Frying of sliced shallot (Allium ascalonium): Product quality and kinetic models at different frying temperatures

Abstract

Shallot (Allium ascalonium) is a popular ingredient in Asian cuisine including Vietnam. Fried shallot is widely used in the preparation of various traditional meals. However, the kinetic models of sliced shallot frying process have not been considered. In this study, the effects of frying temperature on changes in moisture content, oil uptake, hardness and instrumental color of sliced shallot were examined and their kinetic models were investigated. Increase in frying temperature from 130 to 150oC accelerated the moisture loss and oil uptake content of the shallot in order to achieve the equilibrium values within a shorter frying time. At the frying temperature of 130, 140 and 150oC, the final moisture content of fried shallot was 2.60 ± 0.36, 2.92 ± 0.35 and 1.64 ± 0.43 g/100g, while the oil uptake content was 47.26 ± 1.42, 46.36 ± 1.45 and 46.07 ± 0.40 g/100g dry matter, respectively. During the first step of frying, the hardness of shallot was slightly reduced but it was greatly enhanced and achieved maximum at the end of the process. In addition, the darkness level of fried shallot witnessed the same upward trend during frying. Based on the experimental data, the appropriate kinetic models for changes in moisture content, oil uptake level, hardness and color values of sliced shallot during the frying process at different temperatures were being developed with the correlation (R2) larger than 0.95. Page model appeared to be the most appropriate for moisture loss and oil uptake whilst the three models including Newton model, Wang & Singh model, Third-order Polynomial model were shown to be suitable for changes in hardness of fried shallot. However, the changes in color values only fit the Third-order Polynomial model. In conclusion, this study could predict the effects of temperature and time on the shallot quality during the frying process.