Resistant starch and soy protein isolate in instant noodles obtained by conventional and vacuum frying

Health concerns with the consumption of high-fat products and with respect to the intake of fibre are important for consumers. Vacuum frying process is an alternative frying process that increases the quality of foods. The objective was to develop instant noodles aiming to reduce carbohydrate and fat content by adding soy protein isolate (SPI) and resistant starch (RS3), using conventional and vacuum frying processes. A 2² central composite rotational design was used for each type of process, and the formulations were optimized using the Response Surface Methodology. The noodles were characterized with respect to fat absorption, cooking time, final resistant starch content and firmness. The noodles produced at the optimized point were also characterized for their isoflavone content, amino acid profile and by scanning electronic microscopy (SEM). The response surfaces showed that the addition of SPI and RS3 to the formulation resulted in reduced fat absorption and texture. Comparing both frying processes it was found that noodles obtained by vacuum frying absorbed 3% less fat and were less firm than those produced by conventional frying process. The SEM analysis showed that the noodles obtained by conventional frying had a more porous structure, which allowed an easier fat penetration, whereas those produced by vacuum frying showed a more closed structure with fat impregnated on the surface. Regardless of the process used, it was possible to obtain noodles with improved nutritional value, since they showed high fibre (8%) and protein (approximately 11%) contents, considerable isoflavone content (8.20 mg/100 g) and a complete amino acid profile, due to a significant increase in nearly all the amino acids, especially lysine.