Jan Hendrik Swiegers

Background: Over recent decades, considerable research has focused on understanding sweet taste mechanisms and developing new noncarbohydrate sweeteners due to rising noncommunicable diseases. New regulations limiting high sugar levels in food and beverages have driven innovation towards reduced‐sugar and sugar‐free products, often using noncarbohydrate sweeteners. Extensive research was aimed at improving their physical and sensorial properties. However, to the authors′ knowledge no publication has taken a holistic approach by integrating all major sensory and functional challenges of sugar reduction in beverages in one structured framework. Scope and Approach: This review addressed these challenges, which included (i) sweetness, (ii) temporal profile in relation to sweetness onset and linger, (iii) masking, (iv) flavour intensity and delivery and (v) mouthfeel enhancement. It firstly discussed the strategy of replacing the sweetness of sugar by utilizing different sweeteners, investigating mechanisms behind the sensory characteristics and solutions and exploring artificial and natural sweeteners and positive allosteric modulators for sweetness. For the temporal profile, methods to measure sweetness onset and linger were investigated. Solutions for masking off‐tastes and flavours were discussed, including bitter‐blockers, blending of sweeteners, production technologies and flavours with modifying properties. Changes in flavour intensity and delivery were discussed. In the last section, strategies for addressing mouthfeel reduction were summarised including the usage of hydrocolloids, sugar alcohols, fibre syrups and mineral salts. Key Findings and Conclusions: Overall, the need for clearer guidelines and fewer restrictions was debated, highlighting conflicting consumer perspectives on the need for healthy, natural and more sustainable products and regulatory barriers around novel solutions. The advancement of scientific knowledge is emphasised, and collaboration between cross‐functional teams is discussed as essential to move sugar‐free products closer to their sugar‐containing counterparts.

The interactions between lactic acid bacteria (LAB), yeast and other wine microbiota have an impact on the wine quality. Some strains of the LAB Oenococcus oeni possess a cinnamoyl esterase activity that releases hydroxycinnamic acids (HCAs) that can subsequently be processed by some strains of the spoilage yeast Brettanomyces bruxellensis and lead to off-flavor compounds. Using metagenomic analyses, this study investigated the influence of O. oeni and B. bruxellensis on the taxonomic and functional potential profiles of the microbial community of Cabernet Sauvignon wine, particularly regarding flavor formation. Metagenomic datasets were generated from inoculations of three strains of B. bruxellensis, in combination with two O. oeni strains, with and without cinnamoyl esterase activity. It was found that the effect on the microbial profiles depends on the O. oeni and B. bruxellensis strains being combined and on the abundance that the inoculants reach in the final wine, which depends on unidentified conditions (e.g. derived from microbial interactions). It was confirmed that the potential of B. bruxellensis to produce off-flavor compounds from HCAs is strain dependent. Interestingly, the samples without microbial inoculants also had this potential, suggesting that microbiota from the native grape could also influence the levels of HCAs. The metagenomic analyses complemented with experimental validation also found that the presence of B. bruxellensis does not interfere with the microbial functional potential to transform L-malic acid into L-lactic acid, which typically leads to a less acidic flavor. We show that metagenomic approaches can help uncover the complex wine microbial community traits, such as flavor, impacted by the simultaneous presence of O. oeni and B. bruxellensis.

In the wine making process, the interactions between lactic acid bacteria (LAB), yeast and other wine microflora have an impact on the wine quality. In this study, we investigate the influence of the LAB Oenococcus oeni and the spoilage yeast Brettanomyces bruxellensis on the microbial community of a Cabernet Sauvignon wine. We generated metagenomic datasets from inoculations of three strains of B. bruxellensis , in combination with two O. oeni strains, one with and one without cinnamoyl esterase activity. This esterase activity releases hydroxycinnamic acids (HCAs) that can subsequently be processed by some B. bruxellensis strains able to generate off-flavor compounds. We evaluated the influence of the O. oeni and B. bruxellensis on the microbial taxonomic and functional potential profile, particularly regarding off-flavor formation due to HCAs. We found that the effect on the microbial profiles depends on i ) the O. oeni and B. bruxellensis strains being combined and ii ) the abundance they reach in the final wine, which depends on certain unidentified conditions. We confirmed that the potential of B. bruxellensis to produce off-flavor compounds from HCAs depends on the strain. Interestingly, the samples without microbial inoculants also had this potential, suggesting that native grape microbiota could also influence the levels of HCA. We also found that the presence of B. bruxellensis does not interfere with the malolactic fermentation of the evaluated O. oeni strains, which leads to a less acidic taste. We show that metagenomic approaches can help uncover the complex wine microbial community traits, such as flavor, impacted by the simultaneous presence of O. oeni and B. bruxellensis .

In this study, the effect of two Oenococcus oeni strains, Viniflora^® CiNe™ and Viniflora^® CH11 with and without cinnamoyl esterase activity, respectively, on the contents of the hydroxycinnamic acids (HCAs) p-coumaric and ferulic acid and their respective volatile phenols 4-ethylphenol and 4-ethylguaiacol was investigated during a period of six months in Cabernet Sauvignon wines inoculated with two different Brettanomyces bruxellensis strains, CBS 73 and CBS 2499. Both CiNe™ and CH11 showed growth and malolactic fermentation (MLF) in the wines. There were no clear growth interactions between B. bruxellensis and O. oeni. Furthermore, B. bruxellensis did not inhibit MLF by CiNe™ or CH11. The HCA concentrations in all wines increased until 114 days of fermentation, after which they decreased from day 114 to day 180. Wines inoculated with CiNe™ had the highest concentrations of HCAs throughout the fermentations. Even though CiNe™ degraded more of the tartaric ester bound forms of HCAs into free HCAs there was no significant difference in the production of volatile phenols when comparing wines inoculated with CH11. However, there was a significant difference in the level of volatile phenols and HCAs on day 180 between wines with the two strains of B. bruxellensis. Thus, it seems that the level of volatile phenols in wine depends more on strain differences of B. bruxellensis than on cinnamoyl esterase activity of O. oeni.

Industrial synthesis of l-carnitine is currently performed by whole-cell biotransformation of industrial waste products, mostly d-carnitine and cronobetaine, through specific bacterial species. No comparable system has been established using eukaryotic microorganisms, even though there is a significant and growing international demand for either the pure compound or carnitine-enriched consumables. In eukaryotes, including the fungus Neurospora crassa, l-carnitine is biosynthesized through a four-step metabolic conversion of trimethyllysine to l-carnitine. In contrast, the industrial yeast, Saccharomyces cerevisiae lacks the enzymes of the eukaryotic biosynthesis pathway and is unable to synthesize carnitine. This study describes the cloning of all four of the N. crassa carnitine biosynthesis genes and the reconstruction of the entire pathway in S. cerevisiae. The engineered yeast strains were able to catalyze the synthesis of l-carnitine, which was quantified using hydrophilic interaction liquid chromatography electrospray ionization mass spectrometry (HILIC-ESI-MS) analyses, from trimethyllysine. Furthermore, the yeast threonine aldolase Gly1p was shown to effectively catalyze the second step of the pathway, fulfilling the role of a serine hydroxymethyltransferase. The analyses also identified yeast enzymes that interact with the introduced pathway, including Can1p, which was identified as the yeast transporter for trimethyllysine, and the two yeast serine hydroxymethyltransferases, Shm1p and Shm2p. Together, this study opens the possibility of using an engineered, carnitine-producing yeast in various industrial applications while providing insight into possible future strategies aimed at tailoring the production capacity of such strains.

Fermentations using different yeast strains can result in varying concentrations of volatile thiols and substantial sensory effects in young Sauvignon blanc wines. These yeast-derived aroma differences are generally thought to be short lived; therefore, Sauvignon blanc wines made using different yeast strains in two separate studies were investigated after three years of cellar storage. Differences were observed in the volatile composition and sensory profiles of the three-year-old wines that, when compared with the six-month data, demonstrated the continued influence of yeast strains. This observation provides further evidence that choice of yeast strain is important to wine flavor.Ellena S. King, I. Leigh Francis, Jan H. Swiegers, and Chris Curti