Gelation of starch paste cooked with crude extract of labiate herb (Mesona procumbens Hemsl.)

Crude extract of Mesona procumbens Hemsl. (CEM), dark brown liquid was extracted with a weak alkaline from dried labiate herb grown in Taiwan. When tapioca starch was cooked rapidly with dilute CEM solution, sticky cold paste formed hard gel like agar. The gel is one of the popular desserts in Taiwan. Rheological behaviors of the gel were investigated. The cooking viscosity by Rapid Visco-Analyzer and the dynamic modulus of cold paste body were increased as the concentration of CEM. The optimum concentration of CEM was 2% for tan δ, but of starch was saturated at 5% for G'. The similar behaviors of gel were recognized as for potato and waxy corn starch. However, it was no effect on the crude extract of Japanese perilla. Therefore, the gelling effect to starch paste may be the characteristic of Mesona herb. When the same process was applied to the paste that was completely dispersed in an autoclave, it did not form a gel. It appears that the gelation needs to existence of swollen starch granules, though it was glutinous starch of amylose free. Higher modulus of the gel was obtained at pH 7.0 and by dialysis of CEM.