Effect of <i>In vitro</i> Digestion on the Bioaccessibility of Antioxidants Capacity in Boiled and Brewed Bidara Leaf Tea (<i>Ziziphus spina-christi</i>)

Abstract

This study investigated how the total content of phenolic compounds, flavonoids, and antioxidant capacity change in bidara leaf tea after in vitro gastrointestinal digestion. The boiling and brewing tea treatment and different extraction times were also compared. The results revealed that the highest antioxidant capacity of the samples before digestion was in the 15-minute boiling treatment with antioxidant capacity values of 36.02±0.6 mg AEAC/g (dry matter) (DPPH), 58.55±0.09 µmol FeSO4/g (dry matter) (FRAP), 7.97±0.00 mg AEAC/g (dry matter) (ABTS), 43.52±0.63 mg GAE/g (dry matter) (phenolic), and 8.69±0.08 mg QE/ mg (dry matter) (flavonoids). The DPPH and ABTS radical scavenging activity during digestion increased in the final stage. At the same time, the ferric-reducing antioxidant power (FRAP), total phenolic content, and flavonoids decreased at the end of the digestive phase. The boiling method was generally considered to provide the highest antioxidant bioaccessibility, but the impact of boiling time varied. The highest bioaccessibility of antioxidants was 113.2±1.0% (DPPH), 82.8±1.8% (FRAP), 154.1±1.7% (ABTS), and flavonoids (95.1±1.8%) resulted from boiling for 15 min, while the highest bioaccessibility of phenolic compound (95.2±1.4%) resulted from boiling for 5 min. Hence, it was advisable to boil bidara leaf tea for 5-15 min as it yielded the highest antioxidant capacity before and after in vitro digestion.