Radio frequency (RF) was applied to heat Cordyceps militaris for the purpose of quality evaluation and microorganism control. RF heating caused gradual temperature increases ranging from 59.6 to 63.8°C, resulting in good heating uniformity and uniform temperature distribution. Compared with conventional high pressure steam (HPS), RF heating resulted in significant (p < .05) higher total phenolic, flavonoids, and cordycepin contents of C. militaris. In addition to higher reduction of total aerobic bacteria counts, bitterness taste value increased from 2.35 (unpasteurized) to 4.79 (HPS). Umami value significantly decreased from 13.58 (unpasteurized sample) to 12.13 (HPS treated sample). Nuclear magnetic resonance analysis showed that 20 min of RF significantly reduced the loss of water mobility than HPS. Principal component analysis of taste characteristics indicated distinct differences between RF and HPS treated samples. Hierarchical clustering analysis also revealed higher similarity between RF heated samples and the unpasteurized one.
Practical applications
Cordyceps militaris is an edible and medicinal mushroom with high nutritional quality. Results of the present study indicate that radio frequency (RF) contributed to higher umami taste, higher retention of bioactive compounds, and higher water mobility of C. militaris. Therefore, this process can be used to develop a promising alternative to conventional thermal method for the processing of C. militaris. It is highly possible that RF could be applied to healthy food industries.
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