Quality Control: Analyze Food Samples with NMR Spectroscopy

In food science and technology, quality control is a persistent challenge. Liquid foodstuffs have been characterized through the extensive use of high-resolution proton NMR spectroscopy. However, the higher cost of large superconducting NMR systems has largely restricted this technique to research labs.

Magritek’s Spinsolve Benchtop NMR spectrometer can be employed to characterize commercial liquid food samples. NMR has the noticeable capability to measure samples that are colored, murky, or bubbly. Moreover, it does not need the conventional sample preparation, necessitated by other analytical methods. The samples can be fetched directly from their containers and scanned without the need for any further dilution, purification, or other treatment.

Dairy Products

The graph below illustrates how the measured values compare with the characterized fat content for milk and cream samples with different fat contents.

Spinsolve Benchtop NMR spectrometer

Vegetable Oils

Vegetable oils are extracted from different food sources and contain a blend of organic molecules that exhibit vast differences in their ratios of unsaturated and saturated hydrocarbons. The functional groups related to unsaturated fats are the carbon-to-carbon double bond termed olefins or alkenes, and the CH2 group located between two double bonds (linolenics and linoleics). The table below lists the evaluated composition of various cooking oils.

Soy bean canola blend Soy bean Olive
Olefins (%) 9.3 10.2 6.2
Methyl esters (%) 3.4 3.8 3.3
Linole(n)ics (%) 3.8 4.7 1.6
Oleics (%) 17.9 17.1 17.4
Aliphatics (%) 65.3 64.2 71.5
Total (%) 100 100 100

Alcoholic Beverages

As illustrated below, ethanol exhibits a typical signature in the NMR spectrum for different alcoholic beverages.

Spinsolve Benchtop NMR spectrometer

An unknown sample’s alcohol content can be measured using this signal.

Monitoring Fermentations

Tracking the progress of fermentation is vital in industrial processes because unchecked fermentation caused by contamination can ruin the entire batches of a product. A majority of the analytical techniques necessitate the sample to be clear and/or purified, or dissolved in a solvent that is deuterated. Analysis of samples using Spinsolve is unique since it is possible to fetch the sample directly from the vessel without the need for additional processing.

NMR spectra of fresh apple juice, and that of apple cider following controlled and wild fermentation after 10 days of fermentation, are illustrated in the figure below. The prominent water peak dominates the spectra of the juice and cider; however, the vertical expansion by a factor of 50 indicates the presence of smaller peaks, all of which can be assigned. The spectrum of a 99% ethanol/water mixture is also illustrated to assist with peak assignment.

Monitoring Fermentations

The data clearly shows that the wild fermentation generates enormous amounts of acetic acid as an undesirable byproduct. The graph below depicts the time evolution of wild as well as controlled fermentation with the corresponding product conversion rates.

A mechanical arm and a rotating carousel equipped in the Spinsolve Autosampler are used to insert and take out samples from the spectrometer. The autosampler, which can be installed on all Spinsolve models, allows up to 20 individual samples to be measured in any order. The software can be operated intuitively and easily, even with minimal training.

It is useful for customers who usually run a series of samples on their benchtop NMR, and intend to avoid the hassle of returning to exchange samples. An added advantage is the potential to increase the usage by configuring a string of experiments to run on the Spinsolve overnight.

Spinsolve Autosampler

Run NMR Samples Without Leaving the Chemistry Lab

Spinsolve is a groundbreaking multinuclear NMR spectrometer that offers the best performance compared to other benchtop systems currently available in the market. The low cost, low weight, and small footprint of Spinsolve enable high-resolution, powerful NMR spectroscopy in the chemistry lab, along with other analytical instruments such as GC, IR, MS, LC, FTIR and Raman systems. Spinsolve is now available in various convenient models.

multinuclear NMR spectrometer

This information has been sourced, reviewed and adapted from materials provided by Magritek.

For more information on this source, please visit Magritek.

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