Towards a Starter Culture for Cocoa Fermentation by the Selection of Acetic Acid Bacteria

Investigation of aromatic compounds and olfactory profiles in cocoa pulp fermentation using yeast-based starters: A Volatilomics and machine learning approach

The interaction and complex metabolism of microorganisms in cocoa pulp drive the fermentation process. To investigate this, four strains from spontaneous cocoa fermentation, including Hanseniaspora uvarum, Saccharomyces cerevisiae, Lactiplantibacillus plantarum, and Gluconobacter potus were combined to ferment cocoa pulp. Nineteen machine learning algorithms were run with the dataset of volatile compounds quantified by headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) against integrated olfactory evaluation to reveal metabolite-sensory attribute relationships. The models showed high prediction accuracy, ranging from 0.85 for sourness by Gradient Boost Machine to 0.28 for sweetness by linear regression. Ethyl esters, specifically ethyl octanoate and ethyl 9-decenoate, were found positive for aroma development. Polynomial regression, neural network modeling and gradient boosting decision trees highlighted the high carbohydrate consumption rate of S. cerevisiae, the pectin degradation ability of H. uvarum, and the synergy of lactic acid bacteria with G. potus. This study offers new insights into cocoa flavor and the development of fermentation starter cocktails.

The Health Impact of Cocoa from Cultivation to the Formation of Biogenic Amines: An Updated Review

Cocoa and chocolate are known for their health benefits, which depend on factors like cocoa variety, post-harvest practices, and manufacturing processes, including fermentation, drying, roasting, grinding, and refining. These processing methods can influence the concentration and bioavailability of bioactive compounds, such as polyphenols that are linked to cardiovascular health and antioxidant effects. Recent scientific research has led to the development of cocoa-based products marketed as functional foods. However, despite the growing interest in the functional potential of cocoa, the literature lacks crucial information about the properties of different varieties of cocoa and their possible implications for human health. Moreover, climate change is affecting global cocoa production, potentially altering product composition and health-related characteristics. In addition to polyphenols, other compounds of interest are biogenic amines, due to their role and potential toxic effects on human health. Based on toxicological data and recent research on the complex relationship between biogenic amines and cocoa fermentation, setting limits or standards for biogenic amines in cocoa and chocolate could help ensure product safety. Finally, new trends in research on biogenic amines in chocolate suggest that these compounds might also be used as quality markers, and that product formulation and process conditions could change content and diversity of the different amines.

Screening and characterizing indigenous yeasts, lactic acid bacteria, and acetic acid bacteria from cocoa fermentation in Hainan for aroma Development

Fermentation is crucial for inducing desirable flavor and aroma profiles in cocoa products. This research focused on identifying microbial strains isolated from spontaneous cocoa fermentation in Hainan through 16S and Internal Transcribed Spacer (ITS) sequencing. Pectinase activity was screened, and metabolic dynamics of sugars and organic acids were analyzed using high-performance liquid chromatography. Additionally, gas chromatography-mass spectrometry was employed for the quantification of volatile compounds. The fermentation potentials of isolated yeast, lactic acid bacteria, and acetic acid bacteria were analyzed from multiple perspectives. Pichia fermentans XY23.1 and Hanseniaspora uvarum XY23.1 exhibited significant pectinolytic activity, essential for breaking down pectin in cocoa pulp. Moreover, H. uvarum XY23.1, H. occidentalis XY23.1, Saccharomyces cerevisiae XY23.2, and P. fermentans XY23.1 were identified as producers of notable amounts of alcohols and esters, contributing sweet and floral notes to the fermentation profile. Furthermore, Levilactobacillus brevis exhibited strong fructophilicity, and Lactiplantibacillus plantarum strains showed high metabolic rates and lactic acid production abilities, crucial for enhancing fermentation efficiency. Assessment of growth rate and acid production performance revealed that Gluconobacter potus XY23.2 and Acetobacter oryzifermentans XY23.1 can produce less acid during rapid growth, avoiding flavor defects caused by excessive acidity. This study demonstrates the impact of various flavor compounds on the flavor characteristics of cocoa pulp. It highlights the potential of these microbial strains for use in starter culture cocktails, which can significantly improve the quality of cocoa products by enhancing desirable flavor and aroma profiles while maintaining balanced acidity. PRACTICAL APPLICATION: This study screened and characterized microorganisms isolated from the fermentation of Hainan cocoa (Trinitario) through a series of experiments, providing new insights for the future selection of cocoa fermentation starters.

Exploring volatile compounds and microbial dynamics: Kluyveromyces marxianus and Hanseniaspora opuntiae reduce Forastero cocoa fermentation time

Traditional cocoa bean fermentation is a spontaneous process and can result in heterogeneous sensory quality. For this reason, yeast-integrated starter cultures may be an option for creating consistent organoleptic profiles. This study proposes the mixture of Hanseniaspora opuntiae and Kluyveromyces marxianus (from non-cocoa fermentation) as starter culture candidates. The microorganisms and volatile compounds were analyzed during the cocoa fermentation process, and the most abundant were correlated with predominant microorganisms. Results showed that Kluyveromyces marxianus, isolated from mezcal fermentation, was identified as the dominant yeast by high-throughput DNA sequencing. A total of 63 volatile compounds identified by HS-SPME-GC-MS were correlated with the more abundant bacteria and yeast using Principal Component Analysis and Agglomerative Hierarchical Clustering. This study demonstrates that yeasts from other fermentative processes can be used as starter cultures in cocoa fermentation and lead to the formation of more aromatic esters, decrease the acetic acid content.

Investigating luxS gene expression in lactobacilli along lab-scale cocoa fermentations

Previous metagenomic analyses have suggested that lactobacilli present potential for Quorum Sensing (QS) in cocoa fermentation, and in the present research, laboratory scale fermentations were carried out to monitor the expression of luxS, a universal marker of QS. For that, 96 h-fermentations were studied, as follows: F0 (non inoculated control), F1 (inoculated with yeasts, lactic acid bacteria, and acetic acid bacteria), F2 (inoculated with yeasts and acetic acid bacteria), F3 (inoculated with yeasts only). The parameters evaluated were: plate counting, quantification of key enzymes and analysis of volatile organic compounds associated with key sensory descriptors, using headspace gas chromatography-mass spectrometry (GC-MS). Furthermore, QS was estimated by the quantification of the expression of luxS genes by Reverse Transcriptase Real-Time PCR. The results demonstrated that microbial succession occurred in pilot scale fermentations, but no statistical differences for microbial enumeration and α-diversity index were observed among experiments and control. Moreover, it was not possible to make conclusive correlations of enzymatic profile and fermenting microbiota, likely due to the intrinsic activity of plant hydrolases. Regarding to the expression of luxS genes, in Lactiplantibacillus plantarum they were active along the fermentation, but for Limosilactobacillus fermentum, luxS was expressed only at early and middle phases. Correlation analysis of luxS expression and production of volatile metabolites evidenced a possible negative association of Lp. Plantarum with fermentation quality. In conclusion, these data corroborate former shotgun metagenomic analysis by demonstrating the expression of luxS by lactobacilli in pilot scale cocoa fermentation and evidence Lp. Plantarum is the main lactic acid bacteria related to its expression.

Yeasts as Producers of Flavor Precursors during Cocoa Bean Fermentation and Their Relevance as Starter Cultures: A Review

During the fermentation of cocoa beans, the yeasts produce volatile organic compounds (VOCs). Through reactions associated with amino acid metabolism, yeasts generate important aroma precursors as acetate esters and fatty acid ethyl esters are essential in developing fruity flavors and aromas in the final product (usually chocolate). In addition, some yeasts may have pectinolytic and antifungal activity, which is desirable in the post-harvest process of cocoa. The main yeast species in cocoa fermentation are Saccharomyces cerevisiae, Pichia kudriavzevii, and Hanseniaspora opuntiae. These produce higher alcohols and acetyl-CoA to make acetate–esters, compounds that produce floral and fruity notes. However, there are still controversies in scientific reports because some mention that there are no significant differences in the sensory characteristics of the final product. Others mention that the fermentation of cocoa by yeast has a significant influence on improving the sensory attributes of the final product. However, using yeasts as starter cultures for cocoa bean fermentation is recommended to homogenize sensory attributes such as notes and flavors in chocolate.