Food scientists and technologists determine the chemical composition and physical characteristics of foods everyday as part of their quality management, product development, or research activities. However consumers are becoming increasingly hard to please with their food preferences, thanks to greater accessibility of information on the merits and demerits of different foods, their components, origin, processing, and storage conditions. Furthermore, an increasing range of demanding consumers (eg. the elderly, athletes, diabetics, the obese, and those with allergies) needs that food composition is accurately and clearly presented to consumers. Therefore consumer, government, and food industry concern for food quality and safety has increased the importance of analyses that determine composition and critical product characteristics. The ability of some non-invasive and non-destructive physical-chemical techniques to extract information on food in widely described in literature. Nuclear magnetic resonance (NMR), with all its methodologies (spectroscopy, relaxometry, imaging), can characterize food matrices, and it can be used all along its “life chain”, from farm to fork. In last decade NMR applications have been more frequently used in the food chain even if the price to pay to use this technique is still high. The main criticisms concern the staff highly qualified for both use NMR instruments and explain NMR data. Furthermore, only few people knows that NMR is a completely non-ionizing radiation technique. Here an interesting application of NMR Fast Field Cycling to study the molecular dynamics of jelly candies [1]. How can we obtain information about candies quality?
The Fast Field Cycling NMR technique
In NMR relaxometry experiments with Fast Field Cycling technology, the resonance frequency can be varied over several orders of magnitudes (typically from about 10 kHz to tenths of MHz, referring to hydrogen – 1H – resonance frequency). Consequently, one can probe in a single experiment into dynamic processes at very different time scales. In the case of 1H magnetization relaxation processes, the predominating relaxation mechanism is provided by 1H – 1H mutual dipole-dipole interactions that fluctuate in time as a result of molecular motion (such as translational diffusion, molecular tumbling or the internal dynamics of molecules and ions).
Studying the time constant characterizing the evolution of the magnetization, referred to as spin-lattice relaxation time, it is possible to extract parameters on molecular dynamics and structural properties in this case of jelly candies.
Jelly candies NMR parameters for quality characterization
In the study of Kruk et al. [1], two different brands of candies have been evaluated. Following the theory of relaxation of the magnetization, the relaxation data for jelly products can be reproduced in terms of three relaxation contributions associated with dynamic processes referred to as slow, intermediate and fast. The relaxation rates parameters on intermediate dynamics for the first brand samples of candies show some variations, whereas the slow and fast ones are similar. Moreover these parameters are affected by the temperature of the candies. Authors suppose that this is meaningful of the dynamics of water molecules confined in the macromolecular matrix. Intermediate parameters reflect the mole fraction of water molecules in the bound position which becomes lower with increasing temperature.
Slow and fast dynamics don’t show an appreciable variability, also with temperature variation, but it is interesting that their values are similar among the samples of the same brand of candies, so this can be significant for the authenticity of the products. In the case of the second brand of candies, more complex dynamic processes have been highlighted for a group of samples. Probably two pools of water molecules in jelly are involved: a pool of confined water molecules, the dynamics of which are strongly restricted and slowed, and a pool of water molecules, the dynamics of which are affected to a lesser extent by interactions with the macromolecular network.
This study is part of several studies on quality detection of food, adopting combined techniques both invasive and non-invasive. Since NMR techniques are non-invasive and non-destructive it could be worth to enlarge its use in the future.
[1] Molecular Dynamics of Jelly Candies by Means of Nuclear Magnetic Resonance Relaxometry; Danuta Kruk, Leonid Grunin, Aleksandra Stankiewicz, Karol Kołodziejski, Esmanur Ilhan; Mecit Halil Oztop – Molecules, (2023), 28(5)
