David J. Sessa

DSC study of biodegradable poly(lactic acid) and poly(hydroxy ester ether) blends

DSC heating–cooling cycles (0–200 ◦ C) were repeated on poly(lactic acid)/poly(hydroxy ester ether) (PLA/PHEE) blends to study the miscibility of the two polymers. Initial thermograms show two distinguishable Tg values corresponding to the respective neat polymers, accompanied by a crystallization and a melting peak for the PLA. Subsequent DSC runs show that the thermogram profiles depend on the number of heating–cooling cycles the blends are subjected to. As the number of cycles

Lipid-Derived flavors of legume protein products

Abstract and SummaryLegumes contain unsaturated lipids that are susceptible to oxidative deterioration. Enzymic and non-enzymic deterioration of these lipids results in the development of off-flavors. The primary objective of this review is to summarize what is currently known about lipid-derived flavors of soybeans and underblanched pea seeds(Pisum sativum). Identifying the numerous volatile compounds arising from breakdown of lipid hydroperoxides coupled with organoleptic evaluation defines the flavor problem. Major contributors to the green-beaniness of soybeans were found to be 3-cis-hexenal, 2-pentyl furan, and ethyl vinyl ketone. Oxidized phosphatidylchohnes cause some of the bitter taste. The interaction of lipid breakdown products with proteins, carbohydrates, and other constituents can affect flavor characteristics and also increase the problems of their removal from soy protein products. To prepare bland products, it will be necessary to develop processes that effectively remove bound flavor components and prevent formation of derived flavors. Solvent systems based on alcohol have been used to extract flavor principles from soybeans; aqueous alcohol treatment of the intact seed or blanching with hot water or steam inhibits formation of off-flavors in peas and soybeans. A new approach involving infusion of antioxidants into the intact seed to control lipid deterioration during processing and storage is proposed to minimize flavor formation without subsequent undesirable changes in protein which occur with alcohol treatments.

Chemistry and Physical Properties of Melt-Processed and Solution-Cross-Linked Corn Zein

Corn zein was cross-linked with glutaraldehyde (GDA) using glacial acetic acid (HAc) as catalyst. The objectives are to evaluate the swelling characteristics of GDA cross-linked zein gels in water, ethanol, and their combinations. Similar formulations, upon solvent evaporation, form films. The mechanical properties of the films are compared to compression molded tensile bars from GDA melt-processed zein as a second objective. Chemistry of the cross-linking reaction was based on the aldehyde binding characteristics defined by use of fluorescence spectroscopy; sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to demonstrate the cross-linking reaction; FTIR to observe absorption differences of the cross-linked product; differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis to assess thermal properties; and the use of Instron Universal Testing Machine to evaluate mechanical properties. A reaction mechanism for acid catalyzed GDA cross-linking of zein is proposed. Thermal and mechanical properties of tensile bars cut from either film or formed by compression molding were similar, where both showed increased tensile strengths, ductility and stiffness when compared with unmodified controls. Samples that were reacted with 8% GDA by weight based on weight of zein from either process retained their integrity when tensile bars from each were subjected to boiling water for 10 min or soaking in either water or HAc for 24 h. The melt-processed, cross-linked zein is a more environmentally friendly method that would eliminate the need for HAc recovery.

Toasted soybean flour components with trypsin inhibitor activity

Compounds in toasted soybean flour having trypsin inhibitor (TI) activity were isolated and characterized. Sodium hydroxide (0.01N) extracts of toasted soybean flour had an average of 2.59 mg TI/g sample. These extracts, after trichloroacetic acid (TCA) precipitation and dialysis, yielded supernatant and precipitate fractions. Addition of polyvinylpyrrolidone to eliminate free tannins and phenolics in the extracts, which may lead to overestimation of TI activity, was unnecessary. Material balance studies revealed 91% protein recovery and 92% recovery of TI activity in the TCA supernatant (1.1% protein, 2.0% TI) and precipitate (89.8% protein, 90.0% TI) fractions. Column chromatography and electrophoresis showed the TCA supernatant and precipitate fractions to contain proteins, including those having TI activity. Kunitz type TI and Bowman-Birk type protease inhibitors accounted for most residual TI activity of toasted soybean flour, as verified by column chromatography, isoelectric focusing, sodium dodecyl sulfate polyacrylamide electrophoresis, and size-exclusion high performance liquid chromatography, using the two similarly treated protease inhibitors as standards. Immunoblotting was also used to detect and identify Kunitz type TI’s in toasted soybean meal extracts. This study established the proteinaceous nature of residual trypsin inhibitor activity in toasted soybean flour and the presence of both Kunitz and Bowman-Birk inhibitors.

Role of non-covalent interactions in the production of visco-elastic material from zein

The role of non-covalent interactions in the formation of visco-elastic material from zein was investigated. Hydrophobic interactions were evaluated through the addition of various salts from the Hofmeister series. Urea, ethanol, and beta mercaptoethanol (β-ME) were used to evaluate the effects of protein denaturation and disulfide bonds on zeins ability to form a visco-elastic material. The addition of NaI and NaSCN altered the properties of visco-elastic materials made from zein, making them softer and more extensible, as did urea and ethanol. The addition of NaCl and Na2SO4 negatively impacted the ability of zein to from a visco-elastic material and at higher concentrations completely disrupted the formation of visco-elastic material. These results indicate that manipulating non-covalent interactions in zein can alter and in some cases, completely disrupt the formation of a visco-elastic material. Specifically this may be due to disruption of hydrophobic interactions within individual zein proteins or interactions between proteins. The reducing agent β-ME had little effect on zeins ability to form a visco-elastic material. Therefore, the visco-elastic properties of zein arise as a result of non-covalent interactions.

Differential scanning calorimetry index for estimating level of saturation in transesterified wax esters

Differential scanning calorimetry (DSC) thermograms of fatty esters can give valuable information on melting characteristics and heats-of-fusion enthalpy (ΔH). A series of jojoba liquid wax esters was constructed by transesterifying native jojoba oil with 5–50% completely hydrogenated jojoba wax esters. This series, when subjected to a standardized DSC tempering method with heating/cooling cycles, exhibited an excellent correlation for level of saturation based on area changes in endothermic ΔH. Endothermic events were recorded for native (ΔHA) and completely hydrogenated (ΔHC) jojoba wax esters. A third endotherm, ΔHB, was observed when they were transesterified. Based on a multiple regression program, the best fit (R2=0.98) using ΔH data was: % saturation=16.847–0.162 (ΔHA)+0.209 (ΔHB)+0.600 (ΔHC). Standard errors for predictions were approximately 1.045 at 0% saturation, 0.770 at 25% saturation, and 1.158 at 50% saturation. Endothermic events A, B, and C each represent the respective diunsaturated, mounounsaturated, and saturated contents of wax esters in the transesterified blends. This was verified by measuring the dropping points for both the native and completely hydrogenated wax esters. These findings provide an index which can predict the degree of saturation in transesterified wax ester blends and serves as a research tool in process and product developments.