Studies on the Syneresis of Konjac Mannan Gel

Abstract

The analysis of factors affecting the syneresis of konjac mannan (KM) gel was carried out, and an empirical equation was obtained for predicting the degree of syneresis during storage. SEIKO (konjac flour containing ca. 90% of KM) was used as a raw material. The syneresis of KM gel proceeded with the elapse of storage period until the equilibrium was established after 20-30 days. The degree of syneresis, which was defined as the percentage of weight loss of KM gel after 30-day storage, decreased almost linearly with the increase in the concentration of KM and in the pH value of the gelling mixture. With the rise in gelation temperature and the depression in storage temperature, the degree of syneresis fell in a similar manner. The commercial grade of SEIKO (evaluated by the rheological properties of KM sol), partial substitution of KM with another polysaccharide, and the swelling time of SEIKO had little or no influence on syneresis. On the basis of these findings, an equation to estimate the degree of syneresis at equilibrium was given as follows:
Y=-3.0C-0.22T-4.9P+0.17t+89.5
where Y is the degree of syneresis (%), C the concentration of SEIKO (%), T the gelation temperature (°C), P the pH value of gelling mixture, and t the storage temperature (°C). It was confirmed by appling this equation to KONNYAKU (a commercial product) that the equation is available for the prediction of the degree of syneresis of KM gel.