| Tiger lily, Lilium lancifolium Thunb. (L. lancifolium), belongs to the genus Lilium of the family Liliaceae, is widely distributed in China and cultivated in Taihu Lake Basin. L. lancifolium has been used in traditional Chinese medicine for many centuries, as its effect on treating tuberculosis, pertussis, chronic bronchitis and chronic gastritis, etc. Bulb of lily is not only a good source of nutrient substances including starch, protein and dietary fiber, but also contains a variety of bioactive substances, such as polysaccharides, saponin, and colchicine. Recently, lily polysaccharides have attracted a great deal of attention for their effects on antioxidant, antitumor, hypoglycemic and immunomodulatory. In this paper, non-starch polysaccharides (NSP) from the bulb of L. lancifolium were extracted with hot water, pectinase and fermentation of Saccharomyces cerevisiae. The extraction conditions of NSP were optimized, and then the optimal deproteinization conditions were determined. Finally, antioxidant activities of NSP isolated with different methods were investigated. The main results in the paper were concluded as follows:1. Extraction conditions of lily NSP with hot water were optimized using Box-Behnken design and analyzed by response surface methodology (RSM). Results indicated that the optimum condition as follows:extraction temperature 62℃, extraction time 4 hours and ratio of water to raw material 19:1. Under this condition, the NSP yield was 7.82±0.03%, which was in agreement with the prediction.2. NSP from the lily bulb residue left by hot water was extracted with pectinase. The results of extraction condition optimization, obtained by the orthogonal optimization experimental system, indicated that effect of factors on NSP yield showed to be pH value>concentration of enzyme>extraction time>temperature, and the maximum NSP yield was 0.814±0.027% when the pH value, the concentration of enzyme, the extraction time and the temperature were 5.5,1800 U/g,20 min and 30℃, respectively.3. A new method was developed for removing proteins from lily NSP by fermentation of Saccharomyces cerevisiae, which was different from Sevag and trichloroacetic acid methods. Screening results revealed that both lily NSP yield and ratio of protein removed (RPR) of the yeast strain GX were highest among eight strains. And then the variables significantly influenced NSP yield and RPR, identified from the Plackett-Burman screening experiment, were optimized using Central Composite Design (CCD) and RSM. The analysis revealed that the optimum conditions were 60.0 g/L lily bulb powder,1.50 g/L KH2PO4, pH4.8 and temperature 26.9℃. In the verification experiments, the NSP yield and the RPR were 8.81±0.18% and 91.71±0.08%, respectively, which were in agreement with the predictions. The time of aerobic fermentation had non-significant effect on NSP yield and RPR; with time of static fermentation increasing, RPR showed an augment trend and NSP yield decreased first and then increased, lastly, decreased again, and the maximum NSP yield was obtained at the time of static fermentation of 72 h. Compared to polysaccharides extracts with hot water and water-pectinase, the content of NSP in polysaccharides extracts isolated by fermentation was much higher, and the concentration of reducing sugar and protein were much lower.4. With the elevation of concentrations ratio of NSP extracts and deproteinization times by Sevag method, RPR showed an augment trend firstly and then exhibited a non-significant fluctuation, and NSP decreased firstly and no longer changed significantly. The optimal concentrations ratio of polysaccharides extracts isolated with hot water, pectinase and fermentation were 3,6 and 0, respectively, while the optimal deproteinization times of polysaccharides extracts isolated with hot water, pectinase and fermentation were 3, 3 and 4, respectively. After deproteinization, freeze dried powder of NSP isolated with fermentation contained polysaccharides of 61.89±1.29%, which was higher than that of NSP isolated with hot water and pectinase, and the content of protein in freeze dried powder of NSP isolated with fermentation was lower than the others.5. Both NSPs extracted with hot water and fermentation showed good capability of scavenging hydroxyl radical, and the hydroxyl radical scavenging ability was higher than 90% when the concentration of polysaccharides was 1 mg/ml. Compared with NSP extracted with fermentation, NSP extracted with hot water showed higher reducing power and scavenging abilities of superoxide and DPPH radicals. Furthermore, the NSP extracted with pectinase from resdue left by water extraction showed higer reducing power than which with water, while its scavenging abilities of hydroxyl, superoxide and DPPH radicals were weaker than which with water but higer than which with fermentation. |
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