Cereal Chem. 79(5):631-633Mung bean, potato, and rice starch solutions (5%, w/w) were sonicated for up to 5 min after heating, and their physicochemical properties were investigated. Alkaline viscosities, including the apparent and inherent viscosities of starches, decreased. The residues of the swollen starch granules after pasting and centrifugation were also reduced prominently by sonication. Average degree of polymerization did not change with sonication. The starch paste became more transparent, and the hot paste viscosity measured at 70°C decreased remarkably. Results indicate that changes in the physicochemical properties of starch were induced by the disruption of swollen granules rather than the breakage of glucosidic linkages with sonication. 2 Corresponding

Cereal Chem. 77(5):567-571Mung bean starch gels (8% solids) were prepared after annealing at 45-60°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 ≈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, α-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°C annealed starches. Overall paste viscosities of the starches annealed at >55°C were lower than that of the control starch. Final viscosities in RVA were correlated with the yield force of gel (r = 0.99).Starch granules heated in excess water undergo an order-disorder phase transition called gelatinization (Hoover 1995). This phase transition is associated with the diffusion of water into the granule, hydration and swelling of the starch granules, loss of crystallinity, and amylose leaching. As a consequence, swollen granules become embedded in a continuous matrix of entangled amylose molecules. On cooling, the complex composite sets as a viscoelastic gel when starch concentration is >6%. This change is called retrogradation. In this stage, amylose gel network develops relatively fast and remains unchanged during storage. Meanwhile gelation of amylopectin within the swollen granules is slow and progresses slowly during storage, resulting in increasing gel hardness (Biliaderis and Zawistowski 1990, Morris 1990, Biliaderis 1992. Hoover (1995) reviewed the factors affecting starch retrogradation such as starch concentration, temperature, sugar, lipids, salts, and chemical and physical modification.Annealing is a process in which starch granules are heated in excess amounts of water at a temperature slightly below gelatinization temperature for a relatively long time. Tester et al (1998) reported that annealing was restricted unless the moisture content exceeded 60% by weight of the mixture. Annealing decreases swelling power and solubility of starch (susceptibility to amylase (Wang et al 1997), and changes pasting curves (Jacobs et al 1995, Stute 1992.Mung bean starch, along with acorn and buckwheat starches, is widely used to make a gel food called mook in Korea. Mook is prepared by cooking at 8-10% solids followed by cooling the paste in a rectangular or circular plate with a depth of ≈10 cm. Since mook is served with chopsticks, it requires a certain g...