D.L. Pyle

Aqueous and enzymatic processes for edible oil extraction

Abstract Industrial processes for the extraction of edible oil from oilseeds generally involve a solvent extraction step which may or may not be preceded by pressing. Hexane is the preferred solvent; hexane-based processes have been in commercial operation for a long time. For such processes, it is possible to achieve oil yields in excess of 95% with a solvent recovery of over 95%. In the past, the main concern of this process has been the safety implications surrounding the use of hexane. This prompted attempts to develop processes based on the use of aqueous extraction media which were unsuccessful mainly due to low oil yields. The scenario at present appears to be changing. Interest in aqueous extraction processes has been revived by increasing environmental concern. An aqueous process is looked upon as an environmentally cleaner alternative technology for oil extraction. Organic solvents such as hexane, in particular, can contribute to the industrial emissions of volatile organic compounds (VOCs). The production of VOCs in the conventional process is particularly worrisome since these can react in the atmosphere with other pollutants to produce ozone and other photochemical oxidants which can be hazardous to human health and can cause damage to crops. Besides this, the VOCs are themselves “greenhouse gases”; some are carcinogenic and have toxic properties. Other advantages of the aqueous process compared with solvent-based processes include: (1) simultaneous production of edible oil and protein isolate or concentration in the same process, (2) lower protein damage during extraction, and (3) improved process safety due to the lower risk of fire and explosion. It is also reported that aqueous extraction processes may be more cost effective since the solvent recovery step is eliminated. The main limitations of this process appear to be: (1) lower efficiency of oil extraction as evident in earlier studies, (2) demulsification requirements to recover oil when emulsions are formed, and (3) treatment of the resulting aqueous effluent. With the objective of improving the yield of aqueous processes, enzymes have been used to facilitate oil release. Selected enzymes have been tried on different types of oilseeds, resulting in extraction yields much higher than the original aqueous process (in some cases of over 90%). These enzymes mainly hydrolyze the structural polysaccharides which form the cell wall of oilseeds or the proteins which form the cell and lipid body membrane. This article aims to review aqueous and enzyme-based processes and discuss related issues.

Combined effect of operational variables and enzyme activity on aqueous enzymatic extraction of oil and protein from soybean

The individual effect of two different enzymes-protease and cellulase-on oil and protein extraction yields combined with other process parameters-enzyme concentration, time of hydrolysis, particle size and solid-to-liquid ratio-was evaluated by Response Surface Methodology. The selection of the enzymes for the study was based on preliminary experiments that showed higher increments in the extraction yield with the use of the two enzymes when compared to hemicellulase and pectinase. The levels of the quantitative parameters studied were: i) enzyme concentration: 0.1, 0.45, 2 w/w %; ii) liquid-to-solid ratio: 0.05, 0.125, 0.2; iii) mean particle size: 212.5, 449.5, 855 µm; iv) time of hydrolysis: 30; 60; 120 min. Experimental data for both oil and protein extraction yields obtained with and without enzymes correlated very well with process parameters (P < 0.0001), resulting in models with high coefficient of determination for oil and protein extraction yields (r(2) = 0.9570 and r(2) = 0.9807, respectively). The use of protease resulted in significantly higher yields over the control (protein yield increased from 27.8 to 66.2%, oil yield increased from 41.8 to 58.7%) only when heat treated flour was used, or when non-heat treated flour with large particle sizes was used in the extraction. The yields of protein and oil from non-heat treated material in general decreased slightly with the use of enzymes.

Simultaneous Aqueous Extraction of Oil and Protein from Soybean: Mechanisms for Process Design

Aqueous extraction of oil and protein from soybean flour was investigated to elucidate the mechanisms involved. The process variables investigated were: particle size, temperature, time, pH, power input, solid-to-liquid ratio, use of several extraction steps, and the use of preliminary heat treatment prior to the extraction. Protein and oil extraction yields were shown to be closely related, both depending on the level of disruption of cell wall. Experimental investigations show that protein extraction from the disrupted cells follows a solubilization/diffusion mechanism. Conditions that favour protein extraction—i.e., temperature below the level causing denaturation, pH away from the isoelectric point, and use of several extraction steps—generally favour oil extraction. However, the mechanisms governing protein extraction rates are quite different from those governing oil extraction rates. The extraction mechanisms are also elucidated in the context of the cell structure, and the response to different extraction parameters form the basis for the process design and optimization.

Production of polygalacturonases from Kluyveromyces marxianus fermentation: preliminary process design and economics

A simple one-stage purification scheme for the recovery of polygalacturonase from K. marxianus fermentation is described. The optimum pH for ion exchange is 4·5, which, being compatible with the fermentation conditions, means that the broth can be centrifuged and directly applied to an ion-exchange column; the process gives more than 90% recovery of a highly purified enzyme. Economic analysis of a repeated batch process shows that recovery of other by-products (cells and ethanol) is only of marginal importance, whilst pectinase production is highly profitable. There are strong economies of scale, up to a fermentation batch scale of around 20 m3, with 100 batches per year. Under typical conditions our analysis predicts a payback time of under a year.

An investigation into the use of the spinning cone column for in situ ethanol removal from a yeast broth

Abstract The spinning cone column (SCC), previously employed in the food industry for volatile removal at low temperatures, is investigated with the aim of removing ethanol in situ from a yeast broth. A 100 litre fermenter was integrated into the SCC pilot plant and broth passed continuously through the column. Although the SCC effectively removed ethanol from the broth, cell viability declined significantly with time. Laboratory scale experiments suggest that this is a result of various factors, the main one being the effect of reduced pressure upon cell size and shape. It was proposed that passing broth through the SCC at intervals rather than continuously, with periods to allow cells to ‘recover’ could prove to be more effective whilst keeping the broth ethanol concentration low. This process was employed upon cells at both stationary and logarithmic growth phases, and the results compared for cell viability and extent of recovery.

Adsorption of Kluyveromyces marxianus pectinase on CM-Sephadex gels

New results are presented on the equilibria and kinetics of the ion exchange onto CM-Sephadex of polygalacturonase (pectinase) produced by the fermentation of Kluyveromyces marxianus. It is found that the equilibrium behavior follows the form of the Langmuir isotherm; the equilibrium is strongly affected by pH. High partitioning onto the ion-exchange matrix, with good retention of enzyme activity, is achieved in the pH range 3.5-5.0, and this can be qualitatively explained in terms of simple models for protein adsorption by ion exchange. The kinetics of ion exchange is modeled by assuming that the transfer resistances can be lumped into a single coefficient, and the results show that this gives a reasonable description of the adsorption kinetics. Under optimum conditions protein adsorption is enhanced by electrostatic effects and is extremely fast, and it is suggested that in these circumstances external mass transfer resistance is significant. At pH values close to the isoelectric point, electrostatic interactions are weak and intraparticle diffusion is rate-limiting: pore-blocking by adsorbed proteins appears to be important under these conditions. The results also provide the basis for an efficient single-step purification scheme.

Screening of Filamentous Fungi for the Production of Extra-Cellular Tannase in Solid State Fermentation (SSF)

Tannin acyl hydrolase (E.C. 3.1.1.20), commonly called tannase, hydrolyses ester and depside bonds in hydrolysable tannins and gallic acid esters (Dykerhoff and Ambruster, 1933) and is mainly produced by fungal strains belonging to the Aspergillus and Penicillium genera (Lekha and Lonsane, 1997). Tannase acts on hydrolysable tannins and not on condensed tannins (Dykerhoff and Ambruster, 1933). However, the hydrolysis of condensed tannins such as (—) epicatechin gallate and (—) epigallocatechin-3-galate has been reported (Lekha and Lonsane, 1997).

Effect of pH on Polygalacturonase Adsorption in CM-Sephadex Gels

This paper reports the effect of pH on the adsorption characteristics of fungal polygalacturonase in CM-Sephadex ion exchangers, in dilute solutions and in batch operations. The partition coefficient increases sharply at pH below 4.3, reaching a peak at about pH 3.2. Equilibrium isotherms follow the Langmuir law and are strongly affected by pH; the maximum adsorption capacity of adsorbent increases with decreasing pH. These findings reflect the effect of pH on the relative degrees of ionisation of adsorbate and adsorbent, and highlight the need to determine the optimum pH for every specific enzyme system.