The composition of interfacial material from skim milk foams

Cyclodextrin-Promoted Fluorescence Detection of Aromatic Toxicants and Toxicant Metabolites in Commercial Milk Products

The detection of polycyclic aromatic hydrocarbons (PAHs) and their metabolites in food and in agricultural sources is an important research objective due to the PAHs' known persistence, carcinogenicity, and toxicity. PAHs have been found in the milk of lactating cows, and in the leaves and stems of plants grown in PAH-contaminated areas, thereby making their way into both cow milk and plant milk alternatives. Reported herein is the rapid, sensitive, and selective detection of 10 PAHs and PAH metabolites in a variety of cow milks and plant milk alternatives using fluorescence energy transfer from the PAH to a high quantum yield fluorophore, combined with subsequent array-based statistical analyses of the fluorescence emission signals. This system operates with high sensitivity (low micromolar detection limits), selectivity (100% differentiation even between structurally similar analytes), and general applicability (for both unmodified lipophilic PAHs and highly polar oxidized PAH metabolites, as well as for different cow and plant milk samples). These promising results show significant potential to be translated into solid-state devices for the rapid, sensitive, and selective detection of PAHs and their metabolites in complex, commercial food products.

Interfacial properties, thin film stability and foam stability of casein micelle dispersions

Foam stability of casein micelle dispersions (CMDs) strongly depends on aggregate size. To elucidate the underlying mechanism, the role of interfacial and thin film properties was investigated. CMDs were prepared at 4°C and 20°C, designated as CMD_4°C and CMD_20°C. At equal protein concentrations, foam stability of CMD_4°C (with casein micelle aggregates) was markedly higher than CMD_20°C (without aggregates). Although the elastic modulus of CMD_4°C was twice as that of CMD_20°C at 0.005Hz, the protein adsorbed amount was slightly higher for CMD_20°C than for CMD_4°C, which indicated a slight difference in interfacial composition of the air/water interface. Non-linear surface dilatational rheology showed minor differences between mechanical properties of air/water interfaces stabilized by two CMDs. These differences in interfacial properties could not explain the large difference in foam stability between two CMDs. Thin film analysis showed that films made with CMD_20°C drained to a more homogeneous film compared to films stabilized by CMD_4°C. Large casein micelle aggregates trapped in the thin film of CMD_4°C made the film more heterogeneous. The rupture time of thin films was significantly longer for CMD_4°C (>1h) than for CMD_20°C (<600s) at equal protein concentration. After homogenization, which broke down the aggregates, the thin films of CMD_4°C became much more homogeneous, and both the rupture time of thin films and foam stability decreased significantly. In conclusion, the increased stability of foam prepared with CMD_4°C appears to be the result of entrapment of casein micelle aggregates in the liquid films of the foam.