Glucosinolates in broccoli (Brassica oleracea L. var. italica) as affected by postharvest temperature and radiation treatments

Abstract

The purpose of the present study was to examine how glucosinolate (GLS) levels in broccoli flower buds are affected by storage time, temperature and radiation treatments in an experiment with multi-level design simulating mapped commercial storage conditions from harvest until consumer purchase. The GLS content in broccoli flower buds was examined during pre-storage and storage of broccoli heads, representing refrigerated transport with wholesale distribution and retail, respectively. The GLS analysis was conducted also for floret stalks of chosen broccoli. Broccoli heads were pre-stored for four or seven days at 0 or 4°C in the dark and then stored for three days at 10 or 18°C. During storage, the broccoli heads were exposed for 12h per day to three different levels of visible light (13, 19 or 25μmolm−2s−1) or a combination of visible light (19μmolm−2s−1) and UV-B irradiation (20kJm−2d−1), or they were stored in the dark. The GLS contents were not changed in broccoli flower buds during pre-storage at low temperatures (0°C or 4°C) for four or seven days. However, general linear model analysis revealed that pre-storage period significantly influenced total GLS, total indolyl and total aliphatic GLS, and all individual GLS levels, except for 4-methoxyglucobrassicin (4-Me-GB) in broccoli flower buds after storage at higher temperatures (10°C or 18°C). Higher levels of these compounds were found in broccoli pre-stored for seven days than in those pre-stored for four days. Storage temperature affected GLS levels in broccoli flower buds significantly. 4-Hydroxyglucobrassicin (4-OH-GB) content was increased after storage at 18°C, while the levels of all other individual GLS, total GLS, as well as total aliphatic and indolyl GLS were higher in flower buds of broccoli after storage at 10°C than at 18°C. The effect of storage temperature on aliphatic GLS in broccoli flower buds depended on pre-storage temperature and it was negligible for broccoli heads pre-stored at 4°C but significant for those pre-stored at 0°C. Radiation treatments applied during storage did not influence total and individual GLS levels in broccoli flower buds. However, the accumulation of aliphatic GLS in broccoli pre-stored for seven days at 0°C and subsequently stored for three days at 10°C under visible light of 25μmolm−2s−1 appeared both in flower buds and floret stalks. Significant increases in indolyl 4-OH-GB and 4-Me-GB contents were observed only in flower buds or floret stalks after storage at 18°C upon exposure to visible light of 25μmolm−2s−1.