Effect of pretreatment and conditions and period of storage on some quality indices of frozen chive (Allium schoenoprasum L.)

Chive leaves for freezing contained 13.9 g dry matter, 133 mg vitamin C, 4.7 mg β carotene, 121 mg chlorophylls (a+b), 40.4 mg nitrates, and 0.19 mg nitrites in 100 g of edible parts. Blanching of the raw material before freezing reduced the level of dry matter by 22%, vitamin C 29%, β carotene 20%, chlorophylls 21%, and nitrates 26%, while that of nitrites increased three times. Freezing and 12-month storage of frozen material caused further losses in the analysed constituents except dry matter. Losses were distinctly higher on freezing non-blanched chive, a further enhancement of losses being observed with a storage temperature at −20°C. After a 12-month storage of frozen chive, the preserved content of vitamin C ranged from 11 to 66%, β carotene 37 to 65%, chlorophylls 65 to 75%, and nitrates 58 to 81%. If the blanching is omitted and the storage temperature is −20°C, a good preservation of vitamin C is not possible even for a period of 3 months. In contrast, the pretreatment of blanching ensures its good preservation at −20°C and at −30°C, and also yields a very good conservation of all the constituents analysed.