Study On Fourier Transforms Infrared (FT-IR)Spectroscopy For Detection Of Walnut Oil And Walnut Varieties

The walnut (Juglans regia L.) is a member of the family Juglandaceae, as one of the four major famous nuts of the world with almond, cashew and hazelnut. Walnut oil (WO) is the essence pressed from walnut kernel, delicious and nutritious, contains most active components and health functions of walnut kernel. The unsaturated fatty acid of linolic acid and linolenic acid in WO is90%, which can reduce serum cholesterol; Moreover, WO contains other trace function fatty acid, such as DHA, EPA, nervonic acid etc, which are the core component of cranial nerve cells and can adjust plant nerve function. Due to its higher price in the international market, WO can be a target of adulteration with the cheaper oil, tung oil, hogwash oil and other non-edible oil in order to gain economical profit. The adulteration comprises a great hazard not only for the economic development and prosperity of those communities but also for the health and safety of WO consumers. Therefore, the development of rapid and accurate analytical technique is currently highly demanded. The main contents and results were as follows:1. The use of Fourier transform infrared (FT-IR) spectroscopy for detection and quantification of adulteration in walnut oil. FT-IR spectrometer was used to collect mid-infrared spectra of pure WO and walnut oils adulterated with soybean oil (SO), puer tea seed oil (PO) and sunflower oil (SFO). The "fingerprint frequency region" combined with principal component analysis (PCA) and mahalanobis distance were used for detecting the authenticity of WO, all the accuracy rates of the models are100%; Meanwhile, the validation samples were used to predict by the models, all the error rates are0. The partial least square (PLS) correlates the actual and FT-IR estimated values of oil adulterants (SO, PO and SFO) with coefficient of determination (R2) of0.9861,0.9912,0.9930, and the root mean square error of validation (RMSEP) values are0.0473,0.0349and0.0281, respectively. Therefore, the method has potential as a fast method for detection and quantification of WO adulteration.2. Application of FT-IR spectroscopy for the peroxide value (PV) and acid value (AV) evaluation in WO. The oxidation experiments were carried out by heating the oil samples in a convection oven at50℃, the PV and AV were determined by chemical titration and FT-IR spectroscopy method. The information of MIR spectroscopy (4000-650cm-1) combined with PLS to build the calibration model. The validation correlates the actual and FT-IR estimated value of PV and AV with correlation coefficient of0.9903,0.9895, and the RMSEP value is0.3545,0.4281, respectively. The methodology has potential as a rapid and accurate way for quantification of PV and AV of the edible oils.Application of FT-IR spectroscopy for discrimination of walnuts from different cultivars. The walnuts from different cultivars have different nutritional value. In this paper, six cultivars of dried walnuts were ground, extracted and dried, manufactured into KBr disk. The sample spectra were collected in IR region of4000-650cm-1and combined with PLS to build the discrimination model. All the six cultivar samples were used to predict by the model, the accuracy rates are100%.