Furosine content, loss of o-phthaldiadehyde reactivity, fluorescence and colour in stored enteral formulas

Heat effects induced during the storage of enteral formula under laboratory and industrial conditions were evaluated using the following indicators: furosine; loss of available amino groups, measured by decrease in o-phthaldialdehyde (OPA) reactivity; fluorescence associated with the Maillard reaction (345 nm excitation, 415 nm emission); and colour (absorbance at 420 nm). The storage of formulas A and B (with different protein content) at 4, 20 and 30degreesC during 12, 24 and 36 weeks produced an increase in furosine values. Under industrial storage conditions at 55degreesC for between 1 and 12 weeks the behaviour of furosine differed between the two types of formulas. In Formula A (lesser protein content), there was a decrease in furosine level after the third week, whereas in formula B (greater protein content) a decrease was observed after the eighth week. The loss of OPA reactivity reached 18% and 22%, respectively, for formula B and formula A stored at 30degreesC for 36 weeks. In adverse storage conditions (55degreesC), the loss of OPA reactivity reached 50%. Fluorescence intensity (FI) and absorbance at 420 nm increased at all time/temperatures assayed. It reached values of 22.5 and 27.5 for FI and 0.161 and 0.173 for A(420) <x>, respectively, for formula A and B, stored for 36 weeks at 30degreesC. Furosine, loss of OPA reactivity, fluorescence intensity and colour are useful indicators of nonenzymatic browning during storage of enteral formulas.