| Seed-watermelon, Citrullus lanatus ssp. vulgaris convar. megalasperms Lin et Chao(formerly Citrullus), is full of natural and rich source of the phytochemical compounds, and it has high nutritional value and benefit human health. To date, it was only used for seed taking and its remaining which is approximately 95% part of the seed-watermelon was wasted. In the meantime, the remaining brings a problem of environment pollution. Xinjiang is the largest area produced seed-watermelon in China, our objective was to analyse the functional ingredients of several kinds of Xinjiang seed-watermelon, clarify the main function components and extraction method in processing by-products of seed-watermelon, and provide the theoretical basis and technical support for the utilization of seed-watermelon resources.The main conclusions are as follows:1. Cyclic adenosine 3’, 5-monophosphate(c AMP) was identified in seed-watermelon using liquid chromatography coupled to tandem mass spectrometry(LC-MS/MS) method. A high performance liquid chromatography(HPLC) method was established for determination of c AMP from seed-watermelon. The HPLC condition was: separation column, Platisil ODS C18(250 mm×4.6 mm, 5 μm); mobile phase, composed of methanol-0.05 mol/L KH2PO4(V/V, 15:85); detection wavelength,259 nm. The results showed that a good linear relationship between the concentration of c AMP and peak area in the range of 0.1 to 100.0 mg/L and the correlation coefficients(R) was 0.9999. The average recovery rate was 93.50% to 106.33% with the relative standard deviation(RSD) was 2.56%-4.45%(n=3). This method was accurate and reproducible, and it could be used for the determination of c AMP in seed-watermelon.2. The water bath extraction was used to extract c AMP from fresh and dry seed-watermelon. The extraction factors, including solid-liquid ratio, extraction temperature, extraction time and extraction times were evaluated. The optimumconditions for c AMP extraction by using orthogonal optimization and validation experiments were: extracting solution, pure water; solid-liquid ratio, 1:12(fresh) or1:60(dry); temperature, 90 ℃; time, 40 min and 3 extration times. Under the optimal conditions, the c AMP average extraction rate of seed-watermelon was 1.05-12.32μg/g(different varieties of seed-watermelon, fresh).3. L-citrulline was identified in seed-watermelon by LC-MS/MS method. A HPLC method for determination of L-citrulline from seed-watermelon was established.The HPLC condition was as follows: separation column, Platisil ODS C18(250mm×4.6 mm, 5 μm); mobile phase, 0.03 mmol/L phosphoric acid; detection wavelength, 202 nm. The results showed a good linear relationship between the concentration of L-citrulline and peak area in the range of 0.1-100.0 μg/m L with R was 0.9999. The average recovery rate was 95.12% to 104.21% with RSD was1.86-4.75%(n=3). This method was precise, simple rapid and sensitive. It can be used for the determination of L-citrulline in seed-watermelon.4. The ultrasonic-assisted organic solvent extraction was used to extract L-citrulline from fresh seed-watermelon. The extraction condition was analyzed including extraction solvent, solid-liquid ratio and extraction time. Through orthogonal optimization and validation experiments, the optimized conditions were obtained as follows: methanol-1mol/L HCl(V/V, 9:1) was the suitable extraction solvent, the solid-liquid ratio was 1:40, extraction time was 30 min. Under the optimal condition, the L-citrulline average extraction rate of seed-watermelon was0.567-2.688 mg/g.5. By comparing three cation exchange resin columns on extracting L-citrulline of seed-watermelon, the static adsorption, desorption and dynamic balance experiments were carried out. The results indicated that 001×7 resin had better adsorption and purify effect of L-citrulline from seed-watermelon which price was the cheaper. Thus, it was chose for separation of L-citrulline in seed-watermelon and theoptimal purification conditions was: temperature, 40~50 ℃; p H, 3; velocity, 0.5 mol/L ammonia; eluent, 0.5 m L/min; volume of ammonia water, 6 BV(bed volume).6. It was indicated that HZ-801 macroporous adsorption resin had better effect on decolorization and made the minimum loss of L-citrulline by comparing polar resin NKA-II, weakly polar resin AB-8, non-polar resin HZ-801, and static decolorization experiment of activated carbon. The L-citrulline was obtained from the eluent after condensing and precipitating by anhydrous ethanol. The purity of L-citrulline was85.7%, and it could reach up to 96.6% after further recrystallization.7. In traditional, pectin from seed-watermelon was extracted by acid extraction,ion exchange and ammonium oxalate method, and immersed seed-watermelon with Na Cl solution before extraction to improve these methods. It was indicated that the order of extracted pectin yield was: ammonium oxalate>ion exchange>acid formulation method and the improved extraction methods were both higher than before. To further improve ammonium oxalate method of extraction seed-watermelon pectin, the concentration of Na Cl solution, Na Cl solution dosage, and immersing time of Na Cl and the concentration of ammonium oxalate was investigated. After immersing in Na Cl solution(12%) with a solid-liquid ratio(W:V, g/m L) was 1:2 for2.5 h, higher pectin yield would be get by 0.5% ammonium oxalate solution extraction and reached up to 1.13 g / 200 g in fresh seed-watermelon. The physicochemical indexes and appearance of seed melon pectin achieved the GB25533-2010(National food safety, standard food additive, pectin) requirements. |
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