Analysis on the difference of founctional components of Guanxi pomelo fruits during maturity

Abstract:【Objective】The study aimed to investigate the difference of the functional components including flavonoids, phenolic acids, coumarins, limonoids and volatile compounds in the different parts of tissue of Guanxi pomelo fruits at three mature stages (immature, semi mature and mature).【Methods】 Guanxi pomelo fruit samples were harvested from September to November, 2020. The mature stages were defined according to the peel color, that is: cyan was marked as immature, green to yellow as semi mature, and yellow as mature stage, respectively. The fresh samples were cut into four parts and manually divided into flavedo, albedo, capsules, seeds and pulps. The juices were extracted by a household juicer and filtered through four layers of fine cloth. The functional components including flavonoids, phenolic acids, coumarins and limonoids were determined by ultra-high performance liquid chromatography (UPLC) and the volatile compounds were detected by gas chromatography-mass spectrometry combined with headspace solid-phase microextraction (HS-SPME-GC-MS) to detect the difference of functional components in different parts of the fruits and at different mature stages.【Results】The contents of four main flavonoids including naringin, rhoifolin, eriocitrin and neohesperidin in the fruits of Guanxi pomelo decreased with maturity. Naringin was the most dominant flavonoid and decreased ob- servably with maturity. The contents of naringin in the flavedo, albedo, capsule, seed, pulp and juice were in the ranges of 85.41%-89.28%, 94.65%-97.11%, 96.12%-97.18%, 88.41%-90.69%, 65.00%- 73.73% and 75.43%-79.42%, respectively. There was a notable difference of the total contents of phenolic acid in the different parts of Guanxi pomelo fruits at the same mature stage in the order of flavedo＞seed＞capsule＞albedo＞pulp＞juice. The total contents of phenolic acid in the flavedo, albedo, capsule, seed and juice at mature stage were higher than those at immature stage and the total content in the pulp decreased gradually with maturity. The total amount of coumarin in the flavedo increased with maturity, the total amount of coumarin in the albedo, juice and seed decreased with maturity and the total amount of coumarin in the pulp and capsule first increased and then decreased with maturity. The contents of coumarin in the flavedo, albedo, capsule, seed, pulp and juice were in the ranges of 133.189-397.775, 1.528-2.662, 7.589-15.673, 2.276-8.253, 3.110-4.574 and 0.745-1.679 mg·kg^-1 , respectively. The limonoids in the seed were the most abundant. The contents of limonin, nomilin and obacunone in the seed increased by 47.11%, 60.90% and 86.47%, respectively, at the maturity stage. The limonin and nomilin in the flavedo, albedo, capsule, pulp and fruit juice decreased sharply during maturity. 51 kinds of the volatile compounds were detected in the flavedo of Guanxi pomelo fruits at three mature stages by GC-MS. Among them, 33, 27 and 43 kinds of compounds were identified at the three mature stages, respectively. The total contents of volatile compound increased gradually as the fruits matured and they were 7896.769, 8664.805 and 10380.399 μg · g^-1 , at three stages, respectively. There was significant difference in the functional components of the juice of the Guanxi pomelo fruits at three mature stages based on principal component analysis.【Conclusion】The contents of the functional components in the different parts of the Guanxi pomelo fruits varied with the fruit maturity. The most of the flavonoids, phenolic acids, coumarins and limonoids showed a downward trend and a few showed an upward trend with the extension of maturity. The contents of the functional components in the different parts of the fruits were different at the same maturity stage. The contents of the flavonoids, phenolic acids and coumarins in the flavedo were higher than those in the other parts and the content of limonoids in the seed was the highest. The total content of volatile compounds increased with the extension of the mature stage. The study would provide a clew for comprehensive utilization of the functional components in the fruits of Guanxi pomelo.