A study of the effects of pH and water activity on the N-nitrosopiperidine formation in a protein-based liquid system

To estimate the risk of N-nitrosopiperidine (NPIP) formation from piperidine in dry fermented sausages, the influences of pH and water activity (a w) were investigated using two protein-based liquid systems. In the first system (NaCl system), sodium chloride solutions (0-30 %) were used to reduce the a w (between 0.99 and. 0.79) at two pH values (pH 4.0 and 5.0). At pH 4.0, reducing a w through the addition of salt significantly decreased the level of NPIP from 30.8 ± 2.1 to 6.2 ± 0.2 μg/ml. However, these extreme NaCl concentrations do not exist in dry fermented sausages (only ca. 3 %). A second system (polyethylene glycol (PEG) system), in which PEG was added to reduce a w, was also developed. A rotatable central composite design (RCCD) was used to evaluate the influences of pH (3.0–7.0), a w (0.80–0.99) and incubation time (1.3–98.7 h) on the response NPIP in the PEG system. A quadratic polynomial model was built to describe the response behaviour as a function of the factors examined. The response surface plots showed a significant increase in NPIP levels at longer incubation times, higher a w and lower pH. Within the experimental domain, at 79 h, pH 3.8 and a w 0.952, maximum NPIP levels of 110.0 and 113.6 μg/ml were predicted and measured, respectively. The model demonstrated the importance of controlling the pH and a w during the production of the sausages.