FIRD-HPD方式对蓝莓干燥特性及品质的影响

Effect of FIRD-HPD Method on Drying Characteristics and Quality of Blueberry

为探究蓝莓在FIRD-HPD干燥方式下,内部水分含量及迁移状况随贮藏时间的变化规律,采用低场核磁共振(LF-NMR)及其成像技术(MRI),采集不同水分转换点干燥过程的蓝莓弛豫特性以及质子密度图像信息,分析其规律变化,并研究干燥前、后蓝莓品质的变化。结果表明:在水分转换点为30%,40%,50%时,蓝莓到达干燥终点的时间分别为480,420min和360 min。蓝莓的T2反演谱有3个不同的弛豫峰:T21(0.01~10 ms)结合水、T22(10~100 ms)不易流动水和T23(100~1000 ms)自由水。自由水(T23)和不易流动水(T22)向弛豫时间短的方向迁移,在干燥后期,结合水成为蓝莓中主要水分状态,自由水完全消失。基于MRI技术得到不同干燥方式各干燥阶段的磁共振成像,质子信号随干燥进程逐渐减小。LF-NMR和MRI技术可很好地监测干燥过程中动态水分分布和迁移变化。另外,在40%水分转换点联合远红外热泵干燥处理下,蓝莓果干色泽、营养品质等指标均优于30%和50%的水分转换点联合远红外热泵干燥方式。综合考量后,联合红外干燥水分转换点设置为40%是加工蓝莓果干的最优选择。

In order to investigate the changes of internal water content and migration of blueberries with storage time under FIRD-HPD drying method,Low Field Nuclear Magnetic Resonance(LNMR)was used.LF-NMR and its Magnetic Resonance Imaging(MRI)technique were used to collect the relaxation characteristics and proton density image information of blueberry during drying at different water transition points,analyze the changes of their regularity,and further study the changes of blueberry quality before and after drying.The results showed that when the water transfer point was 30%,40% and 50%,the drying time of blueberry was 480 min,420 min and 360 min,respectively.The T2 inversion spectrum of blueberry has three distinct relaxation peaks:T21(0.01-10 ms)bound water,T22(10-100 ms)immobile water,and T23(100-1000 ms)free water.Free water(T23)and non-mobile water(T22)migrated to the direction of short relaxation time.In the late drying period,bound water became the main water state in blueberry,and free water disappeared completely.Based on MRI technology,magnetic resonance imaging of different drying methods at each drying stage was obtained,and the proton signal gradually decreased with the drying process.LF-NMR and MRI techniques can be used to monitor dynamic water distribution and migration during drying.In addition,the dry color and nutritional quality of blueberries under 40% moisture transfer point combined with far-infrared heat pump drying were superior to 30% and 50% moisture transfer point combined with far-infrared heat pump drying.Taking into consideration,the combination of infrared dry moisture conversion point set at 40% is the best choice for processing dried blueberries.