ABSTRACT
The importance of the nature of the amylopectin and the amylose-to-amylopectin ratio in the gelation of high-amylose maize starch was examined by preparing gels of model systems using amylose (AM) from a high-amylose maize starch mixed with an amylopectin (AP): either wx starch, acid-hydrolyzed wx starch (AH-wx), ae wx starch, or wx β-limit dextrin. Mixtures of 7.5% starch in 20% dimethyl sulfoxide (DMSO) were examined by differential scanning calorimetry and dynamic oscillatory rheometry. Mixtures of 1.88 or 3.75% AM with the remainder either wx or AH-wx developed a measurable elastic modulus (G′) within one day, more quickly than for the corresponding AP without AM. Gels of AM with either wx or AH-wx starch developed a higher retrogradation enthalpy (ΔH) than corresponding AP without AM when the ΔH values were normalized to the amylopectin content. The G′ and ΔH of all gels containing ae wx did not change after one day. During heating of the gels to 80°C, most of the G′ at 25°C was lost, indicating that the initial gel structure was not due to a thermally stable AM network. Gelation is proposed to be due to physical junction zones (PJZ) between AM molecules (AM-AM), between AM and amylopectin molecules (AM-AP), and between amylopectin molecules (AP-AP). For wx, AH-wx, or ae wx starch, the higher G′ and ΔH of the gels with 3.75% AM compared with the gels with 1.88% AM suggests that AM-AP PJZ are more important in gel formation when AM makes up half the starch. Gels from the mixture of 3.75% AM and 3.75% ae wx starch behaved most similarly to gels of 7.5% high-amylose maize starch. The development of a starch gel is affected by both the nature of the amylopectin as well as the amylose-to-amylopectin ratio of the gel.
