Effect of Freezing Combined with Coating Treatment on Reducing the Oil Content of Reconstituted French Fries

The effects of two pretreatment methods, freezing and coating, on the oil content of low-temperature deep-fried reconstituted French fries were investigated. The combination of temperature and time that provided the best freezing effect was –24 ℃ and 3 h. Compared with two other coating agents, sodium carboxymethyl cellulose (CMC) and soybean protein isolate (SPI), 0.03 g/mL sodium alginate (SA) was found to be the most effective in reducing the oil content. On this basis, the combined effect of freezing and coating pretreatments on reducing the oil content of reconstituted French fries was explored and the optimal pretreatment combination was determined. The results showed that freezing pretreatment reduced the moisture content of the samples and changed the moisture distribution, and there was a positive correlation between the moisture content before deep frying and the oil content after deep frying. Freezing, coating and their combination decreased the oil content of reconstituted French fries by 35.02%, 10.49%, and 44.83%, respectively (P < 0.05). Combined freezing-SA coating treatment resulted in the lowest surface internal oil contents of reconstituted French fries. Confocal laser scanning microscopy (CLSM) showed that the combined treatment resulted in the smallest area of complex formation. Scanning electron microscopy (SEM) showed that the combined freezing-SA coating treatment resulted in the least number of cracks and pores on the surface of French fries with low surface roughness. Textural characterization showed that the coating treatment significantly increased the hardness and crispness of the samples. In conclusion, all pretreatments changed the moisture content, moisture distribution, surface microstructure and starch characteristics of reconstituted French fries, reduced the oil content and enhanced the crispiness, with the combined treatment being the most effective among them. Furthermore, sensory evaluation showed that the combination of freezing and SA coating was the best pretreatment method for low-temperature deep-fried reconstituted French fries.