Chitosan based edible coatings with essential oils and supercritical extracts on strawberry quality during cold storage
Chitosan based edible coatings with essential oils and supercritical extracts on strawberry quality during cold storage
The plant material, the method utilized to produce the extract influences its chemical and preservative characteristics. In general, hydrodistillation (HD) produce plant products (essential oils) that are well recognized for containing high concentration of antioxidant or antimicrobial volatile compounds. Supercritical fluid technology produces high quality bioactive extracts with higher yield but lower concentration of volatile compounds, in comparison with hydrodistillation. In this work, six different natural extracts of five different plants were produced by hydrodistillation and supercritical fluid extraction, and their antioxidant and antimicrobial activities were compared. The most active extracts were used to produce chitosan-based edible coatings with the aim of assessing the effect of essential oils versus supercritical extracts on the preservation of strawberries.
Materials and methods
Essential oil was extracted from the sample of Rosemary (Rosmarinus officinalis L.), thyme (Thymus vulgaris), centaury (Centaurium erythraea), mugwort (Artemisia vulgaris) leaves and root of licorice (Glycyrrhiza glabra L.). The samples were ground using a Premill 250 hammer mill. All samples were stored in polyethylene bags under vacuum and kept at 4 °C.
Methods for plant extracts preparation
Hydrodistillation
The plant samples were subject to hydrodistillation (HD) using a Clevenger-type apparatus for 3 h, using a 1:10 plant: water ratio. The oil phase was separated from the water phase, recovered by centrifugation and stored at -20 °C. The essential oil yields were calculated with respect to the dry mass of plant subject to hydrodistillation.
Hydrodistillation combined with ultrasound pretreatment
The plant samples in a 1:10 plant: water ratio was subject to ultrasound frequency of 20 kHz, 550 W and 60% of sonication output amplitude pretreatment for 15 min and 25 °C, before the 3 h hydrodistillation process. The essential oil was recovered by centrifugation and stored at -20 °C.
Supercritical fluid extraction
Supercritical fluid extraction (SFE) was carried out using a pilotplant extractor including a 0.273 L cylinder extraction vessel and two-cylinder separators (S1 and S2), each of 0.5 L capacity, with independent control of temperature and pressure. Also, the pilot-plan device includes a CO2 recirculation system. Different extractions were accomplished, with pure CO2 and using 10% mass of ethanol cosolvent, at 313.15 K, 70 g/min of CO2 flow rate, and pressures in the range 15–30 MPa. The plant extracts were obtained by depressurization in the separators of the supercritical stream flowing out of the extractor vessel. In the case of SFE15 and SFE15-EtOH extractions both separators were maintained at the system recirculation pressure (5 MPa) and the extracted mass were collected from both separators and mixed in a single fraction. Moreover, runs SFE30 was carried out at higher pressures (30 MPa) and the extract was fractionated in the decompression cascade system comprising the two separators. For this purpose, the first separator cell (S1) was kept at 15 MPa and the second one was maintained at the recirculation pressure.
Conclusions
SFE yields of all studied plants were considerably higher than HD yields, and yields were significantly higher when ethanol was used as CO2 cosolvent. The ABTS values of all products produced (by SFE and HD) presented a high linear regression coefficient with the TPC content, confirming the influence of phenolic compounds in the antioxidant activity of plant extracts. Rosemary and thyme extracts exhibited the best combination of antioxidant and antimicrobial properties. After 10 days of cold treatment, it can be concluded that berries coated with chitosan and 1% or 5% of supercritical rosemary SFE15 or thyme SFE15-ETOH extracts presented lower fungal decay in comparison with control, but spoilage preservation of the essential oils was better than that of supercritical extracts. No important effects of coatings with SFE or HD extracts on the color appearance of strawberries were established. Furthermore, in general, edible coatings produced with HD extracts exhibited somewhat higher weight loss, but lower pH and content of soluble solids increase, and better preserved the content of phenolic compounds in strawberries, in comparison with the berries coated with SFE extracts.
Reference:
Quintana, S.E., Llalla, O., García-Risco, M.R. and Fornari, T., 2021. Comparison between essential oils and supercritical extracts into chitosan-based edible coatings on strawberry quality during cold storage. The Journal of Supercritical Fluids, 171, p.105198.
