| y-Decalactone(GDL),existed naturally in fruits and fermentation products,has been widely used in food,flavor and other industries because of its attractive peach aroma in low content.The storage of GDL in nature is unable to satisfy the people's increasing demand of it,and the GDL obtained by chemical method does not have the activity of optical.The GDL produced from the biotransformation has the character of high quality,safety and is identical to the nature one.In addition,the biological preparation process is in according with the green and healthy concept of people.Therefore,there is a promising prospect for the biological production of GDL.In this study,the MF013 yeast was choosen as the strain to produce GDL.The quantitative analysis method of the GDL,ricinoleic acid and glycerol was established and the process of biotransformation of two substrates,castor oil and ricinoleic acid,into GDL was compared.When the concentration of substrates was 40 g/L,the yeilds of GDL were 1.76 g/L and 1.61 g/L respectively after 48 h biotransformation.The presence of short chain alcohols and ricinoleic acid methyl esters were found in the medium with castor oil analysis by GC-MS,while there was none of them in the medium with ricinoleic acid.The effect of glycerol,ethylene glycol and 1,2-propylene glycol on the biosynthesis of GDL was investigated in the medium with ricinoleic acid as the substrate.And the result shows that the glycerol could induce the biosynthesis of GDL.When the concentration of ricinoleic acid and glycerol was 40 g/L and 10 g/L respectively,after 84h transformation,the yield of GDL increased by 72.7%compared to the control,which was 2.85 g/L.The key steps of the biotransformation of GDL from ricinoleic acid are the activation of ricinoleic acid and the high efficiency of the ?-oxidation.In this study,we added different concentrations of magnesium sulfate into the biological transformation medium firstly.And the result shows that the present of magnesium ions could effectively activate the thiokinase activity and fatty acids.When 7.0 g/L MgSO4·7H2O was added into the medium,it could effectively improve the yield of GDL.Then nine organic acids were utilized in the experiment to induce the enzymes in the p-oxidation system.When 3.0 g/L myristic acid was added in the medium,the ricinoleic acid was added as the substrate after 6h inducing.The result shows that the yield of the GDL increased by 15.2%compared with the control after the bioconversion of 48 h.In the end,we studied the effect of carnitine on the transfer of activated fatty acid into the mitochondria for ?-oxidation.When the concentration of ricinoleic acid was 40 g/L in the medium with 0.1 g/L carnitine,after 48 h biotransformation,the yield of GDL reached 2.86 g/L which was 13.5%higher than the one in the control medium.And the transformation time was shortened by 12 h,which means that the?-oxidation rate of ricinoleic acid was enhanced.A lot of biotransformation experiments show that in the late stage of biological transformation,GDL would be degraded by yeast MF013.We investigated the effect of four different chain length's lactone compounds on the biotransformation of GDL and found that the addtion of 1.0 g/L ?-octalactone could effectively inhibit the degradation of GDL yeast,and the GDL's final concentration increased by 11.8%.In order to increasing the opportunity of interaction and utilization of substrate by yeast MF013,the porous starch was utilized to adsorb and embed the ricinoleic acid.In this study,the porous starch was utilized as a dispersion slow-release material to increase the dispersion degree of substrate.The scanning electron microscopy,thermogravimetry and fourier transform infrared spectroscopy were employed to investigate whether there was a complex formed between the porous starch and ricinoleic acid.The result showed that the porous starch adsorbed the ricinoleic acid on the surface into the hollow structure.When the complex was utilized in the medium,the initial concentration of ricinoleic acid was reduced to 25 g/L,and the yield of GDL increased by 17.5%which reached 3.36 g/L after 48 h biotransformation. |
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