Effects of Punching and Cutting Epidermis Pretreatment on Freeze Drying Characteristics and Qualities of Blueberry(打孔和划痕预处理对蓝莓粒真空冷冻干燥特性及品质的影响)
摘要
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 Na<sub>2</sub>CO<sub>3</sub> 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 Na<sub>2</sub>CO<sub>3</sub> 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.(真空冷冻干燥能够较好地保留蓝莓中花色苷、维生素等营养功能物质,但蓝莓内部水分在真空冷冻干燥过程中难以透过表皮的致密蜡质层向外扩散,进而引发结构塌陷,导致产品存在表皮皱缩、空心、汁液流失等严重缺陷,限制了真空冷冻干燥技术在蓝莓干燥领域的应用。为改善真空冷冻干燥后的蓝莓品质,研究