The yield, nutritional value, umami components and mineral contents of the first-flush and second-flush Pleurotus pulmonarius mushrooms grown on three forestry wastes

Comparative analyses of Pleurotus pulmonarius mitochondrial genomes reveal two major lineages of mini oyster mushroom cultivars

Pleurotus pulmonarius, commonly known as the mini oyster mushroom, is highly esteemed for its crisp texture and umami flavor. Limited genetic diversity among P. pulmonarius cultivars raises concerns regarding its sustainable industrial production. To delve into the maternal genetic diversity of the principal P. pulmonarius cultivars, 36 cultivars and five wild isolates were subjected to de novo sequencing and assembly to generate high-quality mitogenome sequences. The P. pulmonarius mitogenomes had lengths ranging from 69,096 to 72,905 base pairs. The mitogenome sizes of P. pulmonarius and those of other mushroom species in the Pleurotus genus showed a significant positive correlation with the counts of LAGLIDAG and GIY-YIG homing endonucleases encoded by intronic open reading frames. A comparison of gene arrangements revealed an inversion of a fragment containing atp9-nad3-nad2 between P. pulmonarius and P. ostreatus. The mitogenomes of P. pulmonarius were clustered into three distinct clades, two of which were crowded with commercial cultivars. Clade I, all of which possess an inserted dpo gene, shared a maternal origin linked to an ancestral cultivar from Taiwan. Primers were designed to target the dpo gene, potentially safeguarding intellectual property rights. The wild isolates in Clade III exhibited more divergent mitogenomes, rendering them valuable for breeding.

From waste to protein: a new strategy of converting composted distilled grain wastes into animal feed

Distilled grain waste (DGW) is rich in nutrients and can be a potential resource as animal feed. However, DGW contains as much as 14% lignin, dramatically reducing the feeding value. White-rot fungi such as Pleurotus ostreatus could preferentially degrade lignin with high efficiency. However, lignin derivatives generated during alcohol distillation inhibit P. ostreatus growth. Thus, finding a new strategy to adjust the DGW properties to facilitate P. ostreatus growth is critical for animal feed preparation and DGW recycling. In this study, three dominant indigenous bacteria, including Sphingobacterium thermophilum X1, Pseudoxanthomonas byssovorax X3, and Bacillus velezensis 15F were chosen to generate single and compound microbial inoculums for DGW composting to prepare substrates for P. ostreatus growth. Compared with non-inoculated control or single microbial inoculation, all composite inoculations, especially the three-microbial compound, led to faster organic metabolism, shorter composting process, and improved physicochemical properties of DGW. P. ostreatus growth assays showed the fastest mycelial colonization (20.43 μg·g-1 ergosterol) and extension (9 mm/d), the highest ligninolytic enzyme activities (Lac, 152.68 U·g-1; Lip, 15.56 U·g-1; MnP, 0.34 U·g-1; Xylanase, 10.98 U·g-1; FPase, 0.71 U·g-1), and the highest lignin degradation ratio (30.77%) in the DGW sample after 12 h of composting with the three-microbial compound inoculation when compared to other groups. This sample was relatively abundant in bacteria playing critical roles in amino acid, carbohydrate, energy metabolism, and xenobiotic biodegradation, as suggested by metagenomic analysis. The feed value analysis revealed that P. ostreatus mycelia full colonization in composted DGW led to high fiber content retention and decreased lignin content (final ratio of 5% lignin) but elevated protein concentrations (about 130 g·kg-1 DM). An additional daily weight gain of 0.4 kg/d was shown in cattle feeding experiments by replacing 60% of regular feed with it. These findings demonstrate that compound inoculant consisting of three indigenous microorganisms is efficient to compost DGW and facilitate P. ostreatus growth. P. ostreatus decreased the lignin content of composted DGW during its mycelial growth, improving the quality of DGW for feeding cattle.

Effects of Different Carbon and Nitrogen Ratios on Yield, Nutritional Value, and Amino Acid Contents of Flammulina velutipes

The carbon-to-nitrogen (C/N) ratio in the cultivation medium significantly influences the growth rate, vigor of mycelium, yield of fruiting bodies, and their nutritional composition. Recently, agricultural and forestry wastes have been increasingly used in cultivating Flammulina velutipes. However, systematic research on how these materials affect the nutritional and functional properties of the fruiting bodies is lacking. This study investigated the effects of different C/N ratios on F. velutipes cultivation. We evaluated the agronomic traits, nutritional composition, and flavor compounds of the fruiting bodies. Our findings reveal that an optimal C/N ratio of 27:1 in the composted substrates enhances the total yield of fruiting bodies, with 25.1% soybean straw as the primary raw material. This ratio also significantly increases the levels of crude protein, total amino acids, and essential amino acids in the fruiting bodies (p < 0.05). Fruiting bodies from the high-nitrogen (HN) treatment showed the highest content of umami amino acids and equivalent umami concentration value. Additionally, we employed an untargeted liquid chromatography-mass spectrometry (LC-MS)-based metabolomics approach to analyze the metabolite profiles of fruiting bodies cultivated in high-nitrogen (HN), medium-nitrogen (MN), and low-nitrogen (LN) substrates. We found that the carbon-nitrogen ratio can affect the flavor and quality of fruiting bodies by regulating amino acid biosynthesis and metabolism and other related pathways. Our results suggest that a C/N ratio of 27:1 offers numerous benefits for the cultivation of F. velutipes with comprehensive analyses and has promising application prospects.

Recent advances in the biosynthesis and industrial biotechnology of Gamma-amino butyric acid

GABA (Gamma-aminobutyric acid), a crucial neurotransmitter in the central nervous system, has gained significant attention in recent years due to its extensive benefits for human health. The review focused on recent advances in the biosynthesis and production of GABA. To begin with, the investigation evaluates GABA-producing strains and metabolic pathways, focusing on microbial sources such as Lactic Acid Bacteria, Escherichia coli, and Corynebacterium glutamicum. The metabolic pathways of GABA are elaborated upon, including the GABA shunt and critical enzymes involved in its synthesis. Next, strategies to enhance microbial GABA production are discussed, including optimization of fermentation factors, different fermentation methods such as co-culture strategy and two-step fermentation, and modification of the GABA metabolic pathway. The review also explores methods for determining glutamate (Glu) and GABA levels, emphasizing the importance of accurate quantification. Furthermore, a comprehensive market analysis and prospects are provided, highlighting current trends, potential applications, and challenges in the GABA industry. Overall, this review serves as a valuable resource for researchers and industrialists working on GABA advancements, focusing on its efficient synthesis processes and various applications, and providing novel ideas and approaches to improve GABA yield and quality.

Microbial Inoculation during the Short-Term Composting Process Enhances the Nutritional and Functional Properties of Oyster Mushrooms (Pleurotus ostreatus)

In recent years, short-term composting techniques have been widely applied in oyster mushroom cultivation, but there is still a lack of systematic research on their impact on the nutritional and functional properties of fruiting bodies. In this study, the microbial inoculant Streptomyces thermoviolaceus BUA-FM01 (ST) was applied in the short-term composting process for oyster mushroom cultivation. The agronomic traits, nutritional composition, flavor compounds, and antioxidant activity of fruiting bodies from the first three flushes were evaluated. The results show that microbial inoculation significantly (p < 0.05) reduced the total carbon content and C/N ratio of the composted substrates and, furthermore, increased the total yield of the fruiting bodies. Moreover, microbial inoculation significantly (p < 0.05) increased the crude protein, crude polysaccharide, total amino acid, and essential amino acid contents of the fruiting bodies. The fruiting bodies of the first flush of ST treatment possessed the highest umami amino acid content and equivalent umami concentration value. Furthermore, microbial inoculation significantly (p < 0.05) enhanced the scavenging ability of crude polysaccharides toward free radicals. The results indicate that microbial inoculation has many benefits for the composting cultivating process of oyster mushrooms and good application prospects.

Bacterial communities during composting cultivation of oyster mushroom Pleurotus floridanus using broken eggs as the nitrogen source and study of agronomic and nutritional properties

Introduction

Broken eggs are a byproduct of the poultry industry and a potential nitrogen source for mushroom cultivation. However, its feasibility needs to be evaluated experimentally.

Methods

In this study, a series of different addition amounts (0, 1.8, 3.6, 5.3 and 8.5%, w/w) of broken egg mixture (BEM) were applied in the composting cultivation process of oyster mushroom. The physicochemical properties and bacterial communities of composting substrate, and agronomic and nutritional properties of fruiting bodies were determined.

Results and discussion

The results showed that the BEM addition significantly (P < 0.05) increased the total nitrogen content in the composted substrate, and the contents of crude protein, total amino acids and essential amino acids of mushrooms. The P3 treatment (initial C/N of 26:1) showed the highest biological efficiency (BE) of 100.19% and a low contamination rate (CR) of 7.00%, while the higher dosage of BEM (P4 and P5) led to a sharp decrease in BE and a sharp increase in CR. High throughput sequencing revealed that the addition of BEM significantly (P < 0.05) changed the bacterial communities in the substrate at the beginning of composting. Streptococcus and Lactococcus were predominant bacterial genera in BEM treatments at the beginning stage of composting, while Acinetobacter became predominant at the ending stage. The co-occurrence network analysis showed that the P3 treatment demonstrated a much more complex bacterial community. The structural equation model analysis indicated that the addition of BEM affected the bacterial communities and nitrogen metabolism during composting, which further affected agronomic and nutritional properties of oyster mushrooms. An appropriate amount of BEM combined with composting processes can significantly improve the yield and quality of oyster mushroom, providing a new way for efficient utilization of BEM.

Development of reference genes for RT-qPCR analysis of gene expression in Pleurotus pulmonarius for biotechnological applications

Jatropha curcas is an oilseed crop with biorefinery applications. Whilst cake generated following oil extraction offers potential as a protein source for animal feed, inactivation of toxic phorbol esters present in the material is necessary. Pleurotus pulmonarius is a detoxifying agent for jatropha cake with additional potential as animal feed, edible mushroom and for enzyme production. For the characterization of fungal genes involved in phorbol ester degradation, together with other industrial applications, reverse transcription-quantitative PCR (RT-qPCR) is a tool that enables accurate quantification of gene expression. For this, reliable analysis requires reference genes for normalization of mRNA levels validated under conditions employed for target genes. The stability of potential reference genes β-TUB, ACTIN, GAPDH, PHOS, EF1α, TRPHO, LAC, MNP3, MYP and VP were evaluated following growth of P. pulmonarius on toxic, non-toxic jatropha cake and a combined treatment, respectively. NormFinder and geNorm algorithms for expression stability analysis identified PHOS, EF1α and MNP3 as appropriate for normalizing gene expression. Reference gene combinations contrasting in ranking were compared following normalization of relative expression of the CHU_2040 gene, encoding an esterase enzyme potentially involved in phorbol ester degradation. The reference genes for P. pulmonarius will facilitate the elucidation of mechanisms involved in detoxification of phorbol esters as well as analysis of target genes for application in biorefinery models.

Geographic Pattern of Variations in Chemical Composition and Nutritional Value of Cinnamomum camphora Seed Kernels from China

Cinnamomum camphora (camphor tree) is an important non-conventional edible plant species found in East Asia. Here, a detailed characterization for the chemical composition and nutritional value of C. camphora seed kernels (CCSKs) collected from different regions in China is provided. The results showed that there were significant differences among the CCSK samples in weights (1000 fruits, 1000 seeds and 1000 kernels), proximate composition, minerals, phenolics, flavonoids and amino acid contents. The highest contents of oil (62.08%) and protein (22.17%) were found in the CCSK samples collected from Chongqing and Shanghai, respectively. The highest content of mineral in the CCSK samples was K (4345.05-7186.89 mg/kg), followed by P (2735.86-5385.36 mg/kg), Ca (1412.27-3327.37 mg/kg) and Mg (2028.65-3147.32 mg/kg). The CCSK sample collected from Guizhou had the highest levels of total phenolic and flavonoid contents (TPC and TFC), while that from Chongqing had the lowest levels. In addition, the most abundant fatty acid in the CCSK samples was capric acid (57.37-60.18%), followed by lauric acid (35.23-38.29%). Similarities in the fatty acid composition among the CCSK samples were found. The CCSK sample collected from Guizhou had the highest percentage (36.20%) of essential amino acids to total amino acids, and Chongqing had the lowest value (28.84%). These results indicated that CCSK may be developed as an excellent source of plant-based medium-chain oil, protein, dietary fiber, minerals, phytochemicals and essential amino acids.

Gamma-aminobutyric acid (GABA): a comprehensive review of dietary sources, enrichment technologies, processing effects, health benefits, and its applications

Gamma-aminobutyric acid (GABA) is a naturally occurring potential bioactive compound present in plants, microorganisms, animals, and humans. Especially, as a main inhibitory neurotransmitter in the central nervous system, GABA possesses a broad spectrum of promising bioactivities. Thus, functional foods enriched with GABA have been widely sought after by consumers. However, the GABA levels in natural foods are usually low, which cannot meet people's demand for health effects. With the increasing public awareness on the food securities and naturally occurring processes, using enrichment technologies to elevate the GABA contents in foods instead of exogenous addition can enhance the acceptability of health-conscious consumers. Herein, this review provides a comprehensive insight on the dietary sources, enrichment technologies, processing effects of GABA, and its applications in food industry. Furthermore, the various health benefits of GABA-enriched foods, mainly including neuroprotection, anti-insomnia, anti-depression, anti-hypertensive, anti-diabetes, and anti-inflammatory are also summarized. The main challenges for future research on GABA are related to exploring high GABA producing strains, enhancing the stability of GABA during storage, and developing emerging enrichment technologies without affecting food quality and other active ingredients. A better understanding of GABA may introduce new windows for its application in developing functional foods.