Near‐infrared spectroscopy for analysis of oil content and fatty acid profile in almond flour

Abstract

Almond kernels show large variability for oil content and fatty acid profile. The objective of this research was to evaluate the potential of near infrared (NIR) reflectance spectroscopy (NIRS) for the analysis of these traits in almond flour. Ground kernels of 181 accessions collected in 2009 were used for developing calibration equations for oil content and concentrations of individual fatty acids. Calibration equations were developed using second derivative transformation and modified partial least squares regression. They were validated with samples from 179 accessions collected in 2010. The accuracy of calibration equations was measured through the coefficient of determination (r 2 ) in external validation and the ratio of the SD in the validation set to the standard error of prediction (RPD). Both r 2 and RPD were high for oil content (r 2 ¼ 0.99; RPD ¼ 9.24) and concentrations of oleic (r 2 ¼ 0.97; RPD ¼ 5.37) and linoleic acids (r 2 ¼ 0.98; RPD ¼ 7.35), revealing that calibration equations for these traits are highly accurate. Conversely, the accuracy of the calibration equations for palmitic (r 2 ¼ 0.54; RPD ¼ 1.41) and stearic acids (r 2 ¼ 0.52; RPD ¼ 1.44) was too low for allowing their application in practice. NIRS discrimination of oil content and concentrations of oleic and linoleic acids was mainly based on the spectral region from 2240 to 2380 nm.Practical applications: NIRS is a high-throughput analytical technique that allows fast measurement of several traits in a single analysis without using chemical reagents. We evaluated the feasibility of analyzing oil content and concentrations of palmitic, stearic, oleic, and linoleic acids in almond flour using fruits collected during 2 years from a world germplasm collection. The fruits collected in 2009 were used for NIRS calibration, whereas the fruits collected in 2010 were used for validation. NIRS equations were highly accurate for measuring oil content and concentrations of oleic and linoleic acids, which are important traits defining the quality of almond flour for specific uses in the food industry. These results have applications both in the research laboratory and the food industry, where NIRS is becoming a widely used technique for quality control.

Rapid Characterization of Fatty Acids in Oleaginous Microalgae by Near-Infrared Spectroscopy

“…Recently, NIRS has also been applied to the characterization of fatty acids in meat and food power samples [ 23 , 24 , 25 , 26 , 27 ]. But the models developed in these reports need improvements for better prediction of some fatty acids.…”

“…But the models developed in these reports need improvements for better prediction of some fatty acids. For example, in the study of Fernandez-Cuesta et al [ 24 ], only C18:1 and C18:2 showed good prediction, with R 2 being 0.97 and 0.98, and RPD being 5.37 and 7.35, respectively; in contrast, the prediction performance for C16:0 ( R 2 = 0.54, RPD = 1.41) and C18:0 ( R 2 = 0.51, RPD = 1.44) was far less acceptable. Fatty acids varying in chain length and unsaturation level possess different near-infrared spectra [ 22 ].…”

“…Fatty acids varying in chain length and unsaturation level possess different near-infrared spectra [ 21 , 22 ]. There have been several reports of employing NIRS for predicting individual fatty acids, such as C16:0, C18:0, C18:1 and C18:2, in pig adipose, lamb meat, chicken meat, milk powder and almond flour [ 23 , 24 , 25 , 26 , 27 ]. Recently, NIRS also demonstrated its applications in microalgae, but restricted to the quantification of lipid, carbohydrate, protein, and ash content [ 28 , 29 , 30 , 31 , 32 , 33 ].…”

Comparison of critical methods developed for fatty acid analysis: A review

“…Therefore, sunflower genotypes in traditional and mutant groups must be identified using combined discriminant analytical methods and NIRS to discriminate the profile of FAs. Fernandez-Cuesta et al [72] confirmed that NIRS can be applied for accurate high-throughput analysis of oil content and concentrations of oleic and linoleic acids in almond samples. NIRS discrimination of different traits mainly depended at wavelengths of 2304 and 2344 nm in the spectral regions from 2240 to 2380 nm.…”

“…Fernandez‐Cuesta et al. confirmed that NIRS can be applied for accurate high‐throughput analysis of oil content and concentrations of oleic and linoleic acids in almond samples. NIRS discrimination of different traits mainly depended at wavelengths of 2304 and 2344 nm in the spectral regions from 2240 to 2380 nm.…”