Influence of Ageing Time of Starch Gels Prior to Freeze–Thaw Cycles on the Properties of Pinhão Starch Hydrogel (Araucaria angustifolia)

Abstract

The ageing time of a starch gel can influence the structure of hydrogels as the reorganization of amylose–amylopectin can progressively change over time. This study evaluates the influence of ageing time prior to freeze–thaw cycles on pore formation, water absorption, and mechanical resistance of pinhão starch hydrogels. The hydrogels are prepared by starch gelatinization followed by ageing for 0, 3, 6, and 9 h before the freeze–thaw cycles. Immediately frozen gel (0 h) produces a hydrogel with a honeycomb structure with regular pores size while ageing (3, 6, and 9 h) created a spongy structure. The hydrogels aged for 0 and 3 h fragment after the compression test, while those aged for 6 and 9 h maintain firm and intact structures. The 0 h aged hydrogels have the lowest water absorption (520%) and the highest mechanical resistance (1407.50 g). The hydrogels aged for 3, 6, and 9 h show water absorption between 670% and 700% and mechanical resistance of 635.34–800.79 g. In conclusion, a minimum of 6 h gel ageing before freeze–thaw cycles is necessary to achieve a firm structure and ensure the required functional properties for practical application with pinhão starch.