Food & Function PAPER Cite this: Food Funct., 2016, 7, 227 Received 20th October 2015, Accepted 2nd December 2015 DOI: 10.1039/c5fo01269d www.rsc.org/foodfunction Physical and oxidative stability of functional olive oil-in-water emulsions formulated using olive mill wastewater biophenols and whey proteins Nicola Caporaso,* a Alessandro Genovese, a Róisín Burke, b Catherine Barry-Ryan c and Raffaele Sacchi a The present paper reports on the use of phenolic extracts from olive mill wastewater (OMW) in model olive oil-in-water (O/W) emulsions to study their effect on their physical and chemical stability. Spray- dried OMW polyphenols were added to a model 20% olive O/W emulsion stabilized with whey protein isolate (WPI) and xanthan gum, in phosphate buffer solution at pH 7. The emulsions were characterised under accelerated storage conditions (40 °C) up to 30 days. Physical stability was evaluated by analysing the creaming rate, mean particle size distribution and mean droplet size, viscosity and rheological pro- perties, while chemical stability was assessed through the measurement of primary and secondary oxi- dation products. The rheological behaviour and creaming stability of the emulsions were dramatically improved by using xanthan gum, whereas the concentration of WPI and the addition of encapsulated OMW phenolics did not result in a significant improvement of physical stability. The formation of oxidation products was higher when higher concentrations of encapsulated polyphenols were used, indicating a possible binding with the WPI added in the system as a natural emulsifier. This paper might help in solving the issue of using the olive mill wastewater from olive processing in formulating functional food products with high antioxidant activity and improved health properties. Introduction Olive oil production technology causes major environmental problems in countries where its production is mainly loca- lized, i.e. the Mediterranean area, as the industry produces a high output of liquid by-products represented by the olive mill wastewater (OMW). Due to the high concentration of phenolic compounds, 1 this waste could be conveniently converted into a valuable source of antioxidant compounds, which can be added to a variety of foods to develop a functional product with better nutritional properties. 2 In the last few years, new technologies have been tested and applied for the extraction of phenolic compounds from OMW, particularly membrane processes which involve ultrafiltration in combination with nano-filtration and reverse osmosis. 3 The concepts behind its production by membrane separation tech- niques were reported by other researchers. 4,5 For their con- venient storage and use, water phenolic extracts must be dried, and spray-drying has been applied to the OMW obtained from membrane filtration. The use of these phenolic extracts in emulsions is of interest at the industrial level for the pro- duction of a wide range of functional food products, such as mayonnaise, creams, sauces and other spreads. Emulsions are kinetically unstable systems, and their instability is due to many mechanisms, including creaming, coalescence and flocculation. 6,7 Therefore, stabilizers and emulsifiers are needed to provide physical stability to avoid emulsion phase separation. Food emulsions are often multi- phase systems containing more than one biopolymer, e.g. mix- tures of proteins and polysaccharides. 8 Thickening agents are mainly polysaccharides, e.g. xanthan gum, maltodextrin, galac- tomannans, starches, pectin, carboxymethylcellulose, etc., used to increase the viscosity of the continuous phase. 7,9 Milk proteins (caseinate and whey proteins) are hydro- colloids used in many food systems, owing to their good solubility and behaviour. 10 Being surface active, whey protein isolate (WPI) is adsorbed on the oil–water interface in the form of a protective film. 11–13 Proteins are usually less effective emulsi- fiers than synthetic surfactants, but their use in the food industry has been increasing due to the trend to use “clean label” ingredients or “natural” products. a Department of Agricultural Sciences, University of Naples Federico II, 80055 Portici, NA, Italy. E-mail: nicola.caporaso3@unina.it b School of Culinary Arts and Food Technology, Dublin Institute of Technology, Dublin, Ireland c School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin, Ireland This journal is © The Royal Society of Chemistry 2016 Food Funct. , 2016, 7, 227–238 | 227 Published on 07 December 2015. Downloaded on 18/01/2017 10:32:42. View Article Online View Journal | View Issue