Refrigerated cooked rice can retain its slow starch digestion property only with rice varieties having long amylose chains after microwave reheating

Microwave reheating is commonly used for refrigerated cooked rice, yet its effects on the digestibility of different rice varieties remain poorly understood. Ten rice varieties with different chain-length distributions were selected, and their digestibility was investigated after freshly steaming, retrogradation, and microwave reheating. The results revealed that microwave treatment preferentially disrupted B-type crystallites of retrograded amylopectin double helices, while preserving the V-type crystallites. Rice varieties with a higher proportion of amylopectin chains with DP 24–36 were susceptible to loss of short-range ordered structure upon reheating, leading to increased digestion rates. Conversely, varieties with higher amylose content, greater abundance of long-chain amylose exhibited greater resistance to microwave-induced structural damage. Notably, retrograded Low GI rice retained or formed additional enzyme-resistant structures after microwave heating. These findings demonstrate that the effect of microwave reheating on refrigerated rice is starch-structure-specific, and only certain rice varieties maintain slowly digestible starch property after reheating.