| Sunflower seed containing high quality oil and protein is regarded as an important traditional plant with high nutritional value. However, the utilization of protein is limited because of abundant phenols in kernel which could easily react with protein by influencing its color and functionality. The use of aqueous enzymatic method for sunflower kernel processing has advantages over many other methods because the mild reaction conditions will protect the nutritional value and functional properties of protein. According to the preliminary experiment, the free oil yield could reach up to 86%, while the color of the aqueous phase would be darker till brown under the condition of alkaline because of interaction between chlorogenic acid and protein. In order to avoid the problem arising from oil extraction under alkaline condition, disassociation of polyphenols as a pretreatment for the raw materials is carried out in this study with the purpose of the best use of sunflower kernel.Firstly, the type and content of polyphenols in sunflower kernel were determined. The results showed that chlorogenic acid which mostly existed as free form was the primary polyphenol in sunflower kernel. In view of few combined phenol in kernel, the total chlorogenic acid content was 13.87 mg/g kernel in terms of free chlorogenic acid.Secondly, acid solution was adopted to remove most of the phenolic substances from intact kernels, and the composition of extracting solution, extraction rate of different substances and quality of oil and protein were analyzed. The results showed that there were three isomeric compounds in the extracting solution, i.e., 3-O-CQA, 4-O-CQA and 5-O-CQA. Based on the investigation of the main influencing factors, the optimized extraction conditions were listed as following: 0.001 mol/L hydrochloric acid solution as extractant, 90°C as extracting temperature, ratio of material to liquid 1:5(g/m L), extracting time 1.0 h, extracting 3 times. Under those conditions, the yield of chlorogenic acids from sunflower kernel was 85.80±1.37% and the isomerization rate was 17.31±0.76%, and the extraction rate of solids, protein and oil were 7.78±0.05%, 3.71±0.21% and 1.80±0.15%, respectively. Compared with the untreated control, the yield of free oil increased from 86.76±0.34% to 91.32±0.24%. There was no significant change observed as to the quality of oil compared with untreated material. The color, the oil-absorption ability and emulsion capability of protein had been improved.Thirdly, the composition of extracts from three extraction methods, i.e., methanol extract at room temperature, methanol reflux extract at high temperature and acid liquor extract at high temperature were analyzed and compared. Identified by UPLC-MS/MS, it found that 5-O-CQA was the common compound in three extracts, while chlorogenic acid extracted by acid solution was easily transformed to the other two isomers, 3-O-CQA and 4-O-CQA. Besides, a new substance was detected in the extracting solution which had not been reported so far, namely N-[(2E)-3-(4-Hydroxy-3-methoxyphenyl)-2-propenoyl]glycine(Mr=251.2).Finally, an efficient preparative separation and enrichment process of polyphenols extracted by acid solution had been developed, and XDA-1 resin was affirmed to be the suitable resin for the further study. The result showed that the purity of crude extract could reach up to 15% after ultrafiltration while the initial purity was 4%, then the obtained extract was submitted to purification with resin. The optimum purification conditions were listed as following: a sample concentration in solution of 2.0 mg/m L, a p H value of 3.0, a flow rate of 2 BV/h, a sample volume of 30 BV. When the adsorption finished, 10%(v/v) ethanol with 4 BV/h was used to wipe off impurity, then polyphenols were eluted by 50%(v/v) ethanol with 4 BV/h. After treatment with ultrafiltration and XDA-1 resin, the polyphenol content in the final product was increased 19-fold from 3.8±0.7% to 77.8±1.7%, with a recovery yield of 82.3±1.4%. |
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