The adhesion of food emulsions to food contact surfaces is a problem of utmost importance in the recycling of packages and cleaning of industrial equipment. Bulk adhesion was measured experimentally by weighing the mass of food emulsion remaining on solid surfaces after contact (i.e., amount adhered or adhesion amount), a matter which is of industrial concern. Surfaces of different hydrophilicity have been tested: polytetrafluoroethylene (PTFE), low-density polyethylene (LDPE), poly(ethylene terephthalate) (PET), stainless steel and glass. Their polar free adhesion energy in contact with water (Wa(water)(P)) varied in the range 0.8 to 7 mJ m(-2).The observed decrease in the bulk adhesion amount of oil-in-water (o/w) emulsions, when stabilized by whey protein isolates and soybean lecithin, with decreasing Wa(water)(P) may be explained by increasing hydrophilization of the outside of adsorbed protein layers formed on solid substrates. This phenomenon would be due to conformational rearrangements of the macromolecules by hiding their hydrophobic moieties in contact with hydrophobic substrates, leading to a consequent decrease in adhesion forces between emulsion droplets and the substrates.A correlation was established between adhesion measurements and solid surface tension, gamma s or its electron-donor component from the van Oss model, gamma s(-). Results could be interpreted on the basis of physicochemical mechanics which relates rheological and adhesive properties of emulsions to microscopic adhesion forces acting between liquid droplets and surfaces. The relative importance on adhesion amount of surface thermodynamical properties and emulsion rheology was demonstrated and several hypotheses for bulk adhesion mechanisms are forwarded. (C) 1999 Elsevier Science B.V. All rights reserved.

In the food industry, the adhesion of fluid products to contact surfaces is a major problem as it results in increased cleaning costs, sanitary problems and food product loss. In this study, the influence of glass surface roughness (Ra ≥ 0.2 μm) on the adhesion of edible oils and concentrated oil-in-water emulsions (salad dressing type) was investigated. Glass plates were homogeneously abraded, using carbo silicate (SiC) powders. Adhesion was measured as the residual fluid food mass on the solid after drainage flow. Food emulsion critical stress (apparent yield stress) was found to be a driving parameter in fluid adhesion on rough surfaces. For oils and emulsions with a low critical stress, adhesion depended mainly on the presence of roughness. For these products, the food contact-surface should thus be smooth to reduce adhesion, as a simple decrease of average rugosity would be ineffective. However, the adhesion of higher critical stress food emulsions was also correlated to surface average rugosity. This reduces slippage, indicating that in this case the roughness of worn surfaces should be controlled to improve cleaning, and reduce contamination.

The aim of this study was to predict the mass of fluid food residues remaining adhered to a solid food-contact surface after drainage flow. The measurement method used simulated the drainage occurring on equipment surfaces in the industry, or the flow from a food package when the consumer empties it. Using Newtonian edible oils and power-law food emulsions, the solely fluid mechanical equation derived from the fluid film flow rate expression did not predict residual mass accurately. Therefore, correcting factors were introduced, based on experimental observations, taking into account solid surface properties (surface energy, hydrophilicity, roughness). Edible oils and food emulsions led to two different surface energetic correcting factors, based on the same phenomena, which improved greatly the fit between prediction and experimental measurements. The conclusion was that, for these types of food products, surface hydrophilic character and surface tension were more important than surface roughness in governing adhered mass.

Residual contaminants in processed packaging material could migrate into foodstuffs and alter their quality. To measure contaminant transfer rate through wrapping material, a diffusion cell adapted to "head space" gas chromatography was created in our laboratory. It was composed of two chambers separated by the film to be studied, e.g. low density polyethylene film. A 15 μl mixture of liquid n-propanol and benzene was deposited in the lower chamber of the cell. At 60°C vaporized contaminant diffused through the low density polyethylene film. After calibration, chromatographic analysis of the upper chamber atmosphere allowed measurement of contaminant concentration for various diffusion times. From these results contaminant diffusivities were calculated to be 3.5×1011, 3.9×1011 and 10.4×1011 m2 s1 for 1-propanol, 2-propanol and benzene respectively. It was demonstrated that the method was sensitive and allowed precise determination of contaminant diffusivity. © 1997 John Wiley & Sons, Ltd.

The synergistic effect on the surface activity of the dynamic associations (the surfactant-polyelectrolyte complexes - SPEC) between a polysoap(dagger) and cationic surfactants is remarkably increased with increasing length of all;yl side chains.

This article reviews the various theories of adhesion mechanism and, more specifically, studies concerning foodstuffs adhesion to industrial equipment and packaging surfaces. Adhesion is governed by mechanical interlocking, wetting, electrostatic and chemical forces, and diffusion. Direct conclusions about the validity of one of these theories were seldom made in the empirical studies reviewed. The different food adhesion determination methods were detailed: direct observations, evaluations (weighting, UV absorbance, and adhesive loss), adhesion strength measurements, and indirect measurements via the wetting theory (tilted plane method, contact angle, and surface tension). The importance of proteins, product rheological properties, solid surface rugosity, and wetting phenomena in many adhesion cases is highlighted. Conclusions were made that fundamental mechanisms of food-contact surfaces interactions still need to be investigated to improve understanding in the science of food materials.