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subject of many studies and much information has been accumulated on them. Each has a focus of interest as components of other foods or beverages believed to have health benefits. For example, (+)-catechin, ()-epicatechin and ()-epigallocatechin are found in green tea. Onions are high in quercetin. Wine contains a variety of flavonoids including anthocyanins.

Table 8.4 summarizes information about the protective effects shown for the flavonoids found in cocoa (27). Although many effects have been shown for these compounds in test and animal systems, one important question that remains to be resolved is the extent to which humans absorb these compounds. To have much effect on human health, flavonoids must be taken up by the body. However, the information that is available on this point is fragmentary, but it has been well reviewed by Hollman and Katan (34). The degree of absorption of catechins from a major source, namely tea, is hardly known. Various experiments, mostly with animals, have shown a variable absorption of flavonoid aglycones when administered at very high doses. The figure varies between 458% depending on the flavonoid. Although it might be expected that glycosidically linked flavonoids would be less well absorbed than the aglycone (that is, the 'straight' compound not linked to a sugar molecule), recent studies comparing absorption of quercetin with quercetin glucoside surprisingly showed that the latter was much better absorbed. It would therefore seem that conventional wisdom needs to be reevaluated.

Table 8.4 Summary of protective effects of cocoa polyphenols.

Chemical Effect

Antigenotoxic Anticarcinogenic Antioxidant Other

Antigenotoxic Anticarcinogenic Antioxidant Other

Table 8.4 Summary of protective effects of cocoa polyphenols.

(+)-Catechin

+

+

+

ISC

()-Epicatechin

+

+

+

CHO, ISC

(+)-Gallocatechin

+

+

+

THR

()-Epigallocatechin

+

+

+

CHO

Leucocyanidin

a

a

a

LAT, BL

Polymeric leucocyanidin

a

a

a

3-a-L-Arabinosidyl cyanidin

a

a

a

3-ß-D-Galactosidyl cyanidin

a

a

a

Quercetin

a

+

+

IMM

Quercetin-3-galactoside

a

a

+

THR

Quercetin-3-glucoside

a

a

+

+ = protective activity reported in the literature. a = no relevant data identified.

ISC = improvement in memory impairment caused by reduced blood oxygen levels. CHO = reduction in cholesterol absorption. THR = antithrombotic activity.

LAT = protection against toxicity from intake of lathymus plant seeds. BL = increased vascular tissue strength. IMM = anti-immunogenic effects.

CHD = epidemiological evidence of protection against coronary heart disease incidence and mortality.

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Since so little is known about the absorption of flavonoids, it is not surprising that the factors affecting absorption are hardly understood. It is well known that polyphenols can bind strongly to protein. There is evidence that antioxidant polyphenols are not absorbed from tea drunk with milk (35). This could also be a factor affecting cocoa polyphenols. It is clear that much of the polyphenolic material is complexed with protein during cocoa fermentation. Furthermore, much of the chocolate that is eaten is milk chocolate where additional proteins are introduced from the milk. However, there is very little information on the fate of the complexed polyphenols after ingestion.

Another important issue for chocolate is the amount of flavonoids present. Again, there is not very much information available, but what there is would suggest a large loss of monomeric flavonoids at all stages from fermentation to chocolate production (Table 8.1). This makes it all the more crucial to learn more about the nature of the cocoa polyphenol adducts, and to determine their metabolic fate. Until we know this, it will be hard to judge their effects in vivo. Even the simplest adducts are quite complex, and recent patents (3638) have claimed the presence of polymeric flavonoids up to 12 units or more. The patents have claimed a variety of biological effects for these complex molecules which would lead to health benefits, but the nature of patent disclosure and the information available from them makes it impossible to fully judge the efficacy of the claims.

To give some idea of the amounts of flavonoids needed to have beneficial effects in experimental animals, Table 8.5 is reproduced from the BIBRA (27) review.

It should also be pointed out that the relationship between disease and Table 8.5 Oral doses of cocoa flavonoids needed to demonstrate a protective effect.

Chemical

Effect

Antigenotoxic Anticarcinogenic Inhibition of lipic peroxidation Protection from kidney injury

Effective dose (mg/kg body weight/day)

2.4435 0.0581500 2.4 0.4

Species

Rodents Mice Rats Rats

()-Epicatechin

Antigenotoxic Anticarcinogenic Reduced cholesterol absorption Protection from kidney injury

1.45

0.058100 70 0.8

Mice Mice Rats Rats

()-Epigallocatechin Reduced cholesterol absorption Rats

Leucocyanidin Antidiabetic 100 Rats

Quercetin Anticarcinogenic 10002500 Rodents

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intake of flavonoids remains unclear. In the case of cancer, there is strong epidemiological evidence for a protective effect of vegetables and fruit. Identification of the active molecules is, however, another matter. In a review of the potential health effects of quercetin the most common dietary flavonoid Hertog and Hollman (39) and the recent Committee on the Medical Aspects of Food and Nutrition Policy (COMA) report (28) point out that there is a lack of convincing evidence for an anticancer effect of quercetin and other flavonoids in human populations, even though such effects can be seen in in vitro studies. Populations with a high intake of quercetin are not characterized by low mortality from cancer in a number of organs. In contrast, the epidemiological evidence that flavonoids like quercetin have a protective effect against heart disease is rather stronger, if not completely consistent. The mechanism for such a protective effect remains to be clarified. Janssen et al. (40) present evidence that the effect is not mediated in the main by haemostatic variables. Thus there remains much to be learned about how phytoprotective effects operate.

Biological Effects of Non-Saponifiable Components of Cocoa Butter

Cocoa beans contain around 55% lipid, called cocoa butter, most of which is triacylglycerol. A small fraction of cocoa butter (0.3%) comprises non-saponifiable material (Table 8.3). Thirty-nine sterols or triterpenes were identified or tentatively assigned by Staphylakis and Gegiou (21, 22). They estimated the content of non-esterified sterol in cocoa butter at 216 mg/100 g, much of it b-sitosterol (123 mg/100 g) and stigmasterol (60 mg/100 g). They also found 15 mg/100 g of methyl sterols and 35 mg/100 g of dimethylsterols, predominantly cycloartenol.

Sterols are very similar in structure to cholesterol (Fig. 8.5), and are capable of interfering with the absorption of dietary cholesterol. Sterols may therefore act to lower blood cholesterol, thereby reducing one of the important risk factors for heart disease.

The significance of the non-saponifiables in cocoa butter in lowering cholesterol has recently been reviewed by BIBRA (19). The following summarizes the assessment of this report. There have been a number of studies over the years demonstrating the ability of b-sitosterol to lower cholesterol levels. However, it should be noted that most of the studies were carried out on subjects suffering from primary hypercholesterolaemia or hyperlipoproteinaemia. Such patients are genetically predisposed to synthesise cholesterol excessively, resulting in high blood cholesterol levels. Few studies have been done on subjects with normal or only slightly raised cholesterol levels. Two studies involving normal subjects demonstrated a reduction in cholesterol absorption of 4050% when high levels of b-sitosterol were consumed. However it should be noted that in normal sub

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