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.

Ternary composite gels consisting of carrageenan, hydroxypropyl distarch phosphate and egg white protein were characterized for gel properties and microstructural characteristics. Meanwhile, the interaction between different modified egg white powders (P10, PHG14 and PHG21) and polysaccharides was investigated, as well as their effects on the properties of composite gels. The results showed that compared with carrageenan and a binary composite gel consisting of carrageenan and modified starch, the ternary composite gel showed an increase in gel strength and water-holding capacity, a significant increase in elastic modulus (G’), a significant reduction in relaxation time T₂₃, a decrease in its relative peak area A₂₃, and a decrease in freezable water content. The infrared spectra of the polysaccharide-protein composite gel showed an increase in amplitude and a slight shift in peak position. X-ray diffractometry revealed that the diffraction peak intensity of the polysaccharide-protein composite gel was weakened, implying a reduction in the degree of crystallinity. Microstructural observation by scanning electron microscopy (SEM) revealed that the interaction between the polysaccharides and egg white proteins facilitated the formation of stable, dense and uniform gel networks. Compared with P10, addition of PHG14 or PHG21 to the carrageenan-modified starch composite gel resulted in more stable gel properties and microstructure.

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.