Date

2022-8

Author

Ünal, Kübra

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Nuclear Magnetic Resonance (NMR) relaxometry is a widely used characterization method for the analysis of physiological and biochemical changes in a huge variety of samples. Time domain NMR (TD-NMR) relaxometry provides structural analysis at low magnetic fields. It is basically relies on the relaxation times of proton signals coming from the entire sample. Thus, it provides quantification of water absorption and analyzing its distribution within the biological systems. In this dissertation, plant tissues and starch-water interaction systems were investigated using TD-NMR relaxometry. In the first part of the study, TD-NMR relaxometry was used to investigate the changes in the cell integrity of plant tissues. For plant tissues, tomato seed was selected and subjected to osmotic stress (OS) (10, 20, 30% NaCl solutions), ultrasonication (US) (5, 10 and 20 minutes) at 75% amplitude and high hydrostatic pressure (HHP) (300, 400 and 500 MPa for 15 min at 20°C). NMR relaxation spectra of tomato seed gave four peaks each corresponding to different water compartments due to multiexponential relaxation behavior of the plant cell. According to the results, all the three treatments resulted in cell permeabilization and disruption of cellular compartmentalization. Among the treatments, HHP at 500 MPa for 15 min at 20°C resulted in the most detrimental effect in the cell structure and OS treatment with 10% NaCl solution caused the least changes in the cell structure. Seeds exposed to different treatments were also analyzed by Scanning Electron Microscope (SEM) to determine the extent of damage to the cell. These results have proved that NMR relaxometry is an effective method to analyze the cell membrane integrity of tomato seeds exposed to selected treatments. Use of NMR relaxometry to assess physicochemical characteristics of starch-water interactions was the second part of the study. Quinoa starch was chosen to study starch-water interactions. Following starch isolation, NMR relaxometry was used to investigate the physiological changes in quinoa starch dispersions induced by HHP and US. HHP at 250, 350 and 500 MPa at 20°C and 40°C; ultrasonication (US) at 100% power with constant pulse for 15 min were applied as modification methods. Following the treatments, functional, rheological, particle size, morphological and structural analysis were carried out. Results showed that swelling power and water solubility index of quinoa starch was decreased significantly with both HHP and US treatments (p<0.05). Apparent viscosity of the starch samples decreased with increasing pressure and US treatment. The particle size distribution revealed a more apparent increase in the volume mean diameter (D [4,3]) with HHP treatment (p<0.05) compared to US. Time domain (TD) NMR relaxometry experiments confirmed that HHP treatment caused less granule swelling of starch. NMR relaxation spectra of quinoa seeds revealed mainly two distinct proton populations and HHP treatment at 500 MPa resulted in faster exchange of proton populations compared to the US treatment. DSC results are correlated with the results of NMR relaxometry. SEM images visualized the change in the morphology of the quinoa starches after treatments and structural changes were observed through FTIR and XRD experiments. These results have demonstrated that HHP treatment had a strong modification effect on quinoa starch compared to US and provide modified quinoa starch with better quality. Moreover, the investigation of the quinoa starch and water interactions under these conditions was demonstrated to be effective with the use of NMR relaxometry. To conclude, this dissertation has proved that TD-NMR relaxometry is an effective method for characterization of cell integrity of tomato seeds and physiological changes in quinoa starch dispersions. This study may provide information for further research in food applications.

Subject Keywords

TD-NMR Relaxometry, High Hydrostatic Pressure (HHP), Ultrasonication (US), Plant seed, Quinoa starch

URI

https://hdl.handle.net/11511/98713

Collections

Graduate School of Natural and Applied Sciences, Thesis