Tension of oil‐water interface and properties of O/W emulsions in dependence of faba bean globulins

Abstract

Compared with faba bean globulin the improved flow, gelifying, surface and emulsifying properties of aqueous solution of the corresponding acetylated derivatives are reflected in O/W emulsions by their enhanced stability.Investigations were made concerning the changes of the flow, gelifying [l], surface [2] and emulsifying [2,3] behaviour of aqueous faba bean globulin solutions dependent on their acetylation degree and the rheological properties of O/W emulsions stabilized by acetylated faba bean globulins [4]. The aim of the present paper is to extend our knowledge with regard to the time-dependent interfacial tension of oil-water interface for absorption from faba bean globulin solutions and to the long-term stability of corresponding Om-emulsions. Materials and methodsFaba bean globulin was used, prepared from faba bean flour by extraction at pH 7.5. Acetylation (degree -97 %) occurred during the extraction after adding acetic anhydride [5].Commercial and purified sunflower oil was used as the oil phase. For purification the sunflower oil was mixed 1 : 2 with aluminum oxide (standardized according to BROCKMANN) and shaken for 30 min at room temperature; fitration was repeated twice through a paper (Nr. 238 ; VEB Spaialpapierfabrik Niederschlag, GDR) filter. The so treated oil contained: free fatty acids 0.01 %; carbonyls 13 mg hexana1/100 g; peroxides 2 ml 0.002 N Na,S,O,/g; phosphatides non-detectable.The interfacial tension between aqueous protein solution and oil was measured by the ring method of DU Nouv using a tensiometer (Fa. Kriiss, Hamburg, FRG).O/W emulsions were prepared by dissolving protein in bidistilled water containing 0.02 % NaN, as preservative and stirred continously with a magnetic stirrer for 2 h. The solution obtained was centrifugated at 15,000 x g for 30 min; the content of protein was determined and the solution diluted to the required concentration.Sunflower oil was added slowly to the aqueous phase and dispersed with a magnetic stirrer. This coarse emulsion was then homogenized by an ultrasonic disintegrator USD-20 (Academy of Sciences of the GDR VDE Berlin-Buch) under the following conditions : temperature 50 "C, power 400 W/cm', sonification time 3 times each for 1 min in 3 min intervals. The pH of the homogenized emulsions was 6.5 and was adjusted with 0.5 N NaOH or 2 N HCI with the aid of a special blade stirrer. The emulsions were stored at +4 -6 "C for 24 h before evaluating apparent viscosity and oil droplet size distribution.The apparent viscosity of the emulsions was determined at 25 "C by means of the rotating viscosimeter Rheotest 2 (VEB MLW Medingen, GDR), a coaxial cylinder system with a gap of 1 mm (measuring system s 1).The oil droplet size distribution in the emulsion was assessed with the statistical diameter according to FERET using a light microscope at 600 x magnification WEB Carl Zeiss, Jena, GDR); for this purpose the emulsion is diluted 1 : lo00 with 0.05 % aqueous sodium dodecyl sulphate solution [6]. 25'

Relationships between adsorption and emulsifying of acetylated protein isolates from fabe beans (Vicia faba L.)

“…This is in accordance with results of previous studies on faba bean protein isolates [7,8,9, 241 where a decreasing droplet size and increasing centrifugal stability with progressive acetylation was found.…”

“…The calculated CAC suggests that the affinity of FBPI to the air/water interface significantly increases with acetylation, whereas the dependence of the equilibrium surface pressure on the degree of blockage is not significant. Thus, it is possible to explain previous results on faba bean isolates which showed largely improved emulsifying properties by acetylation but with no [9] or only small measurable differences 181 in the adsorption behaviour. One reason [ S ] , the dissociation seems to proceed more completely up to the protein subunit (about 60 m a ) .…”

Faba bean protein: A promising plant-based emulsifier for improving physical and oxidative stabilities of oil-in-water emulsions

“…Acetylation increased the flow, gelifying, surface and emulsifying properties, as well as the physical stability. (Schmandke et al, 1990) Chemical FBPIs were obtained by aqueous extraction at pH 7.5 followed by isoelectric precipitation from faba bean flours. Acetylation was in combination with methoxy pectin.…”

“…In the early 1990s, chemical modification focused on acetylation of FBPIs. Schmandke et al (1990) compared the emulsifying properties of unmodified and acetylated FBPI (degree ~97%); they found that acetylation improved the flow, gelifying, surface and emulsifying properties, as well as the physical stability of emulsions. This group later examined the association of low methoxylated pectin and acetylated FBPI as emulsifiers in O/W emulsions.…”