Melanoidins formation in roasted cocoa beans

Melanoidins formation in roasted cocoa beans and their effects on the gut microbiota.

Fermented and dried beans or seeds of Theobroma cacao L. are the key raw material for the manufacture of chocolate. Cocoa beans are a high source of polyphenols, these compounds confer astringent, bitter sensations, green and fruity flavours and have antioxidant activity. Cocoa beans should be roasted in order to reduce moisture content, to release undesirable aromas, to intensify the brown colour and to develop the characteristic chocolate aroma. Cocoa processing industry typically do it in convective hot-air roasters at 110 to 150°C  for 15 min to 2 h until the moisture content of the beans is below to 2%. Beside the self-evident sensory improvement of cocoa by roasting, this process comes with certain concerns caused by the “loose” of free phenolic compounds.

Browning and aroma formation are mainly achieved through the Maillard reaction. This reaction is triggered by high temperatures involving amino acids, peptides, sugars, polyphenols, among other compounds from cocoa beans to produce compounds of different molecular weight from the smallest and volatiles ones (responsible of the aroma) to the largest polymers such as Melanoidins. The last ones are highly responsible for the brown tones mentioned above, and due to their complexity and high molecular weght they are not digested so they reach the large intestine without significant modifications. In addition, the polyphenols that are bounded to this polymer still exert antioxidant activity, therefore there could be potential beneficial effects of this polymeric compounds at the level of the gut as antiradicals and/or as feed for microbiota.

The way as melanoidins are produced vastly relies on the roasting parameters time and temperature. Melanoidins formation and polyphenols binding increases when high temperatures and long roasting times are applied. Information about cocoa melanoidins formation and/or free phenolic compounds preservation through different roasting techniques is quite scarce. For instance, fast convective roasting by fluidized bed technique is a promissory alternative that have shown positive results in quality and nutritional characteristics of coffee because of the very short times and high temperatures that it plays. Increasing the roasting rate in cocoa beans could be an alternative to find more free polyphenols without compromising the quality of the final product.

This PhD project is split in to 2 stages: The first one is aimed to compare typical long roasting vs. fast roasting drove by fluidized bed technique on physical properties, microstructural modifications, chemical transformations, volatile profile, cocoa butter characteristics, polyphenols content, antioxidant activity and melanoidins formation of cocoa beans. And the second one will be focused on the interaction of cocoa melanoidins with gut microbiota by in-vitro digestion.

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