大蒜果聚糖∶果聚糖1-果糖基转移酶的酶学特性
Characteristics of fructan∶ fructan 1-fructosyltransferase in garlic
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摘要: 大蒜中主要干物质为多糖,其中主要糖类为果聚糖,具有多种保健作用。本文研究了大蒜中果聚糖∶果聚糖1-果糖基转移酶(Fructan∶fructan 1-fructosyltransferase,1-FFT)的酶学特性,为阐明大蒜在采后贮藏、保鲜及深加工过程中果聚糖含量的变化提供依据。结果表明:当以1-蔗果三糖为底物时,1-FFT仅催化生成蔗果四糖,且无其它结构的四糖生成;大蒜1-FFT主要存在于40%50%硫酸铵部分;其最适p H为6.0,在p H 5.56.5条件下1 h内保持稳定;最适温度为25℃,在1525℃条件下1 h内可保持稳定;低浓度Mn2+、Mg2+、Fe3+促进1-FFT活力,Cu2+、Zn2+、Ag+抑制1-FFT活力;1-FFT活力随底物浓度升高而增大,其米氏常数Km=0.6977 mol/L,最大反应速率Vmax=116.23μg/h。大蒜1-FFT活力受p H、温度、不同金属离子及底物浓度影响,调节以上因素有助于调控大蒜果聚糖代谢、保持大蒜品质及延长大蒜贮藏期。Abstract: Fructans account for the majority of dry weight of garlic bulbs, which possess various health benefits.Characteristics of fructan: fructan 1-fructosyltransferase ( 1-FFT) in garlic was investigated to illustrate the changes of fructans in garlic during storage and processing.The results showed that only 1, 1-Kestotetraose was produced by 1-FFT when 1-Kestose was used as the substrate.1-FFT mainly existed in the 40% ~50% ammonium sulfate fraction.The optimum p H of 1-FFT was 6.0, 1-FFT was stable in a range of p H 5.5~6.5 for 1 h.The optimum temperature was 25 ℃, 1-FFT was stable at 15~25 ℃ for 1 h.1-FFT was activated by low concentration of Mn2+, Mg2+and Fe3+, inhibited by Cu2+, Zn2+and Ag+.Enzymatic activity was increased with the ascending concentration of substrate, and Kmwas 0.6977 mol/L, Vmaxwas 116.23 μg/h. Enzymatic activity of 1-FFT was affected by temperature, p H, various metal ions and substrate concentration, regulating those influence factors could regulate the metabolism of garlic fructan and prolong the storage of fresh garlic.