Nutritional and 13-Week Subchronic Toxicological Evaluation of Lignosus rhinocerotis Mycelium in Sprague-Dawley Rats

Lignosus rhinocerotis (Tiger’s Milk mushroom) is a novel mushroom with sclerotium belonging to the Polyporaceae family and has been reported widely to possess anti-cancer, anti-cough, antioxidant, gastro-protective, immuno-modulating, and neurite-stimulating properties. As numerous studies have proven the tremendous medicinal values of L. rhinocerotis, it is necessary to understand its nutrition as well as its safety for the recipient. Previous research on L. rhinocerotis has mainly focused on the naturally occurring sclerotium and may have overlooked mushroom mycelia from submerged liquid fermentation, which ensures a high uniform quantitative biomass production as well as a high biological value. Hence, this is the first report on the evaluation of nutrition and 13-week repeated oral toxicity of L. rhinocerotis mycelium (LRM). The LRM powder contained 9.0 ± 4.2% moisture, 1.9 ± 1.3% ash, 1.6 ± 2.2% crude lipid, 8.4 ± 5.3% crude protein, 79.3 ± 4.6% carbohydrate, and 364 kcal/100 g energy. The total free amino acid ranged from 349 to 5636 mg/100 g and the umami index of freeze-dried LRM powder was 0.37. For safety assessment, ninety-six rats were divided into four groups, each consisting of twelve male and twelve female rats. Test articles were administered by oral gavage to rats at 850, 1700, and 3400 mg/kg body weight/day for 13 weeks and reverse osmosis water was used as the control. All animals survived to the end of the study. During the experiment period, no abnormal changes were observed in clinical signs, body weight, or ophthalmological examinations. No adverse or test article-related differences were found in urinalysis, hematology, or serum biochemistry parameters between the treatment and control groups. Necropsy and histopathological examination indicated no treatment-related changes. According to the above results, the no-observed-adverse-effect level (NOAEL) of L. rhinocerotis was identified to be greater than 3400 mg/kg body weight (BW)/day in Sprague–Dawley rats.