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

Molecular-Sensory Decoding of the Citrus latifolia Aroma

A modified aroma extract dilution approach (AEDA), followed by the determination of flavor dilution (FD) factors, a quantitative analysis and calculation of the relative flavor activity (RFA) and odor activity values (OAVs) as well as recombination experiments were conducted to evaluate the odor- and taste-relevant components of cold-pressed Citrus latifolia peel oil. A 2-fold concentration by distillation and reanalysis, compared with the original oil, revealed relevant components. Partition of the odor-active substances into four reconstitution groups according to their respective FD factors, followed by a recombination, allowed for a better understanding of the contribution of each FD-factor group to the overall aroma. Especially α-pinene, limonene, γ-terpinene, and 7-methoxycoumarin contribute significantly to the distinct aroma profile of C. latifolia. Heptadecanal (CAS 629-90-3) was described for the first time as an odor-active substance in an enriched C. latifolia peel oil. Campherenyl acetate (CAS 18530-07-9) was identified in nature for the first time and described with a herbal, minty and citrus-like odor. The odor profile of the final recombinant mixture, containing 36 components, was similar to cold-pressed C. latifolia peel oil for most descriptors, whereas the taste profile was described as more aldehydic and citral-like.

Flavor characterization of Citri Reticulatae Pericarpium (Citrus reticulata 'Chachiensis') with different aging years via sensory and metabolomic approaches

Guangchenpi (GCP), which is the peel of Citrus reticulata 'Chachiensis', is widely used as an herbal medicine, tea and food ingredient in southeast Asia. Prolonging its aging process results in a more pleasant flavor and increases its profitability. Through the integration of sensory evaluation with flavoromic analysis approaches, we evaluated the correlation between the flavor attributes and the profiles of the volatiles and flavonoids of GCP with various aging years. Notably, d-limonene, γ-terpinene, dimethyl anthranilate and α-phellandrene were the characteristic aroma compounds of GCP. Besides, α-phellandrene and nonanal were decisive for consumers' perception of GCP aging time due to changes of their odor activity values (OAVs). The flavor attributes of GCP tea liquid enhanced with the extension of aging time, and limonene-1,2-diol was identified as an important flavor enhancer. Combined with machine learning models, key flavor-related metabolites could be developed as efficient biomarkers for aging years to prevent GCP adulteration.

Reduction of anthranilic acid to 2-aminobenzaldehyde by the white-rot fungus Bjerkandera adusta DSMZ 4708

The biocatalytic aerobic "in-water" reduction of anthranilic acid to 2-aminobenzaldehyde by growing cultures of the basidiomycetous white-rot fungus Bjerkandera adusta has been studied. The high specific activity of Bjerkandera adusta towards the carboxylic group of anthranilic acid that allows avoiding the formation of the corresponding alcohol has been demonstrated using different substrate concentrations. The presence of ethanol as co-solvent allows increasing the yield of target product. In contrast to chemical reducing agents that usually yield 2-aminobenzyl alcohol, an overreduction of anthranilic acid is completely suppressed by the fungus and gives the target flavor compound in satisfactory preparative yields. It was shown that the activity of Bjerkandera adusta towards anthranilic acid does not apply to its m- and p-isomers.

Research progress in the synthesis of stable isotopes of food flavour compounds

Stable isotope dilution analysis (SIDA) is a quantitative method widely used in the determination of food flavour components because of its high efficiency and precision. However, many stable isotope reagents cannot be purchased through commercial channels. In this paper, the basic principle of stable isotope dilution analysis is introduced and its historical progress in food flavour analysis are examined. Then, the preparation methods of stable isotope analysis of food flavour compounds in recent years were compiled. In the literature reviewed, from 2012 to 2022, there were 185 stable isotopes of food flavour compounds used for food flavour analysis, of which 126 compounds can be purchased commercially and 59 compounds must be prepared in the laboratory. This review aims to present the methods used in the synthesis of stable isotopes to facilitate the development of food flavour analysis using stable isotope technology.

Novel SPE purification approach using the direct adsorption of vaporised propionic acid in food for rapid HPLC determination

Solid phase extraction (SPE) is a technique widely used in food analysis for the isolation of analytes. Herein, we proposed a novel application of SPE to extract vaporised propionic acid, a common preservative, from a heated sample solution. A sample was heated under acidified conditions and the resulting steam was directly passed through an SPE column to extract the propionic acid, followed by elution and HPLC analysis. Here, the extraction on the SPE column ensures direct capture of propionic acid. The results demonstrated excellent linearity (R² greater than 0.999) and recoveries of 89.9%-97.6% with intra- and inter-day precisions lower than 3.9%. To the best of our knowledge, no study has investigated the applicability of SPE to an analyte vaporised in the headspace of food products. The proposed method is promising in its application to various volatile compounds and in the routine analysis of propionic acid in food.

Identification of colupulone and lupulone as the main contributors to the antibacterial activity of hop extracts using activity-guided fractionation and metabolome analysis

Hop is widely used in beer brewing and as a medicinal product. The present study comprehensively analyzed the main molecular determinants of the antibacterial activity of hop extracts. Minimum inhibitory concentrations (MIC) against Bacillus subtilis between 31.25 and 250 µg/mL were found in the ethanolic extracts of five hop varieties for beer brewing, but not in the tea hop sample. Activity-guided fractionation revealed the highest antibacterial activity for lupulone and adlupulone (MIC 0.98 µg/mL). Metabolome profiling and subsequent multistep statistical analysis detected 33 metabolites out of 1826 features to be associated with the antibacterial activity including humulone, adhumulone, colupulone, lupulone, and adlupulone. Xanthohumol, the three humulone- and three lupulone congeners were quantified in the hop extracts by a validated ultrahigh-performance liquid chromatography-mass spectrometry method. Considering concentrations and MICs, colupulone and lupulone were identified as major contributors to the antibacterial activity of hop extract with the highest antibacterial activity values (concentration/MIC) of 1.59 and 2.56.

Upcycling of black currant pomace for the production of a fermented beverage with Wolfiporia cocos

Pomace as a side stream from black currant juice production is mostly discarded, even though it is rich in nutrients like protein, fiber, sugars, anthocyanins, polyphenols, and other secondary metabolites. Fungi from the division of Basidiomycota have a great enzymatic toolbox to recycle these complex mixtures of nutrients. In particular, the edible medicinal fungus Wolfiporia cocos has been described as a suitable biocatalyst to form pleasant aroma compounds in fermentation processes. Therefore, medium optimization, upscaling, and filtration were performed to produce a beverage based on black currant pomace fermented with W. cocos. A trained panel described the beverage as highly pleasant, reminiscent of honey, flowers and berries with a well-balanced sour and sweet taste. The flavor compounds linalool (citrus), geraniol (flowery), phenylacetic acid (honey), methyl phenylacetate (honey), eugenol (clove), and 2-phenylethanol (rose) were produced during fermentation and the concentrations exceeded their respective odor thresholds. The produced beverage was evaluated with 8.0 ± 1.4 from 10 for the question of whether panelists would buy the product. Fungal fermentation with the edible fungus W. cocos enabled the production of a highly pleasant beverage and additionally may reduce waste by using pomace and table sugar as sole ingredients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05677-4.

Optimization of Methyl Anthranilate Synthesis Process by Response Surface Methodology and Its Reaction Mechanism

In this paper, a unique process for the production of methyl anthranilate (MA) was investigated. The factors of the phthalimide/sodium hypochlorite/methanol molar ratio, reaction temperature, hydrolysis temperature, and water consumption on the yield and purity of MA were analyzed. Response surface methodology (RSM) was used to optimize conditions for the semi-batch synthesis process of MA. The best synthetic conditions for the formation of MA were reaction temperature 0.5 °C, hydrolysis temperature 70 °C and n(phthalimide)/n(sodium hypochlorite)/n(methanol) = 1:2.03:5.87, and water consumption m(H2O)/m(phthalimide) = 7.16:1. The yield of MA could reach 90% under the optimal conditions, which is more than 10% higher than that of the previous semi-batch process. Furthermore, the reaction mechanism was investigated by infrared spectroscopy analysis, and the mechanism of ester group formation and the structure of intermediate products are proposed. The byproduct of the reaction was studied by GC-MS analysis, a byproduct called 2-cyanobenzoic acid has been discovered. Therefore, an unprecedented reaction mechanism of the whole synthesis process is proposed.

A Robust Fermentation Process for Natural Chocolate-like Flavor Production with Mycetinis scorodonius

Submerged fermentation of green tea with the basidiomycete Mycetinis scorodonius resulted in a pleasant chocolate-like and malty aroma, which could be a promising chocolate flavor alternative to current synthetic aroma mixtures in demand of consumer preferences towards healthy natural and ‘clean label’ ingredients. To understand the sensorial molecular base on the chocolate-like aroma formation, key aroma compounds of the fermented green tea were elucidated using a direct immersion stir bar sorptive extraction combined with gas chromatography–mass spectrometry–olfactometry (DI-SBSE-GC-MS-O) followed by semi-quantification with internal standard. Fifteen key aroma compounds were determined, the most important of which were dihydroactinidiolide (odor activity value OAV 345), isovaleraldehyde (OAV 79), and coumarin (OAV 24), which were also confirmed by a recombination study. Furthermore, effects of the fermentation parameters (medium volume, light protection, agitation rate, pH, temperature, and aeration) on the aroma profile were investigated in a lab-scale bioreactor at batch fermentation. Variation of the fermentation parameters resulted in similar sensory perception of the broth, where up-scaling in volume evoked longer growth cycles and aeration significantly boosted the concentrations yet added a green note to the overall flavor impression. All findings prove the robustness of the established fermentation process with M. scorodonius for natural chocolate-like flavor production.