Bezrodnykh et al. 2023 - Crayfish chitosan residual metals

Bezrodnykh and colleagues describe a laboratory-scale route from crayfish shell waste to chitin, chitosan, and oligochitosan hydrochloride, with ICP-MS and EDX checks for residual proteins and metals. This is processed-ingredient evidence for shellfish-derived chitosan, not edible crayfish occurrence evidence. The routeable metal finding is that crude shell waste contained Fe 23.0 ppm, Cr 0.4 ppm, and Ni 0.3 ppm, while processed chitosan and oligochitosan retained only low Fe (3.7 and 2.8 ppm) with Cr and Ni not found; the text states Cd, Pb, Hg, and As were absent.

Key numbers

Processing yield and product identity

The batch began with 4 kg fresh-frozen Actacus leptodactylus crayfish. The protocol yielded 72 g crayfish chitin (1.8%) with 3.4% humidity. Deacetylation of 70 g chitin yielded 56 g dry crayfish chitosan with 96% degree of deacetylation and 3.1% humidity. Depolymerization of 50 g chitosan yielded 40 g oligochitosan hydrochloride with 9.1% humidity and elemental composition C 33.00%, H 6.31%, N 6.55%, and Cl 16.33%.

Residual proteins and metals

Table 1 reports residual proteins, Fe, Cr, and Ni in the starting waste and processed materials. The table also states the USP 34-NF29 acceptance limits: proteins ⇐0.2%, Fe ⇐10 ppm, Cr ⇐1 ppm, Ni ⇐1 ppm, Pb ⇐0.5 ppm, Cd ⇐0.2 ppm, Hg ⇐0.2 ppm, and As ⇐0.5 ppm.

Nf means not found in the paper’s table. The authors state that preliminary ICP-MS found Fe, Cr, and Ni in crude waste and did not find other heavy metals, specifically Cd, Pb, Hg, or As. After washing, deproteination, demineralization, decolorization, deacetylation, and depolymerization, the main Fe burden and all residual Cr and Ni were removed from the chitosan/oligochitosan pathway.

Vessel-material contamination

The study explicitly warns that vessel choice can add residues. EDX showed Al 0.7% and Si 0.3% in chitin when deproteination/demineralization occurred in an alumosilicate glass vessel (Chitin-AlSiG). Using borosilicate glass instead produced Chitin-BSiG, which had residual Si 0.2% and no detected Al. After chitosan preparation, EDX found residual Si <0.1%; oligochitosan hydrochloride showed absence of Al and Si residues.

Molecular and pharmacopeial characteristics

Table 2 reports chitosan molecular characteristics of Mw 370 kDa, Mn 128 kDa, Mp 295 kDa, and polydispersity index 2.88. Oligochitosan had Mw 11.3 kDa, Mn 6.0 kDa, Mp 8.6 kDa, and polydispersity index 1.89.

Table 3 reports that chitosan met the USP chitosan criteria shown in the paper: appearance white, water-insoluble matter 0.15%, degree of deacetylation 96%, proteins 0.11%, chlorides not found, humidity 3.1%, and ash 0.05%. Oligochitosan hydrochloride met the EP chitosan-hydrochloride criteria shown in the paper: appearance white, water-insoluble matter 0.05%, degree of deacetylation 98%, proteins <0.01%, chlorides 16.3%, humidity 9.1%, and ash <0.01%.

Methods (brief)

Crayfish shell waste was washed, deproteinized with 1 M NaOH at 90 C, demineralized with 1 M HCl, decolorized with dilute NaOCl, dried, and milled to chitin. Chitin was deacetylated with 40% NaOH at 120 C in a polytetrafluoroethylene reactor to make chitosan. Chitosan was depolymerized in hydrochloric acid/hydrogen peroxide in borosilicate glass to make oligochitosan hydrochloride. Residual metals were measured by ICP-MS; solid-phase Al/Si residues were checked by EDX. Protein was measured by a Bradford-type colorimetric assay. Molecular weights were measured by size-exclusion chromatography, and degree of deacetylation by proton NMR.

Implications

Certification: This source supports chitosan as a shellfish-derived ingredient with a process-sensitive metal profile. It should not be pooled with edible crayfish or shellfish soft-tissue occurrence data. For chitosan ingredients, the residue risk is partly source-water/shell-metal burden and partly processing-equipment contamination, especially Fe/Cr/Ni from stainless steel and Al/Si from vulnerable glassware.

Courses: Useful teaching example for process controls: demineralization can remove shell-associated metals, but reactor and vessel materials can introduce new residues if the protocol is not controlled.

App: Route to chitosan ingredient context and shellfish-derived additive context. Do not treat this single lab batch as a market distribution for chitosan supplements, cosmetics, or pharmaceutical excipients.

Wiki pages this source may touch

• chitosan
• shellfish
• chromium
• nickel
• iron
• aluminum
• processing

Verification notes

The PDF has author attribution and DOI 10.3390/app13053360; no DOI conflict was observed. The source spells the crayfish genus as Actacus in the title/abstract/methods text; this page preserves that spelling rather than silently correcting it. The RU jurisdiction reflects the Russian laboratory and local-market sampling context; the PDF does not provide a more granular market location. Table 1 visually confirms that only Fe, Cr, and Ni are printed as numeric ICP-MS columns; Cd, Pb, Hg, and As are covered by text statements and pharmacopeial limits, not numeric concentration columns. The chitosan ingredient page was created as a provisional scaffold during this ingest because no existing ingredient slug covered purified chitosan/oligochitosan derivatives.

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.