D. Lorient

Structural changes in oil-in-water emulsions during the manufacture of ice cream

Abstract Ice cream was manufactured on a pilot plant and the product was analysed in terms of droplet size distribution and protein composition of the aqueous phase at three stages of the process: after homogenization, after aging and after freezing-aeration-hardening stages. The components (fat 8% wt, skim milk powder 8% wt, glucose syrup 40 DE 6% wt, sucrose 16.75% wt, stabilizer 0.45% wt) and water were homogenized using a two stage high pressure homogenizer (19 MPa + 3 MPa, 70°C). The fat used was either butteroil or fresh unhomogenized milk cream. After an aging period (4°C, 18 h), ice cream mixes were frozen and aerated using a continuous ice cream freezer (overrun = 100%, outlet temperature = − 4°C), hardened in a blast air hardening tunnel (−40°C, 20 min) and stored (−30°C). Droplet size measurements in homogenized and aged mixes did not show any influence of the type of fat used: fat globule distributions were monomodal with an average surface/volume diameter d 32 ≃ 0.50 μm. For both fats, the aging stage did not affect the initial droplet size distribution. The freezing-aeration-hardening stage led to a partial flocculation of aged mix, the effect being more pronounced in butteroil ice cream than in cream ice cream. Protein analysis carried out on the aqueous phase of butteroil ice cream showed a preferential adsorption of caseins over whey proteins during the homogenization stage. Aging and freezing-aeration-hardening stages gave rise to a partial desorption of the proteins from the surface of fat globules, especially during the freezing-aeration-hardening stage.

Improvement of rheological properties of firm acid gels by skim milk heating is conserved after stirring

The enhancement of the strength of set acid gels by heating milk was related to rheological parameters (water retention capacity, storage modulus) of corresponding stirred gels. To obtain accurate rheological data from stirred gel it was necessary to maintain a constant granulometry of gel particles and to recognize time after stirring as a contributing factor. Two hours after stirring, the gel exhibited a higher storage modulus when milk was heated above 80 degrees C. A measurement of viscosity of just-stirred yoghurt was sufficient to predict correctly the quality of a stirred gel analysed by viscoelastic measurements. Increased resistance to syneresis of just-stirred gels was related to higher viscosity. The quantity of beta-lactoglobulin (beta-Ig) bound to casein micelles explains the improvement of these gel qualities. We have considered that the structure of the initial firm gel (mesostructure level) was conserved in fragments within the stirred gel. Consequently, the explanation given by various authors for the effect of heating milk on the properties of set gels can also be applied to stirred gels. The same mechanism, described in literature for structure formation of set gels from acidified milk is purposed to explain the role of heating milk on the recovery of gel structure after stirring. The beta-Ig association with casein micelles during heating favoured micelle connections during the acidification. It also favoured the association of gel fragments after stirring during the recovery in gel structure.

Effect of surfactant on some physico-chemical properties of dairy oil-in-water emulsions

Abstract Droplet size, fraction of protein adsorbed, and protein surface concentration in dairy oil-in-water emulsions were studied as a function of the surfactant-to-protein molar ratio. Emulsions were made by homogenizing skim milk (96 g/100 g) with anhydrous milk fat (4 g/100 g); the protein content in emulsions was 3.2 g/100 g. Two nonionic surfactants were considered: glycerol monolinoleate (oil-soluble) and Tween 20 (water-soluble). The latter emulsifier was added before or after emulsification. Droplet size, measured in a dissociating medium was not affected by the amount of surfactant. Some significant droplet aggregation occurred in the presence of glycerol monolinoleate at surfactant-to-protein molar ratio >16. Tween 20 prevents the formation of aggregates when present during emulsification whereas aggregates were not completely disrupted when Tween 20 was added after emulsification. In the absence of surfactant, 20% of protein present adsorbed at the oil—water interface and this fraction decreased with increasing amounts of surfactant. A subsequent decrease in surface protein concentration was observed. Provided it was not added in too large amounts to the emulsion, the incorporation of glycerol monolinoleate led to a partial protein displacement from the interface without inducing some resulting droplet aggregation.

Interactions between food components in ice cream. Part 1: unfrozen emulsions

Abstract Ice cream was manufactured on a pilot plant and the structure of the emulsion was estimated in terms of droplet size distribution and protein composition of the aqueous phase after homogenization (two stages: 19 MPa + 3 MPa, 70°C) and after ageing ( 18 h, 4°C). Four different factors were studied: the nature of the milk protein [skim milk powder (SMP), skim milk replacer (SMR) or whey protein concentrate ( WPC) ], the nature of the emulsifier (saturated monoglycerides or Sugin Fl50, which is apolysorbate 80-based emulsifier) and its concentration (0.17–0.67% w/w for Sugin F150; 0.20–0.54% wlw for saturated monoglycerides), and the amount of butter oil (8–12% wlw). Freshly homogenized mixes containing either SMP or an SMR were stable during the ageing stage, irrespective of the nature and the concentration of the emulsifier. WPC-based mixes, however, were destabilized after homogenization: this destabilization was found to be flocculation only, which shows that whey proteins are efficient against coalescence. The quantity of adsorbed protein per surface unit was systematically higher for SMP mix than for both SMR and WPC. After the ageing stage, the structure of the mixes containing monoglycerides or WPC + polysorbate 80 remained unchanged. However, polysorbate 80 used in combination with both SMP and SMR led to a destabilization of the mix during the ageing stage: this destabilization was found to depend upon the mass/surface ratio of polysorbate 80 to butteroil.

Interactions between Whey Proteins and Lipids in Emulsions

Publisher Summary Many of the oil-in-water emulsions produced by the food industry are stabilized by milk proteins. However, the mechanism for emulsion stabilization remains only partially understood. Interactions between proteins and lipids in emulsions are revealed by a change in the mobility of lipid molecules dispersed in solution or incorporated in oil droplets. This chapter presents a study to discuss interactions between proteins and lipids in emulsions and two paramagnetic fatty acids homologues were selected in the study. The study has measured (i) the relative affinities of the whey protein components for the paramagnetic fatty acids, (ii) the amount and nature of the proteins adsorbed on the oil droplets, and (iii) the emulsifying properties of these proteins. The results obtained in the study conclude that in emulsions stabilized by whey proteins: (1) milk proteins and lipids interact preferentially through their polar groups; (2) the polar and very accessible amino-acid residues of the protein participate in the interaction; (3) the milk proteins can be depicted as adsorbing on the fat droplets without affecting the major features of the lipid organization; and (4) the affinity of β-lactoglobulin for fatty acids is higher than the affinity of α-lactalbumin. No close correlation was found between the affinity of the proteins for the lipids and the emulsifying properties of the proteins.

Proteolysis of milk casein micelle and sodium caseinate in oil-in-water emulsions

The topology of casein at an oil-in-water interface was studied by examination of the peptide profile after enzyme hydrolysis.