复水是冷冻干燥食品的重要特性,为明确冷冻干燥豆腐复水后其水分分布的规律,采用低场核磁共振研究了不同超声功率(0、100、200、300、400,500 W)制浆对鲜、复水冷冻干燥豆腐水分分布及微观结构的影响。豆腐持水性测定结果表明:复水冷冻干燥豆腐的持水性显著低于鲜豆腐,这可能是由于冷冻干燥处理使复水豆腐的微观结构发生变化,孔洞的尺寸变大,进而降低对水分子的保留率。水分分布测定结果表明:适宜的超声处理可提供鲜、复水冷冻干燥豆腐更多可用于截流自由水组分的结构,缩短T21弛豫时间,增大M21峰面积百分数。扫描电子显微镜观测结果表明:超声制浆及冷冻干燥工艺均可显著影响两种豆腐的微观结构。
Rehydration is an important characteristic of freeze-dried foods, to clarify the rule of moisture distribution of rehydrated freeze-dried tofu, effects of ultrasound power (0, 100, 200, 300, 400, 500 W) on moisture distribution and microstructure of fresh tofu and rehydrated freeze-dried tofu were studied by low field nuclear magnetic resonance (NMR). The results showed that the water holding capacity of freeze-dried tofu was significantly lower than that of fresh tofu, which may be due to the changes in the size of the hole in the microstructure of rehydrated freeze-dried tofu, and therefore reduced the retention of water molecules. The results of water distribution showed that suitable ultrasound treatment could provide fresh tofu and rehydrated freeze-dried tofu more structures for intercepting free water components, decreased the T21 relaxation time and increased the M21 peak area percentage. The results of scanning electron microscope showed that ultrasound pulping and freeze drying process could significantly influence the microstructures of these two kinds of tofu.
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