Development of pH indicator and antimicrobial cellulose nanofibre packaging film based on purple sweet potato anthocyanin and oregano essential oil

A pH indicator and antimicrobial cellulose nanofibre packaging film was developed based on cellulose nanofibres as film matrix, anthocyanins from purple sweet potato as a natural dye and oregano essential oil as an antimicrobial agent. The colour of the anthocyanin solution was noticeably different from pH 2 to pH 12. The developed film sensitively responded to a change of pH and showed an obvious colour change from red to yellow, with pH ranging from 2 to 12, which indicated that the film had a superior colorimetric performance to pH change. Moreover, the film showed excellent antimicrobial activity and the inhibition rate against Escherichia coil and Listeria monocytogenes reached 99.99%. Bio-compatibility between anthocyanins and cellulose nanofibre matrix was confirmed by the analysis of cross-section morphology of the film. The XRD pattern revealed that the crystallinity index of the film decreased with the addition of anthocyanins and oregano essential oil. The film had a good barrier performance to ultraviolet and visible light; its tensile strength, elongation at break, and elastic modulus was 9.28 MPa, 9.87%, and 0.15 GPa, respectively. The developed pH indicator and antimicrobial film could intuitively indicate the change of food quality during storage and effectively prolong food shelf life. (C) 2020 Elsevier B.V. All rights reserved.