Accelerated life testing of frozen green beans (Phaseolus vulgaris, L.) quality loss kinetics: colour and starch

This study uses the information derived from a computational research for the design of accelerated life testing (ALT) to implement experimentally the step stress methodology for the quantification of frozen green beans (Phaseolus vulgar is, L.) colour and starch degradation kinetics. Colour loss and starch degradation were successfully modelled, respectively, by a first-order reversible and apparent first-order kinetics, under dynamic temperature fluctuations. Results show that the step stress produces models with lower regression standard errors than the conventional isothermal methodology, increasing the accuracy of the estimated kinetic parameters. The ALT methodology, produces however, higher confidence intervals for the estimated kinetic parameters, than the isothermal methodology (e.g. colour b-coordinate by the: (i) isothermal methodology: k-15°C = 22.189±0.349 day-1×10-3; and (ii) ALT methodology: k -15°C = 22.189±0.349 day-1×10 -3). Furthermore, as expected, higher Arrhenius activation energies (Ea) were estimated by the ALT step-stress methodology, than by the isothermal methodology (e.g. Hunter total colour difference (TCDH): (i) isothermal methodology: Ea = 106.272±18.67 kJmol -1; and (ii) ALT methodology: Ea = 140.344±18.670 kJ mol-1). Accelerated tests are valuable tools, that can aid the study of quality losses in frozen foods. Although ALT tests increase the complexity of data analysis, they produce satisfactory results, when applied to frozen green beans kinetics of starch and colour losses.