Multidimensional Gas Chromatography of Organosulfur Compounds in Coffee and Structure-Odor Analysis of 2-Methyltetrahydrothiophen-3-one.

Organosulfur compounds (OSCs) in coffee remain challenging to analyze by conventional gas chromatography (GC) due to their low concentrations amid coffee's complex matrix and susceptibility to chiral-odor influences. In this study, multidimensional GC (MDGC) methods were developed to profile OSCs in coffee. Conventional GC was compared to comprehensive GC (GC×GC) for untargeted OSC analysis in eight specialty coffees, and GC×GC was found to improve the fingerprinting of OSCs in coffee (50 vs 16 OSCs identified). Of the 50 OSCs, 2-methyltetrahydrothiophen-3-one (2-MTHT) was of high interest due to its chirality and known aroma contribution. Following that, a heart-cutting method for chiral GC (GC-GC) was developed, validated, and applied to the coffees. The mean enantiomer ratio of 2-MTHT was observed to be 1.56 (R/S) in brewed coffees. Overall, MDGC techniques allowed for more comprehensive analyses of coffee OSCs, from which (R)-2-MTHT was found to be the predominant enantiomer with the lower odor threshold.

Characterisation of catechins and their oxidised derivatives in Ceylon tea using multi-dimensional liquid chromatography and high-resolution mass spectrometry.

Tea is a complex food matrix comprising of many structurally diverse compounds, of which catechins and their oxidised derivatives are of particular interest due to their nutritional functionality. However, these catechins and derivatives exist in various isomeric forms with few or no pure standards available, rendering their analysis challenging. A method combining multi-dimensional liquid chromatography (MDLC) and high-resolution mass spectrometry (HRMS) was developed for the characterisation of these compounds using Ceylon tea as a model. Based on a Plackett-Burman (PB) design, flow rate and initial methanol percentage were identified as the most significant factors (p < 0.05) affecting chromatogram coverage and resolution (Rs) for comprehensive two-dimensional LC (LCxLC) and heart-cutting two-dimensional LC (LC-LC) respectively. Central composite design (CCD) was then applied using these parameters for method optimisation and to identify second-order relationships between screened parameters. The optimised LCxLC (flow rate: 2.18 mL/min and initial methanol percentage: 28.0%) and LC-LC (flow rate: 0.86 mL/min and initial methanol percentage for different cuts: A- 10.0%; B- 15.8%; and C- 18.7%) methods were applied to the analysis of Ceylon tea samples from seven regions of Sri Lanka and demonstrated an improved separation of co-eluting isomeric compounds. Finally, with the mass spectral information from HRMS, a total of 31 compounds (eight monomers, 17 dimers, five trimers and one tetramer) were detected and putatively identified in Ceylon tea.

Recent advances in analytical strategies for coffee volatile studies: Opportunities and challenges.

Coffee has attracted significant research interest owing to its complex volatile composition and aroma, which imparts a pleasant sensorial experience that remains challenging to analyse and interpret. This review summarises analytical challenges associated with coffee's volatile and matrix complexity, and recent developments in instrumental techniques to resolve them. The benefits of state-of-the-art analytical techniques applied to coffee volatile analysis from experimental design to sample preparation, separation, detection, and data analysis are evaluated. Complementary method selection coupled with progressive experimental design and data analysis are vital to unravel the increasing comprehensiveness of coffee volatile datasets. Considering this, analytical workflows for conventional, targeted, and untargeted coffee volatile analyses are thus proposed considering the trends towards sorptive extraction, multidimensional gas chromatography, and high-resolution mass spectrometry. In conclusion, no single analytical method addresses coffee's complexity in its entirely, and volatile analysis must be tailored to the key objectives and concerns of the analyst.

Enzymatic treatment, unfermented and fermented fruit-based products: current state of knowledge.

In recent years, food manufacturers are increasingly utilizing enzymes in the production of fruit-based (unfermented and fermented) products to increase yield and maximize product quality in a cost-effective manner. Depending on the fruits and desired product characteristics, different enzymes (e.g. pectinase, cellulase, hemicellulase, amylase, and protease) are used alone or in combinations to achieve optimized processing conditions and improve nutritional and sensorial quality. In this review, the mechanisms of action and sources of different enzymes, as well as their effects on the physicochemical, nutritional, and organoleptic properties of unfermented and fermented fruit-based products are summarized and discussed, respectively. In general, the application of enzymatic hydrolysis treatment (EHT) in unfermented fruit-based product helps to achieve four main purposes: (i) viscosity reduction (easy to filter), (ii) clarification (improved appearance/clarity), (iii) better nutritional quality (increase in polyphenolics) and (iv) enhanced organoleptic characteristic (brighter color and complex aroma profile). In addition, EHT provides numerous other advantages to fermented fruit-based products such as better fermentation efficiency and enrichment in aroma. To meet the demand for new market trends, researchers and manufacturers are increasingly employing non-Saccharomyces yeast (with enzymatic activities) alone or in tandem with Saccharomyces cerevisiae to produce complex flavor profile in fermented fruit-based products. Therefore, this review also evaluates the potential of some non-Saccharomyces yeasts with enzymatic activities and how their utilization helps to tailor wines with unique aroma profile. Lastly, in view of an increase in lactose-intolerant individuals, the potential of fermented probiotic fruit juice as an alternative to dairy-based probiotic products is discussed.

Effect of thermal treatment on aroma compound formation in yeast fermented pork hydrolysate supplemented with xylose and cysteine.

BACKGROUND: The present study has revealed an innovative method of coupling enzyme hydrolysis, yeast fermentation and thermal treatment to transform pork trimmings into a seasoning product. The pork trimmings were first enzymatically hydrolysed and fermented into liquid pork hydrolysates, followed by adding xylose and cysteine, then heat treatment. RESULTS: Approximately 28% of xylose and 7% of glucose were consumed, and amino acids increased by around 31% after thermal treatment. The heated yeast fermented pork hydrolysates possessed a characteristic 'savoury, roasted-meat and fruity sweet' aroma as a result of the formation of thermally induced sulfur-containing volatiles such as 2-furfurylthiol, as well as retention of yeast generated esters including isoamyl acetate and hexyl acetate. CONCLUSION: The heat-treated fermented pork hydrolysates impart an attractive and innovative aroma because of yeast fermentation and heat treatment. The innovative heated fermented pork hydrolysates could be further processed into a nutritional and savoury pork broth and/or a meat sauce. © 2021 Society of Chemical Industry.

Untargeted LC-QTOF-MS/MS based metabolomics approach for revealing bioactive components in probiotic fermented coffee brews.

Amidst trends in non-dairy probiotic foods and functional coffees, we recently developed a fermented coffee brew containing high live counts of the probiotics Lacticaseibacillus rhamnosus GG and Saccharomyces boulardii CNCM-I745. However, probiotic fermentation did not alter levels of principal coffee bioactive components based on targeted analyses. Here, to provide therapeutic justification compared to other non-fermented coffee brews, we aimed to discover postbiotics in coffee brews fermented with L. rhamnosus GG and/or S. boulardii CNCM-I745. By using an untargeted LC-QTOF-MS/MS based metabolomics approach coupled with validated multivariate analyses, 37 differential metabolites between fermentation treatments were putatively annotated. These include the production of postbiotics such as 2-isopropylmalate by S. boulardii CNCM-I745, and aromatic amino acid catabolites (indole-3-lactate, p-hydroxyphenyllactate, 3-phenyllactate), and hydroxydodecanoic acid by L. rhamnosus GG. Overall, LC-QTOF based untargeted metabolomics can be an effective approach to uncover postbiotics, which may substantiate additional potential functionalities of probiotic fermented foods compared to their non-fermented counterparts.

In vitro bioactivities of coffee brews fermented with the probiotics Lacticaseibacillus rhamnosus GG and Saccharomyces boulardii CNCM-I745.

Previously, we demonstrated the production of bioactive metabolites (e.g., indole-3-lactate, 4-hydroxyphenyllactate, 3-phenyllactate, 2-isopropylmalate) by the probiotics Lacticaseibacillus rhamnosus GG and Saccharomyces boulardii CNCM-I745 during coffee brew fermentation. However, it remains unclear if in situ production of bioactive metabolites confers additional health benefits to coffee brews. Here, we aimed to investigate the in vitro bioactivities of freeze-dried cell-free coffee supernatants fermented with L. rhamnosus GG and/or S. boulardii CNCM-I745, compared to non-fermented coffee supernatants. In vitro bioactivity assays pertained to α-amylase and α-glucosidase inhibition, antiglycative activities, anti-proliferation against human cancer cell lines (MCF-7, HCT116, and HepG2), cellular antioxidant activities, and anti-inflammatory activities. We demonstrated that non-fermented coffee supernatants displayed weak starch hydrolase inhibition (IC50 > 36.00 mg/mL), but otherwise displayed strong anti-glycative (IC50 0.71-0.74 mg/mL), anti-proliferative (IC50 0.45, 0.36, and < 0.5 mg/mL for MCF-7, HCT116, and HepG2 respectively), cellular antioxidant (85,844.22 µmol quercetin equivalents/100 g coffee supernatant), and anti-inflammatory activities (35.7% reduction in nitrite production at 0.13 mg/mL). In all the assays tested, probiotic fermented coffee supernatants exhibited very similar bioactivities compared to non-fermented coffee supernatants, and improvements were not observed. Overall, in vitro bioactivities of coffee brews were not improved via in situ metabolite production by L. rhamnosus GG and/or S. boulardii CNCM-I745. Therefore, bioactive metabolites produced during probiotic-induced food fermentations may not necessarily confer additional health benefits compared to non-fermented counterparts.

Growth, survival, and metabolic activities of probiotics Lactobacillus rhamnosus GG and Saccharomyces cerevisiae var. boulardii CNCM-I745 in fermented coffee brews.

Amidst rising demand for non-dairy probiotic foods, and growing interest in coffees with added functionalities, it would be opportune to ferment coffee brews with probiotics. However, challenges exist in maintaining probiotic viability in high-moisture food products. Here, we aimed to enhance the viability of the probiotic bacteria, Lactobacillus rhamnosus GG, in coffee brews by co-culturing with the probiotic yeast, Saccharomyces cerevisiae var. boulardii CNCM-I745. The yeast significantly enhanced the viability of L. rhamnosus GG, as bacterial populations beyond 7 Log CFU/mL were maintained throughout 14 weeks of storage at 4 and 25 °C. In contrast, the single culture of L. rhamnosus GG suffered viability losses below 6 Log CFU/mL within 10 weeks at 4 °C, and 3 weeks at 25 °C. Growth and survival of S. boulardii CNCM-I745 remained unaffected by the presence of L. rhamnosus GG. Volatile profiles of coffee brews were altered by probiotic metabolic activities, but co-culturing led to suppressed generation of diacetyl and ethanol compared to single cultures. Probiotic fermentation did not alter principal coffee bioactive compounds and antioxidant capacities; however, declines in peroxyl radical scavenging capacities were observed after ambient storage. Overall, we illustrate that yeasts are effective in enhancing probiotic bacterial viability in coffee brews, which may be useful in developing shelf stable probiotic food products.

The impact of mixed amino acids supplementation on Torulaspora delbrueckii growth and volatile compound modulation in soy whey alcohol fermentation.

Soy (tofu) whey is a liquid side stream generated from tofu production and is often discarded as waste after it is generated. Direct disposal of soy whey can result in environmental issue in the long run. Soy whey has been previously successfully fermented using different types of wine yeasts, but the yeast available nitrogen (YAN) was found to be deficient. In this study, the soy whey YAN was estimated to be approximately 45.9 mg N/L. A mixture of four amino acids (valine, leucine, isoleucine and phenylalanine) was added into soy whey at a total concentration of +40, +80, +120 and +160 mg N/L and fermented with Torulaspora delbrueckii Biodiva for a period of 10 days. Increasing amino acid supplementation did not affect the yeast cell growth, but it sped up the sugar utilization proportionally. Increasing amino acid supplementation resulted in lower organic acid production and higher glycerol production. Amino acid supplementation also enhances the production rate of higher alcohols; increasing amount of higher alcohols and their respective esters were obtained with increasing amount of amino acid supplementation. However, higher levels of amino acid supplementation (particularly at +160 mg N/L sample) resulted in higher residual nitrogen contents which may lead to microbial instability. Supplementation of 120 mg N/L of amino acids was found to be the optimum concentration to enhance the metabolism of the yeast without leaving a high residual amino acid content. Therefore, with proper control of the amino acid addition dosage, the usage of mixed amino acid supplementation may be a strategy to regulate the fermentation kinetics and volatile compound modulation in soy whey alcohol fermentation.

Growth, survival, and metabolic activities of probiotic Lactobacillus spp. in fermented coffee brews supplemented with glucose and inactivated yeast derivatives.

Amidst rising interest in non-dairy probiotic foods, and growing global coffee consumption patterns, it would be opportune to ferment coffee brews with probiotics, yet it remains unexplored. In this study, we aimed to develop a fermented coffee beverage rich in live probiotics, by supplementing nutrient-deficient coffee brews with glucose and inactivated yeast derivatives. This was followed by fermentation with single probiotic bacteria cultures (Lactobacillus rhamnosus GG, L. paracasei Lpc-37, L. plantarum 299v, and L. acidophilus NCFM), and subsequent storage at 4 and 25 °C. We demonstrated that nutrient supplementation was essential in supporting probiotic growth and survival in coffee brews, as viabilities above 7 Log CFU/mL could not be sustained longer than 2 weeks in non-supplemented coffees. In contrast, viabilities above 7 Log CFU/mL were maintained for 10 weeks by L. rhamnosus GG and L. paracasei Lpc-37 in supplemented coffees stored under refrigeration. Probiotic metabolic activities led to consumption of glucose, glutamic acid, and alanine, with simultaneous formation of lactic acid, 3-methylbutanoic acid, and diacetyl. Nevertheless, endogenous coffee volatiles, bioactive components, and antioxidant capacities were retained. Overall, we illustrate the potential functionalities of probiotic fermented coffee brews, arising from high probiotic live counts and retention of major coffee bioactive components.

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.

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.

Understanding the interaction of isoleucine paired with other amino acids in soy whey alcohol fermentation using Torulaspora delbrueckii.

Soy (tofu) whey is a liquid by-product generated from tofu (soybean curd) production and it is often discarded off as a waste liquid by the tofu manufacturers. Previous studies have demonstrated that soy whey can be biotransformed into a soy alcoholic beverage by using Saccharomyces and non-Saccharomyces yeasts even though soy whey is low in yeast assimilable nitrogen (YAN) content. In this study, the initial YAN of the soy whey was estimated to be 46.6 mg N/L and Torulaspora delbrueckii Biodiva was used to ferment soy whey supplemented with either isoleucine only or isoleucine paired with valine, leucine or phenylalanine (each amino acid supplemented at a dosage of 30 mg N/L). Amino acid supplementation was found to enhance sugar utilization by the yeast, which led to higher ethanol production (7.49% v/v in control versus 8.35-8.80% v/v in supplemented samples). Samples supplemented with isoleucine only experienced slower sugar utilization during the fermentation as compared to the paired amino acid samples, but the yeast was still able to utilize the sugar to low levels at the end of the fermentation. The presence of leucine supplementation counteracted the "inhibition" induced by the presence of isoleucine at the first day of the fermentation. Amino acid supplementation slowed down glutamic acid utilization and resulted in higher levels of residual glutamic acid and alanine. Amino acid supplementation increased the corresponding fusel alcohol production and the presence of other amino acids reduced the active amyl alcohol production. Therefore, interactions between amino acids can impact the metabolism of the yeast as well as the flavor modulation during soy whey fermentation.

Effect of single amino acid addition on growth kinetics and flavor modulation by Torulaspora delbrueckii in soy (tofu) whey alcoholic beverage fermentation.

Soy (tofu) whey is a by-product commonly disposed of by tofu manufacturers around the world. Due to its nutritious nature, direct disposal of soy whey into the sewage can result in a detrimental impact on the environment in the long-run. In this study, soy whey supplemented with four individual amino acids (valine, leucine, isoleucine and phenylalanine) equivalent to 120 mg N/L was fermented with a yeast Torulaspora delbrueckii Biodiva. The supplementation of an individual amino acid resulted in faster sugar utilization and lower levels of residual sugar than the unsupplemented whey but did not result in a significantly higher amount of ethanol (7-8% v/v) at the end of fermentation. Isoleucine supplementation resulted in a slightly slower initial yeast growth rate when compared to the control while the other three amino acids had identical yeast growth kinetics to the control. Isoleucine supplementation also resulted in slower sugar utilization during the first four days. Therefore, isoleucine is least preferred by the yeast. The supplementation of amino acids resulted in greater formation of higher alcohols and their corresponding alcohol-derived esters. Overall, the supplementation of a single amino acid enhanced sugar utilization and impacted flavor compounds of the resultant soy whey alcoholic beverage.

Moringin and Its Structural Analogues as Slow H2S Donors: Their Mechanisms and Bioactivity.

Moringin (rhamnobenzyl isothiocyanate) is a major bioactive compound in moringa seeds, which have been used as a healthy food. However, its bioactivity mechanisms are not well understood. We investigated moringin and its structurally similar analogues, including benzyl isothiocyanate and 4-hydroxylbenzyl isothiocyanate, for their hydrogen sulfide (H2S)-releasing activity triggered by cysteine. These isothiocyanates rapidly formed cysteine adducts, which underwent intramolecular cyclization followed by slowly releasing (a) organic amine and raphanusamic acid and (b) H2S and 2-carbylamino-4,5-dihydrothiazole-4-carboxylic acids. The product distributions are highly dependent on para-substituents on the phenyl group. Moringin has higher cytotoxicity to cancer cells and is a more potent anti-inflammatory agent than benzyl and hydroxybenzyl analogues, while benzyl isothiocyanate is a better antibacterial agent. Taken together, their bioactivity may not be directly related to their H2S donation activity. However, other metabolites alone do not have cytotoxicity and anti-inflammatory activity. These findings indicated that their activity may be the combination effects of different metabolites via competitive pathways as well the para-substituent groups of benzyl ITCs.

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.

Aroma modulation of vegetable oils-A review.

Aroma is an important quality factor for unrefined vegetable oils especially the condiment oils, whose application and acceptability largely depend on their aroma attributes. The ever-advanced techniques including extraction, separation, detection and identification in flavor science allow hundreds of volatile compounds and aroma-active compounds with high complexity to be identified, which enables us a deep and comprehensive understanding of the aroma in various type of vegetable oils. Studies show that several avenues, mainly including enzymatic reaction, Maillard reaction, Strecker degradation, caramelization, lipid oxidation and thermal degradation of other compounds, account for the formation of these aroma compounds, though some may dominate over others depending on the processing methods/conditions. Based on these findings, novel approaches such as mild-heat treatment, roasting, microwave processing, infrared radiation, enzymatic treatment and fermentation, among others, have been applied to pretreat oil seeds or fruits with the aim to modulate the flavor generation and sensory quality in oils, whereby promising and insightful results are obtained. This review summarizes and discusses the volatile composition and key aroma compounds in common unrefined vegetable oils, their generation pathways as well as the approaches used to modulate their formations.

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.

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.