Cellulose nanofiber‐based emulsion coatings with enhanced hydrophobicity and surface adhesion for preserving anthocyanins within thermally processed blueberries packed in aqueous media

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Abstract
To enhance hydrophobicity and surface adhesion of edible coatings onto blueberries, an emulsion system consisting of polysaccharides and oleic acid (OA) was developed and incorporated into layer‐by‐layer (LBL) cellulose nanofiber (CNF)‐based coating. The surface tension (ST) of CNF‐based emulsion coating with chitosan (CS), carboxymethyl cellulose (CMC) and OA was 34.28 mN/m, within the range of critical ST (28.41–37.52 dyne/cm) of blueberry surface after washing and copigmentation treatment by phenolic acid, which is essential to ensure good adhesion of coatings on fruit surface. CNF‐based emulsion coating demonstrated lower water sorption (9.47%) and water solubility (35.42%) and higher water contact angle (82.49 °) than CNF‐based coating without emulsion (control; 378.60%, 51.72%, and 67.37 °, respectively). CNF‐based emulsion coating also showed lower tensile strength (5.9 MPa) and elongation at break (2.55%) than control (28.17 MPa and 17.85%, respectively). CNF‐based emulsion coating was validated on thermally processed blueberries for preventing anthocyanin pigment leaching as the first layer in a LBL coating system with sodium alginate as the second layer. The CNF emulsion incorporated LBL coating system significantly preserved anthocyanin pigment in the processed blueberries compared with that of control due to increased surface adhesion and hydrophobicity and decreased mechanical damage. This study demonstrated the effectiveness of emulsion system in coatings for enhancing hydrophobicity and surface adhesion of coatings to preserve the nutritional and organoleptic qualities of thermally processed blueberries.Practical Application: Degradation of anthocyanins in processed fruit and fruit products has been a long‐term challenge for processed food industry. The hydrophobic and heat‐resistant coatings developed in this study can be used to preserve antioxidant anthocyanin pigments within fruit when subjected to thermal (simulated canning) process in aqueous solution, thus overcoming the barriers that the food industry has been facing. CNF plays a critical role to enhance thermal stability and adhesion of coatings onto fruit surface. The developed technology can be utilized for not only improving existing products, but also developing new and novel fruit products.
Funding Information
  • U.S. Department of Agriculture

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