Utilizing natural flavonoid indicators in marine-derived biopolymers to develop new biomaterials for food packaging that provide information about the quality of food products can inform the customer about food safety and diminish food waste. Herein, two novel smart pH-sensitive hydrogel films composed of κ-carrageenan (CG) combined with quercetin (QUE) or eucalyptus leaf extract (ELE) were extended for freshness information of chicken meat at room temperature. As quality indicators, the color changes of the hydrogel films through colorimetric and UV-Vis spectroscopy at pH 1–12 and TVB-N (total volatile basic nitrogen) were investigated. The films’ transparency, mechanical, antibacterial activity, and morphology were investigated. The results showed that the CG film with 0.3% QUE performs best. The CG film containing QUE or ELE had good antibacterial activity and preserved and controlled the freshness of chicken meat. In the case of engaging CG films, they showed visible color changes in informing the freshness of the chicken. The comparison of the film containing QUE and the ELE states that the film containing the ELE had a greater effect in preventing chicken spoilage and revealed distinguished pH-responsive color changes.
Article
Colorimetric pH Sensitive Smart Film Based on Carrageenan Containing Quercetin or Eucalyptus Extract for Freshness Monitoring of Chicken Meat
https://doi.org/10.21203/rs.3.rs-3132202/v1
This work is licensed under a CC BY 4.0 License
Version 1
posted
You are reading this latest preprint version
carrageenan film
quercetin
eucalyptus leaf extract
smart packaging
Researchers have been working on a technology to indicate the spoilage of food and drink products through their packaging for many years. Intelligent packaging is a container. Nowadays, there is a strong fondness for expanding novel packaging with smartness, the ability to control the condition and quality of food products during storage, transport, and distribution1–3. This evolution of traditional packaging will detect and record changes in the product’s environment; this is a big stage forward for the industry, especially in the agri-food sector. The activity of environmental microbes leads to altered degradation of meat proteins and produces basic volatile organic amines4. Therefore, applying color pH indicators is useful for checking the quality of food freshness5–7. Generally, indicators consist of pH colorimetric material made from support with a pH sensing agent such as dye. As an appropriate pH indicator, the safety of the matrix and dye is important. Therefore, utilizing non-toxic natural dyes and polysaccharides such as starch, CG, cellulose, and chitosan has been highly regarded7–10. Our interest is focused on κ-CG due to its excellent film-forming ability, strong gel film, good barrier against oxygen, and restrain lipid oxidation. Previous studies indicate that κ-CG has been successfully employed in food packaging film with different pH indicators. In recent years, several studies have focused on preparing film based on natural dyes such as curcumin2, potato anthocyanin11, anthocyanins-rich grape skin powder12, and extract of fenugreek seeds13. For instance, κ-CG incorporated with polyphenol compounds such as curcumin for freshness monitoring spoilage has been reported.
OUE is a polyphenolic flavonoid found in food products and plants such as eucalyptus and is considered a plant pigment, which has anti-inflammatory14, antioxidant15, and antimicrobial activities16. As far as we have checked, there is no literature on using CG containing OUE or ELE for monitoring chicken freshness. Distinguished from the previous reports, we intend to extend a pH colorimetric indicator with help κ-CG film combined with OUE or ELE to informant the freshness of the chicken. We measured the concentration of quercetin in the extract using a UV-Vis spectrophotometer to make a correct comparison in making the film based on OUE or ELE. Accuracy was focused on the pH sensing properties of the CG based films. Based on pH sensing behavior of film including quercetin and eucalyptus extract was evaluated. Tensile strength, antibacterial activity, and the structure of the films were investigated.
All chemicals were purchased from Aldrich. The FESEM ( ZEISS Sigma 300), and UV-Vis 1700 Spectrophotometer from Shimadzu were used to investigate of films.
2.1. Preparation of eucalyptus extract
According to the instructions of Iranian herbal pharmacopoeia, the leaves of eucalyptus trees were used as organs containing effective and medicinal substances. The leaves were collected in October from the world species of Eucalyptus of the Myrtaceae family with a height of 2 meters17. All steps of collecting plant leaves were done according to Iranian and international rules .Eucalyptus leaves were collected from non-extinct trees on campus for scientific research without harming the trees. Leaves have been collected from wild trees free of any pest located in the east of the capital (Tehran) of Iran. The collected leaves were green and elongated and free of any pests.The collected leaves were packed in a bag away from sunlight and moved to a room free from insects, pollution and dust. Fresh leaves were washed with distilled water and spread as a thin film in a well-ventilated room, were pressed and dried away from sunlight18–20.
10.0 g of dried leave eucalyptus was crushed and macerated with 100.0 mL ethanol:water (70:30). After 24 h, the sample was sonicated for 2 h using an ultrasonic bath at 30 KHz. Subsequently, the material was filtered, and the extract was concentrated by a rotary evaporator and kept at 4°C.
2.2. Spectrophotometric Determination of QUE
The results of total flavonoid content were stated as mg QUE per gram of dry extract. The aluminum chloride colorimetric method was used to specify total flavonoids. The ELE was mixed with methanol (0.5 mL of 1.0:10.0 g/mL), 0.1 mL of 10% AlCl3, 0.1 mL of CH3CO2K 1.0 M, and 2.8 mL of distilled water. The absorbance of the mixture was determined using a spectrophotometer UV-Vis at 415 nm to detect quercetin in triplicate. The same sample without AlCl3 was used as a blank solution. The calibration curve was prepared by preparing QUE solutions at 10.0 to 100.0 µg/mL concentrations in methanol.
2.3. Film preparation
CG solutions were prepared by dissolving CG (1.0 g) in distilled water (50.0 mL) containing 1.0 mL glycerol with stirring and under heat) 90 ºC) for half-hour. After then, a set of methanol/water (10.0 mL, 80/20) solutions containing QUE with different weights of (0.0, 0.3, 0.5, 3.0, and 5.0%) of QUE was prepared, and solution cure of 10 min for the elimination of air bubbles. In the next step, solutions were poured into a petri dish )8×1.5 cm) and dried at 40 ºC for 24 h to form a thin film named CG-QUE0, CG-QUE0.3, CG-QUE0.5, CG-QUE1, CG-QUE3, and CG-QUE5. The above steps were repeated to prepare a film containing ELE. Some extracts of CG solution were added to make the final film contain 2.0 and 5.0% corticosteroids.
2.4. Light-transmittance and UV-vis measurement
For investigation, Light-transmittance of films in the 200 to 600 nm range, pieces (4.0 cm × 1.0 cm) were placed in the device (Shimadzu Corporation UV-2550 spectrophotometer) cell, and the air was considered a transparency reference. UV-vis spectra of CG film, CG film, and eucalyptus extract were measured by spectrophotometer. For this purpose, the eucalyptus extract solutions and film were adjusted to precise values of pH (pH 1–12) with HCl or NH3 )0.1 mol/L( solutions. The pure film was used as blank.
2.5. Usage of films as a freshness representative for chicken
For assessment of pH sensing properties of films on chicken, the films contain eucalyptus extract or quercetin. Fresh chicken was procured from a local store. They were placed on the top space of a packaging box of chicken as a container lid (10.0 g). Ultimately, the dishes were sealed with parafilm and an incubator at 25 ºC and 50% RH.
The chicken sample’s TVBN (total volatile basic nitrogen) level was measured by a Kjeldahl method. The sample of meat (10.0 g) was homogenized in distilled water (100.0 mL) and, in the next step, centrifuged (3500 rmp, 15 min).In the next step, filtrate solution (5.0 mL) was added to a Kjeldahl distillation unit, and 5.0 mL of MgO suspension (10.0 g/L). Collected condensate was titrated in boric acid solution (20.0 g/L) and with 0.1 mol/L of HCl.
2.6. Film morphology and structure
The morphology and structure of the samples were investigated using FESEM TESCAN MIRA3. The interaction between CG and QUE or ELE was determined by FTIR spectroscopy.
2.7. Antibacterial activity
The antimicrobial activities of films against S. aureus ATCC 6538, S. epidermidis ATCC 12228, B. subtilis ATCC 6633, E. coli ATCC 8739, P. aeruginosa ATCC 9027 and K. pneumonia ATCC 10031 were tested as recommended by the Clinical and Laboratory Standards Institute (CLSI). Mueller-Hinton Broth (HiMedia) and RPMI-1640 (Sigma) were prepared as recommended for antimicrobial susceptibility testing of bacterial strains. Two-fold dilutions were made in the 1.0–512.0 µg/mL range for tested compounds. The antimicrobial susceptibility test was accomplished by adding a cell suspension adjusted to the 0.5 McFarland standard (1–2×108 CFU/mL for bacterial strains). Following incubation, the minimum inhibitory concentration (MIC) was established as the lowest concentration of films that completely inhibits the organism’s growth, as detected visually. The steps of the experiments were repeated twice.
2.8. Mechanical properties
The TA-XTPlus Texture Analyzer (Stable Micro Systems, Co., UK) is used for the investigation of the tensile strength (TS) and elongation at break (EB) according to ISO 527. Each experiment was repeated three times, and the results were averaged. The TS and EBB of the specimens (1.0 cm * 2.0 cm) were determined, from which the values of Young’s modulus could be determined.
3.1. Spectrophotometric Determination of Quercetin
The total phenolic content in the methanol was performed, and the quercetin calibration curve shows in Fig. 1. The result of total phenolic content was calculated from the regression equation of the standard plot (y = 0.004x + 0.014, R2 = 0.9746). According to the curve calibration, the concentration of the quercetin was 125 µg / ml.
3.2. Light-transmittance and UV-vis measurement
The colors of quercetin solutions and eucalyptus extract solutions at pH 1–12 are demonstrated in Fig. 2a, c. The color of the eucalyptus extracts solutions conversions from bright yellow to reddish brown and quercetin solutions. The color of the solution changes from bright yellow to light yellow with increasing pH values. Those color changes are due to the chemical structure transformation of quercetin21,22. Figure 2b, d shows the corresponding absorption UV-vis spectra change of the ELE and QUE solutions with pH changes. The structure of quercetin consists of three important parts: (i) the catechol structure in the B-ring; (ii) the 2,3-double bond, in conjugation with the 4-oxo function in the C-ring; and (iii) the 3- and 5-OH groups in the A-ring (Fig. 3)21. the color change is not a simple result of the deprotonation of the QUE hydroxyl groups. The appearance of peaks at a low wavelength related to chemical change involving the C-ring occurs, leading to a loss of electronic resonance between rings A and B. For quercetin solutions, maximum absorption appeared around 250 nm and 375 nm at pH = 6 due to π → π* transitions at rings A and B. Reciprocally, the mentioned peak transmit to 325 nm nm at pH = 11 and 12. Also, the intensity of the peak increased by increasing the pH of the under alkaline conditions.
Eucalyptus, which contains flavonoids (quercetin, rutin) and tannins (Ellagic acid), is a natural dye, yielding several yellowish-brown colorants. The major coloring component of Eucalyptus bark is quercetin. The presence of tannins and other flavonoids (rutin) may cause a difference in the color of the extract solution from the pure quercetin solution23–27. The comparison of pH changes on the prepared films shows that the film containing the extract shows a more obvious color change.
Investigation of light transmission of films shows good light transmission for films. The incorporation of QUE and ELE considerably reduced the light transmittance of the samples (Fig. 4a, b). The reduction may be due to QUE and ELE incorporated in the CG film and can seriously block the light transmittance, as seen in the FESEM images (Fig. 5). Previous research shows that the transparency of the packaging leads to consumer confidence because various food crises have caused consumers to pay more attention to their health. For this reason, transparent product packaging has become especially important to be a good answer for product visibility and consumer decisions28–32. Therefore, CG films contents above 0.3% of QUE or ELE are considered suitable for the monitoring chicken freshness application.
3.3. FTIR characterization
The FTIR spectra of ELE, QUE, and the prepared films (CG-QUE0.3 and CG-ELE0.3) are shown in Fig. 6a,b. In the FTIR spectrum of CG, the two peaks at 3400 cm− 1 and 2945 cm− 1 correspond respectively to the hydroxyl group and C-H stretching vibrations. The absorption bands at 1230 cm− 1 and 1047 cm− 1 correspond to O = S = O asymmetric stretching and a combination of C-O and C-OH modes33. On the other hand, the absorption band at 1017 cm− 1 is attributed to Glycosidic bonds. The absorption band at 930 cm− 1 indicates the presence of 3,6-anhydro-D-galactose 34. Moreover, glycerol’s C-O and C-OH vibrations bond appears in 1421 cm− 1 and 1114 cm− 1, respectively35. The intense absorption band at 1637 cm− 1 was allied to the absorbed water2.
In the FTIR spectrum of QUE (Fig. 6a), the stretching vibration of –OH and C = O were observed at 3320 and 1670 cm− 1. Stretching vibration of cyclobenzene peaks appeared at 1611 cm− 1, 1511 cm− 1, and 1458.8 cm− 1. N-H stretching vibration was observed at 3412 cm− 1 36.
The FTIR spectrum of the ELE (Fig. 6b) shows a typical absorption band around 3477 and 3415 cm− 1 corresponding to the –OH (related to phenolic compound) and N-H group. The presence peak at 2925 cm− 1 and 2853 cm− 1 is associated with the C-H vibration of aldehyde and alken, respectively. The sharp band at 1733 cm− 1 is consistent with C = O stretching vibrations. The absorption peaks at 1630 cm− 1 and 1568 cm− 1 are attributed to the presence of C = C in an aromatic ring. The band observed at 1110 cm− 1 and 1040 cm− 1 are due to the C–O stretching37.
In the FTIR diagram of CG-QUE0.3, all the specified peaks of CG and QUE can be viewed. But, the phenolic -OH stretching of QUE showed a low shift from 3412 cm− 1 to 3375 cm− 1, simultaneously, the C = C stretching in the benzene ring at 1611, 1511, 1457 cm− 1 shifted to 1605 cm− 1, 1454 cm− 1, 1411 cm− 1, which corroborated the existence of hydrogen bond between CG and QUE2. In the spectrum of CG-ELE0.3, -OH stretching low-shift from 3477 cm− 1 to 3412 cm− 1 due to the hydrogen bond between CG and ELE2.
3.4. Usage of films as a freshness representative for chicken
Food spoilage, which is directly related to human health, is caused by the activity of microorganisms. Using suitable materials for food packaging can delay this spoilage. The proteins in the meat are attacked by bacteria and various volatile nitrogenous compounds, which lead to a change in the pH value. As a result of food spoilage, amino compounds such as ammonia, dimethylammonium, and trimethylamine are produced, which can change the pH of the environment. Therefore, pH changes can be a good measure of the freshness of food and its health. Considering the pH sensing behavior of films, the CG-QUE0.3 and CG-ELE0.3 films were employed to monitor chicken freshness. The samples are shown in Fig. 4; CG-QUE 0.3 changed from red to orange on the 3 days, and CG-ELE 0.3 changed from green to yellow. The TVB-N of the chicken in the films is shown in Fig. 7.
As expected, in contrast to the control film, the film containing QUE and ELE changed color with time due to the spoilage of chicken meat and the change in volatile nitrogen compounds (Table 1). It can be deduced that the QUE and ELE combined CG film can be used as a representative for spoilage investigation of protein foods. The comparison of the film containing QUE and the ELE states that the film containing the extract had a greater effect in preventing chicken spoilage. This result can be very economical from the industrial and economic points of view because using pure QUE requires extraction and purification from plant extracts. In fact, the simplicity of making the film, the ease of preparing the extract, the clear color changes, and the beneficial effect of keeping chickens can be considered an advantage for industrial use.
Table 1. TVBN levels for chicken.
3.5. Antimicrobial Activities
The antibacterial activities of the QUE and ELE films were examined against three Gram-positive bacteria, including S. aureus, S. epidermidis, and B. subtilis, as well as Gram-negative such as E. coli, P. aeruginosa, and K. pneumonia. Results based on minimum inhibitory concentration (MIC) are presented in Table 2.
| Microorganisms | Staphylococcus aureus ATCC 6538 | Staphylococcus epidermidis ATCC 12228 | Bacillus subtilis ATCC 6633 | Escherichia coli ATCC 8739 | Pseudomonas aeruginosa ATCC 9027 | Klebsiella pneumonia ATCC 10031 |
|---|---|---|---|---|---|---|
| Compounds | ||||||
| Ciprofloxacin (µg/mL) | 0.195 | 0.195 | 0.195 | 0.012 | 0.195 | 0.006 |
| CG-ELE0.3 | 22 | 16 | 82 | 17 | 14 | 4 |
| CG-QUE0.3 | 45 | 27 | 90 | 37 | 26 | 8 |
In the case of K. pneumonia, CG-ELE0.3, and CG-QUE.03 exhibited promising inhibitory activities with MIC values of 4.0 and 8.0 µg/mL, respectively. The same trend was seen for films loaded with QUE and ELE against P. aeruginosa with MIC of 14.0 and 26.0 µg/mL. The designed films also demonstrated good inhibition against E. coli, S. epidermidis, and S. aureus. However, both films disclosed the least potency against B. subtilis. Overall it can be understood that the designed formulas were potent against tested bacteria. However, film CG-ELE0.3 exhibited slightly better growth inhibition at 4 to 82.0 µg/mL concentrations than film CG-QUE0.3, with 8.0–90.0 µg/mL MIC values. Also, it was understood that both designed films exhibited better MIC against Gram-negative bacteria than Gram-positive strains. The exception in this trend came back to S. epidermidis. Previous studies have shown that QUE inhibits different bacteria with MICs ranging from 80 to 260 µgr/mL. The results of this research on the bacterial activity of quercetin showed that its effect on bacteria leads to the destruction of the cell wall of bacteria and the modification of cell permeability, affecting the synthesis and expression of proteins, reducing the enzymatic activities and inhibiting nucleic acid synthesis. For example, it has been found that QUE can hinder the growth of S. aureus by damaging the cell wall and membrane of S. aureus, or it can cause cell death of E. coli by inhibiting the activity of ATP36,38−41.
Other researchers have shown that the antibacterial property of ELE is due to the presence of various compounds, such as flavonoids, with MICs ranging from 10.0 to 31.0 mg/L. Generally speaking, it is known that the antibacterial activity of ELE is due to their penetration into the phospholipid membrane of bacteria, which causes the release of intracellular contents. This phenomenon leads to a disturbance in the functioning of the bacterial cell, such as a disturbance of the transfer of electrons or the enzymatic activity 42–44. A comparison of the results obtained with previous research shows the remarkable antibacterial properties of the prepared films.
3.6. Mechanical properties
The mechanical behavior of films for food packaging is important during handling and must withstand external stresses45. The mechanical test results are shown in Table 3. According to the values of EB, The CG-QUE0.3 and CG-ELE0.3 films exhibited brittle behavior. Also, the tensile strength for CG-QUE0.3 and CG-ELE0.3 film was 14 ± 0.6 MPa and 13.2 ± 0.6 MPa, respectively, indicating the films’ weak tensile strength. These results can be related to the poor dispersion and aggregation of QUE and ELE in CG film. A similar effect has been reported from adding different materials to polymer substrates. Also, no significant difference was observed between the mechanical properties of CG-QUE0.3 and CG-ELE0.3 film. The obtained Young’s modulus values of TS and ED indicate that the film containing QUE has less flexibility.
| Thin film | TS (MPa) | EB | Young’s modulus |
|---|---|---|---|
| CG-QUE0.3 | 6 ± 0.1% | 14 ± 0.6 | 0.43 |
| CG-ELE0.3 | 5 ± 0.1% | 13.2 ± 0.6 | 0.38 |
Two highly pH-sensing κ-carrageenan films combined with QUE or ELE were successfully prepared in this investigation. The resulting films intelligently monitored the change in the freshness of the chicken meat; however, the pH-sensitive color changes were distinguishable for the film containing ELE. Also, the results obtained from TVBN confirm the better performance of the film containing the ELE compared to QUE in preventing the spoilage of chicken meat. In addition, due to the antibacterial activities, the prepared films can inhibit the growth of E. coli, S. epidermidis, and S. aureus, thus being applied for food packaging. The superiority of the film containing ELE over the film containing QUE is favorable from an economic point of view for industrial use. Although this work offers a viable method for the future design of intelligent packaging of food freshness, which not only accommodates and protects food but also designates food quality, additional experiments should be conducted on large meat samples to obtain adequate data to optimize system design and increase the accuracy of data analysis.
Data aviailabity:
All data generated or analyzed during this study are included in this submitted article (and its Supplementary Information files)
- Niponsak, A., Laohakunjit, N., Kerdchoechuen, O. & Wongsawadee, P. Development of smart colourimetric starch–based indicator for liberated volatiles during durian ripeness. Food Research International 89, 365-372 (2016).
- Liu, J. et al. Films based on κ-carrageenan incorporated with curcumin for freshness monitoring. Food Hydrocolloids 83, 134-142 (2018).
- Zheng, L., Liu, L., Yu, J. & Shao, P. Novel trends and applications of natural pH-responsive indicator film in food packaging for improved quality monitoring. Food Control 134, 108769 (2022).
- Hadi, J. & Brightwell, G. Safety of Alternative Proteins: Technological, environmental and regulatory aspects of cultured meat, plant-based meat, insect protein and single-cell protein. Foods 10, 1226 (2021).
- Ezati, P., Bang, Y.-J. & Rhim, J.-W. Preparation of a shikonin-based pH-sensitive color indicator for monitoring the freshness of fish and pork. Food chemistry 337, 127995 (2021).
- Zhai, X. et al. Novel colorimetric films based on starch/polyvinyl alcohol incorporated with roselle anthocyanins for fish freshness monitoring. Food Hydrocolloids 69, 308-317 (2017).
- Liu, Y. et al. Preparation of pH-sensitive and antioxidant packaging films based on κ-carrageenan and mulberry polyphenolic extract. International journal of biological macromolecules 134, 993-1001 (2019).
- Silva-Pereira, M. C., Teixeira, J. A., Pereira-Júnior, V. A. & Stefani, R. Chitosan/corn starch blend films with extract from Brassica oleraceae (red cabbage) as a visual indicator of fish deterioration. LWT-Food Science and Technology 61, 258-262 (2015).
- Koshy, R. R. et al. Preparation of pH sensitive film based on starch/carbon nano dots incorporating anthocyanin for monitoring spoilage of pork. Food Control 126, 108039 (2021).
- Dong, H. et al. Smart colorimetric sensing films with high mechanical strength and hydrophobic properties for visual monitoring of shrimp and pork freshness. Sensors and Actuators B: Chemical 309, 127752 (2020).
- Choi, I., Lee, J. Y., Lacroix, M. & Han, J. Intelligent pH indicator film composed of agar/potato starch and anthocyanin extracts from purple sweet potato. Food chemistry 218, 122-128 (2017).
- Chi, W. et al. Developing a highly pH-sensitive ĸ-carrageenan-based intelligent film incorporating grape skin powder via a cleaner process. Journal of Cleaner Production 244, 118862 (2020).
- Farhan, A. & Hani, N. M. Active edible films based on semi-refined κ-carrageenan: Antioxidant and color properties and application in chicken breast packaging. Food Packaging and Shelf Life 24, 100476 (2020).
- Lesjak, M. et al. Antioxidant and anti-inflammatory activities of quercetin and its derivatives. Journal of Functional Foods 40, 68-75 (2018).
- Zheng, Y.-Z. et al. Antioxidant activity of quercetin and its glucosides from propolis: A theoretical study. Scientific reports 7, 1-11 (2017).
- Li, X. et al. Antibacterial, antioxidant and biocompatible nanosized quercetin-PVA xerogel films for wound dressing. Colloids and Surfaces B: Biointerfaces 209, 112175 (2022).
- Ghassemi Dehkordi, N. et al. Iranian herbal pharmacopoeia (IHP). Hakim R J 6, 63-69 (2003).
- BWP, D. A. B., CONSULTATION, E., BWP, A. B. & CHMP, A. B. European Medicines Agency Evaluation of Medicines for Human Use. (2006).
- Mardaninejad, S., Janghorban, M. & Vazirpour, M. Collection and identification of medicinal plants used by the indigenous people of Mobarakeh (Isfahan), southwestern Iran. Journal of Medicinal Herbs 4, 23-32 (2013).
- Mohammadi, H.-a., Sajjadi, S.-E., Noroozi, M. & Mirhoseini, M. Collection and assessment of traditional medicinal plants used by the indigenous people of Dastena in Iran. Journal of Herbmed Pharmacology 5, 54-60 (2016).
- Jurasekova, Z., Domingo, C., García-Ramos, J. V. & Sánchez-Cortés, S. Effect of pH on the chemical modification of quercetin and structurally related flavonoids characterized by optical (UV-visible and Raman) spectroscopy. Physical Chemistry Chemical Physics 16, 12802-12811 (2014).
- Masek, A., Latos, M., Piotrowska, M. & Zaborski, M. The potential of quercetin as an effective natural antioxidant and indicator for packaging materials. Food packaging and shelf life 16, 51-58 (2018).
- Mongkholrattanasit, R. et al. Dyeing studies with eucalyptus, quercetin, rutin, and tannin: A research on effect of ferrous sulfate mordant. Journal of Textiles 2013 (2013).
- Ali, S., Nisar, N. & Hussain, T. Dyeing properties of natural dyes extracted from eucalyptus. Journal of the Textile Institute 98, 559-562 (2007).
- Vankar, P. S., Tiwari, V. & Srivastava, J. Extracts of steam bark of Eucalyptus Globules as food dye with high antioxidant properties. Electronic Journal of Environmental, Agricultural and Food Chemistry 5, 1664-1669 (2006).
- Conde, E., Cadahia, E. & García‐Vallejo, M. Low molecular weight polyphenols in leaves of Eucalyptus camaldulensis, E. globulusandE. rudis. Phytochemical Analysis: An International Journal of Plant Chemical and Biochemical Techniques 8, 186-193 (1997).
- Cadahía, E., Conde, E., García‐Vallejo, M. & Fernández de Simón, B. High pressure liquid chromatographic analysis of polyphenols in leaves of Eucalyptus camaldulensis, E. globulus and E. rudis: Proanthocyanidins, ellagitannins and flavonol glycosides. Phytochemical Analysis: An International Journal of Plant Chemical and Biochemical Techniques 8, 78-83 (1997).
- Simmonds, G., Woods, A. T. & Spence, C. ‘Show me the goods’: Assessing the effectiveness of transparent packaging vs. product imagery on product evaluation. Food quality and preference 63, 18-27 (2018).
- Simmonds, G. & Spence, C. in Multisensory Packaging 49-77 (Springer, 2019).
- LARAICHI, S. in Proceedings of the European Marketing Academy. 64604.
- Clement, J. Visual influence on in-store buying decisions: an eye-track experiment on the visual influence of packaging design. Journal of marketing management 23, 917-928 (2007).
- Sofia, L. & Pantin-Sohier, G. The impact of packaging transparency and product texture on perceived healthiness and product trust. (2020).
- Şen, M. & Erboz, E. N. Determination of critical gelation conditions of κ-carrageenan by viscosimetric and FT-IR analyses. Food research international 43, 1361-1364 (2010).
- Mirzaei, A., Jamshidi, E., Morshedloo, E., Javanshir, S. & Manteghi, F. Carrageenan assisted synthesis of morphological diversity of CdO and Cd (OH) 2 with high antibacterial activity. Materials Research Express 8, 065006 (2021).
- Danish, M., Mumtaz, M. W., Fakhar, M. & Rashid, U. Response surface methodology based optimized purification of the residual glycerol from biodiesel production process. Chiang Mai Journal of Science 44, 1570-1582 (2017).
- Wang, S. et al. Bacteriostatic effect of quercetin as an antibiotic alternative in vivo and its antibacterial mechanism in vitro. Journal of Food Protection 81, 68-78 (2018).
- Balaji, S. et al. Green synthesis of nano-titania (TiO2 NPs) utilizing aqueous Eucalyptus globulus leaf extract: applications in the synthesis of 4H-pyran derivatives. Research on Chemical Intermediates 47, 3919-3931 (2021).
- Yang, D., Wang, T., Long, M. & Li, P. Quercetin: its main pharmacological activity and potential application in clinical medicine. Oxidative Medicine and Cellular Longevity 2020 (2020).
- Hossion, A. M. et al. Quercetin diacylglycoside analogues showing dual inhibition of DNA gyrase and topoisomerase IV as novel antibacterial agents. Journal of medicinal chemistry 54, 3686-3703 (2011).
- Zhao, Y., Chen, M., Zhao, Z. & Yu, S. The antibiotic activity and mechanisms of sugarcane (Saccharum officinarum L.) bagasse extract against food-borne pathogens. Food chemistry 185, 112-118 (2015).
- Wang, L. et al. Quercetin protects rats from catheter‐related Staphylococcus aureus infections by inhibiting coagulase activity. Journal of cellular and molecular medicine 23, 4808-4818 (2019).
- Takahashi, T., Kokubo, R. & Sakaino, M. Antimicrobial activities of eucalyptus leaf extracts and flavonoids from Eucalyptus maculata. Letters in applied microbiology 39, 60-64 (2004).
- ALIZADEH, B. B. et al. Effect of aqueous and ethanolic extract of Eucalyptus camaldulensis L. on food infection and intoxication microorganisms “in vitro”. (2013).
- Kotzekidou, P., Giannakidis, P. & Boulamatsis, A. Antimicrobial activity of some plant extracts and essential oils against foodborne pathogens in vitro and on the fate of inoculated pathogens in chocolate. LWT-Food Science and Technology 41, 119-127 (2008).
- Galotto, M. J. et al. Mechanical and thermal behaviour of flexible food packaging polymeric films materials under high pressure/temperature treatments. Packaging Technology and Science: An International Journal21, 297-308 (2008).
No competing interests reported.