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Recent Advances in Enzyme Immobilization Using Nanomaterials and its Applications for the Production of Biofuels
Published in Madan L. Verma, Nanobiotechnology for Sustainable Bioenergy and Biofuel Production, 2020
Sujit Sadashiv Jagtap, Ashwini Ashok Bedekar
2,3-Butanediol (2,3-BDO) is a high-value chemical with a heating value of 27.2 kJ g−1. It can be used to produce cosmetics, fumigants, antifreeze agents, transport fuels, polymers, acetoin, diacetyl and solvents such as 1,3-butadiene, methyl ethyl ketone and gamma-butyrolactone (Celinska and Grajek 2009, Ji et al. 2011, Syu 2001). 2-butanol is a stereoisomer of butanol. It has a higher energy density and hygroscopicity as compared to bioethanol. It is used with gasoline without any change to the vehicle system (Nigam and Singh 2011). It is also used as a paint thinner, base for perfumes and component of brake fluids (Nigam and Singh, 2011). Acetoin is used in the food industry as a flavor enhancer and as a building block for the synthesis of chemicals such as pyrazines, diacetyl and acetylbutanediol (Yang et al. 2017).
Electrode-Assisted Fermentations: Their Limitations and Future Research Directions
Published in Sonia M. Tiquia-Arashiro, Deepak Pant, Microbial Electrochemical Technologies, 2020
Veronica Palma-Delgado, Johannes Gescher, Gunnar Sturm
The concept of electrode-assisted fermentations was introduced by Flynn and his colleagues in 2010. They engineered a Shewanella strain by introducing glycerol consumption as well as an ethanol production module from E. coli and Zymomonas mobilis, respectively. This strain was able to stoichiometrically convert glycerol into ethanol by eliminating two surplus electrons by means of an electrode offered as terminal electron acceptor (Flynn et al. 2010). The additional deletion in the gene coding for phosphate acetyltransferase (pta) increased the carbon conversion rate from glycerol to ethanol from 75% to 85% (Flynn et al. 2010). Electrode-assisted fermentations were also established for the production of other products. One potential substance is 2,3-butanediol or its precursor acetoin. Acetoin (3-hydroxy-2-butanon) was rated as one of the top 30 most promising platform chemicals by the US Department of Energy in 2004 (Werpy and Petersen 2004). Consequently, a great deal of effort was put into the optimization of its production process (e.g., Sun et al. 2012; Zhang et al. 2013, 2016; Wang et al. 2013; Chen et al. 2013). Microbial fermentations, particularly bacterial fermentations, serve as the main source for the biotechnological production of acetoin (Xiao and Lu 2014). Sun et al. showed that a production yield of roughly 75 g l−1 at a rate of 1.88 g l−1 h−1 can be achieved by using Serratia marcescens as producing host and sucrose as substrate (Sun et al. 2012). An engineered strain of Bacillus subtilis was able to produce an average amount of ~62 g l−1 at a rate of 0.864 g l−1 h−1 but used a combination of monosaccharides derived from lignocellulosic hydrolysates (Zhang et al. 2016). Until now, acetoin was produced almost exclusively under oxic conditions as it is more oxidized than glucose (Wang et al. 2013). Recently, Bursac and colleagues established a strain variant of S. oneidensis capable of acetoin production. They introduced a plasmid-based genetic module consisting of codon-optimized versions of B. subtilis derived acetolactate synthase (alsS) and acetolactate decarboxylase (alsD). This strain was capable of converting 40% of the catabolically consumed lactate into acetoin while roughly 60% was further converted into the natural end product of the strain (Bursac et al. 2017). Further strain development was carried out to increase the amount of acetoin produced by considerably reducing the amount of acetate released from the reaction. Knockouts in phosphate acetyltransferase and acetate kinase (e.g., pta, ackA) further increased the ratio of acetoin conversion from lactate to ~86% of the theoretical maximum. Of note these experiments were conducted in cell suspensions using fumarate as the terminal electron acceptor (Bursac et al. 2017).
Production of racemic acetoin by fermentation using Lactobacillus casei
Published in Chemical Engineering Communications, 2020
Maximiliano Ibaceta, Maciej E. Domaradzki, Thomas F. DelMastro
Acetoin (3-hydroxybutan-2-one) is a naturally occurring chemical that contributes to the buttery and creamy aromas in dairy products. Acetoin can be used as a food additive in a variety of products (e.g., food flavoring) and formulations (e.g., artificial butter flavor, fragrance) (Xiao and Lu, 2014). Microbial production of enantioenriched acetoin requires fermentation of lactic acid bacteria such as Lactobacillus (Jyoti et al., 2004), Lactococcus (Roncal et al., 2017), among others. Natural and renewal carbon sources such as glucose or citrate are converted to diacetyl 1, acetoin 2, and 2,3-butanediol 3 (Figure 1), depending on the mixed-acid and butanediol fermentation capabilities of the microorganism and carbon source used (Starrenburg and Hugenholtz, 1991; Neijssel et al., 1997).
Impact of different FD-related drying methods on selected quality attributes and volatile compounds of rose flavored yogurt melts
Published in Drying Technology, 2021
Kay Khaing Hnin, Min Zhang, Bin Wang
A total of 12 species of ketones were detected by GC-MS in fresh and three dried rose flavored yogurt melts. Three different dried samples showed higher ketones contents (7.7%, 7.22%, and 7.64% for FD, IRPSFD, and MPSFD) than fresh ones (5.46%). The amino acid degradation and the enzymatic decomposition of polyunsaturated fatty acids are the key points to create ketones[39] that help to generate the positive odor of floral and fruity sweet.[40] 5-Hepten-2-one, 6-methyl were the dominant ketone in dried rose flavored yogurt melts. IRPSFD samples contained more acetoin (1.06%) compared to the samples obtained from FD (0.50%) and MPSFD (0.64%) and presented similar amounts in fresh (1.06%). Acetoin has the odor of pleasant cream[41] and is commonly applied as an additive in food products to improve the product's flavor.[42] A total of 11 species of alkenes were detected by GC-MS in three different dried rose flavored yogurt melts. The rose flavored yogurt melts produced by FD provided the highest alkenes contents (3.72%), descending order by MPSFD samples (3.18%) and IRPSFD samples (2.21%). For the volatile alkene components, á-myrcene and D-limonene were the main alkene in three different dried samples and it has a pleasant odor[43] and odor of orange peel, orange juice, and other citrus fruits.[44] Among dried samples, the lowest amount of á-myrcene (0.5%) was obtained in IRPSFD samples, whereas MPSFD samples presented the lowest D-limonene content (0.42%).