Development and evaluation of a novel antioxidant and pH indicator film based on chitosan and food waste sources of antioxidants

Chitosan based smart films are developed using blueberry and blackberry pomace extracts as active agents at different concentrations (1, 2 and 4% w/v). The whole concept of film production can be considered as eco-friendly contributing to the reduction of generally wasted material, fruit pomace. Blueberry and blackberry pomace showed excellent antioxidant potential that was not diminished after the film production. Chitosan matrix was not significantly changed to influence permeability to oxygen and mechanical properties, while water vapour permeability slightly decreased. Only the film stiffness increased with the addition of extract. Visible and significant colour changes of dry pH indicator films occurred with changing pH. The film colour was visibly transformed from pale yellow for control film, to blue-green and purple (with negative and positive a* values, respectively) with the addition of blueberry and blackberry pomace extracts, respectively. With changing pH from 2 to 10, films with blueberry changed from rose to blue green and with blackberry from red to dark violet. The most significant change was observed in the pH range from 4 to 7 that is important for determination of pH change due to the food spoilage in real foodstuff. Blackberry pomace extract had 4x more polyphenols than blueberry one. As expected, when extracts were added to chitosan films an increase in polyphenol content was also determined and antioxidant activity significantly increased. Films with blackberry pomace extract showed the highest antioxidant capacity probably due to the fact that already pure blackberry pomace extract was better antioxidant than the blueberry one. This result pointed high antioxidant activity of all produced films.