A MODIFIED HAHN ECHO PULSE SEQUENCE FOR PROTON MAGNETIC-RESONANCE (H-1-MR) MEASUREMENTS OF PERCENT SOLUBLE SOLIDS OF FRUITS

A fruit ripeness sensor being developed uses proton magnetic resonance to nondestructively determine percent by weight soluble solids in who le fruits. Results were compared to refractometer measurements of solu ble solids content. In many fruits, soluble solids is nearly equivalen t to percent sugar content which is in turn related to ripeness. The p rinciple used measures the effect of simple sugars (which constitute t he majority of the soluble solids in many fruits) on Self diffusion of water. Self diffusion can be measured using the Hahn Echo pulse seque nce in the presence of a static magnetic field gradient. A modificatio n of the Hahn Echo pulse sequence is described which solved two practi cal problems related to the application of the technique to rapid sort ing; it increased the speed of the measurement and it greatly reduced the effects of sample size and shape. The improvement was demonstrated using experiments on cylindrical samples cut from apples.