Enzyme Immobilization: Advances In Industry, Ag...
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Ethanol is not only an important raw material in the chemical synthesis industry, but it is also the most promising biofuel. Among the biorefinery products of Jerusalem artichoke, ethanol has been studied extensively. However, the most commonly used alcohol production strains in the industry, S. cerevisiae and Zymomonas mobilis, cannot effectively utilize inulin to produce ethanol, which severely restricts the industrialization of ethanol production of inulin-based biomass [90]. Traditional ethanol production processes firstly convert inulin to fructose via acid hydrolysis, and then reuse the microbes to ferment ethanol. Onsoy et al. used the acid hydrolysates of Jerusalem artichoke juices as the media for ethanol fermentation by Z. mobilis, which led to consistent ethanol yields (0.45 g/g) and a conversion efficiency of 83.19% of theoretical value [91]. The cost of inulin acid hydrolysis technology for ethanol production is low, but the process is relatively complicated as hydrolysates often contain HMF, a microbial growth inhibitor, and is not environment friendly [92]. Therefore, researchers begin to use microbes or enzymes to assist with S. cerevisiae in producing ethanol directly from inulin. Zhang et al. used the recombinant inulinase produced by P. pastoris, X-33/pPICZaA-INU1, to hydrolyze inulin and ethanol fermentation by S. cerevisiae sp. W0. The total sugar utilization rate after 120 h of fermentation was 98.9%, and an ethanol yield of 0.384 g/g inulin was obtained [93]. The study further proved that inulinase pretreatment of inulin products for ethanol fermentation is feasible. Although inulinase-assisted S. cerevisiae ethanol production is an environmentally friendly technology, the formed fructose inhibits inulinase secretion. Therefore, to relieve product inhibition, researchers have developed a co-fermentation technology on ethanol production combined with inulinase-producing microorganisms. Through mutagenesis, Ge and Zhang obtained an inulinase-producing strain, A. niger SL-09, and co-cultured it with the highly ethanol-tolerant S. cerevisiae Z-06. After 48 h of Jerusalem artichoke fermentation, the utilization rate of inulin was 98%, and the ethanol concentration reached 19.6% (v/v) [94]. Therefore, there is a need to further optimize microbial strains and the process, by improving microbial fermentation co-culture parameters to maximize efficiency of ethanol production from inulin. Since the genome of S. cerevisiae is well studied and genetic manipulation techniques are more advanced, more researchers are focusing on the use of genetic engineering strategies to obtain a recombinant Saccharomyces cerevisiae with inulinase that can directly produce ethanol from inulin. Tong et al. expressed the INU1 gene from marine-derived P. guilliermondii and the recombinant Saccharomyces sp. W0 was able to produce 34.2 U/mL of extracellular inulinase activity in 72 h. During 2 L fermentation, 14.9% (v/v) of ethanol was obtained with the conversion efficiency of 99.5% from inulin to ethanol [95]. Yuan et al. cloned the exo-inulinase gene from Candida kutaonensis and expressed in S. cerevisiae for the improvement of inulin utilization, and the recombinant S. cerevisiae was able to produce high ethanol yields from both inulin and Jerusalem artichoke tuber flour [96]. A natural engineering S. cerevisiae engineered with rational strategies such as co-expressing exo- and endo-inulinase gene, inactivated proteases between haploid and diploid was investigated for inulin utilization to produce ethanol. Ethanol fermentation from 200 g/L inulin and 250 g/L raw Jerusalem artichoke tuber powder resulted in productivity of 2.44 and 3.13 g/L/h, respectively [97]. Actually, in addition to building engineering strains, some yeast genus, such as Kluyveromyces fragilis and Kluyveromyces marxianus can both produce inulinase and ethanol. Rosa et al. selected K. marxianus to utilize extracted juice of Jerusalem artichoke tubers for ethanol production, the production of 12.8% (v/v) of ethanol in 70 h with the consumption of 95% of initial sugars, and an ethanol yield 77% of the theoretical maximum were achieved [98]. Yuan et al. studied ethanol fermentation of K. marxianus ATCC8554 using inulin as substrate and the highest ethanol yield of 91.5% of the theoretical value was achieved [99]. Above all, we believe that the use of Jerusalem artichoke in ethanol fermentation will become more economical and practical.
Uses of immobilized enzymes: During the initial years of the development of the field of immobilized enzymology, researchers used to find only the advantage of the immobilized enzymes in comparison to their soluble/free counterparts. Advantages of immobilized versus soluble enzymes included comparative studies in pH profile, various denaturing agents organic solvents, temperature, etc. Now recently during the last couple of decades, immobilized enzyme technology has advanced into and ever-expanding and multidisciplinary fields to analyze clinical, industrial and environmental samples. Here, we present recent developments and used of immobilized enzymes in different fields such as in medicine, antibiotic production, drug metabolism, food industry, biodiesel production, bioremediation, etc.
The yield of hydrolysis and synthesis has been greatly improved by process design including immobilization of the enzyme and the use of alternative reaction media. Significant advances have also been made in the resolution of racemic mixtures by means of stereo-selective acylation/hydrolysis using β-lactam acylases (Sio and Ouax, 2004).
Recent advances in the design of immobilization supporting materials with tailorable pore size and surface functionality has enabled more precise control of immobilization of enzymes. New simulations of the surface characteristics of the target enzymes can be used to aid in the design of appropriate support materials. As the structure and mechanism of action of enzymes becomes available more controlled immobilization methods will be generated. The development of cheaper and disposable array biosensors, bioreactors and biochips for the simultaneous detection of clinically important metabolites and rapid screening of diseases has attracted much attention during the recent past. We believe that the use of more and more immobilized enzymes in clinical, biotechnological, pharmacological and other industrial fields has great promise among future technologies. 59ce067264
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