Antioxidant activity after in vitro gastrointestinal digestion of cheese containing catechins encapsulated within liposomes
Two important green tea phenolic compounds, (+)-catechin and (-)-epigallocatechin gallate (EGCG) were first encapsulated in soy lecithin liposomes and then incorporated into a low-fat hard cheese to determine the effect of cheese ripening and simulated digestion on the antioxidant activity and recovery of incorporated catechins. The total antioxidant activity (TAA) was measured after in vitro gastrointestinal digestion of cheese that was ripened over 90 days at 8°C to evaluate the efficacy of added antioxidants. Total phenolic content (TPC) was measured using the Folin-Ciocalteu assay, while TAA by both ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC) assays. The correlation coefficients among the TPC and TAA assays, and the recovery of the encapsulated phenolics for cheese fortification (measured by HPLC), were calculated.
Fortification of low-fat cheese with either catechin or EGCG encapsulated in liposomes, led to a significant increase (p<0.01) in TPC, FRAP, and ORAC values measured within the digesta matrix, with no significant impact on cheese composition, pH, and yield. Catechin and EGCG were not detected in the cheese whey, indicating their complete retention in the cheese curd. The phenolic recovery from the digesta was about half of the initial concentration for catechin i.e. 51.3, 53.9, and 46.0% for the fresh (Day 0) cheese and cheese ripened for 30 and 90 days (Day 30 and 90 cheese), respectively, and more than one third for EGCG i.e. 38.8, 33.7, and 33.5% for Day 0, 30, and 90 cheese, respectively. TPC values were highly correlated with both the FRAP values (i.e. correlation coefficient was 0.97, 0.98, and 0.96 for Day 0, 30, and 90 cheese, respectively) and ORAC values (i.e. correlation coefficient was 0.98, 0.98, and, 0.97 for Day 0, 30, and 90 cheese, respectively). Moreover, the corresponding FRAP and ORAC values were also highly correlated with the coefficients being 0.98, 0.97, and 0.98 for Day 0, 30 and 90 cheese, respectively, suggesting the suitability of these assays for evaluating the TAA of fortified cheese.
Thus, the manufacture of a low-fat hard cheese fortified with encapsulated catechin and epigallocatechin gallate in liposomes is feasible with good retention of phenolics and high antioxidant activity. Further investigations on aspects such as bioavailability of fortified phenolics, dose for phenolic consumption, and sensory attributes of fortified cheese are still required before product commercialisation.