Optimizing acid-extraction of polysaccharides from Nanfeng tangerine by-products: A sequential study on part selection and extraction process parameters

Massive tangerine by-products from fresh-eating, juicing or plantation management cause pollution and waste. Polysaccharide recovery offers a high-value solution. This study aimed to optimize polysaccharide extraction from Nanfeng tangerine by-products, focusing on part selection and extraction conditions. Polysaccharides from peels (NTPP), leaves (NTLP) and branches (NTBP) of Nanfeng tangerine were extracted with citric acid. Their yield, chemical composition, physicochemical properties, antioxidant activity and α-glucosidase inhibitory activity were compared to select the most suitable part. Extraction parameters for the selected part-derived polysaccharide were optimized using single-factor experiment, Box-Behnken design and response surface methodology. Results showed that NTPP, NTLP and NTBP differed in chemical composition, physicochemical properties, antioxidant activity and α-glucosidase inhibitory activity. NTPP exhibited the highest yield, the strongest 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), 1,1-diphenyl-2-picryl-hydrazyl (DPPH), hydroxyl (OH) and superoxide anion (O 2 - ) radicals scavenging capacities with half maximal inhibitory concentration (IC 50 ) values of 15.89, 4.91, 4.15 and 6.93 mg/mL, and the best Fe 2+ chelating ability with concentration for 50% of maximal effect (EC 50 ) value of 4.40 mg/mL. NTPP and NTBP showed stronger α-glucosidase inhibitory activity with IC 50 values of 2.09 and 1.87 mg/mL. Therefore, peels were selected as the optimal part. Significant correlations existed between the above bioactivities and chemical composition and physicochemical properties. The extraction conditions of NTPP were optimized and adjusted to pH 1.67, extraction temperature 99.0 °C, liquid-solid ratio 16.0 mL/g and extraction time 60.0 min, yielding a validated yield of 26.09%. These findings provide a foundation for the exploitation and utilization of polysaccharides from Nanfeng tangerine by-products.