Non-destructive measurement of internal fruit quality using SQUID-NMR techniques

[摘要] ENGLISH ABSTRACT: The SQUID-NMR technique has been increasingly recommended by many researchersas holding a lot of potential, and it is believed it will become an invaluabletool for non-destructive evaluation in the future. Most of its potential is yet to beexploited. Non-destructive quality control of food products is one of the applicationswhere such a system is being tried.Much of the progress that has been made in improving such a system to the presentdegree of user friendliness and cost effectiveness shows that, with more effort, itwould be possible to implement the technology for on-line sorting, and possibly toreduce it down to hand-held devices.The goal was to investigate the feasibility of the internal fruit quality measurementsusing the NMR technique, and to develop a SQUID system suitable for SQUID-NMRapplication, intended for a later integration in a full SQUID-NMR system.A working dc SQUID was manufactured on an YBCO (Y Ba2Cu3O7���� ) thin filmdeposited on a 10 mm x 10 mm MgO substrate. The SQUID was made of microbridgeJosephson junctions, patterned by using the double resist laser lithographymethod, implemented during the course of this manufacturing process. The test ofthe SQUID showed a non-hysteretic current-voltage characteristic. Under the actionof bringing a magnet closer to the SQUID under test, and then retracting it, themodulation of the I-V curve was observed. The critical current of the SQUID was20 A and the resistance was 5.5A series of experiments were performed on destructive measurements of the sugarcontent in table grapes using NMR, in order to evaluate the feasibility of this technique.The total sugars(TSS) measurements of the same samples were carried outby refractometry, chosen as a conventional method for validation. The NMR measurementswere evaluated to be 5.4% precise and have an accuracy of 9.3% relativeto the refractometry measurements.A further series of experiments were carried out on a high-Tc SQUID-NMR system. A high correlation coefficient (0.85) of the increasing values of the T1 and T2 relaxationtimes to the decreasing concentration of sugar (sucrose) in water was obtained.Non-destructive measurements T1 and T2 in table grapes suggested a possible predictionof sugar content in table grapes from the values of T1 or T2. This technique alsopresented many advantages compared to the conventional high field NMR technique,such as the fast measurements that do not require spectral processing, the ease ofsample preparation, and its non-destructive nature.

[发布机构] Stellenbosch University