Green strategy for pectin extraction: combining grinding with deep eutectic solvents

Pectins are polysaccharides widely used as gelling, thickening, or emulsifying agent in food industry. In other sectors, such as pharmaceuticals or healthcare, their ability to form physical hydrogels is also exploited to manufacture matrices for encapsulating active components (Munarin et al., 2012). Typically, pectins are extracted from food co-products such as lemon peels or apple pomace through acidic extraction, achieving mass yield around 20% (Kumar & Chauhan, 2010). However, these harsh conditions generate large volumes of effluents and can degrade pectin structure. This study explores a greener alternative extraction method combining ball milling and deep eutectic solvents (DES) for the selective extraction of pectin from lemon peels or apple pomace, preserving its structure for optimal gelation performance. Three DES systems with similar polarity but differing in chemical structure, interaction potential, and viscosity were investigated. For apple pomace, extraction yields were higher with both the chloride:lactic acid and the hydrated choline chloride:malic acid DES, whereas lemon peels gave higher yields with the hydrated choline chloride:malic acid system. The mass yield obtained when combining grinding with deep eutectic solvents (DES) was twice as high as that from DES extraction under stirring alone at identical initial particle size. This indicates that the disruption generated by grinding enhances extraction beyond simply increasing cell wall accessibility (Rajaonarivony et al., 2019). Its action, combined with that of DES, promotes the release of polysaccharide through localised energy dissipation and heating, which favours the cleavage of structural molecular bonds within the biomass, ultimately leading to higher yields. A stronger effect of grinding was also observed for lemon peels. These differences likely stem from biomass processing history: lemon peels, simply dried after peeling, retain mostly intact tissues, making them more susceptible to grinding and facilitating extraction. In contrast, apple pomace undergoes crushing and pressing, which partially disrupts its tissues and reduces the impact of grinding during extraction.