Hexane extraction is the most common technique

No abstract

This study was undertaken to determine if the yield and purity of soy protein isolates could be improved by changing the particle size of the starting raw material. Soy protein isolates were extracted from hexane defatted soy flour ground to three different average particle sizes (89.5 ± 1.1, 184.2 ± 1.6 and 223.4 ± 6.4 µm). By decreasing the average particle diameter of the starting raw material (soy flour) from 223.4 to 89.5 µm the total solids recovery increased from 23 to 32% (P = 0.00008), while the protein recovery increased from 40 to 52% (P = 0.00004). Final protein content (i.e., purity) of the soy protein isolates was not significantly impacted by average particle size. The results clearly demonstrated that protein recovery can be increased by >30% by decreasing the average particle size of the starting raw material (i.e., defatted soy flour), without having any detrimental impact on the purity of the final soy protein isolate.

A new FTIR approach was investigated for assessing edible oil oxidative stability with the use of polymer IR (PIR) cards as sample holders. This approach allows oil oxidation to be monitored at moderate temperatures owing to the fairly rapid rate at which unsaturated oils oxidize on the PIR cards. To assess the FTIR/PIR card method, pure TAG-triolein, trilinolein, and trilinolenin-were loaded onto cards and placed in a chamber where warm air (55°C) flowed over them continuously to facilitate oxidation. At periodic intervals, individual cards were removed and their FTIR spectra scanned, after which they were replaced in the aeration chamber. All spectra were normalized to compensate for variations in PIR card path lengths or oil loadings, and for each card the initial spectrum recorded (t = 0) was subtracted from all subsequent spectra taken over time to produce differential spectra. With the use of a peak-find algorithm, the absorbance minimum in the cis region (3017-3000 cm −1 ) and the absorbance maxima in the hydroperoxide (3550-3200 cm −1 ), isolated trans (977-957 cm -1 ), and conjugated trans regions (995-983 cm −1 ) were measured in the differential spectra and plotted as a function of time. For all three TAG, the loss of cis double bonds was linearly related to the development of hydroperoxides and isolated trans bonds for much of the oxidation process, whereas for the polyunsaturated TAG a similar relationship also existed for conjugated trans species. Based on an experimentally determined hydroperoxide (ROOH) absorbance slope factor (0.06 mAbs/PV), ROOH absorbance changes were converted to PV, allowing direct PV monitoring as a function of time using the PIR cards. Trilinolenin, trilinolein, and triolein attained a PV of 100 mequiv/kg oil after 43, 98, and 2889 min, respectively, their relative reaction rates being similar to ratios published in the literature. The assessment of the FTIR/PIR card method using TAG indicates that it may be a practical and rapid means of oxidizing lipids and tracking their oxidative state in terms of PV so as to provide a measure of their oxidative stability.

Disposable polytetrafluoroethylene (PTFE) polymer IR (PIR) cards were used as substrates to rapidly oxidize edible oils and simultaneously monitor the extent of oxidation by FTIR spectroscopy. Four edible oils were oxidized on PIR cards and in bulk at moderate temperature (58°C), and real-time oxidation plots were obtained by measuring changes in the IR hydroperoxide (ROOH) absorbance as a function of time. The relationship between the ROOH absorbance and PV was developed using a reference method to define absorbances corresponding to PV end points of 100 and 200 meq ROOH/kg for the oils oxidized in bulk and on cards, respectively. The real-time oxidation plots obtained for the oils oxidized in bulk and on cards were similar in appearance, but the oils on the cards reached the PV end point 20 times faster than the oils oxidized in bulk. The results indicate that the use of disposable PIR cards coupled with moderate heating and aeration provides a simple, practical, and rapid means for monitoring oxidation and determining the oxidative stability of edible oils at a normal storage temperature.