EFFECT OF THE ADDITION OF COCOA SWEATINGS AND TIME OF FERMENTATION IN FLAVOR COMPOUNDS AND SENSORY PERCEPTION OF COCOA

Restricted (Penn State Only)
- Author:
- Meneses Marentes, Nixon
- Graduate Program:
- Food Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 03, 2022
- Committee Members:
- Robert Roberts, Program Head/Chair
Helene Hopfer, Thesis Advisor/Co-Advisor
Greg Ziegler, Committee Member
Misha T Kwasniewski, Committee Member - Keywords:
- cocoa
flavor
volatiles
non-volatiles
sensory analysis - Abstract:
- The fruit seeds of the Theobroma cacao L. plant are the raw material for chocolate products, and their processing contributes significantly to the characteristic cocoa flavor. Cocoa processing includes fermentation, drying, and roasting, and depending on the final product also grinding, mixing, tempering and molding. During certain processing steps, such as fermentation, drying, and roasting, a chain of numerous chemical reactions transforms bean constituents into flavor compounds in the final cocoa product. Flavor compounds are classified as volatile and non-volatile compounds that are able to elicit basic taste, smell, and/or mouthfeel sensations. Monitoring their changes along the processing steps provides key information about cocoa flavor, which is one of the main drivers of consumption and purchase of cocoa products. During fermentation, the fruit flesh, the so-called cocoa pulp, serves as a substrate for biochemical transformation, including the production of ethanol, lactic acid and acetic acid, alongside other important flavor compounds and precursors. The kinetics of these compounds, and correspondingly, final flavor, are affected by the microbial communities at play, including yeasts, acetic and lactic acid bacteria. Despite some strategies for altering the pulp and thus, shifting cocoa fermentation kinetics, have been explored (such as cocoa pod storage, pre-drying of cocoa seeds, de-pulping of cocoa seeds, etc.), the collection and back-addition of the cocoa pulp draining, the so called cocoa sweatings (CS) during fermentation have not been studied. CS are the lixiviate produced mainly during early stages of cocoa bean fermentation and result from de-pectination of the cocoa pulp, which releases water and other components such as fermentable sugars, pectin, and organic acid from the pulp. CS are typically removed from the fermentation system through drainage, but CS could provide additional substrates during cocoa bean fermentation if not drained away. The addition of CS thus could enhance flavor precursor formation, and consequently, change final flavor composition in cocoa, however, this has not been studied so far. This thesis therefore aims to determine the effect of the addition of CS to cocoa fermentation compared to conventional cocoa fermentation (i.e., without the addition of CS) on cocoa flavor by measuring volatile and non-volatile compounds in unroasted cocoa powder and roasted cocoa liquor. A second aim investigates the effect of the addition of CS (vs. no addition) on fermentation kinetics at later stages, comparing 5, 6 and 7 days of fermentation, by measuring volatile and non-volatile compounds in unroasted cocoa powder and roasted cocoa liquor. Last, this study also assessed the effect of the addition of CS during fermentation on sensory perception of roasted cocoa liquor samples using regular chocolate consumers. The results of this study showed that the addition of CS produced in the first 18 h of fermentation significantly changed the flavor composition of both unroasted cocoa powder and roasted liquor. However, the addition of CS during fermentation did not always increased the content of compounds, and further, fermentation time (5, 6, or 7 days) was also a significant factor. Fat content increased minimally by 0.3 and 0.4% with the addition of CS in unroasted cocoa powder and roasted cocoa liquor respectively, regardless time of fermentation. In terms of volatile compounds, 48 compounds were tentatively identified in unroasted cocoa powder but only 27 of these showed significant differences between samples made with and without the addition of CS and/or different fermentation times (5, 6, 7 days). Within these 27 most discriminating compounds, it is suggested that the addition of CS may serve as some type of stabilizer in the formation of furans over fermentation time in unroasted cocoa powder: In cocoa powder fermented without the addition of CS furans significantly decreased over fermentation time, while furans content in unroasted cocoa powder fermented with the addition of CS did not differ significantly between 5, 6, and 7 days of fermentation. In roasted cocoa liquor, 57 compounds were tentatively identified and 37 of those were classified as most discriminating between samples fermented with vs. without the addition of CS and/or for 5, 6 or 7 days of fermentation. Based on the results, the addition of CS again played a protective role over fermentation time for several compounds, including ethylidene-benzeneacetaldehyde, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, 4-methyl-2-hexanone, acetophenone, furfural, 4-butyrolactone and pantolactone, while these same compounds showed a significant decrease in content with increasing fermentation time in roasted cocoa liquor fermented without the addition of CS. In terms of non-volatile compounds, the addition of CS during fermentation led to unroasted cocoa powders with significantly higher contents of isoquercetin and caffeine. Additionally, cocoa powders fermented with the addition of CS had more stable (over fermentation time) concentrations of trans-clovamide, (-)-epicatechin, procyanidin B2, and isoquercetin. This again implies that the addition of CS during fermentation may stabilize polyphenol and alkaloid levels in unroasted cocoa powder over fermentation time. In roasted cocoa liquors, the addition of CS during fermentation led to samples with significantly higher content of (-)-epicatechin and procyanidin B2. Furthermore, the addition of CS stabilized the contents of cyclo(L-Leu-L-Pro), cyclo(Pro-Val), (-)-epicatechin, and procyanidin B2 over time compared to roasted cocoa liquors fermented without the addition of CS, where levels of cyclo(L-Leu-L-Pro) and cyclo(Pro-Val) increased, while (-)-epicatechin, and procyanidin B2 significantly decreased with increasing fermentation time (5 vs. 6 vs. 7 days). Using triangle tests, regular chocolate consumers were able to perceive significant differences in roasted cocoa liquor samples due to the addition of CS during fermentation, fermentation time, and the interaction between the two factors. Roasted cocoa liquor samples fermented with the addition of CS were perceived as significantly different from samples fermented without CS only after 5 days of fermentation (43 correct out of 99, p = 0.02). Based on open comments collected from those that correctly identified the odd sample, the addition of CS could potentially lead to a more bitter-tasting cocoa liquor after 5 days of time of fermentation. Conversely, cocoa liquors fermented with and without the addition of CS after 7 days were similar (with 9% distinguishers; beta = 10%). For roasted cocoa liquor samples fermented with the addition of CS sensory similarity could be concluded between the 5-day and 7-day fermentation treatments (only 4% distinguishers; beta = 10%), which implies that the sensory perception in samples with addition of CS was not affected by time of fermentation. In contrast, cocoa liquors fermented without the addition of CS for 5 vs. 7 days were perceived as significantly different (43 correct out of 101; p = 0.03). Open comment analysis of distinguishers indicated that the cocoa liquor fermented for 5 days without the addition of CS was less bitter than the cocoa liquor after 7 days. Last, for the interaction test (5 day of fermentation with the addition of CS vs. 7 day of fermentation without the addition of CS) sensory similarity could be concluded (0% distinguishers, beta = 10%). Therefore, the results of this study showed that cocoa liquors produced with the addition of CS are perceptually similar after 5 days of fermentation to cocoa liquors fermented without the addition of CS after 7 days of fermentation. This could be related to the protective effect of CS identified in certain volatile and non-volatile compounds. This potential protective effect of CS may be related to the changes in acidification of the cocoa fermentation mass when CS are added. To test this, further work is needed to characterize the CS as well as the differences in fermentation kinetics and fermentation microbiome when CS are added during fermentation. This exploratory study showed that the addition of CS and the time of fermentation both affect flavor composition of unroasted and roasted cocoa and sensory perception of roasted cocoa. Further studies are needed, such as sampling a broader range of time of fermentation (e.g., 3 days), and screening of flavor precursors to gain insights into the mechanisms how the addition of CS affects cocoa flavor. Lastly, although this study potentially identified changes in perceived bitterness as the attribute that differentiated cocoa liquors with and without the addition of CS over time of fermentation, more targeted sensory methodologies such as descriptive analysis are necessary to determine the qualitative and quantitative effects of adding back CS to the fermentation mas on cocoa flavor attributes.