Effect of phenolic compounds on proteolytic activity and spoilage potential of Pseudomonas aeruginosa in milk

Psychrotrophic bacteria, notably Pseudomonas spp., are common contaminants in raw milk and food industry. This study evaluated the effects of four phenolic compounds (rosmarinic acid, baicalein, curcumin, and resveratrol) on the proteolytic activity of Pseudomonas aeruginosa PAO1 in UHT skimmed milk (UHT-SM) at concentrations from 12.5 to 500 μM, depending on the compound. In vitro and in situ assays were conducted to assess proteolysis, spoilage, and milk protein hydrolysis. Significant inhibition of proteolytic activity was observed in vitro, whereas in UHT-SM the effect was partial. Curcumin and resveratrol reduced proteolysis in solid medium, while baicalein, curcumin, and resveratrol decreased spoilage intensity at higher concentrations. SDS-PAGE confirmed milk protein hydrolysis, especially of caseins, in all treatments, and confirmed delayed proteolysis in the presence of phenolics. These findings suggest that interactions between phenolic compounds and milk components may limit their antimicrobial potential, highlighting the need for further studies to better understand these interactions and enhance their applicability.