Valorisation strategies for cocoa pod husk and its fractions

TLDR: In this paper, the main byproduct of the cocoa harvest, the pod husk (CPH), is used for animal feed, as a starting material for soap making and activated carbon.

Abstract: Cocoa pod husk (CPH) is the main by-product (ca. 70–75% weight of whole fruit) of the cocoa harvest, an important and economic crop in developing countries. It is a rich source of minerals (particularly potassium), fibre (including lignin, cellulose, hemicellulose and pectin) and antioxidants (e.g. phenolic acids). An existing practise is the return of CPH to soil with potential benefits (or disadvantages) for cocoa productivity and soil sustainability that have not been fully characterised. Currently, alternative low-value applications of CPH include its use as animal feed, as a starting material for soap making and activated carbon. Other biotechnological valorisation potentials for CPH and its fractions include the production of bio-fuels and their incorporation in food systems. Physical, chemical or biological pre-treatment approaches are needed in order to achieve desirable fractions in a cost-effective and sustainable manner for novel applications in food and non-food sectors.

Figures

Table 1: Chemical Composition of cocoa pod husk [9, 17-19]

Full text

Accepted Manuscript
Valorisation strategies for cocoa pod husk and its fractions
Fei Lu, Julia Rodriguez-Garcia, Isabella Van Damme, Nicholas Westwood, Liz
Shaw, James S. Robinson, Geoff Warren, Afroditi Chatzifragkou, Simon McQueen
Mason, Leonardo Gomez, Laura Faas, Kelvin Balcombe, Chittur Srinivasan, Fiorella
Picchioni, Paul Hadley, Dimitris Charalampopoulos
PII: S2452-2236(18)30071-3
DOI: 10.1016/j.cogsc.2018.07.007
Reference: COGSC 199
To appear in:
Current Opinion in Green and Sustainable Chemistry
Received Date: 25 June 2018
Revised Date: 9 July 2018
Accepted Date: 23 July 2018
Please cite this article as: F. Lu, J. Rodriguez-Garcia, I. Van Damme, N. Westwood, L. Shaw, J.S.
Robinson, G. Warren, A. Chatzifragkou, S. McQueen Mason, L. Gomez, L. Faas, K. Balcombe, C.
Srinivasan, F. Picchioni, P. Hadley, D. Charalampopoulos, Valorisation strategies for cocoa pod
husk and its fractions, Current Opinion in Green and Sustainable Chemistry (2018), doi: 10.1016/
j.cogsc.2018.07.007.
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Valorisation strategies for cocoa pod husk and its fractions
Fei Lu
1
, Julia Rodriguez-Garcia
1
, Isabella Van Damme
2
, Nicholas Westwood
3
, Liz Shaw
4
,
James S. Robinson
4
, Geoff Warren
4
, Afroditi Chatzifragkou
1
, Simon McQueen Mason
5
,
Leonardo Gomez
5
, Laura Faas
5
, Kelvin Balcombe
6
, Chittur Srinivasan
6
, Fiorella Picchioni
6
,
Paul Hadley
6
, Dimitris Charalampopoulos
1
1
Department of Food and Nutritional Sciences, University of Reading, UK
2
Mars Wrigley Confectionery UK Ltd, Slough, Berkshire, UK
3
School of Chemistry and Biomedical Sciences Research Complex, University of St
Andrews, UK
4
Department of Geography and Environmental Sciences, University of Reading, UK,
5
Department of Biology, University of York, UK
6
School of Agriculture Policy and Development, University of Reading, UK
Abstract
Cocoa pod husk (CPH) is the main by-product (ca. 70-75% weight of whole fruit) of the
cocoa harvest, an important and economic crop in developing countries. It is a rich source of
minerals (particularly potassium), fibre (including lignin, cellulose, hemicellulose and pectin)
and antioxidants (e.g. phenolic acids). An existing practise is the return of CPH to soil with
potential benefits (or disadvantages) for cocoa productivity and soil sustainability that have
not been fully characterised. Currently, alternative low-value applications of CPH include its
use as animal feed, as a starting material for soap making and activated carbon. Other
biotechnological valorisation potentials for CPH and its fractions include the production of
bio-fuels and their incorporation in food systems. Physical, chemical or biological pre-
treatment approaches are needed in order to achieve desirable fractions in a cost-effective and
sustainable manner for novel applications in food and non-food sectors.

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Keywords: Cocoa pod husk, valorisation, extraction, pre-treatment
1. Introduction
Cocoa (Theobroma cacao L) is an important and economic crop in developing countries. The
production of cocoa beans in 2016-2017 was 4.7 million tonnes worldwide [1]. Cote
D’Ivoire, Ghana and Indonesia are the top three producers of cocoa beans, contributing to
67% of the global production. Large quantities of underexploited by-products, including
cocoa pod husk (CPH) and pulp, are generated by removing the beans from the cocoa pods
[2]. CPH weighs about 75% of the whole fruit and is the main process by-product [3-5].
Figure 1: Fresh cocoa pod fruit (A and B) and dried CPH (C and D) from Indonesia. A:
Fresh cocoa pod fruit in which epicarp (in dark brown) has been partially peeled. B:
Transverse section of fresh cocoa pod fruit, with the illustration of the separate parts,
including epicarp, mesocarp, sclerotic part and endocarp. C: Freeze-dried CPH. D:
Milled freeze-dried CPH.
After removal of the cocoa beans, CPH is usually discarded on the farm and can function as
an organic fertiliser, a practice that adds organic matter to soil and enables the return of
nutrients to the soil and their recycling to plant-available forms after decomposition

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(discussed further in Section 3.1) [6*, 7]. However, untreated CPH left on the soil surface
may act as a source of inoculum for plant diseases such as black pod rot due to the presence
of Phytophthora spp. [8, 9]. Black pod rot causes an annual yield loss from 20% to 30%
worldwide, while individual farms may suffer an annual yield loss from 30% to 90% [10].
CPH is under-exploited as a renewable resource that is rich in dietary fibre, lignin and
bioactive antioxidants such as polyphenols [8]. Recovering these lignocellulosic fractions and
bioactive compounds may lead into the development of a profitable commodity and
subsequently this could bring revenue to farmers, thus promoting economic development [11,
12]. Bioconversion of CPH to added-value products, such as biomaterials for food and non-
food uses, it is also a potential approach to maintain the sustainability of cocoa production.
The opportunity of valorising CPH towards added-value applications is enormous, given its
high abundance and the fact that cocoa is mainly cultivated in developing countries. This
review will evaluate existing low-value applications of CPH and the value-added potential of
CPH and its fractions in food applications based on CPH’s chemical composition.
2. Chemical composition of cocoa pod husk
CPH comprises the epicarp, mesocarp, sclerotic part and endocarp (Figure 1). Table 1 shows
the chemical composition of an example of a CPH from Ghana. The CPH consists primarily
of fibrous materials including 19.7-26.1% cellulose, 8.7-12.8% hemicellulose, 14-28% lignin
and 6.0-12.6 % pectin. The epicarp is enriched with lignin, while the mesocarp contains
mainly (~50%) cellulose and the endocarp is rich in pectic substances [13]. Xylan,
arabinoxylan and arabinan are the main hemicellulose in CPH that have been deduced from
the high amount of isolable arabinose and xylose [14]. Other hemicelluloses such as
xyloglucans, galactomannans or (galacto) glucomannans can also be found in CPH [9].
Lignin is a complex aromatic heteropolymer, made from phenylpropane units (p-coumaryl,
coniferyl and sinapyl alcohols) and is strongly attached to cellulose and hemicellulose,
providing rigidity to the plant cell wall [15, 16]. Condensed tannins have highly polymerized
structures and could be bound to lignin in CPH with a dry weight content of 5.2% [8]. Pectin
that is associated with cellulose and hemicellulose is determined as uronic acids, contributing
to 6.7-12.4% of CPH [8, 9]. The ash content of CPH ranges from 6.4-8.4% w/w with a
variety of minerals. Significantly high amounts of K (2.8-3.8% w/w) are observed, followed
by Ca, Mg and P [9]. CPH is also a source of phenolic acids, ranging from 4.6 to 6.9g
GAE/100g.

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Table 1: Chemical Composition of cocoa pod husk [9, 17-19]
Composition Amount (%, w/w, dry weight)
Protein 7-10
Fat 1.5-2
Carbohydrates 32-47
Cellulose 19.7-26.1
Hemicellulose
(Xylan & arabinoxylan)
8.7-12.8
Lignin 14-28
Pectin 6.0-12.6
Ash 6.4-8.4
Minerals
K 2.8-3.8
Ca 0.25-0.46
Mg 0.11-0.25
P 0.19
Na 0.01-0.02
Fe 0.003-0.006
Phenolic content (g GAE
1
/100g) 4.6-6.9
1
Gallic acid equivalent
3. Low value applications of CPH
Fertiliser and soil organic matter
3.1
The high mineral content of CPH, particularly in K, Ca and P, offers the possibility for
partially substituting conventional fertilisers, based on research from Nigeria and Ghana
[5**, 17]. One study in Nigeria reported that combining CPH powder with basal phosphorus
fertiliser could achieve similar plant quality, seed yield and harvest index of black benniseed
cultivation, compared to NPK fertiliser (mixture of (NH
4
)
2
SO
4
, P
2
O
5
and K
2
O) [7]. Other
studies have focused on the use of CPH ash as a fertiliser; replacing up to 50% conventional
NPK fertiliser with CPH ash had a positive effect on grain yield and nutrients uptake in maize
production [20] and on fruit growth, yield and soil fertility in tomato production [21]. Such
eco-friendly applications could potentially replenish the shortage of expensive NPK fertiliser
due to limited distribution and marketing for fertiliser procurement in
developing countries
such as Ghana. Burning CPH to produce ash might also have additional benefits in terms of
improved farm sanitation and control of a potential source of inoculum for black pod rot
disease [20]. To demonstrate the economic feasibility of using CPH fertiliser in cocoa
farming, a study in Nigeria has compared the gross margin of cocoa production between

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Valorisation strategies for cocoa pod husk and its fractions" ?

In this paper, the main byproduct of the cocoa pod husk ( CPH ) is used as animal feed, as a starting material for soap making and activated carbon. 

Q2. What is the main purpose of the enzymatic delignification of biomass?

Enzymatic delignification of biomass utilises oxidases (laccases) and peroxidases (MnPs and LiPs) isolated from white rot fungi, to oxidise both the aromatic rings and aliphatic side chains and generate low-molecular weight compounds [48]. 

Q3. What is the main reason for the inclusion of pectin in food products?

Pectin is an important ingredient in food products because of its gelling, film-forming and thickening properties, which could provide texture enhancement and stability in food products [9, 54]. 

Q4. What is the common method of extracting phenolic compounds from CPH?

Supercritical fluid extraction (SFE), regarded as a green technology, was also used to extract phenolic compounds from CPH in a recent study [70]. 

Q5. What is the potential of CPH in value-added products?

CPH is also a potential source of phenolics/antioxidants, which could be employed as a natural ingredient in value-added products. 

Q6. What is the importance of delignification during the pulping process?

delignification is necessary during the pulping process for lignocellulosic materials such as CPH, in order to avoid the negative effects of lignin on paper performance and paper quality. 

Q7. What is the common method of removing cellulose from hemicellulose?

Steam explosion is a physical approach that can increase the pore size of lignocellulose materials and ultimately lead to hemicellulose solubilisation and hydrolysis [11]. 

Q8. What is the way to extract cellulose from corn?

One study reported that combining steam explosion with dilute sulfuric acid impregnation on wheat straw with high-lignin content significantly improved the cellulose conversion into fermentable sugars [47]. 

Q9. What is the effect of pre-treatment of CPH on the body mass of poultry?

recent studies have shown that the pre-treatment of CPH with multiple enzymes, i.e. Viscozyme and Pectinex [19] and fungus (Phanerochaete chrysosporium) [33], could increase CPH digestibility by about 30%, thus making it suitable for poultry as well as steers. 

Q10. What is the main reason for the use of CPH in soap making?

The successful usage of CPH as a starting material for commercial soap making would also be an alternative way to generating additional income for farmers. 

Q11. What is the main effect of the chemical composition of the lignocellulosic?

The quality of the pulp is directly affected by the chemical composition of the lignocellulosic materials, where a material with high cellulose (34%), low lignin (<30%) and low ash content is preferred [38]. 

Q12. What is the role of CPH in the development of the food industry?

As an important economic crop in developing countries, the valorisation of CPH and its fractions by developing end-user applications in the food and non-food sector is regarded as beneficial for several stakeholders, including farmers, industries, consumers and academic researchers. 

Q13. What is the need for a clean and sustainable technology to convert CPH into energy?

With the identification of product applications with a high commercial value, there is a need to develop/improve clean and sustainable technologies that are easy to process, cost-effective and environmentally friendly, to convert them into high value-added products. 

Q14. How many tonnes of soap could be made with CPH potash?

A market report in Ghana showed that 3 tonnes of liquid soap made by CPH potash could bring the profit of 63,000 Ghanaian cedi [17]. 

Q15. What is the argument that a subsidy-free biorefinery is needed to be?

however, the argument is being made that for a subsidy-free biorefinery to be economically viable, it is necessary to gain more value from the lignin component that arises from, for example, burning it [50, 51]. 

Q16. What is the effect of pre-treated CPH on the texture of bread?

The results showed that bread with CPH became denser and harder in texture indicating that the texture and quality of the food products are affected significantly by the functionality of fibre and its behaviour during food processing. 

Q17. What is the main reason why CPH potash is used in soap making?

Soaps made with CPH potash have great solubility, consistency, cleansing and lathering ability, compared to soaps made with chemical KOH [28]. 

Q18. What is the main reason for the commercialization of soap with CPH potash?

Results also showed that the commercialization of soap with CPH potash is highly feasible, and mainly driven by the demand for natural and less harsh toiletry products [17]. 

Q19. How much of the pre-treated CPH powder in a chocolate muffin could be improved?

Partially (25-75%) replacing vegetable oil with pre-treated CPH powder in a chocolate muffin could, for example, achieve higher moisture, a more tender and a crumbly texture, compared with control samples. 

Q20. What is the process of dissolving the biomass?

From a processing point of view, an initial step is the dissolution of the biomass in an alkali solution, i.e. 20% NaOH at high temperature to obtain a pulp. 

Q21. What is the potential of using CPH in the agricultural sector?

The above studies highlight the potential of utilising CPH in the agricultural sector as animal feed, in order to substitute costly conventional feeding ingredients and diminish any potential environmental effect by reducing CPH disposal on the farm.