Development and validation of a novel method for aroma dilution analysis by means of stir bar sorptive extraction

Characterization of the Aroma Profile of Ginger Powder Produced by a Split-Stream Spray-Drying Process

Freeze-dried ginger (Zingiber officinale) is renowned for its high quality, but it is expensive. As an alternative, spray drying can be explored for producing ginger powder. However, sugar rich feed solutions can lead to stickiness development during the process. Adding carrier materials increases costs and labeling. Accordingly, a split-stream spray-drying process was developed, where ginger fibers in their natural composition were reintroduced as a carrier material into the spray-drying process. The inlet and outlet temperatures were set at 220 and 80 °C, respectively, for optimal aroma retention. Using a stir bar sorptive extraction-gas chromatography-mass spectrometry-olfactometry, the results revealed that reintegrating ginger fibers significantly increased the concentration of eight key odorants. Although freeze-dried ginger retains more aroma, the total concentration of twenty-seven odorants in the developed spray-dried ginger was 1.9 times higher compared to frozen ginger.

Production of a Cheese-Like Aroma via Fermentation of Plant Proteins and Coconut Oil with the Basidiomycetes Cyclocybe aegerita and Trametes versicolor

Cheese is one of the most common dairy products and is characterized by its complex aroma. However, in times of climate change and resource scarcity, the possibility to mimic the characteristic cheese-like aroma from plant-based sources is in demand to offer alternatives to cheese. Accordingly, the production of a natural cheese-like aroma via fermentation of four plant-based proteins and coconut oil with basidiomycetes has been addressed. Mixtures of soy and sunflower protein with coconut oil (15 g/L) have shown the formation of a cheese-like aroma after 72 and 56 h after fermentation with Cyclocybe aegerita and Trametes versicolor, respectively. Isovaleric acid, butanoic acid, ethyl butanoate, 1-octen-3-ol, and various ketones were identified as the key odorants. Similarities to typical cheeses were observed by the principal component analysis. Overall, the finding offered an approach to a sustainable production of a natural cheese-like aroma from a plant source, thus contributing to the development of cheese alternatives.

Optimization of thermal desorption conditions of stir bar sorptive extraction facilitated by machine learning

Stir bar sorptive extraction is an effective technique for trapping odorants, but there are limited studies on the effect of varying thermal desorption conditions on desorption efficiency of odorants. Therefore, we conducted this study to explore the relationship between desorption conditions and desorption efficiency for 18 odorants with diverse physicochemical properties using instrumental analysis and mathematical modeling. We trained four types of machine learning models using a dataset comprising 864 different combinations of four desorption conditions (each three levels) and physicochemical properties. The prediction value of the selected model was validated using a validation dataset of six new odorants. The Random Forest model had the highest performance (R = 0.910). The order of feature importance using this model was as follows: cryo-focusing temperature, molecular weight, log P, boiling point, desorption temperature, desorption time, and helium flow. For testing on new odorants, the correlations between predicted and experimental data for terpene (R = 0.99), alcohol (R = 0.98), ester (R = 0.92), sulfide (R = 0.89), phenol (R = 0.88), and aldehyde (R = 0.61) were determined.

Generation of Meaty Aroma from Onion (Allium cepa L.) with Polyporus umbellatus: Fermentation System, Sensory Profile, and Aroma Characterization

One of the main reasons for consumer rejection of plant-based meat alternatives is the lack of meaty flavor after cooking. In this study, a platform was developed to generate meaty flavors solely from Allium substrates (chives, leeks, ramsons, and onions) using basidiomycete-mediated submerged fermentations. Polyporus umbellatus-mediated fermentation of onions resulted in an intense meaty and liver sausage-like flavor under proper fermentation parameters. Using multisolvent and solvent-free aroma extractions coupled with gas chromatography-mass spectrometry-olfactometry, 5 odorants with high assigned flavor dilution (FD) factors (≥ 256) were identified in the fermented sample that have been reported in the literature as important aroma compounds of meat products: methyl palmitate, bis(2-methyl-furyl) disulfide, (E,E)-2,4-decadienal, γ-nonalactone, and eugenol. Using selected ion monitoring, the presence of bis(2-methyl-furyl) disulfide (meaty, savory, FD 256) after fermentation was confirmed. It was proposed that P. umbellatus enzymatically forms bis(2-methyl-furyl) disulfide from intermediates derived from the thermal degradation of thiamine.

Influence of peeling on volatile and non-volatile compounds responsible for aroma, sensory, and nutrition in ginger (Zingiber officinale)

Industrial use of ginger after peeling results in large amounts of agro-waste. To provide a basic reference for the sustainable processing of ginger products as a spice, we investigated the differences between unpeeled ginger, peeled ginger, and corresponding ginger peel, in terms of aroma, sensory profiles, and nutrition relevant physicochemical properties. The results showed that the total concentrations of identified odor-active compounds in unpeeled ginger, peeled ginger, and ginger peel were 876.56, 672.73, and 105.39 mg/kg, respectively. Unpeeled ginger exhibited more intense citrus-like and fresh impressions compared to peeled ginger, revealed by descriptive sensory analyses. This is relevant to the high odor activity values of odorants such as β-myrcene (pungent, citrus-like), geranial (citrus-like), citronellal (citrus-like, sourish), and linalool (floral, fresh). In parallel, unpeeled ginger contained higher total polyphenol (84.49 mg/100 g) and total sugar content (33.4 g/kg) in comparison with peeled ginger (76.53 mg/100 g and 28.6 g/kg).

Characterization of cheesy odor formed during fermentation of soy drink with Agrocybe aegerita

The market for plant protein-based substitutes for cheeses is growing, but the sensory properties are distinctively different from the original products. Hence, natural and vegan cheesy flavors are needed to aromatize the products. A cheesy, sweaty and parmesan-like aroma was produced by fermentation of soy drink with Agrocybe aegerita. Aroma dilution analysis revealed short-chain fatty acids (SCFAs) as main influencing cheesy odorants analyzed by gas chromatography-mass spectrometry-olfactometry. In comparison to the five cheese varieties, the SCFA profile of the fermented soy drink revealed similarities with Parmesan and Emmental cheese. Meanwhile, principal component analysis showed an approximation of the aroma profile after fermentation with A. aegerita to those of cheeses. 3-Methylbutanoic acid was synthesized from the protein fraction, while the oil fraction contributed to the formation of unbranched SCFAs like butanoic acid. Accordingly, the production of these compounds can be increased by addition of the fractions.

Wild Strawberry-like Flavor Produced by the Fungus Wolfiporia cocos─Identification of Character Impact Compounds by Aroma Dilution Analysis after Dynamic Headspace Extraction

Brown-rot fungi are particularly suitable for the sustainable and cost-efficient biotechnological production of natural flavors. In this study, Wolfiporia cocos was employed for the fermentation of European black currant pomace supplemented with aspartate in surface cultures to produce a flavor reminiscent of wild strawberries. Aroma dilution analysis (ADA) by means of dynamic headspace extraction was developed as a suitable technique for solid samples. The character impact compounds were quantified by stable isotope dilution analysis and standard addition and validated by recombination experiments. (R)-Linalool (1879 μg kg^-1, ADA 2¹¹), methyl anthranilate (2206 μg kg^-1, 2¹⁰), 2-aminobenzaldehyde (771 μg kg^-1, 2⁵), and geraniol (138 μg kg^-1, 2⁵) were identified as key aroma compounds. Recombination experiments demonstrated that the combination of the four analyzed compounds was responsible for the odor impression reminiscent of wild strawberries.

Off-flavor in soy drink: Development, optimization, and validation of an easy and fast method to quantify the key odorants

A detailed molecular flavor profile was necessary to understand the low acceptance of soy drink by Western consumers. Accordingly, key odor-active compounds were detected by means of aroma dilution analyses coupled with gas chromatography-mass spectrometry-olfactometry after application of suitable solvent-free volatile extraction techniques. Four quantification methods (standard addition, external calibration, internal standard, and stable isotope dilution assay) were developed and validated to measure the concentrations after direct immersion-stir bar sorptive extraction. The quantitative methods provided correctness between 97% and 111% and precision ranging from 78% to 99% for the 21 key odorants. Considering the advantages to be efficient, easy to perform and cheap, internal standard method was further applied to four commercially available soy drinks in Germany. Correlated to a sensory acceptance test (n = 52) contents of 1-octen-3-one, (E,E)-2,4-decadienal and 2-methoxy-4-vinylphenol were suggested to be linked to the aversion of Western consumers to soy drink.

Formation of Diastereomeric Dihydromenthofurolactones by Cystostereum murrayi and Aroma Dilution Analysis Based on Dynamic Headspace Extraction

Submerged cultures of the basidiomycota Cystostereum murrayi emit an intensive coconut-like, sweetish, and buttery smell. For identification of the key aroma compounds, an aroma dilution analysis using dynamic headspace was performed by adjusting the split ratio of the GC inlet system. Flavor dilution (FD) factors varied from 2² up to ≥2¹⁸, whereby the largest class of compounds represented terpenoids, including two rare stereoisomers of 3,6-dimethyl-2,3,3a,4,5,7a-hexahydrobenzofuran (dill ether, ee ≥ 99.9). By means of nuclear magnetic resonance spectroscopy, the substances with the highest FD factors (2⁹, 2¹², and 2¹⁸) were identified as diastereomers of 3,6-dimethyl-3a,4,5,6,7,7a-hexayhydro-3H-1-benzofuran-2-one (dihydromenthofurolactone) and as its corresponding C3-unsaturated lactone. The latter two compounds have not been described for Cystostereum murrayi or for any other basidiomycota previously. Supplementation studies using 2-¹³C-d-glucose indicated that these lactones as well as the two stereoisomers of dill ether and other terpenoids were formed de novo by the fungus.

Aroma and catechin profile and in vitro antioxidant activity of green tea infusion as affected by submerged fermentation with Wolfiporia cocos (Fu Ling)

In response to the increasing interest of western consumers in high antioxidant activity of green tea but their low acceptance of its green odor, we employed a new starter culture, Wolfiporia cocos to tune flavor of green tea infusion. After submerged fermentation for 17 h, W. cocos changed the characteristic green odor to an attractive floral, jasmine-like, and slightly citrus-like flavor while preserving most of in vitro antioxidant activity. By application of mSBSE-GC-MS-O combined with sensorial tests, the formed pleasant aroma was mainly attributed to methyl anthranilate (OAV 802), linalool (OAV 190), 2-phenylethanol (OAV165), and geraniol (OAV 118). Concurrently, the catechin profile determined by UHPLC-MS showed diverse reduction rates (10-50%) for the individual catechins after fermentation. Nevertheless, up to 80% of in vitro antioxidant activity in DPPH assay was preserved. Overall, our findings provide an innovative approach to naturally flavor green tea while retaining the antioxidant activity.

Analysis of aroma-active volatiles in an SDE extract of white tea

White tea is a famous Chinese tea that is cooked at boiling point before drinking. The simultaneous distillation-extraction (SDE) was used to collect volatile compounds during tea cooking. The SDE extract was dominated with green, floral, roasted and woody notes, and weak sweet note. There were 32 volatile compounds identified via gas chromatography-mass spectrometry analysis, and 19 of them had strong fragrance based on the gas chromatography-olfactometry analyzed results. Hexanal, 2-hexenal, cis-3-hexen-1-ol, and camphene were the main contributors to the green note. The floral note was mainly contributed by 2-hexanone, benzeneacetaldehyde, trans-linalool oxide, and linalool, and the sweet note was induced by trans-β-damascenone. The roasted note was mainly contributed by 2-pentyl-furan. The woody note was mainly contributed by trans-α-ionone and trans-β-ionone. Four putative reaction pathways, including amino acid degradation, carotene degradation, Maillard reaction, and glycosides hydrolysis, were figured out to explain the generation of aromatic-active volatiles at high temperatures. This study added our knowledge on tea aroma under cooking as well as other thermal treatments.

Reduction of green off-flavor compounds: Comparison of key odorants during fermentation of soy drink with Lycoperdon pyriforme

The consumption of soy drink in Western countries is limited due to its green off-flavor. Hence, fermentation of soy drink with Lycoperdon pyriforme to tailor the aroma has been investigated. After 28 h the green off-flavor was not perceived by 60% of the sensory panel (n = 23). Molecular sensory changes of soy drink during fermentation were decoded by means of direct immersion-stir bar sorptive extraction coupled with gas chromatography-mass spectrometry-olfactometry and aroma dilution analysis. The semi-quantification of key odorants revealed a significant decrease of the representative green odorants (i.e., hexanal, (E)-2-nonenal, (E,E)-2,4-decadienal) of soy drink, among of which hexanal even turned below its odor threshold. The quantitative reduction of these odorants correlated with the organoleptic difference. Besides that, nutritionally relevant parameters of soy drink including protein, fat, and polyphenol content kept consistent during the short fermentation process.

Characterization of the key aroma compounds in Longjing tea using stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O), odor activity value (OAV), and aroma recombination

Longjing tea is the most famous premium green tea, and is regarded as the national tea in China, with its attractive aroma contributing as a prime factor for its general acceptability; however, its key aroma compounds are essentially unknown. In the present study, volatile compounds from Longjing tea were extracted and examined using stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS). Data obtained from the present study revealed that 151 volatile compounds from 16 different chemical classes were identified by GC-MS analysis. Enols (8096 µg/kg), alkanes (6744 µg/kg), aldehydes (6442 µg/kg), and esters (6161 µg/kg) were the four major chemical classes and accounted for 54% of the total content of volatile compounds. Geraniol (6736 µg/kg) was the most abundant volatile compound in Longjing tea, followed by hexanal (1876 µg/kg) and β-ionone (1837 µg/kg). Moreover, 14 volatile compounds were distinguished as the key aroma compounds of Longjing tea based on gas chromatography-olfactometry (GC-O) analysis, odor activity value (OAV) calculations, and a preliminary aroma recombination experiment, including 2-methyl butyraldehyde, dimethyl sulfoxide, heptanal, benzaldehyde, 1-octen-3-ol, (E, E)-2,4-heptadienal, benzeneacetaldehyde, linalool oxide I, (E, E)-3,5-octadien-2-one, linalool, nonanal, methyl salicylate, geraniol, and β-ionone. This is the first comprehensive report describing the aroma characterizations and the key aroma compounds in Longjing tea using SBSE/GC-MS. The findings from this study contribute to the scientific elucidation of the chemical basis for the aromatic qualities of Longjing tea.

Aroma Investigation of Chios Mastic Gum (Pistacia lentiscus Variety Chia) Using Headspace Gas Chromatography Combined with Olfactory Detection and Chiral Analysis

Chios mastic gum (Pistacia lentiscus var. Chia) exhibits intensely sourish, green, resinous, and woody odor notes with hints of citrus and pine. Despite its attractive flavor, no description of its aroma properties by molecular sensory techniques has been published thus far. A total of 25 odor-active compounds with flavor dilution (FD) factors of 1-512 were identified by gas chromatography-mass spectrometry-olfactometry (GC-MS-O) combined with headspace solid-phase microextraction (HS-SPME) and stir bar sorptive extraction (HS-SBSE). Quantitative analyses performed by multiple HS-SPME and calculation of odor activity values of 10 odorants with high FD factors revealed an essential role of several minor components (e.g., β-myrcene, limonene, β-linalool, and perillene) for the overall aroma of mastic gum, besides the dominating compound α-pinene. The indispensable contribution of the minor odorants to mastic gum was further confirmed by aroma recombination and omission tests. Varying enantiomeric excess values of the key odorants were observed by multidimensional GC-MS.

Biosynthesis of Stereoisomers of Dill Ether and Wine Lactone by Pleurotus sapidus

The white-rot fungus Pleurotus sapidus (PSA) biosynthesizes the bicyclic monoterpenoids 3,6-dimethyl-2,3,3a,4,5,7a-hexahydrobenzofuran (dill ether) (1) and 3,6-dimethyl-3a,4,5,7a-tetrahydro-1-benzofuran-2(3H)-one (wine lactone) (2). Submerged cultures grown in different media were analyzed by gas chromatography-mass spectrometry. The stereochemistry of the formed isomers was elucidated by comparing their retention indices to those of reference compounds by enantioselective multidimensional gas chromatography. The basidiomycete produced the rare (3R,3aR,7aS) and (3S,3aR,7aS) stereoisomers of dill ether and wine lactone. Kinetic analyses of the volatilome and bioprocess parameters revealed that the biosynthesis of the bicyclic monoterpenoids correlated with the availability of the primary carbon source glucose. Spiking the media with ¹³C-labeled glucose demonstrated that the compounds were produced de novo. Supplementation studies i.a. with isotopically labeled substrates further identified limonene and p-menth-1-en-9-ol as intermediate compounds in the fungal pathways. PSA was able to biotransform all enantiomeric forms of the latter compounds to the respective isomers of dill ether and wine lactone.

Hydrolysis of chlorogenic acid in apple juice using a p-coumaryl esterase of Rhizoctonia solani

BACKGROUND

Apple juice is rich in polyphenolic compounds, especially in chlorogenic acid. A sour and bitter taste has been attributed to the compound. Chlorogenic acid in coffee powder was quickly hydrolysed by a p-coumaryl esterase of Rhizoctonia solani (RspCAE) at its optimal pH of 6.0. It was unknown, however, if RspCAE would also degrade chlorogenic acid under the strongly acidic conditions (pH 3.3) present in apple juice.

RESULTS

Treatment of apple juice with RspCAE led to a chlorogenic acid degradation from 53.38 ± 0.94 mg L^-1 to 21.02 ± 1.47 mg L^-1 . Simultaneously, the caffeic acid content increased from 6.72 ± 0.69 mg L^-1 to 19.33 ± 1.86 mg/L^-1 . The aroma profile of the enzymatically treated sample and a control sample differed in only one volatile. Vitispirane had a higher flavour dilution factor in the treated juice. Sensory analysis showed no significant difference in the taste profile ( p < 0.05).

CONCLUSION

These results demonstrated a high stability and substrate specificity of RspCAE. An increase in caffeic acid and a concurrent decrease in chlorogenic acid concentration may exert a beneficial effect on human health. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Response of the sesquiterpene synthesis in submerged cultures of the Basidiomycete Tyromyces floriformis to the medium composition

Tyromyces floriformis, a potent fungal sesquiterpene producer, was grown Cerrena unicolor, as a model organism in submerged culture to search for chemicals affecting sesquiterpene biosynthesis in vitro. Thirty-one sesquiterpenes and sesquiterpenoids were identified in the supernatant, among them the fruity α-ylangene as the main volatile. Additives, such as some polysaccharides or lipids, did not affect the qualitative product spectrum but strongly affected the quantitative synthesis. Rye arabinoxylan and other polysaccharides, such as chitin, starch, and agarose, almost blocked the synthesis of α-ylangene. Single addition of the building blocks of arabinoxylan, arabinose, xylose, or ferulic acid showed no inhibitory effect, whereas 0.05% (w/v) 3²-α-l-arabinofuranosyl-xylobiose and larger oligosaccharides resulted in a significant suppression. In contrast, addition of acetyl donors boosted the α-ylangene concentration by 1 order of magnitude up to >40 mg L^-1. Both increased as well as decreased α-ylangene concentrations correlated with the intracellular sesquiterpene cyclase activity. Similar experiments using submerged cultured Cerrena unicolor, Postia placenta, and Coprinopsis cinerea showed that the additives affected fungal sesquiterpenoid synthesis differently. Whereas the addition of acetyl donors boosted the synthesis in all biphasic cultures, it was inhibited by polysaccharides in fungi preferably interacting with lignified plants. In contrast, Cerrena unicolor, known for a symbiotic lifestyle with wasps, responded by forming higher concentrations of the possibly insect-attracting sesquiterpenes.

Aroma Profile Analyses of Filamentous Fungi Cultivated on Solid Substrates

Filamentous fungi have been used since centuries in the production of food by means of solid substrate fermentation (SSF). The most applied SSF involving fungi is the cultivation of mushrooms, e.g., on tree stumps or sawdust, for human consumption. However, filamentous fungi are also key players during manufacturing of several processed foods, like mold cheese, tempeh, soy sauce, and sake. In addition to their nutritive values, these foods are widely consumed due to their pleasant flavors. Based on the potentials of filamentous fungi to grow on solid substrates and to produce valuable aroma compounds, in recent decades, several studies concentrated on the production of aroma compounds with SSF, turning cheap agricultural wastes into valuable flavors. In this review, we focus on the presentation of common analytical methods for volatile substances and highlight various applications of SSF of filamentous fungi dealing with the production of aroma compounds. Graphical Abstract.