COMPRESSION TEST , WATER VAPOR PERMEABILITY AND ANTIOXIDANT ACTIVITY ON SPECIAL GREEN COFFEE BEANS COATED WITH CHITOSAN / BENTONITE / α-TOCOPHEROL BASED BIOCOMPOSITS

Coffee is seasonal, so the storage of green coffee beans (GCB) is necessary. During this time, the GCB must be preserved with all its good quality characteristics, not to lose the commercial value during the year. The big bags are the most frequently used packages to store and transport GCB in large-scale because it is easy to adapt to mechanized handling. However, due to the high storage capacity of the big bags can damage the GCB, causing defects that can lead to the loss of the coffee quality. Moreover, moisture absorption and lipid oxidation are also recurring problems during storage. Edible coatings can provide additional protection for GCB of moisture absorption and damage from compression, without change the traditional packaging. Besides that, active coatings can improve the conservation of GCB. The α-Tocopherol can be used in active coatings, acting as an antioxidant, protecting the GCB from lipid oxidation, and bentonite is a clay having chemical and physical properties that can improve coating properties, such as barrier and mechanical properties. The aim this work was evaluating the coating performance against the compression of the GCB, antioxidant capacity, and water vapor permeability. The suspensions were developed in citric acid aqueous solution 1.6% (w/v), 2% chitosan (w/v) and the following treatments were obtained: control (QUI); with incorporation of bentonite (BNT) 2% (w/w); incorporation of α- tocopherol (TOC) 10% (w/w); incorporation of bentonite 2% (w/w) and α-tocopherol (BNT/TOC) 10% (w/w). These suspensions were used to coat the GCB (Coffea arabica L.) and to form films by casting. The uncoated and coated with the treatments presented GCB were submitted to a compression test in a texture analyzer. With the films were tested the water vapor permeability (WVP) by permeation capsules and antioxidant activity (AA) for treatments with α-tocopherol by the eliminating the stable free radical 2,2-diphenyl-1-picrylhydrazyl method. A completely randomized design was performed, variance analysis was done, and the average was compared by the Tukey test, at 5% probability, by SISVAR® software. The presence of bentonite did not affect the AA of films with tocopherol, and the treatments TOC and BNT/TOC presented 50.3% of antioxidant activity. The α-tocopherol has an aromatic ring in its structure capable of delocalizing the unshielded electron, directly reacting or neutralizing the hydroxyl, alkoxy and lipid peroxyl radicals, forming H2O, alcohol and lipid peroxides, respectively, becoming a phenyl radical. The incorporation of bentonite promoted the decrease of the WVP, for the treatments QUI and TOC, helping to the development of films with a greater barrier to water vapor. When GCB with and without coating were compared, it can be observed that there was a general compressive strength increase in the coated GCB when compared to the uncoated GCB, which proves the effectiveness of the coatings regarding the GCB protection against the compression that occurs during storage. The treatment BNT/TOC offered greater compression protection for the GCB, greater barrier of water vapor permeability and presented a greater antioxidant activity; being a viable option to better the GCB preservation during the storage.

Financial support

FAPEMIG, CNPq e CAPES