Time temperature indicator film based on alginate and red beetroot (Beta vulgaris L.) extract: in vitro characterization

Introduction.This study was aimed to develop and characterize a biodegradable time temperature indicator (TTI) film by incorporating red beetroot (Beta vulgaris L.) extract, which is rich in betalain pigments, into alginate (A) / polyvinyl alcohol (PVA) blend film.Materials and methods.The alginate-PVA blends (APVA) were prepared by mixing the 1% PVA and 3% A solutions at different A:PVA (v/v) ratios (2:3, 1:1, 3:2).TTI films were obtained by addition of ascorbic acid and red beetroot extract to APVA blends and adjusting the pH to 9.5 by adding 2M NaOH.The films were produced by casting technique.The pure A, pure PVA, APVA and TTI films were characterized by using Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM).The mechanical properties of the films were established through stress/strain tests.The CIE L*a*b* color parameters of TTI film were obtained during seven days of storage at 4, 25, 40 and 60 °C.Results and discussion.Increasing the concentration of A provided an increase in elastic modulus, tensile strength and elongation at break (%) of APVA and TTI films.TTI(3:2) film had better film flexibility compared to A, APVA, TTI(1:1) and TTI(2:3) films.The ratio of A to PVA in blend films did not create a significant effect on TGA thermograms.Higher A proportion in TTI films decreased the phase separation observed in SEM images.The intensity of O-H stretching band clearly increased in TTI films compared to other films.TTI (3:2) film stored at 4 °C did not undergo color change for 7 days, whereas the color of TTI stored at higher temperatures changed gradually during storage depending on the storage temperature.The changes in b* parameters and hue angle values were more pronounced; and generally b* and hue angle values of the samples stored above 4 °C started to increase significantly beginning of the first day.Conclusions.The developed TTI film has a potential to monitor the quality changes of the foods, which are improperly stored but normally must be refrigerated, through color changes.