不同冻干工艺对冻干米线复水品质的影响

近年来，干制方便米线作为一种方便食品发展迅速，但是干制方便米线存在复水时间长、易糊汤、易断条、口感不理想、质构特性较差等问题。为了改善干制方便米线的这些特性，本研究采用?10、?20和?40 ℃ 三种冻结温度对米线进行真空冷冻干燥，分别得到三种冻干米线FDRN10、FDRN20、FDRN40样品，通过分析冻干米线在不同水温下的复水速度、微观结构、淀粉回生程度和质构特性的变化，探讨了冻结温度对冻干米线复水品质的影响。结果表明，在相同水温下经相同浸泡时间复水处理后，FDRN10含水量最高，表明其复水速度最快。外表面和横断面微观结构观察发现，三种冻干米线样品中FDRN10结构最为疏松，孔隙最大，为72.58 μm，是孔隙最小的FDRN40的4倍，结构吸水性最好。进一步的DSC检测发现FDRN10焓值最高，为92.98 J/g，焓值最低的FDRN40为12.39 J/g，表明FDRN10在三种冻干米线样品中回生程度最高，淀粉吸水溶胀最慢。同时硬度分析结果表明，在相同浸泡时间下FDRN10硬度值随水温的升高而降低，采用70 ℃热水复水8 min，FDRN10质构特性最接近鲜湿米线。以上结果表明，冻结温度和复水温度对冻干米线品质形成起到关键作用，本研究结果可为方便米线工艺改进提供理论依据。

Effects of Different Vacuum Freeze-drying Processes on Rehydration and Quality Characteristics of Freeze-dried Rice Noodles

Dried instant rice noodles are a convenience food, and they have shown rapid development in recent years. However, there are many disadvantages of dried instant rice noodles, such as long rehydration time, high turbidity of soup, high break rate, poor taste, and disappointing textural properties. In this study, to overcome these disadvantages, freeze-dried rice noodles were prepared at freezing temperatures of ?10, ?20, and ?40 ℃ by the vacuum freeze-drying process, which were called FDRN10, FDRN20, and FDRN40, respectively. The factors that affected the rehydration quality of freeze-dried rice noodles were investigated by analyzing the rehydration speed, microstructure, starch retrogradation, and texture characteristics at different water temperatures. The results showed that FDRN10 had the highest water content of the three freeze-dried rice noodles for the same water temperature and rehydration time. This indicated that the rehydration speed of FDRN10 was the fastest. The microstructures of the external surface and cross section were observed. FDRN10 had the loosest structure and largest aperture. The diameter of the aperture of FDRN10 was 72.58 μm, which was four times larger than that of FDRN40. This microstructure led to FDRN10 showing good water absorption. Differential scanning calorimetry showed that the enthalpy of FDRN10 was 92.98 J/g. The enthalpy of FDRN40 was the lowest (12.39 J/g). Thus, FDRN10 had the highest level of starch retrogradation among the three freeze-dried rice noodle samples, and the lowest level of starch water-absorbing swelling. Hardness analysis showed that the hardness value of FDRN10 decreased with increasing water temperature for the same rehydration time. The texture characteristics of FDRN10 were the closest to those of fresh rice noodles after rehydrating with water at 70 ℃ for 8 min. The above results indicate that the freezing temperature and rehydration temperature play important roles in the quality of freeze-dried rice noodles. This study provides an innovative process for improvement of instant-rice-noodle production.