202 The nutrition handbook for food processors able nutrient that is digested, absorbed, and ultimately utilised. In the case of nutrients or phytochemicals, whose beneficial effects are directed towards inhibit ing degenerative diseases, it is important to know whether or not the nutrient is reaching the particular target organ and in a form which is active. Otherwise the claims for the health benefits of that chemical would not be justified, especially as it is difficult to demonstrate benefits from long-term human studies Diet plays an important role in the uptake of specific nutrients and phyto- hemicals. Those that are lipophilic are absorbed much more readily from a lipid- rich diet. Frying tomatoes in oil dramatically improves the uptake of lycopene compared with the consumption of fresh tomatoes. Raw carrots, which have high levels of pro-vitamin A carotenoids, are poorer sources of B-carotene than gently cooked carrot. The bioavailability of certain trace elements is increased on cooking or processing; for example, the bioavailability of iron is increased in q The chemical form of the phytochemical present in food is very important in termining uptake through the gastro-intestinal tract. Quercitin-B-glucoside is more easily absorbed than the aglycone quercitin. Isorhamnetin-B-glucoside which is chemically similar to quercitin, differing only by a single methoxyl group, is more readily absorbed Flavonoid rutinosides(rhamnosyl 1-6 gluco- sides)are less easily absorbed. Thus whilst some phenols might be better antiox dants than others when tested inin vitro systems, this is of little significance in terms of health relevance. What matters is whether the compounds are easily absorbed, are not quickly degraded in tissues, and are able to reach the target sites. Flavonoids that are not absorbed undergo extensive degradation by gut microorganisms, and may play only a limited role in preventing oxidative damage in the colon 8.6 Nutritional enhancement versus food fortification The importance of enhancing the levels of a natural protective constituent in plant foods is well illustrated in the case of the folates. There is a good chance that folate status even in affluent countries is not optimal. 5.26 The most important sources of folates in the diet are liver, products derived from yeast, eggs, green vegetables, legumes and certain fruits. Plant foods(vegetables, fruits and pota- toes)are by far the single largest contributor to the overall folate intake of adults Some 40%o of the total folate intake is from fruit and vegetable consumption in these countries even when the average consumption is not very Folates have the effect of reducing the levels of plasma homocysteine which is a sensitive biomarker of folate status. A variety of studies have suggested that increased plasma homocysteine levels are a risk factor for cardiovascular disease and stroke. Human studies have shown that if individuals consume a supple- ment of 100 g/day of folic acid their plasma homocysteine is reduced to a levelable nutrient that is digested, absorbed, and ultimately utilised. In the case of nutrients or phytochemicals, whose beneficial effects are directed towards inhibit￾ing degenerative diseases, it is important to know whether or not the nutrient is reaching the particular target organ and in a form which is active. Otherwise the claims for the health benefits of that chemical would not be justified, especially as it is difficult to demonstrate benefits from long-term human studies. Diet plays an important role in the uptake of specific nutrients and phyto￾chemicals. Those that are lipophilic are absorbed much more readily from a lipid￾rich diet. Frying tomatoes in oil dramatically improves the uptake of lycopene compared with the consumption of fresh tomatoes.21 Raw carrots, which have high levels of pro-vitamin A carotenoids, are poorer sources of b-carotene than gently cooked carrot.22 The bioavailability of certain trace elements is increased on cooking or processing; for example, the bioavailability of iron is increased in canned spinach.23 The chemical form of the phytochemical present in food is very important in determining uptake through the gastro-intestinal tract. Quercitin-b-glucoside is more easily absorbed than the aglycone quercitin. Isorhamnetin-b-glucoside, which is chemically similar to quercitin, differing only by a single methoxyl group, is more readily absorbed. Flavonoid rutinosides (rhamnosyl 1–6 gluco￾sides) are less easily absorbed.24 Thus whilst some phenols might be better antiox￾idants than others when tested in in vitro systems, this is of little significance in terms of health relevance. What matters is whether the compounds are easily absorbed, are not quickly degraded in tissues, and are able to reach the target sites. Flavonoids that are not absorbed undergo extensive degradation by gut microorganisms, and may play only a limited role in preventing oxidative damage in the colon. 8.6 Nutritional enhancement versus food fortification The importance of enhancing the levels of a natural protective constituent in plant foods is well illustrated in the case of the folates. There is a good chance that folate status even in affluent countries is not optimal.25,26 The most important sources of folates in the diet are liver, products derived from yeast, eggs, green vegetables, legumes and certain fruits. Plant foods (vegetables, fruits and pota￾toes) are by far the single largest contributor to the overall folate intake of adults.27,28,29 Some 40% of the total folate intake is from fruit and vegetable consumption in these countries even when the average consumption is not very high. Folates have the effect of reducing the levels of plasma homocysteine which is a sensitive biomarker of folate status. A variety of studies have suggested that increased plasma homocysteine levels are a risk factor for cardiovascular disease and stroke.30 Human studies have shown that if individuals consume a supple￾ment of 100 g/day of folic acid their plasma homocysteine is reduced to a level 202 The nutrition handbook for food processors