Correction: Boulaka et al. Genoprotective Properties and Metabolites of ß-Glucan-Rich Edible Mushrooms Following Their In Vitro Fermentation by Human Faecal Microbiota. Molecules 2020, 25, 3554.

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Free Amino Acids in Three Pleurotus Species Cultivated on Agricultural and Agro-Industrial By-Products.

Previous studies have demonstrated the feasibility of employing by-products of the olive and wine sectors for the production of Pleurotus mushrooms with enhanced functionalities. In this work we investigated the influence of endogenous and exogenous factors on free amino acids (FAAs) profile of Pleurotus ostreatus, P. eryngii and P. nebrodensis mushrooms produced on wheat straw (WS), alone or mixed with grape marc (GM), and on by-products of the olive industry (OL). Overall, 22 FAAs were determined in substrates and mushrooms, including all the essential amino acids, the neurotransmitter γ-aminobutyric acid (GABA) and ornithine. On a dry weight (dw) basis, total FAAs ranged from 17.37 mg/g in P. nebrodensis to 130.12 mg/g in P. ostreatus samples, with alanine, leucine, glutamine, valine and serine predominating. Similar distribution patterns were followed by the monosodium glutamate (MSG)-like, sweet and bitter FAAs. Significant differences in FAAs level were observed among the species examined and among the cultivation substrates used. Principal Component Analysis (PCA) performed on the entire FAAs profile of six Pleurotus strains, clearly separated P. ostreatus from P. eryngii and P. nebrodensis, in accordance to their phylogenetic affinity. This is the first report of FAAs in P. nebrodensis.

Effects of Rich in Β-Glucans Edible Mushrooms on Aging Gut Microbiota Characteristics: An In Vitro Study.

Alterations of gut microbiota are evident during the aging process. Prebiotics may restore the gut microbial balance, with ß-glucans emerging as prebiotic candidates. This study aimed to investigate the impact of edible mushrooms rich in ß-glucans on the gut microbiota composition and metabolites by using in vitro static batch culture fermentations and fecal inocula from elderly donors (n = 8). Pleurotus ostreatus, P. eryngii, Hericium erinaceus and Cyclocybe cylindracea mushrooms derived from various substrates were examined. Gut microbiota composition (quantitative PCR (qPCR)) and short-chain fatty acids (SCFAs; gas chromatography (GC)) were determined during the 24-h fermentation. P. eryngii induced a strong lactogenic effect, while P. ostreatus and C. cylindracea induced a significant bifidogenic effect (p for all <0.05). Furthermore, P. eryngii produced on wheat straw and the prebiotic inulin had comparable Prebiotic Indexes, while P. eryngii produced on wheat straw/grape marc significantly increased the levels of tested butyrate producers. P. ostreatus, P. eryngii and C. cylindracea had similar trends in SCFA profile; H. erinaceus mushrooms were more diverse, especially in the production of propionate, butyrate and branched SCFAs. In conclusion, mushrooms rich in ß-glucans may exert beneficial in vitro effects in gut microbiota and/or SCFAs production in elderly subjects.

Genoprotective Properties and Metabolites of ß-Glucan-Rich Edible Mushrooms Following Their In Vitro Fermentation by Human Faecal Microbiota.

A variety of bioactive compounds, constituents of edible mushrooms, in particular ß-glucans, i.e., a group of ß-d-glucose polysaccharides abundant in the fungal cell walls, have been linked to immunomodulating, anticancer and prebiotic activities. The aim of the study was the investigation of the genoprotective effects of edible mushrooms produced by Pleurotus eryngii, Pleurotus ostreatus and Cyclocybe cylindracea (Basidiomycota). Mushrooms from selected strains of the species mentioned above were fermented in vitro using faecal inocula from healthy volunteers. The cytotoxic and anti-genotoxic properties of the fermentation supernatants (FSs) were investigated in Caco-2 human colon adenocarcinoma cells. The FSs were cytotoxic in a dose-dependent manner. Non-cytotoxic concentrations were used for the genotoxicity studies, which revealed that mushrooms' FSs have the ability to protect Caco-2 cells against tert-butyl hydroperoxide (t-BOOH), a known genotoxic agent. Their global metabolic profiling was assessed by 1H-NMR spectroscopy. A total of 37 metabolites were identified with the use of two-dimensional (2D) homo- and hetero-nuclear NMR experiments. Multivariate data analysis monitored the metabolic variability of gut microbiota and probed to biomarkers potentially associated with the health-promoting effects of edible mushrooms.

Application of Fourier transform mid-infrared photoacoustic spectroscopy for rapid assessment of phosphorus availability in digestates and digestate-amended soils.

Digestate is the anaerobic digestion by-product of biogas production that can be used as a phosphorus (P) fertilizer. To achieve the efficient utilization of digestate as a P fertilizer and evaluate P availability in digestate-amended soils, it is necessary to assess both available P in different digestates and digestate-amended soils. In this study, Fourier transform mid-infrared photoacoustic spectroscopy (FTIR-PAS) combined with multivariate analysis was applied to predict water-extractable P (WEP) in digestates and plant-available P in digestate-amended soils. The plant-available P was determined by the diffusive gradients in thin films (DGT) technique. 45 digestate samples were collected both from laboratory-scale digesters (26 samples) and operating biogas plants (19 samples) in Denmark for WEP determination. Three soils amended with the collected 19 digestate samples from biogas plants (that results to 57 digestate-amended soil samples in total) were deployed for DGT measurement of plant- available P. The WEP predicting model had a coefficient of determination (R2) of 0.80 and a root mean square error of 0.78 g kg-1 while the plant-available P predicting model exhibited an R2 of 0.70 and a root mean square error of 134.09 µg P L-1. Furthermore, regression coefficients with a significant contribution of the plant-available P predicting model were identified, indicating that FTIR-PAS is capable for correlating spectra information with plant-available P related chemical bonds. In conclusion, FTIR-PAS can be used as a faster and non-destructive alternative for the assessment of both WEP in digestates and plant-available P in digestate-amended soils.

Enhancing the nutritional and functional properties of Pleurotus citrinopileatus mushrooms through the exploitation of winery and olive mill wastes.

Treatment and disposal of wineries and olive-oil mills waste is usually associated with complex processes, which are often of limited wide-scale applicability. Olive-leaves plus two-phase olive mill waste (OLW) or grape marc plus wheat straw (GMW) were assessed as substrates for the cultivation of the choice edible mushroom Pleurotus citrinopileatus. GMW led to increased mushroom biological efficiency and shorter production cycles. Antioxidant activities, triterpenic acids, free amino acids, lovastatin and ergosterol were significantly higher in fruitbodies from GMW; the latter compound was positively correlated with squalene concentrations in substrates. Glucans, resveratrol and fatty acids content showed minor differences among mushrooms from the three substrates examined, whereas ergothioneine was significantly higher in fruitbodies grown on OLW. High correlations were noted for oleanolic, ursolic and amino acid content in mushrooms and their respective substrates. Moreover, FTIR spectra revealed variations in fruitbodies content in bioactive compounds which were associated with the substrates used.

Prediction of biochemical methane potential of urban organic waste using Fourier transform mid-infrared photoacoustic spectroscopy and multivariate analysis.

Biochemical methane potential (BMP) assays are widely used to assess feedsocks in oder to control the process of biogas production. However, the continuous evaluation of feedstocks using a BMP assay is expensive, time-consuming and challenging. In this study, Fourier transform mid-infrared photoacoustic spectroscopy (FTIR-PAS) was used to predict the BMP values of 87 urban organic waste (UOW) samples derived from different sources in Denmark. The developed model of BMP prediction showed a coefficient of determination (R2) of 0.86 and a root mean square error (RMSE) of 59.3 mL CH4/g VS in prediction. The interpretation of the regression coefficients used in the calibration showed a positive correlation with BMP for relatively easily degradable compounds, such as aliphatics, most likely lipids and amides most likely in proteins, while a negative correlation was found with lignin and hemicellulose.

Volatile Profiling of Pleurotus eryngii and Pleurotus ostreatus Mushrooms Cultivated on Agricultural and Agro-Industrial By-Products.

The influence of genetic (species, strain) and environmental (substrate) factors on the volatile profiles of eight strains of Pleurotus eryngii and P. ostreatus mushrooms cultivated on wheat straw or substrates enriched with winery or olive oil by products was investigated by headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). Selected samples were additionally roasted. More than 50 compounds were determined in fresh mushroom samples, with P. ostreatus presenting higher concentrations but a lower number of volatile compounds compared to P. eryngii. Roasting resulted in partial elimination of volatiles and the formation of pyrazines, Strecker aldehydes and sulfur compounds. Principal component analysis on the data obtained succeeded to discriminate among raw and cooked mushrooms as well as among Pleurotus species and strains, but not among different cultivation substrates. Ketones, alcohols and toluene were mainly responsible for discriminating among P. ostreatus strains while aldehydes and fatty acid methyl esters contributed more at separating P. eryngii strains.

Pleurotus Mushrooms Content in Glucans and Ergosterol Assessed by ATR-FTIR Spectroscopy and Multivariate Analysis.

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was used to monitor the infrared absorption spectra of 79 mushroom samples from 29 Pleurotus ostreatus, P. eryngii and P. nebrodensis strains cultivated on wheat straw, grape marc and/or by-products of the olive industry. The spectroscopic analysis provided a chemical insight into the mushrooms examined, while qualitative and quantitative differences in regions related to proteins, phenolic compounds and polysaccharides were revealed among the species and substrates studied. Moreover, by using advanced chemometrics, correlations of the recorded mushrooms' spectra versus their content in glucans and ergosterol, commonly determined through traditional analytical techniques, allowed the development of models predicting such contents with a good predictive power (R2: 0.80-0.84) and accuracy (low root mean square error, low relative error and representative to the predicted compounds spectral regions used for the calibrations). Findings indicate that FTIR spectroscopy could be exploited as a potential process analytical technology tool in the mushroom industry to characterize mushrooms and to assess their content in bioactive compounds.

Trace elements, polycyclic aromatic hydrocarbons, mineral composition, and FT-IR characterization of unrefined sea and rock salts: environmental interactions.

Unrefined sea salt originates from seawater, typically by natural evaporation. Being minimally processed, it contains the natural minerals and impurities of seawater. Despite the wide applications of salt for culinary and food preservation purposes, the available composition data is particularly limited. Since seawater often contains various harmful substances at a trace or ultra-trace level, their determination in unrefined salt is significant in terms of quality control and food safety. Twenty-four (24) samples of unrefined sea and rock salts retailed in Greece were studied in terms of their trace metals and polycyclic aromatic hydrocarbon (PAH) content, which constitute the usual pollutants examined in seawater. In addition, samples' color and mineralogy were recorded and their attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectra were obtained. No statistically significant differences were found between sea and rock salts regarding their trace metal (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) content (excluding V) and the 15 PAHs examined. ATR FT-IR succeeded to discriminate among sea, rock, flower, and underground salty water salts. Compared with the typical trace metal concentrations in seawater, quite high Pb values were determined in both sea and rock salts, whereas outliers in the rest of the trace elements examined were scarce. Median values of the sum of PAH (ΣPAHs) concentrations were calculated equal to 2.1 and 2.6 ng g-1 for sea and rock salts, respectively. Environmental interactions of salt production with trace elements and PAHs are also discussed.

Three different Fourier-transform mid-infrared sampling techniques to characterize bio-organic samples.

In recent years, there has been a surge in the number of applications of Fourier-transform mid-infrared (FTIR) spectroscopy for the characterization of environmental samples and prediction of some of their properties whose measurement has traditionally involved time-consuming and costly methods. However, there are several different mid-infrared techniques available, and there is a gap in knowledge regarding the best-suited technique for recording informative spectra of different types of environmental samples. This study compared the three most widespread FTIR techniques using solid and liquid samples. A total of 11 environmental samples belonging to four categories were analyzed with attenuated total reflectance (ATR), photoacoustic (PAS), and diffuse reflectance (DR) FTIR spectroscopy. Overall, PAS-FTIR was the best technique, providing a greater amount of information, especially for opaque samples (i.e., organic waste, biochar, and soil), than ATR-FTIR and DR-FTIR spectroscopy. Attenuated total reflectance FTIR provided the best spectra for soft samples, such as plant materials, probably due to their ability to achieve good optical contact with the ATR crystal. Finally, DR-FTIR performed relatively well for most samples but was found to be more sensitive to moisture in the samples, resulting in noise in specific areas, and was less sensitive in bond vibrations related to Si.

Low crystalline apatite in bone char produced at low temperature ameliorates phosphorus-deficient soils.

Globally, more than 30% of soils are poor in phosphorus (P) and the productivity of these soils is severely restricted without the addition of P fertiliser. With future P supplies becoming limited, it is becoming increasingly important to identify ways of optimising the use of waste materials as P fertilisers. One technology that has been promoted extensively in recent years to improve quality of degraded soils is the application of biochar. In this context, char produced from recycled animal bone is of special interest because of its high P content (∼15%). This study investigated how production temperature affects chemical P forms in bone char and the impact on soil P availability in different P-deficient soils. The major P form in dried bone meal was poorly crystalline hydroxyapatite. As the pyrolysis temperature increased to 1050 °C, the hydroxyapatite structure measured with X-ray absorption near edge structure (XANES) spectroscopy persisted. Furthermore, crystallinity increased at temperatures above 750 °C, as revealed by X-ray powder diffraction (XRD). Plant availability was highest for bone char produced between 300 °C and 500 °C in three acidic soils from three continents, and declined rapidly above 750 °C. This strongly indicated that crystallinity of hydroxyapatite limits plant availability at high pyrolysis temperatures. In a high pH soil, all materials resulted in low P availability. As pyrolysis increased the P availability in comparison with dried bone, it was concluded that bone char produced at temperatures between 300 °C and 500 °C has the potential to improve fertility of P-poor, low pH soils.

The effect of different pyrolysis temperatures on the speciation and availability in soil of P in biochar produced from the solid fraction of manure.

Biochar application to agricultural land has been proposed as a means for improving phosphorus (P) availability in soil. The purpose of the current study was to understand how pyrolysis temperature affects P speciation in biochar and how this affects availability of P in the amended soil. Biochar was produced at different temperatures from digestate solids. The primary species of P in digestate solids were simple calcium phosphates. However, a high co-occurrence of magnesium (Mg) and P, indicated that struvite or other magnesium phosphates may also be important species. At low temperatures, pyrolysis had little effect on P speciation; however, as the temperature increased above 600 °C, the P gradually became more thermodynamically stable in species such as apatite. At very high temperatures above 1000 °C, there were indications of reduced forms of P. Biochar production decreased the immediate availability of P in comparison with the original digestate solids. However, for biochar produced at low temperatures, availability quickly increased to the same levels as in the digestate solids. For biochar produced at higher temperatures, availability remained depressed for much longer. The low availability of P in the biochar produced at high temperatures can probably be explained by the formation of less soluble P species in the biochar. In contrast, the transient decrease of availability of the P in the biochar produced at low temperatures can be explained by mechanisms, such as sorption on biochar, which gradually decreases because of oxidation of the biochar surfaces or changes in pH around the biochar particles.

Using FTIR-photoacoustic spectroscopy for phosphorus speciation analysis of biochars.

In the last decade, numerous studies have evaluated the benefits of biochar for improving soil quality. The purposes of the current study were to use Fourier transform infrared-photoacoustic spectroscopy (FTIR-PAS) to analyse P species in biochar and to determine the effect of pyrolysis temperature on P speciation. The photoacoustic detector has a range of advantages for the very dark biochar samples in comparison to more traditional reflectance or transmission FTIR detectors. The spectra turned out to be more informative in the regions with P vibrations for biochar produced at temperatures above 400°C, where most of the remaining organic compounds were aromatic and therefore not overlapping with the P vibrations. For biochars produced from the solid fraction of digestate from biogas production, an increase in the pyrolysis temperature led to the formation of a large variety of P species. Hydroxylapatite and tricalcium phosphate were the most dominant P species in the mid to high temperature range (600-900°C), while at 1050°C apatite, iron phosphates, variscite and calcium phosphates were identified. However, the changes in P speciation in biochars produced from bone meal at different temperatures were smaller than in the biochars from digestate. Hydroxylapatite and calcium phosphates were identified in biochar produced at all temperatures, while there was some indication of struvite formation.

FTIR-PAS: a powerful tool for characterising the chemical composition and predicting the labile C fraction of various organic waste products.

Fourier transform infrared (FT-IR) spectroscopy has been used for several years as a fast, low-cost, reliable technique for characterising a large variety of materials. However, the strong influence of sample particle size and the inability to measure the absorption of very dark and opaque samples have made FTIR unsuitable for many waste materials. FTIR-photoacoustic spectroscopy (FTIR-PAS) can eliminate some of the shortcomings of traditional FTIR caused by scattering effects and reflection issues, and recent advances in PAS technology have made commercial instruments available. In this study, FTIR-PAS was used to characterise a wide range of organic waste products and predict their labile carbon fraction, which is normally determined from time-consuming assays. FTIR-PAS was found to be capable of predicting the labile fraction of carbon as efficiently as near infrared spectroscopy (NIR) and furthermore of identifying the compounds that are correlated with the predicted parameter, thus facilitating a more mechanistic interpretation.

Rapid estimation of the biochemical methane potential of plant biomasses using Fourier transform mid-infrared photoacoustic spectroscopy.

Biochemical methane potential (BMP) is a very important characteristic of a given feedstock for optimisation of its use in biogas production. However, the long digestion time needed to determine BMP is the main limitation for the use of this assay during the operation of anaerobic digesters to produce biogas. Fourier transform mid-infrared photoacoustic spectroscopy (FTIR-PAS) was used to predict the BMP of 87 plant biomasses. The developed calibration model was able to explain 81% of the variance in the measured BMP of a selected test set with a root mean square error (RMSE) of 40NLCH4kg(-1) of volatile solids (VS) and a ratio of performance to deviation (RPD) of 2.38. The interpretation of the regression coefficients used in the calibration revealed a positive correlation of BMP with easily degradable compounds (amorphous cellulose, hemicellulose and aliphatic compounds) and a negative correlation with inhibitors of cellulose hydrolysis (lignin, hemicellulose).

Rapid estimation of sugar release from winter wheat straw during bioethanol production using FTIR-photoacoustic spectroscopy.

BACKGROUND: Complexity and high cost are the main limitations for high-throughput screening methods for the estimation of the sugar release from plant materials during bioethanol production. In addition, it is important that we improve our understanding of the mechanisms by which different chemical components are affecting the degradability of plant material. In this study, Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) was combined with advanced chemometrics to develop calibration models predicting the amount of sugars released after pretreatment and enzymatic hydrolysis of wheat straw during bioethanol production, and the spectra were analysed to identify components associated with recalcitrance. RESULTS: A total of 1122 wheat straw samples from nine different locations in Denmark and one location in the United Kingdom, spanning a large variation in genetic material and environmental conditions during growth, were analysed. The FTIR-PAS spectra of non-pretreated wheat straw were correlated with the measured sugar release, determined by a high-throughput pretreatment and enzymatic hydrolysis (HTPH) assay. A partial least square regression (PLSR) calibration model predicting the glucose and xylose release was developed. The interpretation of the regression coefficients revealed a positive correlation between the released glucose and xylose with easily hydrolysable compounds, such as amorphous cellulose and hemicellulose. Additionally, a negative correlation with crystalline cellulose and lignin, which inhibits cellulose and hemicellulose hydrolysis, was observed. CONCLUSIONS: FTIR-PAS was used as a reliable method for the rapid estimation of sugar release during bioethanol production. The spectra revealed that lignin inhibited the hydrolysis of polysaccharides into monomers, while the crystallinity of cellulose retarded its hydrolysis into glucose. Amorphous cellulose and xylans were found to contribute significantly to the released amounts of glucose and xylose, respectively.

Rapid strain classification and taxa delimitation within the edible mushroom genus Pleurotus through the use of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy.

Fourier transform infrared (FT-IR) spectroscopy has been successfully applied for the identification of bacteria and yeasts, but only to a limited extent for discriminating specific groups of filamentous fungi. In the frame of this study, 73 strains - from different associated hosts/substrates and geographic regions - representing 16 taxa of the edible mushroom genus Pleurotus (Basidiomycota, Agaricales) were examined through the use of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. A binary matrix, elaborated on the basis of presence/absence of specific absorbance peaks combined with cluster analysis, demonstrated that the spectral region 1800-600 cm(-1) permitted clear delimitation of individual strains into Pleurotus species. In addition, closely related species (e.g., Pleurotus ostreatus and Pleurotus pulmonarius) or taxa of the subgenus Coremiopleurotus demonstrated high similarity in their absorbance patterns, whereas genetically distinct entities such as Pleurotus dryinus, Pleurotus djamor, and Pleurotus eryngii provided spectra with noteworthy differences. When specific regions (1800-1700, 1360-1285, 1125-1068, and 950-650 cm(-1)) were evaluated in respect to the absorbance values demonstrated by individual strains, it was evidenced that this methodology could be eventually exploited for the identification of unknown Pleurotus specimens with a stepwise process and with the aid of a dichotomous key developed for this purpose. Moreover, it was shown that the nature of original fungal material examined (mycelium, basidiomata, and basidiospores) had an effect on the outcome of such analyses, and so did the use of different mycelium growth substrates. In conclusion, application of FT-IR spectroscopy provided a fast, reliable, and cost-efficient solution for the classification of pure cultures from closely related mushroom species.