Synthesis of flavor esters and structured lipids by a new immobilized lipase, LipC12, obtained from metagenomics
Ibead-CELipC12 is a metagenomic lipase, LipC12, immobilized directly from a crude extract onto Immobead 150. We evaluated its solvent and thermal stability and its potential for producing flavor esters and structured lipids. Ibead-CELipC12 had residual activities above 88% after 24 h at 40 °C in toluene, iso-octane, n-hexane and n-heptane and 72% after 24 h at 60 °C in n-hexane. In esterification of palmitic acid, Ibead-CELipC12 gave higher activities with ethanol, propanol and butanol than with isopropanol. In esterification of caprylic acid with ethanol, propanol and butanol, Ibead-CELipC12 performed best with butanol, giving 62% conversion in 6 h. Ibead-CELipC12 was sn−1,3-specific during triolein hydrolysis and was therefore used to convert olive oil into an MLM structured lipid containing 23% of caprylic acid in the sn−1 and sn−3 positions. These results demonstrate that Ibead-CELipC12 has good potential to be used in the enzymatic synthesis of flavor esters and structured lipids. Ibead-CELipC12 is a metagenomic lipase, LipC12, immobilized directly from a crude extract onto Immobead 150. We evaluated its solvent and thermal stability and its potential for producing flavor esters and structured lipids. Ibead-CELipC12 had residual activities above 88% after 24 h at 40 °C in toluene, iso-octane, n-hexane and n-heptane and 72% after 24 h at 60 °C in n-hexane. In esterification of palmitic acid, Ibead-CELipC12 gave higher activities with ethanol, propanol and butanol than with isopropanol. In esterification of caprylic acid with ethanol, propanol and butanol, Ibead-CELipC12 performed best with butanol, giving 62% conversion in 6 h. Ibead-CELipC12 was sn−1,3-specific during triolein hydrolysis and was therefore used to convert olive oil into an MLM structured lipid containing 23% of caprylic acid in the sn−1 and sn−3 positions. These results demonstrate that Ibead-CELipC12 has good potential to be used in the enzymatic synthesis of flavor esters and structured lipids.
Dutra Madalozzo A et al (2017) Biocatalysis and Agricultural Biotechnology (in press)
Lipase-catalyzed modification of the flavor profiles in recombined skim milk products by enriching the volatile components
The purpose of this study was to modify the amount and composition of volatile components in bovine milk products, in an attempt to create a recombined skim milk product with full-fat milk flavor but with only 0.5% fat. The experimental plan included lipase-catalyzed hydrolysis and esterification reactions using Palatase 20000L (Novozymes, Bagsværd, Denmark). The results, measured by the methods of volatile compositional analysis and sensory evaluation, showed that the flavor profiles of the optimal recombined milk products were effectively modified in this way, possessing intensified characteristic volatile flavor components with rather low level of fat contents, and the sensory characters were quite realistic to natural whole milk flavor.
Zhang XM et al. (2016) Journal of Dairy Science 99:8665-8679
Formation of volatile compounds, peptidolysis and carbohydrate fermentation by mesophilic lactobacilli and streptoccocci cultures in a cheese extract
Many studies about the influence of Lactococcus lactis on cheese flavour have been reported, while the impact of mesophilic lactobacilli and Streptococcus thermophilus, either as single or mixed cultures, have been less studied. The ability of Lactobacillus paracasei 90, Lb. casei 72 (INLAIN collection) and S. thermophilus 2 (commercial strain) to produce flavour-related biochemical changes, as single or mixed (lactobacilli + streptococci) cultures, was assessed in a cheese model. These three strains, with different activities of glutamate dehydrogenase (GDH) and aminotransferases (AT), were incubated (14d/37 °C) alone or in mixed cultures in a cheese model consisting of a sterile extract of a fresh cheese. Mesophilic lactobacilli showed fermentation of carbohydrates, an increase of peptidolysis and production of volatile compounds that were correlated with their AT activities. In addition, these strains also produced completely different profiles of the amino acceptor compounds: pyruvate and α-ketoglutarate. S. thermophilus 2 increased the level of α-ketoglutarate due to its high GDH activity, but its contribution to flavour compound production was negligible; small additional changes existed when S. thermophilus 2 was mixed with the lactobacilli. Biochemical changes leading to flavour formation were mainly due to the activity of lactobacilli. Our results suggest that the AT profile and the peptidolytic activity of each strain influenced the volatilome of the extracts during incubation. So, both lactobacilli strains could be used as adjunct cultures in cheeses to increase/diversify the flavour, but more studies are needed to deepen the knowledge about the potential of S. thermophilus 2 for the production of flavour compounds.
Peralta GH et al (2016) Dairy Science & Technology 96:603-621
Yeast factories for the production of aromatic compounds: from building blocks to plant secondary metabolites
The aromatic amino acid biosynthesis pathway is a source to a plethora of commercially relevant chemicals with very diverse industrial applications. Tremendous efforts in microbial engineering have led to the production of compounds ranging from small aromatic molecular building blocks all the way to intricate plant secondary metabolites. Particularly, the yeastSaccharomyces cerevisiae has been a great model organism given its superior capability to heterologously express long metabolic pathways, especially the ones containing cytochrome P450 enzymes. This review contains a collection of state-of-the-art metabolic engineering work devoted towards unraveling the mechanisms for enhancing the flux of carbon into the aromatic pathway. Some of the molecules discussed include the polymer precursor muconic acid, as well as important nutraceuticals (flavonoids and stilbenoids), and opium-derived drugs (benzylisoquinoline alkaloids).
Suástegui M and Shao Z (2016) Journal of Industrial Microbiology & Biotechnology 43 :1611-1624
Meta-analysis of the core aroma components of grape and wine aroma
Wine aroma strongly influences wine quality, yet its composition and its evolution during the winemaking process are poorly understood. Volatile compounds that constitute wine aroma are traditionally divided into three classes according to their origin: grape, fermentation, and maturation aroma. We challenge this view with meta-analysis and review of grape and wine volatiles and their precursors from 82 profiling experiments. We compiled a list of 141 common grape and wine volatiles and quantitatively compared 43 of them. Our work offers insight into complex relationships between biosynthesis of aroma in grapes and the changes during the winemaking process. Monoterpenes are one of the largest and most researched wine aroma compounds. We show that their diversity in wines is mainly due to the oxidative metabolism of linalool in grapes. Furthermore, we demonstrate that most of the linalool produced in grapes is converted to these oxidized derivatives.
Ilc T et al (2016) Frontiers in Plant Science Vol 7 Article 1472 doi: 10.3389/fpls.2016.01472
Major phenolic and volatile compounds and their influence on sensorial aspects in stem-contact fermentation winemaking of Primitivo red wines
In red winemaking de-stemming is crucial since the stems contain polymeric phenolic compounds responsible for the astringency of wine. Wine such as Primitivo has low phenolic constituents and tannins and stems affect aroma, taste body and olfactory characteristics. The aim of the study was to evaluate the effects of presence of stems during fermentation on polyphenolic, volatile compounds and sensory characteristics of wine. Primitivo grapes vinified in presence of different percentage of stems: 100 % de-stemmed (D100), 75 % de-stemmed (D75) and 50 % de-stemmed (D50). Results confirmed that the wines vinified in presence of stems were higher in tannins, flavans, to vanillin and proanthocyanidins, colour intensity with lower anthocyanins. The presence of stems during fermentation conferred more structure and flavour to wines. They facilitated must aeration thus promoting synthesis of higher alcohols and ethyl esters by yeast. In particular, a higher content of hexan-1-ol, hex-3-en-1-ol and 2-phenyl ethanol in D50 and D75 gave the wines that suggest green grass, herb and floral. Wine from D75 seemed to be better than D50 in terms of volatile compounds as well as fruity, floral and balsamic components preserved, without any unpleasant taste of long chain fatty acids found in D50.
Suriano S et al. (2016) Journal of Food Science and Technology 53:3329-3339
Influence of the dominance of must fermentation by Torulaspora delbrueckii on the malolactic fermentation and organoleptic quality of red table wine
Torulaspora delbrueckii can improve wine aroma complexity, but its impact on wine quality is still far from being satisfactory at the winery level, mainly because it is easily replaced by S. cerevisiae yeasts during must fermentation. New T. delbrueckii killer strains were selected to overcome this problem. These strains killed S. cerevisiae yeasts and dominated fermentation better than T. delbrueckii non-killer strains when they were single-inoculated into crushed red grape must. All the T. delbrueckii wines, but none of the S. cerevisiae wines, underwent malolactic fermentation. Putative lactic acid bacteria were always found in the T. delbrueckii wines, but none or very few in the S. cerevisiaewines. Malic acid degradation was the greatest in the wines inoculated with the killer strains, and these strains reached the greatest dominance ratios and had the slowest fermentation kinetics. The T. delbrueckii wines had dried-fruit/pastry aromas, but low intensities of fresh-fruit aromas. The aroma differences between the T. delbrueckii and the S. cerevisiae wines can be explained by the differences that were found in the amounts of some fruity aroma compounds such as isoamyl acetate, ethyl hexanoate, ethyl octanoate, and some lactones. This T. delbrueckii effect significantly raised the organoleptic quality scores of full-bodied Cabernet-Sauvignon red wines inoculated with the killer strains. In particular, these wines were judged as having excellent aroma complexity, mouth-feel, and sweetness.
Ramirez M et al. (2016) International Journal of Food Microbiology 238:311-319
Synthesis of taste-active γ-glutamyl dipeptides during sourdough fermentation by Lactobacillus reuteri
This study aimed to assess whether peptides influence the taste of sourdough bread. γ-Glutamyl dipeptides with known kokumi taste threshold, namely γ-Glu-Glu, γ-Glu-Leu, γ-Glu-Ile, γ-Glu-Phe, γ-Glu-Met, and γ-Glu-Val, were identified in sourdough by liquid chromatography–tandem mass spectrometry in MRM mode. γ-Glutamyl dipeptides were found in higher concentrations in sourdough fermented with Lactobacillus reuteri when compared to the chemically acidified controls. Proteolysis was an important factor for generation of γ-glutamyl dipeptides. Sourdoughs fermented with four strains of L. reuteri had different concentrations of γ-Glu-Glu, γ-Glu-Leu, and γ-Glu-Met, indicating strain-specific differences in enzyme activity. Buffer fermentations with L. reuteri confirmed the ability of the strains to convert amino acids to γ-glutamyl dipeptides as well as the strain-specific differences. Sensory evaluation of bread revealed that sourdough bread with higher concentrations of γ-glutamyl dipeptides ranked higher with respect to the taste intensity when compared to regular bread and type I sourdough bread. Sourdough breads fermented with L. reuteri LTH5448 and L. reuteri 100-23 differed with respect to the intensity of the salty taste; this difference corresponded to a different concentration of γ-glutamyl dipeptides. These results suggest a strain-specific contribution of γ-glutamyl dipeptides to the taste of bread. The use of sourdough fermented with glutamate and kokumi peptide accumulating lactobacilli improved the taste of bread without adverse effect on other taste or quality attributes.
Zhao CJ and Gänzle MG (2016) Journal of Agricultural and Food Chemistry 64:7561-7568
Implementing principles of traditional concentrated grape must fermentation to the production of new generation balsamic vinegars. Starter selection and effectiveness
In an effort to implement principles of traditional concentrated grape must fermentation to the production of new generation balsamic vinegars (BVs), the specific goals of the study were the isolation and molecular identification of the predominant yeasts in concentrated grape must (cv. Xinomavro), their technological characterization and the evaluation of the fermentative aptitude of the selected strains. Tolerance against 5-hydroxymethyl-furfural (HMF) and furfural, acetic acid and glucose concentration was examined by appropriate methods and tests. The enological characteristics studied were acetic acid and H2S production, foaming and flocculation ability and key enzymatic activity. PCR–RFLP analysis revealed only the presence of Saccharomyces cerevisiae and Hanseniaspora uvarum among the 14 predominant osmophilic yeast isolates. Tolerance to both HMF and furfural was found strain- and dose-dependent and was suggested as a critical factor in the pre-selection of yeast starters. The most tolerant yeasts to these stress factors, a S. cerevisiae and a non-Saccharomyces strain, showed satisfactory growth in the presence of high glucose and acetic acid content (up to 600 g/L and 2 % w/w, respectively) and desirable enological characteristics. Results from the comparative evaluation of the fermentative aptitude of these strains with a commercial wine strain highlighted that the isolates had glucophilic behaviour and ability to produce desirable amounts of ethanol (100–120 g/kg) in short time (~20 d). The key volatiles useful for varietal discrimination and differentiation between the BVs and the traditional ones were also evaluated.
Lalou S et al. (2016) Journal of Food Science and Technology 53:3424-3436