Formation of complex natural flavours by biotransformation of apple pomace with basidiomycetes

Fermentation of cocoa pod husks with Pleurotus salmoneo-stramineus for food applications

Cocoa pod husks (CPHs), the major side-stream from cocoa production, were valorized through fermentation with Pleurotus salmoneo-stramineus (PSS). Considering ergosterol as a biomarker for the fungal content, the mycelium accounted for 54% of the total biomass after 8 days in submerged cultures. The crude protein content of fermented CPH (CPHF) increased from 7.3 g/100 g DM in CPH to 18.9 g/100 g DM. CPH fermentation resulted in a high biological value of 86 for the protein. The water and oil binding capacities of CPHF were 3.5 mL/g and 2.1 mL/g, respectively. The particle diameter dv,0,90 of CPHF was 373 μm as compared to 526 μm for CPH. The total dietary fiber was 73.4 g/100 g DM in CPHF and 63.6 g/100 g DM in CPH. The amount of soluble fiber was 2.3 g/100 g DM in CPHF and 10.1 g/100 g DM in CPH; the insoluble fraction accounted for 71.1 g/100 g DM and 53.6 g/100 g DM, respectively. Bread doughs with CPH or CPHF were characterized for texture, color, and farinographic properties. The dough hardness, consistency, and browning index increased with the concentration of CPH, whereas for CPHF, springiness and peak viscosities declined. We demonstrate the upcycling of CPH into nutritious and functional ingredients through PSS fermentation.

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.

Formation of a Meat-Like Flavor by Submerged Cultivated Laetiporus montanus

Basidiomycota are natural sources of aroma compounds. When grown in submerged cultures, the fungus Laetiporus montanus (LMO) forms a spicy and meat-like aroma. It thus represents an interesting candidate for the production of natural savory flavors. To identify the key aroma compounds of LMO grown submerged in malt extract peptone medium, the volatiles were isolated by means of automated solvent assisted flavor evaporation (aSAFE). An aroma extract dilution analysis was performed by means of gas chromatography-olfactometry coupled with a flame ionization detector (GC-FID-O). In the aSAFE extract of LMO, 24 aroma-active compounds were detected. 5-Butyl-2(5H)-furanone (FD 4096), perceived as coconut-like, was determined as the compound with the highest FD factor. (E,E)-2,4-Decadienal, (E,Z)-2,4-decadienal, and sotolon were identified as responsible key compounds for the spicy odor of the submerged cultures. Moreover, supplementation of the cultures of LMO, Laetiporus sulphureus, and Laetiporus persicinus with ¹³C-labeled thiamine hydrochloride resulted in the formation of 2-methyl-3-(methylthio)furan (MMTF), a compound with a pronounced meaty flavor. The concentrations of MMTF were further increased to 19-27 μg L^-1 by additional supplementation of the cultures with ascorbic acid. The results of this study indicate potential for the biotechnological production of a meat-like flavor by Laetiporus species.

Production of an Anise- and Woodruff-like Aroma by Monokaryotic Strains of Pleurotus sapidus Grown on Citrus Side Streams

The production of natural flavors by means of microorganisms is of great interest for the food and flavor industry, and by-products of the agro-industry are particularly suitable as substrates. In the present study, Citrus side streams were fermented using monokaryotic strains of the fungus Pleurotus sapidus. Some of the cultures exhibited a pleasant smell, reminiscent of woodruff and anise, as well as herbaceous notes. To evaluate the composition of the overall aroma, liquid/liquid extracts of submerged cultures of a selected monokaryon were prepared, and the volatiles were isolated via solvent-assisted flavor evaporation. Aroma extract dilution analyses revealed p-anisaldehyde (sweetish, anisic- and woodruff-like) with a flavor dilution factor of 2¹⁸ as a character impact compound. The coconut-like, herbaceous, and sweetish smelling acyloin identified as (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone also contributed to the overall aroma and was described as an aroma-active substance with an odor threshold in air of 0.2 ng L⁻¹ to 2.4 ng L⁻¹ for the first time. Supplementation of the culture medium with isotopically substituted l-tyrosine elucidated this phenolic amino acid as precursor of p-anisaldehyde as well as of (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone. Chiral analysis via HPLC revealed an enantiomeric excess of 97% for the isolated product produced by P. sapidus.

Utilization of fruit and vegetable waste to produce value-added products: Conventional utilization and emerging opportunities-A review

Fruit and vegetables are one of the most consumed commodities globally, accounting for more than 42% of total food wastage. These vegetal foods can be consumed raw, processed, or taken as an addition to other food items. The continuous rise in population, in addition to technological advancements, has led to an imbalance in demand supply, resulting in increased food wastage globally. Although source reduction and recycling have shown promising results, more evaluations concerning economics and environmental impacts need to be given importance. The need of the hour lies in finding a possible method towards effective utilization for fruit and vegetable waste to generate value-added products which are more eco-friendly, cheaper, and sustainable. Thus, this article attempts to focus on the conventional and emerging opportunities of fruit and vegetable waste to generate value-added products. Conventional utilization, namely briquetting, waste to energy conversion, enzymatic degradation, and adsorption, as well as emerging opportunities in the areas of nutraceuticals, packaging, flavoring agents, and waste induced nanoparticles, have been emphasized. Additionally, recommendations and future perspectives towards better utilization of vegetal waste have been given importance. This review aims to narrow down the path towards evaluating the most techno-economic and efficient waste management technique for fruits and vegetable valorization, which can be promoted in the long term.

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.

Analysis of the Ability to Produce Pleasant Aromas on Sour Whey and Buttermilk By-Products by Mold Galactomyces geotrichum: Identification of Key Odorants

Currently, there is a growing demand for flavorings, especially of natural origin. It is worth paying attention to the biotechnological processes of flavor production, characterized by simplicity, high efficiency and relatively low cost. In this study, we analyzed the ability of the Galac tomyces geotrichum mold to transform by-products of the dairy industry: sour whey and buttermilk to complex flavour mixtures with pleasant, honey-rose aroma. Furthermore, the aroma complexity of the fermentation product has been carefully identified applying a sensomic approach involving the use of gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC-MS) and stable isotope dilution assay (SIDA) to identify and quantify aroma compounds. Based on the calculation of odor activity value (OAV), 13 key aroma compounds were present in both tested variants. The highest OAVs were found for phenylacetaldehyde (honey-like) in the buttermilk variant (912) and 2-phenylethanol (rose-like) in the sour whey variant (524). High values of this indicator were also recorded for phenylacetaldehyde (319) and 3-methyl-1-butanol with a fruity aroma (149) in the sour whey culture. The other compounds identified are 3-methylbutanal (malty), 2,3-butanedione (cheesy), isovaleric acid (cheesy), 3-(methylthio)-propanal (boiled potato), butanoic acid (vinegar), (E)-2-nonenal (fatty), ethyl furaneol (burnt sugar), dimethyl trisulfide (cabbage), and acetic acid (vinegar).

Efficient bioconversion of high-concentration d-fructose into d-mannose by a novel N-acyl-d-glucosamine 2-epimerase from Thermobifida halotolerans

A novel N-acyl-d-glucosamine 2-epimerase ThMI exhibits high mannose isomerase activity with a maximum bioconversion ratio of 35.8% in 500 g L⁻¹d-fructose. Whole-cell biocatalyst produced 157 g L⁻¹d-mannose from 500 g L⁻¹d-fructose in 60 min.

Biocatalytic Potential of Native Basidiomycetes from Colombia for Flavour/Aroma Production

Aromas and flavours can be produced from fungi by either de novo synthesis or biotransformation processes. Herein, the biocatalytic potential of seven basidiomycete species from Colombia fungal strains isolated as endophytes or basidioma was evaluated. Ganoderma webenarium, Ganoderma chocoense, and Ganoderma stipitatum were the most potent strains capable of decolourizing β,β-carotene as evidence of their potential as biocatalysts for de novo aroma synthesis. Since a species’ biocatalytic potential cannot solely be determined via qualitative screening using β,β-carotene biotransformation processes, we focused on using α-pinene biotransformation with mycelium as a measure of catalytic potential. Here, two strains of Trametes elegans—namely, the endophytic (ET-06) and basidioma (EBB-046) strains—were screened. Herein, T. elegans is reported for the first time as a novel biocatalyst for the oxidation of α-pinene, with a product yield of 2.9 mg of cis-Verbenol per gram of dry weight mycelia used. The EBB-046 strain generated flavour compounds via the biotransformation of a Cape gooseberry medium and de novo synthesis in submerged cultures. Three aroma-producing compounds were identified via GC–MS—namely, methyl-3-methoxy-4H-pyran-4-one, hexahydro-3-(methylpropyl)-pyrrolo[1,2-a]pyrazine-1,4-dione, and hexahydro-3-(methylphenyl)-pyrrolo[1,2-a]pyrazine-1,4-dione.

A Novel Approach to Structure Plant-Based Yogurts Using High Pressure Processing

Current plant-based yogurts are made by the fermentation of plant-based milks. Although this imparts fermented flavors and probiotic cultures, the process is relatively longer and often leads to textural issues. The protein content of these plant-based yogurts is also lower than their dairy counterparts. To overcome these challenges, this paper explores the high pressure processing (HPP) of plant protein ingredients as an alternative structuring strategy for plant-based yogurts. Using mung bean (MB), chickpea (CP), pea (PP), lentil (LP), and faba bean (FB) proteins as examples, this work compared the viscosity and viscoelastic properties of high pressure-structured (600 MPa, 5 min, 5 °C) 12% (w/w) plant protein gels without, and with 5% (w/w) sunflower oil (SO) to commercial plain skim and whole milk Greek yogurts and discussed the feasibility of using HPP to develop plant-based yogurts. HPP formed viscoelastic gels (G' > G'') for all plant protein samples with comparable gel strength (G'~10²-10³ Pa; tan δ~0.2-0.3) to commercial dairy yogurts. The plant protein gel strength decreased in the order: CP~CPSO~LP~LPSO > MBSO~PPSO~FB~FBSO > PP >> MB. Modest addition of sunflower oil led to little change in viscoelastic properties for all plant protein samples except for MB and PP, where gel strength increased with incorporated oil. The emulsion gels were also more viscous than the hydrogels. Nonetheless, the viscosity of the plant protein gels was similar to the dairy yogurts. Finally, a process involving separate biotransformation for optimized flavor production and high pressure processing for consistent texture generation was proposed. This could lead to high protein plant-based yogurt products with desirable texture, flavor, and nutrition.

Valorization of Fruits by-products to Unconventional Sources of Additives, Oil, Biomolecules and Innovative Functional Foods

Owning to the increase in the world population as well as the consumer's awareness on the health benefits of consumption of fruits, the demand for both fresh and processed fruits has been increased. The by-product and waste streams generated from fruit processing industries are extremely diverse, owning mainly to different fruits varieties and the wide range of the processes employed towards the production of the end fruit-based products. Due to the increasing production and processing of fruits, disposal of waste and by-product streams has become a serious issue, since these materials are prone to microbial spoilage. Also, the inappropriate waste management practices pose severe environmental issues. Furthermore, the costs of drying and storage of fruit processing residues are economically limiting factors hindering their further exploitation. Therefore, fruit processing by-products such as peels, seeds and unused flesh are often utilized as fertilizers. On the other hand, plant residues contain biomolecules such as vitamins, proteins, minerals, antioxidants and aromatic oil. Recovery of bioactive compounds holds a great potential for their usage in food industry as functional ingredients and nutraceuticals or in pharmaceutical and in cosmetic applications. So, valorization of plant fruit processing by-products to high-value added compounds, constitute a promising alternative not only for addressing fruit residues management issues but also leading to the production of functional food products of high nutritional value, with several potential beneficial health effects. The aim of this paper is to highlight current trends in addressing environmental issues caused by the production of high volumes of specific categories of fruit processing waste streams by investigating their potential usage as natural raw materials for the recovery of valuable bioactive compounds (such as polyphenols, dietary fibers or aromatic oil). The extracted nutrients may be used in the industrial food sector for the production of functional foods, nutraceuticals or even as health promoting natural pharmaceutical ingredients or additives for the production of innovative enriched foods. Highlights: • Fruit processing by product streams are rich in bioactive compounds. • Integration of fruit by-products and waste streams to value added products such as additives, unconventional oil, bioactive compounds and novel functional products is a very interesting approach regarding fruit processing residues exploitation. • Recovering of biomolecules from fruit residues by non-thermal processes could lead to the efficient production of highly purified functional ingredients. • Negative-valued fruit processing residues could be recycled for the production of health promoting value added products.

Industrial Riboflavin Fermentation Broths Represent a Diverse Source of Natural Saturated and Unsaturated Lactones

Fermentation broths of Ashbya gossypii from the industrial production of riboflavin emit an intense floral, fruity, and nutty smell. Typical Ehrlich pathway products, such as 2-phenylethan-1-ol and 2-/3-methylbutan-1-ol, were detected in large amounts as well as some intensely smelling saturated and unsaturated lactones, e.g., γ-decalactone and γ-(Z)-dodec-6-enlactone. An aroma extract dilution analysis identified 2-phenylethan-1-ol and γ-(Z)-dodec-6-enlactone as the main contributors to the overall aroma, with flavor dilution factors of 32 768. The position of the double bonds of unsaturated lactones was determined by the Paternò-Büchi reaction, and reference compounds that were not available commercially were synthesized to elucidate the structures of the uncommon lactones. The absolute configuration and enantiomeric excess values of the lactones were determined by converting the lactones to their corresponding Mosher's esters. In addition, the odor impressions and odor thresholds in air were determined.

Comparing “Leaf-to-Root”, “Nose-to-Tail” and Other Efficient Food Utilization Options from a Consumer Perspective

The efficient use of natural raw materials is a key element of sustainable development and is also gaining importance in the food sector. Consumers are increasingly realizing that food is too valuable to be used only partially. However, consumer acceptance is an important precondition for establishing efficient food utilization options. A total of 470 German consumers were surveyed through an online-questionnaire where they had to evaluate three options each for the efficient use of plant-based foods as well as animal-based foods with respect to eight different criteria. The results show that the six options differed significantly regarding consumer acceptance. The efficient use of plant-based foods (especially non-standard fruits/vegetables and the “leaf-to-root” principle) was more accepted than the efficient utilization of animal-based foods. Furthermore, it can be seen that options using the by-products in a natural form were considered more acceptable than those which subject the by-products to some form of processing. These results provide an insight into the views of consumers on food waste reduction strategies, which are frequently debated in the sustainability discussion.

Submerged Cultivation of Pleurotus sapidus with Molasses: Aroma Dilution Analyses by Means of Solid Phase Microextraction and Stir Bar Sorptive Extraction

The basidiomycete Pleurotus sapidus (PSA) was grown in submerged cultures with molasses as substrate for the production of mycelium as a protein source for food applications. The volatilomes of the substrate, the submerged culture, and the mycelia were analyzed by gas chromatography-tandem mass spectrometry-olfactometry. For compound identification, aroma dilution analyses by means of headspace solid phase microextraction and stir bar sorptive extraction were performed via variation of the split vent flow rate. Among the most potent odorants formed by PSA were arylic compounds (e.g., p-anisaldehyde), unsaturated carbonyls (e.g., 1-octen-3-one, ( E)-2-octenal, ( E, E)-2,4-decadienal), and cyclic monoterpenoids (e.g., 3,9-epoxy- p-menth-1-ene, 3,6-dimethyl-3a,4,5,7a-tetrahydro-1-benzofuran-2(3 H)-one). Several compounds from the latter group were described for the first time in Pleurotus spp. After separation of the mycelia from the medium, the aroma compounds were mainly enriched in the culture supernatant. The sensory analysis of the mycelium correlated well with the instrumental results.

Side Streams of Plant Food Processing As a Source of Valuable Compounds: Selected Examples

Industrial processing of plant-derived raw materials generates enormous amounts of by-products. On one hand, these by-products constitute a serious disposal issue because they often emerge seasonally and are prone to microbial decay. On the other hand, they are an abundant source of valuable compounds, in particular secondary plant metabolites and cell wall materials, which may be recovered and used to functionalize foods and replace synthetic additives with ingredients of natural origin. This review covers 150 references and presents select studies performed between 2001 and 2016 on the recovery, characterization, and application of valuable constituents from grape pomace, apple pomace, potato peels, tomato pomace, carrot pomace, onion peels, by-products of citrus, mango, banana, and pineapple processing, side streams of olive oil production, and cereal by-products. The criteria used were economic importance, amounts generated, relevance of side streams as a source of valuable compounds, and reviews already published. Despite a plethora of studies carried out on the utilization of side streams, relatively few processes have yet found industrial application.

De Novo Synthesis of Benzenoid Compounds by the Yeast Hanseniaspora vineae Increases the Flavor Diversity of Wines

Benzyl alcohol and other benzenoid-derived metabolites of particular importance in plants confer floral and fruity flavors to wines. Among the volatile aroma components in Vitis vinifera grape varieties, benzyl alcohol is present in its free and glycosylated forms. These compounds are considered to originate from grapes only and not from fermentative processes. We have found increased levels of benzyl alcohol in red Tannat wine compared to that in grape juice, suggesting de novo formation of this metabolite during vinification. In this work, we show that benzyl alcohol, benzaldehyde, p-hydroxybenzaldehyde, and p-hydroxybenzyl alcohol are synthesized de novo in the absence of grape-derived precursors by Hanseniaspora vineae. Levels of benzyl alcohol produced by 11 different H. vineae strains were 20-200 times higher than those measured in fermentations with Saccharomyces cerevisiae strains. These results show that H. vineae contributes to flavor diversity by increasing grape variety aroma concentration in a chemically defined medium. Feeding experiments with phenylalanine, tryptophan, tyrosine, p-aminobenzoic acid, and ammonium in an artificial medium were tested to evaluate the effect of these compounds either as precursors or as potential pathway regulators for the formation of benzenoid-derived aromas. Genomic analysis shows that the phenylalanine ammonia-lyase (PAL) and tyrosine ammonia lyase (TAL) pathways, used by plants to generate benzyl alcohols from aromatic amino acids, are absent in the H. vineae genome. Consequently, alternative pathways derived from chorismate with mandelate as an intermediate are discussed.

A minimal growth medium for the basidiomycete Pleurotus sapidus for metabolic flux analysis

Background

Pleurotus sapidus secretes a huge enzymatic repertoire including hydrolytic and oxidative enzymes and is an example for higher basidiomycetes being interesting for biotechnology. The complex growth media used for submerged cultivation limit basic physiological analyses of this group of organisms. Using undefined growth media, only little insights into the operation of central carbon metabolism and biomass formation, i.e., the interplay of catabolic and anabolic pathways, can be gained.

Results

The development of a chemically defined growth medium allowed rapid growth of P. sapidus in submerged cultures. As P. sapidus grew extremely slow in salt medium, the co-utilization of amino acids using ¹³C-labelled glucose was investigated by gas chromatography–mass spectrometry (GC-MS) analysis. While some amino acids were synthesized up to 90% in vivo from glucose (e.g., alanine), asparagine and/or aspartate were predominantly taken up from the medium. With this information in hand, a defined yeast free salt medium containing aspartate and ammonium nitrate as a nitrogen source was developed. The observed growth rates of P. sapidus were well comparable with those previously published for complex media. Importantly, fast growth could be observed for 4 days at least, up to cell wet weights (CWW) of 400 g L^-1. The chemically defined medium was used to carry out a ¹³C-based metabolic flux analysis, and the in vivo reactions rates in the central carbon metabolism of P. sapidus were investigated. The results revealed a highly respiratory metabolism with high fluxes through the pentose phosphate pathway and TCA cycle.

Conclusions

The presented chemically defined growth medium enables researchers to study the metabolism of P. sapidus, significantly enlarging the analytical capabilities. Detailed studies on the production of extracellular enzymes and of secondary metabolites of P. sapidus may be designed based on the reported data.

Electronic supplementary material

The online version of this article (doi:10.1186/s40694-014-0009-4) contains supplementary material, which is available to authorized users.

Identification of potent odorants in a novel nonalcoholic beverage produced by fermentation of wort with shiitake (Lentinula edodes)

Novel refreshments with pleasant flavors were developed by fermentation of wort with basidiomycetes. Among 31 screened fungi, shiitake (Lentinula edodes) produced the most pleasant flavor. It was perceived as fruity, slightly sour, and plum-like. Flavor compounds were isolated by liquid-liquid extraction (LLE) and by headspace solid phase microextraction (HS-SPME). The key odor-active compounds were analyzed by a gas chromatography system equipped with a tandem mass spectrometry detector and an olfactory detection port (GC-MS/MS-O) and aroma extract dilution analysis (AEDA). For HS-SPME, a revised method of increasing the GC inlet split ratio was used. Most of the key odor-active compounds (e.g., 2-acetylpyrrole, β-damascenone, (E)-2-nonenal, and 2-phenylethanol) were detected with both extraction techniques. However, distinct differences between these two methods were observed.