Effect of partial substitution of refined wheat flour with purple sweet potato flour on the properties and quality of noodles

Noodles are conventionally made with wheat or rice flour, but in order to improve their nutritional content, other crops have been successfully used. Purple sweet potatoes are an important food and phytochemical source world-wide and have the potential for partially substituting wheat or rice in making noodles. The substitution of part of the refined wheat flour in noodles with 5, 10, 15 or 20% of purple sweet potato flour (PSPF) in noodles was, therefore, tested which resulted in them having a darker appearance and an increase its green color. However, these noodles required shorter cooking times, but gave lower cooking yields, had higher cooking loss and a weaker structure in terms of their texture. These noodles also had a slightly increased pH and water activity than noodles made from 100% refined wheat flour as well as increased levels of fat, ash, carbohydrate, total anthocyanin content, total phenolic content and antioxidant capacity but reduced protein levels and moisture content. From the sensory evaluation panel, the addition of purple sweet potato flour (PSPF) to the flour had no significant effects on the color, taste and overall acceptability of the cooked noodles, although there was a significant indication (p>0.05) that the odor increased, elasticity, softness and smoothness all decreased with increasing substation of the refined wheat flour with purple sweet potato flour (PSPF). The sensory evaluation panel detected no significant differences (p>0.05) in the appearance of the noodles whatever the level of substation. In terms of microbial contamination, these noodles complied with Thai standards for microbiological regulations. The noodles preserved acceptable quality for at least 9 days of storage in refrigerator at 4±2oC. Overall, it was concluded that enhancing the noodles by substituting 20% of the refined wheat flour with purple sweet potato flour (PSPF) would be acceptable to consumers, but would also improve their nutritional content.