Activity, thermostability and isozymes of superoxide dismutase in 17 edible mushrooms

Mnsod1 promotes the development of Pleurotus ostreatus and enhances the tolerance of mycelia to heat stress

Background

Superoxide dismutases (SODs, EC 1.15.1.1) are defense proteins that can be used as sweepers to clear reactive oxygen species (ROS). They have been widely studied in the plant. Intensive research demonstrates that SOD plays an essential role in plants. However, in Pleurotus ostreatus, the function and regulatory pathway of SOD in the growth and development and the abiotic stress response have not been clear.

Results

In this study, three MnSOD-encoding genes of the P. ostreatus CCMSSC00389 strain were cloned and identified. Mnsod1, Mnsod2, and Mnsod3 were interrupted by 3, 7, and 2 introns, and encoded proteins of 204, 220, and 344 amino acids, respectively. By comparing the relative expression of three MnSOD-encoding genes in mycelia, the results showed that the gene with the highest primary expression was Mnsod1. Subsequently, the function of P. ostreatus Mnsod1 was explored by overexpression (OE) and RNA interference (RNAi). The results showed that during the growth and development of P. ostreatus, MnSOD1 protein increased gradually from mycelia to the fruiting body, but decreased in spores. The change of Mnsod1 transcription level was not consistent with the changing trend of MnSOD1 protein. Further studies showed that during primordia formation, the expression of Mnsod1 gradually increased, reaching a peak at 48 h, and the transcription level was 2.05-folds compared to control. H₂O₂ content progressively accumulated during the formation of primordia, and its change trend was similar to that of Mnsod1 transcription. OE-Mnsod1-1 and OE-Mnsod1-21 strains accelerated the formation of primordia. The results suggested that Mnsod1 may participate in the formation rate of P. ostreatus primordium by regulating the signal molecule H₂O₂. In addition, OE-Mnsod1-1 and OE-Mnsod1-21 strains shortened the mycelial recovery time after heat stress and improved the tolerance of the strains to 2.5 mM and 5 mM H₂O₂, which showed that Mnsod1 was involved in the response of P. ostreatus mycelium to heat stress.

Conclusions

This study indicates that Mnsod1 plays an active role in the formation of P. ostreatus primordia and the response to abiotic stress.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01878-2.

In vitro digestion and domestic cooking improved the total antioxidant activity and carbohydrate-digestive enzymes inhibitory potential of selected edible mushrooms

This study aimed to investigate the effect of in vitro digestion on the antioxidant activity and carbohydrate-digestive enzymes inhibitory potential of five edible mushrooms after subjected to four domestic cooking; namely, boiling, microwaving, steaming and pressure-cooking. The water extracts of raw (uncooked), cooked and in vitro digested mushrooms were compared for their water-soluble phenolic content (WPC), total flavonoid content (TFC), ferric reducing antioxidant power (FRAP), radical scavenging activity (TEAC and DPPH), anti-α-amylase and anti-α-glucosidase activities. Among the raw samples, Lentinula edodes possessed the highest antioxidant activities (FRAP, TEAC, DPPH) and WPC while Pleurotus sajor-caju displayed the highest TFC, anti-α-amylase and anti-α-glucosidase activities. The antioxidant and carbohydrate-digestive enzyme inhibitory activities significantly varied according to mushroom species and cooking methods applied. Short duration of microwaving (Agaricus bisporus and Flammulina velutipes), boiling (Auricularia polytricha) and pressure cooking (L. edodes and P. sajor-caju) yielded the best antioxidant and carbohydrate-digestive enzymes inhibition values in the mushroom extracts. TFC was positively correlated with the antioxidant activities and anti-α-glucosidase activity in the mushroom extracts. In vitro digestion significantly improved the total antioxidant and anti-α-glucosidase activities but decreased the anti-α-amylase activity in the cooked mushroom extracts. Principle component analysis showed that in vitro digestion and the cooking process accounted for respective 48.9% and 19.7% of variation in the observed activities. Domestic cooking and in vitro digestion could potentiate the total antioxidant and carbohydrate-digestive enzymes inhibitory activities in the selected water extract of edible mushrooms.

Impact of optimised cooking on the antioxidant activity in edible mushrooms

This study aimed to investigate the effect of four cooking methods with different durations on the in vitro antioxidant activities of five edible mushrooms, namely Agaricus bisporus, Flammulina velutipes, Lentinula edodes, Pleurotus ostreatus and Pleurotus eryngii. Among the raw samples, A. bisporus showed the highest total antioxidant activity (reducing power and radical scavenging), total flavonoid, ascorbic acid and water soluble phenolic contents. Short-duration steam cooking (3 min) increased the total flavonoid and ascorbic acid while prolonged pressure cooking (15 min) reduced the water soluble phenolic content in the mushrooms. The retention of antioxidant value in the mushrooms varied with the variety of mushroom after the cooking process. The cooking duration significantly affected the ascorbic acid in the mushrooms regardless of cooking method. To achieve the best antioxidant values, steam cooking was preferred for F. velutipes (1.5 min), P. ostreatus (4.5 min) and L. edodes (4.5 min) while microwave cooking for 1.5 min was a better choice for A. bisporus. Pressure cooked P. eryngii showed the best overall antioxidant value among the cooked samples. Optimised cooking method including pressure cooking could increase the antioxidant values in the edible mushrooms.