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The objective of the present study was to evaluate cellular compartment modifications of kiwifruit ( Actinidia deliciosa) outer pericarp tissue caused by osmotic treatment in a 61.5 % sucrose solution, through the quantification of transverse relaxation time ( T) and water self-diffusion coefficient ( D) obtained by low field nuclear magnetic resonance means. Raw material ripening stage was taken into account as an osmotic dehydration (OD) process variable by analyzing two different kiwifruit groups, low (LB) and high (HB) °Brix. Three T values were obtained of about 20, 310, and 1,250 ms, which could be ascribed to the proton populations, located in the cell walls, in the cytoplasm/extracellular space, and in the vacuoles, respectively. According to T intensity values, vacuole protons represented between 47 and 60 % of the total kiwifruit protons, for LB and HB kiwifruits, respectively. The leakage of water leading to vacuole shrinkage seemed to cause concentration of solutes, retained by the tonoplast, making the vacuole T value decrease along the OD. As expected, the D values of raw kiwifruits were lower than the value of the free pure water. The water mobility (and hence D), depending on the kiwifruit distinctive cellular structures and solutes, decreased even more during OD due to water loss and sugar gain phenomena. D represents an average value of the diffusion coefficient of the whole kiwifruit tissue protons. In order to obtain D values specific for each cellular compartment, a multiple component model fitting was also used. According to these results, the vacuole water self-diffusion coefficient ( D) was much higher than D. [ABSTRACT FROM AUTHOR]

This study investigated mass transfer and water state changes promoted by osmotic dehydration on two kiwifruit species, Actinidia deliciosa and Actinidia chinensis. Osmotic treatment was performed in a 61.5% w/ v sucrose solution at three different temperatures (25, 35 and 45 °C), with treatment time from 0 to 300 min. Treatment time positively influenced kiwifruit water loss and solid gain while temperature significantly affected only water loss. Peleg's model highlighted that the main response differences between the two species occurred during the initial phase of the osmotic treatment. Thermal properties and relaxation time measurements offered a complementary view concerning the effects of osmotic dehydration on kiwifruit. DSC parameters appeared to be sensitive to water and solid exchange between fruit and osmotic solution. LF-NMR proton T revealed the consequences of the water-solid exchange on the cell compartments, namely vacuole, cytoplasm plus extracellular space and cell wall. During the osmotic treatment, the initial freezing temperature and the freezable water content decrease was dependent on time and treatment temperature, showing a similar tendency for both the kiwifruit species. They evidenced the same treatment response also concerning the reduction of vacuole and the increase of cytoplasm plus extracellular space T values. [ABSTRACT FROM AUTHOR]