Purpose: Our objective was to determine the effect of brine acetic acid concentration and packing conditions on the acidification rate of hard boiled eggs.
Methods: Hard boiled eggs were acidified (9 eggs per 32 oz glass jar) at various conditions (brine temperature / heat treatment of filled jars / post-packing temperature): (a) 25 ºC / none / 25 ºC, (b) 25 ºC / none / 2 ºC, (c) 85 ºC / none / 25 ºC, (d) 25 ºC, 100 ºC for 16 min / 25 ºC. Three brine concentrations were evaluated (7.5, 4.9, and 2.5% acetic acid (AA)) and egg pH values (whole, yolk, 4 points within egg) were measured from 4 to 144 h, with eggs equilibrating at pH 3.8, 4.0, and 4.3, respectively. Experiments were conducted in triplicate. Multiple linear regression analysis was conducted to evaluate the effect on pH values at the center of the yolk.
Results: Regression analysis (R2 = 0.94) showed no significant interaction between packing conditions and time (P > 0.05). Only the eggs that were acidified and kept refrigerated showed a significantly slower time to reach pH 4.6 (P < 0.0001). The interaction between brine concentration and acidification time was significant (P < 0.0001). Higher concentrations of brine decreased egg pH at a faster rate. When using linear regression to predict the time for the yolk center to reach pH 4.6, values ranged from 23.5 h for 7.5% AA brine to 220.3 h for 2.5% AA brine.
Significance: These results demonstrate the importance of conducting acidification studies with proper pH measurements to determine safe conditions to manufacture commercially stable pickled eggs.