Enhanced viability of encapsulated probiotics using whey protein isolate-dextran conjugates: Effect of dextran molar...

Encapsulation is an effective strategy to protect labile compounds and maintain the viability of beneficial microorganisms during food processing and storage. This study investigated the use of Maillard reaction conjugates of whey proteins isolate (WPI) and dextran (DX) as wall materials for encapsulation of lactic acid bacteria considered as potential probiotics: Bifidobacterium animalis subsp. lactis INL1 (INL1) and Lactobacillus plantarum 73a (L73a). WPI/DX conjugates were prepared by controlled heating of WPI with dextrans of 6 and 100 kDa, referred to as WPI/DX6 and WPI/DX100. The bacterial cells were suspended in canola oil, used as oil phase of a solid-in-oil-in-water emulsion where the conjugates served as encapsulating agents. The emulsions were spray-dried to produce powdered microcapsules. Compared to native WPI, both conjugates formed more stable emulsions, characterized by smaller droplet sizes, lower creaming indices, and higher interfacial activity. These improvements were attributed to different mechanisms: in WPI/DX6, conjugation with low-molar-mass dextran altered the native protein structure, promoting better interfacial adsorption and more stable emulsions, whereas in WPI/DX100, the protein structure was considerably preserved and the high-molar-mass dextran enhanced the amphiphilic behavior of the conjugate and provided stronger steric stabilization. The emulsification process did not affect bacterial viability; however, spray drying led to a reduction in cell counts across all formulations. Despite this, both WPI/DX conjugates provided superior protection during storage compared to native WPI. Viability was better preserved at lower temperatures (-18 °C > 4 °C > 21 °C), with the highest survival observed in WPI/DX100-L73a microcapsules stored at 4 °C.