温州ミカン品質判定の簡易化に関する研究 (第1報)

Abstract

A research work was conducted to find out the ability of pH meter value applying simplified physical method in stead of a chemical method applying the titrated acid contents in Satsuma mandarin fruit.Then nitrogen, phosphate, potassium and combined acid contents in fruit juice were measured to research the causes of their dispersions as well as a relation of pH value and titrated acid contents, and an analysis of these relations was tried.In addition to that, in order to know if sense factor to acidity is influenced by pH or by free acid contents, citric acid and potassium citrate were mixed and the organoleptic test was carried out. And the relation of acidity between pH and free acid contents was investigated.The results were as follows:1. In case of applying the regression straight line and the second regression curved line to estimate free acid contents from pH value, an error of about ±0.2-0.3% acid contents was measured. Therefore it is difficult to estimate exactly the relation.2. A high positive correlation coefficient in the regression line was recognized in the relation between pH value and combined acid contents/free acid contents.In any area or strain of satsuma mandarin, the slope and the constant articles agreed almost respectively.3. The residual free acid % in the relation of pH and free acid contents was larger in order of phosphate, nitrogen, potassium, combined acid and particularly when the combined acid, potassium contents were increased, the positive residual was caused, and when they were decreased, the negative residual was given rise.4. A high positive correlation was obtained between the combined acid contents and the potassium contents. Particularly in sweet summer orange the correlation coefficient was 0.922.5. A low negative correlation was obtained between the free acid and nitrogen contents. The free acid contents could only explain as much as about 23% (at the coefficient of determination R2=0.233) in N, P, K contents in fruit juice.6. Particulary 0.64, a high positive correlation coefficient value was obtained between pH and nitrogen contents.The determination coefficient of 0.51 for pH value was obtained by nitrogen, phosphate and potassium contents, therefore pH value could explain about a half by the nitrogen, phosphate, potassium contents.7. At the same citric acid content, when citric potassium was added more, the acidity was softened a little.At the same pH value, high citric acid contents strengthened acidity naturally.So far as this experiment was conducted, even if pH value was changed by additional citric acid potassium, the influence of the free acid contents on acidity was greater than that of pH value.