Laktosa boleh ditukarkan kepada produk bernilai tinggi iaitu galakto-oligosakarida (GOS) melalui tindak balas hidrolisis dan transgalaktosilasi bermangkinkan β-galaktosidase (β-Gal). Hasil GOS yang tinggi telah diperolehi apabila proses tindak balas dilakukan dengan menggunakan reaktor enzimatik membran (EMR), namun puncanya masih kurang difahami. Kelakuan pemindahan jisim substrat ataupun zat-zat kearah biopemangkin dan merentasi lapisan membran dijangka boleh mempengaruhi arah tindak balas serta prestasi biopemangkin didalam EMR. Tujuan kajian ini adalah untuk menganalisa kesan profil pemindahan jisim di dalam reaktor enzimatik membran gentian berongga (HFMR) terhadap penukaran laktosa diperantarakan β-Gal disekat gerak. Kajian terhadap proses tindak balas menunjukkan bahawa pembentukan GOS adalah sangat dipengaruhi oleh kepekatan awal laktosa dan activiti β-Gal. Didapati bahawa galaktosa merupakan perencat pesaing dan mampu mengurangkan pembentukan GOS. β-Gal yang disekat gerak pada HFMR telah dibangunkan untuk menyingkirkan perencat (galaktosa) dan meningkatkan prestasi tindak balas. Kajian hidrodinamik ke atas kadar ricih pada permukaan membran telah mencadangkan bahawa HFMR sepatutnya dikendalikan dengan ultraturasan dari bahagian lumen ke bahagian kelompang. Konfigurasi ini memberikan pengagihan kadar ricih yang homogen dimana ianya penting untuk menyekat gerak β-Gal pada permukaan membran. β-Gal telah dipegun di atas permukaan membran berlapiskan polietilenimina (PEI) melalui jerapan dan pengikatan serentak menggunakan glutaraldehid (GA). Hasil aktiviti telah dipengaruhi oleh kepekatan PEI, GA dan β-Gal. Secara umum, produktiviti spesifik bagi GOS telah meningkat di dalam HFMR berbanding sistem kelompok klasik. Tindak balas laktosa bermangkin β-Gal didalam HFMR adalah sangat dipengaruhi oleh tekanan transmembran (TMP) berbanding kadar alir suapan nominal. Pembentukan GOS adalah tertinggi pada TMP = 0.5 bar. Bagi memahami tingkah laku ini, kajian kinetik tindak balas dan pemindahan jisim telah dilaksanakan. Model kinetik yang digabungkan dengan kesan-kesan kepekatan laktosa, glukosa, galaktosa, trisakarida dan tetrasakarida telah berjaya dibangunkan serta disahkan. Sementara itu, model pemindahan jisim bersesuaian yang turut digabungkan dengan kesan-kesan ciri-ciri membran, kepekatan zat-zat terlarut di dalam larutan pukal dan pembentukan lapisan kek telah digunakan. Kajian simulasi telah menunjukkan bahawa, kadar tindak balas bagi pembentukan GOS adalah sangat dipengaruhi oleh operasi TMP. Pembentukan GOS paling maksimum telah berlaku pada TMP = 0.5 bar dimana, sama seperti keputusan yang diperolehi melalui eksperimen. Pembentukan lapisan kek pada TMP yang tinggi (>0.5 bar) mengurangkan pemindahan jisim zat-zat merentasi biopemangkin membran. Oleh yang demikian, kadar tindak balas telah menurun apabila TMP dinaikkan kepada 0.8 bar walaupun pemisahan perencat galactosa meningkat. Maka boleh disimpulkan bahawa pemindahan jisim zat-zat kearah biopemangkin membran merupakan factor penentu untuk memperolehi hasil GOS yang tinggi menerusi penukaran laktosa berperantara β-Gal disekat gerak didalam HFMR.
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Lactose can be converted to valuable product of galacto-oligosaccharides (GOS) through β-galactosidase (β-Gal)-catalyzed reaction via hydrolysis and transgalactosylation. A high yield of GOS is obtained when the reaction process is carried out in enzymatic membrane reactor (EMR) of which the mechanism remain poorly understood. The mass transfer behaviour of substrate or solute to the biocatalytic and through the membrane layers are expected to influence the course of the reaction as well as the biocatalytic performance in the EMR. The aim of this study was to analyze the effect of mass transfer profile in the enzymatic hollow fiber membrane reactor (HFMR) on the immobilized β-Gal-mediated conversion of lactose. Investigation of the reaction process indicated that the formation of GOS was highly influenced by initial lactose concentration and β-Gal activity. Galactose has been found to be competitive inhibitor and able to decrease the formation of GOS. The HFMR with immobilized β-Gal was developed to continuously remove the inhibitor (galactose) and improved the reaction performance. Hydrodynamic study of shear rate on the membrane surface has suggested that the HFMR is best operated with an ultrafiltration from the lumen to shell side. This configuration gives homogeneous distribution of shear rate which is important for the immobilization of β-gal on the membrane surface. The β-Gal was immobilized on the polyethyleneimine (PEI)-layered surface of the membrane via simultaneous adsorption and fixation with glutaraldehyde (GA). The activity yield was influenced by the concentration of PEI, GA and β-Gal. In general, the specific productivity of the GOS was increased in the HFMR compared to the classical batch system. The reaction performance in the HFMR was greatly influenced by the trans-membrane pressure (TMP) compared to the nominal feed flow rate. The formation of GOS was highest at TMP of 0.5 bar. In order to understand this behaviour, kinetic of reaction and mass transfer studies were carried out. The kinetic model incorporated with the effect of lactose, glucose, galactose, trisaccharides and tetrasaccharides concentrations was successfully developed and validated. Meanwhile, an appropriate mass transfer model incorporated with the effect of membrane characteristics, concentration of solutes in bulk solution and the formation of cake layer were employed. The simulation study indicated that, the reaction rate for the formation of GOS was highly influenced with the operating TMP. The maximum formation of GOS was obtained at TMP of 0.5 bar which is in agreement with the result obtained from the experiment. The formation of cake-layer at higher TMP (>0.5 bar) reduced the mass transfer of solutes through the biocatalytic membrane. Therefore, the reaction rates were decreased as the TMP was further increased to 0.8 bar although the separation of the galactose inhibitors was improved. Hence, it was concluded that the mass transfer of solutes to the biocatalytic membrane was the determining factor to obtain high yield of GOS via immobilized β-Gal-mediated conversion of lactose in the HFMR.
Immobilized B-galactosidase-mediated conversion of lactose process, kinetics and modelling studies_Fadzil Noor Gonawan_K4_2017_MYMY