The following exponential function is used in “Peaple” for simulation of changes of acidity, soluble solids content and skin colour coordinates L* and b*:
This function is characterized by three parameters – final asymptote (yfin in above equation), kinetic parameter (k in above equation), and a reference value (yref). That reference value indicates the point at the curve, where the variable t (representing X axis) is equal to 0.
The final asymptote is the mathematical limit for planned simulation. In case of e.g. acidity, we may assume that the final asymptote is TA=0 (each day after harvest acidity gets closer and closer to 0). And we may assume that this is the case for any apple cultivar, grown at any place. In case of soluble solids content the final asymptote depends on selected cultivar, season and growing place.