1. Characterization of Turkish Olive Varieties with NMR Relaxometry and Magnetic Resonance Imaging Experiments Middle East Technical University, Department of Food Engineering, Ankara, Turkey, Mete Kilercioglu, Baris Ozel, Behic Mert, Mecit Halil Oztop
METU
Abstract
Olive is the fruit of a tree that grows in Mediterranean climate. Olive grows in the regions of Turkey where Mediterranean climate is dominant. Olive being an important export product for Turkey, the quality of the olive and the products derived from olive has gained significant importance. In this study, Nuclear Magnetic Resonance Relaxometry and Magnetic Resonance Imaging experiments was used to characterize different oil varieties in terms of tissue structure, fat and water contents. Experiments were performed on a low resolution (13.52MHz) and on a high resolution system (123.5MHz, SIEMENS Scanner). With the low resolution system Saturation Recovery, CPMG and FID_Spin Echo sequences were used to determine T1, T2 times and water/fat contents respectively. With the high resolution system Multi Slice Multi Echo (MSME), Turbo Spin Echo (TSE) and Gradient Recalled Echo (GRE) sequences were used. T2 times were also calculated from MSME images spatially and GRE sequence which was taken at two different flip angles was used for spatial T1 determination. With the auto set parameters at TSE sequence water and fat suppressed images were taken to compare the different olive varieties. Moisture analysis experiments were conducted in a 105oC oven and oil content values were obtained through Soxhlet extraction. Four different olive varieties were used in this study: (black light, black mega, black sele and green Ayvalik). T1 values were detected between 88 and 173ms at the low resolution system. The highest T1 value was found for green Ayvalık whereas the lowest value belonged to black light olive (due to low fat content). In order to determine T2 spectra, the exponential curves obtained by CPMG experiments were analyzed by Inverse Laplace method. Water and oil are the sources of the protons in olive samples. Different proton pools are observed as different peaks in the olive spectrum. The relaxation spectra of three olive samples showed two peaks whereas green Ayvalık showed three peaks. First peak values of black light, black mega and black sele were detected between ms. Second peak values were between 35-57ms. The area of peaks were found for first and second peaks as %10.21-%21.64 and %68-%80 respectively. The T2 value of second peak of black sele olive and the peak area of black sele were observed as the lowest values. In green Ayvalık, in addition to these two peaks, a third peak was observed. NMR Relaxometry experiments has showed that olives can have characteristic T1 and T2 values. FID_Spin echo experiments were performed after decreasing the moisture content of olives below 15%. Calibration curves were obtained through emulsions prepared by olive and water. Fat and water suppressed images obtained from the high resolution system were consistent with the analytically determined fat/water contents. TSE images were also used to calculate seed/tissue ratio for each variety. In this study NMR and MRI have been used to characteristic olive varieties. The information obtained from this study could be further used as markers for certain chemical parameters of the olives.
Introduction
Magnetic resonance imaging (MRI) is a nondestructive and noninvasive technique that can be used to acquire 2-D and even 3-D images of biological products. The signal of each voxel depends on the physical properties of the sample such as proton density, relaxation times, temperature, diffusion, flow, and local differences in magnetic susceptibility. The information within the images can then be manipulated and used for resolved measurements of concentration, structure, temperature, velocity, and diffusivity . There are two main terms related with MRI technique called as T1 and T2 which are time constants. T1 is the longitudinal relaxation time. It indicates the time required for a substance to recover its initial magnetization caused by the external magnetic field (B0) after RF(radio frequency) pulse treatment. On the other hand, T2 is the "transverse" relaxation time. It is a measure of time for transverse magnetization caused by the RF pulse to decay to zero. [1]
In this experiment different olive varieties were examined in terms of tissue structure, fat and water contents. The olive varieties used are Green Ayvalik, Black Sele, Black Mega and Black Light. These olive types grow in Mediterranean climate dominant regions of Turkey. The differences between the time constant of the olive varieties used to determine the interpret the desired properties of the samples.
Results
Type of Olive
Fat Content based on NMR
Green Ayvalık
41.43%±5.71
Black Light
48.78%±4.6
Black Mega
49.68%±2.64
Black Sele
57.26%±5.61
Figure 1: SpinCore Benchtop NMR System 0.32 T at METU
Actual Oil Content
Black Sele
57.1%±3.2
Figure 3: Represented T2 CPMG Curve for Sele Olive
Type of Olive
T1 Value(ms)
Green Ayvalık
±34.49
Black Light
120.66±7.72
Black Mega
159.66±18.18
Black Sele
99.95±7.81
Type of Olive
T2 Value(ms)
Green Ayvalık
69.43±2.13
Black Light
54.29±2.97
Black Mega
56.71±3.23
Black Sele
42.75±2.81
Figure 4: Represented T1 Saturation Recovery Curve for Sele Olive
Type of Olive
Moisture Content
Green Ayvalık
51.43%±2.4
Black Light
46.25%±1.59
Black Mega
42.25%±2.81
Black Sele
35.65%±3.44
Table 1: a) Olive’s Fat Content Based on NMR b) Actual Oil Content Of Black Sele Variety c) T1 values of the olive varieties d) T2 values of the olive varieties e) Moisture Content of Olive Varieties
Figure 2: Calibration Curve prepared by using olive oil
Figure 5: Represented FID Spin Echo
Black Mega
Black Light
Green Ayvalik
Black Sele
Materials and Methods
4 olive types were used in the study. These are black light, black mega, black sele and green Ayvalık olives.
In 0.32 T magnet, a calibration curve was prepared with olive oil to determine the oil contents of different types of olives. After calibration curve, in order to determine T2 and T1 times, CPMG and Saturation Recovery sequences ; to determine oil content of olives FID Spin Echo sequences were used with a 0.32T system ( Resonance Systems Inc., Yoshkar-Ola, Mari El, Russia Federation).
In order to determine T2 and T1, the exponential curves were fitted to a monoexponential equation by using MATLAB.
Before FID Spin Echo was acquired, all olives were dried at 105 oC to eliminate the intererence of water signal to oil signal.
Oil content of all olive types were calculated based on the calibration curve that was prepared by using a commercial olive oil. For accurate measurments calibration should be performed with the oils extracted from each variety.
To validate the oil content measured by NMR, for one type of olive; the Sele variety, Soxhlet extraction method was used.
To obtain MR Images of different olive varieties , a 3T system (SIEMENS, Germany) Bilkent University National Magnetic Resonance Center (UMRAM) was used. Different imaging sequences were used to observ the differences in the olives.
Figure 7: Siemens MAGNETOM Trio 3 T at Bilkent University National Magnetic Resonance Center (UMRAM)
Figure 6: Images For Different Olive Varieties
Figure 8: Sagital Image For Mega Variety
Figure 9: Coronal Image For Mega Variety
Conclusion:
The maximum T1 value found for Green Ayvalik as ± ms and the minimum T1 value found for Black Sele was ± 7.81 ms. On the other hand, maximum T2 value found for Green Ayvalik as ± 2.13 ms whereas the minimum T2 value found for Black Sele as ± 2.80 ms. Measurements were performed at 0.32 T magnet and the relaxation time were calculated by NNLS method using PROSPA software.
After preparing the calibration curve with olive oil (Fig 2) , FID signals of all olive varieties were acquired and the amplitude values were substituted into the calibration curve equation. Black Light FID signal did not fit to the calibration equation. Using commercial olive oil as a standart for the calibration curve could have led this result. In order to check the reliability of the obtained calibration curve Black Sele olives were treated to obtain oil content by Soxhlet Extraction method. The theoretical value which is obtained from the calibration curve equation is 57.28% ± 5.61 while the actual value is 57.10% ± 3.2 for the oil contents (Table 1 a, 1 b).
The Olive MR images were taken by 3 T magnet at UMRAM ( Bilkent MR center ) to see the see the structural differences in the olive varietiess (Fig 6,8,9).
Reference;
[1] Mariette, F., Collewet, G., Davenel, A., Lucas, T., and Musse, M., 2012, Quantitative MRI in Food Science & Food Engineering, Universit´e Europ´eenne de Bretagne, Rennes Cedex, France