A colorimetry-enhanced tri-functional film with high stability by polyphenol-anthocyanin co-pigmentation/conjugate: New prospect for active intelligent food packaging

A highly stable "tannin-anthocyanin conjugated" trifunctional active intelligent film was developed by incorporating bilberry anthocyanins (BA) as an indicator and tannin acids (TA) as a co-pigment into a sodium alginate-carrageenan polysaccharide matrix (SC-BA/TA). The doping of TA conferred outstanding antioxidant (DPPH scavenging rate > 90%) and antibacterial properties to the film, particularly effective against S. aureus. The SC-BA/TA films effectively blocked UV rays (close to 0%, effectively impeding most UVA, as well as nearly all UVC and UVB) within the range of 200-320 nm. The TA-BA co-pigment effect significantly improved the anthocyanins' storage and color stability (retention rate > 70% under UV and natural light conditions). TA forms conjugate with anthocyanins by π-π stacking and hydrogen bonding interactions with co-pigmentation rate increases of 10.5% and 11.0% for pH 2 and pH 3, respectively. The film exhibited good responsiveness to volatile amines within 4 min, and offered real-time monitoring of beef freshness, as indicated by visualizing color changes (from red to dark yellow color). Furthermore, the integration of the film's RGB value with beef quality via a smartphone App effectively reduces the variability in visual recognition among individuals. To sum up, composite films based on the "tannin-anthocyanin conjugate" approach hold great potential in the field of food freshness monitoring, opening new possibilities for the development of highly stable active smart packaging films.

Preparation of multifunctional hydrogels based on co-pigment-polysaccharide complexes and establishment of a machine learning monitoring platform

Economic loss due to fish spoilage exceeds 25 billion euros every year. Accurate and real-time monitoring of the freshness of fish can effectively cut down economic loss and food wastage. In this study, a dual-functional hydrogel based on sodium alginate-co-pigment complex with volatile antibacterial and intelligent indication was prepared and characterized. The characterization results indicated that the sodium alginate-co-pigment complex successfully improved the stability and color development ability of blueberry anthocyanins and bilberry anthocyanins at different temperatures and pH. The double cross-linking network inside the hydrogel conferred it with excellent mechanical properties. During rainbow trout storage, the hydrogel indicated a color difference of 73.55 on the last day and successfully extended the shelf-life of rainbow trout by 2 days (4 °C). Additionally, four dual-channel monitoring models were constructed using machine learning. The validation error of the genetic algorithm back propagation model (GA-BP) was only 5.6e-3, indicating that GA-BP can accurately monitor the freshness of rainbow trout. The rainbow trout real-time monitoring platform built based on GA-BP model can monitor the freshness of rainbow trout in real time through the images uploaded by users. The results of this study have broad applicability in the food industry, environmental conservation, and economic sustainability.

The stable co-pigmented roselle anthocyanin active film extended shelf life of Penaeus vannamei better: Mechanism revealed by the TMT-labeled proteomic strategy

In order to investigate the influences of modified RAE-based film on shrimp quality, the proteomic approach was performed to elucidate preservation mechanism. Results showed that the modified RAE-based film kept better shrimp quality compared with natural RAE-based film in terms of determined biochemical parameters and estimated shelf-life. Totally, 49 differentially abundance proteins (DAPs) were identified compared with shrimp without packaging. Bioinformatics analysis demonstrated that the modified RAE-based film could maintain functional DAPs which were mainly distributed in the binding, catalytic activity, etc., and metabolic signaling pathways like melanogenesis signaling pathway were remarkably enriched. Meanwhile, there were 25 DAPs showing close relationship with quality traits, and some of them, such as myosin chains, troponin I and heat shock protein were considered as the potential biomarkers to evaluate shrimp quality deterioration. In conclusion, this study revealed the preservation mechanism of modified RAE-based active film on shrimp quality at the protein molecular level.

The highly stable indicator film incorporating roselle anthocyanin co-pigmented with oxalic acid: Preparation, characterization and freshness monitoring application

A novel stable PVA/HPMC/roselle anthocyanin (RAE) indicator film co-pigmented with oxalic acid (OA) was prepared, its properties, application effects and stability enhancement mechanism were investigated correspondingly. The structural characterization revealed that more stable network was formed due to the co-pigmentation facilitated generation of molecular interactions. Meanwhile, the co-pigmentation improved film mechanical and hydrophobic properties compared to both PVA/HPMC/RAE newly prepared (PHRN) or stored (PHRS) film, expressing as higher tensile strength values (12.25% and 14.44% higher than PHRN and PHRS), lower water solubility (7.22% and 10.09% lower than PHRN and PHRS) and water vapor permeability values (33.20% and 21.05% lower than PHRN and PHRS) of PVA/HPMC/RAE/OA newly prepared (PHON) or stored (PHOS) film. Compared with the PHRS film, the PHOS film still presented more distinguishable color variations when being applied to monitor shrimp freshness, owing to the stabilization behaviors of co-pigmentation in anthocyanin conformation. Hence, the co-pigmentation was an effective strategy to enhance film stability, physical and pH-responsive properties after long term storage, leading to better film monitoring effects when applied in real-time freshness monitoring.

Effect of co-pigments on anthocyanins of Rhododendron arboreum and insights into interaction mechanism

The impact of intermolecular copigmentation between five phenolic acids, two flavonoid and three amino acids with R. arboreum anthocyanins (ANS) and its isolated cyanidin-3-O-monoglycosides were investigated through experimental and theoretical approach. On addition of different copigments, phenolic acid induced strong hyperchromic (0.26-0.55 nm) and bathochromic shift (6.6-14.2 nm). The color intensity and stability of ANS with, storage at 4 °C & 25 °C, sunlight, oxidation and heat were evaluated by chromaticity, anthocyanin content, kinetic and structural simulation analysis. The strongest copigmentation reaction was observed with narningin (NA) and also showed high thermostability and highest half-life i.e. 3.39 h-1.24 h at 90-160 °C. The cyanidin-3-O-monoglycosides were analysed for their copigmentation effect and observations revealed that NA displayed best copigmentation effect to cyanidin-3-O-arabinoside (B) followed by cyanidin-3-O-galactoside (A), and cyanidin-3-O-rhamnoside (C). Additionally, structural simulation and steered molecular dynamics insights NA is the most favourable co-pigment involving π-π stacking and H-bonding.

Improved thermal stability of roselle anthocyanin by co-pigmented with oxalic acid: Preparation, characterization and enhancement mechanism

The enhancement effects of co-pigmentation on thermal stability of roselle anthocyanin extract (RAE) were investigated. The introduction of organic acids maintained color stability of RAE, and RAE co-pigmented with oxalic acid (OA) presented less color fading rates (19.46 ± 0.33 %) and higher redness (41.33 ± 3.51). Subsequently, suitable co-pigmentation concentration (OA:RAE = 1:2) was obtained regarding with lower ΔE (48.70 ± 2.36). Then, improvement behaviors of co-pigmentation on OA-RAE were evaluated. Results demonstrated that OA-RAE exhibited better thermal stability, as manifested by larger retention rates and more favorable thermal degradation kinetic parameters. Furthermore, both molecular docking simulation and experimental structural characterization revealed that hydrogen bonds and other non-covalent bonds made up the main parts of molecular interactions, leading to formation of stable binary complex. As a result, the aromatic ring of RAE was protected. In conclusion, the co-pigmentation of RAE via introduction of OA was effective in stability enhancement due to the generation of molecular bindings.

Kombucha analogs from maqui juice: Consortium age and sugar concentration effects on anthocyanin stability and its relationship with antioxidant activity and digestive enzyme inhibition

The fermentation of maqui juice (MJ), by incorporating kombucha as a starter culture, produces beverages with variable and stable anthocyanin contents. The metabolic effect of kombucha starter cultures obtained at different fermentation times was explored on the anthocyanin stability of maqui (Aristotelia chilensis (Mol.) Stuntz) juice supplemented at different concentrations of sucrose and fermented at different times. The stability of anthocyanins was associated with the levels of catechin detected in the fermentation system. This study concludes that the fermentation of MJ with sucrose (10%) and kombucha consortium of 7-days old, promotes the release and accumulation of phenolic compounds that act as co-pigments, with the best response in quality parameters of beverages such as color intensity, tone, hyperchromic effect, and a significant bathochromic shift. Finally, the additive effect of phenolic constituents with stable anthocyanins, confers to kombucha analogs an outstanding antioxidant quality and inhibitory effects on key enzymes in digestive processes.

Protective effect of amino acids on the stability of bayberry anthocyanins and the interaction mechanism between l-methionine and cyanidin-3-O-glycoside

The protective effects of three amino acids (l-phenylalanine, l-tryptophan and l-methionine) on the stability of bayberry anthocyanins were investigated. The anthocyanin stability under constant illumination (5000 Lux, 50 Hz) or in the presence of ascorbic acid were evaluated by degradation kinetic parameters, and the interaction between l-methionine and cyanidin-3-O-glucoside (C3G) in a model beverage system was analyzed using Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, X-ray diffraction, molecular docking, and molecular dynamics simulation. Results indicated that the three amino acids significantly reduced the degradation rate of bayberry anthocyanins (p < 0.05), with the most effect by l-methionine. l-methionine could bind to C3G via hydrogen bonds and Van der Waals forces. This study suggested that l-methionine could well protect anthocyanin against degradation in the aqueous solution and have the potential to be used as a co-pigment to improve the sensory property and extend the shelf life of anthocyanin rich berry products.

Co-pigmentation of anthocyanins extracted from sour cherry (Prunus cerasus L.) with some organic acids: Color intensity, thermal stability, and thermodynamic parameters

The co-pigmentation reactions involving anthocyanins of sour cherry (Prunus cerasusL.) were investigated with tannic, caffeic, 4-hydroxybenzoic, gallic, and malic acids at pH 3.5. The influence of the co-pigments with different concentrations (120, 240, 480, and 960 mg/L), and temperatures (20, 40, 60, 80 and 100 ℃), on the co-pigmentation effects, stoichiometric ratio (n), the equilibrium constant (K) and thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were determined.The strongest immediate co-pigmentation reactions were observed at 960 mg/L, being significantly highest using tannic acid; also,the greatest bathochromic and hyperchromic effects were reasonable for itsn,K, and ΔG° values of 0.64, 56.55, and -10.00 kJ/mol, respectively. Furthermore, tannic and caffeic acids, with the highest negative values ofΔH°(-11.74 kJ/mol) andΔS°(-8.08 J/K.mol) led to the most excellent stability at 100 ℃.The presence of anthocyanins in the sour cherry extract was confirmed with the Fourier-transform infrared spectroscopy technique.

Co-pigmentation of black chokeberry (Aronia melanocarpa) anthocyanins with phenolic co-pigments and herbal extracts

The co-pigmentation of black chokeberry (Aronia melanocarpa) anthocyanins with ten phenolic co-pigments was studied. Tested compounds provoked different co-pigmentation effect, manifested by hyperchromic and batochromic shifts. The co-pigmentation was accompanied by a magnification of color intensity and decrease of color hue, both related to a more pleasant color. The hyperchromic effect was the most significant for rosmarinic acid (51.02%), syringic acid (43.24%) and catechin (39.73%). However, it was observed at the highest pigment/co-pigment ratio (1:50), not achievable in plant matter. Targeting the potential practical application of co-pigmentation, we tested eight herbal extracts for their co-pigmentation ability with aronia anthocyanins. The use of herbal extracts led to a significant hyperchromic effect at much lower pigment/co-pigment ratios, compared to pure compounds. The use of selected herbal extracts as co-pigments opens realistic prospects for development of aronia functional foods with improved sensory properties and biological effects, due to enhanced color and anthocyanin stability.

Anthocyanins from purple sweet potato (Ipomoea batatas (L.) Lam.) and their color modulation by the addition of phenolic acids and food-grade phenolic plant extracts

Anthocyanin profiles and contents of three purple sweet potato provenances were investigated by HPLC-DAD-MSⁿ. In contrast to widely uniform profiles, the contents of total (558-2477mg/100gDM) and individual anthocyanins varied widely. Furthermore, quantitative and qualitative effects of intermolecular co-pigmentation were studied by adding chlorogenic and rosmarinic acids, and food-grade phenolic apple and rosemary extracts at various dosages to a diluted purple sweet potato concentrate at pH 0.9, 2.6, 3.6, and 4.6. Addition of co-pigments generally increased pK_{H estimate}-values of anthocyanins from 3.28 (without co-pigments) to up to 4.71, thus substantially broadening the pH range wherein colored forms prevail. The most pronounced hyperchromic shift by up to +50.5% at the absorption maximum was observed at pH 4.6. Simply by blending the co-pigments with purple sweet potato anthocyanins at pH-values ranging from 2.6 to 4.6, purplish-blue, light pink, magenta, brick-red, and intense red hues were accessible as expressed by CIE-L^∗a^∗b^∗ color values.

Effect of genuine non-anthocyanin phenolics and chlorogenic acid on color and stability of black carrot (Daucus carota ssp. sativus var. atrorubens Alef.) anthocyanins

This work aimed at studying the color intensity and stability of black carrot anthocyanins as influenced by intermolecular co-pigmentation. For this purpose, purified anthocyanin solutions were supplemented with purified genuine black carrot phenolics, chlorogenic acid, and an aqueous phenolic-rich green coffee bean extract at various anthocyanin:co-pigment ratios (1:0-1:162; pH 3.6). The hyperchromic co-pigmentation effect depended on the concentration of added co-pigments, resulting in an absorbance increase of up to 22% at the absorption maximum. Anthocyanin stability during heating (90°C, 5h) was barely improved unless the concentrations of co-pigments exceeded those of their natural source. When adding co-pigments at ratios above 1:9.4, anthocyanin heat stability was significantly improved. As acylated anthocyanins were most stable, breeders might aim at increasing their content in the future, while breeding for high levels of colorless polyphenols may be unreachable. Nevertheless, we provided proof-of-concept for the successful color enhancement by the addition of a phenolic-rich green coffee bean extract, being useful for food-grade applications.

Identification of novel C-glycosylflavones and their contribution to flower colour of the Dutch iris cultivars

Seventeen C-glycosylflavones including four novel ones, were isolated from the flowers of Dutch iris (Iris hollandica Hort. ex Todd.) cultivar 'Blue Diamond'. Four new C-glycosylflavones were identified as isovitexin 2″-O-(4″'-acetylrhamnoside) (F1), swertisin 2″-O-(4″'-acetylrhamnoside) (F2), isovitexin 2″-O-(4″'-acetylrhamnoside)-4'-O-glucoside (F3) and swertisin 2″-O-(4″'-acetylrhamnoside)-4'-O-glucoside (F4) by UV spectra, LC-MS and (1)H and (13)C NMR. Furthermore, to understand the contribution of flavones to flower colour, the relationships with flower colours of three Dutch iris cultivars and flavonoid components were examined. The degree of blueness in the bluish cultivars 'Blue Diamond' and 'Blue Magic' were higher than that of the violet cultivar, 'Yesterday', and it was suggested that the flower colour expression from violet to blue colour of Dutch iris cultivars depend on the high ratio of total flavone contents/total delphinidin contents (F/A ratio). In addition, in vitro examination was carried out by the isolated anthocyanin and flavone. The mixture solutions were prepared in respective F/A ratio of three Dutch iris cultivars and could essentially reconstruct their visible absorption spectra of flowers. In conclusion, it was confirmed that isolated flavones contribute to blueness due to intermolecular co-pigmentation with anthocyanins.