A soy protein-polysaccharides Maillard reaction product enhanced the physical stability of oil-in-water emulsions containing citral

• A soy protein-polysaccharide Maillard reaction product (SPPMP) was developed.
• SPPMP-stabilized citral emulsion shows enhanced thermal stability (95 °C, 30 min).
• SPPMP-emulsion exhibits physical stability in simulated gastric fluid for up to 2 h.
• In simulated gastric fluid over 60% of citral is retained in SPPMP-stabilized droplets.
• In simulated intestinal fluid all citral is released from SPPMP-stabilized droplets in 4 h.

The processing parameters for making a Maillard reaction product (SPPMP) from soy protein isolate (SPI) and soy soluble polysaccharide (SSPS) were studied against the yield of the product and its emulsification capacity in an oil-in-water emulsion. The optimized SPPMP was produced by dry-heating the SPI-SSPS mixture (SPP) at a ratio of 3:5, temperature of 60 °C and 75% relative humidity for 3 days. The formation of SPI-SSPS conjugates was confirmed by gel electrophoresis, FTIR spectroscopy and high performance size exclusion chromatography. The citral (10 wt%) oil-in-water emulsions stabilized by SPPMP exhibited superior physical stability than those stabilized by SPI or SPP during prolonged storage, after thermal treatment or under simulated gastrointestinal conditions. At pH 7.0, all the emulsions studied exhibited monomodal particle size distribution initially, however, only those stabilized by SPPMP remained monomodal distribution for up to 70 days during storage at 25 °C. The SPPMP-stabilized emulsion maintained its physical stability to the thermal treatment at 95 °C for 30 min or under simulated gastric conditions for 2 h; while the emulsions stabilized by SPI or SPP exhibited various degrees of instability. The release rate of citral from the emulsion droplets was found inversely related to the stability of emulsion. The emulsion droplets retained approximately 70% of citral after 2 h incubation in simulated gastric fluid, whereas, complete release of citral from the droplets occurred in 4 h in simulated intestinal fluid. These results indicate that SPPMP-stabilized emulsions have a good potential as a carrier system for intestinal delivery of hydrophobic compounds such as citral.

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