Production and Characterization of Potato Flour and Its Application in Noodles Processing

Abstract

Potato (Solanum tuberosum L.) is an excellent source of carbohydrates and dietary fibre whose nutritional characteristics are essential in human consumption. However, freshly harvested potatoes are perishable and undergo postharvest loss partly due to limited availability of cold storage facilities. Drying is a common practice for preserving perishable food crops. Potato tubers can be dried and processed into flour using conventional or innovative drying technologies. The flour has a long shelf-life stability due to its low moisture content, and it maintains the nutritional and flavor quality of fresh potatoes. This study aimed to demonstrate the potential use of potato flour produced using different processing in noodle processing, while highlighting its unique nutritional and functional properties. The first part of this study investigated the effects of pre-treatments: low-temperature blanching (LTB) at 60°C for 30 minutes, high-temperature blanching, (HTB) at 95°C for 1 minute, boiling, and drying methods: oven drying (OD) at 50°C for 48 hours and freeze-drying (FD) on the physicochemical, functional, rheological, and morphological properties of potato flour. The flour was derived from three potato varieties namely, Shangi, Unica, and Dutch Robjin obtained from a farmer in Nyandarua county. The percentage flour yield, physical properties, microstructural characteristics, nutritional quality and functional (swelling power, solubility index and pasting) properties were determined. Potato flours that demonstrated good pasting properties were used to substitute wheat flour at 10%, 30% and 50% levels to make composite flours for instant noodles production. Particle size and pasting properties of composite flour, dough mixing behaviour and microstructure of the dough were also investigated. The substitution effects on colour, cooking, textural, and sensory properties noodles were evaluated. The results showed that Unica recorded the least peeling loss (8%), while the Dutch Robjin variety had the highest (25%). The pre-treatments and drying methods significantly affected colour parameters (p < 0.05). Freeze drying produced lighter potato flour (L* = 92.86) compared to the other methods. Boiling_OD and HTB_OD recorded a low angle of repose and compressibility index, indicating better flow characteristics. The smallest particle size (56.5 µm) was recorded for the freeze-drying treatment, while Boiling_OD had the largest particle size (307.5 µm). Microstructural results indicate that Boiling_OD and HTB_OD, resulted in damaged starch granules, while freeze-drying and LTB_OD maintained the native starch granule. The results indicated that freeze-dried flour exhibited higher protein content, sucrose, and magnesium content in all different varieties. In comparison, Boiling_OD flour showed the lowest protein, sucrose, and magnesium content in different varieties. The swelling power and solubility index significantly increased as the temperature increased from 50 to 90°C. Particle size and the solubility index of potato flour showed a strong positive correlation. All the potato flour types demonstrated a decrease in apparent viscosity with increasing shear rate, with freeze-dried flour having the highest apparent viscosity. Freeze-dried flour showed the highest peak viscosity (7098.33 cP) and breakdown viscosity (2672.00 cP). The highest final viscosity (7989.00 cP) was recorded in HTB_OD potato flour. Substituting wheat flour with freeze-dried flour significantly decreased the mean particle size of the blended flour, while LTB_OD flour increased the mean particle size. Adding potato flour significantly increased the pasting properties of wheat flour, with freeze-dried flour blends having the highest pasting properties compared to LTB_OD flour blends. Substitution of wheat flour with potato flour caused increases in water absorption as well as dough development time. The highest dough development time was attained when LTB_OD potato flour was substituted up to 50 %. The microstructure images showed that the control sample (wheat dough 100%) was characterized by small and large starch granules. The brightness (L*) of noodles decreased while the redness (a*) and yellowness (b*) increased when potato flour was added. Cooking loss significantly (p ≤ 0.05) increased, with noodles made from LTB_OD flour blends having the highest loss. When the ratio of potato flour reached 30%, the noodle textural properties, including hardness, cohesiveness, gumminess, and chewiness, decreased significantly (p ≤ 0.05). Substitution of up to 30 % with freeze-dried flour resulted in noodles with the highest overall liking scores. In conclusion, pre-treatments and drying methods affected potato flour’s physicochemical parameters differently, resulting in changes in its functionality. Partial replacement of wheat flour with up to 30% freeze-dried potato flour and 10% LTB_OD potato flour produced noodles with acceptable texture and sensory properties. This demonstrates the potential application of potato flour in noodle processing.