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Sponge-Like Ionic Liquids for Clean Biocatalytic Processes
Published in Pedro Lozano, Sustainable Catalysis in Ionic Liquids, 2018
Susana Nieto-Cerón, Elena Álvarez-González, Juana M. Bernal, Antonio Donaire, Pedro Lozano
In the cited work, the highly hydrophobic IL [C16mim][NTf2] provided a homogeneous liquid medium with the reactants above 50°C [99]. In these conditions, esterification was straightforward (more than 80% in two hours for the four studied carboxylic acids), the longer the cation alkyl side chain, the more efficient the process (C18tma > C16tma > C14mim > C12mim). Microwaves even more accelerate the rate of biocatalysis [125]. These yields must be compared with those obtained when solvent-free esterification was carried out (14.9% in four hours reaction for isoamyl acetate). In the absence of ILs, the high concentrations of polyols tended to deactivate the enzyme, and, moreover, a biphasic system was created. The hydrophobic ILs keep the enzyme folded, but also sequester the alcohols, preventing them from reaching high concentrations in the surroundings of the enzyme. These two features are crucial for a high reaction efficiency.
Production of Fermented Foods
Published in Nduka Okafor, Benedict C. Okeke, Modern Industrial Microbiology and Biotechnology, 2017
Nduka Okafor, Benedict C. Okeke
Sauerkraut is produced by the fermentation of cabbages, Brassica oleracea, and has been known for a long time. Specially selected varieties which are mild-flavored are used. The cabbage is sliced into thin pieces known as slaw and preserved in salt water or brine containing about 2.5% salt. The slaw must be completely immersed in brine to prevent it from darkening. Kraut fermentation is initiated by Leuconostoc mesenteroides, a heterofermentative lactic acid bacterium (i.e. it produces lactic acid as well as acetic acid and CO2). It grows over a wide range of pH and temperature conditions. CO2 creates anaerobic conditions and eliminates organisms which might produce enzymes which can cause the softening of the slaw. CO2 also encourages the growth of other lactic acid bacteria. Gram-negative coliforms and pseudomonads soon disappear and give way to a rapid proliferation of other lactic acid bacteria, including the heterofermentative L. brevis and the homofermentative L. plantarum; sometimes, Pediococcus cerevisiae also occurs. Compounds which contribute to the flavor of sauerkraut begin to appear with the increasing growth of the lactics. These compounds include lactic and acetic acids, ethanol, and volatile compounds such as diacetyl, acetaldehyde, isoamyl alcohol, n-hexanol, ethyl lactate, ethyl butarate, and isoamyl acetate. Besides the 2.5% salt, it is important that a temperature of about 15°C is used. Higher temperatures cause a deterioration of the kraut.
Solid-State Chemical Microsensors and Wireless Instrumentation
Published in Robert B. Northrop, Introduction to Instrumentation and Measurements, 2018
Arrays of differentially doped tin oxide gas sensors can be used to make E-noses that can identify several VOCs at the same time. Fort et al. (2003) reported on their work with an eight-element tin oxide sensor array with the goal of developing analyte selectivity for gas mixture classifications. With wine characterization as a goal, they used aqueous test mixtures of l%wt ethanol, 0.05%wt ethyl acetate, 0.08%wt glycerol, 0.05%wt isoamyl acetate, 0.05%wt linalool, and 0.05%wt hexanol, one at a time and in pairs. (Linalool is a commercial odorant/flavorant, aka 3,7 – dimethyl-1,6-octadieri-ol, found naturally in cinnamon, bergamot, sassafras, and orange blossom.) Three classification protocols were tested: (1) a transient analysis of Rs(t) for various analytes at constant temperature, (2) SS AC vector impedance Zs of the sensor for various analytes at constant temperature, and (3) RS(T) for sinusoidally programmed sensor temperature T with periods P of 40 and 180 s. These researchers found that the programmed temperature method, in which T ≅ 220{1 + 65 sin [(2π/P)t]} °C, gave better discrimination results than measurements using chemical transients or AC impedance. There was better separation of a given sensor’s responses to the test analytes at the beginning and end of each sinusoidal cycle, presumably when the sensors’ temperature returned to the baseline 220°C. There was a single peak in the responses to the test analytes over one heating cycle, but poor resolution at the peak between analytes.
Green synthesis of banana flavor using different catalysts: a comparative study of different methods
Published in Green Chemistry Letters and Reviews, 2020
Mahdieh Zare, Mohammad-Taghi Golmakani, Alireza Sardarian
Short-chain esters are compounds with widespread applications that dominate the food and cosmetic industries because of their unique characteristics in flavor and fragrance (1). Banana flavor (isoamyl acetate) is one of the most widely-used short-chain esters in food preparations, in addition to the cosmetic and pharmaceutical industries (2,3). The annual demand for isoamyl acetate is more than 195,000 lb (4).