Glycoalkaloids in Commercial Kenyan Potato Varieties

Abstract

The potato (Solanum tuberosum) is an important staple food crop contributing to food and nutrition security of many households globally. However, of concern to food safety is the fact that potatoes can accumulate glycoalkaloids which are a family of steroidal toxic secondary metabolites. Although they contribute to flavor, at high levels, glycoalkaloids which are naturally occurring in potatoes, pose food safety concerns as they can lead to bitterness and intoxication to consumers. Their concentrations in potatoes are dependent on postharvest handling, variety and stress factors that tubers are exposed to. Variation of glycoalkaloids in commercial potatoes is yet to be established hence the current research. This study was carried out in three phases to fulfil three objectives. The first phase fulfilling objective one and it involved a survey that was cross-sectional in design where the post-harvest handling practices and perception of potato safety among potato traders in open-air markets in Nairobi County were assessed. A total of 100 potato traders were interviewed using a semi-structured questionnaire that determined post-harvest handling practices such as potato transportation, exposure to sunlight and storage. The second objective focused on determining the levels of glycoalkaloids in commercial potato varieties in the Kenyan Market. Three potato varieties, Shangi, Dutch Robjin and Royal sold in open air markets and supermarkets in Nairobi County were randomly sampled and their glycoalkaloid levels determined by HPLC method. The third objective sought to establish the influence of storage conditions on the glycoalkaloid levels of potatoes. Three potato varieties, Shangi, Dutch Robjin and Royal, were stored for 12 weeks at different conditions of temperature (5, 10 and 25 oC) and light intensity, with glycoalkaloids in both flesh potato (peeled) and whole potato (unpeeled) being determined at 4-week intervals. Results showed that 42% of the potatoes on the market were stored for a period ranging from 2 to 3 days. Forty seven percent (47%) of the vehicles and hand-pulled carts used to transport potatoes to the market had open backs while 53% had closed backs. Over half (69%) the potatoes xv in the markets were directly exposed to sunlight, with 75% of the traders leaving their potatoes in the open covered with a polythene bag after the day‘s activities. This exposed the tubers to potential risk of glycoalkaloid accumulation. Greening, sprouting or bruised potatoes were sold to consumers at a lower price (20%), which may pose a serious health risk to consumers if these potatoes are consumed. Additionally, more than half of the traders did not think that consumption of greened potatoes is harmful to health, meaning that they had poor knowledge on the effects of glycoalkaloids on health. For the market samples collected, Shangi variety had the highest levels of glycoalkaloids with a mean of 410.35 mgkg-1 dry weight; with samples from supermarkets having the highest levels (550.8 mgkg-1). The same variety (Shangi) from open air markets averaged glycoalkaloid levels of 382.26 mgkg-1 dry weight. Dutch Robjin (129.2 mgkg-1 dry weight) and Royal variety (98.2 mgkg-1 dry weight) had the least levels of glycoalkaloids. However, the levels in sampled tubers did not exceed the recommended levels of 1000mg/kg on dry weight basis and, therefore, consumption of these potatoes would not raise safety concerns. For storage trials, results indicated that storage conditions and potato variety were factors that significantly (p<0.05) influenced glycoalkaloids levels; with glycoalkaloid levels in both whole potatoes and potato flesh significantly (p<0.05) increasing with increasing period of storage. Storage of all the varieties of whole potatoes beyond eight weeks at elevated temperatures (>10oC) and in light resulted in accumulated levels of 1000 mg/kg dry weight (converted to 200 mg/kg fresh weight), which are levels deemed unsafe for consumption. However, Storage of the potatoes in the dark and at 5 oC resulted in the lowest accumulation of total glycoalkaloids (<1000 mg/kg). Therefore, storage of the potatoes at lower temperatures (<10oC); in dark and for shorter period of storage (less than 8 weeks) is recommended to assure their safety