Single-Laboratory Validation Study of a Rapid TD-NMR Method for Quantitation of Total Fat in Sunflower Oil Powder

A rapid total fat quantitation method for sunflower oil powder was developed using time-domain nuclear magnetic resonance (TD-NMR). Currently, industry has three major methods for the total fat quantitation: gravimetric analysis after ether extraction (AOAC Methods 933.05 and 989.05), gas chromatography with flame ionization detector (GC-FID; AOAC Method 996.06), and High-resolution NMR. The gravimetric analysis method takes a day using highly flammable solvents, and the GC-FID method takes two days requiring harsh chemicals for hydrolyzation, extraction, and methylation. The High-resolution NMR spectroscopy method requires simpler sample preparation and shorter analysis time compared to the other two methods. Often, the only required sample preparation step is to dissolve a sample in a solvent. The acquisition time depends on types of analyzing nuclei and sample. The vegetable oil analysis by 13C NMR takes about 4 h per sample. 1H NMR usually takes less time to analyze. In contrast, the TD-NMR relaxometry method takes only 1 h to prepare and analyze samples if the test is for total fat only. The acquisition time is 40 s per sample, and samples are analyzed "as is". A rapid analysis method in a quality control laboratory is very crucial for laboratory efficiency in releasing products. In this paper, a single-laboratory validation study is described for a rapid TD-NMR method to quantitate total fat in sunflower oil powder.

This validation work is to provide documented evidence for the method validity as well as the method performance.

The method used a Bruker minispec mq-20 NMR analyzer® with minispec plus® software. A Hahn echo pulse program was used in the method to collect spin echo signal to determine total fat content.

The linearity/range result from 10 standards (0, 21, 42, 63, 83, 92, 100, 108, 117, and 125%) has coefficients of determination (R2) of 1.0000. The 100% level is 1.2 g-fat in 2.5 g sample, which is targeted fat content in a sunflower oil powder raw material. The method is specific for the quantitation of total fat in sunflower oil powder with no background interference from the matrix. The precision result of the 6 replicate samples at 100% level is 0.3% RSD. The accuracies measured from triplicate analysis of 80, 100, and 120% sample matrices are 100, 100, and 100% average recoveries, respectively. The ruggedness of the test method is 0.4% RSD of 12 analysis from 2 analysts (6 results from each analyst) on the different days.

The test method is proven to be specific, linear, precise, accurate, rugged, and suitable for the intended use of quantitative analysis for total fat in sunflower oil powder.

Traditional methods of gravimetric or GC-FID for total fat analysis of raw materials require lengthy sample preparation and experiment time. Laboratory needs to spend a day to perform gravimetric analysis following ether extraction method and 2 days for the GC-FID method. In addition, these test methods use highly flammable and harsh chemicals that generate hazardous chemical wastes. These hazardous wastes are harmful to analysts and environments. In contrast, the TD-NMR method is safe, environmentally friendly, and fast. Therefore, TD-NMR is a preferred method for quality control laboratories.