Acid Diffusion in Solid Foods

Foods acidified to pH levels below 4.5 can be thermally treated at lower temperatures under pasteurization conditions offering reduced thermal damage to product quality. Considering practical criterion, the main objective of this study was to investigate the proper acidification procedures of solid food particles immersed in liquid solutions. This was performed by testing a variety of factors, including particle type and size, temperature, and type and concentration of acids. Furthermore, the minimum acidification time of food particles was also determined. A standard model for mass transfer (e.g. Fick’s second law) was applied. Mass diffusion coefficients (DAB) were calculated based on experimental data. Average values of DAB were in the range of 10-8 to 10-10 m2/s and in agreement with existing literature data. Minimum acidification times varied depending on the type of acid, food, and treatment temperature, and ranged between 7 to 26 min. Meat particles were slowest to acidify, and acetic acid and tomato juice acidified by citric acid were the strongest acidifying agents.