Improving the energy efficiency and the quality of fried products using a novel vacuum frying assisted by combined ultrasound and microwave technology

Abstract

Abstract The effectiveness of hybrid frying based on vacuum frying with application of ultrasound (USVF) and combined ultrasound and microwave (USMVF) enhancement was presented in this study. The ultrasound revealed significantly the “vibration effect”, and the combination of ultrasound and microwave had a synergistic effect on the energy efficiency and quality attributes of vacuum fried potato chips, shortening the frying time by 36.4%–54.5% and improving the effective moisture diffusivity by 60.5%–144.5% with the ultrasound power levels ranged 300 W–600 W. The USMVF process was found to consume about 34.9%–48.3% less energy compared to that in VF. The oil uptake of vacuum fried potato chips was reduced by 27.4%–32.3%, the texture (crispness) and the color was greatly improved, and the volume shrinkage and water activity were diminished by the combination of ultrasound and microwave. The moisture loss kinetics and quality parameters were also improved markedly when higher ultrasound power was used. The SEM revealed a more porous microstructure in USMVF samples. The vacuum frying technology that combines both ultrasound and microwave found to be much more effective technology in terms of energy efficiency and product quality. Industrial relevance In recent years, the fruit-vegetable crisp produced by vacuum frying (VF) has been widely concerned due to natural color, superior sensory and nutritional quality. However, there are certain defects in the application of VF technology, such as backward heating method, low efficiency especially with low-temperature frying, relatively high oil uptake in products and the quality attributes of fried products need to be improved. One of the recommended methods to overcome the limitation of low-temperature dehydration is to utilize the synergistic effect of different energy, which providing the energy by a combination of several mechanisms, such as vacuum frying with microwave radiation, or with ultrasounds, which leads to a significant improvement in energy efficiency and quality attributes of fried fruits and vegetables. Focused on these problems, this research investigated the effects of low-frequency ultrasound and the synergistic effect of ultrasound and microwave on the efficiency and quality of vacuum frying with potato chips as experimental material. The effect of variable hybrid drying conditions was analyzed with different power levels of ultrasound. The application of ultrasound showed improve the moisture loss rate and quality attributes of vacuum fried products as a non-thermal technology. The combination of ultrasound and microwave in vacuum frying system achieved better energy efficiency, lower oil uptake, crispier, better shaped and colored products compared to the VF produced samples. The storage stability and safety of vacuum fried products also improved by the combined ultrasound and microwave. Thereby, the experimental results will contribute to the development of modern vacuum frying technologies of fruits and vegetables, which reduced the oil uptake and retained their high quality, with reduced process time and lower power consumption at much lower frying temperature.