SCALE TRANSLATIONS OF FIRMNESS TESTS ON FRUITS

In many fruits and vegetables, it is desired to replace destructive fi rmness measurement methods by nondestructive ones. The inevitable ques tion is to what degree do two firmness measurement methods agree? The present article proposes a new approach for method comparison in firmn ess tests of fruits, by optimal translation of the readings taken on t he scale of one test, to the scale of another test and vice versa. The proposed scale translation mode is based on minimizing the sum of squ ares of the differences between the absolute values of the Fast Fourie r Transform (FFT) series, derived from the readings of the compared me asurement methods. The line taken is illustrated by a comparative stud y on a large sample of Red Delicious apples, assessing the performance of a nondestructive fruit firmness sensor versus the conventional des tructive test which measures the applied piercing force on the fruit b y a penetrometer.