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 & nbsp;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.

Automated summary

This study aimed to understand the gelation mechanisms of starches with different molecular structures. The results showed that granular starches exhibited strong gelling ability due to the presence of swollen starch granules and amylose molecules acting as glue. In contrast, non-granular starch HA7, mainly composed of linear amylose, could form a firm and rigid gel through the re association and alignment of amylose chains. This study provided fundamental knowledge for using starch as a gelling agent to achieve desirable textural attributes of foods and other industrial products.