POTENTIAL FOR CONTROLLED ABIOTIC STRESS AS A QUALITY ENHANCER OF BABY LEAF SPINACH

Applying abiotic stress in a controlled fashion during growth, preharvest, to leafy vegetables has been suggested as a strategy that may increase levels of bioactive compounds, and in some cases, increase shelf life potential. In a two-year project, change in ascorbic acid (AA) content in baby leaf spinach (Spinacia oleracea L.) was studied in response to a wide range of preharvest abiotic stress factors. AA is one of the main antioxidants found in leafy vegetables and the total amount and proportion of the oxidised form dehydroascorbic acid (DHA), could potentially be a parameter giving an indication of the stress level of the leaves. The assumption is that the higher the content of AA and the lower the proportion of DHA, the better the shelf life potential. AA and DHA concentrations were determined by HPLC. The analyzed leaves were grown under green house conditions. Foliar application of water solutions of common salts resulted in higher AA levels, but the leaves were damaged with necrotic spots and brown edges. Both cold treatment (10°C day/5°C night) of whole plants a few days prior to harvest as well as heat treatment (40°C) a few hours prior to harvest increased the AA levels. This approach needs further technical development to be commercially applicable. Restricted water supply leading to mild drought stress, a few days prior to harvest turned out to be the most promising preharvest treatment leading to increased AA content without any visual quality differences compared to full watered treatments. The extent of drought stress as well as timing of the treatment in the growth cycle needs further investigation.