The Monthly Digest – Aromas and flavours – February & March 2018

Aromas and flavours

R & D abstracts – February & March 2018

Biosynthesis and production of sabinene: current state and perspectives (review)

Sabinene is an important naturally occurring bicyclic monoterpene which can be used as flavorings, perfume additives, fine chemicals, and advanced biofuels. Up to now, this valuable terpene is commercially unavailable since there is no applicable manufacturing process. Microbial synthesis can be a promising route for sabinene production. In this review, we summarize knowledge about the metabolic pathway and key enzymes for sabinene biosynthesis. Recent advances that have been made in production of sabinene by microbial fermentation are highlighted. In these studies, researchers have identified the general synthetic pathway of sabinene from simple intermediate metabolites. Sabinene synthases of different origins were also cloned and characterized. Additionally, heterologous systems of the model microbes Escherichia coli and Saccharomyces cerevisiae were constructed to produce sabinene. This review also suggests new directions and attempts to gain some insights for achieving an industrial level production of sabinene. The combination of traditional molecular biology with new genome and proteome analysis tools will provide a better view of sabinene biosynthesis and a greater potential of microbial production.

Cao Y et al (2018) Applied Microbiology and Biotechnology 102:1535-1544

Bioflavoring by non-conventional yeasts in sequential beer fermentations (research)

Non-conventional yeast species have great capacity for producing diverse flavor profiles in production of alcoholic beverages, but their potential for beer brewing, in particular in consecutive fermentations with Saccharomyces cerevisiae, has only poorly been explored. We have screened 17 non-conventional yeast species for production of an appealing profile of flavor esters and phenolics in the first phase of alcoholic fermentation, followed by inoculation with S. cerevisiae to complete the fermentation. For measurement of phenolic compounds and their precursors we developed an improved and highly sensitive methodology. The results show that non-conventional yeast species possess promising potential for enhancement of desirable flavors in beer production. Notable examples are increasing isoamyl acetate (fruity, banana flavor) by application of P. kluyverii, augmenting ethyl phenolic compounds (spicy notes) with Brettanomyces species and enhancing 4-vinyl guaiacol (clove-like aroma) with T. delbrueckii. All Pichia strains also produced high levels of ethyl acetate (solvent-like flavor). This might be selectively counteracted by selection of an appropriate S. cerevisiae strain for the second fermentation phase, which lowers total ester profile. Hence, optimization of the process conditions and/or proper strain selection in sequentially inoculated fermentations are required to unlock the full potential for aroma improvement by the non-conventional yeast species.

Holt S et aal (2018) Food Microbiology 72:55-66

Microbe participation in aroma production during soy sauce fermentation (research)

Soy sauce is a traditional Japanese fermented seasoning that contains various constituents such as amino acids, organic acids, and volatiles that are produced during the long fermentation process. Although studies regarding the correlation between microbes and aroma constituents have been performed, there are no reports about the influences of the microbial products, such as lactic acid, acetic acid, and ethanol, during fermentation. Because it is known that these compounds contribute to microbial growth and to changes in the constituent profile by altering the moromi environment, understanding the influence of these compounds is important. Metabolomics, the comprehensive study of low molecular weight metabolites, is a promising strategy for the deep understanding of constituent contributions to food characteristics. Therefore, the influences of microbes and their products such as lactic acid, acetic acid, and ethanol on aroma profiles were investigated using gas chromatography/mass spectrometry (GC/MS)-based metabolic profiling. The presence of aroma constituents influenced by microbes and chemically influenced by lactic acid, acetic acid, and ethanol were proposed. Most of the aroma constituents were not produced by adding ethanol alone, confirming the participation of yeast in aroma production. It was suggested that lactic acid bacterium relates to a key aromatic compound, 2,5-dimethyl-4-hydroxy-3(2H)-furanone. However, most of the measured aroma constituents changed similarly in both samples with lactic acid bacterium and acids. Thus, it was clear that the effect of lactic acid and acetic acid on the aroma profile was significant.

Harada R et al (2018) Journal of Bioscience and Bioebgineering (2018)