An overview of cocoa nibs shell waste potential to achieve sustainable agriculture

Around 40 cocoa industries were established in Indonesia, and about 400 thousand kg of cacao beans were used for end-product. Deforestation decreases the productivity of cocoa beans and increases greenhouse gas emissions. Besides, 80% of cocoa fruit also consists of pod, shell, and pulp, contributing to residual biomass increment in cocoa industries. Research on cocoa biomass potencies has been carried out in cocoa plantations and the cocoa industry. Cocoa shells have several chemical compounds that benefit agriculture products and environments, such as minerals and nutritional compositions. Cocoa Nibs Shell (CNS), one of the by-products of cocoa processing, wastes about 13% of its production. Therefore, this research aims to give an overview and determine the potential use of CNS waste in agriculture by analyzing the bioactive compound in CNS to add more value to cocoa waste and reduce greenhouse gas emissions from the waste. The authors used X-Ray Fluorescence (XRF) to identify the bioactive compound in CNS. Subsequently, several bioactive compounds found in the XRF assay were P2O5, SO3, K2O, TiO2, MnO, Fe2O3, NiO, CuO, ZnO, Rb2O, SrO, BaO, Yb2O3, Re2O7. These bioactive compounds have a positive benefit in agriculture. MnO and Fe2O compounds are essential for fertilizer application. P2O5 and SO3 have potential benefits in crop protection. Moreover, CNS has a great characterization which is potential for biochar and bio-adsorbent on water irrigation treatment since it has carbon, nitrogen, and oxygen compounds. Those potencies are also essential to reduce industrial waste in cocoa and to achieve sustainability.


Introduction
Cocoa is one of the most fundamental plantation commodities in the world, its end-products, such as cocoa powder, liquor, cake, and butter, are the most needed in the food industry.Moreover, cocoa plants influenced farmers' livelihood in main producer countries.Indonesia ranks sixth in world cocoa production in 2022 [1].According to the Central Statistics Agency (BPS) [2], Indonesia's cocoa productivity is 706,500 tons and has continuously declined for the last three years.Around forty cocoa industries were established in Indonesia, and about 400 thousand kg of cocoa beans were used for endproduct.Many cocoa industries in Indonesia have not required their environmental management properly.Unfortunately, cocoa productivity is predicted to decrease by 11% due to deforestation and climate change.Thus, farmers choose to divert their agricultural commodities.This issue is reinforced by the statement of Kadir et al. [3] that climate change will affect crop yields which are likely to decrease due to increasingly dry land due to limited water due to a long dry season [3].Another problem also occurs in the cocoa industry, where 80% of the remaining biomass is produced from pods, shells, and pulp.This biomass can increase greenhouse gas emissions in the agricultural sector if it is not properly utilized.Other problems also occurred in the cocoa industry, where 80% of residual biomass resulted from pod, shell, and pulp, which can contribute to greenhouse gas emission increment in the agriculture sector if the biomass is not utilized well.
Comprehensive research on cocoa biomass potencies has been carried out in cocoa plantations and the cocoa industry.Some studies stated that cocoa shells contain polyphenols that have potential phytotoxic activity for non-human mammals and environmental issues [4].Moreover, Cocoa Nibs Shell (CNS), one of the by-products of cocoa processing, wastes about 13% of its production [5].Therefore, this research aims to give an overview and determine the potential use of CNS waste in agriculture by analyzing the bioactive compound in CNS to add more value to cocoa waste and reduce greenhouse gas emissions from agriculture waste.

Bioactive compound in cocoa nibs shell
Cocoa nibs shell was produced from the cocoa factory as a by-product and it has great potency to utilize in many other uses such as agriculture, feedstuff, biofuels, adsorbent, dye, and food products [6].However, to determine the specific potencies in the agriculture sector by analyzing the bioactive compound in cocoa nibs shell ash using X-Ray Fluorescence (XRF).This method aims to analyze the minerals and other compounds in the sample with a non-destructive technique [7], it is done by lab analysis to strengthen this review paper.The table above shows that the CNS is rich in macro and micronutrients such as nitrogen, potassium, iron, manganese, zinc, and copper, which are beneficial to improve plant growth.Both macro and micro are important for soil health and agroecological systems' sustainability [8].Furthermore, those bioactive compounds in CNS can also be used for crop protection, soil amendment, and water quality improvement for agricultural uses.

Cocoa nibs shell application in agriculture practices
The major agricultural practices include fertilizer, crop protection, soil management, and water quality.The potency of CNS for the substitution of additional material into those three practices is described in this paper.Figure 1 illustrates the CNS waste utilization recommendation.

Fertilizer application
In some cocoa plantations, it is prevalent to use the cocoa shell as compost and mulch [6], proved by the high phosphorus and potassium content in CNS bioactive compound analysis.The experimental study on soil analysis shows that there is N, P, K, and 49% organic matter from cocoa shell waste addition.The nitrification rate was increased when the soil was mixed with cocoa shell powder and manure.It reduced the maturation time on composting because the microbial content also increased in the soil mixed with cocoa shells [9].Based on the XRF analysis, potassium has the highest content in the cocoa shell, 78.5%, and 9.37% for phosphorus.Cocoa trees in shade conditions need fertilizer containing P and K to increase their yield [10].Researchers state that the ratio of macronutrients on cocoa trees is 18% N, 20% P, and 25% K [11].Sustainable practices can be achieved in cocoa plantations if they use CNS as their fertilizer since cocoa trees also need high K content compared to other nutrients and K value (%) in cocoa nib's shell waste.
Besides macronutrients N, P, and K, micronutrients like B, Cu, Fe, Mn, Zn, Mo, and Ni play a significant role in plant growth, especially in plant metabolism, including chlorophyll synthesis and reproductive growth [12].Nowadays, high technology requires micronutrients from nanoparticles (NPs).It has been found that micronutrients in CNS are beneficial for agriculture and the environment since they are made from agricultural biomass.An experimental study of Mn in mung bean found that Mn nanoparticles enhance plant growth by around 52% and nutrient increment [13].Research from Salama et al. [14] also shows that MnO2-NPs application by foliar spraying in mung beans is not toxic and environmentally friendly.Another study also reported that chlorophyll content could increase when wheat plants are treated with manganese (Mn) in MnSO4 form because of its role in the metabolism of carbohydrates and phosphorylation by stimulating the enzyme [15,16].Fe2O3, also can be used as nanoparticles for essential micronutrients in plants.An article published that iron oxide has a potential role as fertilizer, especially in peanut plants.The research shows that it can increase plant and root length [17].In most cases, peanuts were cultivated in sandy soil, which is easy to leach and lost some nutrients in the fertilizer.Moreover, Fe2O3-NPs could reduce the toxic elements (PTEs) in planting media [18] of Leguminosae plants.Fe is needed in leghaemoglobin formation as the Nitrogenous enzyme constituent [12].Hence, the capability of Fe2O3-NPs to adsorb in sandy soil can enhance Fe availability which will protect the plant from deficiency [17].Another micronutrient needed for plant is Zinc (Zn), it is responsible for metabolic reactions of crops such as photosynthesis, plant resistance against disease, pollen formation, and increased antioxidant enzymes level [19].More studies on nanoparticles also show that zinc oxide or ZnO-NPsffects plant growth and yield [20].

Crop protection application
Crop protection is one of the most critical practices in agricultural production.Through the years, agrochemical has been heavily used for pest and disease management as synthetic pesticides are readily available, practical, and have a longer shelf life than most organics.However, excessive and indiscriminate use of synthetic pesticides could lead to the decline of beneficial insect and microorganism populations, environmental damage, and the emergence of pest resistance [21].Dosis usage of synthetic pesticides continues to rise as pests and diseases develop resistance.The greater the exposure, the greater the toxicity and the effects of the pesticide, leading to environmental toxicity and reduced productivity.Water, soil, and other vegetation can be contaminated by pesticides that adversely affect other organisms, including human health.[22].Hence, biopesticides can be applied to achieve sustainable agriculture through Integrated Pest Management (IPM) [23].
According to Rajamani and Negi [23], biopesticide is a pest control agent derived from natural materials.One of the biopesticide materials commonly used as a pesticide substitute is flavonoids.Flavonoids have four flavonols described by Poveda et al. [6]: epicatechin, catechin, procyanidin B1, and procyanidin B2 (table 2).Further research about biofungicide documented that catechin and epicatechin reduced fungal pathogens (Puccinia triticina, Fusarium oxysporum, Rhizoctonia solani) and nematode Meloidogyne javanica, which are infecting wheat, tomato, and rice [24].Flavonoid-containing extract (quercetin) acts as a biopesticide, has a mortality effect, and reduces the growth rate of the cotton cutworm, Spodoptera litura larvae [25].Quercetin also affects decreased fecundity and increased mortality of the pea aphid and Acyrthosiphon pisum [26].
Moreover, minerals like sulphur, copper, iron, and zinc derived from plants are also beneficial as biocontrols.The most common active ingredient of fungicide is sulphur [27], which is available in CNS as a form of SO3 for 4.78%.Moreover, 0.31% copper in the CNS is an essential ingredient for fungicides to control plant disease [28].Phytophthora spp. is one of the important plant pathogens that cause major plant diseases.A study from Gopi et al. [29] also shows that copper fungicide reduces late blight (Phytophthora infestans) disease in tomatoes.Thus, CNS has a big potential to be utilized as biopesticides in crop protection.However, CNS must be stored in a dry environment because it is easily infested with mycotoxin [30].Hence, it needs extra effort to store CNS as fungicides.

Soil amendment application
Mining land is one of the environmental issues in agriculture due to the destroyed soil properties like biological and bio-chemical, so they can no longer store nutrients as they should.To improve soil health in degraded land, biochar, compost, and fly ash are used within organic materials, including biomass, living beings, and inorganic materials or minerals based on and living beings, and inorganic materials or minerals based like gypsum and fly ash [32].Biochar is charcoal made from crop biomass with a thermochemical process in an oxygen-limited condition rich in carbon substance [33,34].Using biochar as soil organic carbon (SOC) for emission reduction application can increase the carbon stock and improve soil health in the long term [35].An experimental study from Najafabadi et al. [36] uses CNS as biochar, which shows that CO2 uptake was high because of the influence of particle size in CNS, compared to other commercial biochar.Cocoa nibs shell has a small surface area which can more effectively process in pyrolysis to become a biochar.The practicality of biochar as a soil amendment in agriculture crops can improve soil moisture and increase production by 65.48% [37,38].

Bio-adsorbent application for water treatment
Irrigating agricultural land plays an important role in crop growth.Irrigation source relies on surface water and groundwater [39].Therefore, farmers need good-quality water for their crops to enhance their productivity.It is indispensable that industry development has deteriorated water quality, especially by synthetic dyes.Thus, the presence of a polar functional group in CNS makes this by-product can be used as a bio-adsorbent.The adsorbent process happens through the presence of O-N-O groups, N-O groups, and surface acid in the carboxylic group [40].Recently, several studies have been conducted to identify the effectiveness of CNS as an adsorbent agent.Research by Pereira et al. [41] has found that CNS interaction between oxygen-free Lewis basic sites can contact the free electron of the dye molecules.Hence, it can adsorb the dye waste in the water.Another experiment was conducted by Saucier et al. [42], and they found that using CNS microwave-assisted carbon could effectively remove around 95% of different organic compounds in high sugar content and salinity solution.In addition, cocoa shells have the capability to remove heavy metals in water [9].

Sustainable agriculture on cocoa nibs shell utilization
The environmental changes in agriculture affect the ecosystem and productivity.To balance ecosystems and productivity, we need to apply a sustainable system in agriculture.Sustainable agriculture is a system where the activities of agriculture are designed to have a better quality of yield while protecting the environment and balancing the communities by improving the availability, access, utilization, and stability from all the sustainability dimensions [43,44].Several practices involve CNS waste utilization in sustainable agriculture, such as building healthy soil and carbon storage biochar, using organic crop protection, managing water quality for irrigation, and fertilizer application.Those are aligned with key principles for sustainability in agriculture which consist of 1) Improving efficiency in the use of resources, 2) Direct action to conserve, protect and enhance natural resources, 3) Protect and improve rural livelihoods, 4) Enhanced resilience of people, communities, and ecosystems, and 5) Requires responsible and effective governance mechanisms [45].

Conclusion
Cocoa Nibs Shell (CNS) waste shows several bioactive compounds such as minerals (P2O5, SO3, K2O, TiO2, MnO, Fe2O3, NiO, CuO, ZnO, Rb2O, SrO, BaO, Yb2O3, Re2O7) resulted from XRF analysis and nutritional composition that are beneficial for the agricultural sector.These bioactive compounds can be applied to organic fertilizer and crop protection.Moreover, the characterization of CNS also can be used for bio-adsorbent and biochar.CNS is applied for broader uses in agricultural practices to achieve sustainable agriculture.

Table 1 .
Table1shows the bioactive component of CNS with oxygen bond.Bioactive compound using X-Ray Fluorescence (XRF) analysis