Chemical Compositions and Antioxidant Activities of 16 Wild Edible Mushroom Species Grown in Anatolia

An insight into the nutritional and medicinal value of edible mushrooms: A natural treasury for human health

Edible mushrooms have been cherished worldwide because of their nutraceutical and medicinal properties. They are recognized as the new superfood for the future due to their low-calorie content, high-protein content, low lipid levels, low cholesterol levels, and abundance of essential vitamins. The fruiting body of edible mushrooms contains a plethora of primary and secondary metabolites. However, submerged cultivation is a more reliable and controlled way of production of mycelium biomass and many bioactive compounds. Several bioactive metabolites present in mushrooms possess a range of beneficial properties, including antioxidant, antimicrobial, anticancer, antidiabetic, anti-inflammatory, antiviral and anti-COVID-19 activities. Consumers have turned more intrigued in mushroom-containing products as the world needs to diversify its protein sources to meet the growing demand for protein. In this context, mushrooms are viewed as a promising source of bioactive chemicals that can be employed as an alternative to meat products. This review aims to summarise the most recent data regarding the beneficial health effects and the development of mushroom-based food products.

Purification and Biochemical Characterization of Novel Galectin from the Black Poplar Medicinal Mushroom Cyclocybe cylindracea (Agaricomycetes) Strain MEST42 from Algeria

In the present study, a new galectin designated Cyclocybe cylindracea lectin (CCL) was extracted from the fruiting bodies of the wild black popular mushroom C. cylindracea grown in Algeria. The protein was isolated using sepharose 4B as affinity chromatography matrix, and galactose as elutant. The purified galectin was composed of two subunits of 17.873 kDa each, with a total molecular mass of 35.6 kDa. Its agglutinant activity was impeded by galactose and its derivatives, as well as melibiose. Lactose showed the highest affinity, with a minimal inhibitory concentration of 0.0781 mM. CCL was sensitive to extreme pH conditions, and its binding function decreased when incubated with 10 mM EDTA, and it could be restored by metallic cations such as Ca2+, Mg2+, and Zn2+. CCL agglutinated human red blood cells, without any discernible specificity. Circular dichroism spectra demonstrated that its secondary structure contained β-sheet as dominant fold. In addition, bioinformatics investigation on their peptide fingerprint obtained after MALDI-TOF/TOF ionization using mascot software confirmed that CCL was not like any previous purified lectin from mushroom: instead, it possessed an amino acid composition with high similarity to that of the putative urea carboxylase of Emericella nidulans (strain FGSC A4/ATCC 38163/CBS 112.46/NRRL 194/M139) with 44% of similarity score.

Bioactivity Profiling of Infusion, Decoction, and Hydroalcoholic Fraction Obtained from Wild Golden Chanterelle Mushroom, Cantharellus cibarius (Agaricomycetes)

Cantharellus cibarius Fr. is one of the most desirable, popularly known wild edible mushrooms of the genus Cantharellus. Besides having nutritional benefits, this mushroom is reported to harbor significant medicinal potential. In present study, we describe for the first-time bioactive metabolites content and medicinal activities of three different types of extracts including infusion, decoction, and hydroalcoholic fraction from wild Cantharellus cibarius of West Bengal. Bioactive metabolites quantification revealed the phenol and flavonoids present in the range between 0.56-1.46 mg of GAE/g of dried fruit bodies and 0.12-0.29 mg of QE/g of dried fruit bodies, respectively, whereas ascorbic acid contents were also found. Antioxidant activity was assessed using six in vitro systems; decoction displayed better results in all investigated assays with EC50 values ranging between 0.05 and 0.34 mg/ml whereas hydroalcoholic extract showed highest total antioxidant capacity (18 ± 1.61 μg AAE per mg of extract) than other extracts. Moreover, infusion and decoction were found to scavenge highly reactive free radicals like hydroxyl and nitric oxide with their EC50 values ranging between 0.26 and 0.91 mg/ml. Additionally, anti-inflammatory potential of the extracts was evaluated using protein denaturation assay. Hydroalcoholic extract at a concentration range of 0.005-0.1 mg/ml showed comparatively better activity than decoction and infusion, although all the extracts presented dose dependent inhibition of heat induced protein denaturation. Altogether, the present investigation is expected to extend the existing knowledge of this species and recommended its use in pharmaceutical industries as an effective mycomedicine.

Antioxidant Potential and Stability of Oxidative Sunflower Oil by Using the Ethanolic Extracts of Saprophytic Edible Cultivable Mushrooms from Pakistan

During this study, ethanol extracts of four edible mushrooms i.e., Macrocybe gigantea, Podaxis pistillaris, Lentinus tigrinus, and Pleurotus cystidiosus were prepared and investigated by TFC, TPC, FRAP, ABTS and DPPH for their antioxidant potential. The extracts were also used to check the oxidative stabilization of sunflower oil for a period of 45 d using standard methods i.e., peroxide value, free fatty acid contents and iodine value. M. gigantea extract showed the maximum flavonoids and phenolic contents and exhibited the maximum antioxidant potential among the four edible mushrooms. BHA was observed to have maximum oil stabilization potential followed by the ethanol extract of M. gigantea of 1000 ppm concentration, BHT and extract of 1000 ppm concentration of P. pistillaris. Thus, it is concluded from this study that ethanolic extracts of these mushrooms can be used as a healthy supplement to stabilize oil by replacing synthetic antioxidants that are harmful to humans.

Selected fungi of the genus Lactarius - screening of antioxidant capacity, antimicrobial activity, and genotoxicity

It is well-known that mushrooms of the genus Lactarius constitute a natural food resource providing health benefits as a nutritient. This genus contains 4 mushrooms identified as L. deliciosus, L. volemus, L. sanguifluus, L. semisanguifluus and L. piperatus which were collected in Serbia. The aim of this study aimed was to identify and characterize the content of phenolic compounds and examine the antioxidant potential of 5 wild edible mushrooms. L. sanguifluus contained the highest content of total phenol compounds (75.25 mg gallic acid equivalents (GAE) per g dry extract weight (GAE/g DE) and exhibited the greatest antioxidant activity through the ability to remove radicals as evidenced by ABTS assay (8.99 mg of trolox equivalents (TE) per g dry extract weight (mg TE/g DE); total reducing power (TRP) assay mg ascorbic acid equivalents per mg of dry extract weight (0.42 mg AAE/g DE) and CUPRAC (14.23 mg TE /g DE). L. deliciosus methanolic extract produced greatest scavenging of the DPPH radical (46%). The methanol mushroom extracts were screened for in vitro antimicrobial activity against a panel of pathogenic bacterial strains using the microdilution method. Of all the extracts tested, L. sanguifluus extract showed the best antibacterial properties. The cytokinesis block micronucleus assay results for the examined mushrooms demonstrated that extracts at a concentration of 3 μg/ml decreased the number of micronuclei (MN) in the range of 19-49% which is significant bearing in mind that radioprotectant amifostine reduced the frequency of MN by only 16.3%. Data thus demonstrate that the 5 wild edible mushrooms of genus Lactarius contain constituents that are beneficial not only as nutrients but also have the potential as antioxidants, antibacterial and antigenotoxic properties.

UV induced conversion during drying of ergosterol to vitamin D in various mushrooms: Effect of different drying conditions

BACKGROUND

Mushrooms are increasingly popular around the world as a nutritional food which is an excellent source of vitamin D2. Although natural mushrooms often contain very little vitamin D2 as many are grown in the dark, they are rich in ergosterol, a precursor to vitamin D2. Ergosterol can be converted to vitamin D2 under ultraviolet radiation. Due to the high water content of fresh mushroom, its quality deteriorates rapidly after harvest, and drying is the most commonly used technology to extend the shelf life. The vitamin D2 content of dried mushrooms depends on the drying conditions used.

SCOPE AND APPROACH

In this review, the chemistry of the photo-conversion process of ergosterol to vitamin D2 under ultraviolet radiation is introduced. The ergosterol and vitamin D contents in different mushroom varieties are discussed. The effects of several drying methods and the influence of different drying conditions are reviewed.Key findings and conclusions: Thermal drying in the presence of UV has been proven to convert ergosterol into vitamin D and enhance the nutritional content of all types of edible mushrooms. Solar drying, hot air drying, freeze drying, microwave drying and infrared drying can be used for mushrooms drying under selected operating conditions. A critical evaluation of published literature demonstrates the importance of applying appropriate drying methodology to maximize the nutritional value of various types of edible mushrooms.

The two faces of Coprinus comatus-Functional properties and potential hazards

Mushrooms have been used for centuries not only as food but also in traditional medicine as a source of components with pro‐health activity. One of them is Coprinus comatus (O.F.Müll.) Pers. also called shaggy mane, chicken drumstick mushroom, or lawyer's wig. In Asian countries, C. comatus (CC) is approved as edible mushroom and often cultivated for consumption, whereas in many other countries, although it is widespread, it is unrecognized and not used. In this review, for the first time, we discussed about the composition related to functional properties as well as the potential risks associated with consumption of CC by reviewing scientific literature. The information has been collected in order to get to know this species thoroughly. Various studies show many of the physiological activities, such as antioxidant, anticancer, antiandrogenic, hepatoprotective, acetylcholinesterase inhibitory, antiinflammatory, antidiabetic, antiobesity, antibacterial, antifungal, antinematode, and antiviral. Besides positive physiological properties, CC has also negative features, for example, skin reactions in patients with dermatitis and atopic predisposition, risk of confusion with poisonous mushrooms, quick autolysis after collection, and contamination of toxic elements.

Partial Purification and Characterization of Polyphenol Oxidase from the Wild Edible Mushroom Lepiota Procera Using Three-Phase Partitioning

Polyphenol oxidase (PPO) from the wild edible mushroom Lepiota procera is partially purified and biochemically characterized using three-phase partitioning (TPP), which is an easily applied and effective method. This method includes ammonium sulfate saturation at different concentrations, t-butanol addition (1:1; 1:5), and adjustment of pH. Optimum purification parameters with 20% ammonium sulfate saturation and 1:1 t-butanol conditions led to the highest activity at bottom phase with 8.4 fold purification. Sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed the molecular weight of the purified enzyme to be 35 kDa. The partially purified PPO presented a high level of activity with L-DOPA (Michaelis-Menten constant, Km – 0.12 mM), followed by caffeic acid (0.27 mM) and 4-methylcatechol (0.46 mM) and it is classified as a catecholase type of PPO. The enzyme had peak activity at a temperature of 40 °C and a pH value of 7.0. These results demonstrate a new enzyme source and easy purification method, useful for various industrial applications.

Chemical composition and bioactive properties of the wild mushroom Polyporus squamosus (Huds.) Fr: a study with samples from Romania

In Eastern Europe, wild mushrooms are widely collected in mountain areas and used for their medicinal properties or as healthy foods. This study aimed at determining the chemical composition (nutritional value, free sugars, organic acids, phenolic compounds, fatty acids and tocopherols) and bioactive properties (antioxidant, antimicrobial and antiquorum sensing) of wild Polyporus squamosus (Huds.) Fr from Romania. The results indicate that the fruiting bodies of P. squamosus are rich in carbohydrates (74.22 g per 100 g dw) and proteins (18.7 g per 100 g dw). Trehalose was the main free sugar, while malic acid was the organic acid detected in the highest amount (2.21 g per 100 g dw), and p-hydroxybenzoic acid was the main phenolic compound. Among tocopherols, β-tocopherol was the most abundant form (114.7 μg per 100 g dw). Additionally, regarding the fatty acids' pattern, polyunsaturated acids represent more than 57% of all fatty acids, followed by monounsaturated fatty acids (24.96%). The highest measured antioxidant effect of P. squamosus extract was found using the TBARS inhibition assay (EC₅₀ = 0.22 mg mL^-1), followed by the β-carotene/linoleate assay (EC₅₀ = 1.41 mg mL^-1). A minimal inhibitory concentration of the tested extracts was obtained between 0.61-20.4 mg mL^-1, while the bactericidal effect was achieved between 1.2-40.8 mg mL^-1. Antibiofilm potential was obtained at all tested concentrations, and subinhibitory concentrations of the extract exhibited an antiquorum effect and reduced the formation of P. aeruginosa pili, which all together influenced the virulence of this bacterium. Due to the investigated bioactivities and compounds of P. squamosus and its well-balanced nutritional profile, this mushroom can be further used as a medicinal ingredient based on its antioxidative and antimicrobial potential.

Pressurized hot water extraction of β-glucans from Cantharellus tubaeformis

Cantharellus tubaeformis was processed by pressurized hot water extraction (80-240°C) with the aim of maximizing the extraction of oligomeric fractions, β-glucans, and the in vitro antioxidant properties of the extracts. Increased severity of treatment enhanced the extraction yields above 62% at temperatures of 210ºC or higher, corresponding to the maximum β-glucan yields. The highest antioxidant capacity was obtained at 170ºC, although the highest content of phenolic compounds was obtained at the highest severity studied. This hydrothermal treatment can be considered a suitable process to obtain extracts with antioxidant properties and rich in β-glucans.

Evaluation of heavy metal concentrations of edible wild-grown mushrooms from China

The heavy metal contents (Co, Cu, Fe, Mn, Ni, and Zn) of eight species of wild edible mushrooms from China were determined. The analyses were performed using inductively coupled plasma atomic emission spectrophotometry after microwave digestion. The contents of Co, Cu, Fe, Mn, Ni, and Zn in caps of mushroom samples were 0.7-7.2, 16.2-70.4, 371-1315, 12.5-29.8, 7.1-58.5, and 77.8-187.4 mg kg^-1 dry matter (dm), respectively, while considerable differences were found to be 1.8-25.9, 9.8-36.3, 288-6762, 13.3-103.9, 5.9-78.7, and 38.7-118 mg kg^-1 dm for stipes. The results indicated that higher levels of Co, Fe, and Ni were found in the mushrooms samples analyzed. Zinc and manganese levels were similar to previous reports, whereas Cu was lower than literature values. Correlation analysis suggested that significant correlations were found between the minerals determined and the greatest amount of contamination is associated with Co, Mn, Ni, and Fe. The results of this study indicate that heavy metal contents in mushroom species are mainly related to the mineral resources of sampling sites.

NIR hyperspectral imaging and multivariate image analysis to characterize spent mushroom substrate: a preliminary study

Commercial mushroom growth on substrate material produces a heterogeneous waste that can be used for bioenergy purposes. Hyperspectral imaging in the near-infrared (NHI) was used to experimentally study a number of spent mushroom substrate (SMS) packed samples under different conditions (wet vs. dry, open vs. plastic covering, and round or cuboid) and to explore the possibilities of direct characterization of the fresh substrate within a plastic bag. Principal components analysis (PCA) was used to remove the background of images, explore the important studied factors, and identify SMS and mycelia (Myc) based on the pixel clusters within the score plot. Overview PCA modeling indicated high moisture content caused the most significant effects on spectra followed by the uneven distribution of Myc and the plastic cover. There were well-separated pixel clusters for SMS and Myc under different conditions: dry, wet, or wet and plastic covering. The loading peaks of the related component and the second derivative of the mean spectra of pixel clusters of SMS and Myc indicated that there are chemical differences between SMS and Myc. Partial least squares discriminant analysis (PLS-DA) models were calculated and classification of SMS and Myc was successful, whether the materials were dry or wet. Peak shifts because of high moisture content and unexpected peaks from the plastic covering were found. Although the best results were obtained for dried cylinders, it was shown that almost equally good results could be obtained for the wet material and for the wet material covered by plastic. Furthermore, PLS-DA prediction showed that a side face hyperspectral image could represent the information for the entire SMS cylinder when Myc was removed. Thus, the combination of NHI and multivariate image analysis has great potential to develop calibration models to directly predict the contents of water, carbohydrates, lignin, and protein in wet and plastic-covered SMS cylinders.

Factors affecting mushroom Pleurotus spp

Pleurotus genus is one of most extensively studied white-rot fungi due to its exceptional ligninolytic properties. It is an edible mushroom and it also has several biological effects, as it contains important bioactive molecules. In basidiomycete fungi, lignocellulolytic enzymes are affected by many typical fermentation factors, such as medium composition, ratio of carbon to nitrogen, pH, temperature, air composition, etc. The survival and multiplication of mushrooms is related to a number of factors, which may act separately or have interactive effects among them. Out that understanding challenges in handling Pleurotus species mushroom requires a fundamental understanding of their physical, chemical, biological and enzymatic properties. This review presents a practical checklist of available intrinsic and extrinsic factors, providing useful synthetic information that may help different users. An in-depth understanding of the technical features is needed for an appropriate and efficient production of Pleurotus spp.

Golden Needle Mushroom: A Culinary Medicine with Evidenced-Based Biological Activities and Health Promoting Properties

Flammulina velutipes (enoki, velvet shank, golden needle mushroom or winter mushroom), one of the main edible mushrooms on the market, has long been recognized for its nutritional value and delicious taste. In recent decades, research has expanded beyond detailing its nutritional composition and delved into the biological activities and potential health benefits of its constituents. Many bioactive constituents from a range of families have been isolated from different parts of the mushroom, including carbohydrates, protein, lipids, glycoproteins, phenols, and sesquiterpenes. These compounds have been demonstrated to exhibit various biological activities, such as antitumour and anticancer activities, anti-atherosclerotic and thrombosis inhibition activity, antihypertensive and cholesterol lowering effects, anti-aging and antioxidant properties, ability to aid with restoring memory and overcoming learning deficits, anti-inflammatory, immunomodulatory, anti-bacterial, ribosome inactivation and melanosis inhibition. This review aims to consolidate the information concerning the phytochemistry and biological activities of various compounds isolated from F. velutipes to demonstrate that this mushroom is not only a great source of nutrients but also possesses tremendous potential in pharmaceutical drug development.

Traditional knowledge and use of wild mushrooms by Mixtecs or Ñuu savi, the people of the rain, from Southeastern Mexico

BACKGROUND

Mexico is an important global reservoir of biological and cultural richness and traditional knowledge of wild mushrooms. However, there is a high risk of loss of this knowledge due to the erosion of traditional human cultures which is related with the rapid acculturation linked to high migration of rural populations to cities and the U.S.A., and the loss of natural ecosystems. The Mixtec people, the third largest native group in Mexico only after the Nahua and the Maya, maintain ancient traditions in the use and knowledge of wild mushrooms. Paradoxically, there are few studies of the Mixtec ethnomycology. This study shows our ethnomycological research, mainly focused on knowledge and use of wild mushrooms in communities of the Mixteca Alta, in southeastern Mexico. We hypothesized that among the studied communities those with a combination of higher vegetation cover of natural pine and oak forests, lower soil erosion and higher economic margination had a greater richness and knowledge of wild mushrooms. Our study therefore aimed to record traditional knowledge, use, nomenclature and classification of wild mushrooms in four Mixtec communities and to analyze how these aspects vary according to environmental and cultural conditions among the studied communities.

METHODS

In order to analyze the cultural significance of wild mushrooms for the Mixtec people, 116 non-structured and semi-structured interviews were performed from 2009 to 2014. Information about the identified species, particularly the regional nomenclature and classification, their edibility, toxicity and ludic uses, the habitat of useful mushrooms, traditional recipes and criteria to differentiate between toxic and edible species, and mechanisms of knowledge transmission were studied. The research had the important particularity that the first author is Mixtec, native of the study area. A comparative qualitative analysis between the richness of fungal species used locally and the official information of the natural vegetation cover, soil erosion and economic marginalization in each of the studied communities was conducted.

RESULTS

A total of 106 species of mushrooms were identified growing in pine and oak forest, deciduous tropical forest and grassland; among the identified mushrooms we recorded 26 species locally consumed, 18 considered toxic, 6 having ludic uses and the remaining 56 species not being used in the studied areas but some of them having potential as food (56 species) or medicine (28 species). We recorded that 80, 22 and 4 species are ectomycorrhizal, saprotrophic and parasites, respectively. Our study shows that a complex and accurate knowledge related with the use, nomenclature, classification, ecology, gastronomy of wild mushrooms has been developed by Mixtecs; and that there is a relation between natural vegetation cover, lower soil erosion and higher economic marginalization and richness, knowledge and use of mushrooms in the studied communites.

CONCLUSION

Our study showed that conservation and adaptation of ancestral mycological knowledge survives mainly through oral transmition, maintenance of cultural identity, forest protection, preservation native language and also paradoxically through the current socieconomical marginality among the Mixtec people. We also found that those studied communities with a combination of higher vegetation cover of natural pine and oak forests, lower soil erosion and higher economic marginalization showed a greater richness and knowledge of wild mushrooms. Use and sustainable management of wild mushrooms can be an alternative for local integrated development, but local knowledge and traditional worldview should be included into the regional programs of Mixtec biocultural conservation.

Nutraceutical properties of the methanolic extract of edible mushroom Cantharellus cibarius (Fries): primary mechanisms

The methanolic extract of the wild edible mushroom Cantharellus cibarius Fr. (chanterelle) was analyzed for in vitro antioxidative, cytotoxic, antihypertensive and antibacterial activities. Various primary and secondary metabolites were found. Phenols were the major antioxidant components found in the extract (49.8 mg g(-1)), followed by flavonoids, whose content was approximately 86% of the total phenol content. Antioxidant activity, measured by four different methods, was high for inhibition of lipid peroxidation (EC50 = 1.21 mg mL(-1)) and chelating ability (EC50 = 0.64 mg mL(-1)). The antioxidant activity of the C. cibarius methanol extract was achieved through chelating iron compared to hydrogen atom and/or electron transfer. The extract showed good selectivity in cytotoxicity on human cervix adenocarcinoma HeLa, breast carcinoma MDA-MB-453 and human myelogenous leukemia K562, compared to normal control human fetal lung fibroblasts MRC-5 and human lung bronchial epithelial cells BEAS-2B. The extract had inhibitory activity against angiotensin converting I enzyme (ACE) (IC50 = 0.063 mg mL(-1)). The extract revealed selective antimicrobial activity against Gram-positive bacteria with the highest potential against E. faecalis. The medicinal and health benefits, observed in wild C. cibarius mushroom, seem an additional reason for its traditional use as a popular delicacy food.

Expanding current knowledge on the chemical composition and antioxidant activity of the genus Lactarius

Despite the presence of toxic compounds in inedible mushrooms, the question whether the chemical nutrients and non-nutrients compositions in edible and inedible Lactarius species are similar remains unanswered. To answer this question, Lactarius citriolens Pouzar and Lactarius turpis (Weinm.) Fr., two inedible species, were studied in order to obtain information about their chemical composition and bioactivity. Free sugars, fatty acids, tocopherols, organic and phenolic acids were analysed by chromatographic techniques coupled to different detectors. L. citriolens and L. turpis methanolic extracts were tested regarding antioxidant potential (reducing power, radical scavenging activity and lipid peroxidation inhibition). The composition of macronutrients varied among the two species, but the profiles were similar between them and among other Lactarius species; L. citriolens gave the highest energy contribution, saturated fatty acids and organic acids, while the L. turpis sample was richer in free sugars, mono- and polyunsaturated fatty acids, tocopherols and phenolic compounds. L. turpis methanolic extract showed the highest antioxidant activity. The absence of hepatoxicity of the methanolic extracts was confirmed in porcine liver primary cells (in vitro conditions). The present study provided new information about wild L. citriolens and L. turpis, comparing their chemical composition and antioxidant properties with other Lactarius species, and expanding the knowledge about this genus.

A review of chemical composition and nutritional value of wild-growing and cultivated mushrooms

Fruit bodies of about 200 mushroom species are consumed throughout the world, preferably as a delicacy. Knowledge of their chemical composition, nutritional value and health-promoting effects has expanded dynamically during the last few years. Dry matter (DM) is low: commonly about 100 g kg⁻¹ . The usual contents of protein, lipids and ash are 200-250, 20-30 and 80-120 g kg⁻¹ DM, respectively. Various carbohydrates form the remaining DM. Nevertheless, great variations occur both among and within species. Energy is low, usually 350-400 kcal kg⁻¹ of fresh fruit bodies. The nutritional contribution of mushroom protein derived from earlier data seems to be overestimated. Fat content is low with markedly prevailing in linoleic acid and oleic acid, while the proportion of n-3 fatty acids is nutritionally marginal. The main carbohydrates are chitin, glycogen, trehalose and mannitol. Information on fibre content and composition is limited. Health-promoting β-glucans are an auspicious group of polysaccharides. High potassium content is characteristic of mushrooms. Several species can accumulate very high levels of both detrimental trace elements, particularly cadmium and mercury, and radiocaesium isotopes if growing on heavily polluted substrates. Mushrooms seem to be a considerable source of ergosterol, provitamin D₂, and phenolids with antioxidative properties. Hundreds of flavour constituents have been identified, particularly with eight-carbon aliphatic chains. Data on changes of mushroom components under various preservation conditions and culinary treatments have been fragmentary. Even more limited is knowledge of nutrient bioavailability.