以‘美红'和‘富士'苹果为研究对象,利用热风和真空冷冻干燥对苹果片进行干制,探究不同干燥方法对‘美红'红肉苹果水分、质构和营养品质的影响。结果表明,热风和真空冷冻干燥过程均为降速干燥,且热风干燥速率快。从水分状态来看,干燥前期以自由水去除为主,‘美红'苹果片的水分束缚力弱于‘富士'苹果。热风干燥降低了‘美红'苹果片的亮度(L*值),而真空冷冻干燥增加了苹果片的亮度,且含水量高于40%时,总色差值(△E)显著增加(P＜0.05)。热风干燥后,‘美红'苹果片的干基总酚和总黄酮含量显著降低(P＜0.05),组织结构致密、硬度高、表面皱缩明显,而真空冷冻干燥后干基总酚和总黄酮变化不显著(P＞0.05),苹果片外观舒展,复水性显著优于热风干燥。综上,真空冷冻干燥适用于类黄酮含量高的红肉苹果片的干制加工。
In this study, the effect of hot air drying and vacuum freeze-drying on the drying characteristics and quality of ‘Meihong' and ‘Fuji' apple slices was investigated. Water status, texture characteristics, nutritional quality, and sensory evaluation of ‘Meihong' apple slices during drying were evaluated. Results showed that both the hot-air drying and vacuum freeze-drying were reduced-speed drying, and the drying rate of hot-air drying was faster. As to the water status, it could be seen that free water disappeared primarily in the early drying stage. The water binding ability of ‘Meihong' apple slices was weaker than that of ‘Fuji' apple. The brightness (L*) value of ‘Meihong' apple slices reduced after hot-air drying and increased after vacuum freeze-drying. When the moisture content was higher than 40%, the total color difference (△E) of apple slices significantly increased (P＜0.05). The content of dry-based total phenols and flavonoids in ‘Meihong' apple slices significantly decreased after hot-air drying(P＜0.05), while vacuum freeze-drying had no significant changes (P＞0.05). Hot-air drying led to compact structure, higher hardness, and obvious surface shrinkage. Vacuum freeze-drying slices showed a uniform appearance, porous structure, and higher rehydration. In conclusion, vacuum freeze-drying is suitable for the drying of high-flavonoid red-fleshed apple slices.
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