nutrients(VC,anthocyanins,total phenols,and flavonoids),and texture characteristics(hardness and chewiness).The experimental results show that the higher quality of blueberries was protected in the combination of a single freeze-drying protectant immersion or ultra-low temperature treatment,compared with the single one.Especially,the hardness was effectively maintained for blueberries that soaked and frozen at-80℃,while the retention of nutrients was significantly improved with less duration in vacuum freeze-drying.Three-factor three-level Box Behnken design was adopted to clarify the effects of soaking time,freeze-thaw frequency and freezing time on the comprehensive indicators of blueberries.It was found that the soaking time was 3.7 h,and the single freezing time was 4.2 d when the number of freezethaw cycles was 2.The highest comprehensive indicators of blueberries were achieved in the retention of nutrients.Feature and sum normalizations were performed on the experimental data.All data was between(0,1)and the sum was 1.The lipid membrane interaction of calcium pectinate and trehalose was formed by the interaction between Ca^(2+) and the cell wall.There was a great reduction in the structural damage caused by freeze-thaw.At the same time,the finer ice crystals were formed in the ultra-low temperature environments.The quality of freeze-dried blueberries was significantly improved when combined with the freeze-dried protective agents.The freeze-drying protectant impregnation pretreatment and ultra-low temperature freeze-thaw were combined to improve the quality of vacuum freeze-drying blueberries.A systematic investigation was implemented to clarify the effects of immersion time,freeze-thaw frequency,and freezing time on the quality of dried products.The optimal parameters were then determined for the vacuum freeze-drying pretreatment.In summary,the combination of immersion freeze-drying protectant(trehalose CaCl_(2))and ultra-low temperature freeze-thaw pretreatment can be expected to improve the active substances and quality of blueberries.The pretreatment conditions and parameters were optimized to successfully improve the nutrient retention and quality of blueberries.The findings can provide useful and practical references for the processing of blueberry products.The application scope can be further expanded for vacuum freeze-drying in the field of food processing.