Effect of Frying Process on Nutritional Property, Physicochemical Quality, and in vitro Digestibility of Commercial Instant Noodles

The effects of frying process on the nutritional property, physicochemical quality, and in vitro digestibility of instant noodle products are investigated in this study. Scanning electron microscope (SEM) and Fourier transform infrared spectrometer (FT-IR) were also used to explore the changes in the microstructure and protein transformation. Noodles, after the frying process, showed a lower proportion of carbohydrate, protein, fiber, and also total starch and digestible starch, but higher content of fat and resistant starch in the proximate analysis. The frying process was also considered to improve the texture, surface color, and sensory properties of instant noodle products, accompanied by better cooking quality, including shorter cooking time and lower cooking loss during the rehydration. The honeycomb-like, porous, and less uniformed structure, and also the higher levels of beta-sheets and beta-turns, and the lower proportion of alpha-helixes of protein structure from fried instant noodle was also observed. The in vitro digestibility of starch and protein were downregulated in the fried group (81.96% and 81.31, respectively, on average) compared with the non-fried group (97.58% and 88.78, respectively, on average). Thus, the frying process lowered the glycemic index and regulated protein secondary structure by inhibiting continuous digesting enzyme activity, generating starch-lipid complexes, and changing the levels of protein transformation. In conclusion, our findings will provide an innovative evaluation of the frying process on instant noodles and even other various starch-based prepared food products.

Automated summary

This study investigates the effects of the frying process on the nutritional properties, physicochemical quality, and in vitro digestibility of instant noodle products. The frying process leads to a decrease in carbohydrate, protein, fiber, total starch, and digestible starch, but an increase in fat and resistant starch. It also improves the texture, surface color, and sensory properties of instant noodle products, as well as the cooking quality. The fried instant noodles have a unique structure and protein transformation. The frying process also decreases the in vitro digestibility of starch and protein. Overall, the findings highlight the importance of the frying process in instant noodles and other starch-based prepared food products.