Bugarin et al. 2025 — Cocoa pod husk valorization: conventional and emerging technologies

Bugarin and colleagues review conventional and emerging technologies for extracting the lignocellulosic structural compounds (cellulose, hemicellulose, lignin, and pectin) from cocoa pod husk (CPH) — the agro-industrial residue that accounts for roughly 76 percent of the cocoa fruit by weight — and the application of the resulting by-products across the food, biopolymer, biofuel, medicine and cosmetics, and agriculture-and-environment sectors. Heavy-metal-relevant content in the review is confined to two short subsections plus scattered paragraphs in the application sections. The authors highlight high-voltage electric discharge (HVED) as the principal emerging technology proposed for reducing cadmium in CPH prior to downstream extraction, and describe CPH-derived biochar as a high-efficiency adsorbent for Pb, Hg, and Cd from aqueous phase. The review reports no original heavy-metal measurements, no occurrence distributions for finished cocoa products, and no analytical method validation; all quantitative heavy-metal figures are second-hand from cited primary studies.

Key numbers

All values below are reported by the review as drawn from cited primary studies. The review does not contribute new measurements.

Section 4.1 — High-voltage electric discharge (HVED) effect on cadmium in cocoa (p. 8, citing refs 11 and 82)

The review states: “Experimental studies recommend treating the raw material for 15 min, at a concentration of 3% (in demineralized water) and a frequency of 40 Hz, allowing for a reduction in heavy metal levels [82].” Equipment is described as a 30 kV high-voltage pulse generator with variable pulse frequency 20–100 Hz.

The review further states: “The HVDE method was able to decrease the levels of cadmium in cocoa by 30.33%, because pretreatment with HVDE generates reactive species that could have an oxidative effect on the treated material [82].” The 30.33 percent figure is reproduced verbatim from the review’s body text; the primary source for this value is ref 82 in the review’s reference list, which the review does not re-quantify against pre- and post-treatment cadmium concentrations or sample sizes.

The review attributes the metal-removal mechanism to CPH’s carboxyl, hydroxyl, and amine functional groups, which it describes as predisposing CPH to adsorb metals (ref 83).

Section 5.1 — CPH consumption safety in animal studies (p. 15, citing refs 132 and 133)

The review states that, “Despite concerns about cadmium accumulation, studies show that when CPH by-products are consumed in low doses, there are no significant adverse effects on organs and tissue histopathology [132].” It further states that OECD-guideline genotoxicity testing demonstrated that CPH “was neither a direct nor indirect mutagen, demonstrating that this product is safe for human consumption, even when maximum permitted doses are used [133].” No dose levels, animal model details, study durations, sample sizes, or organ-specific histopathology endpoints are quoted in the review for refs 132 or 133.

Section 5.5 — CPH biochar adsorption of Pb, Hg, and Cd from aqueous phase (p. 17, citing ref 151)

The review states: “Also, biochar from CPH can efficiently adsorb lead (Pb²⁺), mercury (Hg²⁺), and cadmium (Cd²⁺) from the aqueous phase, and the removal efficiency of CPH biochar for Pb²⁺, Hg²⁺, and Cd²⁺ is higher than 99% [151], highlighting its potential as an eco-friendly material for remediating water contaminated by heavy metals.” No adsorption isotherm parameters, equilibrium times, biochar dose, initial-metal concentration, or final-effluent concentration values are quoted in the review for ref 151; the >99 percent figure is reproduced verbatim from the review’s body text.

Section 2 introductory hazard framing (p. 2)

The review introduces cadmium as the heavy metal of primary concern for CPH valorization: “Cadmium is one of the heavy metals that pose the greatest risks to human health [12] and can be found in soil and food, with several studies indicating high concentrations of it in food, including cocoa [13].” No cadmium concentration ranges or geographic distributions are reported in this introduction; refs 12 (Srivastava et al. 2018, Trends in Food Science & Technology) and 13 (Zhou and Li 2022, Toxics) are flagged as the underlying primary literature for cocoa-cadmium occurrence claims.

Concluding remarks (p. 17)

The review concludes that “considering that cocoa has a high level of cadmium, technologies such as high electrical discharges should be used to reduce the levels to permissible limits for application in products that can be sold in any industry,” and that future research should prioritize “optimization of HVED parameters for effective cadmium removal, scale-up studies of combined emerging and traditional technologies, techno-economic and environmental assessments of integrated extraction chains, and physicochemical and microbiological validation of CPH by-products.”

Evidence Fitness

This is a narrative review of CPH valorization technologies. It contributes no primary heavy-metal measurements and no occurrence distributions. The four quantitative heavy-metals statements it carries (the 30.33 percent HVED-cadmium reduction in cocoa, the “no adverse effect” CPH consumption finding, the OECD genotoxicity negative result, and the >99 percent CPH-biochar Pb/Hg/Cd aqueous-phase removal efficiency) are second-hand summaries of the underlying primary studies (refs 82, 132, 133, 151 in the review). Public evidence label “Context only” is appropriate.

The source supports process-context claims about CPH as a feedstock requiring cadmium pre-treatment for safe downstream food, pharmaceutical, and cosmetic use, and about HVED and CPH-biochar as emerging mitigation and remediation technologies. It does not support occurrence claims for Cd, Pb, or Hg in finished cocoa or chocolate products, and should not be used as the basis for HMTc threshold work or for ingredient contamination_profile values on the cocoa or chocolate ingredient pages. Threshold work on cocoa-derived ingredients should rely on the primary occurrence studies already in the corpus (e.g., Abt et al. 2018, Abt and Robin 2020, Blommaert et al. 2022, Bravo et al. 2024, Burgon et al. 2023).

Methods (brief)

Narrative literature review of CPH valorization without an explicit search-and-selection protocol or PRISMA-style inclusion criteria. The review compiles published process-outcome data on conventional pretreatments (acidic, alkaline, aerobic and anaerobic fermentation) and emerging technologies (HVED, pyrolysis, supercritical and subcritical fluid extraction, ionic liquids, deep eutectic solvents, microwave-assisted extraction, ultrasound, hydrothermal treatment, enzymatic hydrolysis) applied to CPH. Process parameters, yields, and product characteristics are tabulated across six summary tables (Tables 1–6) covering pectin extraction degree-of-esterification, fermentation products, pyrolysis-derived biochar and bio-oil, enzymatic-hydrolysis by-products, emerging-method by-products, and conventional-emerging integration outcomes.

The review does not present an analytical-methods section for the heavy-metal claims it summarises; the underlying analytical detail (ICP-MS or other instrumentation, LOD/LOQ, digestion protocol, certified reference materials) would need to be retrieved from the cited primary studies (notably refs 82 for HVED-cadmium-reduction, 132 and 133 for CPH consumption safety and genotoxicity, and 151 for CPH-biochar aqueous adsorption).

The review is structured into six numbered sections: Introduction, Cocoa Pod Husk Compounds, Conventional Technology for Obtaining By-Products from the Cocoa Pod Husk, Emerging Technology for Obtaining By-Products from the Cocoa Pod Husk, Application of By-Products from the Cocoa Pod Husk, and Concluding Remarks and Future Trends. Author contributions, funding (declared as none), and conflicts-of-interest statement (declared none) are appended on the final body page. The reference list contains 151 numbered references; the heavy-metals-relevant references identified above are nested within an otherwise process-engineering-focused bibliography.

Implications

Certification: Process context only. The review supports the general claim that CPH as a raw material carries elevated cadmium, that HVED pretreatment can reduce this cadmium burden, and that CPH-derived biochar is a high-efficiency adsorbent for Pb, Hg, and Cd from aqueous phase. None of these claims map to occurrence values for finished cocoa or chocolate products; primary occurrence studies of cocoa beans, cocoa products, and chocolate remain the appropriate basis for HMTc thresholds.

Courses: Useful as background reading for the cocoa value chain and the agro-industrial residue stream. The Bugarin et al. characterization of HVED as a cadmium-reduction technology and the CPH-biochar Pb/Hg/Cd adsorption claim provide concrete examples of process-engineering-based mitigation that could be folded into a “supply-chain interventions for heavy metal reduction” course module. Primary sources (refs 82, 151) are worth pursuing for the quantitative detail.

App: No ingredient contamination_profile impact. The review contributes no concentration values usable for the consumer-app pipeline.

Wiki pages this source may touch

• Cadmium
• Lead
• Mercury
• Cocoa

Verification notes

• 2026-06-02 fresh ingest (Claude Opus 4.7, manual-fetch ingest from raw/Manual Fetch Kimi /June 2 Manual Fetches/): DOI 10.3390/pr13051264 verified against the article’s first page; received 25 March 2025, revised 14 April 2025, accepted 17 April 2025, published 22 April 2025 in Processes 2025, 13, 1264. The article carries the MDPI Open Access banner and the Creative Commons Attribution (CC BY 4.0) licence statement; license recorded as CC BY 4.0.
• Author affiliations: Universidad San Ignacio de Loyola, Lima, Peru (Bugarin, Iquise, Olivera-Montenegro) and Federal University of Santa Maria, Cachoeira do Sul, RS, Brazil (Motta Dolianitis, Vinícius Tres, Zabot). Academic Editors named on the masthead: Wilgince Apollon and Alejandro Isabel Luna Maldonado. Funding declared as none received.
• The review is structured around six numbered sections covering CPH composition, conventional pretreatments, emerging technologies, and application sectors. Total heavy-metals-relevant body content is approximately one paragraph in Section 4.1 (HVED), one paragraph in Section 5.1 (CPH consumption safety), and one sentence at the end of Section 5.5 (biochar adsorption), plus framing sentences in Section 2 and the Concluding Remarks.
• The HVED-cadmium-reduction figure (“30.33%”) is reproduced verbatim from the review’s body text in Section 4.1; the underlying primary source (ref 82) is not retrievable from this review’s reference list as supplied on pages 17–25 without the complete reference detail being checked against the full bibliography. The 30.33 figure is treated here as a review-attributed number, not as a verified primary measurement.
• The CPH-biochar adsorption efficiency (“>99%”) for Pb²⁺, Hg²⁺, and Cd²⁺ is reproduced verbatim from Section 5.5; the underlying primary source (ref 151) is similarly treated as a review-attributed number.
• The review uses “HVDE” and “HVED” interchangeably for the same high-voltage electric discharge technology; “HVED” is the form used in section headings and is the form preserved in the body of this wiki page. The “HVDE” abbreviation appears in the body text of Section 4.1 in the review itself.
• The review uses the abbreviation “CPH” throughout for cocoa pod husk; the wiki page preserves CPH on first use with definition and uses the abbreviation thereafter.
• The review does not separate inorganic from total arsenic (no arsenic measurement is discussed at all), does not separate Cr-VI from total Cr, and does not separate MeHg from total Hg. The frontmatter metals: array uses Cd, Pb, and tHg to reflect the review’s actual coverage. iAs, tAs, MeHg, Ni, Al, Cr, Cr-VI, Sn, and U are not discussed in the heavy-metals-relevant content.
• jurisdictions: is left empty: this is a global narrative review citing primary studies from multiple regions. The Peruvian and Brazilian institutional affiliations of the authors do not bound the scope of the review; the introductory production-volume framing uses Ivory Coast as illustrative but the technologies discussed are not Ivory-Coast-specific.
• matrices: uses cacao-pod-husk (the in-vocabulary slug for the cocoa fruit by-product fraction, distinct from cacao-bean / cocoa-bean), biochar (for the Section 5.5 biochar-adsorption content), and literature-survey (to mark this as a narrative review without primary measurements).
• products: is left empty. The review discusses CPH valorization end-products (pectin-as-food-ingredient, biofuels, biochar fertilizer, cosmetics excipients) but does not report occurrence values for any finished product, and CPH-derived ingredients are not currently in the HMI product taxonomy. The cocoa ingredient slug covers the upstream raw-material framing.
• No brand names are reported in the review’s heavy-metals body content. The review does name enzyme product lines (Cellic HTec 2®, Cellic CTec®, Xylanase-X2753 / Pentopan Mono BG®, Cellulase-C2730 / Celluclast®, Cellulase enzyme Viscozyme Cassava CL, Cellic Ctec2 — Novozymes Araucaria Brazil, Sigma-Aldrich Taiwan, Novozymes A/S Denmark) and microbial strains (Aspergillus niger Tiegh F359, Candida boidinii XM02G) in Tables 4 and Section 3.3.1. These are scientific-method reagent and reference-material names and fall under the Part 12 Exception 2 carve-out for instrument and reference-material vendor names. They are not reproduced as a list here.
• evidence_tier: B reflects the narrative-review character of this source. evidence_fitness: EF-4 (Context only) and public_evidence_label: Context only reflect that the source contributes no primary heavy-metal occurrence values.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.