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

Summary The combined copigmentation and layer‐by‐layer (LBL) hydrophobic coating technique was developed to preserve anthocyanins in thermally processed (TP) whole blueberry fruit in our previous study. This study investigated the impact of the developed technique on the cell wall composition and structure, anthocyanin stability and fruit firmness in non‐thermally (high hydrostatic pressure (HHP)) processed whole blueberry fruit during the refrigerated storage at 4 °C ~ 7 °C. Meanwhile, the wet‐milling process was utilised to treat cellulose nanofiber (CNF) based first layer coating for enhancing adhesion and improving the appearance of LBL coating on the fruit. The developed anthocyanin preservation technique retained significantly ( P < 0.05) higher chelator‐soluble pectin in both thermally and HHP processed fruit (102.8 ± 7.0 and 100.8 ± 5.1 mg g −1 dry fruit skin, respectively). The technique also enhanced fruit anthocyanin stability reflected by the bathochromic and hyperchromic effect on fruit skin extract. In addition, it significantly ( P < 0.05) enhanced the firmness of HHP (551.2 ± 80.7 g) or TP (579.8 ± 90.9 g) processed fruit during the refrigerated or ambient storage compared with control (488.9 ± 75.8 g). The wet‐milling process was able to fibrillate aggregated cellulosic fibres in the coating suspension, thus improved the adhesion and appearance of LBL coating onto the fruit surface. This study demonstrated that the combined copigmentation and LBL coating, along with wet milling treatment of CNF‐based coating, can effectively preserve anthocyanins in HHP processed whole blueberry fruit during extended refrigeration storage owning to the modification of fruit surface cell wall composition and structure.