The mechanism of reducing the oil content of fried instant noodles by adding sugar alcohol: microstructure, surface...

Sugar alcohols are characterized by anti-caries properties, low glycemic response, low calorie value and non-participation in the Maillard reaction. Our preliminary experimental demonstrated that erythritol (ET), xylitol (XT), and lactitol (LT) significantly reduce the oil content of fried instant noodles, though the mechanism was unclear. This study therefore aimed to elucidate how these sugar alcohols reduce oil content by examining the alterations in oil distribution, pore characteristics, and molecular structures of starch and protein from macro-, micro-, and molecular levels. Low-field nuclear magnetic resonance and magnetic resonance imaging confirmed that sugar alcohols effectively lowered the fat content and reduced the macroscopic oil distribution within instant noodles. Sugar alcohols increased the contact angle between oil and the dough sheet, thereby decreasing oil wettability and spreading capacity. The incorporation of sugar alcohols also reduced the surface roughness of instant noodles, yielding a more compact internal structure with lower open porosity and total porosity. This relatively intact, less porous microstructure formed an effective physical barrier, inhibiting oil absorption and penetration, and consequently reducing the fat content of instant noodles. The Fourier transform infrared spectra of starch demonstrated that sugar alcohols significantly intensified the peak at 1653 cm^-1, indicating enhanced hydrogen bonding within the system. Furthermore, the addition of sugar alcohols promoted a more tightly packed molecular arrangement of starch during frying, which consequently reduced starch's capacity for oil absorption and limited the formation of starch-lipid complexes. Additionally, sugar alcohols enhanced the β-sheet content, suggesting an improved secondary structure of protein.