Food grade fungal stress on germinating peanut seeds induced phytoalexins and enhanced polyphenolic antioxidants

Effects of solid-state fermentation with Aspergillus cristatus (MK346334) on the dynamics changes in the chemical and flavor profile of dark tea by HS-SPME-GC-MS, HS-GC-IMS and electronic nose

Aspergillus cristatus, the predominant microbe of Fuzhuan brick tea (FBT), is responsible for the creation of distinctive golden flower and unique floral aroma of FBT. The present study examined the alterations in chemical and aromatic components of raw dark tea by solid-state fermentation using A. cristatus (MK346334), the strain isolated from FBT. As results, catechins, total ployphenols, total flavonoids, theaflavins, thearubigins and antioxidant activity were significantly reduced after fermentation. Moreover, 112 and 76 volatile substances were identified by HS-SPME-GC-MS and HS-GC-IMS, respectively, primarily composed of alcohols, ketones, esters and aldehydes. Furthermore, the calculation of odor activity values revealed that 19 volatile chemicals, including hexanal, heptanal, linalool and methyl salicylate, were the main contributors to the floral, fungal, woody and minty aroma of dark tea. The present research highlights the pivotal role played by the fermentation with A. cristatus in the chemical composition, antioxidant property and distinctive flavor of dark tea.

Determination of short-chain fatty acids as putative biomarkers of cancer diseases by modern analytical strategies and tools: a review

Short-chain fatty acids (SCFAs) are the main metabolites produced by bacterial fermentation of non-digestible carbohydrates in the gastrointestinal tract. They can be seen as the major flow of carbon from the diet, through the microbiome to the host. SCFAs have been reported as important molecules responsible for the regulation of intestinal homeostasis. Moreover, these molecules have a significant impact on the immune system and are able to affect inflammation, cardiovascular diseases, diabetes type II, or oncological diseases. For this purpose, SCFAs could be used as putative biomarkers of various diseases, including cancer. A potential diagnostic value may be offered by analyzing SCFAs with the use of advanced analytical approaches such as gas chromatography (GC), liquid chromatography (LC), or capillary electrophoresis (CE) coupled with mass spectrometry (MS). The presented review summarizes the importance of analyzing SCFAs from clinical and analytical perspective. Current advances in the analysis of SCFAs focused on sample pretreatment, separation strategy, and detection methods are highlighted. Additionally, it also shows potential areas for the development of future diagnostic tools in oncology and other varieties of diseases based on targeted metabolite profiling.

Decoding Metabolic Reprogramming in Plants under Pathogen Attacks, a Comprehensive Review of Emerging Metabolomics Technologies to Maximize Their Applications

In their environment, plants interact with a multitude of living organisms and have to cope with a large variety of aggressions of biotic or abiotic origin. What has been known for several decades is that the extraordinary variety of chemical compounds the plants are capable of synthesizing may be estimated in the range of hundreds of thousands, but only a fraction has been fully characterized to be implicated in defense responses. Despite the vast importance of these metabolites for plants and also for human health, our knowledge about their biosynthetic pathways and functions is still fragmentary. Recent progress has been made particularly for the phenylpropanoids and oxylipids metabolism, which is more emphasized in this review. With an increasing interest in monitoring plant metabolic reprogramming, the development of advanced analysis methods should now follow. This review capitalizes on the advanced technologies used in metabolome mapping in planta, including different metabolomics approaches, imaging, flux analysis, and interpretation using bioinformatics tools. Advantages and limitations with regards to the application of each technique towards monitoring which metabolite class or type are highlighted, with special emphasis on the necessary future developments to better mirror such intricate metabolic interactions in planta.

Cocultivation of pigeon pea hairy root cultures and Aspergillus for the enhanced production of cajaninstilbene acid

Pigeon pea hairy root cultures (PPHRCs) have been proven to be a promising alternative for the production of health-beneficial phenolic compounds, such as the most important health-promoting compound, i.e., cajaninstilbene acid (CSA). In this study, PPHRCs were cocultured with live Aspergillus fungi for further improving phenolic productivity via biological elicitation. Aspergillus oryzae CGMCC 3.951 (AO 3.951) was found to be the optimal fungus that could achieve the maximum increment of CSA (10.73-fold increase) in 42-day-old PPHRCs under the inoculum size of mycelia 0.50% and cocultivation time 36 h. More precisely, the contents of CSA in hairy roots and culture media after fungal elicitation increased by 9.87- and 62.18-fold over control, respectively. Meanwhile, the contents of flavonoid glycosides decreased, while aglycone yields increased upon AO 3.951 elicitation. Moreover, AO 3.951 could trigger the oxidative stress and pathogen defense response thus activating the expression of biosynthesis- and ABC transporter-related genes, which contributed to the intracellular accumulation and extracellular secretion of phenolic compounds (especially CSA) in PPHRCs. And PAL2, 4CL2, STS1, and I3'H were likely to be the potential key enzyme genes regulating the biosynthesis of CSA, and ABCB11X1-1, ABCB11, and ABCG24X2 were closely related to the transmembrane transport of CSA. Overall, the cocultivation approach could make PPHRCs more commercially attractive for the production of high-value phenolic compounds such as CSA and flavonoid aglycones in nutraceutical/medicinal fields. And the elucidation of crucial biosynthesis and transport genes was important for systematic metabolic engineering aimed at increasing CSA productivity. KEY POINTS: • Cocultivation of PPHRCs and live fungi was to enhance CSA production and secretion. • PPHRCs augmented CSA productivity 10.73-fold when cocultured with AO 3.951 mycelia. • Several biosynthesis and transport genes related to CSA production were clarified.

Stimulation of antioxidant activity and γ-aminobutyric acid synthesis in germinated wheat grain Triticum aestivum L. by ultrasound: Increasing the nutritional value of the product

The use of ultrasound to intensify the germination process of Triticum aestivum L. wheat was studied. This method of controlled germination can be used in several sectors of food industry, in particular in bakery. The effect of low-frequency ultrasound (20 kHz) at different intensities and duration on the germination process of Triticum aestivum L. wheat was systematically studied. We have found that 3-minute processing at 227 W/l output reduces the duration of wheat grain germination by 25% (12 ± 2 h) compared to the control samples. The use of ultrasound stimulated γ-aminobutyric acid (GABA) synthesis (18.9 ± 0.5 mg/100 g), increased the antioxidant activity (AOA) (2.86 ± 0.2 mg/g Trolox equivalents) and the amount of flavonoids (0.19 ± 0.03 mg QE/g). The SEM analysis of powder particles of whole-wheat flour made from wheat germinated with ultrasound exposure showed densely packed aggregates of protein matrix. To sum up, controlled ultrasound during wheat grain germination increases the amount of GABA and AOA. The whole-wheat flour is useful for food enrichment.

Naturally occurring prenylated stilbenoids: food sources, biosynthesis, applications and health benefits

Prenylated stilbenoids are a unique class of natural phenolic compounds consisting of C6-C2-C6 skeleton with prenyl substitution. They are potential nutraceuticals and dietary supplements presented in some edible plants. Prenylated stilbenoids demonstrate promising health benefits, including antioxidant, anti-cancer, anti-inflammatory, anti-microbial activities. This review reports the structure, bioactivity and potential application of prenylated stilbeniods in food industry. Edible sources of these compounds are compiled and summarized. Structure-activity relationship of prenylated stilbenoids are also highlighted. The biosynthesis strategies of prenylated stilbenoids are reviewed. The findings of these compounds as food preservative, nutraceuticals and food additive are discussed. This paper combines the up-to-date information and gives a full image of prenylated stilbenoids.

Antioxidant Assessment of Prenylated Stilbenoid-Rich Extracts from Elicited Hairy Root Cultures of Three Cultivars of Peanut (Arachis hypogaea)

Peanut produces prenylated stilbenoids upon biotic stress. However, the role of these compounds against oxidative stress have not been thoroughly elucidated. To this end, the antioxidant capacity of extracts enriched in prenylated stilbenoids and derivatives was studied. To produce these extracts, hairy root cultures of peanut cultivars Hull, Tifrunner, and Georgia Green were co-treated with methyl jasmonate, cyclodextrin, hydrogen peroxide, and magnesium chloride and then the stilbenoids were extracted from the culture medium. Among the three cultivars, higher levels of the stilbenoid derivatives arachidin-1 and arachidin-6 were detected in cultivar Tifrunner. Upon reaction with 2,2-diphenyl-1picrylhydrazyl, extracts from cultivar Tifrunner showed the highest antioxidant capacity with an IC₅₀ of 6.004 µg/mL. Furthermore, these extracts had significantly higher antioxidant capacity at 6.25 µg/mL and 3.125 µg/mL when compared to extracts from cultivars Hull and Georgia Green. The stilbenoid-rich extracts from peanut hairy roots show high antioxidant capacity and merit further study as potential nutraceuticals to promote human health.

Impact of Environmental Factors on Stilbene Biosynthesis

Stilbenes are a small family of polyphenolic secondary metabolites that can be found in several distantly related plant species. These compounds act as phytoalexins, playing a crucial role in plant defense against phytopathogens, as well as being involved in the adaptation of plants to abiotic environmental factors. Among stilbenes, trans-resveratrol is certainly the most popular and extensively studied for its health properties. In recent years, an increasing number of stilbene compounds were subjected to investigations concerning their bioactivity. This review presents the most updated knowledge of the stilbene biosynthetic pathway, also focusing on the role of several environmental factors in eliciting stilbenes biosynthesis. The effects of ultraviolet radiation, visible light, ultrasonication, mechanical stress, salt stress, drought, temperature, ozone, and biotic stress are reviewed in the context of enhancing stilbene biosynthesis, both in planta and in plant cell and organ cultures. This knowledge may shed some light on stilbene biological roles and represents a useful tool to increase the accumulation of these valuable compounds.

Extracts of Peanut Skins as a Source of Bioactive Compounds: Methodology and Applications

Peanut skins are a waste product of the peanut processing industry with little commercial value. They are also significant sources of the polyphenolic compounds that are noted for their bioactivity. The extraction procedures for these compounds range from simple single solvent extracts to sophisticated separation schemes to isolate and identify the large range of compounds present. To take advantage of the bioactivities attributed to the polyphenols present, a range of products both edible and nonedible containing peanut skin extracts have been developed. This review presents the range of studies to date that are dedicated to extracting these compounds from peanut skins and their various applications.

Effects of White LED Light and UV-C Radiation on Stilbene Biosynthesis and Phytochemicals Accumulation Identified by UHPLC-MS/MS during Peanut (Arachis hypogaea L.) Germination

In this study, the effects of white light-emitting diode (LED) and UV-C radiation (with the same intensity) on stilbene biosynthesis and phytochemicals accumulation of peanut sprouts were investigated. Results showed that white light radiation promoted the growth of peanut sprouts while UV-C radiation had the opposite effect. Contents of total phenolics, total flavonoids, and phytochemicals significantly increased in peanut sprouts treated by white light or UV-C radiation. Besides, light radiation significantly induced stilbene accumulation by upregulating the expression of genes and enzymes in stilbene biosynthesis-related pathway, and UV-C was more effective to promote stilbene accumulation. Compared with piceid and piceatannol, resveratrol showed the highest accumulation in peanut sprouts treated by light radiation. In summary, white light or UV-C radiation could be used as a method to promote stilbene biosynthesis and phytochemicals accumulation in peanut sprouts and UV-C was more effective.

Bioconversion of Kaempferol and Quercetin Glucosides from Plant Sources Using Rhizopus spp

Fermentation with filamentous fungi is known for the ability to convert bioactive compounds. The aim of this research was to investigate the metabolism of glycosidic derivatives of kaempferol and quercetin during fungal fermentation of extracts from cauliflower outer leaves and onion by Rhizopus oryzae and R. azygosporus. The highest release of kaempferol and quercetin was observed after 2 days and 1 day of fermentation with R. oryzae, respectively. It was proposed that glycosidic compounds were initially deglycosylated to form kaempferol-3-glucoside and quercetin-3-glucoside and then further metabolized into their aglycones. Clear differences in conversion efficiency towards the aglycones were observed between the two Rhizopus strains. Although both flavonoids only differ in one hydroxyl group, the metabolism of the glycosides towards their respective aglycones, kaempferol or quercetin, was different. It is concluded that the fermentation with R. oryzae and R. azygosporus could be considered as a way to produce kaempferol and quercetin aglycone from their glycosidic derivatives.

Stilbenoid prenyltransferases define key steps in the diversification of peanut phytoalexins

Defense responses of peanut (Arachis hypogaea) to biotic and abiotic stresses include the synthesis of prenylated stilbenoids. Members of this compound class show several protective activities in human disease studies, and the list of potential therapeutic targets continues to expand. Despite their medical and biological importance, the biosynthetic pathways of prenylated stilbenoids remain to be elucidated, and the genes encoding stilbenoid-specific prenyltransferases have yet to be identified in any plant species. In this study, we combined targeted transcriptomic and metabolomic analyses to discover prenyltransferase genes in elicitor-treated peanut hairy root cultures. Transcripts encoding five enzymes were identified, and two of these were functionally characterized in a transient expression system consisting of Agrobacterium-infiltrated leaves of Nicotiana benthamiana We observed that one of these prenyltransferases, AhR4DT-1, catalyzes a key reaction in the biosynthesis of prenylated stilbenoids, in which resveratrol is prenylated at its C-4 position to form arachidin-2, whereas another, AhR3'DT-1, added the prenyl group to C-3' of resveratrol. Each of these prenyltransferases was highly specific for stilbenoid substrates, and we confirmed their subcellular location in the plastid by fluorescence microscopy. Structural analysis of the prenylated stilbenoids suggested that these two prenyltransferase activities represent the first committed steps in the biosynthesis of a large number of prenylated stilbenoids and their derivatives in peanut. In summary, we have identified five candidate prenyltransferases in peanut and confirmed that two of them are stilbenoid-specific, advancing our understanding of this specialized enzyme family and shedding critical light onto the biosynthesis of bioactive stilbenoids.

Peanut sprout extract attenuates cisplatin-induced ototoxicity by induction of the Akt/Nrf2-mediated redox pathway

OBJECTIVE

Cisplatin is commonly used to treat solid tumors. However, permanent hearing loss is a major side effect of cisplatin chemotherapy and often results in dose reduction of the cisplatin chemotherapy. Peanut sprouts show cytoprotective properties owing to their antioxidant activities. This study was designed to investigate the effect of peanut sprout extract (PSE) on cisplatin-induced ototoxicity in an auditory cell line, HEI-OC1 cells.

METHODS

Cells were exposed to cisplatin for 24 h, with or without pre-treatment with PSE, cell viability was examined using the MTT assay. Apoptotic cells were identified by double staining with Hoechst 33258 and propidium iodide. Western blot analysis was performed to examine apoptotic proteins including C-PARP and C-caspase, anti-apoptotic protein Bcl-2, and Nrf2 redox system activation. Mitochondrial reactive oxygen species (ROS) were investigated to examine whether PSE could scavenge cisplatin-induced ROS. Real-time PCR analyses were performed to investigate the mRNA levels of antioxidant enzymes including NQO1, HO-1, GPx2, Gclc, and catalase.

RESULTS

The cisplatin-treated group showed reduced cell viability, increased apoptotic properties and markers, and increased ROS levels. PSE pre-treatment before cisplatin exposure significantly increased cell viability and reduced apoptotic properties and ROS production. These effects resulted from the up-regulation of antioxidant genes, including NQO1, HO-1, GPx2, Gclc, and catalase through Akt phosphorylation and Nrf2 activation.

CONCLUSION

Our results demonstrate that PSE protects from cisplatin-induced cytotoxicity by activating the antioxidant effects via the Akt/Nrf-2 pathway in this auditory cell line, and indicate that PSE may provide novel treatment to prevent cisplatin-induced ototoxicity.

Modification of Prenylated Stilbenoids in Peanut (Arachis hypogaea) Seedlings by the Same Fungi That Elicited Them: The Fungus Strikes Back

Aspergillus oryzae and Rhizopus oryzae were compared for inducing the production of prenylated stilbenoids in peanut seedlings. The fungus was applied at two different time points: directly after soaking (day 1) or after 2 days of germination (day 3). Aspergillus- and Rhizopus-elicited peanut seedlings accumulated an array of prenylated stilbenoids, with overlap in compounds induced, but also with compounds specific to the fungal treatment. The differences were confirmed to be due to modification of prenylated stilbenoids by the fungus itself. Each fungus appeared to deploy different strategies for modification. The content of prenylated stilbenoids modified by fungi accounted for around 8% to 49% (w/w) of total stilbenoids. The contents of modified prenylated stilbenoids were higher when the fungus was applied on day 1 instead of day 3. Altogether, type of fungus and time point of inoculation appeared to be crucial parameters for optimizing accumulation of prenylated stilbenoids in peanut seedlings.

Improved release and metabolism of flavonoids by steered fermentation processes: a review

This paper provides an overview on steered fermentation processes to release phenolic compounds from plant-based matrices, as well as on their potential application to convert phenolic compounds into unique metabolites. The ability of fermentation to improve the yield and to change the profile of phenolic compounds is mainly due to the release of bound phenolic compounds, as a consequence of the degradation of the cell wall structure by microbial enzymes produced during fermentation. Moreover, the microbial metabolism of phenolic compounds results in a large array of new metabolites through different bioconversion pathways such as glycosylation, deglycosylation, ring cleavage, methylation, glucuronidation and sulfate conjugation, depending on the microbial strains and substrates used. A whole range of metabolites is produced, however metabolic pathways related to the formation and bioactivities, and often quantification of the metabolites are highly underinvestigated. This strategy could have potential to produce extracts with a high-added value from plant-based matrices.

Hormesis of glyceollin I, an induced phytoalexin from soybean, on budding yeast chronological lifespan extension

Glyceollin I, an induced phytoalexin isolated from soybean, has been reported to have various bioactivities, including anti-bacterial, anti-nematode, anti-fungal, anti-estrogenic and anti-cancer, anti-oxidant, anti-inflammatory, insulin sensitivity enhancing, and attenuation of vascular contractions. Here we show that glyceollin I has hormesis and extends yeast life span at low (nM) doses in a calorie restriction (CR)-dependent manner, while it reduces life span and inhibits yeast cell proliferation at higher (μM) doses. In contrast, the other two isomers (glyceollin II and III) cannot extend yeast life span and only show life span reduction and antiproliferation at higher doses. Our results in anti-aging activity indicate that glyceollin I might be a promising calorie restriction mimetic candidate, and the high content of glyceollins could improve the bioactivity of soybean as functional food ingredients.

Laxative effect of peanut sprout extract

Certain phenolic compounds are known to exhibit laxative properties. Seed sprouts, such as those of peanut, are known to promote de novo biosynthesis of phenolic compounds. This study was conducted to examine the potential laxative properties of 80% (v/v) ethanolic extract of peanut sprout (PSE), which contains a high concentration of phenolic compounds such as resveratrol. For this, SD rats were orally administered PSE while a control group was incubated with saline. Laxative effects were examined in both groups of rats. Constipation induced by loperamide in SD rats was improved by administration of PSE. Constipated rats showed increased intestinal movement of BaSO₄ upon administration of PSE compared to the control, and the groups administered 100 or 1,000 mg PSE/kg bw were not significantly different in transit time of the indicator. However, colon length was not statistically different among the experimental groups, although it was longer in the group incubated with 1 g PSE/kg bw compared to other groups. Further, there was no significant difference in stool number among the experimental groups. Taken together, these findings show that PSE has a laxative effect in a rat model of loperamide-induced constipation.

Germination dramatically increases isoflavonoid content and diversity in chickpea (Cicer arietinum L.) seeds

The effect of germination on bioactive components in legume seeds was investigated in terms of the antioxidant capacity and total phenolic contents. Germination increased the total phenolic content and antioxidant capacity of most seeds. Particularly in chickpea seeds, the isoflavone contents increased by over 100 fold, mainly due to the increase of formononetin and biochanin A level. As a result, these two compounds were conveniently isolated from the germinated seeds in preparative scale and structurally confirmed by UV-vis, ESI-MS, and (1)H NMR spectroscopies. Isoflavonoid fingerprints analyzed by HPLC-PDA and LC-ESI-MS demonstrated that germination could significantly increase isoflavonoids diversity. Twenty-five isoflavonoids were detected and identified tentatively. These include 20 isoflavones, 2 isoflavanones, and 3 pterocarpan phytoalexins. Total isoflavonoid content of germinated chickpea was approximately 5-fold of that of germinated soybean. Our findings suggest that the germinated chickpea seeds could serve as a promising functional food rich in isoflavonoids.

Effect of Aspergillus oryzae-challenged germination on soybean isoflavone content and antioxidant activity

Application of microbial stress to soybean during germination induces the accumulation of phytoalexins, which have many health benefits. In this study, the effects of stress induced by Aspergillus oryzae on the phytochemical composition of germinating soybeans were investigated, and their radical scavenging activity was compared with those of ungerminated (US) and germinated (GS) soybeans. Additionally, the antioxidant activity of coumestrol, a soybean phytoalexin, against hydrogen peroxide-induced reactive oxygen species (ROS) was investigated in HepG2 cells. A. oryzae exposure significantly decreased the total isoflavone content and induced coumestrol and glyceollin I. A. oryzae-challenged germinated soybeans exhibited the highest radical scavenging activity (IC(50) = 0.55 mg/mL) as compared to US and GS. Coumestrol exhibited significantly higher radical scavenging activity than daidzein and genistein. Furthermore, coumestrol significantly prevented hydrogen peroxide-induced ROS production and lipid peroxidation and inhibited decreases in cell viability, intracellular glutathione (GSH) levels, and superoxide dismutase (SOD) activity. These results indicate that using food-grade A. oryzae to elicit the biosynthesis of phytoalexins alters the secondary metabolite profiles of the soybeans and offers enhanced bioactivity of soybean as a functional food ingredient.

Phytoalexins in defense against pathogens

Plants use an intricate defense system against pests and pathogens, including the production of low molecular mass secondary metabolites with antimicrobial activity, which are synthesized de novo after stress and are collectively known as phytoalexins. In this review, we focus on the biosynthesis and regulation of camalexin, and its role in plant defense. In addition, we detail some of the phytoalexins produced by a range of crop plants from Brassicaceae, Fabaceae, Solanaceae, Vitaceae and Poaceae. This includes the very recently identified kauralexins and zealexins produced by maize, and the biosynthesis and regulation of phytoalexins produced by rice. Molecular approaches are helping to unravel some of the mechanisms and reveal the complexity of these bioactive compounds, including phytoalexin action and metabolism.