Impact of frying conditions on hierarchical structures and oil absorption of normal maize starch

Knowledge about oil absorption during frying is crucial for the design and production of healthier reduced-fat food products. For this reason, we systematically investigated the structural changes and oil absorption of normal maize starch (NMS) during simulated frying conditions. In particular, the impact of initial moisture content, frying temperature, and frying time were examined. The hierarchical structures of the fried samples were firstly characterized using scanning electron microscope (SEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR), and size exclusion chromatography. Furthermore, the impact of frying conditions on oil absorption by NMS was investigated using LF-NMR and ATR-FTIR based methods. During frying, the granular morphology of the starch granules was lost, their internal crystalline structures were disrupted, their double helices were broken down, and starch molecules were degraded. These changes were related to the absorption of oil by the starch granules during frying. The initial moisture content of the starch samples had the most pronounced influence on the amount of oil absorbed during frying. The oil content first increased and then decreased with increasing moisture content, being 0.2396, 0.6602, 0.3614, and 0.2531 g/g starch for 20, 40, 60 and 80% moisture content, respectively. The fraction of oil present at the exterior of the samples after frying increased with increasing moisture content, frying temperature, and frying time. The variation in oil absorption were attributed to changes in the hierarchical structures of the fried samples, including granule morphology, crystalline property, double helices, and molecular features.