Soybean buffer systems

Emulsification properties in model food systems. Pearson et al. (25) investigated the emulsification properties of caseinate and NFDM in model emulsion systems produced by blending soybean oil into an aqueous buffer system as a function of pH and ionic strength (Figures 7 and 8). They found that caseinate exhibited good emulsification properties under all pH and ionic strength conditions studied, but was particularly effective at pH 10.4. 

In our experience with cultivated and wild soybean tissues, a discontinuous buffer system using 5 mM L-histidine (pH 7.0) as the gel buffer and 0.13 M Tris-40 mM citrate (pH 7.0) as the electrode buffer works well for the 23 enzymes we routinely assay. We employ this single buffer system whenever possible so that we can assay for as many enzymes as possible on a single gel. 

We previously described [25] the function of soybean lipoxygenase-1 in a biphasic system (modified Lewis cell) composed of an aqueous phase (borate buffer) and octane. The substrate of the reaction is linoleic acid (LA) and the main product is hydro-peroxyoctadecadienoic acid (LIP). The system involves two phenomena LA transfer from the organic to the aqueous phase and lipoxygenase kinetics in the aqueous medium. 

AS/. The AV is the number of milligrams of potassium hydroxide necessary to neutralize the acids in 1 g of lecithin (62). A product s AV is representative of the acidity contributed by both the phospholipids and any free fatty acids that are present. The AV is usually not indicative of pH, as the chemical nature of the phospholipid imparts buffering quahties to most systems. Lecithins typically exhibit a neutral pH value in aqueous media. An AV above 36 may indicate degradation of the lecithin because of improper processing or substandard quality soybeans. AV should not be confused with free fatty acid content, pH, or mineral acids. The correct method to assay for free fatty acids is to titrate only the acetone-soluble portion of the lecithin, whereby any contribution from the phospholipids in the acetone-insoluble portion is eliminated. AV is determined by the AOCS Official Method Ja 6-55 (77). 

A solution of 1 mg.mr NBD-PE (Avanti) In HEPES buffer (10 mM HEPES, 35 mM sodium nitrate, pH 7.4) was prepared In vesicle form. 60 ul of this was added to 100 ul of stock AChR solution and sonicated for different periods of time, yielding a final system of vesicles approximately 2 molt NBD-PE In I Ipid component, assuming a mean molecular weight of 750 gjK>l for the soybean lecithin. 

From Stockmann and Schwarz (1999). Oil-in-water emulsions were prepared with 20% corn oil and 1% emulsifier in 0.2 M acetate buffer (pH 5). SDS = sodium dodecyl sulfate, CTAB = cetyltrimethyl ammonium bromide, Brij 58 = polyoxyethylene 20 cetyl ether, PHLC = partially hydrolysed soybean lecithin. Amount of solute solubilized in oil lipid phase of emulsions was calculated from the difference between the total amount in the system and the amount of oil solubilized in the aqueous phase determined by ultrafiltration and semiequiUbrium dialysis. 

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