Bidirectional Solid-State Fermentation of Highland Barley by Edible Fungi to Improve Its Functional Components, Antioxidant Activity and Texture Characteristics.

In food industry, the characteristics of food substrate could be improved through its bidirectional solid-state fermentation (BSF) by fungi, because the functional components were produced during BSF. Six edible fungi were selected for BSF to study their effects on highland barley properties, such as functional components, antioxidant activity, and texture characteristics. After BSF, the triterpenes content in Ganoderma lucidum and Ganoderma leucocontextum samples increased by 76.57 and 205.98%, respectively, and the flavonoids content increased by 62.40% (Phellinus igniarius). Protein content in all tests increased significantly, with a maximal increase of 406.11% (P. igniarius). Proportion of indispensable amino acids increased significantly, with the maximum increase of 28.22%. Lysine content increased largest by 437.34% to 3.310 mg/g (Flammulina velutipes). For antioxidant activity, ABTS radical scavenging activity showed the maximal improvement, with an increase of 1268.95%. Low-field NMR results indicated a changed water status of highland barley after fermentation, which could result in changes in texture characteristics of highland barley. Texture analysis showed that the hardness and chewiness of the fermented product decreased markedly especially in Ganoderma lucidum sample with a decrease of 77.96% and 58.60%, respectively. The decrease indicated a significant improvement in the taste of highland barley. The results showed that BSF is an effective technology to increase the quality of highland barley and provide a new direction for the production of functional foods.

Cross Talk between GlAQP and NOX Modulates the Effects of ROS Balance on Ganoderic Acid Biosynthesis of Ganoderma lucidum under Water Stress.

Water stress affects both the growth and development of filamentous fungi; however, the mechanisms underlying their response to water stress remain unclear. In this study, water stress was found to increase intracellular reactive oxygen species (ROS) level, ganoderic acid (GA) content, and NADPH oxidase (NOX) activity of Ganoderma lucidum by 148.45%, 75.32%, and 161.61%, respectively. Water stress induced the expression of the G. lucidum aquaporin (GlAQP) gene, which facilitated water transfer for microbial growth. Compared to wild type (WT), exposure to water stress increased growth inhibition rate, ROS level, and GA content of GlAQP-silenced strains by 37 to 41%, 36 to 38%, and 25%, respectively. Furthermore, at the early stage of fermentation in GlAQP-silenced strains, water stress resulted in 16 to 17% and 9 to 10% lower ROS level and GA content compared to WT, respectively. However, in GlAQP-overexpressing strains, ROS level and GA content were 22 to 24% and 12 to 13% higher than in WT, respectively. In GlAQP-silenced strains, water stress at the late stage resulted in 35 to 37% and 29 to 30% higher ROS level and GA content, respectively, while in GlAQP-overexpressing strains, levels were 16 to 17% and 9% lower than WT, respectively. Cross talk between GlAQP and NOX positively regulated the GA biosynthesis of G. lucidum via ROS under water stress at the early stage but this regulation became negative at the late stage. This study deepens the understanding of fungal signaling transduction under water stress and provides a reference for analyzing environmental factors that influence the regulation of the fungal secondary metabolism. IMPORTANCE Ganoderma lucidum is an advanced basidiomycete that produces medicinally active secondary metabolites (especially ganoderic acid [GA]) with high commercial value. Water stress imposes an important environmental challenge to G. lucidum. The mechanism of GA biosynthesis under water stress and the role of G. lucidum aquaporin (GlAQP) during its biosynthesis remain unclear. Moreover, the effect of the relationship between GlAQP and NADPH oxidase (NOX) on the level of reactive oxygen species and GA production under water stress is unknown. This study provides information on the biological response mechanism of G. lucidum to water stress. A new theory on the cell signaling cascade of G. lucidum tolerance to water stress is provided that also incorporates the biosynthesis of secondary metabolites involved in NOX and GlAQP.

Roles of water in improved production of mycelial biomass and lignocellulose-degrading enzymes by water-supply solid-state fermentation of Ganoderma lucidum.

The liquid phase was proved to be a significant influencing factor among the three phases in solid-state fermentation (SSF), which determined water control was crucial. However, obvious water loss was caused by microbial utilization and moisture evaporation. Super absorbent polymer (SAP) was utilized to supply water in SSF owing to its high water-holding capacity. Adding 0.15% SAP could significantly increase the biomass of Ganoderma lucidum by 33.59% and promote filter paper activity (FPA), endocellulase activity and laccase activity by 27.11%, 29.14% and 47.39%, respectively. Water states of fermentation substrates were detected by the low-field nuclear magnetic resonance (LF-NMR). Results revealed that water present and lost was dominated by the capillary water. At the end of fermentation, the capillary water content (Ccw) in water-supply SSF was 20.48% and 17.20% higher than that in static SSF and cold-model SSF. The relaxation time of the capillary water was reduced by 56.53% in water-supply SSF and by 53.40% in static SSF, but it just reduced by 6.82% in cold-model SSF. In addition, the Ccw in SSF had a high correlation with the biomass and lignocellulose-degrading enzyme activities of G. lucidum. These results clearly demonstrated that capillary water played a very important role in improved production of G. lucidum.