Application of membranes and enzymes in processing vegetable oils

The thesis was initiated through an exhaustive review of research conducted
worldwide towards degumming, dewaxing, decolourizing and deacidifying
edible oils using membrane technology. To begin with, the influence of
phospholipid (PL) composition and solvent (hexane) medium on critical
micelle concentration levels in crude oil and crude oil-hexane systems was
investigated, which explained the dependency of ultrafiltration membranes on
the initial PL concentration in their degumming performance and how the
nonporous membranes achieved near complete degumming in vegetable oils
under various conditions. Attempts made to enhance oil flux showed that the
nonporous membrane did not reject triglycerides (TG) over a wide range of
hexane dilution due to a positive flow coupling with hexane while improving
the oil flux by an order of magnitude. Besides, the results revealed that the oil
flux followed an inverse relationship with average molecular weights of TG
despite their narrow range of existence in various vegetable oils, interestingly
even under hexane-diluted conditions. Assessing the potential of nonporous
membranes revealed its prospect as a single-step pretreatment process for
simultaneous degumming, dewaxing and decolourizing crude rice bran oil
besides eliminating the problem causing phosphoglycolipids. Enzymatic
degumming employing phospholipase-A1 was found to be effective in oil
system, however only to a moderate extent in hexane-oil system. Further,
potential applications of membrane technology in nonaqueous systems were
examined, specifically for enriching beneficial oryzanol in rice bran oil (RBO)
and deoiling lecithin. Nonporous membrane exhibited moderate rejection of
oryzanol (ferulate esters) in RBO owing to their hydrophilic nature, suggesting
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a physical method for enriching oryzanol in RBO and thereby the possibility of
producing a standard RBO with a guaranteed oryzanol content. The
phenomenally high selectivity of nonporous membrane for PL was responsible
for its high efficacy in deoiling lecithin in a favourable solvent (hexane) scoring
over the industrially-practiced acetone-extraction method. Nonporous
membranes possess the potential for being employed in various steps of
vegetable oil processing, however the flux needs further improvement for
industrial adoption. Thus present study has clearly brought out the
effectiveness of nonporous membranes on their suitability in nonaqueous
applications, principally in vegetable oil processing.