Inhibitory Effects of Different Pretreatment Methods on Oil Adsorption Characteristics of Formulated French Fries

This study aimed to explore the effects of hot air-drying pretreatment (60, 90 and 120 min) and baking pretreatment (24, 27 and 30 min) on reducing oil adsorption by formulated French fries and the underlying effects and to determine the optimal pretreatment method. The results showed that compared with the untreated samples, the oil contents after hot air drying and roasting pretreatment were decreased by 5.37%–15.75% and 16.30%–16.51%, respectively (P < 0.05). We found that the moisture contents of the pretreated samples and the oil contents after frying were reduced compared with those of the control group, and showed a linear positive correlation with each other. Low-field nuclear magnetic resonance (LF-NMR) analysis showed that the content of free water was greatly reduced after pretreatment, and the free water was partially transformed into bound water and semi-bound water. Magnetic resonance imaging (MRI) analysis found that the distribution of oil on the surface and inside of the samples after baking pretreatment was less than that after hot air-drying pretreatment. Confocal laser scanning microscope (CLSM) observation showed that a small amount of oil was distributed in the gap between starch cells after baking pretreatment, and the amount of starch-lipid complexes produced in baked samples was significantly less than those in hot air-dried and untreated samples. Scanning electron microscope (SEM) showed that compared with hot air-drying pretreatment, the surface roughness of samples and the number of cracks and pores on the surface were reduced after baking pretreatment. Therefore, pretreatment could inhibit oil adsorption by formulated French fries by changing the initial moisture content, moisture state, surface microstructure and starch characteristics. The effect of baking pretreatment was more pronounced than that of hot air-drying pretreatment. Taking the sensory evaluation results into consideration, 27-min baking pretreatment was selected as the optimal pretreatment method to prepare low-oil quality potato snacks.