Impact of Phytic Acid on the Physical and Oxidative Stability of Protein-Stabilized Oil-in-Water Emulsions
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ORIGINAL ARTICLE
Impact of Phytic Acid on the Physical and Oxidative Stability of Protein-Stabilized Oil-in-Water Emulsions Yaqiong Pei 1,2 & Qianchun Deng 3 & David Julian McClements 4
&
Jing Li 1 & Bin Li 1
Received: 5 May 2020 / Accepted: 11 June 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The effects of phytic acid on the physical and oxidative stability of flaxseed oil-in-water emulsions containing whey proteincoated lipid droplets were investigated. The surface potential, particle size, microstructure, appearance, and oxidation of these emulsions were monitored when they were stored at pH 3.5 and 7.0 for 25 days in the dark (37 °C). The phytic acid and proteincoated lipid droplets had similar charges (both negative) at pH 7.0, but had opposite charges (negative and positive) at pH 3.5. At pH 7.0, the addition of phytic acid had no impact on the physical stability of the emulsions but significantly improved their oxidative stability, which was attributed to its ability to sequester pro-oxidant transition metals (iron ions). At pH 3.5, extensive droplet aggregation and creaming occurred in the emulsions containing phytic acid, which was ascribed to charge neutralization and ion bridging. The oxidative stability of the acidified emulsions, however, still increased after addition of phytic acid, which was again attributed to its ability to chelate iron ions. Interestingly, the antioxidant activity of phytic acid decreased as its level was increased. Our results suggest that phytic acid may be used as a natural antioxidant to improve the oxidative stability of food emulsions containing polyunsaturated fatty acids, but its level must be carefully controlled. Keywords Phytic acid . Whey protein . Physical stability . Oxidative stability . Emulsion
Introduction The oxidation of lipids during processing and storage leads to a deterioration in their nutritional value, safety, and flavor [1]. Lipids rich in polyunsaturated fatty acids (PUFAs) are particularly susceptible to oxidative degradation because of the high number of labile conjugated dienes they contain [2–5]. The lipids in many foods exist in the form of fine droplets dispersed in water, for example dressings, beverages, creamers, * David Julian McClements [email protected] * Bin Li [email protected] 1
College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China
2
College of Culinary and Food Engineering, Wuhan Business University, Wuhan 430056, China
3
Oil Crops Research Institute, Chinese Academy of Agricultural Sciences, Wuhan 430062, China
4
Department of Food Science, University of Massachusetts Amherst, Amherst, MA 01003, USA
desserts, and sauces [6]. Due to their small dimensions, the lipids in these emulsified systems have a large specific surface area exposed to the surrounding water [7]. As a result, emulsified lipids are often more susceptible to oxidation than bulk lipids. For this reason, antioxidants are often employed to inhibit the lipid ox
