Effect of the temperature on the kinetics of cocoa bean shell fat extraction using pressurized ethanol and evaluation of the lipid fraction and defatted meal
Introduction
Cocoa derivatives are extremely important inputs to the food industry, since chocolate-flavored food products are among the main consumer preferences, and a large number of food products use these derivatives as ingredients. In recent decades, the consumption of these products has been reported to increase (Jonfia-Essien et al., 2008), while the production of cocoa beans has reportedly decreased considerably in the last ten years. In four of the last ten years, deficits in the production of cocoa beans were observed, which left the market out of stock (International Cocoa Organization, 2018). In this scenario, one of the strategies to improve market supply is to identify and commercialize new products or find new applications for existing products and byproducts.
Part of the effort to identify other applications of cocoa and its products has focused on the utilization of the cocoa shell (CS). CS is a byproduct of the cocoa industry, and every year, hundreds of tons of this material is disposed of as waste, with the main application of this material being fuel for boilers (Okiyama et al., 2017). This use alone is sufficient reason for researchers find an applicable and gainful alternative for this byproduct. The use of CS as an additive in human foods has been reported in several studies. There are already patents for the application of CS in the food industry; however, most of these studies have addressed the use of CS as a source of dietary fiber and phenolic compounds with antioxidant activity (Okiyama et al., 2017, 2018).
The chemical composition of CS has been reported by several studies, showing that it also has significant contents of protein, ranging from 11 to 18%, and lipids, with highly variable values of 2 to 18.5% (Okiyama et al., 2017). Although several works report the chemical composition of CS, few references have been found describing more extensive characterization or the behavior of these compounds during the processing of CS.
It is known that the protein content of CS is very similar to that of cocoa nibs (Martín-Cabrejas et al., 1994). However, the production of CS protein concentrates is discouraged by Greenwood-Barton (1965), as most of the alpha-amino nitrogen is bound to polyphenols.
El-Saied et al. (1981) observed that the physical-chemical characteristics of lipids from CS (cocoa shell fat, CSF) and almond (cocoa butter) from the same roasted bean were extremely similar, with the exception of a higher acidity of CSF. This work by El-Saied et al. (1981) has been the only study to report the characteristics of cocoa bean shell fat; other investigations related to the composition of this fat, especially regarding the existence of minor compounds of nutritional interest, were not found.
The industrial recovery of the oil contained in plant matrices can be carried out by mechanical pressing, the use of organic solvents or a combination of these two methods, depending on the characteristics of the material to be processed (Colivet et al., 2016). Organic solvents, such as the mixture of isomers of n-hexane derived from petroleum, are widely used in the extraction of oils from vegetable matrices with low fat contents, such as cocoa shells (Kemper, 2005; Okiyama et al., 2017). This solvent is selected for industrial processes because it presents remarkable advantages such as a high oil extraction capability associated with its high stability, but it inherently toxic, highly flammable and poses a great pollution risk when not adequately recovered (Johnson and Lusas, 1983; Hammond et al., 2005; Tir et al., 2012).
Despite the potential of CS, there are no studies about environmentally friendly extraction techniques that aim to extract the lipids from this material, producing highly concentrated extracts in short periods of time using small amounts of nontoxic solvents.
In this scenario, one of the green techniques that has stood out is pressurized liquid extraction (PLE). Liquid solvents at high pressure and temperatures are used, showing improved performance compared to processes performed under atmospheric pressure (Mustafa and Turner, 2011). Furthermore, this technique promotes a lower consumption of solvent and considerably reduces the extraction time, since the operational conditions, high pressure and high temperature, facilitate the diffusion of the solvent into the solid matrix as a result of the reduction in the cohesive forces of the liquid, which hasten the penetration of the solvent into the pores of the solid to carry out the extraction (Mustafa and Turner, 2011). The higher pressure employed in PLE reduces the occurrence of air bubbles inside the solid; the existence of these bubbles prevents the solvent from reaching the desired solute. Additionally, the solubility and desorption of the key compounds are increased by the high temperature and pressure conditions (Mustafa and Turner, 2011).
Various raw materials such as watermelon seeds (Colivet et al., 2016), macauba pulp (Trentini et al., 2017), corn and oats (Moreau et al., 2003) have been subjected to oil extraction using pressurized solvents. These authors reported high extraction yields in short extraction times, indicating that this technique is efficient for this purpose.
The aim of this study was to perform an experimental and mathematical evaluation of the kinetics of the extraction of fat from cocoa bean shells by PLE at temperatures of 60, 75 and 90 °C using a generally recognized as safe (GRAS) solvent, absolute ethanol. The influence of the process parameters on the extraction of tocopherols and on the solubility of proteins from the defatted solid was also evaluated.
Section snippets
Materials
Dried cocoa shell, hereafter referred to as CS, was donated by a cocoa processing facility located in the south of Bahia state (Ilheus, BA, Brazil). For the extraction assays, absolute ethanol (purity ≥ 99.8% - CAS 64-17-5) from Merck (Darmstadt, Germany) was used. The other reagents and standards used in this study were as follows: isopropanol (purity ≥ 99.9% - CAS 67-63-0), acetonitrile (purity ≥ 99.9% - CAS 75-05-8), alpha-tocopherol standard (purity ≥ 96% - CAS 10191-41-0), delta-tocopherol
Characterization of cocoa shell
The results from the characterization of the industrially dried CS are shown in Table 1. The contents of moisture, protein, fiber, ash and nonfiber carbohydrate are in accordance with Okiyama et al. (2017); however, the lipid content was considerably higher than those previously reported by Arlorio et al. (2001) and Lecumberri et al. (2007). The variable lipid content of CS is probably associated with the efficiency of the peeling process and the processing step at which this waste was
Conclusions
Dried cocoa shells present high lipid and protein contents. The lipid profile of CCSF was similar to that of cocoa butter but with a higher content of linoleic acid and high acidity, leading us to suggest its application as a partial substitute for cocoa butter, for instance. The proteins in CS presented high solubility at basic pH values, which is very interesting since it indicates the possibility of using this raw material as a protein source.
The extraction process with pressurized ethanol
Acknowledgments
The authors wish to acknowledge the FAPESP (grants 2017/20840-0, 2016/15865-5, 2015/03579-5, 2014/09446-4, 2014/21252-0, São Paulo Research Foundation), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico – grant 303797/2016-9), and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil - Finance Code 001) for the financial support.
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