Impacts of combined ultrasound and freeze-drying pretreatments on the frying quality of plantain chips during deep fat frying

Abstract

Background

In a bid to lower the oil uptake and moisture content of plantain chips during deep fat frying, plantain chips prior to frying were pretreated in ultrasound with distilled water (UP), freeze-drying (FP), and ultrasound-assisted freeze-drying (UFP). Ultrasound frequency of 20 kHz, power of 600 W, and time of 10 min were used for the UP. Freeze-drying was done at a temperature of −34°C and pressure of 45 Pa for 16 h. The pretreated and untreated samples were subjected to frying at a temperature of 160°C for 2, 4, 6, 8, and 10 min.

Results

The lowest moisture content and oil uptake were obtained in FP and UFP fried samples. The percentage oil reduction for FP and UFP fried samples at frying time of 10 min was 73.91% and 74.01%, respectively, compared with the untreated. The effective moisture diffusivity obtained in this work ranged from 4.89 × 10⁻⁹ to 5.54 × 10⁻⁹ m² s⁻¹. The sensory results showed that FP and UFP fried samples were significantly preferred by the panelists compared to the UP and untreated fried samples. However, UFP had a negative effect on the color quality of the fried plantain chips.

Conclusion

This work therefore showed that ultrasound-freeze-drying pretreatment is a novel technique that can significantly reduce the moisture content and oil uptake of plantain chips during frying, thus promoting healthy and safe consumption of fried plantain chips. Furthermore, the information on frying kinetics obtained from this work would be useful in the design and control of an efficient frying system in the food industry.