Functional properties of plant proteins. Part 2. Selected physicochemical properties of native and denatured protein isolates from faba beans, soybeans, and sunflower seed

Effects of hexane on protein profile and techno-functional properties of pea protein isolates

The defatting of legume flours with hexane is usually the first step in producing protein-rich ingredients. However, its impact on protein profiles, zeta potential, surface hydrophobicity and techno-functionality of pea proteins has not been evaluated. Consequently, this work aimed to evaluate the impact of the hexane defatting step on pea protein profiles, surface hydrophobicity and zeta potential, as well as techno-functional properties of non-defatted and defatted pea protein isolates. The results showed that alkaline extraction of hexane-defatted pea flour increased the net surface charge (zeta-potential) and reduced particle size of the pea protein isolate. Moreover, only the foaming properties of pea protein isolate generated from defatted pea flour were improved. Consequently, except for improving foaming properties, the defatting step is not essential for the production of pea protein isolate.

Modifying Faba Bean Protein Concentrate Using Dry Heat to Increase Water Holding Capacity

We investigated the effect of dry-heat treatment on the properties of faba bean protein concentrate using soy protein concentrate as a benchmark. While soy protein-widely used as an ingredient in meat replacers-is recovered through a wet fractionation, protein recovery from starch bearing pulses like faba bean can be done via dry fractionation. This process does not require drying or heating steps and therefore, keeps the original protein functionality intact. This results in differences in properties such as water binding capacity of the protein fraction. Faba bean protein concentrate was dry-heated at temperatures from 75-175 °C, which resulted in higher water-holding capacity and less soluble protein, approaching values of soy protein concentrate. These changes were due to partial denaturation of protein, changing the structure of the protein, and exposing hydrophobic sites. This led to protein aggregation, as observed by light microscopy. Only noncovalent bonds caused the decrease of solubility of dry-heated faba bean protein concentrate. We conclude that dry-heating of dry fractionated faba bean protein can change the functional properties of the protein fraction to desired properties for certain applications. The effect is similar to that on soy, but the underlying mechanisms differ.

Recovery and techno-functionality of flours and proteins from two edible insect species: Meal worm (Tenebrio molitor) and black soldier fly (Hermetia illucens) larvae

Depending on the species, edible insects are highly nutritious and thus represent a noteworthy alternative food and feed source. The current work investigates the protein extractability and techno-functionality of insect flour fractions recovered from Tenebrio molitor and Hermetia illucens. T. molitor and H. illucens flours contained about 20% crude fat and 60% and 36 % crude protein, respectively. Defatting reduced the crude fat content to 2.8% (T. molitor) and 8.8% (H. illucens) and increased the crude protein content to 68% and 47%, respectively. To isolate proteins from the flours, protein solubility was optimized by varying the pH, the ionic strength, and the extraction temperature of the solvent. All products and by-products accumulated in the protein production process were characterized by composition, selected techno-functional properties, protein solubility, composition and structure as well as their microbial load.

Application of high-performance liquid chromatography to the assessment of subunit heterogeneity in plant 11S storage globulins

Plant 11S storage proteins from a wide range of species have been resolved into their component subunits by ion-exchange fast protein liquid chromatography under denaturing conditions. The complex profiles obtained were reproducible and characteristic for each plant species analysed. The technique is shown to have distinct advantages over the more conventional electrophoretic approaches used to assess 11S subunit heterogeneity. The potential for the fast protein liquid chromatographic method as a simple screening system is discussed.

Functional properties of plant proteins. Part IV. Foaming properties of modified proteins from faba beans

The foaming ability (foam capacity and stability) of protein isolates from faba beans (Vicia faba L.) depends closely on the manner of isolation and treatment of the isolates. Unmodified isolates possess a moderate foaming ability with a maximum foam capacity of 210% in alkaline solution (pH 10.0) at concentrations of about 3%. The foam capacity and stability can be improved by treatment with isopropanol or moderate temperature, as well as by denaturing by alkali or by specially heating at 80 degrees C. Thereby modified preparations are formed possessing a foam capacity of more than 400% and a foam stability of 80-100%. High concentrations of protein favour the formation of stable foams. Succinylation improves the foam formation properties of proteins. Maximum values of foam capacity (approximately equal to 400%) are produced at a high degree of succinylation, that is after blocking more than 80% of protein amino groups, in neutral solution, while the foam stability under these conditions decreases. Heating at 80 degrees C, high protein concentrations (10%) and a weak acidic milieu (pH 5.5) favour the formation of stable foams from succinylated proteins.

[Characterization of the water-binding capacity of proteins]

A general method for determining the water-absorbing capacity of proteins is described. To calculate their water-absorbing capacity, the proteins are centrifuged off and then added with portions of water to determine the amount of water required for just obtaining an aqueous supernatant (in case of insoluble proteins) or for obtaining a paste which is beginning to flow (in case of soluble proteins). The correlation between the "modified centrifugation method" and the Grau-Hamm pressing method for determining the "juice loss", a method that is currently used in practice, is demonstrated by some examples.

Preparation and application of vegetable proteins, especially proteins from sunflower seed, for human consumption. An approach

About 80% of the world protein production are of vegetable origin. More than half the vegetable protein is fed to animals, whereas merely 10 kg protein per capita are obtained from meat, milk and eggs per year. Therefore, and because of rising prices for raw materials and energy the production and the firsthand utilisation of proteinacous plants for foodstuffs are a worldwide problem. As future source of protein for human nutrition sunflower seed and oil extraction residues from sunflower seed, respectively, are of great significance. Sunflower seed does not contain anti-nutritive and toxical compounds. After crossing of species having a high oil content, the today cultivated sunflower hybrids bring seeds containing 17-22% crude protein and 30-52% oil. The cultivation also has led to a considerable reduction of the hull content. In processing of sunflower proteins colour problems occur resulting from finely ground particles of dark hulls and from polyphenolic acids which are easily oxidized and converted into brown polymerics. Essential components of the sunflower protein production are, therefore, the at least 98% dehulling before processing as well as the separation of polyphenolic acids and/or the prevention of their oxidation. In principle, the variation and combination of technological steps in pre-treating and defatting of sunflower seed, in extracting, precipitating, washing and drying of proteins, the chemical modification of proteins obtained, the interaction with neutral salts or complexing agents, and the admixture of lysine or proteins of high lysine content allow to adapt sunflower proteins to each type of application.

[Chemical modification of proteins. 7. Effect of succinylation on some physico-chemical and functional properties of casein]

Succinylation of amino groups of the casein complex results in a spontaneous dissociation of the protein into low-molecular 1.8-S components. Succinylated samples of casein are characterized by a higher electrophoretic mobility of the components in alkaline mediums and by a lower mobility in acidic buffer systems. The anodic migration in alkaline buffer systems increases depending on the degree of modification. This effect is more pronounced for the beta-casein than for the alpha s-casein fraction. In the potentiometric acid-base titration of the modified casein a hysteresis occurs during the back-titration. Increasing with the degree of modification, this effect points to a more or less strong break-up of the structure (entropy production). The solubility minimum of casein is shifted to lower pH values by succinylation. Samples succinylated to 90 or more per cent of the amino groups are insoluble at pH less than 3.5. Succinylated casein shows at a moderate degree of substitution (approximately equal to 40%) a highly increased water adsorption capacity. The oil adsorption capacity of the protein decreases after succinylation. Amongst the modified casein samples those ones with the highest water adsorption show the highest oil adsorption, too. The emulsifying capacity of low (approximately equal to 20%) succinylated casein samples decreases below the value determined for the unmodified protein. At higher modified samples the emulsifying capacity increases as the degree of succinylation increases. The emulsifying activity and emulsion stability of modified samples are lower than that measured for the parent protein. The foaming capacity of the casein is not improved by succinylation.