Abstract: The one-factor-at-a-time method was used to investigate the effect of slice thickness, hot air temperature and loading amount on the hot air drying characteristics of shiitake mushrooms including moisture content on a dry basis, moisture ratio and drying rate. The drying parameters were optimized by response surface methodology with a three-variable, three-level experimental design. The changes in soluble protein content, total phenolics and 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging capacity before and after hot air drying were compared. The results showed that slice thickness, hot air temperature and loading amount in the range of 3–12 mm, 50–70 ℃ and 5–15 g/dm2, respectively were suitable for moisture content on a dry basis, moisture ratio and drying rate. The optimized drying parameters obtained by response surface methodology were as follows: slice thickness, 4.99 mm; hot air temperature, 55.21 ℃; and loading amount, 7.88 g/dm2. The phenolics and DPPH scavenging capacity but not soluble protein or free amino acid contents of shiitake mushrooms were significantly decreased after hot air drying. These results indicate that hot air drying can maintain the contents of protein and free amino acids, but severely destroy the total phenolics and antioxidant activity of shiitake mushrooms.

Key words: shiitake mushroom, hot air drying, response surface optimization, nutrient compounds