Alginate-Edible Coatings for Application on Wild Andean Blueberries (Vaccinium meridionale Swartz): Effect of the Addition of Nanofibrils Isolated from Cocoa By-Products

Abstract

Edible coatings and films are appealing strategies for the postharvest management of blueberries. In the current work, alginate and alginate/cellulose nanofibril (CNF) edible coatings crosslinked with calcium chloride were developed for application on Andean blueberry (a promissory wild blueberry). Cocoa by-products were valorized through the isolation of their CNFs, and these were incorporated in the edible coatings. Edible coating formulations were based on blends of alginate (2% w/v), CNFs (0%, 0.1%, or 0.3%), glycerol, and water. In addition, stand-alone films were prepared, and their light and water vapor barrier properties were studied before applying the coating on the fruit surface. The results show that the addition of CNFs caused a significant decrease in the transparency and the water vapor permeability of the alginate films. After applying on the Andean blueberry fruits, the alginate and alginate/CNF coatings enhanced the appearance and the firmness of the fruits. Moreover, they significantly reduced the respiration rate and the water loss of the Andean blueberries throughout the 21 days of refrigerated storage. Alginate and alginate/CNFs coatings may be considered a useful alternative for the delay of the postharvest deterioration of Andean blueberries.

Improvement of Andean Blueberries Postharvest Preservation Using Carvacrol/Alginate-Edible Coatings

“…Coating solutions with and without carvacrol (CVR) were prepared as described in a previous work [ 25 ]. Alginate solutions were made by dissolving sodium alginate powder (2% w / v ) in distilled water while heating at 70 °C under constant stirring until the mixture became clear.…”

“…The surface solid density (SSD) was estimated as an indicator of the coating’s average thickness. Andean blueberries were covered as indicated in Section 2.3 and their surface solid density (g/m 2 ) was estimated with the following equation [ 4 , 25 ]: where M CA is the mass of the coating solution adhered to the fruit surface (g); X S is the mass fraction of solid in the coating solution and A S is the surface area of Andean blueberries (m 2 ). The average sample surface area ( A s ) was estimated by considering each blueberry as a sphere.…”

“…To characterize the coatings to water solubility, water vapor permeability and chemical conformation, films were performed by casting according to Medina-Jaramillo et al [ 25 ]. Each coating solution was poured into polypropylene plates and dried at 50 °C for 24 h. Then, dried films were peeled from the plates, submerged in a gelling bath of calcium chloride solution (1% w / v ) for 30 min, cleaned with distilled water, and air-dried at room temperature.…”

“…Control samples (without coating) were prepared by immersion in distilled water and air-dried at room temperature. These uncoated fruits were kept under the same storage conditions as the treated ones, for comparison [ 25 ].…”

“…Therefore, there is a need to overcome these difficulties through the application of safe and environmentally friendly postharvest technologies for its preservation such as edible coatings. In our previous study, the effect of coatings based on starches and alginate/nanocellulose blends on the postharvest preservation of Andean blueberries was reported for the first time [ 6 , 25 ]. It was found that alginate coatings exhibited better performance on the weight loss reduction and the fruit firmness, in comparison with starch ones.…”