Gelation mechanisms of granular and non-granular starches with variations in molecular structures

Gelation is a critical functional property that determines the applications of starch. This study aimed to elucidate the gelation mechanisms of granular and non-granular starches varying in molecular structures. Five representative starches – including waxy maize (containing 1.9% amylose), normal maize (32.0% amylose), tapioca (29.1% amylose), pea (39.2% amylose), and high-amylose maize (HA7; 69.7% amylose) – were pasted in both physical forms at 95 °C with 8.0% concentration (w/w, dry basis) to examine the gelation behaviors. The gelation process of cooling (2 °C/min) and 2-h curing at 25 °C was monitored using dynamic rheological tests. The derived starch gels/pastes were further characterized using uniaxial compression test and scanning electron microscopy (SEM). The granular starches showed gelling ability in an order of pea > normal maize > HA7 > tapioca, waxy maize. For native, granular starches, the existence of swollen starch granules/remnants that were able to deform with each other to fill the whole volume of a mold was crucial for developing a strong, true gel; additionally, amylose molecules diffusing out from granules could act as a glue to further enhance the firmness of gel network, such as in pea starch gel. After the granular structure was destroyed, only non-granular HA7 – having linear amylose as the predominant component – could generate a firm and rigid gel, resulting from the re-association and alignment of amylose chains to establish stable junction zones. This study provided fundamental knowledge for using starch of various physical states as a gelling agent to achieve desirable textural attributes of foods and other industrial products.