Investigation On Water Status And Distribution In Broccoli And The Effects Of Drying On Water Using NMR Methods

Many quality attributes of food products are influenced by the water status and the microstructure,such as nutrition and security.Due to high water content,fresh fruits and vegetables are easy to degrade,such as tissue softening,discoloration,nutrient loss and so on.So,it is important to investigate water status inside fresh fruits and vegetables and the effects of processes on water status.Nuclear magnetic resonance(NMR)and magnetic resonance imaging(MRI)methods are applied to non-destructively monitor the water status and structure of food.The aim of this study is to investigate the water status and distribution inside broccoli tissues and the effects of hot-air drying on the water status by using NMR and MRI methods.Transverse relaxation times(T2)provide the information of water status and water distribution.Results show that three water fractions with different T2 relaxation times were detected inside broccoli,named as bounding water,semi-combined water and free water,which corresponded to different cell compartments including cell wall,cytoplasm,vacuole,cellular space,xylem and phloem.Proton weighted imaging could monitor the spatial distribution of water.Image analysis indicates that the water distribution inside broccoli was heterogeneous and the water content reduced from the stalk to the buds.During hot-air drying experiments,different drying kinetics were of observed in the florets and stalks,which were related to their different structures.The results of this study show that the NMR methods can precisely provide the quantitative information of water status inside broccoli,and can be used to monitor changes of water status and distribution non-destructively during drying and other pretreatment process.