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Title: Effects of acid, salt and soaking time on the dielectric properties of acidified vegetables

Author
item KOSKINIEMI, CRAIG - North Carolina State University
item Truong, Van Den
item McFeeters, Roger
item SIMUNOVIC, JOSIP - North Carolina State University

Submitted to: International Journal of Food Properties
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2011
Publication Date: 7/1/2013
Citation: Koskiniemi, C.B., Truong, V., McFeeters, R.F., Simunovic, J. 2013. Effects of acid, salt and soaking time on the dielectric properties of acidified vegetables. International Journal of Food Properties. 16:917-927.

Interpretive Summary: Knowledge of the dielectric properties of foods is a critical aspect to any microwave process, as it characterizes the ability of materials to store and convert electromagnetic energy into heat. In order to design a continuous microwave process for pasteurization of acidified vegetables, equilibration phenomena in acid and salt solutions must be examined with regards to changes in dielectric properties. The objective of this study was to examine the effects of acid and salt concentration on the dielectric properties of acidified vegetables. Broccoli florets, red pepper pieces and sweet potato cubes (1.2cm) were acidified in solutions of 1-2% sodium chloride with 0.5-2% citric acid. Dielectric properties were measured at 915 MHz from 25 to 100 °C after 0, 4, and 24 h equilibration periods in the solutions. The results indicated that equilibration occurred within 4 h of salting and acidification. Acid and salt concentration had no significant effect on the dielectric constant. However, dielectric constant was significantly different among vegetables (p<0.05). Dielectric loss factor was not affected by acid, but significantly increased with salt concentration. This research provides necessary information to apply microwave heating technology in processing of acidified vegetables.

Technical Abstract: In order to design a continuous microwave process for pasteurization of acidified vegetables, equilibration phenomena in acid and salt solutions must be examined with regards to changes in dielectric properties. The objective of this study was to examine the effects of acid and salt concentration on the dielectric properties of acidified vegetables. Broccoli florets and sweetpotato cubes (1.2cm) were blanched to facilitate acid and salt equilibration by heating for 15 s in boiling de-ionized water. Red bell pepper cubes were not blanched. The vegetable samples were then acidified in solutions of 1-2% sodium chloride with 0.5-2% citric acid. Dielectric properties were measured at 915 MHz from 25 to 100°C after 0, 4, and 24 h soaking periods in the solutions using an open-ended coaxial probe connected to a network analyzer. Equilibration occurred within 4 h of salting and acidification. Acid and salt concentration had no significant effect on the dielectric constant. However, dielectric constant was significantly different among vegetables (p<0.05). Dielectric loss factor was not affected by acid, but significantly increased with salt concentration. These results provide necessary dielectric property information to apply microwave heating technology in processing of acidified vegetables.