Interactions of caseins with phenolic acids found in chocolate

• Casein–protocatechuic acid interactions led to aggregates formation.
• Casein–phenolic interactions were identified in milk chocolate.
• Casein–phenolic interactions led to decreases in the degree of hydrolysis.

To investigate the interactions between caseins and phenolic acids, such as the ones present in chocolate, casein was incubated with protocatechuic acid or p-coumaric acid at 55 °C. In addition, casein was isolated from chocolate and the phenolic compounds within these caseins were quantified. Electrophoresis results revealed that casein–phenolic interactions were induced by incubation; minor aggregation of casein subunits was observed after incubation of casein with protocatechuic acid. Minor aggregation of casein isolated from milk chocolate was also observed. In vitro hydrolysis of casein control, casein–protocatechuic acid, casein–p-coumaric acid, caseins isolated from milk chocolate and white chocolate using trypsin showed degree of hydrolysis of 19.3, 18.6, 17.7, 10.4 and 17.8% respectively. The presence of protocatechuic acid and p-coumaric acid in the model system and the presence of phenolic compounds in milk chocolate, in addition to the structural changes occurring during processing, affected the peptide profiles of casein hydrolysates.