A high-throughput analysis of volatile compounds with various polarities using headspace stir bar sorptive extraction.

Long sample extraction time is usually necessary in the analysis of volatile flavour compounds to achieve high extraction efficiency. However, the long extraction time reduces sample throughput, which results in waste of labour and energy. Therefore, in this study, an improved headspace-stir bar sorptive extraction was developed to extract volatile compounds with varying polarities in a short time. With the aim of achieving high throughput, extraction conditions were selected and optimised based on the combinations of different extraction temperatures (80-160 °C), extraction times (1-61 min), and sample volumes (50-850 µL) through the response surface methodology with Box-Behnken design. After obtaining the preliminary optimal conditions (160 °C, 25 min, and 850 µL), the effect of cold stir bars with shorter extraction time on the extraction efficiency was evaluated. The cold stir bar improved the overall extraction efficiency with better repeatability, and the extraction time was further shortened to 1 min. Then, the effects of different ethanol concentrations and salt additions (sodium chloride or sodium sulfate) were studied, and 10% ethanol concentration with no salt addition provided the highest extraction efficiency for most compounds. Finally, it was verified that the high-throughput extraction condition was feasible for the volatile compounds spiked in a honeybush infusion.

Biovalorization of spent Konacha tea leaves via single-culture fermentation involving wine yeasts and lactic acid bacteria.

AIMS: The objective of this study was to explore the potential of fermentation as a biovalorization strategy for spent tea leaves (STL), a major agrifood waste generated from the tea extraction industry. Fermentation by wine yeasts or lactic acid bacteria (LAB) has shown promising results in previous studies across various substrates. METHODS AND RESULTS: Konacha (green tea) STL slurries were inoculated with single strains of wine yeasts or LAB respectively. After a 48-h fermentation, changes in selected nonvolatile and volatile compositions were evaluated. Fermentation by LAB increased organic acid content by 5- to 7-fold (except Lactobacillus fermentum) and modulated the composition of major tea catechins, whereas wine yeast fermentation resulted in a 30% increase in amino acid content. Strain-specific production of specific volatile compounds was also observed such as butanoic acid (L. fermentum), isoamyl acetate (Pichia kluyveri) and 4-ethylphenol (L. plantarum). CONCLUSIONS: Both volatile and nonvolatile compound compositions of Konacha STL were successfully modified via wine yeast and LAB fermentation. SIGNIFICANCE AND IMPACT OF STUDY: Our findings indicate that Konacha STL is a suitable medium for biovalorization by wine yeasts or LAB via the generation of commercially useful volatile and nonvolatile compounds. Future optimizations could further render fermentation an economically viable strategy for the upcycling of STL.

Ingredients, Processing, and Fermentation: Addressing the Organoleptic Boundaries of Plant-Based Dairy Analogues.

Consumer interest and research in plant-based dairy analogues has been growing in recent years because of increasingly negative implications of animal-derived products on human health, animal wellbeing, and the environment. However, plant-based dairy analogues face many challenges in mimicking the organoleptic properties of dairy products due to their undesirable off-flavours and textures. This article thus reviews fermentation as a viable pathway to developing clean-label plant-based dairy analogues with satisfactory consumer acceptability. Discussions on complementary strategies such as raw material selection and extraction technologies are also included. An overview of plant raw materials with the potential to be applied in dairy analogues is first discussed, followed by a review of the processing steps and innovative techniques required to transform these plant raw materials into functional ingredients such as plant-based aqueous extracts or flours for subsequent fermentation. Finally, the various fermentation (bacterial, yeast, and fungal) methodologies applied for the improvement of texture and other sensory qualities of plant-based dairy analogues are covered. Concerted research efforts would be required in the future to tailor and optimise the presented wide diversity of options to produce plant-based fermented dairy analogues that are both delicious and nutritionally adequate.

UPLC-Q-TOF-MS based metabolomics and chemometric analyses for green tea fermented with Saccharomyces boulardii CNCM I-745 and Lactiplantibacillus plantarum 299V.

UPLC-Q-TOF-MS was employed to analyse the non-volatile components of green teas fermented with probiotic yeast (Saccharomyces boulardii) and lactic acid bacteria (LAB, Lactiplantibacillus plantarum). The flavone glycosides in yeast-fermented and stored tea decreased significantly, together with the increases of flavone aglycones and other simple flavone glycosides. LAB-fermented tea presented different flavone glycoside profiles; in which, both C-glycosides and O-glycosides decreased and the flavone aglycones were further degraded. The profiles of flavone glycosides and aglycones in co-cultured tea differed from that in yeast- or LAB-fermented tea; less glycosides were degraded but a greater number of aglycones were produced. Two unique LAB metabolites with bioactive and antifungal properties, D-phenyllactic acid (PLA) and p-OH-PLA, were found in both L. plantarum and co-cultured teas, and the co-fermentation showed a synergic effect on the production of these two compounds that would enhance the quality and preservation of fermented teas.

Effect of three milling processes (cyclone-, bead- and stone-millings) on the quality of matcha: Physical properties, taste and aroma.

Analysis of three matcha (cyclone-, bead- and stone-milled) revealed differences in their sizes and surface morphologies. Using liquid chromatography, 4 sugars, 6 organic acids, 18 amino acids and 9 polyphenols were detected in all matcha samples and shown to present in different amount. Moreover, 108 volatile compounds were detected and 30 potential flavour-contributing compounds were quantified by gas chromatography time-of-flight mass spectrometry using headspace-stir bar sorptive extraction-thin-film solid-phase microextraction (HS-SBSE-TFSPME). Sensory evaluation by a trained panel found that the matcha samples possess different notes (cyclone-milled: leafy; bead-milled: fishy; and stone-milled: roasty) which is supported by the volatile compound analysis. Finally, the three matcha were differentiated based on non-volatile and volatile components using principal component analysis, and the correlation between chemical composition and sensory evaluation data was carried out using partial least square regression. In conclusion, milling processes clearly affected the physical, chemical and sensory qualities of matcha.

Effect of solid-state fungal fermentation on the non-volatiles content and volatiles composition of Coffea canephora (Robusta) coffee beans.

In this study, the effects of fungal fermentation on green canephora coffee beans were evaluated by observing the changes to selected non-volatile parameters before roasting, and subsequently the volatile profile after roasting. Solid-state fermentation (SSF) by Aspergillus spp. and Mucor spp. on green canephora coffee beans was shown to modulate the contents of free sugars, free amino acids and polyphenolic compounds such as caffeoylquinic acids (CQAs). Significant strain-specific differences were observed in the contents of aroma compounds after roasting. A significant increase in pyrazines was observed in the Aspergillus oryzae-fermented samples, while higher levels of furans were detected in the Mucor plumbeus-fermented samples. The present work shows that fungal fermentation of green canephora coffee beans is a potentially promising method for the modulation and improvement of coffee flavour and aroma.

Fermentation characteristics of four non-Saccharomyces yeasts in green tea slurry.

The fermentation characteristics of non-Saccharomyces yeasts (Pichia kluyveri FrootZen, Torulaspora delbrueckii Prelude, Williopsis saturnus var. mrakii NCYC2251 and Torulaspora delbrueckii Biodiva) were evaluated in green tea slurry fermentation. Each yeast showed different fermentation performances: strains Prelude and Biodiva utilized sucrose faster than the other two yeasts; strain NCYC2251 was the only species that metabolized xylose. Strain FrootZen increased the caffeine content significantly and strain Prelude showed the opposite trend, both at a statistical level, while theanine contents in four samples were relatively stable. Biodiva and FrootZen significantly improved polyphenols content and the oxygen radical absorbance capacity of fermented teas. Some endogenous volatiles such as ketones, lactones and aldehydes decreased to lower or undetected levels, but one of the key tea aroma compounds methyl salicylate increased by 34-fold and 100-fold in P. kluyveri and W. saturnus samples respectively. Therefore, green tea fermentation by appropriate non-Saccharomyces yeasts can enhance its antioxidant capacity and alter the aroma compound profile.

Identification of key odorants in honeysuckle by headspace-solid phase microextraction and solvent-assisted flavour evaporation with gas chromatography-mass spectrometry and gas chromatograph-olfactometry in combination with chemometrics.

At present, the identification of honeysuckle aroma depends on experienced tasters, which results in inconsistencies due to human error. The key odorants have the potential to distinguish the different species and evaluate the quality of honeysuckle. Hence, in this study, a more scientific approach was applied to distinguish various honeysuckles. The volatile compounds of different species and parts of honeysuckle were separately extracted by headspace-solid phase microextraction (HS-SPME) and solvent assisted flavor evaporation (SAFE). Compounds with greater volatility such as aldehydes, limonene, γ-terpinene, and terpinolene were preferentially extracted by HS-SPME. As a complementary extraction method to HS-SPME, SAFE was found to recover comparatively more polar compounds such as eugenol, decanoic acid, and vanillin. Subsequently, key odorants with the highest flavour dilution (FD) factors were detected by aroma extract dilution analysis (AEDA). These were benzaldehyde, 4-ethylphenol, decanoic acid, vanillin, 3-methyl-2-butenal, and ß-ionone in honeysuckle flowers and γ-octalactone, 4-ethyl phenol, and vanillin in honeysuckle stem. Finally, principal component analysis (PCA) was conducted to analyze not only the key odorants of species and parts of honeysuckle but also their different origins. The results of PCA suggested that the species of honeysuckle contributed much more to variations in aroma rather than their origins. In conclusion, the application of the key odorants combined with PCA was demonstrated as a valid approach to differentiate species, origins, and parts of honeysuckle.

Coffee flavour modification through controlled fermentation of green coffee beans by Saccharomyces cerevisiae and Pichia kluyveri: Part II. Mixed cultures with or without lactic acid bacteria.

This study attempted to achieve coffee flavour biotransformation through controlled fermentation of sterilsed green coffee beans with a coculture of Saccharomyces cerevisiae and Pichia kluyveri (FYco) and a sequential inoculation of Lc. lactis subsp. cremoris and the yeast coculture (FLYco). Isoamyl acetate, 2-phenylethyl acetate, and ethyl octanoate were produced by 5.76, 1.35 and 0.54 mg/kg, respectively, in FYco fermented green coffee beans. Compared to the green coffee bean fermented by the yeast monocultures in previous study, FYco led to a 1.2- and 4.1-times elevation in production of isoamyl acetate and 2-phenylethyl acetate, respectively. FLYco further increased acetate ester production by more than 2 times relative to FYco. The esters produced in FYco and FLYco partially survived the roasting process and imparted the roasted coffees with considerable fruity and winey aromas. The lactic acid fermentation in FLYco increased the acidity in green coffee beans, which promoted the formation of caramel-smelling furfurals and preservation of acidity and sweetness in the roasted coffees. Apart from the mere additions of flavour modification from individual strains, the proper combination of multiple strains can result in synergistic effects that enhanced the modulating activities of individual strains and further enhance flavour complexity of the resulted coffee.

Coffee flavour modification through controlled fermentations of green coffee beans by Saccharomyces cerevisiae and Pichia kluyveri: Part I. Effects from individual yeasts.

Direct fermentations of sterilised green coffee beans by monocultures of Saccharomyces cerevisiae and Pichia kluyveri were investigated for coffee flavour biotransformation. During fermentation, fruity esters were generated in the green coffee beans by yeasts. 2-Phenylethyl acetate was elevated by 1.1 mg/kg and 0.03 mg/kg in P. kluyveri- and S. cerevisiae-fermented green beans, respectively, as compared to the untreated sample. Ethyl octanoate (0.51 mg/kg) and isoamyl acetate (1.69 mg/kg) only existed in S. cerevisiae- and P. kluyveri-fermented green beans, respectively. After roasting, higher levels of 2-phenylethyl acetate were detected in fermented coffees, and ethyl octanoate was found only in the S. cerevisiae-fermented sample, despite the loss of isoamyl acetate in P. kluyveri-fermented coffees during roasting. The fruity esters generated by the yeasts during green coffee bean fermentations were directly transferred to the volatile profiles formed after roasting and enhanced the fruity attribute in the roasted coffees, with a more noticeable effect observed from S. cerevisiae fermentation. Higher productions of N-heterocyclic volatiles occurred during roasting of S. cerevisiae-fermented coffees and contributed to elevated nutty and roasted aromas. S. cerevisiae and P. kluyveri are considered suitable starter cultures for controlled coffee flavour biotransformation through controlled fermentations of green coffee beans.

Biotransformation of green tea (Camellia sinensis) by wine yeast Saccharomyces cerevisiae.

Wine yeast Saccharomyces cerevisiae 71B was used in fermentation of green tea to modulate the volatiles and nonvolatiles. After fermentation, higher alcohols, esters, and acids, such as isoamyl alcohol, isobutanol, ethyl octanoate, ethyl decanoate, octanoic, and decanoic acids were generated. Some key aroma compounds of tea including linalool, hotrienol, dihydroactinidiolide, and 2-phenylethanol increased significantly. Among these compounds, linalool and 2-phenylethanol increased by 1.3- and 10-fold, respectively, which impart floral and fruity notes to fermented green tea. Alkaloids including caffeine, theobromine, and theophylline were reduced significantly after fermentation, while the most important free amino acid in tea, theanine, was not metabolized by S. cerevisiae. Tea catechins decreased whereas gallic and caffeic acids increased significantly, resulting in the unchanged antioxidant capacity of the fermented green tea. Hence, this work highlighted the potential of using S. cerevisiae to modulate green tea aroma and nonvolatiles. PRACTICAL APPLICATION: A novel fermented tea is produced by yeast fermentation. Saccharomyces cerevisiae led to significant changes in tea volatiles and nonvolatiles. Antioxidant capacity remained stable after fermentation.

Improved detection of key odourants in Arabica coffee using gas chromatography-olfactometry in combination with low energy electron ionisation gas chromatography-quadrupole time-of-flight mass spectrometry.

Four Arabica coffees (Brazil, Colombia, Ethiopia, and Guatemala) yield highly variant odours, attesting to the complexities of coffee aroma that command advanced analytical tools. In this study, their volatiles were extracted using solvent-assisted flavour evaporation (SAFE) and headspace solid-phase microextraction (HS-SPME). Due to matrix complexity, some trace odourants were detected in SAFE extracts by aroma extract dilution analysis (AEDA) but remained difficult to quantify by gas chromatography-mass spectrometry (GC-MS). This prompted the application of low energy electron ionisation (EI) coupled with GC-quadrupole time-of-flight (GC-QTOF). Optimal low EI GC-QTOF parameters (EI energy: 15 eV, acquisition rate: 3 Hz) were applied to achieve improved molecular ion signal intensity and reproducibility (relative standard deviation < 10%) across five compounds, which resulted in good linearity (R2 ≥ 0.999) and lowered detection levels (e.g. 0.025 ±â€¯0.005 ng/mL for 4-hydroxy-5-methyl-3(2H)-furanone). Therefore, this method potentially improves the measurement of trace odourants in complex matrices by increasing specificity and sensitivity.

A systematic study of molecular ion intensity and mass accuracy in low energy electron ionisation using gas chromatography-quadrupole time-of-flight mass spectrometry.

Molecular ions, which contain accurate mass information, are valuable for providing elemental composition elucidation. Under the most common electron ionisation (EI) condition (electron energy, 70 eV and temperature, 230 °C), molecular ions are often in relatively low intensities or completely unapparent. In this research, low energy EI source parameters (electron energy and temperature) in a gas chromatography-quadrupole time of flight (GC-QTOF) were systematically studied to evaluate their correlative impact on the intensity and mass accuracy of molecular ions. Lower temperatures were generally associated with higher molecular ion intensities under various EI energies. Apart from compounds with more chemically stable molecular ion structures, the lowest electron energy (12 eV) corresponded to higher intensities. On the other hand, mass accuracy appeared to be mostly constant (≤5 ppm) at different temperatures, while improvement was observed with the use of lower electron energies (12 eV). Moreover, the effect of compound concentration on molecular ion intensity and mass accuracy was studied from 50 to 5000 ppm, and the compound-specific concentration profiles were constructed. Finally, it was found that higher column flow rates corresponded to higher intensities, while the response under 12 eV was higher than that of 70 eV. Mass accuracy remained approximately constant across different flow rates. Therefore, these findings suggest that the use of low energy EI may be a viable approach for the preservation of molecular ions.

Potential of lactic acid bacteria to modulate coffee volatiles and effect of glucose supplementation: fermentation of green coffee beans and impact of coffee roasting.

BACKGROUND: Coffee flavor can be significantly influenced by microbial activities in spontaneous fermentation of coffee cherries. The potential of lactic acid bacteria for flavor modulation through controlled fermentation of green coffee beans has not been explored. RESULTS: Fermentation by Lactobacillus rhamnosus HN001 with and without 1% w/w glucose supplementation led to modification of flavor-related constituents in green coffee beans, which translated into modulation of coffee volatiles upon roasting. The lactic acid bacteria consumed almost all glucose and fructose, leaving sucrose behind. Amino acids and malic, citric, and succinic acids were partially catabolized. Glucose supplementation enhanced lactic acid production but repressed acetic acid formation. After roasting at 235 °C for 9 min, 12 min, and 15 min, the levels of furfurals in glucose-supplemented-fermented coffee were 10.5-, 2.7-, and 1.1-fold higher than those in the controls (nonsupplemented-unfermented coffee); furthermore, the levels of pyrazines in the controls were 11.9-, 10.1-, and 6.5-fold higher than those in the treated coffee. Glucose-supplemented fermentation yielded roasted coffee with stronger caramelic and burnt characteristics but weaker nutty notes. In roasted non-supplemented-fermented coffee, volatile production was generally reduced, resulting in a milder overall aroma. CONCLUSION: Lactic acid fermentation of green coffee beans is a new strategy for coffee flavor modulation, creating novel aroma characteristics. © 2018 Society of Chemical Industry.

Effects of physicochemical parameters on volatile sulphur compound formation from L-methionine catabolism by non-growing cells of Kluyveromyces lactis.

The present study investigated for the first time the effects of various physicochemical parameters on the production of volatile sulphur compounds (VSCs) by non-growing cells of Kluyveromyces lactis supplemented with L-methionine. The results showed that the production of VSCs positively correlated with the cell biomass, but it seemed that no clear relationship with L-methionine concentration existed. Temperature and pH significantly affected the formation of VSCs with more production at 30 °C and pH 5, respectively. Nitrogen supplementation (in the form of diammonium phosphate, DAP) repressed the production of VSCs. It is interesting to note that DAP and yeast extract supplementation induced the production of methional, but not Mn2+ supplementation. The presence of Mn2+ improved the production of methionol and dimethyl disulphide, but inhibited the formation of S-methyl thioacetate. The study indicated that optimization of physicochemical conditions and media composition would be crucial for producing L-methionine-derived VSC bioflavor.

Chemical and enzymatic synthesis of a library of 2-phenethyl esters and their sensory attributes.

We report a simple enzymatic approach to synthesise phenethyl esters as natural flavouring materials. Chemical and lipase-catalysed esterification reactions between fatty acids of C4-C18 and 2-phenethyl alcohol were studied. Both methods were compared qualitatively and quantitatively by GC-MS/FID. The acid and thermal stabilities of 2-phenethyl esters were excellent and can meet the requirements of food matrices under most processing conditions. Sensory evaluation showed that each 2-phenethyl ester with a different carbon-chain-length fatty acid had unique sensory notes. Moreover, through Lipozyme TL IM-mediated transesterification, valuable 2-phenethyl alcohol-derived esters were synthesised from butter oil and 2-phenethyl alcohol. The influence of several physicochemical parameters (temperature, substrate molar ratio, enzyme loading, shaking speed and time) on the transesterification reaction was investigated to give optimal reaction conditions, leading to a high yield of 80.0%.

Synthesis and evaluation of odour-active methionyl esters of fatty acids via esterification and transesterification of butter oil.

Methionol-derived fatty acid esters were synthesised by both chemical and lipase catalysed esterification between fatty acids and methionol. Beneficial effects of both methods were compared qualitatively and quantitatively by GC-MS/GC-FID results. And the high acid and heat stability of our designed methionyl esters meet the requirement of the food industry. Most importantly, the sensory test showed that fatty acid carbon-chain length had an important effect on the flavour attributes of methionyl esters. Moreover, through Lipozyme TL IM-mediated transesterification, valuable methionol-derived esters were synthesised from the readily available natural material butter oil as the fatty acid source. The conversion of methionol and yield of each methionyl ester were also elucidated by GC-MS-FID.

Lipase-catalysed ester synthesis in solvent-free oil system: is it esterification or transesterification?

Ester synthesis was carried out in a solvent-free system of lipase, coconut oil and ethanol or fusel alcohols to ascertain the reaction mechanism. During ester formation, octanoic and decanoic acids increased initially and then decreased gradually, indicating that ester production was a two-step reaction consisting of hydrolysis and esterification, rather than alcoholysis. With ethanol as the alcohol substrate, added butyric acid inhibited ester synthesis. However, when fusel alcohols were used as the alcohol substrate, no significant inhibitory effect by butyric acid was observed. Added octanoic acid did not show any adverse effect on the synthesis of corresponding esters. The results suggest that polarity of the reactants determines lipase activity. This study provides the first evidence on the mechanism of immobilised lipase-catalysed ester synthesis in a solvent-free system involving both hydrolysis and esterification.

Optimisation of flavour ester biosynthesis in an aqueous system of coconut cream and fusel oil catalysed by lipase.

Coconut cream and fusel oil, two low-cost natural substances, were used as starting materials for the biosynthesis of flavour-active octanoic acid esters (ethyl-, butyl-, isobutyl- and (iso)amyl octanoate) using lipase Palatase as the biocatalyst. The Taguchi design method was used for the first time to optimize the biosynthesis of esters by a lipase in an aqueous system of coconut cream and fusel oil. Temperature, time and enzyme amount were found to be statistically significant factors and the optimal conditions were determined to be as follows: temperature 30°C, fusel oil concentration 9% (v/w), reaction time 24h, pH 6.2 and enzyme amount 0.26 g. Under the optimised conditions, a yield of 14.25mg/g (based on cream weight) and signal-to-noise (S/N) ratio of 23.07 dB were obtained. The results indicate that the Taguchi design method was an efficient and systematic approach to the optimisation of lipase-catalysed biological processes.