Influence of annealing on gel properties of mung bean starch

Mung bean starch gels (8% solids) were prepared after annealing at 45-60 degrees C for 1-24 hr, and the relationship between the physical properties of gels and the swelling power (SP) and solubility of starch was investigated. The SP and solubility decreased with increasing annealing temperature and time, mostly in the first 6 hr. The solubles were mainly composed of amylose. Gel hardness at a 5 mm depth of annealed starch was larger than that of native starch, and gel hardness increased as SP decreased (r = -0.94). Upon continued compression, the yield force of gel showed a different function. Above SP of approximate to 12.5, the yield force of annealed starch gels decreased, but at <12.5 the yield force increased with increasing SP. Both granular rigidity and extent of packing appeared to determine the yield force. Although annealing increased the gel hardness, alpha-amylase digestibility of gel was not affected. Pasting analysis in the Rapid Visco Analyser (RVA) revealed that annealing increased pasting temperature. A pasting peak was found only in 45 and 50 degrees C annealed starches. Overall paste viscosities of the starches annealed at >55 degrees C were lower than that of the control starch. Final viscosities in RVA were correlated with the yield force of gel (r = 0.99).