Polyphenols form the largest group of compounds among natural antioxidants, which largely affect the overall antioxidant and antifree radical activity of cocoa beans. The qualitative and quantitative composition of individual fractions of polyphenolic compounds, even within one species, is very diverse and depends on many factors, mainly on the area of cocoa trees cultivation, bean maturity, climatic conditions during growth, and the harvest season and storage time after harvest. Thermal processing of cocoa beans and cocoa derivative products at relatively high temperatures may in addition to favorable physicochemical, microbiological, and organoleptic changes result in a decrease of polyphenols concentration. Technological processing of cocoa beans negatively affects the content of polyphenolic compounds.

Cocoa beans and their co-products are a rich source of beneficial compounds for health promotion, including polyphenols and methylxanthines. Knowledge of bioavailability and in vivo bioactivity of these phytochemicals is crucial to understand their role and function in human health. Therefore, many studies concerning bioavailability and bioactivity of cocoa bioactive compound have been done in both in vivo animal models and in humans. This critical review comprehensively summarizes the existing knowledge about the bioavailability and the major metabolic pathways of selected cocoa bioactive compounds (i.e. monomeric flavan-3-ols, procyanidins, anthocyanins, flavonols, phenolic acids, N-phenylpropenoyl-L-amino acids, stilbenes, and methylxanthines). The compiled results indicated that many of these compounds undergo extensive metabolism prior to absorption. Different factors have been suggested to influence the bioavailability of polyphenols and methylxanthines among them the role of gut microbiota, structure of these compounds, food matrix and occurrence of other substances were the most often considered. Aforementioned factors decided about the site where these bioactive compounds are digested and absorbed from the alimentary tract, as well as the pathway by which they are metabolized. These factors also determine of the type of transport through the intestine barrier (passive, involving specific enzymes or mediated by specific transporters) and their metabolic path and profile.

This study explored the effects of roasting parameters on the yield, proximal composition, free phenolic compounds content, CIE L*a*b* color characteristics, browning index, fluorescence intensity, and molecular weight distribution of high-molecular-weight (HMW) melanoidin fractions isolated by dialysis (> 12.4 kDa) from cocoa beans of three Theobroma cacao L. types. The beans were roasted at four temperatures (110, 120, 135, and 150 °C) and two relative air humidity levels (RH 0.3 and 5.0%). To understand how roasting conditions affect the physicochemical properties of HMW fractions, changes in the content of carbohydrates, proteins, lipids, and phenolic compounds were determined for the tested cocoa beans. The yields of HMW products decreased after thermal processing at 110 and 120 °C, but increased at 135 and 150 °C. It was found that the applied roasting temperatures and RH levels caused a significant decline in carbohydrates, proteins, and free phenolic compounds in all HMW fractions obtained from cocoa beans. Roasting led to a considerable decrease CIE lightness. In addition, degree of browning and fluorescence intensity of HMW fractions tended to increase with increasing thermal treatment temperature. High-performance size-exclusion chromatography revealed that roasting led to significant changes in the molecular weight distribution of HMW fractions.