Rapeseed aqueous processing

Several factors make the process particularly appealing to the rape-seed/canola industry. As such, most of the developmental work on the process has been done with canola/rapeseed. Although seed varieties with low levels of glucosinolates are now in use in the rapeseed/canola industry, other compounds such as tannins, sinapine and phytic acids are still significantly abundant in the seeds and remain in the meal produced by conventional extraction processes. The enzymatic aqueous process yields a final meal with significantly reduced levels of these compounds (Table 12.4). 

FIGURE 4.4 Aqueous processing of rapeseed. (From Embong, M. B. and Jelen, P. 1977. J. Inst. Can. Sci. Technol. Aliment. 10 239-243. With permission.)... 

A patent by Shigeru et al. (2003) (Patent 2003030888) disclosed a method for obtaining 4-VS as a methanolic extract from crude rapeseed oil. In this method, crude rapeseed oil was treated with alcohols or aqueous alcohols and a concentration of the vinylphenols prepared by distillation. Sinha et al. (2006) (US patent 6989,467 B2) invented a microwave-induced process for the preparation of substituted 4-VP from 4-hydroxyphenylaldehydes and malonic acid in the presence of organic acid and organic base. 

These results concurred with the findings of Thiyam et al. (2006a) that rapeseed meal extracts contained free sinapic acid, which was equivalent to just one-tenth of the content of sinapine. This was further illustrated by the Iree-phenolic fractions of the meal extracts that could recover the free sinapic acid safisfactorily. Usually in analysis, the phenofic extracts are hydrolysed with NaOH and the released-phenolics are extracted with diethyl ether, ethyl acetate or both. Comparisons between the aqueous fraction (rich in sinapine) before and after hydrolysis producing the released fraction (rich in sinapic acid) showed reasonable results with minimum hydrolysis losses affecting the accuracy of the process. Additionally, fiactionation of the 70% methanolic extract showed comparable extraction efficiency to the original extract before fractionation. 

The concentration of enzyme in the extraction medium greatly affects the enzymatic reaction rate and the oil extraction yield. It has been demonstrated that an increase in enzyme concentration from 0.2 to 2.5% (v/w) resulted in significant improvement in oil recovery, but further increase to 5% did not bring additional enhancement in rapeseed oil extraction yield (Zhang et al., 2(X)7). The amount of enzyme needed to achieve acceptable oil yields needs to be determined to optimize yield and the cost of enzyme for economic feasibility. Action of enzyme on oilseeds and mass transfer between the aqueous medium and the seed material are time dependent processes. In most cases an increase in extraction time results in an improvement in the oil extraction yield, but the improvement slows down and eventually stops as time prolongs (Sharma et al., 2002). Hence, extraction time is a variable... 

---