Abstract:

The changes in the release of total polyphenols and total flavonoids, as well as antioxidant activity in terms
of oxygen radical absorbance capacity (ORAC) of citrus (Citrus reticulata, Navel orange and kumquat) during in vitro
simulated gastrointestinal digestion were determined. The results showed that the citrus polyphenols were mainly free
phenols, and that the release of polyphenols via organic solvent extraction method was higher than that from simulated
gastrointestinal digestion. Specifically, the release of polyphenols from Citrus reticulata, Navel orange and kumquat at the
third hour of simulated gastric digestion were 1.02-, 0.93- and 1.21-fold higher than those at 0 h, the release of flavonoids
were 1.46, 2.37 and 2.16 times higher than that at 0 h, and ORAC values were raised 1.10, 1.23 and 1.62 times after 3 h
digestion for the three citrus species, respectively. In addition, after 4 h of simulated intestinal digestion, preceded by 2 h
simulated gastric digestion, the release of polyphenols from Citrus reticulata, Navel orange and kumquat were 0.99-, 0.80-
and 1.29-fold higher than those before gastric digestion, and 0.91-, 0.81- and 0.90-fold higher than those before intestinal
digestion; the release of flavonoids were increased by 73%, 39% and 64% during the gastrointestinal digestion period (namely
2 h gastric digestion followed by 4 h intestinal digestion) and by 51%, 17% and 39% during the intestinal digestion, with
an increase in ORAC values by 1.67, 1.09 and 1.76 times during the whole digestion period, and 1.31, 0.88 and 1.22 times
during the intestinal digestion, respectively. The finding in this study indicate that pepsin, pancreatin, bile and gastric acid
can promote the release of antioxidant substances from citrus during simulated gastrointestinal digestion.

Key words: citrus, in vitro simulated gastrointestinal digestion, polyphenols, flavonoids, antioxidants activity