Effect of microwave heating and vacuum oven drying of potato strips on oil uptake during deep-fat frying

The properties of moisture and starch in potatoes affect the quality and oil absorption of final fried products. In this study, changes in moisture state, starch properties, and micromorphology of potato strips pretreated by microwave heating (MH) and vacuum oven drying (VOD) were investigated using low-field nuclear magnetic resonance, magnetic resonance imaging (MRI), differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy (SEM) analyses. The influence of changes in these properties on the oil content and distribution of fried potato strips was analyzed. Results showed that the decreased moisture content and changed moisture state in the pretreated samples had a positive effect on reducing the oil content. The pregelatinized starch facilitated the formation of V-type starch–lipid complexes, which formed a protective layer to prevent oil absorption. Analysis of MRI and confocal laser scanning microscopy images confirmed this finding. SEM observation showed microstructural changes might have an effect on oil absorption and its results exhibited crusts of the MH-pretreated samples thickened after frying, and the internal pores and structures of the VOD-pretreated samples became small and dense, respectively; both changes negatively affected oil absorption. Results could help understand the oil absorption behavior of starch-based food during frying and provide a basis for improving the quality and controlling the final oil content of the product.