Effects of storage and heat treatment on metabolism and quality of fresh tomato and potato

Potato and tomato are two highly consumed vegetables in Norway as well as throughout the rest of the world, with high consumer demands of sensory and nutritional quality. In addition to being sold fresh, a large use for vegetables are found in processed food for convenient preparation at home. All plant products continue to live and undergo metabolic processes after harvest, and these processes are affected by environmental conditions such as temperature and light as well as processing conditions. This study was designed to address how the nutritional content in tomato and potato change over time due to these metabolic processes when the plant products are stored at different temperatures as well as how processing by heat treatment affect the nutritional content compared to the fresh produce.Potatoes were stored at 4 °C and 20 °C over 14 days and tomatoes in the same temperatures over 10 days. Each sampling day samples were taken from storage at 4 °C and dried at 40 °C and 60 °C for approximately 18 hours. The biochemical composition of the samples was then analysed to find total soluble solids content (°Brix), total phenolic content (Folin-Ciocalteu assay), antioxidant activity (FRAP) and relative concentrations of individual metabolites using gas chromatography-mass spectrometry (GC-MS). The results showed a clear difference between fresh and dried samples in both potato and tomato. Fresh potatoes stored at 4 °C increased in reducing sugars indicating low temperature sweetening, whereas fresh tomatoes underwent less biochemical changes in low temperature storage compared to room temperature storage. Heat treatment resulted in significant decreases of metabolite levels, total phenolic content and antioxidant activity in both potato and tomato. Some metabolites were however found to increase, including glucose, fructose, chlorogenic acid and several fatty acids in potato, and glucose, fructose and α-tocopherol in tomato. The dried samples generally followed the trends seen in the samples stored at 4 °C over the storage period. A large number of studies assessing quality in both potatoes and tomatoes have been published, but all with different cultivars that have been grown, stored and processed under different conditions. Large-scale studies that monitor all aspects of growth, storage and processing could therefore be of importance, as well as thorough literature reviews that can provide a collected source of information for researchers in the food industry