Preparation and characterization of smart indicator films based on gellan gum/modified black rice anthocyanin/curcumin for improving the stability of natural anthocyanins

Effect of metal cation crosslinking on the mechanical properties and shrimp freshness monitoring sensitivity of pectin/carboxymethyl cellulose sodium/anthocyanin intelligent films

Although many preparation methods have been reported so far, it is still a great challenge for intelligent packaging films with both excellent mechanical properties and very high sensitivity. Herein, we report a facile method to prepare performance-enhanced pectin (PC)/carboxymethyl cellulose sodium (CMC)/anthocyanins (ACNs)/metal ion films by crosslinking with metal ions (Zn2+, Mg2+ and Ca2+). Cross-linking reaction between PC/CMC and metal ions significantly improved water resistance and mechanical properties of composite films (P < 0.05). Even at high relative humidity (RH = 84 %), cross-linking of Ca2+, Mg2+, and Zn2+ significantly increased the tensile index of the films by 1.37, 1.41, and 1.52 times (P < 0.05), respectively. Moreover, the complexation of metal ions/polysaccharides with ACNs reduced the decomposition rate of ACNs, improved the storage stability and antioxidant capacity of ACNs, and also increased the sensitivity of the colorimetric response of the indicator films in monitoring shrimp freshness. Thus, with this high sensitivity, the Red, Green and Blue (RGB) values of the films can be determined using a mobile phone application to monitor shrimp safety in real time. These results suggest that ACNs-metal cation-polysaccharide composite films have great potential for smart packaging applications.

Smart nano-inks based on natural food colorant for screen-printing of dynamic shelf life of shrimp

Intelligent packaging embedded with food freshness indicators can monitor food quality and be deployed for food safety and cutting food waste. The innovative nano-inks for dynamic shelf-life printing based on natural food colorant with application in real-time monitoring of shrimp freshness were prepared. Co-assembly of saffron petal anthocyanin (SPA) with hydrophobic curcumin (Cur) into chitin nano-scaffold (particle sizes around 26 ± 8 nm) could deliver hindering SPA leaching, confirmed by FT-IR, FE-SEM, AFM, and color stability test. The best response to pH-sensitivity was found in a ratio of (1:4) Cur/SPA (30% (v/w) in ChNFs that was correlated with the chemical and microbial changes of shrimp during shrimp freshness. However, smart screen-printed inks signified higher responsiveness to pH changes than FFI films. Therefore, smart-printed indicators introduced the excellent potential for a short response time, easy, cost-effective, eco-friendly, co-assembly, great color stabilities, and lifetime for nondestructively freshness monitoring foods and supplements.

Development of amine-sensitive intelligent film with MIL-100(Fe) as function filler based on anthocyanins/pectin for monitoring chilled meat freshness

To enhance the amine-sensitivity of intelligent films for accurate monitoring of chilled meat freshness, different additions (0, 1, 2, 3 wt%) of MIL-100(Fe) were incorporated into the matrix composed of anthocyanins (ANs) and pectin (P). Results indicated that the tensile strength, thermal stability, barrier performance and absorption capacity of the films with MIL-100(Fe) were improved significantly (p < 0.05). Especially, the film with 2 % MIL-100(Fe) exhibited the best performance due to its compact structure and the highest crystallinity. Additionally, adsorption isotherms of the films with MIL-100(Fe) were fitted on the Langmuir and the Freundlich isotherm, and adsorption kinetics were fitted on the pseudo-second-order model and Elovich model, respectively (R2 > 0.96), suggesting a combined mechanism of chemisorption and intraparticle diffusion. Besides, when the films were exposed in ammonia environment, they changed color from purple to blue-violet, finally to green. Ultimately, film with 2 % MIL-100(Fe) was used to monitor the chilled meat freshness, as expected, similar color variation was observed at three stages of meat freshness (fresh, sub-fresh, and spoiled), which enabled the accurate differentiation of meat freshness. Thus, films with MIL-100(Fe) demonstrated the potential to be amine-sensitive intelligent packaging for monitoring chilled meat freshness in real time.

Intelligent double-layer film based on gellan gum/modified anthocyanin/curcumin/sodium alginate/zinc oxide for monitoring shrimp freshness

In this study, intelligent double-layer films were prepared using modified black rice anthocyanin (MBRA)-curcumin (CUR)-gellan gum (GG) as the inner indicator layer and sodium alginate (ALG)‑zinc oxide (ZnO) as the outer antimicrobial layer. The bilayer films were successfully prepared, as revealed by scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction measurements. The mechanical characteristics, moisture content, and water vapor resistance of GG-MBRA/CUR1@ALG-ZnO, GG-MBRA/CUR2@ALG-ZnO, and GG-MBRA/CUR3@ALG-ZnO films showed significant enhancement compared to GG-MBRA/CUR3 and ALG-ZnO films. The bilayer films exhibited excellent pH responsiveness and reacted effectively to ammonia. The outer layer significantly improved the antioxidant and antibacterial properties of the inner layer. When the films were applied to shrimp, it was found that the double-layer films not only monitored the freshness of the shrimp in real-time but also were influential in extending the shelf life of the shrimp by about 1 d. Therefore, the double-layer film demonstrated potential as a smart packaging material for real-time monitoring of meat product freshness.

Time-temperature indicator of hydroxyethyl cellulose ink labels for assessing pork freshness

Pork is widely consumed worldwide, and many consumers now utilize sensory evaluation techniques to determine the freshness of pork when buying it. A color-changing ink label utilizing bromocresol purple (BCP) and N-hydroxyphthalimide (NHPI) had been created to help consumers better and more rapidly determine the freshness of pork while it is stored. The ink was easy to prepare and could be readily transferred to A4 paper using screen printing technology. This study delved deeper into the impact of hydroxyethyl cellulose (HEC) on the functional properties of inks to enhance printing performance. The experiment demonstrated that a 1 % mass fraction of HEC improved thixotropy and facilitated the even distribution of ink on A4 paper, as confirmed by scanning electron microscopy. Screen-printed labels with varying concentrations displayed distinct color change rates when stored at different temperatures, indicating their capability to assess pork freshness. FT-IR, laboratory, and stability tests verified the ink's exceptional color change capabilities and printing attributes. An analysis using the Arrhenius equation revealed a substantial synergistic effect between BCP and NHPI, resulting in improved sensitivity and accuracy of the ink. This study offers a practical and feasible method to monitor the storage quality of pork effectively.

Development of smart packaging film incorporated with sodium alginate-chitosan quaternary ammonium salt nanocomplexes encapsulating anthocyanins for monitoring milk freshness

This study focused on the preparation, functionality, and application of smart food packaging films based on polyvinyl alcohol (PVA) and anthocyanins (ACNs) -loaded sodium alginate-chitosan quaternary ammonium salt (HACC-SA) nanocomplexes. The average encapsulation rate of anthocyanins-loaded nanocomplexes reached 62.51 %, which improved the hydrophobicity and water vapor barrier of the PVA film. FTIR confirmed that the nanocomplexes were immobilized in the PVA film matrix by hydrogen bonding, which improved the mechanical properties of the film. The SEM and XRD results demonstrated that the HACC-SA-ACNs nanocomplexes were uniformly distributed in the film matrix and the crystallinity of PVA was decreased. The P/HACC-SA-ACNs film showed a significant response to buffers of pH 2-13 and high color stability after 21 days of storage compared to the P/ACNs film. Furthermore, the color of the composite film changed from purple to red as the milk freshness decreased during 72 h of milk freshness monitoring, indicating that the P/HACC-SA-ACNs films were suitable and promising for application as smart packaging materials.

Smart colorimetric sensing films based on carboxymethyl cellulose incorporated with a natural pH indicator

This study aimed to combine various natural pH indicators of anthocyanin from Karanda (CA) with anthocyanin from butterfly pea flower (BA) or curcumin (CC) to improve the sensitivity of CA. CA75/BA25 and CA25/CC75 enhanced the sensitivity of the endpoint colour change of CA. A smart colorimetric sensing film was also developed and characterised by loading different natural pH indicators on carboxymethyl cellulose (CMC) films. The addition of different natural pH indicators increased the thickness, elongation, colour (a* and b* values), and contact angle of CMC films (p < 0.05). However, the tensile strength, water vapour permeability, film solubility, light transmission, and L* value decreased when different natural pH indicators were added (p < 0.05). The indicator films demonstrated enhanced antioxidant capacity and thermal stability. The FTIR spectra showed that natural pH indicators were successfully immobilised into the CMC films. Notably, the CMC/CA75/BA25 film was the most sensitive film to changes in volatile ammonia and different pH buffer solutions. The CMC/CA75/BA25 film changed from purple to green with exposure to ammonia solution and from pink to purple to blue to green with increasing pH. Therefore, the CMC/CA75/BA25 film has potential as a colorimetric sensing film, providing a more accurate assessment result.