Development of an instant potato soup powder from small non-marketable potatoes (solanum tuberosum)

Abstract

Potato (Solanum tuberosum) is an important food crop grown by many farmers in Uganda especially in the highland regions. Post-harvest losses are a major hindrance to increasing production of potatoes. One of the causes of such losses is the small size of some of the potatoes harvested that do not meet the demand of traders and consumers. The small sized potatoes are mainly used as seed which however results in low yields due to seed degeneration. This therefore presents a need to find an alternative use for small sized potatoes so as to generate additional income to farmers. In this study, an instant soup powder was developed from the small unmarketable potatoes. The potatoes were washed, sliced to thin pieces and soaked in 1% citric acid for 20 minutes. The sliced potatoes were divided into two equal portions and given two separate treatments; steaming and heating at 80 oC for 5,10 and 15 minutes. The cooked potatoes were dried in an electric hot air drier maintained at 65 oC for 8 hours. The dry potato slices were milled into potato flour using a motorized hammer mill. The flour from small sized potatoes was used as a major ingredient in the formulation of an instant soup powder using Nutri Survey software 2007. The formulations were based on the heat treatments subjected to the potatoes and all contained; 60% potato flour and 20% full cream milk powder as the major ingredients. The proximate and physio-chemical properties of the instant soup powder were determined using AOAC standard methods while the sensory acceptability of the soup was rated on a nine-point hedonic scale using untrained panelists comprised of 17 male and 13 female students from the School of Food Technology, Nutrition and Bioengineering at Makerere University. The results indicate that there was no significant difference (p>0.05) in moisture, fiber and sugar content between the small and large sized tubers. The Starch content of small sized potatoes (12.94%) was significantly (p<0.05) lower than that of large sized potatoes (14.93%). The protein content of small sized potatoes (1.92%) was higher than for large sized potatoes (1.73%). The soup formulations contributed over 15% of the adult RDI requirements for carbohydrates (20.25%) and vitamin C (64%) but not for fat (8.35%) and dietary fiber (8.567%). The six soup formulations showed desirable reconstitution characteristics owing to their good water solubility (3.05-3.80%), swelling capacity (3.70-4.54%) and water absorption capacity (271.01-652.37%). The sensory acceptability of the soup formulations was within a range of 5.77-6.40 and was not significantly different from commercial soup (6.19). These results indicate the potential of the small unmarketable potatoes to be processed into an instant soup powder.