Abstract
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.
Highlights
Cocoa beans (Theobroma cacao L.) and their derivative products are highly valued by consumers around the world for their essential nutrients and bioactive phytochemicals [1]
The main objective of this work was to evaluate the effect of roasting temperature (110, 120, 135, or 150 °C) and relative air humidity (0.3 or 5.0%) on the yield, phytochemical composition, CIE L*a*b* color characteristics, browning and fluorescence intensity, and molecular weight distribution of HMW fractions isolated from Criollo, Forastero, and Trinitario beans of different origins
The results presented in this study clearly demonstrated that the roasting of cocoa beans at temperature above 135 °C and relative air humidity of 0.3% led to significantly greater formation of HMW Maillard reaction products
Summary
Cocoa beans (Theobroma cacao L.) and their derivative products are highly valued by consumers around the world for their essential nutrients and bioactive phytochemicals [1]. Several previous studies have indicated that temperature and Maillard reactions are initiated by interactions between carbonyl groups (mainly of reducing sugars) and the nucleophilic amino groups of amino acids, peptides, or proteins, resulting in the sugar–amine condensation and rearrangement to Amadori or Heyns products. The subsequent stages involves sugar dehydration and fragmentation, amino acid degradation, and many other fragmentation steps [5, 6]. These reactions are very complex and lead to the simultaneous or consecutive formation of highly reactive lowmolecular-weight (LMW) compounds, such as α-dicarbonyl and α-hydroxycarbonyl compounds, furfurals, reductones, and Strecker aldehydes [2, 5, 6]. In the final stage of Maillard reaction, condensation and polymerization reactions of the highly reactive intermediates result in the formation of
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