To enzymatically synthesize aroma acetoin fatty acid esters, useful as flavor and fragrance ingredients in foods.Immobilized Candida antarctica lipase B (CALB), performed significantly better than lipases from Rhizopus niveus and Candida rugosa in carrying out the esterification of acetoin and fatty acids. C4–C12 straight chain fatty acids were suitable acyl donors and CALB had a strong preference for longer straight chains up to ten carbon atoms. Higher temperatures, 40–60 °C, and higher acetoin/fatty acid molar ratios favored the conversion. The maximum yield of acetoin octanoate obtained was (51 ± 1) % after 24 h reaction time in hexane with 0.25 M octanoic acid, 5:1 excess acetoin and an enzyme concentration of 6 g/mol fatty acid at 60 °C. The enzyme activity declined at a steady rate during reuse at 60 °C and after the 10th cycle, 65 % of initial activity was still be retained.This is the first report of acetoin fatty acid ester synthesis by biological method and CALB has been shown to be effective for the lipase-catalyzed esterification of acetion and C4–C12 straight chain fatty acids.

Acetoin is a common food flavor additive. This volatile compound widely exists in nature. Some microorganisms, higher plants, insects, and higher animals have the ability to synthesize acetoin using different enzymes and pathways under certain circumstances. As a very active molecule, acetoin acts as a precursor of dozens of compounds. Therefore, acetoin and its derivatives are frequently detected in the component analysis of a variety of foods using gas chromatography–mass spectrometry. Because of the increasing importance of these compounds, this paper reviews the origins and natural existence of these substances, physiological roles, the biological synthesis pathways, nonenzymatic spontaneous reactions, and the common determination methods in foods. This work is the first review on dietary natural acetoin.

In the effluents of a biologically treated wastewater from a heavy oil-refining plant, C5-C8 fatty acids including pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, and 2-methylbutanoic acid are often detected. As these residual fatty acids can cause further air and water pollution, a new Myroides isolate ZB35 from activated sludge was explored to degrade these C5-C8 fatty acids in this study. It was found that the biodegradation process involved a lag phase that became prolonged with increasing acyl chain length when the fatty acids were individually fed to this strain. However, when fed as a mixture, the ones with longer acyl chains were found to become more quickly assimilated. The branched 2-methylbutanoic acid was always the last one to be depleted among the five fatty acids under both conditions. Metabolite analysis revealed one possible origin of short chain fatty acids in the biologically treated wastewater. Aroma volatiles including 2-methylbutyl isovalerate, isoamyl 2-methylbutanoate, isoamyl isovalerate, and 2-methylbutyl 2-methylbutanoate were subsequently identified from ZB35 extracts, linking the source of the fruity odor to these esters excreted by Myroides species. To our best knowledge, this is the first finding of these aroma esters in bacteria. From a biotechnological viewpoint, this study has revealed the potential of Myroides species as a promising source of aroma esters attractive for food and fragrance industries.

Acetoin is a volatile compound widely used in foods, cigarettes, cosmetics, detergents, chemical synthesis, plant growth promoters and biological pest controls. It works largely as flavour and fragrance. Since some bacteria were found to be capable of vigorous acetoin biosynthesis from versatile renewable biomass, acetoin, like its reduced form 2,3-butanediol, was also classified as a promising bio-based platform chemical. In spite of several reviews on the biological production of 2,3-butanediol, little has concentrated on acetoin. The two analogous compounds are present in the same acetoin (or 2,3-butanediol) pathway, but their production processes including optimal strains, substrates, derivatives, process controls and product recovery methods are quite different. In this review, the usages of acetoin are reviewed firstly to demonstrate its importance. The biosynthesis pathway and molecular regulation mechanisms are then outlined to depict the principal network of functioning in typical species. A phylogenetic tree is constructed and the relationship between taxonomy and acetoin producing ability is revealed for the first time, which will serve as a useful guide for the screening of competitive acetoin producers. Genetic engineering, medium optimization, and process control are effective strategies to improve productivity as well. Currently, downstream processing is one of the main barriers in efficient and economical industrial acetoin fermentation. The future prospects of microbial acetoin production are discussed in light of the current progress, challenges, and trends in this field.

•ZB35 can produce more than 20 kinds of aroma esters by solid-state fermentation.•Its complete genome reveals six putative novel esterase genes.•ZB35 is the first bacterium capable of producing so many kinds of aroma esters.•ZB35 could be used as a source of aroma esters in food and fragrance industries.Consumers prefer biotechnological food products with high nutritional values and good flavors. Solid-state fermentation is a commonly used technique with a long history. In the present study, Myroides sp. ZB35 was used in solid-state fermentative production of aroma volatiles on a rice medium. Using the headspace solid phase microextraction coupled with gas chromatography–mass spectrometry technique and authentic standards, 22 esters with molecular weight ranging from 102 to 172 were identified. At 192 h, the esters reached a total concentration of 1774 μg/kg. Subsequently, the complete genome of ZB35 was sequenced using the PacBio RS II platform. ZB35 has a single circular chromosome of 4,065,010 bp with a GC content of 34.1% and six putative novel esterase genes were found. ZB35 is the first bacterium here discovered being capable of producing so many kinds of aroma esters. The data revealed here would provide helpful information for further developing this strain as a promising source of aroma esters relevant in food and fragrance industries and the source of novel enzymes with potential usages.