Acylation Of Flavone C-Glycosides And Characteristics Of Oil-soluble Antioxidant Of Bamboo Leaves

Antioxidant of bamboo leave (AOB) is a natural antioxidant approved by China in2004and the main component includes four flavone C-glycosides (isovitexin, vitexin, isoorientin and orientin). AOB exhibits excellent antioxidant capacity and acrylamide inhibition in heat-processed food. But AOB has been characterized as a natural phenolics as functional components, which exhibits good solubility in water and poor solubility in lipid and oil. Thus, natural AOB which has been extracted from bamboo leaves is also marked as water-soluble AOB (AOB-w). In order to enhance the lipid solubility of AOB-w, four characteristic flavone C-glycosides has been used to established the chemical acylation and enzymatic acylation model. Results indicated that lipid solubility of the acylated flavone C-glycoside products was significantly enhanced. Structure and kinetic study of the enzymatic acylation products were also investigated. Based on the chemical and enzymatic acylation of flavone C-glycosides, AOB-w was also acylated by chemical and enzymatic method to obtain high-efficiency oil-soluble AOB (AOB-o). The main contents in this study have been listed as below:1. Oxygen acylation was chosen as the chemical acylation method by comparing the effect of oxygen acylation and carbon acylation on the yield, lipid solubility of the acylated products and lipid antioxidant capacity. The lipid solubilityand antioxidant capacity in lipid system of flavone C-glycoside esters by chemical acylation was signficantly enhanced.2. Immoblized lipase CALB was chosen as catalyst, lauric acid (C12fatty acid) as acyl donor and solvent-free system with certain water as the reaction system. The predictive model between conversion yield and lipid antioxidant capacity indicated lipid antioxidant capacity of flavone C-glycoside esters by enzymatic acylation acchieved the highest when the conversion yield was about60%. Only monoester could be determined in the enzymatic acylation of flavone C-glycoside in solvent-free system catalysed by CALB. Kinetic study indicated that the reaction was followed by Michaelis-Menton mechanism, which was consistent with Ping-Pong Bi-Bi reaction mechanism.3. Optimal parameters for the preparation of cAOB-o and eAOB-o was determined by Response surface analysis. High safety and efficiency oil-soluble AOB (AOB-o, including cAOB-o and eAOB-o) was obtained under the optimal parameter, to exhibit excellent lipid oxidation and thermal stability. Total phenolic content of AOB-o was above20%, p-coumaric acid was above0.5%and ethyl acetate solubility was above3g/100g. FT-IR spectra showed the increase of a carbonyl (C=O) peak at1701cm-1and a decrease in the intensity of the absorption at3400cm-1(O-H stretching) in AOB-o. A weaker UV absorption between240nm-280nm and300nm-350nm ofAOB-o was noticed in comparison of the UV spectra of AOB-w.4.0.02%cAOB-o and eAOB-o could significant enhance the frying stability of palm oil under frying temperature (180℃). THe performanc of cAOB-o was considerable with BHT and BHA. eAOB-o exhibited considerable capacity compared with Rosemary extract (RE) and just a litter weaker than TBHQ. eAOB-o exhibited the best capacity to prevent the second oxidation products and the oxidation of polyunsaturated fatty acids.5. eAOB-o, RE, oil-soluble tea polyphenol (OTP) and TBHQ could sighnificantly inhibited the acrylamide formation of French Fries and Chinese Fried Twist by preventing lipid oxidantion. eAOB-o exhibited the best inhibiton, with the inhibiton rate at (27.8±2.03)%(French Fries) and (23.1±1.96)%(Chinese Fried Twist). The acrylamide inhibition by the combined inhibition through asparagine pathway and lipid acrolein pathway showed the excellent inhibiton compared with asparagine pathway alone or acrolein pathway alone. The combined inhibition rate against acrylamide formation was (94.9±6.81)%(French Fries) and (97.7±7.07)%(Chinese Fried Twist)。...