Physico-chemical properties and storability of selected Irish potato varieties grown in Kenya

Abstract

Potato is the second most important food crop after maize in Kenya. It is valuable as it yields more nutrients per unit area and time than any other crop. Potato is a short-duration crop, easy to propagate, versatile in use, and a good source of nutrients. While different potato varieties do exist, the nutritional value, storability, and suitability of each variety for domestic and industrial application is not well documented. This study aimed to characterize the physical properties, nutrient content, and storability of three popular Kenyan potato varieties (Shangi, Dutch Robjin, and Unica). The three potato varieties were obtained from Jaconta farms ltd in Ol Kalou, Nyandarua County where they were all cultivated under the same conditions in one season. Physico-chemical characteristics were determined using standard methods and procedures. Tuber storability was evaluated at room temperature and relative humidity (RH), 10°C/75% RH, 10°C/ ambient RH, and 7°C/75% RH. Parameters analyzed for tuber storability included weight loss, sprouting, greening, rotting, and simple sugars. The results for physical characteristics revealed that Unica, Shangi, and Dutch robjin had tuber lengths above 50mm recommended for French fry processing. Dutch robjin and grade two tubers of Shangi and Unica varieties would be suitable for crisp processing as they had widths ranging between 40-60mm. Shangi and Unica were oval in shape making them suitable for French fry processing while Dutch robjin was round in shape and would thus be suitable for crisp processing. All varieties had specific gravity ranging between 1.08±0.01 and 1.12±0.02 for both grades hence suitable for processing. All the varieties had deep eyes (>0.6mm). There were significant differences in the nutrient content among the three varieties with Dutch Robjin having the highest content of carbohydrates (20.43±1.03%, P=0.0003), crude fibre (1.11±0.15%, P=0.0246), total ash (1.10±0.03%, P=0.0004), iron (0.87±0.05mg/100g, P=0.0028), thiamine (0.04±0.01mg/100), niacin (0.93±0.09mg/100, P=0.0439), pyridoxine (1.92mg/100g, P=0.0001) and folic acid (34.62±1.06 µg/100g, P<0.0001). Reducing sugar content across the three varieties differed significantly (P= 0.0083) and increased during storage, with Shangi variety exhibiting the highest accumulation. Potato storability varied across the storage conditions and varieties. The degree of change in tuber physical quality was highest at room conditions and least at 7°C/75%RH. Shangi generally had the highest rate and extent of change in physical quality as indicated by the rate of sprouting, weight loss, greening, and rotting under all the storage conditions while Unica had the best storability attributes. Storage at 7°C/75%RH best preserved the tuber physical characteristics increasing the storability of Shangi from 2 weeks to 3 months. These findings indicate that Shangi, Unica, and Dutch robjin varieties differ in terms of physical, nutritional, and storability properties. The physicochemical properties of these varieties such as tuber weight, greening and simple sugars concentration are influenced by different storage conditions.