Title: Chitosan-based layer-by-layer edible coatings application for the preservation of mandarin fruit bioactive compounds and organic acids
Journal: Food Chemistry
Published: 2023
Background
Mandarins, a popular citrus fruit, are highly perishable and prone to quality loss during postharvest handling, storage, and transportation. To improve the shelf life and quality of mandarin fruits, various postharvest treatments, such as edible coatings, are employed. These coatings can reduce moisture loss, slow down respiration, and minimize microbial growth, ultimately extending the fruit's lifespan. Chitosan, a biopolymeric coating, is widely used due to its ability to delay browning, water loss, and fungal diseases. However, traditional single coatings sometimes fail to meet all requirements such as adequate gas and water vapor permeability and antibacterial activity. This research investigates the application of chitosan-based layer-by-layer (LbL) edible coatings in combination with other polysaccharides like sodium alginate, hydroxypropyl methylcellulose, and locust bean gum, aiming to preserve mandarin fruit's bioactive compounds, antioxidant activity, and organic acids content during storage.
Layer-by-layer (LbL)electrostatic deposition technique
Materials & Methods
Plant Material
Mandarins 'Owari' (Citrus unshiu Marcovitch) were harvested on October 21, 2021, from a commercial orchard in Opuzen, Croatia. Harvest maturity parameters were recorded for 30 fruits.
Chemicals
- Chitosan, sodium alginate, locust bean gum, hydroxypropyl methylcellulose from Sigma-Aldrich and Alfa Aesar.
- Analytical grade chemicals used for analysis.
Coating Preparation
- Chitosan (1% w/v) in 2% citric acid solution.
- Sodium alginate (1.5% w/v), hydroxypropyl methylcellulose (1% w/v), locust bean gum (0.2% w/v) in distilled water. Mandarins were dipped in each solution for 3 min, air-dried, and re-dipped in chitosan for a second layer.
Storage
Mandarins stored at:
- Room temperature (20 ± 2 °C, 60 ± 10% RH) for 2, 4, 7, and 10 days.
- Cold storage (5 ± 1 °C, 90–95% RH) for 7, 14, 21, and 28 days.
Fruit Gloss & Color
Gloss measured on a 0-10 scale. Color parameters (CIE Lab*) measured with a colorimeter.
Weight Loss & Firmness
Weight loss was measured, and firmness was assessed using a texture analyzer with a 5 mm probe.
Juice Preparation
Mandarins were peeled, blended, centrifuged, and filtered for analysis.
Chemical Analysis
- TSS: Measured with a refractometer.
- TA: Titrated with NaOH.
- Polyphenols: Folin-Ciocalteu method (gallic acid standard).
- Flavonoids: Spectrophotometric method (quercetin standard).
- Antioxidant Activity: DPPH and ABTS methods (Trolox standard).
- Organic Acids: HPLC for oxalic, malic, ascorbic, citric acids.
Statistical Analysis
Data analyzed using Repeated measure ANOVA, Pearson correlation, and PCA (IBM SPSS, XLSTAT).
Results
Fruit Gloss and Visual Observation:
- Layer-by-layer (LbL) composite coatings, particularly with chitosan as the outer layer, enhanced the gloss of mandarin fruits.
- No negative sensory qualities (e.g., stickiness, peeling) were observed in treated fruits during storage.
- Coated fruits maintained glossiness and showed less decay compared to uncoated fruits, especially at room temperature (RT).
CIE Color Variables:
- Total color difference (ΔE) was higher at RT than in cold storage (CS), indicating more pronounced color changes at higher temperatures.
- Alginate/chitosan-treated mandarins showed the highest color difference at RT, while hydroxypropyl methylcellulose/chitosan (HC) coatings showed the highest difference at CS.
Weight Loss and Firmness:
- All coatings significantly reduced weight loss after 10 days at RT, with no significant changes observed during CS.
- No significant differences in firmness were observed between coated and uncoated fruits, contrary to some previous studies.
Total Soluble Solids (TSS) and Titratable Acidity (TA):
- No significant influence of coatings on TSS or TA was observed, consistent with existing literature.
- Chitosan-coated fruits showed higher TA values compared to controls, but the differences were not statistically significant.
Bioactive Compounds and Antioxidant Activity:
- Chitosan and LbL coatings significantly increased total polyphenols (TPC) and total flavonoids (TF) in mandarin fruits.
- HC coatings showed the highest increase in TPC and TF during CS.
- Antioxidant activity (measured by DPPH and ABTS methods) was significantly higher in coated fruits, with chitosan and HC coatings showing the most pronounced effects.
Organic Acids
- Chitosan and LbL coatings increased the content of organic acids (oxalic, malic, ascorbic, and citric) in mandarin fruits.
- HC coatings showed the highest levels of ascorbic acid during CS.
- The combination of LbL coatings and CS significantly increased the content of organic acids compared to controls.
Principal Component Analysis (PCA)
- PCA revealed two significant components explaining 80.22% of the total variance.
- Factor 1 (67.24% variance) was associated with bioactive compounds, antioxidant activity, and ascorbic/citric acids.
- Factor 2 (12.97% variance) was associated with oxalic/malic acids and titratable acidity.
- Control samples showed the lowest values in bioactive compounds and antioxidant activity, while HC and chitosan-coated samples showed the highest values.
Reference
- Jurić, Slaven, et al. "Chitosan-based layer-by-layer edible coatings application for the preservation of mandarin fruit bioactive compounds and organic acids." Food Chemistry: X 17 (2023): 100575. https://doi.org/10.1016/j.fochx.2023.100575
