Determination of Water Contents in Soy Sauce, Dehydrated Soy Sauce and Wines by Means of Karl-Fischer Titration

Abstract

A precise method of analysis has not been established yet, as for the determination of water contents in some fermented products such as soy sauce and wine. The Karl-Fischer automatic moisture titration method was applied to the determination of water in these products. The apparatus employed in this paper, consisted of so-called closed system in which the atomosphere was kept dry with silica-gel, and was equipped with an automatic burette and also an end-point buzzer indicator. After placing approximately 20ml of formamide-methanol mixture reagent in the titration vessel, the Karl-Fischer reagent was titrated to the end-point. Then accurate quantity of soy sauce (25-50μl), wine (25μl), or dehydrated soy sauce (300-500mg) was put into the vessel and the titration was again brought up to the end-point. As the results of these experiments, it is concluded that the recoveries of water from soy sauce and also from wines were almost satisfactory. According to the present method, the water content in soy sauce and wines indicated 71-82%, w/v and 77-89%, w/v, respectively. On the other hand, the water content of dehydrated soy sauce tested, was in the range of 1.6-2.5%, w/w. In the case of the last products, however, the precise water determination seemed to be difficult for the lump or coasely granulated sample.