Temperature control for high-quality oil-free sweet potato CHIPS produced by microwave rotary drying under vacuum

Abstract

Healthy and convenient foods have drawn consumers' attention and represent an opportunity for the food industry. This study is about the production of sliced sweet potato snacks by microwave vacuum drying (MWVD) in a rotary container with temperature control by power modulation. The average temperature of samples' surfaces was measured with an infrared sensor and controlled at 60 °C by a PID controller. The resulting product properties were compared to those from freeze- (FD), air- (AD), and conductive multiflash (KMFD) drying. Rotary container coupled to the temperature control guaranteed uniform heating and resulted in chips without burnt spots in MWVD. MWVD and KMFD produced sweet potato chips in less than 3 h, while AD and FD required 16 h. The drying method influenced chips' porosity: 58% (FD), 44% (MWVD), 39% (KMFD), and 18% (AD). AD chips had a compact structure, while FD chips were spongy with small pores. MWVD and KMFD expanded the material during fast water evaporation under vacuum, creating large and irregular pores. The puncture tests of these chips resulted in jagged force-penetration curves, typical of crispy products, with higher acceptance. Therefore, MWVD and KMFD have the potential for the industrial production of high-quality oil-free and crispy chips.