pH Indicator Films Research Articles

Intelligent Packaging Systems with Anthocyanin: Influence of Different Polymers and Storage Conditions

With the aim of meeting the growing demand for safe food, intelligent packaging has emerged, which monitors the conditions of the food and informs the consumer about its quality directly at the time of purchase. Among intelligent packaging options, colorimetric indicator films, which change color in response to changes in the food, such as the release of volatile compounds, have been widely studied. Among them, pH indicator films composed of dyes sensitive to small variations in the pH value of the food surface have received greater attention in recent years. Anthocyanins, which are natural pigments, have stood out as one of the most commonly used sources of dyes in the production of these indicator films. In this context, the present review aims to present an updated overview of research employing anthocyanins in indicator films, including their stability under different storage conditions, the influence of different polymers used in their production, and alternative techniques for maintaining stability.

Preparation and characterization of starch-based pH indicator films for anthocyanin release

Preparation and characterization of starch-based pH indicator films for anthocyanin release

Indicator Films Containing Dendrobium Orchid Flower Extract and TiO2 Nanoparticles for Monitoring Fish Fillet Spoilage

This work aimed to study a novel pH indicator film prepared from carboxymethyl cellulose (CMC)/tapioca starch (TS) incorporating Dendrobium orchid flowers and TiO2 nanoparticles for monitoring fish fillet freshness. The films were prepared based on carboxymethyl cellulose (CMC) and tapioca starch (TS) blend (CMC/TS) incorporated with TiO2 nanoparticles and Dendrobium orchid flower (DOF) extract. The result showed that the DOF extract contained peonidin-3,5-O-diglucoside and exhibited distinguishable color changes in different pH buffers. Likewise, the CMC/TS+TiO2+DOF film’s color changed corresponding to the extract. The X-ray diffraction analysis revealed the expansion of the film’s amorphous region, due to the intermolecular interactions. Analyzing scanning electron microscope images showed the effects of TiO2 and DOF extract on the surface morphology of films. The incorporation of TiO2 and DOF extract into the film formulation improved various film properties, such as redness, opacity, tensile strength, and water solubility. For the sensitivity testing, the color of the CMC/TS+TiO2+DOF film responded to ammonia vapor more than acetic acid vapor, suitable for monitoring seafood spoilage behavior. In addition, the application of film for monitoring the freshness of fish fillets was conducted. The CMC/TS+TiO2+DOF film color changed from purple to bluish-purple corresponding to the spoilage of samples. Indicating its potential as an indicator for monitoring fish fillets' freshness.

Gelatin/agar pH-indicator film based on cranberry extract loaded with linalool nanoparticle: Survey on physical, antimicrobial, and antioxidant properties

In this study, linalool-nanoparticles (L-NPs) were prepared (encapsulation efficiency was 68.54 %) and introduced pH-indicator film based on cranberry-extract (CEF) to develop multifunctional smart films. XRD analysis and FTIR spectroscopy indicated that cranberry-extract (CE) and L-NPs were uniformly distributed in the gelatin/agar matrix and could change the intermolecular structure of the film. Color change of smart films showed that CE endowed the film with pH-sensitive property. As CE and L-NPs were added to the film, the water contact angle (WCA) was increased from 57.03° to 117.73°, the elongation at break (EAB) was increased from 12.30 % to 34.60 %. Additionally, the introduction of L-NPs enhanced the antioxidant activity (DPPH free radical scavenging rate increased from 26.80 % to 36.35 %) and antibacterial activity (against S. aureus and E. coli) of the smart film, which were verified by its retarding effect on pork spoilage.

Development of a novel colorimetric pH-indicator film based on CMC/flaxseed gum/betacyanin from beetroot peels: A powerful tool to monitor the beef meat freshness

A novel indicator film based on carboxymethyl-cellulose (CMC)/flaxseed gum (FG) was developed by introducing betacyanin (BC) from beetroot peel extract. Remarkably, CMC/FG/BC film exhibited a dynamic color transition from pink to yellow in response to pH changes from 1 to 12. Beyond its pH sensitivity, the newly developed film demonstrated exceptional sensitivity to ammonia solution concentrations, detecting variation from 0.125 to 0.5 mg/mL with a significant ΔE (P < 0.05) change when a concentration of 0.5 mg/mL was added. Moreover, the inclusion of BC not only heightened the film's colorimetric capabilities but also enhanced the antioxidant, physical (moisture content, swelling index, thickness and biodegradability), and mechanical (elongation at break) properties. On the other hand, the CMC/FG/BC film's ability to provide real-time monitoring of minced beef meat quality was examined during 14 days of storage at 4 °C. The CMC/FG/BC film displayed a distinctive color change (from light pink to purple) corresponding to changes in meat samples' total volatile basic nitrogen (TVB-N) and microbial count (aerobic plate, psychrotrophic total and Enterobacteriaceae counts) during the storage period. The CMC/FG/BC film could be considered as a novel colorimetric pH indicator to monitor meat and meat derivatives' freshness. Its multifaceted properties make it valuable as an intelligent packaging used in food quality control, offering real-time insights into both pH changes and the freshness of stored meat products.

Butterfly Pea Flower Anthocyanin Immobilized pH Sensitive Intelligent Nanocomposite Films of Starch/Chitin with Improved Thermal and Mechanical Properties

AbstractThin films with pH sensitivity have been a trendsetter in the current research scenario. Edible films for packaging are comparatively newer ones, where the study uses conventional food materials as a source or precursor to fabricate the films. Starch(S) is one such material that is not much exploited in packaging and pH sensing. Here, the study presents the preparation of a new type of sensitive, intelligent film from starch‐chitin(CHN) composites and adds the anthocyanin pigment extracted from the Butterfly Pea flower (BPE). The combination films are much more sensitive to ammonia and formalin and thus suggested for the detection of adulteration in fish. All the films (S, S/BPE, S/CHN, and S/BPE/CHN) are fabricated by the solution casting method. The addition of 10 wt% CHN results in the enhancement of the thermal and mechanical properties of pH indicator films. Owing to the presence of anthocyanin pigment, the films can change their color changes in pH. The developed starch‐based intelligent films display wide color differences from bright red to green over the 1–12 pH range, which is discriminated by the naked eye.

Development of Semolina Starch/Agar-Based Intelligent Films by Incorporating Butterfly Pea Flower Anthocyanins to Monitor the Freshness of Prawns

The natural plant-derived pH indicator film which monitors food freshness during storage has gained attention among researchers due to consumer awareness of food quality, freshness, and food safety. This study aims to develop a semolina/agar-based film (S/A) incorporated with anthocyanins from butterfly pea flower extract (BPE) as a freshness indicator for tiger prawns and freshwater prawn during 4 days of storage at 4±1 °C. The semolina/agar-based butterfly pea extract (S/A/BPE) films were developed with different concentrations of BPE (3, 6, and 9%) by casting method. Increasing BPE up to 9% in the S/A film increased the thickness and moisture content, lowering the films’ water permeability. The film also had a smoother surface structure with a darker colour. Different pH solutions (pH 2.0-12.0) also changed the colour of films, depending on the BPE concentrations. The application of S/A/BPE films on tiger prawns and freshwater prawns caused colour changes from dark blue at day 0 (fresh stage) to intense green at day 2 (beginning of spoilage) indicating the spoilage of samples. The pH values of both prawns were gradually increased. However, no major changes were observed in the texture profile analysis. These results indicate that S/A/BPE film has the potential to be used as a pH indicator film to detect the freshness of prawn samples.

A pH indicator film based on dragon fruit peel pectin/cassava starch and cyanidin/alizarin for monitoring the freshness of pork

To detect the freshness of pork in real-time without damaging the testing sample, visual pH-sensing films were created containing cyanidin and alizarin as indicator labels. The film-forming matrices were made from dragon fruit peel pectin and cassava starch, with Fourier infrared spectroscopy analysis confirming successful immobilization of the natural dyes. Adding different concentrations of natural pigments did not noticeably affect the film's moisture content and solubility, water vapor permeability, or oxygen barrier properties. The colorimetric film responded sensitively to both ammonia (pH=11) and acidic (pH=2.4) environments, and was applied to pork stored at 4 ℃ based on the volatile salt nitrogen released from the meat. As the pork deteriorated, the color of colorimetric film varied from red to blue-black, allowing for accurate monitoring of freshness without opening the package and avoiding direct contact between indicator film and pork. Therefore, this colorimetric film has fantastic prospective as a perceptive packaging material for real-time non-destructive monitoring of meat product freshness.

Fabrication Of Butterfly Pea Flower Anthocyanin-Incorporated Colorimetric Indicator Film Based On Gelatin/Pectin For Monitoring Fish Freshness

Novel visual intelligent pH-indicator film was prepared from the eggshell membrane- gelatin, pectin, and anthocyanin pigment from butterfly pea flower (BP) (Clitoria ternatea). It was used as a real-time pH indicator for predicting food freshness. Eggshells are useful biowaste, gelatin has been extracted from the eggshell membrane and was used for fabricating the film. The Anthocyanin content of BP extract was 198.3 mg g−1. The film's surface morphology and chemical nature were estimated using a Scanning electron microscope, Fourier transform infrared spectroscopy, and X-ray diffraction technique. The film was pH responsive and exhibited color variation ranging from shades of red, purple, blue, green, and yellow at different pH (1-13). The applicability of the developed pH- indicator film was studied on fresh Tilapia fish by monitoring its deterioration for a specific time period. The film showed a visible color change after seven days of storage at 4ºC from dark blue, bluish-grey to olive, and deep green. Change in the total volatile basic nitrogen (TVB-N) content and pH change had an effect on the color response of the film. The findings demonstrated that the fabricated pH indicator film proved to be pH sensitive and could be used to monitor fish freshness.

Colorimetric pH indicators based on well-defined amylose and amylopectin matrices enriched with anthocyanins from red cabbage

This study aimed to prepare a novel colorimetric indicator film from virtually pure (99 %) amylose (AM) and anthocyanins extracted from red cabbage (RCA). The AM used was a unique engineered bulk material extracted from transgenic barley grains. Films produced by solution casting were compared to normal barely starch (NB) and pure barley amylopectin (AP), with amylose contents of 30 % and 0 %, respectively. The pH-indicator films were produced by incorporation of RCA into the different starch support matrices with different amylose contents. Barrier, thermal, and mechanical properties, photo degradation stability, and release behavior data revealed that RCA interact differently through the glucan matrices. Microstructural observations showed that RCA were evenly dispersed in the glucan matrix, and AM+RCA indicator films showed high UV-barrier and mechanical performance over normal starch. FTIR revealed that RCA was properly affected by the AM matrix. Moreover, the AM+RCA films showed sensitive color changes in the pH range (2–11) and a predominant Fickian diffusion release mechanism for RCA. This study provides for the first time data regarding AM films with RCA and their promising potential for application as support matrices in responsive food and other industrial biodegradable packaging materials.

Development and application of pH‐indicator film based on freeze‐dried purple‐fleshed sweet potato, starch, and CMC

SummarySmart packaging is an emergent solution commonly used to indicate the current quality and freshness of the food. In this study, a pH indicator film without an anthocyanin‐extraction step was developed, based on purple‐fleshed sweet potato powder (SPP) prepared by freeze drying process, with starch or starch and carboxymethyl cellulose (CMC). The colour of the powder and the films changed from pink to green with the pH change from 1 to 11. The effectiveness of the indicator films was assessed by the ground beef spoilage trial, which resulted in a colour change from purple to green when the pH of the meat raised from 5.54 to 7.92. The microbiological growth and the sensory changes of the meat confirmed the deterioration process. Therefore, developed indicator films could successfully indicate the spoilage of packaged ground beef.

A pH indicator film based on sodium alginate/gelatin and plum peel extract for monitoring the freshness of chicken

To monitor the freshness of chicken, a pH-sensitive film based on sodium alginate, gelatin, and plum peel extract (SGPE) was created. Thickness, color, water contact angle, mechanical characteristics, water content, water vapor transmission, light transmission, and pH sensitivity were used to evaluate the performance of the film sample. SEM and FTIR graphs demonstrated that adding plum peel extract made the SGPE film's internal structure more denser and increased its mechanical property, while decreasing the water contact angle, water content, and WVP value. The color of the SGPE15 film clearly changed from red to yellow-green in various buffer solutions (pH = 1–14), demonstrating more pH sensitivity than the SG, SGPE5, and SGPE10 films. On day 6, when checking the freshness of chicken kept at 4 °C, the SGPE15 film's color changed from orange-pink to yellow-green with TVB-N level beyond the allowable limit (15 mg/100 g). The result revealed that the SGPE film might be applied to monitor the freshness of chicken breast flesh.

Stable smart packaging betalain-based from red prickly pear covalently linked into cellulose/alginate blend films

Smart materials based on biomaterials have been shown growing interest by researchers. This paper investigated pH-indicator film with less leaching containing betalain molecule extracted from red prickly pear fixed in the cellulose-alginate blend as a matrix. Herein, the film was manufactured from a blend containing covalently bounded cellulose with betalain via the creation of a Fischer esterification (FE) to solve the leaching problem of dyes in contact with food. The structural, thermal, morphological optical, and mechanical properties and the pH-sensitive properties of films were examined. The FTIR and color analysis confirmed the fisher esterification. The fisher esterification led to a pH-indicator film with less leaching with significant color stability against UV light. The smart film changes colors with the pH values, where it goes from purple at a pH below 10 to yellow color at a pH above 10. All those proprieties with contact angles helped this film to be used as an intelligent film for monitoring salmon spoilage.

Plasticizers' effect on pH indicator film based on starch and red grape skin extract for monitoring fish freshness

AbstractThis work aimed to develop a novel colorimetric indicator film from cassava starch, isomalt and glycerol with 20% wt.% of grape skin extract (GSE) by casting to be used as an indicator of fish freshness. The plasticizers were used in the concentration of 33% at five levels: 100/0, 70/30, 60/40, 50/50 and 0/100 (%w/w isomalt/glycerol). Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and RGB colour analysis showed the homogenous distribution of GSE in the starch matrix. The presence of GSE reduces the thermal stability, k1 value, solubility, swelling values and the %E and increases the tensile strength (TS), revealing its plasticizing potential action in the presence of isomalt. The influence of pH on the colours of the film containing GSE and its indicator activity were evaluated. The results showed that the film produced operates in a wide pH range, being an excellent candidate as an indicator for monitoring fish freshness.

Monitoring freshness of chicken using intelligent pH indicator packaging film composed of polyvinyl alcohol/guar gum integrated with Ipomoea coccinea extract

With enormous amounts of food being wasted at every level of consumption, the future of food security is in jeopardy. The confusion aroused due to “best before” or “use by” can be eliminated by intelligent colorimetric indicators which communicate the quality of food. pH indicators have gained their attention because they are simple and visually informative. Using natural pigments to fabricate pH indicators can help reducing use of carcinogenic chemicals in packaging. In this work, anthocyanins extracted from a novel flower source named Ipomoea coccinea (ICE) were added to polyvinyl alcohol (PVA) and guar gum (GG) matrix in varying amounts and was applied as antioxidant and intelligent pH indicator film to monitor the freshness of chicken fillets and to visually communicate the quality of chicken. The pH indicator was characterized for halochromism, antioxidant activity, thermogravimetry, water solubility, water contact angle, surface morphology, colorimetry and X-ray diffractograms. The color change of the extract was observed from orange to red to yellow. Film with highest amount of anthocyanin extract has increased thickness of 150.5 ± 17.86a (μm), decreased water vapor transmission rate of 4.95 ± 0.29a (mg day−1 cm−2) and has a crystallinity of 52.35%. Anthocyanins started to degrade at 65 °C according to thermogravimetric analysis. The film with 20% ICE showed an excellent color change in pH solutions and the highest antioxidant activity of ∼91%. The food study results suggested that the developed film has the potential to be employed as an active and intelligent visual indicator in poultry packaging.

Edible pH sensitive polysaccharide-anthocyanin complex films for meat freshness monitoring

One of the innovative methods for real-time determination of food freshness is the application of pH-indicator sensors, where the color change can be used for the visual detection of acidic/basic volatile compounds formed during product storage due to microbial growth. The aim of the present study is to develop a pH-responsive freshness indicator based on anthocyanins from chokeberry (Aronia melanocarpa Elliot) and black carrot (Daucus carota ssp. sativus var. atrorubens Alef.), incorporated into an alginate/pectin/arabic gum composite film. The resulting films show distinct color changes as the pH varies. The color changes from red (pH 2.0 - 3.0) through pink and pale pink (pH 4.0, 5.0 and 6.0) to purple and blue (pH 7.0 - 8.0). The most distinct is the color transition between pH 6.0 and 7.0 for the black carrot extract and the chokeberry: black carrot mixture (1:3). The applicability of the developed pH-indicator films was demonstrated in chicken meat by tracking the changes during its storage at 4°C for 7 d. The observed results show a distinct color change from pink (day 1-3) to violet and blue on day 7. The developed pH- sensitive films have potential for use in a smart packaging system as a sensor for meat freshness monitoring.

Preparation of NH3- and H2S-sensitive intelligent pH indicator film from sodium alginate/black soybean seed coat anthocyanins and its use in monitoring meat freshness

The pH, ammonia, and H2S sensitivity of sodium alginate/black soybean seed coat anthocyanin (SA/BSSCA) films and their response mechanism were analyzed based on stability, intermolecular interactions, and microstructure. The results showed that the with the BSSCA content increased from 0.02% to 0.30%, SA/0.02–0.12BSSCA films had the highest color stability. The highest sensitivity to pH, ammonia, and H2S was observed for the SA/0.12–0.30BSSCA films, meanwhile, the SA/0.12BSSCA film had the highest sensitivity to meat unfreshness and spoilage. The incorporation of BSSCAs reduced the water solubility, water vapor absorption, and permeability of the films. With the BSSCA addition, the intermolecular interaction between BSSCAs and SA intensified, reducing the film roughness and number of aggregated particles, resulting in compact microstructures, which improved the film sensitivity. Thus, the SA/0.12BSSCA film was sensitive to pH, ammonia, and H2S and, therefore, meat spoilage, while having higher stability, moderate water barrier properties, and denser microstructure.

Polyphenol-loaded bacterial cellulose nanofiber as a green indicator for fish spoilage

Seafood products as a source of vitamins, minerals, and polyunsaturated fatty acids represent an important component of the human diet. However, they are susceptible to spoilage even under appropriate storage conditions, making it indispensable to develop freshness indicators. In this study, we introduce a green user-friendly pH indicator film for the naked-eye monitoring of fish spoilage. The pH indicator was prepared by successful loading of a mixture of anthocyanin and curcumin on bacterial cellulose (BC) nanofiber substrate. BC nanofiber with the advantages of biocompatibility, biodegradability, high purity, and superior mechanical strength was promising for generating pH-sensing arrays. The Fourier transform infrared (FT-IR) analysis proved the incorporation of anthocyanin and curcumin into the BC skeleton. Besides, the scanning electron microscopy (SEM) results clarified the morphology of the modified film by anthocyanin and curcumin. The pH indicator film was still stable after preserving for 60 days at different temperatures. The curcumin-anthocyanin loaded nanofiber indicated a distinct color change after spoilage by its exposure to fish meat in a transparent plastic package. Hence, the modified film by the anthocyanin-curcumin mixture is potent for the naked-eye monitoring of meat spoilage.

Bio-Based pH Indicator Films for Intelligent Food Packaging Applications.

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.

Development of Starch-Polyvinyl Alcohol Films-based pH indicator for Detection of Penicillin G Residue in Raw Milk

The detection of residual penicillin G (Pen G) in raw milk is very crucial to prevent the adverse effect from the allergy of Pen G to dairy consumer. However, the conventional detection methods require highly expensive instruments, high-skill technicians and complicated sample preparation process. In this research, a Lab-on-a-Disc (LOAD) to detect the residual Pen G in raw milk was introduced. The LOAD (ϕ: 9.0 cm) consisted of 10 micro-channels with the maximum volume of 200 μL was fabricated by laser machining of PMMA sheets. The 8.0 μm-thick polyvinyl alcohol, PVA (0.03125 % w/v) mixed with corn starch at a ratio of 3:7 (v/v) and bromocresol purple (BCP) pH indicator (0.025 % w/v) film that used as a Pen G indicator was prepared by hydrogel method and coated on the micro-channels by drop casting method. After the LOAD was rotated at 5000 rpm for 5 min at 25 °C, the BCP-(S-PVA) indicator film with the solubility of 93.56 % was dissolved in a raw milk mixed with Pen G (4.0 ng/mL) and the color of BCP-(S-PVA) film has changed from dark violet to light violet. The detection limit of BCP-(S-PVA) film to detect the Pen G in raw milk that obtained from the linear dose response curve (R2: 0.9630) is 0.17 ng/mL. Therefore, the LOAD with the BCP-(S-PVA) pH indicator is the fast and accurate promising method to determine the residual Pen G in raw milk at room temperature.