Use of non-conventional time domain (td) nmr approaches for characterisation of gelatin based soft candies

Uğuz, Şirvan Sultan
TD-NMR technique mostly involves the use of T1 (spin-lattice) and T2 (spin-spin) relaxation times to explain the changes occurring in food systems. However, these relaxation times are affected from many factors and might not always be the best indicators to work with in food related TD-NMR studies. In this thesis, to our knowledge, the non-conventional TD-NMR approaches of Solid Echo/Magic Sandwich Echo and Spin Diffusion in food systems were used for the 1st time. As the system of interest, soft confectionery gels were selected due to the simplicity of their composition and the flexibility of preparing standardized formulations. Two problems have been identified related with the confectionery gels. And in that regard, the thesis was structured in 2 parts. In the first part of the study, soft confectionary gelatin gels were formulated and conventional (T1, T2) and non-conventional (SE, MSE and Spin Diffusion) TD-NMR experiments were performed. Corn syrups differing in their glucose/fructose compositions were used to prepare the soft candies and five different syrup types were used. Hardness, oBrix and water activity (aw) were also measured as the complementary experiments to NMR. Relaxation times changed with syrup type (p<0.05) but not an obvious trend was detected. On the other hand, SE/MSE experiments which were performed to calculate the crystallinity vi of the samples yielded valuable results. Samples prepared with fructose had the lowest crystallinity values (p<0.05) as expected due to the higher solubility of fructose compared to glucose. Spin Diffusion experiments were performed by using Goldman-Shen pulse sequence and the interface thickness (d) was calculated after a detailed data analysis. Interface thickness showed a wide range of variation (p<0.05) thus it was proposed as an indicator for differentiating the candies prepared with different syrups. In the 2nd part of the study, gelatin-based candies were prepared with the same formulations by just one syrup type but by using bovine and porcine gelatin as the polymer sources. Water activity and oBrix values were measured. T1 times did not differ (p>0.05) whereas T2 times were found to be higher for the bovine gels despite their lower water activity. This time, crystallinity values calculated from SE/MSE did not show differences wrt to gelatin source (p>0.05). Interface thickness values calculated from SD experiments showed that porcine gelatin-based candies were more stable compared to bovine samples (p<0.05). Results showed that non-conventional NMR approaches had high potential to be utilized in food systems for quality control purposes.


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Citation Formats
Ş. S. Uğuz, “Use of non-conventional time domain (td) nmr approaches for characterisation of gelatin based soft candies,” M.S. - Master of Science, Middle East Technical University, 2020.