Gas Chromatography/Olfactometry and Electronic Nose Analyses of Retronasal Aroma of Espresso and Correlation with Sensory Evaluation by an Artificial Neural Network

Abstract

To develop a method for evaluating and designing the retronasal aroma of espresso, sensory evaluation data was correlated with data obtained from gas chromatography/olfactometry (GC/O, CharmAnalysis™) and from an electronic nose system αFOX4000 (E-nose). The volatile compounds of various kinds of espresso (arabica coffee beans from 6 production countries: Brazil, Ethiopia, Guatemala, Colombia, Indonesia, and Tanzania; 3 roasting degrees for each country: L values, 18, 23, and 26) were collected with a retronasal aroma simulator (RAS) and examined by GC/O and E-nose. In addition, sensory descriptive analysis using a 7-point scale for RAS effluent gas was performed by 5 trained flavorists using sensory descriptors selected based on the frequency in use and coefficient of correlation. The charm values of 10 odor descriptions obtained from GC/O analysis exhibited the significant (P < 0.05) differences among both roasting degrees and origins. Also, linear discriminant analysis (LDA) on the E-nose-sensor resistances and factor analysis on the sensory evaluation scores showed that the differences of aroma characteristics among the roasting degrees were larger than those among the origins. Based on an artificial neural network (ANN) model applied to the data from GC/O analyses and sensory evaluations, the perceptual factor of the RAS aroma was predicted to be mainly affected by sweet-caramel, smoke-roast, and acidic odors. Also, 3 metal oxide semiconductor sensors (LY2/Gh, P30/1, and T40/1) of E-nose were selected for analyses of RAS aroma and correlated with the sensory descriptive scores by the ANN to support sensory evaluation.

Volatile compounds profiles in unroasted Coffea arabica and Coffea canephora beans from different countries

“…2-propionylpyrrole (1H-Pyrrole) was found in roasted coffee (Toci & Farah, 2008), in green Mexican coffee (Cantergiani et al, 2001) and in black coffee beans (Agresti et al, 2008). Dimethyl trisulfide marked in our study by the e-nose was also shown in the study by Blank (2002) in roasted and ground coffee and in roasted coffee by Michishita et al (2010).…”

Effect of Milk Components on Release of Retronasal-aroma Compounds from Coffee with Milk

“…An RA simulator (RAS) developed by Roberts and Acree (1995) as one of various mouth models (van Ruth et al, 1994;Roberts and Acree, 1995;Elmore and Langley, 1996) has been used to analyze coffee aromas (Michishita et al, 2010;Watanabe et al, 2012;Akiyama et al, 2014) and how the amount of milk added affects the aroma of coffee beverages (Akiyama et al, 2009). …”

The compositional basis of coffee flavour

“…As known contributors the boquet of wines and beers, these monoterpenes are also likely to influence coffee flavour. Indeed, linalool is reported to contribute to a woody or flowery note in coffee depending on concentration (Bonnländer et al, 2006 (Blank et al, 1992); 3 (Michishita et al, 2010), 4 , 5 (Mosciano, 2016), 6 (Akiyama et al, 2007), 7 (Milo and Grosch); 8 (Belitz et al, 2009), 9 (Burdock, 2010), 10 (Salo, 1970), 11 , 12 (Buttery and Ling, 1997), 13 (Czerny et al, 2008), 14 (Holscher and Steinhart, 1992).…”

“…In an attempt to unlock the compositional basis of coffee flavour there have been numerous studies involving the extraction and analysis of the volatile profiles of coffee from green bean to roasted ground bean and brew, from espresso style to instant coffee (Akiyama et al, 2007, Akiyama et al, 2003, Blank et al, 1992, Borém et al, 2013, Czerny et al, 1996, Kumazawa and Masuda, 2003, Michishita et al, 2010, Ribeiro et al, 2009, Ribeiro et al, 2010. The overriding objective of these studies has been to identify those volatiles that are key contributors to the flavour of coffee.…”

“…As important example is 2-furfurylthiol, which is reported to have a very low sensory threshold (0.01 ppb) and exhibits a strong roasted aroma (Blank et al, 1992). This compound is considered by many as a key impact aroma compound in coffee and has been reported widely in roasted and brewed coffee (Akiyama et al, 2007, Blank et al, 1992, Holscher and Steinhart, 1992, Michishita et al, 2010. Other thiols, such as 2-methyl-3-furanthiol and 3-methyl-2-butene-1-thiol, are also present in coffee and have very low sensory thresholds while exhibiting meaty characters (Akiyama et al, 2003, Blank et al, 1991, Blank et al, 1992.…”