Production and characterization of pectin from prickly pear (Opuntia ficus-indica) peel by organic acid extraction using response surface methodology

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The improper disposal of agro-industrial waste has emerged as a crucial environmental issue. Therefore, the extraction of valuable compounds from these residues presents a promising strategy to mitigate their environmental impact while promoting resource efficiency. Prickly pear (Opuntia ficus-indica) peels, which constitute about 45% of the whole fruit, represent an abundant and significant by-product of food processing. These peels have garnered scientific interest due to their potential as a sustainable source of pectin, a polysaccharide widely used in the food and pharmaceutical industries. Therefore, the aim of this research was to extract and characterize pectin obtained from prickly pear peels using citric acid as an environmentally friendly solvent. The effects of temperature and pH on pectin yield were evaluated using a central composite design, which allowed the identification of significant interactions and effects of these factors. The results revealed that pH significantly influences (p = 0.001) pectin yield, while temperature is an important factor to take into account during experiments (p = 0.089). The optimal conditions were found to be a temperature of 94.1°C and a pH of 1.8, under which a predicted pectin yield of 11.1% was obtained. Physicochemical characterization of the extracted pectin showed that its equivalent weight ranged from 224.2 to 897.8 g/mol. Methoxyl content varied between 3.6% and 5.0%, while degrees of esterification and anhydrouronic acid content ranged from 20.5% to 59.2% and from 48.0% to 98.6%, respectively. The degree of esterification of 20.5% at the optimal pH of 1.8 classified this pectin as low-ester pectin, which has distinct gelling and functional properties suitable for various applications. These results suggest that pH significantly affects both pectin yield and its physicochemical properties. In conclusion, prickly pear peels, typically considered waste, have the potential to be a viable and sustainable source of pectin. The extracted pectin exhibits physicochemical characteristics comparable to those of commercial pectins, highlighting its potential for industrial utilization in food formulations. Key words: prickly pear peel, pectin, citric acid, acid hydrolysis, green process

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