Effects of Maturity of Ume Fruit and Amounts of Calcium Hydroxide in Brine on Shrinking of Hardened Brined Ume Fruit

Abstract

It is generally accepted that brined ume fruit treated with Ca(OH)₂ becomes hard in texture, though in some cases wrinkles appear on the peel of the brined fruit. The hardened brined ume fruit having wrinkles is known as shrunk fruit. Since the reason for this phenomenon hasn't been clarified, we thought that it was very important to research the mechanism of the shrinking of the hardened brined ume fruit. In this paper we report the relationships between the shrinking, maturity of fresh ume fruit, and the amount of Ca(OH)₂ added as a hardening agent, and speculate the mechanism of the shrinking. The results obtained were as follows: (1) Scanning electron microscopic observation showed that shrinkage of the fruit was a result of shrinkage of cells. (2) The shrunk fruit occurred when ume fruit used as materials was unripe, and the additional amount of Ca(OH)₂ was in small quantity. (3) The NaCl failed to permeate the ume fruit in sufficient amounts, and the acid flow from the fruit was greatly restricted. (4) The peel of the shrunk ume fruit contained markedly larger amounts of Ca than the flesh, whereas that of the hardened brined fruit contained the same amounts of Ca in both peel and flesh. (5) The flesh of the shrunk fruit contained a high ratio of water soluble pectin (WSP), but the hardened brined ume fruit contained very little WSP. As a result, it was found that the shrinking of the hardened brined ume fruit occurred when unripe ume fruit was used as a material and the added Ca(OH)₂ was in small amounts. It was presumed that the shrinking might occur by the change of permeability of peel resulting from the difference in tissue structure of the peel and flesh.