Document Type : Research Paper
Authors
Department of Wood and Cellulosic Products Engineering, Sari Agricultural Sciences and Natural Resources University, Mazandaran, Iran
10.22034/ijwp.2026.2078226.1741
Abstract
Abstract
Problem definition and objectives: The global trend toward sustainable valorization of agro-industrial residues has increasingly emphasized the recovery of high-value bioactive compounds. Among these, pectin is one of the most important polysaccharides, widely utilized in the food, pharmaceutical, and bio-based packaging industries. Despite its significance, conventional extraction methods, such as hot acid extraction, are associated with high energy and solvent consumption and often result in degradation of the pectin polymeric structure, thereby reducing the quality of the final product. Accordingly, the present study aimed to develop and optimize a green process for pectin extraction from lime (Citrus aurantifolia) peel using microwave-assisted extraction (MAE). Response surface methodology (RSM) based on a Box–Behnken design was employed to evaluate the effects of three key variables—microwave power, irradiation time, and pH—on extraction yield, degree of esterification (DE), and galacturonic acid (GalA) content, with the objective of identifying optimal conditions that maximize both the yield and purity of the extracted pectin.
Methodology: Fresh lime albedo (white peel) was dried at 50 °C, milled, and sieved. The independent variables were microwave power (270–470 W), irradiation time (2–4 min), and pH (1–3), each examined at three levels. Based on the Box–Behnken design, 15 experimental runs were conducted. The extraction yield was determined gravimetrically, galacturonic acid (GalA) content was quantified using the m-hydroxydiphenyl colorimetric method at 520 nm, and the degree of esterification (DE) was calculated by acid–base titration. Data were analyzed using Design-Expert® version 13, and second-order polynomial models were fitted for each response.
Results: The mathematical models developed for all three responses exhibited high coefficients of determination (R²Y = 0.9990, R²DE = 0.9974, and R²GalA = 0.9994), and the lack-of-fit test was not significant for any response (P > 0.05). Response surface analysis indicated that decreasing the pH to a strongly acidic range (approximately 1) had the greatest enhancing effect on extraction yield, while moderate increases in microwave power and irradiation time promoted the release of the polygalacturonic network. The optimal conditions for maximum extraction yield were identified as 450 W, 4 min, and pH 1, resulting in a yield of 50.6 ± 0.3%. In contrast, the highest degree of esterification (DE = 64.07%) was achieved at 470 W, 2 min, and pH 3, corresponding to the production of high-methoxyl pectin (HM-pectin). Moreover, the maximum galacturonic acid content (GalA = 92.16%) was obtained under conditions of 470 W, 3.78 min, and pH 2.98. Excessive microwave power or harsh acidification (pH < 2) led to degradation of polymer chains and a subsequent reduction in GalA purity.
Conclusion: Overall, the findings demonstrate that MAE, with appropriate control of process variables, can produce pectin with high yield, desirable purity, and tunable structural properties. Extraction under low pH and moderate power enhanced recovery while preserving the polygalacturonic backbone, whereas more moderate conditions with shorter irradiation favored retention of esterified groups and higher DE. Thus, MAE not only outperforms conventional extraction in terms of efficiency, but also offers environmental advantages by reducing energy and chemical consumption and enabling the targeted production of low-methoxyl (LMP) and high-methoxyl (HMP) pectins. These results provide a robust basis for the industrial development of green pectin extraction from citrus processing residues and the production of sustainable bio-based ingredients for food, pharmaceutical, and packaging applications.
Keywords
