The in-vitro digestibility of instant noodles: Interplay of texture, microstructure and starch structure

Instant noodles are a worldwide food staple. However, the correlation between its production methods and nutritional characteristics remains unclear. This study aims to elucidate the effects of hydrothermal (steaming and boiling) and cooling techniques on instant noodles in-vitro digestibility. Texture of rehydrated noodles, microstructure observed by SEM and starch molecular structure measuring techniques were used to identify the underlying mechanisms. Our results demonstrate that boiling results in incomplete gelatinization of internal starch, leading to a microstructure with numerous pores and channels due to irregular starch distribution. This microstructure facilitates α-amylase diffusion and subsequent attachment to the substrate, yielding a higher starch digestion rate coefficient for boiled noodles (N_boiled) within the first 120 min (K1, 5.7 min^-1) compared to steamed noodles (N_steamed, K1, 4.4 min^-1). However, from 120 to 360 min, N_boiled exhibited a lower rate coefficient (K2, 4.5 min^-1) due to the retarding effect of incompletely melted starch structure and greater texture rigidity, contrasting with N_steamed (K2, 6.1 min^-1). Moreover, noodles subjected to boiling and subsequent cooling exhibited the lowest starch degradation by α-amylase throughout hydrolysis. This is attributed to their increased hardness, denser microstructure, and presence of ungelatinized or recrystallized starch. Therefore, the study concludes that cooking and cooling processes significantly influence noodle texture, microstructure, and starch structure, collectively impacting the nutritional value of instant noodles. Our findings provide valuable insights for the development of nutritionally enhanced instant noodles.