The Monthly Digest – Flavours – April 2017

Aromas and flavours
R & D abstracts – April 2017
Role of lactic acid bacteria on the yogurt flavour: a review

Considerable knowledge has been accumulated on the lactic acid bacteria (LAB) that affect the aroma and flavour of yogurt. This review focuses on the role of LAB in the production of flavour compounds during yogurt fermentation. The biochemical processes of flavour compound formation by LAB including glycolysis, proteolysis and lipolysis are summarized, with some key compounds described in detail. The flavour-related activities of LAB mostly depend on the species used for yogurt fermentation and some strategies have been developed to obtain more control of the flavour-forming process. Metabolic engineering can be a powerful tool to reroute the metabolic flux towards the efficient accumulation of the desired flavour compounds with the knowledge of the complex network of flavour-forming pathways and the availability of genetic tools. Further progress made in the omics-based techniques and the use of systems biology approaches are needed to fully understand, control, and steer flavour formation in yogurt fermentation processes.

Chen C et al (2017) International Journal of Food Properties (in press)

Milk-clotting properties of plant rennets and their enzymatic, rheological and sensory role in cheese making: a review

Plant rennets hold an important position amongst various coagulants used in cheese technology. The selection of a suitable plant coagulant is important due to the increasing global demands of cheese alongside reduced supply of calf rennet. Thus, a literature synthesis is presented to investigate recent achievements on their functional properties and enzymatic role in cheese making. Efforts have also been done to compare certain rheological and sensory properties of final products, arising from some plant and animal based rennets. In fact, some coagulants such as actinidin or dubiumin produce cheeses with sensory qualities similar to those produced by animal rennet. Others, like ginger, cucumisin or hieronymain proteases contribute to develop very different textures and flavors, due to excessive proteolytic activity and production of bitter peptides. For milk-clotting enzymes with high non-specific action, several improvement strategies have been developed to produce cheeses with sensory properties close to those of animal rennet. For example, the mixture of coagulants (cardosins/chymosin), the selection of appropriate milk or its ultrafiltration, as well as the increase of salting time of cheese during ripening could be efficient ways to improve texture and reduce bitterness. Concerning cheeses with high yield loss, the whey could be used for a traditional production of whey cheese. To conclude, the selection of appropriate plant rennet with high MCA/PA ratio and the optimization of all coagulation parameters play a central role in manufacturing cheese with superior rheological and sensory properties.

Ben Amira A et al (29017) International Journal of Food Properties (in press)

Flavour-active volatile compounds in beer: production, regulation and control

Many classes of compounds have been shown to play an important role in the development of flavour characteristics of beer. This significantly influences its taste and sensory properties, thus affecting its market performance. Despite the intensive research aimed at unravelling the precise mechanism and regulation of flavour formation in beer, current knowledge remains far from complete. Several reviews are available on the general composition of beer and yeast metabolic pathways involved in the production of volatile compounds in beer. However, a limited amount of work has been reported concerning the influence of some of the beer constituents and other important parameters on beer flavour. This paper reviews the current knowledge of the biochemistry behind flavour formation in beer and discusses the different factors that influence its formation and how it can be controlled during brewery fermentation.

Olaniran AO et al (2017) Journal of the Institute of Brewing (in press)

Aroma recovery of beer flavors by pervaporation through polydimethylsiloxane membranes

Five commercial beers and their corresponding no-alcohol presentations have been analyzed in terms of five aroma compounds: three alcohols and two esters (isobutyl alcohol, ethyl acetate, 2-methyl butanol, 3-methyl butanol, and isoamyl acetate). Substantial reductions of volatile aroma compounds have been encountered in these nonalcoholic beers. Pervaporation of these aromas in order to allow their recovery has been tested through two commercial membranes with polydimethylsiloxane active layers (Pervatech and Sulzer). Total fluxes are higher through the Pervatech membrane while individual aroma ones are similar for both the membranes. Mass recovery is higher for the Pervatech membrane for most of the aromas whereas their enrichment factors are better for the Sulzer membrane. The rest of the beer profile modulates to some extent the general trends referred. Mass recoveries and enrichment factors from 5 to 35% were obtained for the aromas tested. Mass recovery and enrichment factors could be improved by increasing membrane area or time of treatment. Pervaporation is a membrane technique which effectiveness has been proven to separate volatile organic compounds from aqueous mixtures. It could be useful in beer industry in a significant way, helping nonalcoholic beers to improve their organoleptic characteristics. In a near future, by controlling operating parameters involved in the full process, it will be possible to introduce this technique into the factories and produce a tastier and better quality beer by minimizing the lack of valuable aroma compounds.

Paz AI et al (2017) Journal of Food Process Engineering (in press)

Key volatile aroma compounds of lactic acid fermented malt based beverages – impact of lactic acid bacteria strains

This study aims to define the aroma composition and key aroma compounds of barley malt wort beverages produced from fermentation using six lactic acid bacteria (LAB) strains. Gas chromatography mass spectrometry–olfactometry and flame ionization detection was employed; key aroma compounds were determined by means of aroma extract dilution analysis. Fifty-six detected volatile compounds were similar among beverages. However, significant differences were observed in the concentration of individual compounds. Key aroma compounds (flavor dilution (FD) factors ≥16) were β-damascenone, furaneol, phenylacetic acid, 2-phenylethanol, 4-vinylguaiacol, sotolon, methional, vanillin, acetic acid, nor-furaneol, guaiacol and ethyl 2-methylbutanoate. Furthermore, acetaldehyde had the greatest odor activity value of up to 4266. Sensory analyses revealed large differences in the flavor profile. Beverage from L. plantarum Lp. 758 showed the highest FD factors in key aroma compounds and was correlated to fruity flavors. Therefore, we suggest that suitable LAB strain selection may improve the flavor of malt based beverages.

Dongmo NS et al (2017) Food Chemistry 229:565-573

Lactic acid fermentation drives the optimal volatile flavor-aroma profile of pomegranate juice

Pomegranate juice (PJ) fermented with Lactobacillus plantarum C2, POM1, and LP09, unstarted-PJ, and raw-PJ were characterized for the profile of the volatile components (VOC) by PT–GC–MS. Lactic acid fermentation through selected strains enhanced the flavor profile of PJ. Concentrations of desired compounds (e.g., alcohols, ketones, and terpenes) were positively affected, whereas those of non-desired aldehydes decreased. Unstarted-PJ mainly differentiated from fermented PJs for the highest levels of aldehydes and sulfur compounds, and in lesser extent of furans, whereas alcohols, ketones, and alkenes followed by terpenes and benzene derivatives mainly differentiated fermented PJs. As expected, the lowest level of VOC was found in raw-PJ. VOC profile reflected on the sensory features of fermented PJs, unstarted-PJ, and raw-PJ, which were evaluated using a consensus modified flavor profile based on 13 attributes. Fermented PJs were mainly discriminated by the higher intensity of floral, fruity and anise notes than the controls.

Di Cagno R et al (2017) International Journal of Food Microbiology 248:56-62

Biotransformation of α- and β-pinene into flavor compounds

Products that bear the label “natural” have gained more attention in the marketplace. In this approach, the production of aroma compounds through biotransformation or bioconversion has been receiving more incentives in economic and research fields. Among the substrates used in these processes, terpenes can be highlighted for their versatility and low cost; some examples are limonene, α-pinene, and β-pinene. This work focused on the biotransformation of the two bicyclic monoterpenes, α-pinene and β-pinene; the use of different biocatalysts; the products obtained; and the conditions employed in the process.

Vespermann KAC et al (2017) Applied Microbiology and Biotechnology 101:1805-1817

Optimizing bioconversion of ferulic acid to vanillin by Bacillus subtilis in the stirred packed reactor using Box-Behnken design and desirability function

A stirring bioreactor packed with a carbon fiber textiles (FT) biofilm formed by Bacillus subtiliswas used to produce vanillin from ferulic acid. Biofilm formation was characterized by scanning electron microscopy. The interactive effects of three variables on vanillin molar yield (M) and conversion efficiency of ferulic acid (E) were evaluated by response surface methodology (RSM) with a Box-Behnken design (BBD). The optimal conversion conditions with a maximum overall desirability D of 0.983 were obtained by a desirability function. Considering the actual operation, the confirmation tests were performed using the slightly modified optimal conditions (initial ferulic acid concentration 1.55 g/L, temperature 35°C, stirring speed 220 rpm). The results showed that M and E were 57.42 and 93.53%, respectively. This was only 1.03% and 1.87%, respectively, different from the predicted values, confirming the validity of the predicted models. These revealed that the stirred packed reactor could be successfully used in vanillin bioconversion from ferulic acid.

Chen P et al (2017) Food Science and Biotechnology 26 :143-152

Breeding of a sake yeast mutant with enhanced ethyl caproate productivity in sake brewing using rice milled at a high polishing ratio

Sake yeast produces a fruity flavor known as ginjo-ko—which is mainly attributable to ethyl caproate and isoamyl acetate—during fermentation in sake brewing. The production of these flavor components is inhibited by unsaturated fatty acids derived from the outer layer of rice as raw material. We isolated three mutants (hec2, hec3, and hec6) with enhanced ethyl caproate productivity in sake brewing using rice milled at a high polishing ratio from a cerulenin-resistant mutant derived from the hia1 strain, which shows enhanced isoamyl acetate productivity. The hec2 mutant had the homozygous FAS2 mutation Gly1250Ser, which is known to confer high ethyl caproate productivity. When the homozygous FAS2 mutation Gly1250Ser was introduced into strain hia1, ethyl caproate productivity was increased but neither this nor intracellular caproic acid content approached the levels observed in the hec2 mutant, indicating that a novel mutation was responsible for the high ethyl caproate productivity. We also found that the expression of EEB1 encoding acyl-coenzyme A: ethanol O-acyltransferase (AEATase) and enzymatic activity were increased in the hec2 mutant. These results suggest that the upregulation of EEB1 expression and AEATase activity may also have contributed to the enhancement of ethyl caproate synthesis from ethanol and caproyl-CoA. Our findings are useful for the brewing of sake with improved flavor due to high levels of isoamyl acetate and ethyl caproate.

Takahashi T et al (2017) Journal of Bioscience and Bioengineering (in press)

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