Finding natural food coloring options from plant-based sources to substitute artificial dyes is a challenging task because natural dyes often present low water-solubility, not very vibrant hues, and ...instability due to interactions with food ingredients. Chemometric approaches can be used to evaluate color differences and patterns resulting from natural and synthetic dyes when applied to food systems. Here, the Mixture Design and the Principal Component Analysis (PCA) were applied to evaluate the substitution of the following artificial food dyes: yolk yellow, apricot yellow, strawberry red, and tartrazine by natural dyes (water-soluble curcumin, yellow shade; Hibiscus sabdariffa extract, red shade; Spirulina platensis extract, blue/green shade), in three food simulated systems (phosphate buffer, pH 6.9; yogurt, pH 4.0 and citrate buffer, pH 3.0). The color parameters L*, a*, b*, C* and °h were determined and color difference (ΔE*) with artificial dyes resulted in 11 empirical models. PCA yielded a clear map for the identification of the closely matches natural/artificial dyes for the food simulated systems in three subregions. Furthermore, the antioxidant capacity of the natural dyes was determined by OxHLIA and TBARS. It was possible to make an assessment guide that may be useful for other food systems and dyes.
•Curcumin, hibiscus and spirulina are great sources of natural dyes.•Color difference (ΔE*) between their blends and artificial dyes was evaluated.•Mixture experimental design yielded empirical models to describe ΔE*.•Principal Component Analysis yielded a visual tool to identify color proximity.•Curcumin, hibiscus and spirulina showed antioxidant action in OxHLIA/TBARS assays.
A vast array of colorants obtained from natural sources such as plants, insects/animals and microbes have been scrutinized in recent past for their use in different kinds of applications. Research ...into new natural dyes sources along with eco-friendly, robust and cost-effective technologies for their processing and application have greatly aided in widening the scope of natural dyes in various traditional and advanced application disciplines. This review encompasses a summary of research performed in last 15 years (1998–2013) in different arenas of applications of natural dyes, with specific reference to technological development in natural textile dyeing and use of natural dyes in functional finishing of textiles, food coloration and dye-sensitized solar cells. In addition, some newly discovered applications of natural dyes have also been discussed.
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•Many different kinds of applications of natural dyes are under active study.•Reports technological developments in natural textile dyeing and finishing.•Natural dye-sensitized solar cells have been critically discussed.•Special attention has been given to recent developments in natural food colorants.•Some newly discovered applications of natural dyes have also been highlighted.
In this work, six plants are presented to obtain different molecules with distinct properties to be used in dye-sensitized solar cells (DSSC). Cells have been assembled using Opuntia joconostle ...(xoconostle), Rhus microphylla (limilla), Tagetes erecta (marigold flower), Euphorbia pulcherrima (poinsettia flower), Bougainvillea spectabilis (bougainvillea) and Camellia sinensis (green tea) as individual and mixed pigments. In the case of xoconostle and limilla this is the first time that their extracts have been used as sensitizers in DSSC. Having these natural dyes, the co-sensitization technique was adopted to improve the photovoltaic performance of the solar cells. The best performance with the individual extracts was from the poinsettia flower having a conversion efficiency of 0.0022 % with Voc of 0.29 V, Jsc of 0.014 mA/cm2 and FF of 48.56, in the case of co-pigmentation, the best mixture was poinsettia flower with xoconostle and green tea (NXT) having a conversion efficiency of 0.0044 % with Voc of 0.34 V, Jsc of 0.035 mA/cm2 and FF of 44.50, using irradiation of 1000 W/m2 at 25°C. The purpose of mixed dyes is to absorb a wider interval of the electromagnetic spectra. Computational calculations based on the Density Functional Theory were used to calculate each molecule’s HOMO and LUMO levels.
•Rhus microphylla and Opuntia joconostle were used for the first time as a dye in DSSC.•Co-sensitization technique with six different dyes demonstrates to be useful in the improvement of the efficiency of DSSC.•Computational calculations correlate with the experimental results, aiding in explaining dye behavior in DSSC.
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•Photoelectrochemical parameters of Aloe Vera and Cladode as DSSCs investigated.•Reported a method to combine two plant-based dyes for efficient DSSCs.•Chlorophyll in Cladode DSSC ...performed better than Anthocyanin in Aloe Vera DSSC.•Plant dyes analyzed using Absorption Spectroscopy and Fourier Transform Infrared Spectroscopy.
The purpose of this study is to develop dye-sensitized solar cells (DSSCs) from natural plant-based dyes, extracted from the Cladode (nopal) of the Thornless Prickly Pear Cactus (Opuntia ficus-indica), the gel of Aloe Vera (Aloe barbadensis miller), and the combination of Cladode and Aloe Vera extracts on side-by-side configuration. Optical properties were analyzed using UV–Vis Absorption and Fourier Transform Infrared Spectroscopy. Open circuit voltages (Voc) varied from 0.440 to 0.676V, fill factors (FF) were greater than 40%, short-circuit photocurrent densities (Jsc) ranged from 0.112 to 0.290mA/cm2 and highest conversion efficiency of 0.740% was reported for the Cladode DSSC.
Recently research catering to the use of natural dyes has garnered worldwide attention due to their non-toxic and eco-friendly nature. However, dyeing with natural dyes has some inherent challenges ...like low color fastness, the requirement of mordents and chemicals as fixers, lower yields, which have greatly restricted their use on an industrial scale. Eco-friendly surface modification techniques like plasma treatment, enzyme treatment or irradiation with UV and sonication are gaining popularity nowadays for surface modification of natural polymers because of health hazards associated with the use of conventional methods. All of them are essentially dry processes providing modification of the top nanometer surface leaving bulk properties of the material unaffected without using solvents or generating any chemical waste. This paper reviews the recent studies involving modification techniques applied on commonly used natural fibers like cotton and silk for enhancement of dye uptake using natural dyes and also various application of natural dyes to provide antimicrobial, UV resistant or insect repellent finishing to the fabrics.
In this study, we compare pH-sensitive bioindicators fabricated via the facile one-pot reaction of biopolymers (chitosan or chitin) and natural red dyes (carminic acid and purpurin). The relationship ...between the biocomponents and the structure, stability, and pH-sensing activity of the resulting materials is also investigated. XPS, FT-IR, SEM and pH assessments confirmed the presence of interactions between the biopolymers and the natural dyes, leading to the formation new functional smart colorants. The type of biopolymer determined the stability of the materials, and the incorporation of natural dyes significantly increased their chemical and thermal stability. All the colorimetric indicators were highly sensitive to HCl and NH3 vapors, changing color after just a few minutes. Their application as new biocolorants for ethylene-norbornene copolymer (EN) resulted in composites with attractive color performance and good photostability. This was evidenced by the lower color changes and carbonyl index increment of the samples containing the new color systems after 50 h, 100 h, and 200 h of UV irradiation compared to pure natural dyes. For the real-time analysis of the application of colorimetric pH indicators, the colored EN composites were applied to colorimetric monitor the freshness of shrimps at room temperature. The findings indicated that the designed biopolymer-dye materials could be used simultaneously as colorants, pH indicators, and additives for polymers, providing protection against unfavorable aging conditions. Importantly, the new colorants also exhibited lower tendency to leach from the polymer matrix compared to natural dyes. This could elegantly overcome the strong migration problems associated with natural dyes and enable widespread application of the new biocolorants in packaging systems.
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•pH indicators were successfully prepared based on the natural dyes and biopolymers.•Red natural dyes were incorporated into chitin and chitosan biopolymers.•Biopolymer/natural dye systems were highly sensitive to acidic and alkaline vapors.•Hybrid pH indicators showed better chemical and thermal stability than natural dyes.•New hybrid colorants exhibited reduced tendency to migration and good UV resistance.
The use of natural dyes such as anthocyanins in foods has disadvantages due to their relatively high costs and low stability. Striking advantages, however, include natural origins and favourable ...bioactivities. Therefore, the use of a pigment extract from coloured-flesh potatoes is proposed here as a natural dye in dairy foods. The phenolic compound composition, antioxidant activities, and sensorial parameters under different storage conditions were evaluated. In milk stored at room temperature (20 °C) and yogurt, a decrease between 26% and 32% in anthocyanin concentrations was observed after eight weeks, whereas in cooled milk (4 °C), the pigments were stable throughout the same storage time. Similar tendencies were observed between total phenolic compounds and antioxidant activities in milk and yogurt, suggesting that other phenolic compounds contained in dairy foods and potato extract are also affected by storage conditions. In the case of yogurt, the addition of the potato pigment extract did not affect the organoleptic properties. Based on these results, phenolic extracts from coloured-flesh potatoes are an optimal natural and stable alternative for colouring dairy food products, which also provides added value through the addition of biologically active anthocyanins.
•An extract from purple flesh-coloured potatoes was used as natural dye in dairy foods.•Anthocyanins from extract were stable during a time similar to commercial storage.•Cooled storage conditions showed high stability of purple potato dyes in dairy foods.•Flesh-coloured potato extract represent a natural dye with high functional properties.
Zinc sulfate and magnesium sulfate were used as additives to provide an effective simultaneous mordanting and dyeing process (meta mordant) for wool yarns with madder dyes extracted by ultrasound. In ...the dyeing procedure, aluminum sulfate and ferrous sulfate were used as mordants. A response surface methodology (RSM) experimental design was used to optimize the dyeing technique. Results showed that the highest color strength of dyed samples was achieved at 105–110 min at 1:30 ratio of aluminum sulfate to zinc sulfate, 1:10 ratio of aluminum sulfate to magnesium sulfate, and pH of 2.5–3. It was observed that the dyeing of yarns with extracted dye and ferrous sulfate could be carried out without using additives. The color properties of dyed yarns using the novel approach were compared to samples dyed using the conventional method (pre-mordant). The findings revealed that dyed samples using the novel approach had the same or greater color strength as dyed samples using the pre-mordant procedure. L* , a* , and b* of the dyed yarns by extracted dyes and aluminum sulfate in the presence of magnesium sulfate were approximately the same with yarns dyed by the pre-mordant method. Also, the color fastness properties of dyed samples by meta mordant method were acceptable in terms of wash, light, and rub fastnesses. Nearly similar or better color stability was achieved compared to the common method. In this respect, a novel efficient one bath method was introduced for deep dyeing of wool yarns with extracted madder dyes which can decrease the negative environmental impacts such as pollutants, water consumption, and energy in comparison to other conventional methods.
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•A new strategy and efficient for dyeing of wool fibers with Rubia tinctorum dyes.•Eco-friendly dyeing of wool fibers with extracted madder dyes and safe mordants.•Performance of additives in simultaneous dyeing of wool fibers with madder dyes.•Reduction of effluents and saving energy and water in dyeing of wool with madder.
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