Cocoa (Theobroma cacao L.) pod husk: Renewable source of bioactive compounds

Highlights

• CPH is an important industrial waste from which no benefit has been taken yet.

• The investigation is limited to produce high-value-added products from CPH.

• Bio compounds such as dietary fiber, pectins, antioxidants and minerals can be obtained from CPH.

• Compounds from CPH may have applications in food industry, among others, because their potential health benefit.

Abstract

Background

Cocoa Pod Husk (CPH) is the main by-product from the coca industry constituting 67–76% of the cocoa fruit weight. This waste represents an important, and challenging, economic, environmental renewable opportunity, since ten tons of wet CPH are generated for each ton of dry cocoa beans.

Scope and approach

This review highlights the value that can be added to this industrial co-product to generate new pharmaceutical, medical, nutraceuticals or functional food products.

Key findings and conclusions

The quality and functionality of cocoa pod husk (CPH) has being improving through processing (fermentation, enzymatic hydrolysis, and combustion, among others), guiding to their use as source of volatile fragrance compounds, lipase extraction, skin whitening, skin hydration and sun screening, ruminants’ food, vegetable gum, organic potash, antibacterial and nanoparticles synthesis with antioxidant and larvicidal activities. However, their exploration to produce high-value-added products, specially for the food industry, is limited as well as their potential health benefits. Cocoa pod husk, the main by-product from cacao industry (up to 76%), is an abundant, inexpensive, and renewable source of bioactive compounds like dietary fiber, pectin, antioxidant compounds, minerals and theobromine, justifying their valorization. This review highlights the value addition that can be achieved with this valuable industrial co-product to generate new pharmaceutical, medical, nutraceuticals or functional food products.

Introduction

Theobroma cacao L. is claimed to be the only commercially cultivated and most prominent in the market among the 22 species of the Theobroma genus (World Agriculture, 2011). The Theobroma cacao tree probably originated from divergent areas in Central and South America; the Upper Amazon region (10,000–15,000 years ago), the upper Orinoco region of north east Colombia and North West Venezuela, the Andean foothills of North West Colombia, Central America from southern Mexico (Chiapas-Usumacinta) to Guatemala (Young, 1994). However, Central and South American countries account for only about 14% of the current (2016, latest available data) world cocoa production compared to those from African countries (⅔ of world production) (FAOSTAT, 2018). Three countries, Cote D'Ivoire, Ghana and Indonesia together cultivate and produce 61 and 67%, respectively of globally traded cocoa, whereas the top ten countries account for ∼93% of total world cocoa production (Table 1). Global cocoa production is estimated at 4.59 million tonnes for 2017/2018 (ICCO, 2018). In 2016, the annual production of cocoa, in decreasing order, by the eight largest cocoa producing countries were Côte D'Ivoire, Ghana, Indonesia, Nigeria, Ecuador, Cameroon, Brazil and Malaysia. These countries together produced about 4.23 million tonnes, representing ∼95% of the world production (ICCO, 2015, p. 72).

The cocoa bean constitutes one third (33%) of the fruit weight, leaving behind 67% of the fruit as CPH as a waste by-product (Oddoye, Agyente-Badu, & Gyedu-Akoto, 2013) (Fig. 1). In other words, ten tons of wet CPH are generated for each ton of dry cocoa beans, thereby representing a serious disposal problem and an underexploited resource (Vriesmann, Amboni, & Petkowicz, 2011). Pods are fully developed (100–350 mm long, 0.2–1 kg wet weight) from pollinated flowers after 5–6 months. Three of the major cocoa diseases (black pod, pod rot and cocoa pod borer), also known as the disease trilogy (Evans, 2007) affect the pod specifically resulting in significant crop loss (Fowler & Coutel, 2017). Several initiatives have therefore been undertaken to counter the severe crop loss, for example, development of varieties with thicker cuticle that are more resistant to the common black pod rot and/or other pathogens (Fowler & Coutel, 2017). Pod size, type and index (>60 pods/tree, low disease incidence) are discriminating morphological characteristics among cocoa genotypes and therefore variation on pod traits (mainly pod size; length, width, thickness) may be associated with different morpho-geographic groups (Ballesteros, Logos & Ferney, 2015).

The pod has been described as a natural laminated material consisting of three distinctly different layers: epicarp, mesocarp and endocarp (outer, middle and inner pericarp, respectively) (Fig. 1). The endocarp is a soft whitish tissue protecting the delicate cocoa beans in a well-lubricated inner chamber; the mesocarp displays a hard-composite structure able to hold the cocoa beans in place even under high impact; and the outermost relatively soft layer is the yellow cover (when ripe) that is directly exposed to sunshine, after which it turns black indicating rot due to degradation (Babatope, 2005). These three distinct layers have been analyzed for their chemical composition and compared to the whole CPH when incorporated as feed component in broiler chick diets (Sobamiwa & Longe, 1994). High proportion of ash (47% CPH), hemicellulose (50%) and minerals (K, Ca and P) (41–66%) predominated in the epicarp; fiber (crude, NDF and ADF-44-48%) and cellulose (53%) in the mesocarp; protein (50%), crude fat (50%) and pectin (59%) in the endocarp (Table 2). The epicarp was the most limiting portion of CPH in the feeding trial, presumably due to the antagonistic inhibitory effect of lignin and pectin on CPH utilization in broiler diets (Sobamiwa & Longe, 1994).

Cocoa pod vary in color (from green [Forastero] to red [Criollo] or variable [Trinitario, the Forastero x Criollo hybrid]) and thickness when ripe depending on their clone. Pod color is a reflection of the exocarp (the outer 1–3 mm layer fruit tissue of pods harvested 18 weeks after pollination [18WAP]). This exocarp accumulates high levels of soluble and insoluble proanthocyanidins [PAs] (170 and 8 mg/g dw, respectively) compared with flowers, leaves and seeds due to highly expressed PAs synthesis genes [anthocyanidin synthase (TcANS), anthocyanidin reductase (TcANR) and leucoanthocyanidin reductase (TcLAR)]. Furthermore, epicatechin and catechin contents in the exocarp (18WAP) were: ∼30 and 0.5 mg/g dry weight (dw), respectively (Liu, Shi, Maximova, Payne, & Guiltinan, 2013); such information is unavailable for the pericarp.