Vassilios Kiosseoglou

Improvement of emulsifying properties of soybean protein isolate by conjugation with carboxymethyl cellulose

Abstract Soybean protein isolate (SBPI) was mixed with sodium carboxymethyl cellulose (NaCMC) and dry-heated at 60C for a time period of up to 5 weeks. An improvement in emulsifying properties of the mixture, especially in oil droplet size reduction and emulsion stabilization against creaming was observed, depending on polysaccharide molecular weight, SBPI/NaCMC weight ratio and time of incubation. This is attributed to formation, upon heating, of a covalent protein–polysaccharide conjugate which, following adsorption through its protein moiety at the oil–water interface, may enhance repulsive steric forces between the oil droplets as a result of polysaccharide chain overlapping. The conjugate formation was confirmed by SDS-PAGE and the results are discussed in terms of protein solubility and surface adsorption behaviour.

Aqueous extraction of oil bodies from maize germ (Zea mays) and characterization of the resulting natural oil-in-water emulsion.

Oil bodies in the form of an adequately dispersed suspension were extracted from maize germ by applying aqueous extraction. The effect on the yield of oil body extraction of parameters, such as pH of aqueous medium, state of germ comminution, and number of successive extraction steps applied, was evaluated, indicating that an extraction yield as high as 95% could be reached when a finely comminuted germ material is extracted 3 times under alkaline conditions. The extracted oil body suspension was coagulated by pH manipulation, and the resulting cream, consisting of intact oil bodies, was studied with respect to protein composition, particle size distribution, and oil body zeta potential. Changes in particle mean diameter resulting during oil body cream storage as well as the creaming behavior of emulsions prepared by cream dilution with water were also investigated. The findings are discussed in terms of the presence at the oil body surface of an adsorbed mixed layer made up of phospholipids, oleosins, and extraneous germ proteins that determine the physical stability of oil droplets upon long-term storage.

Functionality of lupin seed protein isolate in relation to its interfacial behaviour

The foaming and emulsifying properties of lupin seed protein isolate (LSPI) were investigated following protein structure modification by heating and/or dithiothreitol (DTT) addition. Heat-treatment of protein solution resulted in an increase of both foamability and foam-stabilization ability while disulfide bond reduction by DTT brought about an improvement in the protein foaming capacity only. Additionally, heat-treated LSPI solutions exhibited markedly improved emulsification and emulsion-stabilization properties. Disulfide bond reduction, on the other hand, brought about an increase in the ability of the protein to stabilize the emulsions against creaming only. The influence of lupin protein structure modification on its solubility and surface-adsorption properties has also been studied in order to elucidate the protein structure/functionality relationship of lupin protein.

Chickpea protein isolates obtained by wet extraction as emulsifying agents

BACKGROUND Wet extraction of protein from defatted chickpea (variety Thiva (T), Greece) flour, at alkaline or slightly acidic pH, followed by isoelectric precipitation (pI) or ultrafiltration (UF) to recover the protein, was employed to obtain a number of chickpea protein isolates, enriched either in protein constituents belonging to the globulin (TpI, TUF, TUFG) or to the albumin fraction (TUFA). RESULTS The interfacial activity and film-forming ability of the isolate protein constituents as well as their emulsifying properties were evaluated. The method applied for chickpea protein isolate preparation influenced to an appreciable extent their composition, adsorption behaviour to oil-water interfaces and emulsion formation and stabilization characteristics, especially with respect to oil droplet flocculation and coalescence. The isolates also differed in their ability to stabilize emulsions subjected to thermal processing or following storage under freezing conditions. The results are discussed in terms of compositional and, possibly, structural differences existing between the protein constituents of the chickpea isolates that may influence their functional behaviour in emulsion systems. CONCLUSION The method applied for isolate preparation influenced to an appreciable extent the ability of proteins to adsorb to the oil-water interface and stabilize emulsions during long-time ageing or following heat treatment or freezing.

Physicochemical Stability of Maize Germ Oil Body Emulsions As Influenced by Oil Body Surface-Xanthan Gum Interactions

Two types of oil body cream, differing in protein content and composition, were prepared from maize germ. The cream rich in extraneous germ proteins (OB-A) constituted of oil bodies with a significantly lower size compared to the cream (OB-W) which was practically free from the extraneous germ proteins. In addition, the stability of the former cream against oil body coalescence was much higher upon long-term aging. Dilution of both creams to a 5% oil body level produced emulsions that were very unstable against creaming. The creaming stability was greatly improved following addition of 0.1% xanthan, the result being more spectacular in the case of the cream rich in extraneous maize germ proteins. The enhancement of the physical stability of oil droplets upon long-term storage is attributed to electrostatic xanthan gum-oil body surface protein interactions, verified by zeta-potential measurements, that lead to the diminution of depletion flocculation effects and to enhancement of steric stabilization due to the adsorption of the polysaccharide molecules to the oil body surface.

Purified oleosins at air–water interfaces

Oleosins are low molecular mass proteins that are distinguished from other proteins for their extended central hydrophobic domain which covers almost half of its entity. For this work, they were extracted from isolated maize germ oil bodies. The purification steps included washing with diethylether and a chloroform–methanol–water mixture. Their amphipathic terminal domains positioned at the organelle surface, where they strongly interact with the surface polar phospholipids, made the application of a third washing step with acetone essential. Although oleosins are well known for their insolubility in water, we were able to prepare aqueous buffer solutions of 0.008 wt% at pH 8.0. The interfacial behaviour of oleosins was studied, in order to predict their ability to stabilize foams. Even at low concentrations they were capable of decreasing the interfacial tension of air–water interfaces to values similar to those obtained from milk protein or egg yolk apolipoproteins adsorption. Pendant drop profile analysis showed that the dilatational elastic modulus was frequency-dependent, but at the same time the elastic to viscous modulus ratio was frequency-independent and below 0.1. The results indicate that oleosins might have a high potential as foam stabilizers, a fast developing and challenging field.

Fracture and textural properties of low fat egg yolk gels containing emulsion droplets

The influence of corn oil content and the type of emulsifier on the fracture and textural properties and the expressible liquid of gels prepared by heat-treatment of low-fat yolk protein concentrate (YPC) containing emulsified oil has been investigated. Oil incorporation in the form of fine droplets results in a decrease of gel network strength, the textural parameter values depending on the amount of added oil. Tween 20 (polyoxyethylene sorbitan monolaurate) when used as the oil emulsifier brings about a reduction in gel textural parameter values compared to liquid egg yolk, the result depending on the emulsion droplet size. Additionally, the gels differ in their yielding behaviour since the latter yield but do not fracture at strain values as high as 0.7 while the former fracture at relatively low strains and their fracture stress and strain parameter values depend on oil droplet size. This behaviour is explained in terms of the effect of the surfactant on the yolk constituents and, particularly, its interactions with the yolk apoproteins, which result in stiffer bulk gel network structure.

Functionality of medium molecular weight xanthan gum produced by Xanthomonas Campestris ATCC 1395 in batch culture

Abstract Xanthan gum of medium molecular weight was produced by Xanthomonas Campestris ATCC 1395 in a laboratory fermenter without pH control by applying a stirrer speed of 600 rpm and its stabilization properties in salad dressing emulsions were evaluated. The gum performed satisfactorily as an emulsion stabilizer and thickener although it had to be used in higher concentrations in order to be as effective as the commercially available xanthan gum. Furthermore, resilient gel structures resulted when the gum was used in an admixture with locust bean gum. The gel texture profile was different compared to that of the commercial sample/locust bean gum mixture, suggesting that the gum could present an alternative for the preparation of gels of acceptable textural properties.

Exploitation of hazelnut, maize germ and sesame seed aqueous extraction residues in the stabilisation of sesame seed paste (tahini).

BACKGROUND Sesame seed paste is a highly nutritious food product which, upon long-term storage, tends to exhibit undesirable phenomena of oiling-off and particle sedimentation. The ability of rich-in-fibre aqueous extraction powders originating from oleaginous raw materials to enhance the physical stability of sesame paste is investigated in this study. RESULTS The extraction residues remaining after treating hazelnut, sesame seed or maize germ with aqueous media in order to extract and exploit their oil bodies, were collected, dehydrated and milled into fine powders. The powders were then incorporated at various levels into a commercially available sesame paste product to assess their potential as paste stabilisers against oil separation. The solids from maize germ exhibited the highest stabilising ability followed by the solids from hazelnut. In contrast, the solids originating from the sesame seed were less effective in stabilising the sesame paste. Shear stress-rate of shear measurements of sesame paste incorporating the extraction residue solids were conducted in an attempt to explain the different stabilising behaviour of the three powders. CONCLUSION The intensity of interactions between the incorporated solids within the sesame paste structure may determine the rheological properties of the blend and hence its stability against oiling-off upon long-term storage.

Chios Mastic Gum and Its Food Applications

This chapter reviews the traditional Greek product Chios Mastic Gum or Mastiha, primarily known for its distinctive flavor. This is the dried exudate of the shrub-like tree Pistacia lentiscus L. var. chia of the Anacardiaceae family, cultivated exclusively in the south of the Greek island Chios. Emphasis is given on its chemistry and physicochemical properties, health effects, antioxidant and antimicrobial properties. The preparation of traditional food products based on mastic gum or essential oil, such as chewing gum, confectionery, bakery products as well as alcoholic and nonalcoholic beverages, is also discussed.