Extraction, characterization, and comparative evaluation of citrus peel pectin for biotechnological applications

Abstract

Pectin is a natural polysaccharide widely used in the food industry as a gelling, thickening, and stabilizing agent. Citrus peels are abundant agro-industrial by-products and represent an economical and sustainable source of pectin. This study aimed to extract pectin from lemon and orange peels using the acid hydrolysis method and characterize the extracted pectin by comparing its physicochemical and structural properties with commercial pectin samples. Pectin extraction was carried out using hydrochloric acid (HCl) and sulfuric acid (H2SO4) under different extraction conditions, including pH, extraction time, and temperature. The extracted pectin was purified by ethanol precipitation, dried, and subjected to physicochemical and Fourier Transform Infrared (FT-IR) spectroscopic analyses. The evaluated physicochemical parameters included pectin yield, equivalent weight, methoxyl content, anhydrouronic acid (AUA), degree of esterification (DE), ash content, alkalinity of ash, carbonate-free ash, moisture content, and color. FT-IR spectroscopy was used to identify the characteristic functional groups of the extracted and commercial pectin samples and to assess their structural similarities. The results showed that extraction conditions significantly influenced pectin yield and quality. Sulfuric acid produced a higher pectin yield and a more desirable yellowish-brown color than hydrochloric acid, which resulted in blackish-colored pectin. The highest pectin yield obtained in this study was 25% under optimized extraction conditions. Orange peel pectin exhibited the highest methoxyl content (5.52%) and degree of esterification (73.1%), while lemon peel pectin showed the highest equivalent weight (156.09 g/moL). The moisture contents of all samples ranged from 1.46% to 4.02%, indicating good storage stability. FT-IR spectra confirmed the characteristic functional groups associated with pectin, including hydroxyl (O–H), aliphatic C–H, esterified carbonyl (C=O), carboxylate (COO−), and glycosidic (C–O–C) groups, supporting the presence of pectin in the extracted samples. Overall, the findings demonstrate that citrus peels are promising raw materials for pectin production and that extraction conditions strongly influence the physicochemical and structural characteristics of the extracted pectin. This study highlights the potential of citrus peel waste as a sustainable and value-added resource for producing natural pectin suitable for food science and technology applications. Further optimization of extraction and purification conditions is recommended to improve pectin quality and expand its industrial applications.