Bioactive Compound Accumulation and Antioxidant Activity in Tomato Fruit Skin at Different Ripening Stages

This study was conducted to determine the differences in bioactive compounds and antioxidant activity according to the ripening stage of tomato fruits with different skin colors. The tomato samples used three tomato cultivars distinguished by their skin colors as yellow, black, and red at the mature stage. Tomato samples were analyzed for soluble sugars, lycopene, ascorbic acid, polyphenols, and antioxidant activity after being harvested at green, breaker, turning, and mature. The major sugars in tomato fruits are fructose and glucose. The content of fructose and glucose in yellow tomatoes gradually increased during the ripening stages. However, red and black tomatoes, their levels exhibited an initial increase at the breaker points, followed by a period of relative constancy. The lycopene contents in fruits of all skin colors showed a significant increase during ripening stages. The highest content of lycopene was observed at the mature stage in red tomato fruits. Differential patterns in the accumulation of ascorbic acid between yellow and black or red tomato fruits were detected during the entire ripening stages. In yellow tomato fruit, the content of ascorbic acid remained consistently low throughout the ripening stages. Ascorbic acid content in black tomato fruits significantly increased to 2,249 mg·kg⁻¹ of tomato fruits at the mature stage, while in red tomato fruits, it gradually increased to 3,529 mg·kg⁻¹ of fruits at the mature stage. Quercitrin content in tomato fruits gradually decreased during the ripening stages. In yellow tomato fruits, the ABTS radical scavenging activity abruptly increased at the turning stages, while in black and red tomato fruits, it gradually increased according to the ripening stages. The DPPH radical scavenging activity in tomato fruits significantly increased at the turning stages.