Effects of freezing, freeze drying and convective drying on in vitro gastric digestion of apples

• Processing changes the microstructure and composition of apples compared to raw apples.
• The structural modifications resulted in behavioral changes in apples during in vitro digestion.
• These changes were satisfactory simulated and better evaluated by using mathematical models.

The influence of processing (freezing at −196 °C in liquid N2, FN sample; freeze-drying at −50 °C and 30 Pa, FD sample; and convective drying at 60 °C and 2 m/s, CD sample) on apple (var. Granny Smith) behavior during in vitro gastric digestion was investigated. Dried apples (FD and CD samples) were rehydrated prior to digestion. Changes in carbohydrate composition, moisture, soluble solids, acidity, total polyphenol content (TPC), and antioxidant activity (AA) of apple samples were measured at different times during digestion. Processing resulted in disruption of the cellular structure during digestion, as observed by scanning electron microscopy, light microscopy, and changes in carbohydrate composition. Moisture content increased (6–11% dmo), while soluble solids (55–78% dmo), acidity (44–72% dmo), total polyphenol content (30–61% dmo), and antioxidant activity (41–87%) decreased in all samples after digestion. Mathematical models (Weibull and exponential models) were used to better evaluate the influence of processing on apple behavior during gastric digestion.