The Monthly Digest – Aromas and Flavours September 2017

Aromas and flavours
R & D abstracts – September 2017
Microbial diversity of traditional kefir grains and their role on kefir aroma (research)

Kefir grains consist of rich bacterial and fungal microflora responsible for the production of this traditional fermented milk beverage with unique flavour properties. Here, a pyrosequencing approach was applied for the identification of microbial flora of four kefir grains collected from different regions of Turkey and the volatile compounds in kefir samples produced with these grains were determined. Lactobacillus kefiranofaciens presented in all grains at important levels and EnterobacterAcinetobacterEnterococcus and Pseudomonas spp. were observed in traditional kefir grains. The fungal microflora of kefir grains was dominated by yeast species and Dipodascaceae family was dominant and Saccharomyces cerevisiaepresented in all grains. Other yeast species belonging to KazachstaniaCandidaIssatchenkia and Rhodotorula species were also detected in kefir grains. Volatile compounds of kefir samples were also diverse related to the microbial diversity of kefir grains. This study revealed the rich microflora of Turkish kefir grains and their interactions with the aromatic properties of kefir.

Dertli E and çon HA (2017) LWT Food Science and Technology 85A:151-157

 

Influence of different yeast/lactic acid bacteria combinations on the aromatic profile of red Bordeaux wine (research)

The typical fruity aroma of red Bordeaux wines depends on the grape variety but also on microbiological processes, such as alcoholic and malolactic fermentations. These transformations involve respectively the yeast Saccharomyces cerevisiae and the lactic acid bacterium Oenococcus oeni. Both species play a central role in red winemaking but their quantitative and qualitative contribution to the revelation of the organoleptic qualities of wine has not yet been fully described. The aim of this study was to elucidate the influence of sequential inoculation of different yeast and bacteria strains on the aromatic profile of red Bordeaux wine. All microorganisms completed fermentations and no significant difference was observed between tanks regarding the main oenological parameters until 3 months’ aging. Regardless of the yeast strain, B28 bacteria required the shortest period to completely degrade the malic acid, compared to the other strain. Quantification of 73 major components highlighted a specific volatile profile corresponding to each microorganism combination. However, the yeast strain appeared to have a predominant effect on aromatic compound levels, as well as on fruity aroma perception. Yeasts had a greater impact on wine quality and have more influence on the aromatic style of red wine than bacteria.

Gammacurta M et al (2017) Journal of the Science of Food and Agriculture

 

Fed-batch production of vanillin by Bacillus aryabhattai BA03 (research)

Bacillus aryabhattai BA03, a strain isolated in our laboratory, has interesting properties related to the production of natural aromas and flavors. Specifically, we have found that it was able to produce vanillin from ferulic acid (FA). Furthermore, this strain produces high amounts of 4-vinylguaiacol in only 14 h, this being the only intermediate metabolite observed in the process. FA is an inexpensive feedstock for the production of natural value-added compounds when extracted from lignocellulosic wastes. In this study, we optimized the operational conditions (temperature, pH and agitation), medium composition and bioconversion technology (batch or fed-batch) to produce vanillin. In a fed-batch process conducted with just one additional supplementation after 24 h, the maximal concentration of vanillin (147.1 ± 0.9 mg/L) was observed after 216 h (QV = 0.681 mg/L h; YV/fFA = 0.082 mg/mg) after degrading 90.3% FA. In view of our data, we postulate that Bacillus aryabhattai BA03 carries out a decarboxylation of ferulic acid as a metabolic pathway.

Paz A et al (2017) New Biotechnology (in press)

 

Performance of selected P. fermentans and its excellular enzyme in co-inoculation with S. cerevisiae for wine aroma enhancement (research)

This study evaluated aroma enhancement in dry white wines made via a specific Pichia fermentans strain and its excellular enzyme in co-inoculation with Saccharomyces cerevisiae. The inoculation ratios of two yeasts ranged from 0.1 to 10 and fermentations with pure S. cerevisiae were utilized as control. Esterase activities that expressed as C2-C8 chain substrate specificity were surveyed during mixed fermentation. Finally, wine aroma was analyzed via GC-MS and a trained sensory panel. The results revealed that C2-C8 esterase activities were superior during mixed fermentation to the control. Mixed fermentations significantly increased the contents of acetates, ethyl esters, fatty acids, and numerous other fermentative volatiles; particularly those of medium-chain fatty acids and their corresponding esters, with an increased inoculation ratio of the isolate. Extracellular enzyme treatment highly improved the release of varietal aroma compounds, such as terpenols, C13-norisoprenoids, and C6 compounds. Sensory analysis indicated that the risk of negative earth odor emerged in the wine characterized by strong sweet and acid fruit trait. Therefore, mixed fermentations at yeasts inoculation ratios between 1:4 and 4:1 may provide better fermentation strategies for appropriate wine aroma enhancement.

Ma D et al (2017) LWT – Food Science and Technology 86:361-370

 

Strains of the Lactobacillus casei group show diverse abilities for the production of flavor compounds in 2 model systems (research)

Cheese flavor development is directly connected to the metabolic activity of microorganisms used during its manufacture, and the selection of metabolically diverse strains represents a potential tool for the production of cheese with novel and distinct flavor characteristics. Strains of Lactobacillus have been proven to promote the development of important cheese flavor compounds. As cheese production and ripening are long-lasting and expensive, model systems have been developed with the purpose of rapidly screening lactic acid bacteria for their flavor potential. The biodiversity of 10 strains of the Lactobacillus casei group was evaluated in 2 model systems and their volatile profiles were determined by gas chromatography-mass spectrometry. In model system 1, which represented a mixture of free AA, inoculated cells did not grow. In total, 66 compounds considered as flavor contributors were successfully identified, most of which were aldehydes, acids, and alcohols produced via AA metabolism by selected strains. Three strains (DPC2071, DPC3990, and DPC4206) had the most diverse metabolic capacities in model system 1. In model system 2, which was based on processed cheese curd, inoculated cells increased in numbers over incubation time. A total of 47 compounds were identified, and they originated not only from proteolysis, but also from glycolytic and lipolytic processes. Tested strains produced ketones, acids, and esters. Although strains produced different abundances of volatiles, diversity was less evident in model system 2, and only one strain (DPC4206) was distinguished from the others. Strains identified as the most dissimilar in both of the model systems could be more useful for cheese flavor diversification.

Stefanovic E et al (2017) Journal of Dairy Science 100:6818-6929

 

Physiology, ecology and industrial applications of aroma formation in yeast (review)

Yeast cells are often employed in industrial fermentation processes for their ability to efficiently convert relatively high concentrations of sugars into ethanol and carbon dioxide. Additionally, fermenting yeast cells produce a wide range of other compounds, including various higher alcohols, carbonyl compounds, phenolic compounds, fatty acid derivatives and sulfur compounds. Interestingly, many of these secondary metabolites are volatile and have pungent aromas that are often vital for product quality. In this review, we summarize the different biochemical pathways underlying aroma production in yeast as well as the relevance of these compounds for industrial applications and the factors that influence their production during fermentation. Additionally, we discuss the different physiological and ecological roles of aroma-active metabolites, including recent findings that point at their role as signaling molecules and attractants for insect vectors.

Dzialo MC et al (2017) FEMS Microbiology Reviews 41:S95-S128