A novel polysaccharide from Macadamia peel: Extraction, purification, structural characterization and antioxidant activity

Abstract BACKGROUND Macadamia peels are the main by‐product of postharvest treatment of the whole fresh fruit weight, they contain various bioactive substances, such as polysaccharides, phenols, flavonoids, phenolic acids, saponins, and other nutritional and functional components, that are known to have anti‐tumor and anti‐oxidation functions. RESULTS Two purified polysaccharide fractions were obtained (MPP‐1 and MPP‐2) by extracting with ultrasonic‐microwave‐aided water extraction and purifying by with DEAE‐52 and Sephadex G‐50 columns, and then characterized using Fourier‐transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy and NMR, and the antioxidant activity was also investigated. The results indicated that MPP‐1 and MPP‐2 were mainly glucose, the molecular weight was 8.16 kDa and 7.73 kDa, respectively. Methylation with gas chromatography‐mass spectrometry and NMR analyses confirmed that two fractions comprised of →4) ‐α‐ d ‐ Glcp ‐(1→, →6) ‐β‐ d ‐ Glcp ‐(1→ and →3,4) ‐β‐ d ‐ Glcp ‐(1→) as the main chain. In addition, MPP‐1 and MPP‐2 polysaccharides showed significant antioxidant activity with respect to 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH), hydroxyl group and reducing power, and MPP‐2 demonstrated excellent antioxidant activities compared to MPP‐1 with IC 50 values of 35.12, 18.82 and 40.12 μg mL −1 , respectively. CONCLUSION The novel polysaccharide, MPP‐1 and MPP‐2, mainly containing glucose, showed significant antioxidant activity with respect to DPPH, hydroxyl group and reducing power. This study has enhanced waste utilization and reduced environmental pollution, providing some inspiration for the reuse of the waste generated during agricultural production. It may bring good prospects for their use as antioxidants in functional foods. © 2024 Society of Chemical Industry.