Bioactive Compounds in Baby Spinach (Spinacia oleracea L.) Effects of Pre- and Postharvest Factors

Bergquist, S. 2006. Bioactive compounds in baby spinach (Spinacia oleracea L.). Effects of preand postharvest factors. Doctoral dissertation. ISSN 1652-6880, ISBN 91-576-7111-7. A high intake of fruit and vegetables is well known to have positive effects on human health, and has been correlated to a decreased risk of most degenerative diseases of ageing, such as cardiovascular disease, cataracts and several forms of cancer. These protective effects have been attributed to high concentrations of bioactive compounds (ascorbic acid, flavonoids, carotenoids) in fruit and vegetables, partly due to the antioxidative action of some of these compounds. Maintaining a high level of these compounds in fruit and vegetables is therefore desirable. In addition, a high concentration of antioxidants in horticultural produce is believed to improve its storability and reduce the rate of deterioration. This thesis investigated the effects of preand postharvest factors on the concentrations of bioactive compounds in baby spinach (Spinacia oleracea L.). The factors studied included sowing time, growth stage at harvest, use of shade nettings and postharvest storage temperature and duration. Bioactive compounds were analysed using reversed-phase HPLC and chlorophylls using a spectrophotometric method. Visual quality of the fresh and stored leaves was scored on a 1-9 scale, where 9 was the best. The concentrations of ascorbic acid and flavonoids most often decreased during plant growth. Carotenoids showed relatively small increases or decreases, but nevertheless, plant growth had the largest impact on carotenoid concentration of the factors studied. Harvesting the leaves slightly earlier than is currently common practice may thus give increased concentrations of bioactive compounds. The variation in these compounds during the season was relatively small except for the flavonoids, which doubled in concentration in April-sown spinach compared to August-sown. Shading generally decreased ascorbic acid and total vitamin C concentrations, but most often increased carotenoid concentration. Flavonoid concentration showed different responses at different times of the season and at different growth stages. In some cases the concentration decreased due to shading, while in others it did not change significantly. There were considerable losses of ascorbic acid during storage, whereas carotenoids and flavonoids were more stable and sometimes increased. Ascorbic acid concentration at harvest was correlated with visual quality after storage, indicating that the antioxidative action of ascorbic acid may protect the plant tissue against oxidative stress and subsequent deterioration.