酚酸对红肉苹果花色苷辅色效果及稳定性的影响

Effects of Phenolic Acids on Copigmentation and Stability of Anthocyanins in Red-Fleshed Apple

【目的】研究酚酸对‘紫红1号’新疆红肉苹果花色苷的辅色效应,以及辅色后花色苷的稳定性,旨在为红肉苹果花色苷利用提供理论依据和参考。【方法】利用超声辅助法提取红肉苹果花色苷,采用pH示差法测定总花色苷含量,高效液相色谱法(HPLC)分析花色苷组分及含量。在pH 3.0缓冲液体系中,分别选用咖啡酸、阿魏酸、绿原酸、没食子酸对红肉苹果花色苷进行辅色,并将不同处理的样品分别置于水浴加热、光照、H2O2氧化和Fe^(3+)4种不同条件下,研究4种酚酸对红肉苹果花色苷的辅色效果和稳定性的影响。【结果】‘紫红1号’红肉苹果中花色苷含量为268.6 mg·kg^(-1),主要成分为矢车菊-3-半乳糖苷、矢车菊-3-葡萄糖苷、矢车菊-3-阿拉伯糖苷,其中矢车菊-3-半乳糖苷占总花色苷含量的75.34%。在水体系中,红肉苹果花色苷的最大吸收波长为515 nm,花色苷的颜色和515 nm处吸光度(A515nm)随pH变化而改变。浓度为0.01 mol·L^(-1)的咖啡酸、阿魏酸、绿原酸、没食子酸对红肉苹果花色苷均能产生明显的辅色效应,辅色后花色苷溶液产生了不同程度的增色及红移效应(5—11nm),其中阿魏酸处理组的红移效应最为显著,红移幅度高达11 nm。各试验组样品分别在60℃、80℃、100℃水浴中加热1 h后,绿原酸和没食子酸对红肉苹果花色苷的保护作用最好,其次是阿魏酸和咖啡酸。在室外自然光照条件下,红肉苹果花色苷溶液的半衰期少于7 d,酚酸辅色后,显著增强了花色苷的光稳定性(P<0.05),其中绿原酸使红肉苹果花色苷半衰期延长了170.87%,咖啡酸、没食子酸、阿魏酸分别使花色苷半衰期延长了142.68%、39.56%、23.05%。浓度为0.1%—0.6%的H2O2使红肉苹果花色苷的红色迅速褪去,加入酚酸后花色苷的抗氧化性显著提高,当花色苷溶液中H2O2浓度为0.1%时,氧化1 h后,对照组花色苷保留率仅为38.39%,而阿魏酸、绿原酸、咖啡酸、没食子酸处理组花色苷保留率分别为63.10%、59.95%、57.95%、48.81%,均显著高于对照组(P<0.05)。浓度为2.5×10^(-4)—1.0×10^(-3) mol·L^(-1)的Fe^(3+)对花色苷有不利影响,加入酚酸后花色苷稳定性明显增强,其中没食子酸处理组红肉苹果花色苷稳定性最强,绿原酸、咖啡酸次之,阿魏酸处理组花色苷稳定性最弱,各处理组花色苷A_(515nm)均显著大于对照组花色苷(P<0.05)。【结论】红肉苹果花色苷颜色受pH影响较大,pH<3.0时,色泽鲜红且性质稳定。咖啡酸、阿魏酸、绿原酸、没食子酸使红肉苹果花色苷产生不同程度的增色及红移效应,且显著增强了花色苷在加热、光照、氧化、Fe^(3+)条件下的稳定性。

【Objective】‘Zihong NO.1＇ red-fleshed apple is cultivated widely in Xinjiang Autonomous Region of China. Through investigating copigmentation of phenolic acids on anthocyanins in red-fleshed apple and their stability, this paper aims at providing a theoretical basis and reference for industrial utilization of red-fleshed apple anthocyanins. 【Method】 Ultrasonic-assisted method was used to extract anthocyanins, and p H differential method was adopted to determine the total content of red-fleshed apple anthocyanins. Besides, the constituents of red-fleshed apple anthocyanins and content of monomeric anthocyanins were also analyzed by HPLC. In phosphate buffer（p H 3.0） of red-fleshed apple anthocyanins, the copigmentation effect of these four acids was evaluated. The absorption spectra and absorbance at λmax of all treatment groups as well as the contrast groups were measured before and after the treatments of heating, light exposure, oxidation and adding metal ions（Fe^3＋）.【Result】The content of total anthocyanins in red-fleshed apple is 268.6 mg·kg^-1 and mainly consist of cyanidin-3-galactoside, cyanidin-3-arabinoside and cyanidin-3-glucoside, and cyanidin-3-galactoside accounts for the largest proportion of 75.34%. The wavelength of maximum absorption of red-fleshed apple anthocyanins in water system is at 515 nm, and the color and A515 mn of red-fleshed apple anthocyanins change due to different p H values. At the concentration of 0.01 mol·L^-1, caffeic acid, ferulic acid, chlorogenic acid and gallic acid all showed evident copigmentation, which led to the phenomena of hyperchromic effect and the bathochromic shift in varying degrees. Especially, ferulic acid caused the greatest extent of redshift（11nm） in anthocyanins solution. After anthocyanins was heated in water-bath at 60℃, 80℃, and 100℃ for one hour, respectively, chlorogenic acid and gallic acid showed the best protection effect, which is better than caffeic acid and ferulic acid. Under the natural lighting, the half-life of anthocyanins solution without copigments was less than 7 days, while the stabilities of anthocyanins with phenolic acids as copigments increased evidently（P〈0.05）. The half-life of anthocyanins with chlorogenic acid, caffeic acid, gallic acid, and ferulic acid increased by 170.87%, 142.68%, 39.56% and 23.05%, respectively. When the concentration of H_2O_2 in anthocyanins solution was at a range of 0.1%-0.6%, anthocyanins was oxidized rapidly, but phenolic acids can protect anthocyanins from oxidation apparently. After being oxidized by 0.1% H2O2 for one hour, the content of anthocyanins in contrast group decreased to 38.39%, however, the retention rate of treatment groups with caffeic acid, ferulic acid, chlorogenic acid and gallic acid were 57.95%, 63.10%, 59.95% and 48.81%, respectively. The solution of Fe^3＋ with concentration of 2.5×10^-4-1×10^-3 mol·L^-1 had an adverse effect on anthocyanins color. In the solution containing Fe^3＋, the stability of anthocyanins with gallic acid as copigment was the highest. Additionally, the A515 nm of treatment groups were higher than contrast group（P〈0.05）. 【Conclusion】The color of red-fleshed apple anthocyanins depends on p H value of solutions obviously. The property of anthocyanins remained stable and the color kept bright red when p H3.0. Caffeic acid, ferulic acid, chlorogenic acid and gallic acid showed varying degrees of hyperchromic effect and the bathochromic shift on red-fleshed apple anthocyanins and evidently improved the stability of anthocyanins（P〈0.05） under various conditions of heating, light exposure, oxidation and adding metal ion of Fe^3＋.