Halotolerant Aspergillus niger Catalyzed Synthesis of Esters in Ionic Liquids
저자
발행사항
인천 : 인하대학교 대학원, 2018
학위논문사항
학위논문(박사)-- 인하대학교 대학원 일반대학원 : 해양과학생물공학과 2018. 2
발행연도
2018
작성언어
영어
주제어
DDC
660.6 판사항(21)
발행국(도시)
인천
기타서명
염소성 Aspergillus niger 촉매를 이용한 이온 성 액체의 에스테르 합성
형태사항
xvii,169 p. ; 26cm
일반주기명
지도교수:Prof.Yoon-Mo Koo
인하대학교 논문은 저작권에 의해 보호받습니다.
참고문헌 : p.155-169
소장기관
Abstract:
For development of greener process, biocatalysis gains an importance in the production of high value fine and bulk chemicals, as well as pharmaceutical ingredients. The advent of isolated enzyme or whole cell as biocatalyst, those value-added chemicals targeting enantio- and regioselectivities is achieved well, which could be the advantage over the chemical mode of synthetic reaction. Lipase is one of the industrially important enzymes as biocatalyst for synthesis of value-added esters through esterification and transesterification reactions. Among the microorganism as a lipase producer, fungi are predictably best lipase sources for bioconversion because of its rigid, sustainable filamentous structure. Whole cell biocatalyst having an industrial interest that itself a protective barrier for the enzyme and significantly cheaper in production and purification than isolated enzyme, that needs tedious isolation and refinement. In this study, halotolerant filamentous fungi Aspergillus niger (A. niger), was selected as whole cell biocatalyst for the synthesis of esters in nonconventional medium. We confirmed the lipase production from A. niger with standard rhodamine B assay and used as biocatalyst to produce industrially important esters in nonconventional ionic liquid medium. Here ionic liquids are molten salts being an alternative to the organic solvents, and could act as solvent, co-solvent, additive and catalyst for many biocatalytic reactions. In depth of this study, spores a reproductive part and mycelia a vegetative part of halotolerant A. niger are used as biocatalyst for the biosynthesis of esters in ionic liquids and the contents are divided into four parts: (1)Halotolerant A. niger mycelia as biocatalyst for the synthesis of caffeic acid phenylethyl ester (CAPE), a phenolic ester in ionic liquid medium; (2) Halotolerant A. niger mycelia as biocatalyst for the synthesis of isoamyl acetate (IA), a flavor ester in solvent free medium containing ionic liquid as additive; (3) Halotolerant A. niger spore as biocatalyst for the synthesis of caffeic acid phenylethyl ester (CAPE), a phenolic ester in ionic liquid medium; (4) Halotolerant A. niger spore as biocatalyst for the synthesis of isoamyl acetate (IA), a flavor ester in solvent free medium containing ionic liquid as additive.
In the first part of this study, we utilized mycelia of halotolerant A. niger as lipase source for the synthesis of phenolic acid ester. As a model reaction, we chose the caffeic acid, a phenolic acid as substrate for synthesis of its ester in ionic liquid medium. Caffeic acid (CA) and its esters have wide range of biological activities, however the isolation is hurdle for medicinal application. Besides, caffeic acid ester have more obvious biological activity than CA. Due to the low solubility of caffeic acid in non-polar solvents, usage of CA in oil, food and cosmetic industry is limited. To concern the environment friendly process, and the usage of organic solvent, we used ionic liquids as solvent for esterification of caffeic acid. Ionic liquids itself having the good physical properties provide the good solvent for synthesis of medically important esters of caffeic acid. This processes which involve the using of halotolerant A. niger mycelia along with ionic liquids were compatible as biocatalyst. A. niger was active at low temperature of about 30 ºC and maximum conversion of about 84 % was achieved with ionic liquid medium.
On the second part, we employed mycelia of halotolerant A. niger as a lipase producer for the synthesis of flavor ester in a solvent free medium containing ionic liquid as additive. Utmost of the flavor compounds are traditionally extract from the natural sources using organic solvent system or chemically synthesized. Moreover, natural extraction process is insufficient for bulk usage and chemically synthesized flavor are not to be considered as natural one. Mycelia of halotolerant A. niger is compatible with solvent free medium along with the ionic liquid as additive for the ester synthesis. In this study, ionic liquid improves the catalyst efficiency of the mycelia, and correlation of mycelial activity and effect of ionic liquids are well understood from the study of protein secondary structure using FTIR analysis. Employing ionic liquid improves the catalyst activity of mycelia and influencing the efficient biocatalytic process to produce flavor ester with maximum conversion of 97% at 24 h reaction time.
In the third part of this study, utilizing reproductive part of halotolerant fungus A. niger spore for the synthesis of caffeic acid esters in ionic liquid medium. Spores of fungi are metabolically inert, often used as starter culture, strain conservation and dissemination purpose. The metabolically inert spores are used as catalyst for many bioconversion reactions while the spores are maintained in non-germinated condition. Spore itself have ability for bioconversion in many steroidal compounds and flavor compounds than vegetative. In this study, spores of A. niger as a well compatible in ionic liquid medium to catalyze the esterification reaction for the synthesis of CAPE. Reaction conditions were optimized, effective substrate conversion of 79% at 40 ºC was achieved at 24 h reaction time.
In the final part, study was carried out using spores of A. niger as lipase source for the synthesis of IA in solvent free medium containing ionic liquid as additive. Spores are well documented catalyst to produce flavor and aroma compounds. In this study, the efficiency of spore while utilizing as biocatalyst in non-conventional media of ionic liquid was investigated. Ionic liquids are screened as an additive for IA synthesis in solvent free medium. In optimized reactions conditions, the maximum conversion of about 85% was achieved with using minimal quantity of ionic liquid as additive in IA synthesis.
In summary of the research, successful biocatalytic conversions were carried out and conditions were optimized for employing halotolerant fungi in ionic liquid. Ionic liquids are favored for the product conversion as solvent and additive. The conversion was quantified using standard HPLC method. The product conversion was estimated in different time and temperature. Experimentally we used the same fungi and different ionic liquids for the synthesis of esters, as model reaction. Fourier-transform infrared spectroscopy (FTIR) technique was used for the study of structural changes in protein of the fungi. Overall, this study revealed that both vegetative (mycelia) and reproductive (spore) part of halotolerant A. niger are well compatible and good candidate biocatalyst for the synthesis of esters using ionic liquid.
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