The first part of the present publication treats first-order quality attribute variations in a flow-through type food reactor assembled of serially connected units. Approximative formulae have been created for decreasing time-dependent attribute changes to calculate the average outlet attribute intensity, introducing relations between the relative exit attribute intensity and the rate constant. An example is given to help better understanding. The second part analyzes how the concept of equivalent heat treatment time, widely used in the sterilization and pasteurization processes of packed food, can be interpreted in the case of flow-through type treatments. It has been concluded that the ’plug-flow time equivalent’ always has an additive nature (irrespective of the reaction order of the empirical kinetics). The average equivalent exhibits this additive nature only in case of zero- and first-order variations. This part of the publication is also supplemented by an example.