Pretreatment enhanced the physical and antioxidant stability of dried Cordyceps militaris by different drying conditions

Cordyceps militaris has been treated as a functional food and supplementary food for several years. In recent studies, active components in Cordyceps militaris have received great attention and promoted health. Drying technology is a common method and it was applied to Cordyceps spp. many times for extending their shelf life and preserving their nutrients. A combination of pretreatment with drying technology could promote processing efficiency. The aim of this study is to study the effect of pretreatments (Soaking in 0.5% citric acid, boiling, steaming and desiccating) combined with drying method by vacuum dryer (VD) at 50, 60 and 70 °C on physical quality and antioxidant capacity in dried Cordyceps militaris . The result showed pretreatment by soaking in acid 0.5% citric acid, boiling and steaming took drying time more than those desiccating and untreated dried sample to desire the final moisture content (approximately 8% db.). Increasing of drying temperature in VD could reduce drying time. Desiccating prior to drying samples exhibited the highest L* value and the lowest of a* and b* values when compared with other pretreatments. High drying temperature tend to decrease L* value while a* and b* values are increasing. It was due to the occurring of browning reaction during drying process. Desiccating samples showed color value closest to fresh samples. These results were consistent with all photographs from digital camera. The glass transition temperature of all samples was about 39.43-45.82 °C and the highest value was found in the case of desiccating sample. Antioxidant properties, pretreatment by soaking in acid combined with drying at 70 °C by VD showed the highest content of phenolic compound, DPPH and superoxide radical scavenging activity. It was concluded that pretreatment could preserve important substances, for example, cordycepin and adenosine contents of Cordyceps militaris during drying.