Transglutaminase and protease: How starch granule-associated protein modification affects starch retrogradation

This study investigated the effects of transglutaminase (TG) and protease on starch granule-associated proteins and their impact on starch properties, especially retrogradation. TG incorporated storage protein onto the starch surface, while protease removed starch-granule associated proteins from it. Neither treatment altered the basic structural characteristics of starch such as its crystallinity or thermal properties, but could significantly affect swelling power, amylose leaching, and retrogradation. TG-treated wheat starch (WST) showed reduced swelling power (11.50) and amylose leaching (28.92 mg/g) compared with the control wheat starch (WSC) at 11.95 and 30.53 mg/g, respectively, suggesting a more stable structure. Conversely, protease-treated starch (WSP) exhibited increased swelling power at 12.47 and amylose leaching at 33.17 mg/g, suggesting a disintegration of starch granules. Both WSC and WST showed the same degree of retrogradation at the equilibrium state (a) a ) at 0.06, whereas WSP, with a higher degree at 0.08, promoted retrogradation. The rate constant (k) k) for WST was lower (1.41 d- 1 ) than that for WSC (2.37 d-- 1 ), indicating that TG treatment effectively inhibited retrogradation. These findings illustrated the distinct mechanisms through which TG and protease modify starch properties by acting on starch granule-associated proteins. This also highlighted the potential of TG and protease to control starch modifications for specific applications.