Download - FFC application notes: Fast Field Cycling for analysis of ... food a4 pr.pdf · Fast Field Cycling for analysis of foodstuffs ffc application note: food In the last decade, there

Fast Field Cycling for analysis of foodstuffs

ffc application note: food

In the last decade, there has been a growing interest in ap-plying 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. [1-10] The NMRD profiles, produced from FFC measurements, reflect the molecular dynamics of the components of com-plex food systems and provide important information that can be exploited in different ways by food manufacturers.

The major applications of FFC to foodstuffs include:

• Quality control (QC);

• Shelf-life stability;

• Aging/varieties/geographical origin;

• Food fraud and authentication

Foods that may benefit from the FFC method are: edible oils, fruit juices, wines, vegetables, meats, dairy products such as cheese and yoghurt, and many others. Herein, some indicative examples from scientific papers are re-ported with the purpose of showing the potential of the FFC method for the food industry.

M. Pasina, R. Steelea, G. Ferranteªa Stelar Srl, Via E. Fermi, 27035 Mede (PV), Italy

Introduction

FFC applied to foodstuffs

FFC application notes: food© 2018 Stelar srl- AN 180801_food

www.stelar.it [email protected]

Quality control for spoilage and shelf lifeSpoilage of milk-based products, shelf-life of fruit and meat, ham dry-curing process monitoringFFC can be applied in the food industry to spoilage, ageing (shelf-life) and dry-curing processes of food.Fig. 1 reports the change in the NMRD profile of an un-spoiled milk-based refrigerated drink product, within its expiry date, and a sample of the same product after induced spoilage.

NMRD is able to clearly show how quickly meat, such as the pork loins shown in Fig. 3, can dehydrate over a period of 20 hours.

Indeed, Apih and co-workers showed that use of a combined FFC NMR/qMT-NMR method (using the area under quadrupolar peaks in the NMRD profiles and the restricted magnetization pool size from qMT-NMR) proved to be a good approach for the fast, non-destructive characterization of different fresh and dry-cured ham tissues and thus a powerful tool for dry-curing process monitoring. [3]

All the above results show that, in particular at lower magnetic fields, it is easy to distinguish the differences (from differences in 1/T1) between different states of the same product.

02


fig. 3: 1H NMRD profiles of pork loin open to air at ambient temperature over a twenty- hour time period.

fig. 4: 1H NMRD profiles allow discrimination between oils obtained from different cultivars sampled in the same geographical location. (From [4])

FFC is a powerful tool that can be applied to discriminate between different features of edible oils. Conte and co-workers showed how FFC can be successfully employed to distinguish between pistachio oils (1) obtained from seeds subjected to different thermal desiccation pro-cesses; (2) retrieved from seeds belonging to the same cul-tivar grown in different geographical areas; (3) produced by using seed cultivars sampled in the same geographical region. [4]

Moreover, the oil kinematic viscosity was reliably correlated with the relaxation parameters obtained using FFC. Relying on the FFC results, Conte and co-workers came to the the conclusion that the origin of pistachio seeds ap-peared to be important for discrimination of oils with a dif-ferent quality ranking. Indeed Fig. 4 shows results at low fields (below 10 MHz) were essential for this study.


Geographical origin and varietiesEdible oils

Conte and coworkers also applied the FFC technique to extra-virgin olive oils [5]. The results suggested that olive oils are not disordered and amorphous liquids but rather systems whose constituents are arranged in tidy supramolecular aggregates. These results are important for further un-derstanding related to absorption, transport and metabolism of extra-virgin olive oils which are fundamental ingredients of the Mediterranean diet.

fig. 1: 1H NMRD profiles of a milk-based refrigerated drink product within expiry date (unspoiled, black squares), and after induced spoilage (spoiled, red diamonds). (From [1])

fig. 2: 1H NMRD profiles of a piece of banana measured as a function of the time with the aim to monitor the aging effects. (From [1])

FFC showed large differences in the 1/T1 for spoiled and non-spoiled products at low frequencies (between 10 and 100 kHz). A large food manufacturer intended to use this data to carry out in-line production quality control checks on these products. It is possible to discriminate between fresh and older pro-ducts according to the amount of water these contain and results can be correlated and transferred to quality control applications including freshness and shelf-life monitoring.[1, 2]. Fig. 2, for example, shows how the proton NMRD profile of a piece of fresh banana changes over a period of 20 hours as it loses water.

03


fig. 5: 1H NMRD profiles can be used as a fingerprint for cheeses made from pasteurized (sample 1) and unpasteur-ized sheep’s milk (samples 2 and 3). Sample 3 is a more seasoned cheese than sample 2 (data from Stelar in-house studies).

fig. 6: 1H NMRD profiles for 12-year aged balsamic vinegar (blue) and counterfeit product, with thickening agents added (black). (From [6])

Food authentication is an important issue for the food industry: unscrupulous producers would have an economic advantage from manufacturing fraudulent products which can be sold at the higher price of an “original” product and indeed consumers have the right to know the authenticity of the product they purchase, which merits the higher price tag.Baroni et alii showed that the NMRD profile is a very useful tool for characterization of genuine balsamic vinegars, pro-viding useful insights for recognizing fraudulent products [6]. 1H NMRD profiles were able to show a huge difference be-tween a genuine 12-year old TBVM and a suspected fraudu-lent product (TBVM, Fig. 6).

FFC application notes: food© 2018 Stelar srl_ AN 180801_food Cheeses made from

unpasteurized and pasteurized milks

Food fraud and authenticationBalsamic vinegar and rape-seed oil

TBVM is a protected designation of origin product and its cost on the market is rather high in accordance with its age-ing process.

Rachocki et al. reported that, after calculating the diffusion coefficient for a particular type of authentic rape-seed oil, it was possible to run measurements on a series of oil sam-ples, to check their authenticity [7]. This is due to the fact that the diffusion coefficient is sensitive to the environment in which the molecules diffuse, e.g. chemical composition, the oil production process and the geographical growth area of the cultivar. The diffusion coefficient of the rape oil, which can be calculated from the NMRD profile, becomes a unique parameter, characteristic of that particular oil.

It was possible to use NMRD profiles as a fingerprinting method to distinguish between cheeses of a specific protected origin made from unpasteurized and pasteurized sheep’s milk (see Fig. 5).

It was also notable that in cheese made from unpasteurized milk, differences in 1/T1 were particularly evident at fields lower than 0.2 MHz between the young (fresher) and more seasoned (older) cheeses.

Cheeses are solid emulsions of milk fat in a matrix of water and proteins. Identifying these regions and checking chang-es in them can be helpful for monitoring the structure of the final cheese. Godefroy et al. reported that, using the FFC re-sults from Gouda-type and Mozzarella-type cheeses, it was possible to determine the degree of hydration of proteins as a function of ageing [8].

Food ageingCheese

fig. 8: 1H NMRD dispersion curves of young and old dry salted mozzarella-type cheese at 5 °C. (From [8])

fig. 7: 1H NMRD profiles of young and old dry salted gouda-type cheese at 5 °C. (From [8])


04

(1) Steele R. M., Korb J. P., Ferrante G., Bubici S. (2016). New applications and perspectives of fast field cycling NMR relaxometry, Magnetic Resonance in Chemistry, 54, 502-509;

(2) Capitani D., Sobolev A. P., Delfini M., Vista S., Antiochia R., Proietti N., Mannina L. (2014), NMR methodolo-gies in the analysis of blueberries, Electrophoresis, 35, 1615-1626;

(3) Bajd F., Gradisek A., Apih T., Sersa I. (2016), Dry-cured ham tissue characterization by fast field cycling NMR relaxometry and quantitative magnetization transfer, Magn. Reson. Chem, 54, 827-834;

(4) Conte P., Mineo V., Bubici S., De Pasquale C., Aboud F., Maccotta A.; Alonzo, G. (2011), Dynamics of pistachio oils by proton nuclear magnetic resonance relaxation dispersion, Analytical and bioanalytical chemistry, 400, 1443-1450;

(5) Conte P., Maccotta A., De Pasquale C., Alonzo G., (2010). Supramolecular organization of triglycerides in ex-tra-virgin olive oils as assessed by NMR relaxometry, Fresenius Environ Bull, 19, 2077-2082;

(6) Baroni S., Consonni R., Ferrante G., Aime S., (2009), Relaxometric studies for food characterization: the case of balsamic and traditional balsamic vinegars, Journal of agricultural and food chemistry, 57, 3028-3032;

(7) Rachocki A., Tritt-Goc J., (2014), Novel application of NMR relaxometry in studies of diffusion in virgin rape oil, Food chemistry, 152, 94-99;

(8) Godefroy S., Korb J. P., Creamer L. K., Watkinson P. J. Callaghan P. T., (2003), Probing protein hydration and aging of food materials by the magnetic field dependence of proton spin-lattice relaxation times, Journal of colloid and interface science, 267, 337-342.

(9) Berns A. E., Bubici S., De Pasquale C., Alonzo G., Conte P., (2011), Applicability of solid state fast field cycling NMR relaxometry in understanding relaxation properties of leaves and leaf-litters, Organic geochemistry, 42, 978-984.

(10) Conte P., Bubici S., PalazzoloE., Alonzo G., (2009), Solid-state 1H-NMR relaxation properties of the fruit of a wild relative of eggplant at different proton Larmor frequencies. Spectroscopy Letters, 42, 235-239;

(11) Rachocki A., Latanowicz L., Tritt-Goc J, (2012), Dynamic processes and chemical composition of Lepidium sa-tivum seeds determined by means of field-cycling NMR relaxometry and NMR spectroscopy, Analytical and bioanalyt-ical chemistry, 404, 3155-3164.

references:


The Stelar relaxometer works by fast electronic switch-ing of the magnetic field from an initial polarizing magnetic field (BPOL), where the equilibrium of nucle-ar magnetization is attained in about 4T1, to a field of interest (relaxation field; BRELAX) at which the nucle-ar spins relax to the new equilibrium state with a characteristic relaxation time constant T1. After a delay time, τ, the BRELAX is switched to the field of acquisi-tion (BACQ) and the NMR signal is detected after a π/2 RF pulse (Fig. 9).

FFC technique

fig. 9: Fast Field Cycling NMR method.

fig.10: Example of NMRD profile. A Gadolinium-based contrast agent measured from 0.01MHz to 40MHz (from in-house data).

The magnetic field dependence of 1/T1 is shown in the graphical form as a Nuclear Magnetic Resonance Disper-sion (NMRD) profile (Fig. 10).Each point of the NMRD profile (i.e. a certain BRELAX) is obtained detecting the NMR signal using a num-ber of different delay times τ .