Organosolv pretreatment of cocoa pod husks: isolation, analysis and use of lignin from an abundant waste product

Daniel James Davidson, Fei Lu, Laura Faas, Daniel McLean Dawson, Geoffrey P. Warren, Isabella Panovic, James Montgomery, Xiaoyan Ma, Boris G. Bosilkov, Alexandra Martha Zoya Slawin, Tomas Lebl, Afroditi Chatzifragkou, Steve Robinson, Sharon E. Ashbrook, Liz J. Shaw, Smilja Lambert, Isabella Van Damme, Leonardo D. Gomez, Dimitris Charalampopoulos, Nicholas James Westwood

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Abstract

Cocoa pod husks (CPHs) represent an underutilized component of the chocolate manufacturing process. While industry’s current focus is understandably on the cocoa beans, the husks make up around 75 wt % of the fruit. Previous studies have been dominated by the carbohydrate polymers present in CPHs, but this work highlights the presence of the biopolymer lignin in this biomass. An optimized organosolv lignin isolation protocol was developed, delivering significant practical improvements. This new protocol may also prove to be useful for agricultural waste-derived biomasses in general. NMR analysis of the high quality lignin led to an improved structural understanding, with evidence provided to support deacetylation of the lignin occurring during the optimized pretreatment. Chemical transformation, using a tosylation, azidation, copper-catalyzed click protocol, delivered a modified lignin oligomer with an organophosphorus motif attached. Thermogravimetric analysis was used to demonstrate the oligomer’s potential as a flame-retardant. Preliminary analysis of the other product streams isolated from the CPHs was also carried out.
Original languageEnglish
JournalACS Sustainable Chemistry & Engineering
Early online date21 Sept 2023
DOIs
Publication statusE-pub ahead of print - 21 Sept 2023

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