| Summary: | 碩士 === 國立宜蘭大學 === 食品科學系碩士班 === 106 === Kumquat is one of the local farm crops in Yilan city. The main cultivar is Fortunella margarita Swingle. In our previous study, over 90% of total flavonoids identified were C-glycosyl compounds. The most abundant compound was 3', 5'-di-C-β-glucopyranosylphloretin (DGPP), which exhibited antioxidant and tyrosinase inhibition activities. However, due to DGPP structure, its application is limited by its weak stability and low solubility in lipophilic media. In this study, the flavonoid compositions of immature kumquat extracts prepared by using different solvents (90 oC hot water and methanol) and extraction methods (water bath shaking and ultrasound) established an optimal extraction conditions of kumquat flavonoids. After the collection of DGPP by C18 preparative column, an enzymatic esterification conditions of DGPP using Candida antarctica lipase B (Novozym 435) was investigated. Purification processes with solid phase extraction (SPE), the bioactivity (e.g., antioxidant, antibacterial activities) and solubility measurements in water and 1-octanol of the obtained compounds are also described. The results showed that the highest flavonoids content for immature kumquat was obtained by methanol extraction arrested with ultrasound for 30 min. Five flavonoids were identified, including DGPP, margaritene, isomargaritene, fortunellin and poncirin. The most abundant compound was DGPP. A 100g whole fresh immature kumquat could obtain 57 mg pure DGPP powder (97%) through C18 preparative column collection. Using Candida antarctica lipase B (Novozym 435) as a biocatalyst, the ideal esterification of DGPP with vinyl laurate (VL) in acetone were resulted from reaction for 24 hr, at molar ratio of 10：1. The main products were DG-1 (m/z 779) and DG-2 (m/z 962). LC/MS/MS data exhibited that they were DGPP combined with a molecule of laurate and two molecules of laurates, respectively. In optimal esterification conditions, the content of DG-1 and DG-2 were 24.4 ± 4.2 and 4.3 ± 0.7 mM. DG-1 and DG-2, which were effectively isolated by solid phase extraction (SPE), of which the recovery rates were 54.3% and 34.1%, respectively. In solubility data of DGPP and its esters, an 97.7% of the solubility in 1-octanol and a 2.3% of the solubility in water were clearly observed when the laurate introduced in the DGPP. DG-1 and DG-2 significantly inhibited linoleic acid oxidation. Antibacterial activity of DGPP and its esters were assayed based on inhibition zones. DG-1 and DG-2 were both antagonistic to B. cereus. DG-1 showed stronger effect than DG-1 at 2 mg/mL, which similar to that of sorbic acid (1 mg/mL). Therefore, DG-1 had the potential as a preservative. Among the vinyl alkanoic acid of 4C to 18C reacting with DGPP, vinyl butyrate (4C) and vinyl laurate (12C) had highest total conversion yield. In sum, the modification technology applied in this study was effectively convert DGPP to DG-1(DGPP mono-laurate) and DG-2 (DGPP di-laurate), making them suitable to use in food hydrophobic matrices, cosmetic and pharmaceutical industries.
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