Study of the volatile compounds produced by Debaryomyces hansenii NRRL Y-7426 during the fermentation of detoxified concentrated distilled grape marc hemicellulosic hydrolysates

Key aroma compounds and metabolic profiling of Debaryomyces hansenii L1-1-fermented Flos Sophorae

The extract from Debaryomyces hansenii L1-1-fermented Flos Sophorae has a unique aroma and could be used as a natural spice. The influence of yeast growth and culture medium pH on organoleptic properties of fermented substrates, as well as on the content of volatile aromatic compounds, total sugars, polysaccharides, reducing sugars, total proteins, and amino acids, were analyzed. Metabolic pathways were annotated to compare and contrast key aromatic compounds and metabolic profiles of water and ethanol extracts of D. hansenii L1-1-fermented Flos Sophorae. We found that cells grew most rapidly, pH values changed significantly, and the largest consumption of sugars and amino acids occurred within 48 hr, producing bouquet-like, fruity, and sweet odors, as well as the highest content of volatile aromatic compounds in the extracts. The main aroma metabolites were 2-phenylethanol, linalool, and α-terpineol. The sensory quality of the ethanol extracts was superior to that of the water extracts. Five aromatic compounds, isoamyl alcohol, 2-methylbutan-1-ol, isobutyric acid, 2,3-hexanedione, and 1-hexanol, were positively correlated with the water extract group and negatively correlated with the ethanol extract group, whereas 13 aromatic compounds, styrene, acetophenone, 2-octen-1-ol, linalool, naphthalene, α-terpineol, dihydrocarveol, (-)-myrtenol, methyl anthranilate, eugenol, γ-nonanolactone, jasmone, and β-ionone, showed the converse trend. Although 2-phenylethanol displayed the highest concentration in the extracts, it did not significantly contribute to the separation of ethanol and water extracts. In Flos Sophorae medium, D. hansenii mainly produces 2-phenylethanol from phenylalanine by the Ehrlich reaction, whereas it produces linalool and α-terpineol by the terpenoid backbone and monoterpenoid biosynthetic pathways; the variable contents of proline, arginine, and glutamate could respond to the arginine and proline metabolic pathways. PRACTICAL APPLICATIONS: Flos Sophorae, a collection of buds of Sophora japonica L., is a traditional Chinese medicinal and edible plant for its good aroma, taste, and nutritional value. Debaryomyces hansenii is a common, aroma-producing yeast. D. hansenii L1-1-fermented Flos Sophorae had a unique, bouquet-like aroma, slightly softer than the typical Flos Sophorae-like aroma. This study enriches our understanding of predominant aroma components and determines their contribution to the profiles of Flos Sophorae ferments obtained using D. hansenii L1-1. Researchers and manufacturers specializing in spices making can use these data to improve the aromatic profiles of natural spices produced by microorganisms, thereby obtaining unique aromas.

New kids on the block: emerging oleaginous yeast of biotechnological importance

There is growing interest in using oleaginous yeast for the production of a variety of fatty acids and fatty acid-derived oleochemicals. This is motivated by natural propensity for high flux through lipid biosynthesis that has naturally evolved, making them a logical starting point for additional genetic engineering to improve titers and productivities. Much of the academic and industrial focus has centered on yeast that have significant genetic engineering tool capabilities, such as Yarrowia lipolytica, and those that have naturally high lipid accumulation, such as Rhodosporidium toruloides and Lipomyces starkeyi; however, there are oleaginous yeast with phenotypes better aligned with typically inhibitory process conditions, such as high salt concentrations and lignocellulosic derived inhibitors. This review addresses the foundational work in characterizing two emerging oleaginous yeast of interest: Debaryomyces hansenii and Trichosporon oleaginosus. We focus on the physiological and metabolic properties of these yeast that make each attractive for bioprocessing of lignocellulose to fuels and chemicals, discuss their respective genetic engineering tools and highlight the critical barriers facing the broader implementation of these oleaginous yeast.

The potency of Saccharomyces cerevisiae and Lactobacillus plantarum to dissipate organophosphorus pesticides in wheat during fermentation

The degradation behaviour of pirimiphos methyl with Saccharomyces cerevisiae and chlorpyrifos methyl with Lactobacillus plantarum in wheat during fermentation was studied. Yeast fermentation was especially effective for reduction of pirimiphos methyl applied at 5 mg kg-1 (maximum residue limit-MRL) causing dissipation for max 48.8%. Pesticide reduction rate decreased with an increase of fortification rate. Thus in samples fortified with 25 and 75 mg kg-1 a reduction up to 27.1%, and 23.7% respectively, was observed. Activity of L. plantarum was especially effective for reduction of chlorpyrifos methyl applied at 3 mg kg-1 (MRL) causing dissipation for max 56.7%. This reduction rate decreased with an increase of fortification rate. In samples contaminated with 15 and 45 mg kg-1 dissipation reached up to 38.6% and 34.7% respectively. For both experiments, initial inoculums sizes had no statistically significant effect on pesticides dissipation level, while concerning fermentation temperatures at all fortification levels the highest degradations occurred at 30 °C. Overall, regardless fermentation parameters, the degradation rate constants of pirimiphos methyl fermented with yeast were increased comparing with control samples by 255-573, 56-116 and 119-594% in samples contaminated at MRL, 5MRL and 15MRL of pesticide, while the degradation rate constants of chlorpyrifos methyl fermented with lactobacilli were increased by 74-769, 59-237 and 46-469% respectively. These results evidenced that yeast and lactobacilli played an important role in promoting pirimiphos methyl i.e. chlorpyrifos methyl dissipation in wheat.

Characterization of odor-active compounds of various Chrysanthemum essential oils by gas chromatography-olfactometry, gas chromatography-mass spectrometry and their correlation with sensory attributes

Volatiles of five kinds of Chrysanthemum essential oils with different manufactures were characterized by descriptive sensory analysis, gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC-MS) and statistics analysis. Six sensory attributes (floral, woody, grassy, fruity, sour and minty) were selected to assess Chrysanthemum essential oils. A total of 38 volatile compounds were detected and quantified using standard substances by GC-O and GC-MS. Terpenes constituted the largest chemical group among the volatiles of the essential oils. Then partial least squares regression (PLSR) was used to elucidate the relationship between sensory attributes and aroma compounds. The result showed that α-pinene, β-thujene, α-terpinolen, β-cubebene, caryophyllene, (Z)β-farnesene, (-)-spathulenol, linalool, camphor, camphene, 4-terpineol, Z-citral and 4-isopropyltoluene were typical aroma compounds covaried with characteristic aroma of Chrysanthemum essential oils.

Bioflavour production from tomato and pepper pomaces by Kluyveromyces marxianus and Debaryomyces hansenii

Bioflavours are called natural flavour and/or fragrance compounds which are produced using metabolic pathway of the microorganism and/or plant cells or their enzyme systems with bioengineering approaches. The aim of this study was to investigate bioflavour production from tomato and red pepper pomaces by Kluyveromyces marxianus and Debaryomyces hansenii. Obtained specific growth rates of K. marxianus and D. hansenii in tomato pomace were 0.081/h and 0.177/h, respectively. The bioflavour profile differed between the yeasts. Both yeasts can produce esters and alcohols such as phenyl ethyl alcohol, isoamyl alcohol, isoamyl acetate, phenyl ethyl acetate and isovaleric acid. "Tarhana" and "rose" were descriptive flavour terms for tomato and pepper pomaces fermented by K. marxianus, respectively. Tomato pomace fermented by D. hansenii had the most intense "green bean" flavour while "fermented vegetable" and "storage/yeast" were defined as characteristic flavour terms for pepper pomaces fermented by D. hansenii.

Utilization of coffee by-products obtained from semi-washed process for production of value-added compounds

The semi-dry processing of coffee generates significant amounts of coffee pulp and wastewater. This study evaluated the production of bioethanol and volatile compounds of eight yeast strains cultivated in a mixture of these residues. Hanseniaspora uvarum UFLA CAF76 showed the best fermentation performance; hence it was selected to evaluate different culture medium compositions and inoculum size. The best results were obtained with 12% w/v of coffee pulp, 1 g/L of yeast extract and 0.3 g/L of inoculum. Using these conditions, fermentation in 1 L of medium was carried out, achieving higher ethanol yield, productivity and efficiency with values of 0.48 g/g, 0.55 g/L h and 94.11% respectively. Twenty-one volatile compounds corresponding to higher alcohols, acetates, terpenes, aldehydes and volatile acids were identified by GC-FID. Such results indicate that coffee residues show an excellent potential as substrates for production of value-added compounds. H. uvarum demonstrated high fermentative capacity using these residues.