Bio-Based pH Indicator Films for Intelligent Food Packaging Applications

Abstract

The widespread concerns about the environmental problems caused by conventional plastic food packaging and food waste led to a growing effort to develop active and intelligent systems produced from renewable biodegradable polymers for food packaging applications. Among intelligent systems, the most widely used are pH indicators, which are generally based on a pH-sensitive dye incorporated into a solid support. The objective of this study was to develop new intelligent systems based on renewable biodegradable polymers and a new bio-inspired pH-sensitive dye. The structure of the dye was elucidated through FT-IR and 1D and 2D NMR spectroscopic analyses. UV-VIS measurements of the dye solutions at various pH values proved their halochromic properties. Their toxicity was evaluated through theoretical calculations, and no toxicity risks were found. The new anthocyanidin was used for the development of biodegradable intelligent systems based on chitosan blends. The obtained polymeric films were characterized through UV-VIS and FT-IR spectroscopy. Their thermal properties were assessed through a thermogravimetric analysis, which showed a better stability of chitosan–PVA–dye and chitosan–starch–dye films compared to those of chitosan–cellulose–dye films and the dye itself. The films’ sensitivity to pH variations was evaluated through immersion in buffer solutions with pH values ranging from 2 to 12, and visible color changes were observed.

Functional Filaments: Creating and Degrading pH-Indicating PLA Filaments for 3D Printing

“…Recently, the incorporation of pH indicators in PLA-based composites has been investigated in the context of creating packaging capable of signifying changes in food freshness [ 41 , 42 , 43 , 44 ]. For this application, both the PLA composite and the indicator must be food-safe, leading to the use of indicators derived from plants [ 42 , 44 ] or microorganisms [ 43 ]. Though biodegradation was a consideration in these studies, the effects of the indicators on the degradation of the PLA was not investigated [ 41 , 42 , 43 , 44 ].…”

“…For this application, both the PLA composite and the indicator must be food-safe, leading to the use of indicators derived from plants [ 42 , 44 ] or microorganisms [ 43 ]. Though biodegradation was a consideration in these studies, the effects of the indicators on the degradation of the PLA was not investigated [ 41 , 42 , 43 , 44 ]. Additionally, there are currently no commercially available pH-indicating filaments for 3D printing.…”

pH Responsive Properties of Methyl Red/PVA Polymers for Smart Food Packaging Applications

“…The MR/PVA polymers treated with buffer solution of pH 6.5 have shown maximum absorption peak at 435 nm confirming the yellowish appearance after the treatment. Whereas, MR/PVA polymers treated with buffer solution with pH 4.5 have shown maximum absorption peak at 525 nm confirming reddish appearance after treatment [12]. The intensity of the characteristic absorbance peak of the samples against both 6.5 and 4.5 pH buffer solutions found to be increased with increasing MR concentration confirming better pH response of MRPVA3 sample compared to others.…”

“…The pure PVA polymer has shown an absorption peak at ~215 nm which can be attributed to the carbonyl group or the presence of residual acetate group of PVA. The MR/PVA polymers have shown a significant absorption peak at 283 nm and 408 nm along with the PVA characteristic peak [3,12]. The MR/PVA polymers treated with buffer solution of pH 6.5 have shown maximum absorption peak at 435 nm confirming the yellowish appearance after the treatment.…”

Innovative Packaging Strategies for Freshness and Safety of Food Products: A Review

“…Under alkaline pH, this structure deprotonates to form charged trans-chalcone, a reddish-coloured compound. In this way, the structural change contributes to the colour change [36]. These pH-sensitive indicators have recently been gathering market attention because they differentiate between fresh and altered food and are easy to fabricate [24,37].…”