Rice bran FFA determination by diffuse reflectance IR spectroscopy

Abstract

Rice bran with FFA levels above 0.1% cannot be used as a food ingredient due to oxidative off-flavor formation. However, extracting high FFA oil from bran by in situ methanolic esterification of rice bran oil to produce methyl ester biodiesel produces greater yields relative to low-FFA rice bran oil. Therefore, high-FFA bran could be exploited for biodiesel production. This study describes an FTIR spectroscopic method to measure rice bran FFA rapidly. Commercial rice bran was incubated at 37°C and 70% humidity for a 13-d incubation period. Diffuse reflectance IR Fourier transform spectra of the bran were obtained and the percentage of FFA was determined by extraction and acid/base titration throughout this period. Partial least squares (PLS) regression and a calibration/validation analysis were done using the IR spectral regions 4000-400 cm −1 and 1731-1631 cm −1 . The diffuse reflectance IR Fourier transform spectra indicated an increasing FFA carbonyl response at the expense of the ester peak during incubation, and the regression coefficients obtained by PLS analysis also demonstrated that these functional groups and the carboxyl ion were important in predicting FFA levels. FFA rice bran changes also could be observed qualitatively by visual examination of the spectra. Calibration models obtained using the spectral regions 4000-400 cm −1 and 1731-1631 cm −1 produced correlation coefficients R and root mean square error (RMSE) of cross-validation of R = 0.99, RMSE = 1.78, and R = 0.92, RMSE = 4.67, respectively. Validation model statistics using the 4000-400 cm −1 and 1731-1631 cm −1 ranges were R = 0.96, RMSE = 3.64, and R = 0.88, RMSE = 5.80, respectively.

Visible Raman spectroscopy for the discrimination of olive oils from different vegetable oils and the detection of adulteration

“…It shows that the sunflower oil labeled 'sunflower2', which is organic oil, offers the optimum calibration model among all other sunflower oils, with lowest RMSE and highest R. That could be due to the higher content of free fatty acid in organic oil since this oil showed the lowest intensity of the band at 1750 cm −1 , which is reported to decrease with the increase of FFA in edible oils. [43,44] This high content of FFA in organic oil can be attributed to the absence of refining, whereas conventional oils (the two remaining ones in the table) had lower FFA content. [45] In order to further assess the capability and also the limitation of the PLS model, we have extended the calibration range by minimizing the sunflower oil content in extra virgin olive oil from 3, 2, 1, 0.5 down to 0.05%, corresponding to a detection limit of 500 ppm.…”

Rapid Oil Extraction from Potato Chips

“…Similarly, total oil in 2 g of rice bran samples was obtained by a rapid 1 min hexane or isopropanol extraction that produced the same results as Goldfisch extraction [2]. This method allowed large number of rice bran samples to be quickly extracted for free fatty acid determination by wet chemistry to obtain a diffuse reflectance FTIR chemometric model of the free fatty content [3]. Similarly, the total surface oil on milled rice was determined by rapid solvent extraction [4].…”

Simple and rapid determination of free fatty acids in brown rice by FTIR spectroscopy in conjunction with a second-derivative treatment

“…In the obtained spectra, the 1710 cm À1 band was observed and its intensity increased with storage time. The partial least squares regression models predicted the FFA concentrations in milled rice (Lam et al, 2001) and rice bran (Özgül-Yücel & Proctor, 2004) successfully.…”

“…FTIR spectra of fat and oils provide information regarding functional groups; for example, the bands at 966 and 1710 cm À1 are assigned to the out-of-plane CAH deformation vibrational mode of trans fatty acids (Mahesar et al, 2010) and the C@O stretching vibrational mode of FFAs (Ismail et al, 1993), respectively. Through FTIR spectroscopy, the transmittance (Sato, Tanno, Sato, & Tanaka, 2005) and diffuse-reflectance (Lam, Proctor, & Meullenet, 2001;Özgül-Yücel & Proctor, 2004) methods for FFA determination in rice were developed. In the method of Sato et al (2005), the FFAs in rice bran were extracted with carbon tetrachloride (CCl 4 ), and the FTIR spectra of the extracts were recorded using CCl 4 for the background spectrum.…”

“…The absorbance at 1710 cm À1 increased with storage time, and the single linear regression model using this absorbance showed a strong correlation with a titration method. In the diffuse-reflectance FTIR method (Lam et al, 2001;Özgül-Yücel & Proctor, 2004), the spectra were recorded without extraction of FFAs with an organic solvent (i.e., directly from the sample surface). In the obtained spectra, the 1710 cm À1 band was observed and its intensity increased with storage time.…”