Effect of FIRD-HPD Method on Drying Characteristics and Quality of Blueberry
In order to investigate the changes of internal water content and migration of blueberries with storage time un-der 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 informa-tion 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 wa-ter,and T23(100-1 000 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 disap-peared 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 com-bination of infrared dry moisture conversion point set at 40％is the best choice for processing dried blueberries.
blueberryfar-infrared combined heat pump dryinglow field nuclear magnetic resonancewater distributionquality
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