Study on the preservation of agricultural products by means of hydrophobic hydration

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The suppression of metabolism plays an important role in keeping agricultural products fresh. Metabolism is based on intracellular chemical reactions which are, for the most part, enzyme mediated. As the diffusion of substrate regulates the enzyme reaction rate, the decrease in the diffusion rate of substrate may lead to the suppression of metabolism. When the water in a cell becomes "structured", the viscosity of water increases and the diffusion rate of substrates desreases. Hence, a way for suppression of metabolism can be thought to make intracellular water structured. On this basis, the present study was designed to develop a preservation method that controls the state of intracellular water by means of the formation of structured water.When nonpolar gas dissolves in water, the number of hydrogen-bonded water molecules increases by creation of hydrophobic hydration and the water becomes structured. Among many nonpolar gases that create hydrophobic hydration, inert gases are most suitable since they are expected not to cause chemical changes in cells. Xenon was selected because of the greater degree of structured water formation with xenon compared to other inert gases. The increase of the number of hydrogen-bonded water molecules caused by the dissolution of xenon was confirmed by the NMR experiment. The proton chemical shift indicated the greater chemical shift for the xenon solution compared to the water without xenon.The method was applied to the preservation of broccoli and eggplant. The concentration and quantity of CO2 measured for the broccoli and eggplant during preservation under given pressure of xenon were distinctly smaller compared to those preserved in an air-tight condition at the same temperature. The results supported the validity of the proposed preservation method.