Abstract:Changes in the amount of 5-hydroxymethylfurfural (5-HMF), a harmful substance, in dried Ganoderma lucidum extract mixtures were investigated in order to find the most suitable drying method. The G. lucidum extract mixtures were processed using the following drying methods: spray, vacuum, infrared, heat pump, hot air, and vacuum freeze-drying. The 5-HMF content under different process parameters was measured. In the case of the spray drying method, the 5-HMF content increased initially and then decreased when the feed rate and air flow were gradually increased. In the vacuum drying method, the increase of drying temperature or material thickness led to an increase in 5-HMF content, and the 5-HMF and moisture content decreased as the vacuum degree increased (P<0.05). The 5-HMF content increased with the increase of temperature in the infrared, heat pump and hot air drying methods. The 5-HMF content of the samples after vacuum freeze-drying was 779.29 mg/kg, and the processing time, 50 h, was the longest of all the drying methods. The 5-HMF and moisture content of the sample obtained by vacuum drying under each optimal scheme were 774.32 mg/kg and 4.97%, respectively, and the processing time, 17 h, was the shortest of all the methods. However, the sample obtained from vacuum drying was dark brown, brittle, and hard, and was not easily redissolved. Considering the content of 5-HMF and drying time, as well as other factors, the vacuum drying method should be preferred, but further measures should be taken to improve the appearance and re-solubility of the product.
