Influence of antioxidant spices on the retention of β-carotene in vegetables during domestic cooking processes

Abstract

Considerable amounts of β-carotene were lost during the two domestic methods of cooking commonly used, namely, pressure cooking and open pan boiling, the loss ranging from 27 to 71% during pressure cooking and 16–67% during boiling for the four vegetables examined in this study. Pressure cooking of green leafy vegetables resulted in a greater retention of this provitamin. In the presence of red gram dhal, which is a common ingredient in the diet, there was an underestimation of β-carotene due to poor extractability. Inclusion of acidulants—tamarind and citric acid-along with these vegetables brought about some changes in the level of retention of β-carotene. The antioxidant spice turmeric generally improved the retention of β-carotene in all four vegetables studied. Onion also had a similar effect. The combinations of acidulants and antioxidant spices also improved the retention of β-carotene during cooking. This effect seemed to be additive in the case of processing of amaranth by boiling.

Introduction

Malnutrition, particularly micronutrient deficiency, is one of the major public health problems in the developing countries, including India (Gopalan, Ramasastri, & Subramanian, 1999). The results of countrywide surveys have revealed that vitamin A deficiency is very common in India and many children below the age of 5 years become blind due to vitamin A deficiency (Thylefors, 1985). Vitamin A, in addition to preventing nutritional blindness, has been considered to promote growth and prevent morbidity and mortality in young children (Chandra & Au, 1981). Deficiency of vitamin A leads to impaired cellular functioning, since it has a role in numerous physiological processes in animals (Machlin, 1984). Carotenoids are the precursors of vitamin A and those commonly occurring in nature include α, β and γ-carotene, lycopene and cryptoxanthin. Among these precursors, a major proportion of vitamin A activity is accounted for by β-carotene which is widely distributed, in green leafy vegetables, yellow-orange fruits and some other vegetables (Goodwin, 1986). β-Carotene accounts for more than 90% of total carotenoids in vegetables. In human beings, β-carotene not only serves as valuable source of vitamin A, but also serves as a potent antioxidant, scavenging free radicals and quenching singlet oxygen. By this latter property, β-carotene is understood to reduce the risk of development of certain types of cancer (Bafidu, Akapapunam, & Mybemere, 1995).

Animal foods, such as eggs, milk and liver, which are good sources of preformed vitamin A, are expensive. The poorer segments of the population in India are therefore dependent on plant foods, which provide β-carotene to meet their requirements of vitamin A. Green leafy vegetables, in general are rich sources of β-carotene, in addition to ascorbic acid, calcium, iron and folic acid. These leafy vegetables are grown abundantly in India and are relatively inexpensive and easily and quickly cookable (Gopalan et al., 1999).

Compared with vitamin A, the provitamin carotenoids are more stable to light and oxidation. This may be due to the location of the carotenoids within the plant tissues. However, heat treatments, which disintegrate tissue if coupled with exposure to oxygen, light and acid, can result in the destruction of the provitamin A carotenoids. In addition, heat, acid and light have been reported to cause isomerization of vitamin A and carotenoids. These adverse factors can cause isomerization of the all-trans form to the cis form which is biologically less potent (Zechmeister, 1949).

In view of the above, information on the possible losses of β-carotene from vegetables, during preparation by traditional cooking methods, is of major importance. Several reports have documented the losses of β-carotene from vegetables during cooking procedures such as boiling, stewing, frying, blanching, and pressure cooking, etc. (Akapapunum, 1984, Bafidu et al., 1995, Ogulensi & Lee, 1979, Onayemi & Bafidu, 1987, Padmavathi et al., 1992, Park, 1987, Sood & Bhat, 1974, Sweeney & Marsh, 1971, Yadav & Sehgal, 1995, Yadav & Sehgal, 1997). It would, however, be interesting to see whether the presence of certain food components, such as antioxidant spices and acidulants, have a protective role against such losses. This study was therefore conducted to determine the extent of retention of β-carotene in representative vegetables, which are rich sources of the same during conventional cooking procedures. This study also examines the influence of commonly used acidulants and of spices known to have antioxidant properties on the extent of retention of β-carotene.

The objectives of the present study were to: (1) quantify the loss of β-carotene from vegetables—Carrot (Dacus carota), Pumpkin (Cucurbita maxima), Amaranth leaves (Amaranthus gangeticus) and Drumstick leaves (Moringa oleifera) during pressure cooking and boiling in water; (2) study the influence of acidulants—tamarind and citric acid, and antioxidant spices—turmeric and onion powder, as well as their combinations, on the retention of β-carotene during the two cooking procedures.