Valorisation of Pomegranate Peel Waste into Nanocellulose: A Critical Appraisal of Extraction Routes, Characterisation Evidence and Environmental Applications

Abstract

Pomegranate (Punica granatum L.) processing generates a peel fraction that dominates the residue stream of juice and arils production, and this residue has been targeted for polyphenol recovery, pectin extraction and conversion into carbonaceous adsorbents. Conversion of the same residue into nanocellulose has been proposed as a higher-value route, yet the evidence base supporting that proposition has not been examined critically. This review evaluates the strength, internal consistency and methodological quality of the literature linking pomegranate peel to cellulose nanocrystals, cellulose nanofibrils and bacterial nanocellulose, and to environmental applications in water treatment and pollutant capture. Studies were identified through structured searching of open scholarly databases and indexes, supplemented by backward and forward citation tracking, and were appraised for feedstock characterisation, process transparency, metrological adequacy and the strength of the inference drawn from reported performance data. Three findings emerge. First, the primary evidence in which pomegranate peel serves as the cellulose feedstock is small, geographically concentrated and dominated by packaging-oriented investigations; most publications that pair the words pomegranate and nanocellulose in fact use the peel as a source of polyphenolic extract added to nanocellulose obtained elsewhere, and this conflation has inflated the apparent size of the field. Second, the compositional heterogeneity of pomegranate peel, and in particular its high extractive and pectin content, imposes purification demands that are poorly reported and that plausibly explain divergent yields and crystallinity values across studies. Third, no published investigation appears to have tested pomegranate peel derived nanocellulose as an adsorbent, membrane or aerogel for pollutant removal, so environmental claims for this feedstock rest on extrapolation from other cellulose sources rather than on direct evidence. The field would benefit from mass-balanced processing studies, harmonised crystallinity and dimensional metrology, and adsorption experiments conducted in realistic water matrices before the environmental promise of this residue is asserted.