Impact of pH, freeze–thaw and thermal sterilization on physicochemical stability of walnut beverage emulsion

• The effect of environmental stresses on the stability of walnut emulsion was examined.
• The emulsifiers and XG could effectively stabilize the walnut emulsion.
• The mechanism of stabilizing walnut emulsion with emulsifiers and XG was proposed.
• Emulsifiers and XG improved the physical stability of walnut emulsion under extreme conditions.

The effects of environment stresses on the stability of walnut emulsion were investigated. The physical stability of walnut emulsion was characterized by droplet size, zeta potential and chemical stability of walnut oil in the emulsion was evaluated by determining the peroxide concentration during the storage. The results showed that emulsion in the presence of xanthan gum and mixed emulsifiers exhibited better stability after 4 freeze–thaw cycles. At pH 3–10, the mixed emulsifiers could improve the stability through their absorption on the oil–water interface. However, xanthan gum couldn’t protect the droplets against the aggregation in high acid environment, but greatly enhanced the physical stability at pH 6–10. During the thermal sterilization process, the physical stability of walnut emulsion was decreased with a rise of sterilization temperature and the extension of sterilization time. The sterilization temperature above 121 °C and time over 25 min led to the poor physical and oxidative stability.