Effects of various whey protein hydrolysates on the emulsifying and surface properties of hydrolysed lecithin.

Oil-in-water emulsions (30 wt% sunflower oil) containing various concentrations of commercial whey protein hydrolysates (0-4 wt%) and hydrolysed lecithin (0.4-1.8 wt%) were prepared by means of a high pressure homogeniser. The degrees of hydrolysis used ranged from 10 to 27%. The individual and interactive effects of these factors on the particle size distribution, emulsion stability, consistency and interfacial tension were investigated using a three-level factorial design according to the principle of response surface methodology. The properties of the emulsions containing both hydrolysed lecithin and whey protein hydrolysate (WPH) were significantly influenced by the degree of hydrolysis of WPH, the protein content and the second-order interaction between both. Addition of WPH, with a 10-20% degree of hydrolysis, improved the stability of lecithin-stabilised emulsions and slightly decreased the average droplet size, compared to those emulsions with only protein or hydrolysed lecithin. However, when extensively hydrolysed WPH (DH=27%) was mixed with hydrolysed lecithin, rapid coalescence and oiling-off of the emulsion droplets resulted, suggesting competition between the surface active components of this WPH and the hydrolysed lecithin. High amounts of such an extensively hydrolysed WPH, together with low lecithin concentrations, were found to be especially detrimental. The different behaviour of partially and extensively hydrolysed WPH in oil-in-water emulsions containing hydrolysed lecithin, was in good agreement with their interfacial activity, as measured by the drop volume method.

Physico-chemical characteristics of oil-in-water emulsions based on whey protein-phospholipid mixtures.

Emulsions prepared with whey proteins, phospholipids and 10% of vegetable oil were used for a model typifying dressings, coffee whitener and balanced diets. For the present study, two whey proteins (partial heat-denatured whey protein concentrate (WPC) and undenatured whey protein isolate (WPI)) in combination with different phospholipids (hydrolysed and unmodified deoiled lecithin) were chosen to investigate the interactions between proteins, phospholipids and salt (sodium chloride) in such emulsion systems. Oil-in-water (o/w) emulsions (10 wt.% sunflower oil) containing various concentrations of commercial whey proteins (1-2%), phospholipids (0.39-0.78%) and salt (0.5-1.5%) were prepared using a laboratory high pressure homogeniser under various preparation conditions. Each emulsion was characterised by droplet size, creaming rate, flow behaviour and protein load. The dynamic surface activity of the whey proteins and lecithins at the oil-water interface was determined using the drop volume method. The properties of emulsions were significantly influenced by the content of whey protein. Higher protein levels improved the emulsion behaviour (smaller oil droplets and increased stability) independent of the protein or lecithin samples used. An increase of the protein content resulted in a lower tendency for oil droplet aggregation of emulsions with WPC to occur and emulsions tending towards a Newtonian flow behaviour. The emulsification temperature was especially important using the partial heat-denatured WPC in combination with the deoiled lecithin. A higher emulsification temperature (60 degrees C) promoted oil droplet aggregation, as well as an increased emulsion consistency. Emulsions with the WPC were significantly influenced by the NaCl content, as well as the protein-salt ratio. Increasing the NaCl content led to an increase of the droplet size, higher oil droplet aggregation, as well as to a higher creaming rate of the emulsions. An increase of the lecithin content from 0.39 to 0.78% in the emulsion system resulted in a small reduction of the single droplet size. This effect was more pronounced when using the hydrolysed lecithins.

Behaviour of formula emulsions containing hydrolysed whey protein and various lecithins.

Formula emulsion systems are used as enteral, sports and health products. In some formulas addition of hydrolysed protein is necessary to guarantee ease of digestion and hypoallergenicity. In the low fat emulsion model an increase in the content of lecithin (phospholipid mixture) was required, in consideration of the advice of the Food and Nutrition Board (USA) for choline supplementation. The individual and interactive effects of whey protein isolate (WPI) or hydrolysate (WPH) (3.7 and 4.9% w/w), unmodified deoiled or hydrolysed lecithin (0.48 or 0.7% w/w) and carbohydrate in the form of maltodextrin with dextrose equivalent (DE) 18.5 or glucose syrup with DE 34 (11% w/w) on the properties of formula emulsions with 4% v/w sunflower oil, were investigated using a full factorial design. The emulsions were characterised by particle size distribution, coalescence stability, creaming rate, and also surface protein and lecithin concentration. WPI-containing emulsions proved to be stable against coalescence and showed only little creaming after 1 and 7 days standing. There was a significant increase in the mean droplet size and a significant deterioration of coalescence and creaming stability when WPH instead of WPI was used as the protein source, due to the lower number of large peptides and lower surface activity of the WPH. Increasing the WPH concentration led to an increase in oil droplet size and further deterioration of the stability of the emulsions. The starch hydrolysate and lecithin also significantly influenced the emulsion properties. Their influence was less strong when the emulsion contained WPI. Under the conditions used WPH-based emulsions were more stable, in terms of creaming and coalescence, when a low level of protein was used in conjunction with hydrolysed lecithin and glucose syrup. Oil droplets in emulsions containing unmodified lecithin in either the continuous or disperse phase and WPH in the continuous phase were very sensitive to coalescence. The addition of starch hydrolysates (DE 18.5) induced intensive flocculation and phase separation in these emulsions.

[Changes in the nutritive physiological value of proteins modified by dialdehyde starch]. / Die Beeinflussung des ernährungsphysiologischen Wertes von mit Dialdehydstärke modifizierten Proteinen

The reaction of dialdehyde starch with the proteins of certain model protein texturates produces changes in the nutrition physiological quality of the proteins. Under the experimental conditions chosen, these changes were barely or not at all detectable by amino-acid analysis. On using the technique of aminoacid liberation under in vitro conditions, these changes were evidenced only for lysine and arginine. The determination of the lysine availability, however, testifies to a reversible or irreversible change of lysine which reduces significantly the PER values (animal experiments) of protein texturates treated with 100% oxidized dialdehyde starch. The differences between the NPU values were but insignificant. In spite of the detectable change in protein quality, the quality of the model protein texturates tested still satisfies the criteria for proteins with a composition which is favourable from the viewpoint of nutrition physiology.

Production, characterization and application of protein isolates from shark. Part 3. Characterization of protein isolates.

The functional and nutritional characterization of two isolates elaborated through cleaning-extraction processes, as well as that of a third isolate obtained by means of a chemical modification (alkaline heat treatment) from one of the former, was carried out. The first two isolates exhibit in general similar properties, are nutritionally comparable with casein and show a fairly high water absorption, having a potentially great value for instance in bakery and meat products and pastes. The modified isolate is essentially different from the isolate used as raw material in many of the characterized parameters, having a high nitrogen solubility index (NSI) by pH 3.5 and 7.0 and thus offering its possible use in such food systems as soft drinks where a high solubility is desired.