Application of edible coatings composed of chitosan and tea seed oil for quality improvement of strawberries and visualization of internal structure changes using X-ray computed tomography

Abstract

Edible film composed of chitosan (CH) and tea seed oil (TSO) was prepared by casting method and its physicochemical and structural properties were evaluated. Strawberries were coated with the edible coatings by dipping method and physicochemical properties (weight loss, moisture content, color change, firmness, pH and total soluble solids (TSS)) and internal structures were determined during storage at 2 °C for 24 days. Non-destructive X-ray computed tomography (CT) was used to visualize strawberry internal structure, with CT measured in terms of grayscale (GS) values. As expected, the CH + TSO film decreased water vapor permeability (WVP), with TSO conferring a reduction of 20.83 %. The CH + TSO film decreased moisture content (26.43 %) and water solubility (22.93 %). Incorporation of TSO in CH films significantly increased opacity by 204.76 %, greatly improving the ability to block light. Changes in the surface and structure of the films were obtained by Scanning electron microscopy (SEM), Atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) analysis. The properties of CH + TSO film were improved compared to pure CH film. Moreover, the results of storage for 24 days from the coating application to strawberries showed that CH and CH + TSO coatings effectively reduced fruit weight loss; retained firmness, color, moisture content by 86.69 % and 84.93 %, respectively, compared to the control (82.45 %), TSS by 10.22 % and 9.70 %, respectively, compared to the control (9.48 %); delayed pH changes by 3.49 % and 3.54 %, respectively, compared to the control (3.58 %) and ∆E by 8.06 % and 10.31 %, respectively, compared to the control (13.37 %). In particular, the CH and CH + TSO treated strawberries still remained the firmness by 68.36 % and 63.35 %, respectively, compared to the control (59.38 %) and the weight loss of CH and CH + TSO treated samples was 5.83 % and 6.93 %, respectively, compared to 8.11 % for the control. X-ray CT observations revealed that the coating treatments could inhibit the development of voids in the strawberries. These results demonstrate CH and CH + TSO film maintain the physicochemical properties and internal structure of strawberries during storage.