Abstract
The application of modified tuber starches in particle-stabilized emulsions was studied to obtain surfactant-free emulsions, called Pickering emulsions. Three different starches, namely, potato (P), sweet potato (S) and tapioca (T) starches were modified using dry-heat treatment (HD, 120°C, 150 mins), hydrothermal treatment (HM, 50°C, 30 mins), OSAmodification (OSA, 2.9%) and hydroxypropylation (HP, 2 mL of 20% propylene oxide) before being used as stabilizer for stabilizing emulsion. The physicochemical properties of the starches and the characteristics of the stabilized emulsion were studied. Potato OSAtreated starch (POSA) had significantly higher degree of substitution (DS) (DS = 0.0154) than SOSA (DS = 0.0081) and TOSA (DS = 0.0083). For the starches undergone treatment of hydroxypropylation, SHP had the highest molar substitution (MS) value of 0.20, followed by PHP (0.11) and THP (0.10). The amylose content of starches reduced significantly after all modifications (HD, HM, OSA, and HP). All OSA-treated starch (POSA, SOSA, and TOSA) had higher fat binding capacity compared to their native and starches that modified using different treatments (HD, HM, and HP). Based on the emulsification index values and optical microscopic images, all starch particles were able to stabilize emulsions except for SC, SHM, TC, and THM. Optical microscopic images showed that the starch particles accumulated and formed a densely packed layer at the oilwater interface. At the starch concentration of 400 mg/mL oil, emulsion stabilized by dryheated potato starch and all hydroxypropylated-starch-stabilized emulsions had a high emulsification index value of 1. Significantly highest viscosity was noticed from the emulsion stabilized by POSA. Overall, by comparing the physico-chemical properties of the modified starches and the characteristics of emulsions stabilized, potato OSA-treated starch (POSA) had the best emulsifying ability.
Highlights
Emulsion systems can be found in both food products and non-food products
This study focused on the effect of modifications namely, dry-heat treatment, hydrothermal treatment, octenyl succinic anhydride (OSA)-modification and hydroxypropylation on the properties and emulsifying ability of tuber starches including potato, sweet potato, and tapioca
The efficiency of the OSA modification is commonly determined by measuring the degree of substitution (DS), which is the average number of OS derivatives per glucose unit
Summary
Emulsion systems can be found in both food products (milk, butter, mayonnaise, and salad dressings) and non-food products (cosmetics and pharmaceutical products). Surfactants, proteins, and hydrocolloids are commonly used as an emulsifier in food emulsions (Timgren et al, 2013). Some emulsifiers may contain residual allergens, for example, milk, egg, soy lecithins, Tragacanth (E413), Acacia gum (E414), Karaya gum (E416), Mannitol (E421) and gelatin (E441) (Gelfand, 1943; Hannuksela et al, 1976; Sakaguchi et al, 1996; Palm et al, 1999; Friberg et al, 2003). The permitted level of emulsifier in food is relatively low and the amount might not enough to maintain a stable emulsion (McClements, 2015). As an example, according to the EU standards, polyglycerol esters of fatty acids (E475) which commonly used in fat and oil emulsions (butter, margarine and spreads) is only permitted to use with a maximum limit of 5000 mg/kg. Studies to obtain surfactant-free emulsions, such as Pickering emulsions ( called as particlestabilized emulsions) are extensively been studied (Pickering, 1907; Rayner et al, 2012; Timgren et al, 2013; Song et al, 2015)
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