Effect of different blanching treatments on ascorbic acid retention in green leafy vegetables

Blanching is a prerequisite for preservation of green leafy vegetables. However, it may cause partial destruction of some nutrients like ascorbic acid which is highly oxidizable with time in the post harvest period on atmospheric exposure. The objective of the present study is to identify a suitable blanching treatment and conditions (temperature, time and media) for commonly consumed green leafy vegetables that ensures enzyme inactivation and maximum ascorbic acid retention. Ten commonly consumed leafy vegetables, viz. Amaranth (Amaranthus gangeticus Linn.), Ambat chuka (Rumex vesicarius Linn.), Bathua (Chenopodium album Linn.), Brahmi [Centella asiatica (Linn.) Urban], Drumstick (Moringa oleifera Linn.), Fenugreek (Trigonella foenum-graecum Linn.), Keerae (Amaranthus sp.), Kilkeerae (Amaranthus tricolor Linn.), Shepu (Anethum graveolens Linn. syn. Peucedanum graveolens Linn.), and Spinach (Spinacia oleracea Linn.) were blanched for 1, 2 and 4 min at 80, 90 and 98C in water and chemical media, steamed for 5 and 10 min with and without chemical treatment and microwaved for 1 and 1.5 min, unblanched greens served as control. Retention of ascorbic acid was reduced as the blanching time and temperature increased in all greens. It was comparatively higher in chemically treated samples both in conventional and steam blanched samples. Steam blanched samples (5 min) had a higher level of ascorbic acid than conventional blanched samples irrespective of blanching media. Ascorbic acid content of microwaveblanched samples was better in some greens compared to conventionally blanched greens. Blanching at 80C for 1 min, steaming for 5 min and microwaving for 1 min was sufficient to inactivate peroxidase in all except two green leafy vegetables irrespective of the blanching media. From the nutrition point of view, chemical blanching proved to be advantageous both in steam and conventional blanching for short period and it also ensured enzyme inactivation.