On-farm implementation of a starter culture for improved cocoa bean fermentation and its influence on the flavour of chocolates produced thereof

Abstract

Cocoa bean fermentations controlled by means of starter cultures were introduced on several farms in two different cocoa-producing regions (West Africa and Southeast Asia). Two starter culture mixtures were tested, namely one composed of Saccharomyces cerevisiae H5S5K23, Lactobacillus fermentum 222, and Acetobacter pasteurianus 386B (three heaps and one box), and another composed of L. fermentum 222 and A. pasteurianus 386B (seven heaps and one box). In all starter culture-added cocoa bean fermentation processes, the inoculated starter culture species were able to outgrow the natural contamination of the cocoa pulp-bean mass and they prevailed during cocoa bean fermentation. The application of both added starter cultures resulted in fermented dry cocoa beans that gave concomitant milk and dark chocolates with a reliable flavour, independent of cocoa-producing region or fermentation method. The addition of the lactic acid bacterium (LAB)/acetic acid bacterium (AAB) starter culture to the fermenting cocoa pulp-bean mass accelerated the cocoa bean fermentation process regarding citric acid conversion and lactic acid production through carbohydrate fermentation. For the production of a standard bulk chocolate, the addition of a yeast/LAB/AAB starter culture was necessary. This enabled an enhanced and consistent ethanol production by yeasts for a successful starter culture-added cocoa bean fermentation process. This study showed possibilities for the use of starter cultures in cocoa bean fermentation processing to achieve a reliably improved fermentation of cocoa pulp-bean mass that can consistently produce high-quality fermented dry cocoa beans and flavourful chocolates produced thereof.

Introduction

Selected functional starter cultures are already widely implemented in several fermented food productions, such as alcoholic beverages, (sourdough) breads, fermented dairy products, and fermented sausages (Leroy and De Vuyst, 2004). However, cocoa bean fermentations are still spontaneous, uncontrolled, on-farm processes that generally result in end-products of variable quality (Beckett, 2009; De Vuyst et al., 2010a; Schwan and Wheals, 2004). A good quality of fermented dry cocoa beans is correlated with good agricultural and post-harvest practices on the farms, encompassing plant breeding, cocoa pod/bean selection, placenta removal before fermentation, mixing of the fermenting cocoa pulp-bean mass, correct drying, and maintenance of fermentation and drying equipment (Papalexandratou, 2011; Papalexandratou et al., 2011a). Furthermore, the quantity of the cocoa crop has declined over the past years (Anonymous, 2009a).

When good agricultural and fermentation practices are applied, a restricted yeast (mainly Hanseniaspora opuntiae and Saccharomyces cerevisiae), lactic acid bacteria (LAB, mainly Lactobacillus fermentum), and acetic acid bacteria (AAB, Acetobacter pasteurianus) species diversity dominates the cocoa bean fermentation process consecutively and leads to high-quality fermented dry cocoa beans (Camu et al., 2007, 2008; Nielsen et al., 2007; Daniel et al., 2009; Garcia-Armisen et al., 2010; Papalexandratou, 2011; Papalexandratou et al., 2011a,b; Papalexandratou and De Vuyst, 2011). Well-performed spontaneous cocoa bean fermentations are even independent of the fermentation method and cocoa-producing region (Papalexandratou, 2011; Papalexandratou et al., 2011a,b). Many chocolate-producing companies and organisations invest more in intensive training programs on sustainable cocoa farming practices to reach the customers’ demand for superior quality cocoa and chocolate (Anonymous, 2009a,b). Also, they try to improve the living conditions of the cocoa farmers and their families by producing cocoa in a socially and environmentally responsible way (Anonymous, 2009b). Additionally, by carefully controlling the cocoa bean fermentation process, in particular by the use of defined microorganisms, the cocoa farmers will be able to provide consistent, predictable, and high-quality fermented dry cocoa beans and, hence, get a better price for their well-fermented dry cocoa beans and better living conditions for themselves and their families (De Vuyst et al., 2010a).

Up to now, no starter culture has yet been developed for the commercial production of well-fermented cocoa beans, mainly due to lack of knowledge on the cocoa bean fermentation process in particular, and costs, maintenance of the starter culture, a lacking inoculation procedure for small-scale fermentation processes, and logistics in (sub)tropical regions in general (De Vuyst et al., 2010a; Holzapfel, 2002). Nevertheless, successful use of a defined microbial starter culture composed of yeast (Saccharomyces chevalieri, synonym of S. cerevisiae), LAB (Lactobacillus delbrueckii subsp. lactis and Lactobacillus plantarum), and AAB (Acetobacter aceti and Gluconobacter oxydans) has been reported in the case of Brazilian cocoa bean box fermentations, albeit that these fermentations were not accelerated neither had the chocolates produced from the concomitant fermented dry cocoa beans an improved flavour (Schwan, 1998). Also, the influence of a LAB/AAB starter culture on the cocoa bean fermentation process and on the flavour of the chocolates produced from the concomitant fermented dry cocoa beans has been shown (De Vuyst et al., 2010b). Therefore, the introduction of starter cultures composed of desirable strains of the prevailing microbial species will be able to improve and even to control and steer the cocoa bean fermentation process. In the past, only specific starter cultures, in particular (pectinolytic) yeast starter cultures, have been selected for the enhanced production of cocoa pulp sweatings to produce cocoa pulp-derived products, such as wines, spirits, vinegars, and jams, without influencing the quality of the fermented dry cocoa beans (Buamah et al., 1997; Dias et al., 2007; Dzogbefia et al., 1999; Leal et al., 2008; Schwan et al., 1997).

Recently, the functional roles and the physiological adaptations of LAB and AAB species most frequently found in the cocoa pulp ecosystem have been reported through laboratory fermentations of selected cocoa-specific LAB and AAB strains in cocoa pulp simulation media (Lefeber et al., 2010, Lefeber et al., 2011b). Also, the prevalence of these strains as a LAB/AAB starter culture has been tested through starter culture-added cocoa bean fermentations carried out in vessels on 20-kg scale (Lefeber, T., Gobert, W., Camu, N. and De Vuyst, L., unpublished results).

The present study aimed at the implementation of a defined LAB/AAB starter culture, whether or not in the presence of an added yeast strain, for an improved cocoa bean fermentation process at multiple farms in West Africa (Côte d’Ivoire and Ghana) and Southeast Asia (Malaysia). Therefore, cocoa bean heap and box fermentations initiated with yeast and/or LAB and AAB strains compared with spontaneous cocoa bean heap (Ghana) and box (Malaysia) fermentations, respectively, were analysed multiphasically, encompassing microbiological analysis (culture-dependent and culture-independent) and metabolite target analysis. Chocolates from the concomitant fermented dry cocoa beans were produced to investigate the influence of the use of a starter culture on their flavour, independent of cocoa-producing region and/or fermentation method.