To examine the effect of mechanical processing for plant-based materials on antioxidant properties during digestion, relationships between the size of pulverized plant tissue and changes in antioxidant activities during simulated in vitro digestion were investigated. The citrus peel tissue was pulverized and classified into four powder fractions followed their particle size distributions as 125−180 m, 180−355 m, 355−500 m and 500−710 m. These fractions were regarded as a plant tissue model with various degrees of cell damages. Powder samples were collected during the digestion and measured their particle sizes and colors. Besides, total phenolic content and antioxidant activities of digested fluid were also evaluated. The results showed that the powder color of smaller particles were significantly changed than the bigger ones. The bio-properties of digested fluid for the bigger particle sizes comparatively retained more than smaller ones at the simulated gastric stage. It also showed mostly stable during simulated gastric or small intestinal digestion stage. This suggested that the release of bioactive compounds from plant tissues during digestion could be related to their structural attributes such as degrees of cell damages which could be affected by processing methods and conditions.