Beta-carotene retention as retinol activity equivalent at different cooking and storage variants

Provitamin A carotenoids from various foods have been shown to have approximately eight-fold difference in β-carotene conversion factors (on a weight basis) ranging from 3.6:1 to 28:1, thereby yielding different values in terms of vitamin A. The major factor that affects the conversion of plant provitamin A to vitamin A is the nature of the food matrix. Therefore, to study the effect of different food processing on a selected food matrix (carrot was chosen in the present work) as retinol precursor, three boiling methods namely open flame boiling in open containers (gas oven; OF), open flame boiling in closed containers (pressure cooker; PC) and microwave irradiated boiling (MW) were selected. The differently boiled carrots were refrigerated for 24 and 48 h followed by reheating by open flame and microwave irradiation. Results showed that the characteristic three peak spectrum of all trans-β-carotene has not been altered much irrespective of different treatments, times and temperatures. Spectrum of raw carrot and all types of boiled products showed no peak for bio-available cis-isomer of β-carotene. Refrigeration for 24 and 48 h of the boiled mass (all types) resulted in the formation of cis-isomer. Reheating post 24 h refrigeration revealed total loss of cis-isomer while reheating post 48 h refrigeration revealed partial retention of cis-isomer in cases of MW and OF boiled products only. For PC boiled carrot, reheating post 24 and 48 h refrigeration resulted in total loss of cis-isomer. The results suggest that while the MW boiled carrot yielded the highest vitamin A (in IU), further refrigeration and reheating (in either way) lessened the bio-availability. For future application, the amount of carrot required to meet the daily value (DV) of vitamin A can be projected based on the loss/gain effect of boiling types demonstrated in the present work, provided the rate of consumption of carrot is known.