The potential for the improvement of carotenoid levels in foods and the likely systemic effects

Carotenoids form one of the most important classes of plant pigments and pl ay a crucial role in defining the quality parameters of fruit and vegetable s. Their role in the plant is to act as accessory pigments for Light harves ting and in the prevention of photo-oxidative damage, as well as acting as attractants for pollinators. Their function as antioxidants in the plant sh ows interesting parallels with their potential role as antioxidants in food s and humans. Carotenoids are products of the isoprenoid biosynthetic pathw ay. The enzymes leading to carotenoid biosynthesis have all been characteri sed, and more recently the genes encoding these enzymes have been cloned fr om bacteria, fungi and plants. New information on enzyme activities and the factors leading to the regulation of the pathway is reviewed. Vitamin A de ficiency is a widespread problem in the developing world, causing blindness , particularly in the young. This has driven research into finding ways of introducing provitamin A carotenoids into staple crops, and this has recent ly been achieved in rice and canola through genetic manipulation. The fact that carotenoids show protective activity in vitro and in vivo against a va riety of degenerative disease end points has also give impetus to studying whether increasing intakes of the commonly consumed carotenoids would have public health benefits in the developed world. Human intervention studies h ave been undertaken using supplements of beta-carotene rather than utilisin g foods with enhanced carotenoid levels, but no potential benefit has been shown. Indeed, there is evidence of an increased health risk from the consu mption of beta-carotene supplements. These observations suggest that the th reshold between the beneficial and adverse effects of some carotenoids is l ow and provides a strong stimulus to further understanding the functional e ffects of specific carotenoids. Specific needs for future research are iden tified in the review. (C) 2000 Society of Chemical Industry.