Multi-platform metabolomic approach to discriminate ripening markers of black truffles (Tuber melanosporum)

Mechanisms of formation and consumption of VSCs in thermal dehydration of Lentinula edodes: A transcriptomic analysis utilizing WGCNA

The aroma of Lentinula edodes, primarily attributed to volatile sulfur compounds (VSCs), is a crucial factor influencing its commercial and culinary quality. This study investigated cellular activity and transcriptomic changes during gradient hot-air drying (40-60 °C) at various stages. AO/EB staining and tissue culture confirmed cell viability throughout the drying process. Transcriptomic analysis identified 4255 significantly different expressed genes (|log2FC| > 1, p < 0.05), including 366 associated with sulfur metabolism. WGCNA, KEGG, and GO analyses revealed that glutathione synthesis and degradation were inhibited during drying. The gene LeGGT_3 (C8R40DRAFT_1158952) was identified as a regulator of γ-GTase synthesis. Five cysteine desulfurase (C-Dase)-encoding genes were enriched in the cysteine and methionine pathways, with LeNifs_3 (C8R40DRAFT_1079603) transcriptionally modulating C-Dase activity, which positively correlates with the production of cyclic thioethers (p < 0.05). The upregulation of DNA repair genes between 4 and 8 h enhanced cyclic thioethers (e.g., lentinionine). Early drying (0-4 h) suppressed methionine biosynthesis but activated cys synthesis. Compared to fresh samples, changes in sulfur assimilation genes during 6-8 h of drying consumed VSCs. The upregulation of LeNifs_3 increased C-Dase activity, thereby promoting the formation of cyclic thioethers. This study underscores the pivotal role of LeNifs_3 in the biosynthesis of cyclic sulfides in hot-air-dried Lentinula edodes, providing valuable insights for the development of high-quality mushroom products.

A critical analysis of Adaptive Box-Cox transformation for skewed distributed data management: Metabolomics of Spanish and Argentinian truffles as a case study

BACKGROUND

Metabolic variations retrieved in metabolomic data are considered a benchmark for detecting biomatrix variability. Therefore, identifying target metabolites is crucial to keep track of any substrate modification and preserve it from any undesired alteration. Unfortunately, such a task can be negatively affected by detecting false positives, often triggered by complicated data distributions. In this work, we undertook an investigation of the metabolic profile of Spanish and Argentine truffles using a robust methodology. The issue of skewed data distributions has been effectively addressed through a normalization preprocessing, enhancing biomarker identification and samples classification.

RESULTS

A data normality-improved parametric test (ANOVA) was employed to define the target metabolites, which significantly vary between two regions of origin: Spain and Argentina. Specifically, Adaptive Box-Cox transformation was employed to improve the ANOVA test's performance so that data distributions were fitted to a Gaussian variable. Using the Bonferroni-Holm method for false discovery rate correction, we demonstrated the effectiveness of this transformation for the case under investigation. Results were compared with two non-parametric tests (Kruskall-Wallis and Permutation test), selected as a reference methodology, to provide a better understanding of non-normal distributions often encountered in metabolomic data analysis. 17 metabolites out of the 57 investigated metabolites exhibited notable variability across the two geographical regions. The validity of this methodology was supported through the discrimination of samples belonging to different groups. In this regard, both univariate and multivariate statistical models were tested through Monte Carlo simulations and yielded consistent results.

SIGNIFICANCE

Data analysis outcomes are sensitive to variables distributions. The present study shows an effective tool to increase data normality, thereby enhancing the statistical power for biomarker discovery and improving models' classification performances. These results find justification from the current knowledge within the field of food sciences, enabling their application in advancing research in the truffle analysis domain.

Hunting dog behaviour is a key driver impacting harvest quantity and quality of truffles

Truffles are an iconic food that have long held high regard. Here we explore the seasonality and eco-physiological interactions affecting truffle quality and quantity across time and space. Collaborating with professional truffle hunters working eight different locations, detailed metrics of 3180 recovered truffles from 236 hunt events and spanning a full fruiting period, were recorded. Contrary to expectations, truffle weight showed no correlation with climate variables, suggesting a limited influence of environmental factors such as temperature and precipitation on truffle size. We also found that truffle maturity and damage from mycophagy were strongly linked, with deeper truffles being more mature but also more susceptible to damage. Finally, we observe that scent-dog behaviour significantly impacts the quantity and quality of recovered truffles, and we address the necessity of considering this in truffle ecophysiology studies. Alongside advances in our biological understanding, we make recommendations of how training methods can be improved to lead to greater detection and quality targeting with immediate socioeconomic impact. These findings highlight the complex interplay between truffle physiology, environmental factors, and human and animal behaviours, emphasizing the need for further considered research to enhance our understanding of truffle biology and to improve truffle cultivation practices.

Peat-based amendment of soils reduces the complexity of the volatile profile in cultivated black truffles

BACKGROUND

Truffle cultivation is evolving rapidly and new agronomic practices such as 'truffle nests' (localized peat amendments of the orchard soil) are being developed. Truffle nests improve the shape of truffles and their depth in the soil and reduce the occurrence of insect damage but have also raised concerns about their impact on the ripeness and maturity of the harvested truffles. In this study, the effect of the nests on the volatile organic compounds profile and the aromatic profile of black truffles was evaluated, as well as the existence of perceptible sensorial differences in truffles. For this, truffles growing in nests were compared with truffles growing in the bulk soil of the same host tree.

RESULTS

Gas chromatography showed that nest truffles had a less complex volatile organic compound profile than bulk-soil truffles. Olfactometry indicated that nest truffles were associated with higher modified frequency values of odorants corresponding to sulfur-containing compounds. Despite this, sensory evaluation with consumers could not clearly show that nest truffles can be distinguished sensorially from bulk-soil truffles.

CONCLUSION

The results prove that soil conditions can influence the aromatic profile of truffles and thus suggest the possibility of managing truffle aroma using agronomic practices. © 2024 The Author(s). Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Volatilome changes during black truffle (Tuber melanosporum) ontogeny

The aroma is critical in the reproductive biology of truffles and in their commercial quality. However, previous research has almost exclusively focused on characterizing ripe ascocarps. We characterized the volatilome of the highly-prized black truffle (Tuber melanosporum) ascocarps from July, in an early development stage, to March, in the late harvesting season, and investigated the relationships among aroma, ascocarp growth and morphogenetic development. The aroma profile was analyzed using a head space gas chromatography technique coupled with mass spectrometer. Seventy-one volatile compounds were identified and three development stages were clearly distinguished according to the volatile profile. In unripe ascocarps of July-September, the profile was dominated by methanethiol (19 %), 4-penten-2-ol (11 %) and acetone (11 %), the monthly mean weight of ascocarps ranged 2-20 g, and morphogenetic stages 4-6a were prevalent. In unripe ascocarps of October-December, the most abundant volatiles were 4-penten-2-ol (21 %), methanethiol (20 %) and ethanol (13 %), the monthly mean ascocarp weight ranged 28-43 g, and morphogenetic stages 6a, 6b-c were prevalent. In ripe ascocarps (December-March), the most abundant volatiles were 4-penten-2-ol (17 %), dimethyl sulfide (16 %) and ethanol (10 %), ascocarp weight did not increase significantly, and 6b-c was practically the sole morphogenetic stage. Thirty volatiles were associated to one of these three development stages. Amongst those with higher occurrence, 4-penten-2-ol, dimethyl sulfide, ethyl acetate, 2-pentanol and 2-butanone were associated to ripe truffles, whereas methanethiol, isobutyl isobutyrate, butanedione and 3-methylanisole were associated to unripe truffles.

Key components, formation pathways, affecting factors, and emerging analytical strategies for edible mushrooms aroma: A review

Aroma is one of the decisive factors affecting the quality and consumer acceptance of edible mushrooms. This review summarized the key components and formation pathways of edible mushroom aroma. It also elaborated on the affecting factors and emerging analytical strategies of edible mushroom aroma. A total of 1308 volatile organic compounds identified in edible mushrooms, 61 were key components. The formation of these compounds is closely related to fatty acid metabolism, amino acid metabolism, lentinic acid metabolism, and terpenoid metabolism. The aroma profiles of edible mushrooms were affected by genetic background, preharvest factors, and preservation methods. Molecular sensory science and omics techniques are emerging analytical strategies to reveal aroma information of edible mushrooms. This review would provide valuable data and insights for future research on edible mushroom aroma.

Attraction of entomopathogenic nematodes to black truffle and its volatile organic compounds: A new approach for truffle beetle biocontrol

The European truffle beetle, Leiodes cinnamomeus, is the most important pest in black truffle (Tuber melanosporum) plantations. Entomopathogenic nematodes (EPNs) are a promising biological control agents against L. cinnamomeus. EPNs may employ multiple sensory cues while seeking for hosts, such as volatile organic compounds (VOCs) and CO2 gradients. We report for the first time the attraction of EPNs to truffle fruitbodies, and identified some VOCs potentially playing a key role in this interaction. We conducted olfactometer assays to investigate the attraction behavior of Steinernema feltiae and Steinernema carpocapsae towards both T. melanosporum fruitbodies and larvae of L. cinnamomeus. Subsequently, a chemotaxis assay using agar plates was performed to determine which of the 14 of the main VOCs emitted by the fruitbodies attracted S. feltiae at low (0.1 %) and high (mg/100 g truffle) concentrations. Both EPN species were attracted to mature fruitbodies of T. melanosporum, which may enhance the likelihood of encountering L. cinnamomeus during field applications. L. cinnamomeus larvae in the presence of truffles did not significantly affect the behavior of EPNs 24 h after application, underscoring the importance of the chemical compounds emitted by truffles themselves. Chemotaxis assays showed that four long-chain alcohol compounds emitted by T. melanosporum fruitbodies attracted S. feltiae, especially at low concentration, providing a first hint in the chemical ecology of a little-studied ecological system of great economical value. Further studies should be conducted to gain a finer understanding of the tritrophic interactions between T. melanosporum, EPNs, and L. cinnamomeus, as this knowledge may have practical implications for the efficacy of EPNs in the biological control of this pest.

Aromatic profile of black truffle grown in Argentina: Characterization of commercial categories and alterations associated to maturation, harvesting date and orchard management practices

Black truffle (Tuber melanosporum) is one of the most appreciated fungi in the world mainly due to its aromatic properties. In the emerging markets such as Argentina, the aroma of locally produced truffles has not been described yet. The volatile organic compounds (VOCs) from 102 black truffles from Argentina were analyzed using solid phase microextraction gas chromatography coupled with mass spectrometer detector (SPME-GC-MS). Several factors such as commercial category, maturity stage, host tree, geographical origin, and aromatic defects detected during classification were also registered and considered. As a result, 79 VOCs were detected, among which 2-methyl-propanal, 2-butanone, 2-methyl-1-propanol, butanal-3-methyl, 3-methyl-1-butanol, 2-methyl-1-butanol were present in high percentage in fresh mature truffles, whereas immature truffles were associated with 3,5-dimethoxytoluene, 2-phenyl-2-butenal, 2,3-dimethoxytoluene. The Argentine black truffles showed significant similarities in their aromatic profile when compared with their Australian and European counterparts, but with some distinctive notes.

Phenolics, flavonoids content and antioxidant activities of Tuber indicum at different maturity stages

The Chinese black truffle   Tuber indicum   (Ascomycota, Pezizales) is a ectomycorrhizal fungus forming hypogeous edible ascocarps. As a famous wild edible mushroom in the world, this species also attracted an increasing interest in their chemical composition and pharmacological activity. In this study, the total phenolic content, total flavonoid content and antioxidant activities of Tuber indicum collected from July to November at different maturity stages in China were analyzed. Our results showed that T. indicum collected in July (immature stage) possessed the highest amount of flavonoids (3.89 mg/g dw) and the highest ABTS⦁+  scavenging activity (EC50 =3.73 mg/ml). In addition, those samples collected in August (moderate mature stage) contained the highest phenolics content (4.78 mg/g dw), the highest DPPH⦁  radical scavenging activity(EC50 =3.73 mg/ml) and ferric reducing activity power(243.63 μmol FeSO4 /g). The study reveals T. indicum in the early maturity stage yield significantly higher content of phenolics and flavonoids and possessed stronger antioxidant activity than those collected in other months. This study provided important data for understanding the relationship between maturity stages and truffle formation and evaluating the quality of Chinese black truffle at different maturity.

Nontargeted metabolomic and multigene expression analyses reveal the mechanism of oil biosynthesis in sea buckthorn berry pulp rich in palmitoleic acid

Sea buckthorn berry pulp (SBP) oil is abundant in palmitoleic acid (C16:1). However, metabolic mechanisms of oil biosynthesis in SBP (non-seed tissues) are not clear. Thus, comparative nontargeted metabolomic analysis of the four developmental stages of berry pulp in two lines, Za56 and TF2-36, was performed. The results revealed that glycerol-3-phosphate (G3P) was critical for high oil accumulation in the mid-early developmental stages. In particular, the metabolism of phosphatidylcholine (PC) (16:0/16:0), PC (16:0/16:1), and PC (16:1/16:1) was also significantly altered. Sufficient supply of G3P and 16:1-CoA, coupled with upregulated expression of the glycerol-3-phosphate dehydrogenase (GPD1) and delta-9 desaturase (Δ9D) genes, were associated with high oil content enriched in C16:1 in SBP. Our results provide a scientific basis for the development of metabolic engineering strategies to increase the oil content in SBP with a high level of C16:1.

Increased Extracellular Saponin Production after the Addition of Rutin in Truffle Liquid Fermentation and Its Antioxidant Activities

Saponins possess a variety of pharmacological effects and exhibit great potential in the food industry as bioactive substances. In this study, extracellular saponin production via the liquid fermentation of Tuber melanosporum occurred with the addition of rutin. For this purpose, medium composition and culture conditions were optimized using single-factor experiments and an orthogonal experiment design. The optimal medium consisted of glucose (43.5 g/L), peptone (6 g/L), KH2PO4 (1.15 g/L), NaCl (0.2 g/L), vitamin B2 (0.082 g/L), vitamin B6 (0.1 g/L), vitamin C (0.02 g/L), and rutin (4.8 g/L). The culture conditions were as follows: 12.5% (v/v) inoculation, medium volume of 50 mL/250 mL flask, culture temperature of 24 °C, shaker speed of 190 rpm, initial pH of 5.7, and culture time of 96 h. Finally, a maximal extracellular saponin content of 0.413 g/L was obtained, which was 134.7% higher than that in the base medium. Rutin proved to be an excellent promoter, because the saponin production was increased by 50.2% compared to that in the optimized medium without rutin. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity, hydroxyl radical scavenging activity, and ferric reducing antioxidant power of truffle saponins reached 94.13%, 79.26%, and 42.22 mM, respectively. This study provides a useful strategy for fungal bioactive saponin production by liquid fermentation with the addition of flavonoid compounds.

Lack of Linkages among Fruiting Depth, Weight, and Maturity in Irrigated Truffle Fungi Marks the Complexity of Relationships among Morphogenetic Stages

The highly prized black truffle (Tuber melanosporum) has become a model species for ectomycorrhizal fungi biology. However, several questions concerning its reproductive phase remain unanswered. To provide new hypotheses on the fruitbody formation process, we have explored the causal links among development characters of black truffle fruitbodies that are primarily linked to either the mating process, fruitbody growing stage, or maturation. Path analysis was applied to test causal models outlining the relationships among fruitbody development characters such as fruiting depth, weight, shape, and spore maturity. These characters were investigated over a two-season survey and three soil typologies (plus peat-based substrate) under irrigated conditions. We found a clear and generalized relationship between fruitbody weight and shape. Among clusters of fruitbodies we found a positive relationship between the weight of the largest fruitbody and the weight of the remaining fruitbodies. However, no generalized relationships among characters linked to different development stages appeared. Our results were noticeably consistent across soil typologies, both for fruitbodies growing singly and in clusters, indicating that early-developing fruitbody characters did not influence characters linked to subsequent morphogenetic stages. The lack of links among stages opens new perspectives for pre-harvest quality management with stage-specific cultivation practices.

An Overview on Truffle Aroma and Main Volatile Compounds

Truffles are underground edible fungi that grow symbiotically with plant roots. They have been globally considered as one of the most expensive foods because of their rarity, unique aroma, and high nutritional value as antioxidant, anti-inflammatory, antiviral, hepatoprotective, anti-mutagenic, antituberculoid immunomodulatory, antitumor, antimicrobial, and aphrodisiac. The unique flavor and fragrance of truffles is one of the main reasons to get worldwide attraction as a food product. So, the aim of this review was to summarize the relevant literature with particular attention to the active aroma components as well as the various sample preparation and analytical techniques used to identify them. The major analytical methods used for the determination of volatile organic compounds (VOC) in truffles are gas chromatography (GC), proton-transfer-reaction mass spectrometry (PTR-MS), and electronic nose sensing (EN). In addition, factors influencing truffle aroma are also highlighted. For this reason, this review can be considered a good reference for research concerning aroma profiles of different species of truffles to deepen the knowledge about a complex odor of various truffles.

The 287,403 bp Mitochondrial Genome of Ectomycorrhizal Fungus Tuber calosporum Reveals Intron Expansion, tRNA Loss, and Gene Rearrangement

In the present study, the mitogenome of Tuber calosporum was assembled and analyzed. The mitogenome of T. calosporum comprises 15 conserved protein-coding genes, two rRNA genes, and 14 tRNAs, with a total size of 287,403 bp. Fifty-eight introns with 170 intronic open reading frames were detected in the T. calosporum mitogenome. The intronic region occupied 69.41% of the T. calosporum mitogenome, which contributed to the T. calosporum mitogenome significantly expand relative to most fungal species. Comparative mitogenomic analysis revealed large-scale gene rearrangements occurred in the mitogenome of T. calosporum, involving gene relocations and position exchanges. The mitogenome of T. calosporum was found to have lost several tRNA genes encoding for cysteine, aspartate, histidine, etc. In addition, a pair of fragments with a total length of 32.91 kb in both the nuclear and mitochondrial genomes of T. calosporum was detected, indicating possible gene transfer events. A total of 12.83% intragenomic duplications were detected in the T. calosporum mitogenome. Phylogenetic analysis based on mitochondrial gene datasets obtained well-supported tree topologies, indicating that mitochondrial genes could be reliable molecular markers for phylogenetic analyses of Ascomycota. This study served as the first report on mitogenome in the family Tuberaceae, thereby laying the groundwork for our understanding of the evolution, phylogeny, and population genetics of these important ectomycorrhizal fungi.

Differentiation of European and Chinese Truffle (Tuber sp.) Species by Means of Sterol Fingerprints

The increasing demand of valuable truffles (Tuber sp.) has prompted new areas of naturally growing truffles entering the market. Hence, the identification of valueless Tuber species is an important task to prevent food fraud. Here, we show that sterol patterns are suited to differentiate five Tuber species (Tuber magnatum, Tuber melanosporum, Tuber aestivum, Tuber albidum, and Tuber indicum varieties) from each other. Next to the known main sterols of Tuber, ergosterol and brassicasterol, occurrence of minor sterols in differing shares resulted in characteristic fingerprints in the five Tuber species, irrespective of the country of origin. A total of 27 sterols were evaluated, and we proposed assignment criteria of main sterol relations as well as eight distinct biomarkers within the minor compounds for the differentiation of European and Chinese truffles.

Species and geographic variability in truffle aromas

The gastronomic relevance and price of truffles are related mainly to its unique aroma. In this study, we explore the impact that different volatile compounds have on the aroma quality of fresh truffles using gas chromatography-mass spectrometry (GC-MS). Four hundred sixty fresh ascocarps of nine truffle species (Tuber aestivum, Tuber magnatum, Tuber melanosporum, Tuber mesentericum, Tuber brumale, Tuber excavatum, Tuber rufum, Tuber indicum and Tuber macrosporum) harvested in 2018/19 and 2019/2020 from 11 different countries (Slovenia, Croatia, Bosnia in Herzegovina, Macedonia, Italy, Spain, France, United Kingdom, Germany, Poland and China) were collected. Our investigation included the classification of species based on their aroma profile, a study of the differences in the volatile organic composition of truffle species over a geographical area, and, in more detail, a study of T. aestivum from four natural truffle growing sites in Slovenia. Our models can distinguish between groups, with small classification error. These models could form the basis of a predictive framework to detect fraud concerning truffle products and to determine the influence of different growing parameters on the aroma profile of truffles.