Chunfei Wu

Chunfei Wu

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Materials characterisation - Liquid – Composition analysis - Nuclear magnetic resonance (NMR) - Application of NMR (liquid)

Rapid Detection of Avocado Oil Adulteration Using Low-Field Nuclear Magnetic Resonance

https://doi.org/10.3390/foods11081134

“Avocado oil (AO) has been found to be adulterated by low-price oil in the market, calling for an efficient method to detect the authenticity of AO. In this work, a rapid and nondestructive method was developed to detect adulterated AO based on low-field nuclear magnetic resonance (LF-NMR, 43 MHz) detection and chemometrics analysis. PCA analysis revealed that the relaxation components area (S23) and relative contribution (P22 and P23) were crucial LF-NMR parameters to distinguish AO from AO adulterated by soybean oil (SO), corn oil (CO) or rapeseed oil (RO). A Soft Independent Modelling of Class Analogy (SIMCA) model was established to identify the types of adulterated oils with a high calibration (0.98) and validation accuracy (0.93). Compared with partial least squares regression (PLSR) models, the support vector regression (SVR) model showed better prediction performance to calculate the adulteration levels when AO was adulterated by SO, CO and RO, with high square correlation coefficient of calibration (R2C > 0.98) and low root mean square error of calibration (RMSEC < 0.04) as well as root mean square error of prediction (RMSEP < 0.09) values. Compared with SO- and CO-adulterated AO, RO-adulterated AO was more difficult to detect due to the greatest similarity in fatty acids’ composition being between AO and RO, which is characterized by the high level of monounsaturated fatty acids and viscosity. This study could provide an effective method for detecting the authenticity of AO.”

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2.2. Acquisition of LF-NMR Signals

The 1H relaxation time curve of the oils was acquired on a 43 MHz NMI20-040H-I LF-NMR spectrometer (Niumag Corporation, Suzhou, China). During measurement, each sample (5 g) was transferred into the probe (40 mm). The Carr–Purcell–Meiboom–Gill sequence (sampling frequency = 200 KHz, repeated waiting time = 5000 ms, echo count = 8000, the time between 90° and 180° pulse was 0.1 ms and repeat scan times = 8) was applied to detect the transverse relaxation time (T2) of each sample. All the oil samples were transferred to a thermostatic water bath and equilibrated to 32 °C, and then were placed in the probe for 1 min before sampling [26]. As shown in Figure 1, the relaxation time of three characteristic relaxation components was determined as T21, T22 and T23. The start time of relaxation components (T21S, T22S and T23S), peak time of relaxation components (T21P, T22P and T23P), end time of relaxation components (T21E, T22E and T23E), single component relaxation time (T2W, inverted from CPMG decay data using a single-exponential fitting), percentage relative contribution (P21, P22 and P23), relaxation components area (S21, S22 and S23) of each relaxation components and total area (STotal) of all relaxation components were collected as key parameters for the following chemometrics analysis.
Foods 11 01134 g001 550
Figure 1. The T2 distribution of AO adulterated by SO (A), CO (B) or RO (C) (0–100%).

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