EFFECT OF CALCIUM HYDROXIDE AND CALCIUM L ACTATE ON HARDNESS AND TISSUE STRUCTURE OF BRINED SMALL TYPE UME FRUIT

To make clear the effect of calcium hydroxide and calcium lactate on h ardness and tissue structure of brined small type ume fruit (Prunus mu me Sieb. et Zucc), small type ume fruit were brined with a NaCl soluti on, a NaCl solution containing either calcium hydroxide or calcium lac tate. After that, controlled amounts of NaCl were added to each group once a day for 20 days until NaCl in the ume fruit reached 18% concent ration. Two weeks after the final addition of NaCl the hardness, calci um content and pectin content in each group were measured with a rheom eter, high performance liquid chromatography and the m-hydroxy-dipheny l method, respectively. In addition, tissue prepared from fresh fruit and the brined ume fruit were observed with a scanning electron micros cope. The results obtained were as follows: (1) The ume fruit brined w ith a normal NaCl solution softened in texture. Those ume showed a rem arkably smaller ratio of 0.05 N HCl soluble pectin (HSP) against total pectin than fresh fruit, and a significantly larger ratio of water so luble pectin (WSP). (2) The brined ume fruits, to which calcium compou nds were added, was'nt soft. Those ume fruits had a remarkably larger ratio of HSP and the 0.4% hexametaphosphate soluble pectin (HXSP) agai nst total pectin than the fruit brined with the normal solution, and a markedly smaller ratio of WSP. (3) The hardness of the brined fruit i ncreased with added amounts of calcium compounds. (4) The hardness of the brined ume fruit with calcium hydroxide was almost similar to that of the brined fruit with calcium lactate. (5) The brined fruit with c alcium hydroxide increased in 0.05 N NaOH soluble pectin (SSP) and dec reased in WSP relative to the amounts of calcium hydroxide added, but the ume fruit with calcium lactate increased in HSP and decreased in W SP. (6) In the observtion with a scanning electron microscope, the cel l wall of the brined ume fruit looked thinner than fresh ume fruit, an d the cell had changed to a flat shape a little. But the cell of brine d fruit with calcium compounds were almost similar to that of fresh fr uit. As a result of those experiments, it was concluded that the softe ning of the brined ume fruit is the destruction of the tissue structur e arising from the change of HSP into WSP, and the hardness of the bri ned fruit with calcium hydroxide or calcium lactate is kept up with a maintenance of the tissue structure occuring with an obstruction of ch ange of HSP into WSP, which is caused by cross-linkage between pectin and Ca ion.