Effect of freezing on the pungency and antioxidants activity in leaves and bulbs of green onion in Giza 6 and Photon varieties

摘要

The shelf life of green (spring) onions was short (from 3 to 4weeks). Therefore, the aim of this investigation is to elongate green onion shelf life by freezing at ?18°C with slight changes in antioxidant activities and pungency for each spring onion Allium cepa L. varieties (Giza 6 and Photon) which cultivated in Egypt. This study included leaves and bulbs in each varieties of spring onion. Results showed high contents of total phenols and flavonoids in leaves compared with bulbs either of Giza 6 or Photon types, therefore Giza 6 had high content of total phenols and flavonoids than Photon variety, in parallel the results were obtained of total chlorophyll and total carotenoids contents. While, chlorophyll a content showed higher than chlorophyll b in leaves than in bulbs for each variety. Results indicated that the diversity in kind of polyphenolic and flavonoids components either leaves or bulbs in each spring onion types. Benzoic acid showed the major polyphenolic compounds in the bulbs of either Giza 6 or Photon spring onions varieties (11.92% and 27.43%), while salicylic acid (8.37%) and ellagic acid (9.10%) were major ones of the leaves of Giza 6 and Photon variety. The major components of flavonoids were myricetin, quercitin and rutin in leaves and bulbs for each variety. Myricetin which was the highest flavonoids components was the major; it also showed higher percentage in the leaves than bulbs of two varieties (Giza 6 and Photon). It also was higher in Photon leaves than Giza 6 leaves. Giza 6 bulbs was highest content of pungency, then Photon bulbs followed by Giza leaves and Photon leaves at zero time till 3months of storage at freezing. Also, results of pungency and antioxidants activity by DPPH method in leaves and bulbs for each variety indicated that there were slightly decrease during storage (3months). Results indicated that export onion spring can be stored under freezing at ?18°C during 3months without high changes in pungency.