Rickey Y. Yada

Structure-function relationships of cowpea (Vigna unguiculata) globulin isolate: influence of pH and NaCl on physicochemical and functional properties

Abstract Physicochemical and functional properties of cowpea globulin isolate were determined as a function of pH and NaCl concentrations. Protein solubility (PS) increased with increasing pH from 3 to 8, while at low pH, PS decreased with increasing ionic strength. At low pH and all ionic strengths, the protein isolate was extensively coagulated by heat, while aromatic hydrophobicity, fluorescence intensity and emulsifying activity index were all higher than results obtained at high pH. Emulsion stability was lowest at low pH and ionic strength. Foaming capacity increased with increasing pH and ionic strength. Foam stability was affected more by pH changes than by ionic strength. The results were discussed on the basis of protein-protein and protein-solvent interactions, as affected by the balance between electrostatic repulsions and hydrophobic interactions.

Inhibition of phospholipase D

Phospholipases A2 are involved in inflammatory processes such as the liberation of free arachidonic acid from the membrane pool for the biosynthesis of eicosanoids. Inhibitors of these enzymes are proving useful in determining the biological roles of phospholipases A2 in complex cellular processes and may also have therapeutic potential. Inhibition of these lipolytic enzymes is more difficult to characterize as the enzymatic reaction occurs at a lipid/water interface. This review focuses on the description of a number of classes of rationally designed phospholipase A2 inhibitors. The development of a theoretical framework for the proper analysis of inhibitors is presented. Structural studies of phospholipase A2‐inhibitor complexes suggest how the lipolysis reaction is catalyzed. Finally, some recent results on the use of phospholipase A2 inhibitors in living cells and tissues are revealed.— Gelb, M. H., Jain, M. K., Berg, O. G. Inhibition of phospholipase A2. FASEB J. 8: 916‐924; 1994.

Physicochemical properties of starches during potato growth

The characterization of physicochemical properties of starch during potato growth is critical to the development of new starch products. Desired functional properties may be achieved by controlling the growth period, without further physical or chemical modification of the starch. In this study, starch was extracted from three potato cultivars (Shepody, Snowden, and Superior) during growth. The physicochemical properties of starches were characterized by different analytical techniques. Gelatinization and retrogradation of starches were measured using differential scanning calorimetry. Starch crystalline structure was evaluated by X-ray diffraction. Rapid viscosity analysis was employed to measure starch paste viscosity and pasting temperature. Starch obtained from potatoes with a shorter growth time had higher gelatinization temperature, pasting temperature, lower peak viscosity (half that of normal starch) and higher final viscosity (double the value of normal starch). Results indicate that physicochemical properties of starches varied among the potato cultivars, as well as growth time. Different starch granular size, phosphorous content and amylose content could be major factors influencing starch functional properties.

Salt-soluble seed globulins of various dicotyledonous and monocotyledonous plants—I. Isolation/purification and characterization

Abstract Detailed characterization of 21 purified seed globulins derived from both monocotyledonous and dicotyledonous plants indicated that globulins from both class types (as well as within the same class type) lay within a narrow molecular weight range between 300000 and 370000 Da and were composed of multiple subunits. In all cases, purified globulins could be classified as hetero-oligomers being composed of a non-equimolar ratio of various subunits. The vast majority of subunits forming these globulins were shown to be held together by non-covalent bond forces. A small percentage of linkages between subunits were also shown to be disulfide linked, in the case of dicotyledonous seed globulins. It was also found that the majority of subunits composing the dicotyledonous and monocotyledonous seed globulins examined fell within two very narrow molecular weight ranges, i.e. 20000–27000 and 30000–39000 Da and were believed to correspond to basic and acidic subunits, respectively. Unlike monocotyledonous seed globulins, globulins derived from dicotyledonous plants were found to undergo alkaline-induced dissociation due to electrostatic repulsion between subunits. The amino acid composition of both dicotyledonous and monocotyledonous seed globulins suggests that they have a storage role and may be similar proteins based on a high content of amides (glutamic acids-glutamine and aspartic acid-asparagine and arginine). From the results of the structural and chemical data obtained in this study, it is concluded that the 11S storage globulin, having several similar properties, exists in many leguminous and non-leguminous dicotyledonous plants as well as monocotyledonous plants. This similarity among 11S storage globulins could be due either to convergent evolution in response to a common functional need, or to common ancestry.

Proteins in food processing.

Introduction: properties of proteins in food systems. Part 1 Sources of proteins: The caseins Whey proteins Muscle proteins Soy proteins Proteins from oil-producing plants Cereal proteins Seaweed proteins. Part 2 Analysing and modifying proteins: Testing protein functionality Modelling protein behaviour Modifying seeds to produce proteins Extraction and purification of proteins Detecting and removing proteins with allergenic potential. Part 3 Applications: Using proteins as additives in foods: an introduction Edible films and coatings from proteins Protein gels Textured soy protein as an ingredient Functional value of dairy proteins and peptides The impact of proteins on food colour The use of immobilised enzymes.

Salt-soluble seed globulins of dicotyledonous and monocotyledonous plants II. Structural characterization

Abstract Structural characterization of 21 seed globulins from monocotyledonous and dicotyledonous plants revealed that they generally possessed low levels of α-helix and high levels of β-sheet secondary structure fractions. This finding suggested that the interior conformation of these globulins was very similar. In contrast to internal conformations, tertiary conformations indicated that very distinct surface properties existed between these two globulin classes. It now appears that surface properties are the most variable physico-chemical properties measured between globulins. Calorimetric analysis revealed that both classes of globulins possessed temperatures of denaturation (Td) which were in the temperature range of 83.8 to 107.8 °C. Although dicotyledonous seed globulins had more pronounced thermal transitions than their monocotyledonous counterparts, most endothermic transitions occurred as co-operative events indicating that the various domains present in these globulins were held together by interdependent structural domains. These interdependent domains rendered the globulins stable to high temperatures and in connection with previous data (Marcone and Yada, 1998), it was believed that both monocotyledonous and dicotyledonous seed globulins share similar structural domains.

The structure and function of Saccharomyces cerevisiae proteinase A

Saccharomyces cerevisiae proteinase A (saccharopepsin; EC 3.4.23.25) is a member of the aspartic proteinase superfamily (InterPro IPR001969), which are proteolytic enzymes distributed among a variety of organisms. Targeted to the vacuole as a zymogen, its activation at acidic pH can occur by two different pathways, a one‐step process to release mature proteinase A, involving the intervention of proteinase B, or a step‐wise pathway via the autoactivation product known as pseudo‐proteinase A. Once active, S. cerevisiae proteinase A is essential to the activities of other yeast vacuolar hydrolases, including proteinase B and carboxypeptidase Y. The mature enzyme is bilobal, with each lobe providing one of the two catalytically essential aspartic acid residues in the active site. The crystal structure of free proteinase A reveals that the flap loop assumes an atypical position, pointing directly into the S1 pocket of the enzyme. With regard to hydrolysis, proteinase A has a preference for hydrophobic residues with Phe, Leu or Glu at the P1 position and Phe, Ile, Leu or Ala at P1′, and is inhibited by IA3, a natural and highly specific inhibitor produced by S. cerevisiae. This review is the first comprehensive review of S. cerevisiae PrA. Copyright

Modulation of phospholipase D and lipoxygenase activities during chilling. Relation to chilling tolerance of maize seedlings

Phospholipase D (phosphatidylcholine choline hydrolase, EC 3.1.4.4) and lipoxygenase activities (linoleate: oxygen oxidoreductase, EC 1.13.11.12) were analysed in chilling-susceptible and chilling-tolerant maize (Zea mays L.) seedlings in relation to their chilling tolerance. Before chilling, phospholipase D activity in the leaf microsomal fraction was 2-fold higher in the chilling-susceptible CO 316 when compared to that of paclobutrazol-treated, chilling-tolerant CO 316. Phospholipase D activity in the heavy membrane fraction comprising chloroplast and mitochondria showed a 3 to 4-fold increase during chilling and post-chilling periods, albeit with temporal variations. An increase in cytosolic phospholipase D activity was observed only in CO 316 and CO 328. Also, phospholipase D activity in the heavy membrane and cytosolic fractions of roots increased in CO 316 during chilling and post-chilling periods. Lipoxygenase activity was low in both leaves and roots of CO 328. Paclobutrazol treatment of CO 316 did not appear to affect the level of cytosolic lipoxygenase activity in roots during the early part of chilling and post-chilling, but increased the activity in leaves. The results suggest that during chilling and post-chilling periods, temporal variations in phospholipase D and lipoxygenase activities in both leaves and roots of CO 316, CO 316P and CO 328 could result in differential metabolism of phospholipids. Enhanced degradation coupled with low levels of turnover could lead to development of chilling injury in the tissue.

Methodologies for Increasing the Resistant Starch Content of Food Starches: A Review

Research involving resistant starch (RS) is becoming more prominent. RS has the ability to modulate postprandial blood-glucose levels and can be fermented by the colonic microflora to produce short-chain fatty acids, which exert positive health benefits on the consumer such as increased colonic blood flow to ease colonic inflammation and a decreased risk of colon and/or other cancers. This paper reviews the effects of genetic manipulation on amylose levels in plants, enzymatic hydrolysis, physical treatments, chemical modifications, exposure to γ-rays, and the effects of lipid complexation on the RS content of starches from various botanical sources. All treatments reviewed increased the RS content; however, select treatments (namely genetic manipulation, enzymatic debranching, hydrothermal treatments, high hydrostatic pressure, most chemical modifications, γ-irradiation exposure, as well as lipid complexation) were more effective to varying degrees than were extrusion and mineral acid treatments. Various methods commonly used for measuring RS were compared. Additionally, the effects of food matrix components were also examined to gauge their effectiveness at inhibiting or enhancing RS formation, with lipids and gums known to be the most effective at enhancing (or apparently enhancing) RS. This review draws largely, but not exclusively, from research published post 2009.

Engineered Nanoscale Food Ingredients: Evaluation of Current Knowledge on Material Characteristics Relevant to Uptake from the Gastrointestinal Tract

The NanoRelease Food Additive project developed a catalog to identify potential engineered nanomaterials (ENMs) used as ingredients, using various food-related databases. To avoid ongoing debate on defining the term nanomaterial, NanoRelease did not use any specific definition other than the ingredient is not naturally part of the food chain, and its dimensions are measured in the nanoscale. Potential nanomaterials were categorized based on physical similarity; analysis indicated that the range of ENMs declared as being in the food chain was limited. Much of the catalogs information was obtained from product labeling, likely resulting in both underreporting (inconsistent or absent requirements for labeling) and/or overreporting (inability to validate entries, or the term nano was used, although no ENM material was present). Three categories of ingredients were identified: emulsions, dispersions, and their water-soluble powdered preparations (including lipid-based structures); solid encapsulates (solid structures containing an active material); and metallic or other inorganic particles. Although much is known regarding the physical/chemical properties for these ingredient categories, it is critical to understand whether these properties undergo changes following their interaction with food matrices during preparation and storage. It is also important to determine whether free ENMs are likely to be present within the gastrointestinal tract and whether uptake of ENMs may occur in their nanoform physical state. A practical decision-making scheme was developed to help manage testing requirements.