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Understanding the Formation of CO2 and Its Degassing Behaviours in Coffee

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Title: Understanding the Formation of CO2 and Its Degassing Behaviours in Coffee
Author: Wang, Xiuju
Department: Department of Food Science
Program: Food Science
Advisor: Lim, Loong-Tak
Abstract: In the present study, the effect of roasting temperature-time conditions on residual CO2 content and its degassing behaviours in roasted coffee was investigated. The results show that the residual CO2 content in the roasted coffee beans was only dependent on the degree of roast and independent on the roasting temperature applied. However, CO2 degassing was shown significantly faster (p<0.05) in roasted coffee processed with high-temperature-short-time (HTST) than those roasted with low-temperature-long-time (LTLT) process. Moreover, the CO2 degassing rate increased with the degree of roast. CO2 degassing in ground coffee was significantly faster than in whole beans with the rate highly dependent on the grind size and roasting temperature, but less dependent on the degree of roast. CO2 degassing rate increased with the increasing of environmental temperature and relative humidity. Although CO2 degassing has been a challenging problem in the coffee industry for decades, there is still no clear understanding of precursors of CO2. In the present study, the hypothesis of “chlorogenic acid (CGA) is the principal precursor of CO2” was tested. Although strong negative linear correlation (R2>0.9) between total CGA and residual CO2 content during coffee roasting was detected, and vanishing of IR bands of the C=O group in caffeic acid and quinic acid moieties during heating of pure CGA at coffee roasting temperature was observed, the quantification analysis of CO2 generation from pure CGA heating indicated only ~ 8% yields at 230°C, which led us to conclude that CGA was one of the CO2 precursors but not the principal one. Accordingly, an alternate idea was put forward, hypothesizing that Maillard reaction could account for the CO2 formed. Roasting studies of glycine-sucrose simple models showed that large amount of CO2 was formed from Maillard reaction under coffee roasting conditions, confirming the importance of Maillard reaction in CO2 formation in roasted coffee. The isolation and roasting studies of green coffee fractions showed that CO2 was generated from various green coffee components, including water insoluble proteins and polysaccharides. Around 50% of CO2 was formed from lower molecular weight compounds with this fraction representing ~25% of green coffee by weight.
Date: 2014-05
Rights: Attribution-NonCommercial-NoDerivs 2.5 Canada

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