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

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 CNFbased 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 ApplicationDegradation of anthocyanins in processed fruit and fruit products has been a longterm 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

Investigation of cell wall characteristics of copigmented and coated whole blueberry fruit for improving anthocyanin stability under high hydrostatic pressure process and refrigerated storage

“…A 20 g of original and wet milled coating suspensions were casted on 15 cm diameter plastic petri‐dish and dried at ambient condition overnight. Films were peeled and conditioned at ~11% relative humidity (RH) to reach equilibrium until further analysis (Lin et al ., 2023). The film was placed over a paper printed with Oregon State University's logo for photos.…”

“…Copigmentation and coating were applied consecutively. For copigmentation, fruit was dipped into 1% (w/v) Tween 80 solution for 10 min, then soaked into 0.5% (w/v) tannic acid solution bath for 30 min, followed by transferring into 1% CaCl 2 ·2H 2 O solution for 10 min at room temperature (Jung et al ., 2022; Lin et al ., 2023). The LBL hydrophobic coating was applied on copigmented fruit following the procedures of Lin et al .…”

“…The LBL hydrophobic coating was applied on copigmented fruit following the procedures of Lin et al . (2023). Briefly, for the first layer of CNF‐based coating, CNF (0.75%, w/w wet basis) was mixed with CMC solution (0.25%, w/w wet basis) and homogenised at 20000 r.p.m.…”

“…Moisture content (MC), water absorption (WA) and water solubility (WS) were analysed using methods from Lin et al . (2023). For MC, film (20 × 20 mm 2 ) was measured for the initial weight ( W i ) and dried weight ( W d ) after drying at 105 °C for 24 h, and calculated as MC (%) = (( W i – W d )/ W i ) *100%.…”

“…We have previously developed a consecutive preservation technique via combined copigmentation and layer‐by‐layer (LBL) hydrophobic coating to preserve anthocyanins in thermally processed whole blueberry fruit (Lin et al ., 2023; Jung et al ., 2022; Jung et al ., 2018). In the LBL hydrophobic coatings, the first layer applied onto the fruit surface consists of CNF, polysaccharides (chitosan and carboxymethyl cellulose) and oleic acid for providing good surface adhesion and hydrophobicity against aqueous packing solution (Lin et al ., 2023). CNFs with 5–70 nm diameter, 200–2000 nm length and >50 aspect ratio form entangled nanofibril network structures and are reconcilable with other hydrophilic biopolymers through non‐covalent linkages or electrostatic crosslinking (Jung et al ., 2019).…”