In the last decade, there has been a growing interest in applying the Fast Field Cycling (FFC) NMR method to food science and several scientific papers have been published. FFC is a non-destructive technique which is versatile, allows quick evaluation of results and can be applied to a wide range of foods.
The NMRD profiles, produced from FFC NMR measurements, reflect the molecular dynamics of the components of complex food systems and provide important informations that can be exploited in different ways by food manufacturers.
The major applications of FFC NMR to foodstuffs include:
• Fingerprinting foodstuffs
• Quality control (QC);
• Shelf-life stability;
• Aging/varieties/geographical origin;
• Food fraud and authentication
Foods that may benefit from the FFC NMR method are: edible oils, fruit juices, wines, vegetables, meats, dairy products such as cheese and yoghurt, and many others.
Please contact Stelar for further details on unlisted applications or to assess the feasibility of new experimental approaches.
Cocoa butter is an important ingredient of chocolate, whose crystallization behavior plays a key role in determining the formation of the hard, shiny commercial product. Indeed, cocoa butter crystallizes in six different polymorphic forms, of which only the β-form is desirable for high-quality chocolate. However, studies on the liquid, pre-crystallization state of cocoa butter are limited. In this context, FFC NMR relaxometry has proven useful for investigating molecular diffusion and phase transitions. The technique was applied to study both molten and cooled states of cocoa butter and showed a high sensitivity to phase changes, particularly in the low-frequency region (below 1 MHz).
This behavior is clearly evidenced in the NMRD profiles (in Figure), where significant variations in relaxation rates occur at low frequencies, highlighting the capability of FFC NMR to probe phase transitions.
Milk sours when bacterial fermentation transforms the sugars to lactic acid. Acid may denature proteins present and drive protein aggregation both of which affect the NMRD profile. Fermentation may be monitored by FFC NMR relaxometry, as demonstrated by a Stelar in-house case study, which was able to monitor spoilage of a refrigerated milk-based drink product. In this case, low magnetic field measurements were a critical advantage, and the shape of the NMRD profile was diagnostic.
1H NMRD profiles of an unbranded milk-based refrigerated drink product before and after artificial spoilage (acidification). Data from a Stelar in-house study.
The dry-curing ham process involves salt diffusion and moisture migration in opposite directions. Conventional analytical methods used to monitor this process are typically destructive and time-consuming. It has been demonstrated that a combined approach using fast field cycling (FFC) NMR relaxometry and quantitative magnetization transfer (qMT) provides a fast and non-destructive characterization of dry-cured ham tissues with different protein contents.
The two techniques enable the quantification of both the quadrupolar contribution derived from FFC relaxation dispersion and the restricted macromolecular magnetization pool obtained from qMT analysis. These parameters are strongly correlated with the amount of partially immobilized, nitrogen-containing muscle proteins and can therefore be used as markers of tissue composition during the dry-curing process.
This is reflected in the pure quadrupolar peaks extracted from the FFC dispersion curves (in Figure), whose area varies among samples and thus provides a quantitative marker of the dry-cured ham system.
Meat has a short shelf-life and thus needs to be stored rigorously at cold temperatures. A Stelar in-house study showed that FFC NMR relaxometry can show how quickly meat, such as pork loins, can dehydrate over a period of 20 hours and over 12 days. The “quadrupole” peaks shown in the NMRD profile of pork are due to the immobilized proteins in the meat. The FFC technique could indeed be used to elucidate the freshness of meat products by monitoring water loss.
FFC NMR relaxometry enables fast and simple measurements of water status in intact blueberries, which can be applied to quality control, including freshness and shelf-life monitoring
Honey fermentation is promoted by microbial activity, which is influenced by the variation in water mobility associated with the temperature. Honey is of large value to the food industry, thus choice of the storage temperature which can prevent honey deterioration is highly important. FFC NMR relaxometry was used to understand the amount and nature of the water present in honey, which is important to predict its conservation and stability. The technique found dramatic changes in honey component distributions, which suggested an elevated risk of spoilage.
As an example figure shows (b) NMRD profiles of loquat (a) and multifloral (b) honey stored at room temperature (triangled dots) and after refrigeration at 4°C (circled dots).
A method of recognizing liquified honey has also been proposed: heating the honey at 30 °C resulted in irreversible molecular structure changes as shown by FFC NMR relaxometry.
As an example in figure: Temperature dependences of the 1H spin–lattice relaxation dispersion data for the crystalline honey samples and the corresponding theoretical curves obtained as least-square fits of the Eq. (4). Dispersion profiles of the relaxation rate were recorded at: 23 °C (×), 30 °C (○), 40 °C () and 60 °C (●). Triangles represent measurements recorded at 23 °C after heating samples at: 30 °C (Δ), 40 °C () and 60 °C (▲)
FFC NMR relaxometry has been shown to be a very promising tool for quick evaluation of vegetable oil quality with advantages over other time-consuming extraction and purification procedures.
FFC was used to obtain the diffusion coefficient of rape oil and was compared with that obtained by the well-recognized pulse gradient spin echo (PGSE) NMR method and showed a good agreement. The advantages of FFC NMR relaxometry over the PGSE NMR method, are that it is not limited by the strength of the gradients, is not time-consuming, and determination of the diffusion coefficient from the experimental data requires only a simple mathematical operation.
D. Capitani, A.P. Sobolev, M. Delfini, S. Vista, R. Antiochia, N. Proietti, S. Bubici, G. Ferrante, S. Carradori, F. R. De Salvador, L. Mannina, Electrophoresis2014, 35, 1615–1626
) and 60 °C (●). Triangles represent measurements recorded at 23 °C after heating samples at: 30 °C (Δ), 40 °C (
) and 60 °C (▲)