The consumption of plant secondary metabolites-rich foods shows a positive effect on the regulation of human health. However, due to their poor solubility and chemical instability, the bioavailability of those secondary metabolites is usually low. The destruction of food composition caused by food processing is an important condition for the release of plant secondary metabolites, while food composition affects the absorption of plant secondary metabolites. In this review, we summarize the effects of different food components such as lipids and proteins as well as food processing methods such as thermal processing, mechanical processing and fermentation on the bioavailability of plant secondary metabolites. We expect that this review will provide a theoretical basis for improving the bioavailability of plant secondary metabolites in the daily diet.

In order to explore the effect of different dietary structures (normal diet, high-protein diet, high-fat diet, high-sugar diet) on the bioavailability and antioxidant activity of citrus carotenoids, the changes in the carotenoid content, ferric reducing capacity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging activity of mandarin pulp were monitored during in vitro simulated digestion. The correlation between carotenoid content and antioxidant activity was also evaluated. The results showed that as digestion progressed, the contents of total carotenoids and two carotenoid monomers in mandarin pulp mixed with whey protein, soybean oil and corn starch in four different proportions decreased continuously and the antioxidant activity of carotenoids in the four groups also decreased significantly (P < 0.05). Among these groups, the content of carotenoids in the high-fat diet group was higher at all digestion stages, and the antioxidant activity of carotenoids in this group was also stronger. There was a significantly positive correlation between the antioxidant activity and content of citrus carotenoids (P < 0.05). The comprehensive analysis showed that dietary structures had a great impact on the bioavailability and antioxidant activity of citrus carotenoids. The bioavailability of carotenoids in the high-fat diet group was (24.08 ± 1.78)% and significantly higher than that ((19.26 ± 1.06)%) in the normal diet group (P < 0.05), and the antioxidant activity of carotenoids in the high-fat diet group was the strongest. The bioavailability of carotenoids in the high-protein diet group was (15.27 ± 0.90)% and significantly lower than that in the normal diet group (P < 0.05), while there was no significant difference in carotenoid bioavailability between the high-sugar ((19.71 ± 1.58)%) and normal diet groups. This study suggests that high-fat diet can significantly improve the bioavailability and antioxidant activity of citrus carotenoids.