Infrared, Convective, and Sequential Infrared and Convective Drying of Wine Grape Pomace

Abstract

In this paper, effects of infrared drying and/or convective drying on drying kinetics of wine grape pomace were examined, and drying characteristics, sterilizing efficacy, and effects on pomace's polyphenols and pro-anthocyanidins content were determined. Infrared drying had the highest drying rate, which reduced the drying time by more than 47.3% compared with other methods. Sequential infrared and convective drying had a faster drying rate than convective drying. Five empirical models were chosen to fit the drying curves and the Midilli et al. model had the highest R ² and lowest RMSE and χ ² . For sterilizing efficacy, infrared drying and convective drying (90°C) performed the best with minimum survival yeasts, molds and bacteria, while higher drying temperatures resulted in better pasteurization efficacy. Sequential infrared and convective drying did not yield a satisfactory sterilizing effect, with efficacy not being enhanced by prolonging the infrared drying. The wine grape pomace dried by infrared drying had the highest content of polyphenols and pro-anthocyanidins, showing that decreasing the drying temperature led to less damage to these two substances.

Keywords:

• Convective drying
• Infrared drying
• Mathematical models
• Sterilization
• Wine grape pomace

ACKNOWLEDGMENTS

The authors want to thank Han Qi'an (College of Food Science and Engineering, Northwest A&F University) for the instruction on microorganism counting and Martin Parker (Northwest A&F University) for help with writing this paper.

Notes

Values in the same row with different letters (a–c) are significantly different at p < 0.05.