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Composition and antioxidant activity of full-fat cheese fortified with (+)-catechin, and recovery of (+)-catechin after simulated in vitro digestion
(+)-Catechin, the principal catechin in green tea, was incorporated into a full-fat hard cheese at concentrations from 125 to 500 ppm to determine the extent of retention in the cheese matrix, the total cheese antioxidant activity, and recovery of catechin after <i>in vitro</i> digestion. Cheeses were ripened for 90 days at 8°C and digested in a gastrointestinal simulated digestion model. Measurement of pH, proximate composition, total phenolic content (TPC), and antioxidant activity after manufacture and ripening showed that the addition of (+)-catechin significantly (p≤0.05) decreased the pH of both whey and curd during cheese manufacture and ripening, but there were no significant (p>0.05) differences found for moisture, protein, and fat content between the cheeses. (+)-Catechin increased TPC and antioxidant activity (measured by ferric reducing antioxidant power and oxygen radical absorbance capacity assays) although the increase was not proportional with an increasing concentration of added (+)-catechin. The retention coefficient of (+)-catechin in the curd and recovery from the mature cheese after digestion were determined by HPLC. Between 57-69% of (+)-catechin was retained in the cheese curd, and 19-39% (depending upon the concentration) was recovered from the cheese digesta. Transmission electron micrographs showed that the ripened control cheese had a homogeneous pattern of milk fat globules with regular spacing entrapped in a homogenous structure of casein proteins, whereas the presence of (+)-catechin disrupted this homogenous structure. Evidence for interaction between (+)-catechin and cheese fat globules was provided by Fourier transform infrared spectroscopy. Association between catechin and fat globules should be taken into account when incorporating polyphenolic compounds, such as (+)-catechin, into functional cheese products to maximally retain catechin and maintain the required level of antioxidant activity without disrupting the microstructure of the cheese.
Keywords: catechin, antioxidant, digestion