Contribution of coffee proteins to roasted coffee volatiles in a model system

Abstract

A simple roasting model using a mineral oil bath was set up to study the effects of coffee proteins on the formation of coffee volatiles during roasting. Green coffee powder was separated into four fractions, and the highest concentration of volatile compounds was observed in the roasted sample of the water extract fraction. Sugar degradation products were the dominant compounds. The addition of coffee proteins into the nonprotein water extract fraction catalysed sugar degradation and enhanced the production of selected volatiles. Higher amounts of coffee protein correlated with the concentration of pyrazines. Coffee protein also increased sucrose degradation in the roasting of sucrose with coffee protein. However, the results from colour measurements indicated that a greater amount of protein produced a lighter colour. These results demonstrated the important contribution of coffee proteins in the formation of coffee volatiles and colour.

Contribution of volatile compounds to the antioxidant capacity of coffee

“…A great variety of furans are originated during roasting process in coffee as Maillard-reaction products, but they are also the result of thermal oxidation of lipids and thermal degradation of thiamine, nucleotides, terpenes (Flament, 2001) and proteins (Hwang, Chen, & Ho, 2012). In furan model system (Fu), no appreciable antioxidant activity at coffee furan concentration was observed.…”

Farm to Consumer: Factors Affecting the Organoleptic Characteristics of Coffee. II: Postharvest Processing Factors

“…Generally, aldehydes and sulfur compounds are the only degradation products of amino acids/proteins, as compared to furans, cyclotenes, pyrans, acids, and carbonyl compounds, which are simple sugar fragmentation products. But it has been found that protein content also controls the amount of sugar degradation products, because proteins/amino acids usually catalyze various sugar degradation reactions during the Maillard reaction (Hwang, Chen, & Ho, ). Detailed interactions of volatiles both from sugars and proteins have been discussed (above and below) from different perspectives to a lesser or greater degree, so here we will only describe the role of protein‐bound amino acids on the induction of sugar degradation.…”

“…Protein‐bound amino acids also influence the physical and sensory characteristics of coffee by altering its profile of volatiles. Different protein levels in green beans not only produce different levels of protein‐based odorants, but they also produce different levels of furan and pyrazine volatiles (Hwang et al., ). Hwang and coworkers removed the protein from coffee beans and studied the effect of proteins by adding different proteins in an ideal roasting system.…”

“…The decrease in furans may be due to less degradation of polysaccharides, while higher protein levels lead to an increase in the breakdown of amino acids that take part in Maillard reactions, and a rise in pyrazine levels. As CGAs and proteins are also involved in melanoidin formation, protein content also influences roast color, and increased protein content gives a lighter roast color (Hwang et al., ). The reason behind this lighter color is that proteins participate in complex color pigment formation reactions by condensing carbonyl compounds to yield cross‐linked or polymerized color products.…”

“…The reason behind this lighter color is that proteins participate in complex color pigment formation reactions by condensing carbonyl compounds to yield cross‐linked or polymerized color products. The addition of proteins also gives rise to high levels of other volatiles such as methylacetate, acetic acid, 2‐furfuryl alcohol, maltol, 2,5‐dihydro‐3,5‐dihydroxy‐6‐methyl‐4H‐pyran‐4‐one, 3,5‐dimethyl‐1,2,4‐trithiolane, 2‐cyclohexen‐1‐one until a further increase in protein content (beyond 50%) results in the suppression of sugar degradation products (Hwang et al., ). So, the protein content of coffee plays a vital role in its sensory/quality attributes by contributing a distinct type/level of volatiles after roasting.…”