In the present work the drying of blueberry (mortiño) leaves (Vaccinium meridionale‐Swartz) was done using a hybrid equipment with infrared drying and normal microwave drying. During the drying tests there was a record of moisture content versus time; samples of leaves were taken during the drying time to analyze total phenol (PT) content, FRAP assay and catechin measures by HPLC‐DAD. The PT analysis shows that its content in dry blueberries, increased 12 times more with the microwave drying than infrarred drying. While FRAP assay shows that dry blueberries antioxidant capacity increased nine times more with microwave process in comparison to infrared process. In the catechins content by HPLC‐DAD in dry blueberries, a better result for concentration was found in microwave process than in infrared process. Similar result occurred for (−) epicatechin. Finally, (+) catechin concentrations in blueberry leaves were compared with commercial materials such as tea leaves and mate leaves.
Practical applications
The consumption of nutraceutical products rich in polyphenols has become important in the last decades. In this research, the effect of microwave and infrared drying on the content of polyphenols on blueberry leaves (Vaccinium meridionale, Swartz) was studied because it was found in previous studies that the leaves contain a potential of polyphenols that can be used to develop nutraceutical beverages similar to tea drinks.
Canadian blueberry leaves (Vaccinium corymbosum) are a potential source of polyphenols (catechins) and antioxidants (FRAP and PT). In this study, the technique of drying by microwave-assisted forced convection was carried out to find the optimal conditions which would allow obtaining the highest polyphenol content under control parameters such as microwave power (100, 300, and 400 W), hot air velocity (0.5 and 2.0 m/s), leaf size (whole and fractional), and temperatures (50, 60, and 70°C). It was found that 30 W/g microwave powers and a 60°C temperature for the process in whole leaves were the optimal conditions that allowed obtaining the highest content of polyphenols (>10 mg/gdb (+) catechin) and antioxidant capacities (100-150 mg GAE/gdb), more than in fractional leaves. It was observed that different hot air velocities did not affect the concentration of the polyphenol's contents; this was verified using the factor mixture analysis technique.
Practical applicationsThe MWFC process allows the preservation of antioxidants in Canadian blueberry leaves (Vaccinium corymbosum). These leaves have high antioxidant capacity for nutraceutical and pharmaceutical uses. This leaf, with high polyphenol content, can be used to obtain extracts in infusions and human food through the mixture of this leaf with multiple powdered products traditionally consumed or food supplements. This research presents the optimal conditions for the preservation of antioxidant compounds in dried Canadian blueberry leaves.
Highlights• Polyphenolic compounds (catechins) are retained under controlled conditions of microwave drying assisted by forced convection in Canadian blueberry leaves.
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