Enrichment of pasteurized skim milk with grape seed oil multilayer emulsions: Investigating the effect of emulsion layers on physicochemical, microbial, and sensory characteristics

Cow milk is a nutritionally valuable food, although it lacks essential UFA. Enriching milk with these fatty acids can reduce risks associated with cholesterol and saturated fats while meeting consumers' dietary needs. Grape seed oil (GSO), which is rich in n-6 and n-9 fatty acids, is one potential additive to replace milk fat and increase the unsaturated fat content. However, these essential UFA are hydrophobic, making them difficult to dissolve in water, and are prone to oxidation, which can negatively affect the aroma and flavor of the milk. The layer-by-layer emulsion method is a promising approach to mitigate these challenges. This study investigated the enrichment of pasteurized skim milk with optimized multilayer emulsions of GSO and evaluated the physicochemical, microbial, and sensory characteristics of the milk over a storage period of 7 d at 4°C. Results indicated that single- and triple-layer emulsions remained stable within the milk matrix, but the 2-layer emulsion became unstable by d 3 of storage. During storage, acidity increased in all samples (from 0.16 to 0.44, 0.24 to 0.48, and 0.2 to 0.36 for single-, double-, and triple-layer emulsions, respectively), as did viscosity (from 1.53 to 1.9, 1.55 to 2.2, and 1.46 to 1.78 mPa·s, respectively), total microorganism count, peroxide value (from 5.52 to 17.6, 4.7 to 19.38, and 3.09 to 10.3 mEq/kg oil, respectively), and thiobarbituric acid index (from 0.43 to 0.52, 0.44 to 0.63, and 0.39 to 0.47 mg malondialdehyde/kg of oil, respectively). The pH values decreased slightly across all samples (from 6.6 to 6.5). No mold, yeast, or coliforms were detected in any sample throughout the study. Overall, the use of bioactive compounds such as essential fatty acids through milk enrichment can greatly enhance the quality of widely consumed dairy products.