Time-Domain Nuclear Magnetic Resonance (TD-NMR) and Chemometrics for Determination of Fat Content in Commercial Products of Milk Powder

Abstract

This study shows the use of time-domain (TD)-NMR transverse relaxation (T2) data and chemometrics in the nondestructive determination of fat content for powdered food samples such as commercial dried milk products. Most proposed NMR spectroscopy methods for measuring fat content correlate free induction decay or echo intensities with the sample's mass. The need for the sample's mass limits the analytical frequency of NMR determination, because weighing the samples is an additional step in this procedure. Therefore, the method proposed here is based on a multivariate model of T2 decay, measured with Carr-Purcell-Meiboom-Gill pulse sequence and reference values of fat content. The TD-NMR spectroscopy method shows high correlation (r = 0.95) with the lipid content, determined by the standard extraction method of Bligh and Dyer. For comparison, fat content determination was also performed using a multivariate model with near-IR (NIR) spectroscopy, which is also a nondestructive method. The advantages of the proposed TD-NMR method are that it (1) minimizes toxic residue generation, (2) performs measurements with high analytical frequency (a few seconds per analysis), and (3) does not require sample preparation (such as pelleting, needed for NIR spectroscopy analyses) or weighing the samples.

Multiblock Analysis Applied to TD-NMR of Butters and Related Products

“…The best results are obtained using the SO-PLS model at 6 • C, which presents a SEP of 0.68% and a bias almost null. This result is very satisfactory compared to those reported in the literature using the T2 signal for the fat content estimation: 3.1% in [28], from 2.7% to 4.4% in [13], from 0.45% to 0.84% in [9] and 1.2% in [8]. The repeatability error is 0.32%, which is almost two times lower than the repeatability error achieved using the standard Soxhlet method in [29].…”

An Overview of Determination of Milk Fat: Development, Quality Control Measures, and Application

“…After allowing a few minutes for complete separation and clarification, the volume of the chloroform layer is recorded and the alcoholic layer removed by suction. Nevertheless, this method was used by Nascimento et al (2017) for determination of fat content in commercial dried dairy products. Maxwell et al (1986) used a "dry-column method" for determination of fat.…”

“…Compared with lipid extraction or NIR spectroscopy methods, TD-NMR has certain benefits. TD-NMR is rapid, non-invasive and provides analysis of the bulk milk composition (Nascimento et al, 2017).…”

Selected Instrumental Techniques Applied in Food and Feed: Quality, Safety and Adulteration Analysis

“…To circumvent mass dependence during the assay, Nascimento and coworkers [ 40 ] extracted and analyzed the fat fraction of commercial dried milk products. The authors also corroborated their results obtained with NMR by constructing a multivariate model based on NIR.…”