(中国农业科学院 农产品加工研究所/农业农村部农产品加工综合性重点实验室, 北京 100193)
(Institute of Food Science and Technology, Chinese Academy of Agricultural Science/Key Laboratory of Agro-Products Processing, Ministry of Agriculture and Rural Affairs, Beijing 100193, China)
Freeze drying can better retain nutritional and functional substances in blueberries such as anthocyanins and vitamins. However, it is difficult for internal water to diffuse outward through the dense waxy layer of the blueberry epidermis during the freeze drying process, which triggers structural collapse as well as a series of serious quality defects of products, including epidermis shrink, hollowness, and juice loss. These limited the application of the freeze drying technology in the field of blueberry drying. To improve the quality of freeze-dried blueberries, the influence of pretreatment with soaking in Na2CO3 solution (3,10, 30min), peeling (top, bottom, top and bottom), punching (12,14, 36 holes), and cutting epidermis (2,8, 16 incisions) on the drying characteristics, hygroscopicity, and sensory qualities such as texture, color and aroma of freeze-dried blueberry were investigated. The results indicated that compared with non-pretreated freeze-dried blueberries, both punching and cutting epidermis treatment could effectively avoid the collapse and shrink of freeze-dried blueberries, which obtained better quality than the treatment of soaking in Na2CO3 solution and peeling. Among them, the freeze-dried blueberries with punching (36 holes) and cutting epidermis (16 incisions) remained their intact appearance and microstructure with reduced drying time by 6 h and 4 h, respectively. Meanwhile, the brittleness was increased by 31.55% and 4.06%, respectively. There was no obvious shrink and collapse of epidermis and interior structure in these two processed blueberries, and the color and aroma were closer to the fresh blueberries than that of other treatments. This study aimed to provide a guiding reference for the preparation of high-quality whole blueberry fruits by freeze drying.