Key Aroma Compounds of Dark Chocolates Differing in Organoleptic Properties: A GC-O Comparative Study

Abstract

Dark chocolate samples were previously classified into four sensory categories. The classification was modelled based on volatile compounds analyzed by direct introduction mass spectrometry of the chocolates' headspace. The purpose of the study was to identify the most discriminant odor-active compounds that should characterize the four sensory categories. To address the problem, a gas chromatography-olfactometry (GC-O) study was conducted by 12 assessors using a comparative detection frequency analysis (cDFA) approach on 12 exemplary samples. A nasal impact frequency (NIF) difference threshold combined with a statistical approach (Khi 2 test on k proportions) revealed 38 discriminative key odorants able to differentiate the samples and to characterize the sensory categories. A heatmap emphasized the 19 most discriminant key odorants, among which heterocyclic molecules (furanones, pyranones, lactones, one pyrrole, and one pyrazine) played a prominent role with secondary alcohols, acids, and esters. The initial sensory classes were retrieved using the discriminant key volatiles in a correspondence analysis (CA) and a hierarchical cluster analysis (HCA). Among the 38 discriminant key odorants, although previously identified in cocoa products, 21 were formally described for the first time as key aroma compounds of dark chocolate. Moreover, 13 key odorants were described for the first time in a cocoa product.Molecules 2020, 25, 1809 2 of 32 Thus, quality attributes of dark chocolate produced from Vietnamese cocoa were recently investigated [2], as well as the influence of the cocoa variety on the fermentation step studied [3][4][5], influence of the cocoa origin on the cocoa flavor examined [6][7][8][9], and the link between the origin and process searched for [10]. The process, starting with fermentation [11][12][13][14][15][16] and followed by drying [17] and roasting [18][19][20][21][22][23] steps, has been the subject of many studies. Specialized reviews and treatises gathered such knowledge [1,[24][25][26].Among these investigations, studies aiming to identify the only aroma-active compounds in dark chocolate (the dark chocolate key aroma compounds) are scarce. Nevertheless, some important gas chromatography-olfactometry (GC-O) studies, completed by GC-MS, allowed identification of the major dark chocolate key aroma compounds. Thus, the influence of conching was examined, with the aim of identifying the key odorant compounds in dark chocolate [27]. Aroma-active compounds in dark and milk chocolate in relation to sensory perception were investigated [28], and recently, key aroma compounds in two commercial dark chocolates with high cocoa contents were characterized [29]. As already cited, the major results are reported in reviews on cocoa and cocoa products [24][25][26] as well as in a specialized treatise dedicated to chocolate [1].Direct injection mass spectrometry (DIMS) methods, such as proton transfer reaction mass spectrometry (PTR-MS), have been used in some studies conducted on dark chocolates. Their obje...

Fermentation Enhanced Biotransformation of Compounds in the Kernel of Chrysophyllum albidum

“…An intermediate (I-3) in this study was one of the several derivatives of butanoic acid. The butanoic acid and the associated derivative were intermediates for fermentation [ 44 , 45 , 46 ]. This particular derivative (I-3) of butanoic acid was linked to fermentation for the first time in this study.…”

Multiblock Analysis to Relate Polyphenol Targeted Mass Spectrometry and Sensory Properties of Chocolates and Cocoa Beans

“…The present study aimed at exploring the relationships between chocolate sensory and polyphenol data and between cocoa and chocolate polyphenol compositions. The link between the chocolate polyphenols and sensory date is rather weak, consistent with the large impact of aroma compounds on sensory pole discrimination [ 1 , 2 ]. The CCSWA multiblock method coupling sensory data and chocolate polyphenol data differentiated the four sensory core poles, even in a better way than using sensory data alone, meaning that the two datasets contained relevant and complementary information.…”

“…A wide range of molecules causes the flavor perceived while tasting dark chocolate. Volatile compounds [ 1 , 2 , 3 , 4 ], including pyrazines [ 5 , 6 , 7 , 8 ], and nonvolatile compounds such as fatty acids [ 9 ] and polyphenols are directly involved in the chocolate flavor (taste and odor). Both the composition of the beans and the different parameters applied along the chocolate-making process have an influence on the chocolate flavor [ 10 , 11 , 12 , 13 , 14 ].…”

Special Issue “Volatile Compounds and Smell Chemicals (Odor and Aroma) of Food”

“…Six of the research papers were mainly focused on the sensory aspects related to volatile compounds [ 1 , 2 , 3 , 4 , 5 , 6 ], and another six papers investigated aspects related to processing [ 7 , 8 , 9 ], five papers were more oriented to the quality of the products [ 10 , 11 , 12 , 13 , 14 ], cultivation practice [ 15 ] and storage [ 16 , 17 ], two further papers were more focused on measurement techniques and procedures [ 18 , 19 ]. Lastly, the two review papers reviewed the sensory characteristics (flavour and texture) linked to a physiological disorder of apple, namely watercore [ 20 ] and the influence of ruminant diet on the volatile flavour compounds in cheese [ 21 ].…”

“…Deuscher et al [ 3 ] used gas chromatography–olfactometry to classify dark chocolates differing in organoleptic properties by the key aroma compounds. Thirty-eight discriminant key odorants were identified, 13 of which were described for the first time in a cocoa product.…”