An evaluation of the role of PromOat® on the stability of oil-in-water emulsions
Abstract: Background. In the past years, there has been a major shift towards the consumption of healthier, more sustainable, and more convenient food products. These trends have triggered a response from the food industry, instigating the reformulation of several products. The challenge is removing or replacing certain ingredients, without sacrificing certain elements such as taste, texture, or shelf-life. Swedish cooperative Lantmännen produces and sells PromOat®, a β-glucan product derived from oats. β-glucans have been used in product formulations as a means to improve quality and stability during storage, by modifying the texture and appearance of sauces, salad dressings, cakes, bread, and ice creams. Successful applications with oat β-glucans require an understanding of the rheological behavior of the hydrocolloid and an investigation of the underlying mechanisms that are generated when the ingredient is added into a food matrix. Methods. The study involved three main steps: (1) the determination of the critical overlap concentration of the hydrocolloid (2) an evaluation of the potential surface activity of the contaminant proteins present in the powder, and (3) an evaluation of the role of oat β-glucans on the stability towards creaming of a reference oil-in-water emulsion using droplet profiling. Results. The critical overlap concentration of the hydrocolloid is 0.0309 g/mL (3.09% m/m). There is a tenfold increase in the viscosity of the solution when the critical overlap concentration is reached due to enhanced entanglement and overlapping of the polymer chains. Oat β-glucan solutions exhibit a shear-thinning behavior and there is no evidence of gel formation, presumably due to the high molecular weight of the polysaccharide. The contaminant proteins in the powder have little-to-no surface activity mainly as a consequence of the poor solubility of oat proteins. The oat β-glucan powder does not provide long-term stability on its own and the addition of an emulsifier in the system is a necessary step to achieve kinetic stability. Emulsion systems containing oat β-glucans at a concentration of c' or higher have remained stable over a period of 30 days, achieving creaming rates in the order of 0.002 mm.min-1. Although no visual evidence of instability was detected, the droplet profile of these samples exhibited mild flocculation. A mechanism of depletion is generated when the hydrocolloid is added into the food matrix, given the concentration gradient between the depletion zones in the vicinity of the oil droplets and the bulk polymer solution. At concentrations lower than c', the depleting mechanism dominates over the stabilizing effect provided by the increase in viscosity from the addition of the hydrocolloid, and the emulsions are rendered unstable. On the other hand, the threshold concentration at which the repulsive effect from the rising viscosity starts to compensate for the attractive flocculating effect from depletion is in the order of 0.6 of the c'. Other possible food matrices including, for instance, a lower oil fraction have not been tested and could be investigated in future research. Conclusion. Oat β-glucans in PromOat® appear as an alternative to other more traditional hydrocolloids used in the food industry. The critical overlap concentration of the powder is 0.0309 g/mL (3.09% m/m) and the application of this hydrocolloid in food emulsions, in combination with an emulsifier, imparts kinetic stability for over 30 days, when the range of application is above or equal to the c'.
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