Enhancing submerged fermentation of Antrodia camphorata by low-frequency alternating magnetic field

Antrodia camphorata (A. camphorata) is a precious edible medicinal basidiomycete fungus with high nutritional and commercial value (Kuang, Li, Wang, Qiao, and Ye, 2021). Literature has shown that A. camphorata possesses a wide array of beneficial bioactivities, such as hepatoprotective (Li et al., 2017), antioxidant (Chu et al., 2022), anti-inflammatory (Lu, Chao, Hsu, and Chang, 2021), anti-tumor (Huang et al., 2019), and anti-obesity (Chang et al., 2018). These pharmaceutical activities of A. camphorata are believed to be attributed to its various bioactive metabolites, such as polysaccharides, triterpenoids, ubiquinone derivatives, succinic acids, and maleic acid derivatives (Zhang et al., 2019). However, the wild fruiting bodies of A. camphorata are scarce and expensive due to the host specificity and slow growth rate in nature (Shu, Wu, Ko, Lin, and Jaiswal, 2016; Zhang et al., 2019). Therefore, biotechnological cultivation methods, including basswood cultivation, solid-state fermentation, and submerged fermentation, have been widely applied to obtain sufficient quantities of A. camphorata with high efficiency and high quality. Submerged fermentation is an effective strategy for producing A. camphorata mycelia with valuable bioactive metabolites (Meng et al., 2021). In comparison with basswood cultivation and solid-state fermentation, submerged fermentation possesses a shorter fermentation period, easier monitoring, and control of critical operational parameters. It is feasible for large-scale industrial production to satisfy the increasing consumption demand of A. camphorata (Meng et al., 2021; Zhang et al., 2019).

As a non-thermal physical processing technology, the magnetic field has been extensively applied in various food processing in recent years due to its advantages of being non-toxic and pollution-free without a medium (Zhao et al., 2022). Low-frequency (30–300 kHz) alternating magnetic field (LF-AMF) is gradually applied in microbial fermentation since the weak magnetic field can activate microorganisms and promote their growth via electromagnetic waves, thereby promoting microbial metabolism and improving fermentation efficiency (Li, Ma, He, Ren, and Zhou, 2021; Minano, Silva, Souto, and Costa, 2020). Literature has shown that the LF-AMF can produce positive biological effects in the fermentation process by affecting the medium properties, the morphological structure of microbial cells, the design of biological macromolecules, enzyme activities, and gene expression (Li et al., 2021; Liao, Liu, Zhang, Li, and Gao, 2019). However, there are still some limits to the domestic and international research on applying LF-AMF in submerged fermentation. Firstly, one-off stimulation is used chiefly in magnetic field assisted-submerged fermentation, which does not provide a sustained effect because of the rapid decay of the magnetic effect. Secondly, conventional magnetic field equipment has fewer modes and parameters, which is not conducive to finding the optimal mode for promoting microbial fermentation. Thirdly, most studies were conducted at the laboratory level, with few feasibility studies for large-scale industrial applications. Finally, the molecular mechanism of promoting microbial growth via LF-AMF needs to be explored at the cell and gene levels using modern molecular biology techniques. Therefore, our research group designed and developed a magnetic shaker device (Fig. 1A) and a 5 L magnetic field-enhanced fermenter (Fig. 1B), enabling the application of LF-AMF at the laboratory and scale-up levels during the submerged fermentation process.

However, to our knowledge, few studies have applied the LF-AMF technology to producing A. camphorata mycelia by submerged fermentation. Therefore, this study focuses on the following aspects: i) investigate the influence of LF-AMF treatment parameters (magnetic intervention time, magnetic process mode, magnetic exposure time, times of magnetic treatments given, and magnetic induction) on the mycelial biomass of A. camphorata during the submerged fermentation process; ii) characterize the microstructure and the cytomembrane fluidity of A. camphorata mycelia under optimal LF-AMF assisted-submerged fermentation conditions; iii) explore the molecular mechanism of enhancing the product ion of A. camphorata mycelia by LF-AMF treatment according to the gene transcriptional expression features of A. camphorata; iv) study the feasibility of the LF-AMF enhanced the production of A. camphorata mycelia in the scale-up test. The outcome of this work would provide new insights into the efficient, high-quality, and large-scale production of A. camphorata mycelia.

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