Walter J. Wolf

Bowman–Birk inhibitors in soybean seed coats☆

Abstract Soybean Bowman–Birk inhibitor (BBI), possessing a molecular weight (MW) of 8 kD, is a known cancer chemopreventative and anticarcinogenic agent Aqueous extracts of soybean seed coats, rigorously screened to remove cotyledons, contained peroxidase along with three unknown proteins each of which possessed an estimated MW of

Ultracentrifugal and polyacrylamide gel electrophoretic studies of extractability and stability of almond meal proteins

Solubility and stability properties of almond proteins were determined using ultracentrifugation and gel electrophoresis to gain a better insight into the complexity of these proteins. Ultracentrifugal analyses of the water-extractable proteins of defatted almond meal revealed four fractions of 2S, 9S, 14S and 19S. The 14S fraction corresponds to amandin, the classical globulin isolated earlier, and constitutes 65–70% of the extractable proteins. Variation of ionic strength from 0 to 1·0 at pH 6–8 showed no evidence of association–dissociation reactions that are typical of many oilseed and legume proteins. Polyacrylamide gel electrophoresis of the water-extractable proteins under reducing conditions separated two pairs of major polypeptides of 44 and 42 kDa and 27 and 25 kDa that appeared to be the respective acidic and basic polypeptides of amandin corresponding to the classical legumin model. Sodium chloride had no effect on total protein extractability but variation of extraction pH showed a broad minimum in extractability at pH 3–5. In contrast, when a pH 9 extract was lowered in pH, the minimum in protein solubility was narrower and shifted upward to pH 5 largely as a result of the precipitation of amandin. Interaction of amandin with phytate may explain the lower pH of minimum solubility when the meal was extracted directly as opposed to lowering the pH of an alkaline extract. Amandin is a cryoprotein and was obtained in 90% purity by cooling a water extract of defatted meal. Incubation of a water extract of meal in the presence of azide for about 12 days revealed proteolytic nicking of the acidic polypeptides of amandin apparently as a result of attack by endogenous proteinase(s).

Polyacrylamide-Gel Electrophoresis of Soybean Whey Proteins and Trypsin Inhibitors

Abstract Polyacrylamide-gel electrophoresis with glycine buffer (pH 9.2) containing 8 m urea separated soybean whey proteins into at least 24 bands. In contrast, ultracentrifugation indicated only 2 fractions; moving-boundary electrophoresis, 8–9 components; and column chromatography, 13 or more proteins. A prominent, fast-moving band in the gel pattern appeared to be identical to crystalline soybean trypsin inhibitor. Examination of 9 commercial samples of trypsin inhibitor showed multiple bands in all; most samples separated into 6 or more bands, and one preparation resolved into at least 13 bands in the gel. An inhibitor sample isolated by column chromatography and apparently identical to crystalline inhibitor also appeared heterogeneous although it contained fewer minor bands than the commercial samples. Three other trypsin inhibitor fractions recently isolated by column chromatography likewise yielded multiple bands but distinctly different from crystalline soybean trypsin inhibitor. Polyacrylamide-gel electrophoresis appears to be a sensitive tool for examining soybean whey protein fractions and should greatly facilitate future fractionation studies on this complex protein mixture.

FT-IR analysis of Jojoba protein conformations in D2O

FT-IR methods in the literature for determining the secondary structure of proteins in D2O solution involve a curve-fitting step which is somewhat subjective. In an effort to reduce the subjectivity of curve-fitting of protein amide carbonyl absorbances, initial estimations of peak heights and widths were used which were independent of operator judgment. Other restrictions on the curve-fitting procedure were imposed so that different operators would arrive at values for secondary structure consistent with each other and with the literature for papain, hemoglobin, ribonuclease, myoglobin, and alpha-chymotrypsin. This goal was partially achieved by the preliminary method described in this paper. The method was then applied to jojoba proteins and a jojoba protein isolate, the 2S fraction. The jojoba 2S fraction is predominantly beta-structure (51%) and retains its beta-structure in pD 13 solution or at neutral pD when its disulfide linkages are reduced and alkylated. However, dissolving the reduced alkylated protein in pD 13 solution gives a totally random structure by infrared analysis.

Air Classification of Pin-Milled Soybean Hulls

ABSTRACT Commercial soybean hulls (14.6% crude protein) were pin milled and then air classified into five fractions to determine whether the hull structure can be disrupted and the protein constituents concentrated. The number of pin millings had only a small effect on the weight distribution of the five fractions. After one grinding, the sum of fractions 1 and 2 ( 30 μm) shifted from 75 to 69% on three pin millings to compensate for the shifts noted in fractions 1–3. Scanning electron microscopy revealed that fractions 1 and 2 consisted of the parenchymal cell layers (innermost portion) of the hulls; these fractions had three times the protein content and more than twice the amount of lipids found in the ground starting material. Fraction 3 contained many of the hou...

A Simple Technique to Improve the Firmness of Cooked Potato Tissue

Potato tissue samples with varying cell turgor pressures were prepared by soaking in mannitol solutions (0 to 0·5 M). Increased concentration of mannitol in the soaking solutions decreased the cell turgor pressure in potato tissues providing samples with varying degrees of turgidity or plasmolysis. Firmness changes in potato tissues of differing turgor pressure during cooking were examined using a Zwick universal testing machine and also by chewing tests. A modified device attached to a Zwick machine facilitated complete immersion of a potato disc in circulating boiling water, providing rapid and reproducible heat transfer in the tissue during firmness measurements. Tissue firmness expressed as the force required to cause 10% strain in the sample varied in potato discs treated with differing mannitol solutions. Potato discs soaked in 0 to 0·3 M mannitol solutions were more turgid at 20°C than other samples and showed higher tissue firmness. However, when discs of potato were heated in the range of 20–90°C, samples treated with 0·4 and 0·5 M mannitol solutions showed some increase in tissue firmness while all other samples exhibited a rapid decline. Bite-force measurements on potato discs also indicated a rapid loss of tissue firmness in turgid samples. Potato tissues when cooked after soaking in 0·4 or 0·5 M mannitol solution showed more intact and inflated cells than other samples.