Dye Leaching Research Articles

Edible thermochromic beads from flavonoid, fatty acid, and lecithin for smart packaging

Enzymatic browning and microbial growth are two natural phenomena that occur when fruits and vegetables are exposed to abnormal conditions, i.e., temperatures in the range of 12–22 °C, leading to their spoilage. Controlling the temperatures during the supply chain aims to optimize the product's shelf life. Irreversible thermochromic beads were fabricated using a simple extrusion technique containing fatty acid, lecithin, and anthocyanin solution-alginate. The pigmentation durability was adjusted based on electrostatic interactions, as evidenced by the reduction in dye leaching in the case of the produced bead at pH = 6 to less than 0.007 after 45 min. Characterization shows that the chosen combination of fatty acids and the quinonoid molecule is useful for producing thermochromic beads, with a color change at 12 °C–22 °C, from blue to purple. Using the prepared thermochromic beads in the supply chain of fresh-cut salad and brussels sprouts showed a great result for monitoring their freshness after 21 ± 1 min.

Enhanced long-term stability of stained microplastics with carbon nitride fluorescent polymer for tracking

Fluorescent labeling and imaging is a useful tool to track the temporal and spatial distribution of microplastics (MPs) with size and shape features. However, the limited fluorescently labeled MPs spheres, photo-bleaching and leaching of organic small molecular dyes hamper the tracking of MPs in the environment. In this work, phenyl-modified carbon nitride (PMCN) fluorescent polymer was prepared and applied for the staining of eight different types of MPs. The interface interaction mechanism between PMCN fluorescent polymer and MPs was investigated by the desorption experiments. The long-time photo-stability of the stained MPs against ultraviolet (UV) light irradiation, freeze-thaw cycles, various environmental factors and real environmental water samples was evaluated. The MPs stained with PMCN fluorescent polymer showed more robust stability than the common dye (Nile red) against the damage when exposure to UV light for 72 h, treatment with freeze-thaw cycles for 60 days, exposure to strong acid, strong alkali, high salinity, freshwater (river and lake) or seawater for 60 days. Results indicate PMCN fluorescent polymer is promising as a convenient, efficient and universal fluorescent tracer for visually tracking the migration and distribution of MPs in environmental water system.

Modeling the Transport of Inorganic Arsenic Species through Field Soils: Irrigation and Soil Structure Effect

Dissolved arsenic (As) may appear at the tile line level through preferential flow (PF), leading to contamination of shallow water bodies. Limited work on the movement of As forms in field soils urged the need for more research. The PF of arsenate (As(V)) and arsenite (As(III)) compared to chloride (Cl) at constant flow under saturated (10 mm), slightly unsaturated (−10 mm), and unsaturated (−40 mm) pressure heads was evaluated in replicated large field columns varying in subsoil structure. A solute containing As(V), As(III), and Cl was pulsed until the Cl concentration ratio in the drainage samples reached maxima and flushed with solute-free irrigation. HYDRUS-1D software version 4.15 was utilized to fit the breakthroughs of As(V) and As(III) in the dual-porosity physical non-equilibrium model (DP-PNE). The Langmuir equation was used to fit the As(V) and As(III) sorption isotherms, and blue dye staining was used for the marking of flow paths. Dye leaching was observed up to 50 cm or deeper in the soils. Under saturated conditions (+10 mm), Kotli, Guliana, and Mansehra soils showed chemical non-equilibrium (CNE) for As(V) and As(III); however, the extent of CNE was less under unsaturated conditions (−40 mm). These results implied that these well-structured soils had enough large macropores, which cause PF, but at the same time, they were also small enough to retain water and leach solutes under unsaturated conditions (−40 mm). It is concluded that irrigation of contaminated water or dumping solid waste on well-aggregated soil may exhibit PF of dissolved As during and after rains, and additionally As(III), which is more toxic and mobile under reduced conditions, has equal or greater potential for movement.

Plasma‐assisted surface engineering for value added in starch bioplastics: A study on enhanced surface properties and natural dye immobilization

AbstractThis study examines the enhancement of starch‐based bioplastic sheets for immobilizing natural dyes (ND) using plasma processes. The effects of poly(vinyl alcohol) (PVA) as a binder for ND were also assessed. Starch substrates were treated with air plasma, air plus 1,7‐octadiene (OD) plasma, and air plus 2‐methy‐2‐oxazoline (Ox) plasma before immobilizing curcumin and telang NDs, followed by an OD overcoating. Surface morphology, wettability, chemical composition, tensile strength, and surface charge were analyzed. Results showed improved wettability and dye immobilization, particularly for telang with a PVA binder and plasma treatment. OD overcoating prevented dye leaching. Air plasma reduced, while OD plasma maintained the starch's negative charge. XPS analysis indicated increased oxygen and nitrogen presence after air plasma and enhanced aliphatic carbon from OD overcoating. Tensile strength was largely unaffected, but elongation at break was reduced, especially after air and OD plasma treatment.

Phenol red hydrogel as pH indicator with protection against nanoceria degradation

Phenol red (PR) is a standard acid-base indicator in cell and tissue culture media, as well as multiple detection protocols. Meanwhile, catalytic nanomaterials such as nanozymes demonstrate great potential in biomedical applications, but there were few studies about the direct impact of nanozymes on the ubiquitous pH indicators. We demonstrate for the first time the degradation of phenol red by highly active nanoceria. The results provide evidence that phenol red is a redox active molecule and it may be oxidized quickly by nanoceria so that its pH-indicating functionality may be lost. Investigators need to be cautious in their routine use of phenol red, particularly when it is exposed to active nanozymes. Herein, we construct a PR-hydrogel as a protective strategy for phenol red against oxidation. Results show that the PR-hydrogel maintained the quantitative acid-base indicating capability while resisting the degradation by nanoceria. The hydrogel exhibits high stability, good pH sensitivity and recyclability, negligible cytotoxicity and dye leaching, which provides a strong practical resolution to the application of phenol red in future challenges of nanomedicines.

A new optical pH sensor based on a mixture of Alizarin and Orange dyes immobilized on an agarose membrane

Two techniques, including chemical immobilization of a combination of two indicators of Alizarin and Orange dyes and the epoxy activation of the agarose membrane, were used for the preparation of a new optic pH sensor. For this purpose, the mentioned dyes were immobilized on agarose support activated by an epoxy, followed by optimizing the impacts of the coupling pH, as well as the ratio and concentration of the two dyes. The sensor was set up in a flow cell and effectively employed for online pH calculations. The new optic pH sensor could be applied between 4.5 and 11pH values. The sensor could quickly respond to pH alterations in nearly 25 s. The sensor's response is adjustable and replicable. Ionic strengths of up to 0.5 mol L−1 could have no meaningful impact on the response signal. In addition, no proof of any signal drift or dye leaching was detected over a three-month period.•The chemical immobilization of two indicators on agarose membranes activated by an epoxy could lead to a sensitive optic pH sensor for a wide range of pH.•The intended sensor was mounted in a flow cell and effectively utilized for the purpose of online pH measurement.•The suggested optode was employed to determine pH in real samples of water.

A study on red cyanine dyes employing bis(fluorosulfonyl)imide anions for color filters of virtual and augmented reality displays

Novel cyanine dyes were designed and synthesized for use in high-resolution OLED red color filters suitable for virtual/augmented reality applications. To enhance stability and solubility in organic solvents, four different weakly coordinating bis(fluorosulfonyl)imide anions were introduced to the cyanine moiety. Additionally, to prevent dye leaching during etching, a substituent containing a methacrylate group was incorporated into the cyanine dye. The spectral properties, solubility in industrial solvents, and stability of the synthesized dyes were investigated to evaluate the dyes for dye-based color filters. Subsequently, spin-coated color filters were fabricated using the optimized photoresists containing the synthesized dyes. The transmittance, chromaticity, and stability of the fabricated color filters were examined. The dyes showed sufficient optical properties and improved solubility in industrial solvents because of their weakly coordinating counter anions. Additionally, the synthesized dyes and prepared color filters exhibited sufficient thermal stability for applications. Furthermore, the prepared color filters exhibited superior transmittances compared to those of their parent dyes.

Facile and eco-friendly dyeing process based on UV-induced photografting to immobilize halochromic dye on nylon 6 fabric for acidic gas detection

The employment of colorimetric textile sensors based on halochromic dyes enable the visual detection of gas leaks, without the need for additional instruments, and are thus advantageous for the immediate detection of hydrochloric acid. Despite their potential utility, the widespread use of halochromic dyes is impeded by their poor dyeability and washfastness on nylon fibers. Herein, we introduce an environmentally sustainable UV-induced photografting method to dye nylon 6 fabrics and enhance the dyeability and wash fastness of halochromic dyes. This method employs UV radiation to generate radicals that facilitate the covalent bonding of the radical-sensitive groups on the dye and fiber, which significantly reduces dye leaching. Colorimetric nylon sensors fabricated using a graftable rhodamine dye with exceptional pH sensitivity via a UV-induced photografting method. The sustainability of the UV-induced photografting method and the gas detection performance, durability, and reusability of the fabricated textile sensors are investigated. The fabricated sensors demonstrate rapid detection rates of <10 s, exhibit distinctive color changes (ΔE >20) upon exposure to hydrogen chloride at concentrations as low as 1 ppm, and show excellent durability (washfastness level: 4–5, performance retention rate after washing: 97 %) and reusability after ten washing/drying cycles. Furthermore, the UV-induced photografting method is more environmentally sustainable than conventional dyeing methods owing to its low solvent consumption (~97 %), low energy consumption (~84 %), and relatively short process time (~45 %).

Cast, Dip, Spray, and Print─Covalently Embedded Photochromic Materials from a Versatile Spiropyran Conjugate

Dynamic photochromic dyes are in great demand for various applications. These are used as active materials with tunable optical properties. However, producing photochromic materials in significant quantities is still a challenge. The ability to retain and prolong the interconversion of switching between open and closed forms is affected by undesirable aggregation of dyes in the matrix. The often-employed method of adding photochromic dyes into bulk materials causes issues such as aggregation, leaching of dye, and photoinstability. A versatile light-responsive spiropyran substituted azo-initiator was conveniently synthesized and utilized for incorporating photochromic units at the α-chain end of the vinyl polymers. Accordingly, processes in bulk, solution, and emulsion/dispersion were developed by radical polymerization of common vinyl monomers such as styrene and acrylates. This approach enabled the preparation of light-responsive polymers possessing photochromic spiropyran units covalently incorporated at the polymer chain end. Thus, monodisperse, covalently embedded photochromic colloidal particles with low dye content (<0.1 mmol) were prepared. The fabrication and high-resolution spatiotemporal control of materials such as gels, elastomers, resins, and transparent films of commodity polymers embedded with photochromic units are demonstrated with detailed coloring, fading, and fatigue behavior. The facile and straightforward approach developed to prepare photochromic colloidal particles can be applied to any substrate through cast, dip, spray, or print to make “smart” photochromic materials.

Evidence on Invasion of Blood, Adipose Tissues, Nervous System and Reproductive System of Mice After a Single Oral Exposure: Nanoplastics versus Microplastics

ObjectiveThis study was designed to provide the evidences on the toxicokinetics of microplastics (MPs) and nanoplastics (NPs) in the bodies of mammals. Methods100 nm, 3 μm, and 10 μm fluorescent polystyrene (PS) beads were administered to mice once by gavage at a dose of 200 mg/kg body weight. The levels and change of fluorescence intensity in samples of blood, subcutaneous fat, perirenal fat, peritesticular fat, cerebrum, cerebellum, testis, and epididymis were measured at 0.5, 1, 2, and 4 h after administration using an IVIS Spectrum small-animal imaging system. Histological examination, confocal laser scanning, and transmission electron microscope were performed to corroborate the findings. ResultsAfter confirming fluorescent dye leaching and impact of pH value, increased levels of fluorescence intensity in blood, all adipose tissues examined, cerebrum, cerebellum, and testis were measured in the 100 nm group, but not in the 3 and 10 μm groups except in the cerebellum and testis at 4 h for the 3 μm PS beads. The presence of PS beads was further corroborated. ConclusionAfter a single oral exposure, NPs are absorbed rapidly in the blood, accumulate in adipose tissues, and penetrate the blood-brain/testis barriers. As expected, the toxicokinetics of MPs is significantly size-dependent in mammals.

Fabrication and Characterization of Intelligent Multi-Layered Biopolymer Film Incorporated with pH-Sensitive Red Cabbage Extract to Indicate Fish Freshness.

This study aimed to fabricate an intelligent monolayer and multi-layered biodegradable films incorporated with red cabbage extract (RCE) to act as a safe and reliable freshness indicator. A film-forming solution (FFS) of gelatin, carboxymethyl cellulose (CMC) and chitosan was prepared and fortified with 0.5% (w/v) of RCE for developing intelligent monolayer films. The intelligent multi-layer film was prepared via layer by layer casting of gelatin, chitosan (added with 0.5% of RCE) and CMC biopolymers. The thickness of the multi-layered film was the highest (0.123 ± 0.001 mm) compared to gelatin-, CMC- and chitosan-based monolayer films (p &lt; 0.05). Chitosan film has the highest tensile strength (p &lt; 0.05), followed by multi-layer, CMC and gelatin films. Elongation at break was slightly higher in CMC (35.67 ± 7.62%) compared to the multi-layer film (33.12 ± 9.88%) and gelatin film (p &gt; 0.05). Water vapor permeability was higher in the multi-layer film (1.244 ± 0.05 × 10-5 g mm h-1cm-2 P-1) than the other monolayer films. Moisture content was highest in chitosan film followed by the multi-layered film (p &lt; 0.05) and then the CMC and gelatin films. CMC film showed the highest solubility compared to multi-layered and chitosan film (p &lt; 0.05). Additionally, transmittance and transparency values in the multi-layered film were the lowest compared to the chitosan-, CMC- and gelatin-based films. L* and a* values were the lowest, while b* values increased in the multi-layered film compared to the other film samples (p &lt; 0.05). pH sensitivity and ammonia gas tests revealed similar color changes in chitosan and multi-layer films. However, FTIR spectra confirmed that dye leaching was not detected for the multi-layered film soaked in ethanol. The biodegradability test showed rapid degradation of multi-layered and chitosan films within 1 month. Based on the optimum results of the multi-layered film, it was applied to monitor the fresh quality of tilapia fish fillets at 4 °C for 10 days. The results of freshness acceptability were noted on day 6 due to the change in color of the multi-layer film with an estimated total volatile basic nitrogen content of 21.23 mg/100 g. Thus, the multi-layered film can be used as an indicator to monitor the quality of the fish freshness without leaching dye onto the food surface.

Fabrication of Polysaccharide-Based Halochromic Nanofibers via Needle-Less Electrospinning and Their Characterization: A Study of the Leaching Effect.

Responsive materials, i.e., smart materials, have the ability to change their physical or chemical properties upon certain external signals. The development of nanofibrous halochromic materials, specifically combining the pH-sensitive functionality and unique nanofiber properties, could yield interesting new applications, especially when the common problem of dye leaching is successfully tackled. Therefore, in this article, we studied the fabrication process of polysaccharide-based halochromic nanofibrous materials by using a combination of various halochromic dyes (bromothymol blue, bromocresol green, and thymol blue) and cellulose acetate in a spinning solution using a one-pot strategy. The inhibition of leaching was addressed by using a complexing agent: poly-diallyl-dimethylammonium chloride (PDADMAC). The preparation of hybrid spinning solutions, their characterization, and ability to form continuous nanofibers were studied using a high production needle-less electrospinning system. The produced hybrid solutions and nanofibers were characterized, in terms of their rheological properties, chemical structure, morphology, and functionality. Fabricated nanofibrous halochromic structures show a clear color change upon exposure to different pH values, as well as the reduced leaching of dyes, upon the addition of a complexing agent. The leaching decreased by 61% in the case of bromocresol green, while, in the case of bromothymol blue and thymol blue, the leaching was reduced by 95 and 99%, respectively.

Facile and eco-friendly fabrication of a colorimetric textile sensor by UV-induced photografting for acidic gas detection

For the immediate detection of strong acids, it is advantageous to employ colorimetric textile sensors based on halochromic dyes, as such systems permit the detection of gas leaks with the naked eye. Here, we introduce a UV-induced photografting method to dye cotton fabrics in an eco-friendly manner and to improve the dyeability and wash fastness of halochromic dyes. In this UV photografting method, the radical-sensitive groups of the dye and the fiber were covalently bonded through radicals formed under UV irradiation to greatly reduce dye leaching. Two types of graftable-rhodamine dyes were synthesized by introducing a radical-sensitive group to a rhodamine derivative with a superior pH sensitivity, and textile sensors were fabricated via UV photografting. Subsequently, the eco-friendliness of the UV-induced photografting method and the gas detection performances, durabilities, and reusabilities of the fabricated textile sensors were investigated. All fabricated sensors exhibited distinctive color changes (ΔE >15) under acidic conditions, in addition to an outstanding durability (washfastness level: 4–5, performance retention rate after washing: 91%) and reusability after ten washing/drying cycles. Furthermore, the low consumption of solvent (∼91%), the salt/alkali-free nature of this method, its low energy consumption (∼85%), and the relatively short process time (∼41%) render this UV-induced photografting technique more environmentally friendly than conventional dyeing methods. Our results therefore indicate that textile sensors fabricated using the UV-induced photografting method are promising candidates for acid gas sensors in a wide range of applications.

Covalent incorporation of metalloporphyrin in luminescent polymer dot transducer for continuous glucose monitoring

Luminescent dye-doped polymer dots (Pdots) have been demonstrated for various biosensing applications. However, the dye doping strategy may suffer from dye aggregation and dye leaching issues which limit the long-term sensor performance. Here, we show that covalent incorporation of metalloporphyrin in polyfluorene backbone for continuous glucose monitoring. The resulting polymer was used to develop luminescent Pdots transducer that overcome the dye-aggregation problem. We characterized the spectroscopic properties of the metalloporphyrin covalently-linked Pdots, which showed reduced batch-to-batch variation, enhanced intra-particle energy transfer, and improved luminescence stability as compared to the metalloporphyrin-doped Pdots. After bioconjugation with glucose oxidase (GOx), the oxygen-sensitive phosphorescence is highly sensitive to glucose variations. The metalloporphyrin-linked Pdots transducer showed good performance in long-term continuous glucose monitoring in mouse models. This work demonstrates that covalent incorporation of porphyrin dyes in Pdots transducer is a reliable strategy to improve their stability and reproducibility for long-term continuous glucose monitoring in vivo.

Ultra-High Tg Thermoset Fibers Obtained by Electrospinning of Functional Polynorbornenes.

Insertion polynorbornenes (PBNEs) are rigid-rod polymers that have very high glass transition temperatures (Tg). In this study, two functional PNBEs were electrospun in the presence of a variety of cross-linkers, resulting in fibers with Tgs greater than 300 °C. The fibers are long (several mm), rigid, and with diameters that can be tuned in the range 300 nm–10 μm. The electrospinning process can be used to encapsulate dyes or graphene dots. Due to the high cross-linking density of the fiber, dye leaching is prevented. In contrast with other rigid-rod polymers, electrospinning of PNBE is facile and can be performed at injection rates as high as 1 mL/min.

The Leaching of Natural Dyes from Avocado (Persea Americana Mill) Seeds Using the Ultrasonic-Assisted Extraction Method and Its Application to Cellulose Fibers

The textile industry uses synthetic dyes because they are cheaper and easier to obtain. Moreover, the color availability is guaranteed and more varied. However, these synthetic dyes have a negative impact on health and the environment. The natural dye from avocado (Persea Americana Mill) seeds can become an alternative for synthetic dyes. Polyphenol compounds, such as tannins and flavonoids, are natural color sources found in avocado seeds. The extraction of natural dyes from avocado seeds is carried out by using a non-conventional method, namely ultrasonic-assisted extraction which has great efficiency and short operating time. In this study, researchers examined the parameters that affect the yield of dye extraction from avocado seeds, namely solvent concentration and extraction time. In addition, researchers also conducted qualitative analysis on the pigment content in the yield of extraction using UV-Visible Spectrophotometry and GC-MS tests. The results indicated that the highest yield obtained from avocado seeds was 16.6742% with 90 minutes extraction time using 70% ethanol solvent. Furthermore, if the dye is applied to cellulose fibers, such as the cotton cloth, the color will change depending on the fixator added. Based on the result of the UV-Visible Spectrophotometry test, the avocado seeds contain flavonoids. Meanwhile, from the result of the GC-MS test, the compound with the largest percentage detected in avocado seeds is the 13-Tetradecynoic acid, methyl ester (C15H26O2). The compound contains a chromophore, such as a carbonyl group (C = O) which is a common feature of flavonoids.

Hydrophobic halochromic aerogel capable of reversibly measuring acidic and basic vapors

A halochromic sensor that can visually and quickly monitor the information regarding the exposure of harmful chemicals to the human body is highly valuable in the safety and industrial fields. A general halochromic sensor uses a hydrophilic matrix to increase its detection sensitivity by promoting the diffusion of foreign materials. However, it is difficult to maintain the reversibility, durability, and stability of the color change in the halochromic sensor due to the loss of halochromic dyes under continuous exposure to chemicals. This study investigates a hydrophobic halochromic aerogel sensor that is stable even when exposed to various external environments and reacts to both acids and bases. By embedding halochromic dyes in silica aerogels with a porous structure and hydrophobicity, the leaching of halochromic dyes can be prevented even when the aerogels are placed in aqueous solutions. Hydrophobic halochromic aerogels can detect vapors generated in acidic and basic solutions, and the color change in hydrophobic halochromic aerogels reacts stably even with repeated acid and base environmental changes, enabling accurate acid or base concentration detection. In addition, halochromic aerogels can be easily applied to various platforms because they can be combined with fabric, concrete blocks, pipes, and polymers such as polydimethylsiloxane to create composites. The halochromic aerogels derived in this study are expected to contribute to the development of color change sensors applicable to various work environments by greatly improving the color change reversibility, durability, and stability that are the most important characteristics of robust halochromic sensors.

Hybrid inorganic-organic fluorescent silica nanoparticles—influence of dye binding modes on dye leaching

Silica nanoparticles with embedded fluorescent dyes represent an important class of markers for example in biological imaging. We systematically studied the various incorporation mechanisms of fluorescent xanthene dyes in 30–40 nm silica nanoparticles. An important parameter was the interaction of the dye with the matrix material, either by weak electrostatic or strong covalent interactions, which also has implications on the stability of fluorescence and brightness of the dyes. Factors that can influence leaching of dyes such as the position of the dyes in particles and the intensity of the particle-dye interaction were investigated by using the solvatochromic effect of xanthene dyes and by stationary fluorescence anisotropy measurements. We compared uranine and rhodamine B, which were physically embedded, with modified fluorescein isothiocyanate and rhodamine B isothiocyanate, which were covalently bound to the silica matrix within a usual Stöber synthesis. Systematic leaching studies of time spans up to 4 days revealed that covalent bonding of dyes like fluorescein isothiocyanate or rhodamine B isothiocyanate is necessary for fluorescence stability, since dyes bound by physical interaction tend to leach out of porous silica networks. Coverage of silica particles with hydrophobic protection layers of alkyltrialkoxysilanes or hydrophilic polyethylene glycol (PEG) groups resulted in a better retention of physisorbed dyes and provides the possibility to adapt the particles to the polarity of the medium. Best results were archived with PEG groups, but even small trimethylsilyl (TMS) groups already reduce leaching.

Thermally stable ZnO doped SiO2–TiO2 nanocomposite based Opto-chemical sensor

Sol-gel-based zinc doped silica-titania (ZST) nanocomposite matrix coated optical fiber has been prepared for pH sensing. Finding relies on evanescent wave absorption in a thin film deposited on the PCS fiber core. Four different dyes are encapsulated in silica-titania and zinc doped silica-titania nanocomposite and the formulation is optimized to suppress dye leaching and enhanced the dynamic pH range. Both matrices show porous, smooth, and crack-free films with low surface roughness (15 nm and 1 nm). The grain sizes are calculated ranged 66–166 nm and 43–105 nm for D-ST (dyes encapsulated silica-titania) and D-ZST (dyes encapsulated zinc doped silica-titania) nanocomposite matrix, respectively. Both matrices exhibited thermal stability at ≤ 500 °C. The D-ST and D-ZST showed pronounced pKa values 9.8 and 9.7, suggesting a broader response range. The D-ST and D-ZST matrix demonstrated sensitivity 28.43 counts/pH at 460 nm with R2 ~ 0.96 and 13.90 counts/pH with R2 ~ 0.98 at 441 nm, respectively. Fast time responsive signals are observed ~1.69 s–0.12 s from pH 1–12 for D-ST and 0.48 s–0.14 s for D-ZST nanocomposite matrix confirmed fast response towards basic media. No traces of leaching are determined by multiple measurements in DI water.

Fabrication of natural colorimetric indicators for monitoring freshness of ready‐to‐cook idli batter

Natural colorimetric indicators have been fabricated using annatto and pomegranate extract powder and compared with chemical colorimetric indicator fabricated using bromophenol blue (BPB) to monitor the freshness of ready‐to‐cook (RTC) idli batter. The fabricated colorimetric indicator labels work on increasing headspace carbon dioxide (CO2) concentration and decreasing pH of stored batter, where indicators showed visible color change from lightest to darkest for spoiled samples. The headspace CO2 concentration of RTC idli batter increased from 0.15 ± 0.05 to 18.07 ± 0.21% (v/v) and pH decreased from 6.7 ± 0.06 to 4.5 ± 0.06 at optimum storage condition (35 ± 1°C) up to 24 h. The percent titratable acidity (% TA) increased from 0.44 ± 0.02 to 0.90 ± 0.02% up to 24 h. The viable lactic acid bacteria count (LABC) and total bacterial count (TBC) increased while yeast and mold count (YMC) was decreased with increasing fermentation time up to 24 h for batter stored at optimum condition. The color change of indicators was quantitatively measured with captured red, green, and blue (RGB) images. Pixel intensity for natural and chemical colorimetric indicators were decreased with increasing fermentation time. The leaching of chemical dye was observed on stored batter, and natural colorimetric indicators are nontoxic and successfully used as “on package sticker” for monitoring freshness of RTC idli batter.