Evaluation of amino group losses for monitoring storage of infant cereals containing milk

A fluorometric method was applied to determine amino group losses in infant cereals containing powdered milk, using o-phthaldialdehyde. The studies were carried out in four infant cereal samples, including gluten and gluten-free products, which were stored at 28 °C for 4 or 16 weeks or under modified water activity conditions at 25 or 55 °C for 1, 2, 3 or 4 weeks. Precision studies showed coefficients of variation of 0.28% and 0.51% for “7-cereals + soy + milk” and “rice–corn + milk” respectively. Losses of amino groups were detected under all time, temperature and water activity conditions assayed. At 28 °C, the losses reached values of 0.6–3% after 4 weeks and 1.7–7% after 16 weeks. Higher water activity (0.65) produced a major loss (17.6–21.5%) after four weeks of storage at 25 °C in all samples. These losses increased to 82–94% after four weeks of storage under drastic conditions (55 °C and aw=0.65). The method assayed is useful to monitor nutritional modifications produced during the long shelf-life of these products.