Enhancing anthocyanin–phenolic copigmentation through epicarp layer treatment and edible coatings to retain anthocyanins in thermally processed whole blueberries

Abstract

Anthocyanins in processed fruit degrade significantly due to their heat and oxygen sensitivity and water solubility. Copigmentation for stabilizing anthocyanins is less effective for whole fruit due to anthocyanins’ location within cell vacuoles surrounded by the epicarp layer as barrier to prevent copigment complexing with anthocyanins. This study investigated strategies for enhancing anthocyanin–phenolic copigmentation on blueberry surface, and integrated copigmentation with layer‐by‐layer (LBL) coating to retain anthocyanin stability in thermally processed blueberries. Results indicated that epicarp layer treatment of fruit by Tween 80 (T80) and CaCl2 is important for enhancing anthocyanin–phenolic copigmentation. The sequential copigmentation treatment using T80, ferulic acid, and CaCl2 (T80→FA→CaCl2) or T80, tannic acid, and CaCl2 (T80→TA→CaCl2) resulted in higher (p < 0.05) retention of total monomeric anthocyanin (3.18 mg/g and 3.38 mg/g, respectively) in thermally processed blueberries after 7‐day ambient storage than that of untreated fruit (2.79 mg/g). Percent polymeric color (PPC) of blueberries treated by T80→FA→CaCl2 (15.5%) or T80→TA→CaCl2 (17.4%) was lower (p < 0.05) than that treated by TA alone (22.5%). The LBL coating enhanced microstructure stability for preserving anthocyanins in thermally processed blueberries. This study demonstrated the effectiveness of sequential copigmentation of blueberries after epicarp layer treatment followed by LBL coating for enhancing anthocyanin stability in processed whole fruit. Practical Application When anthocyanin‐rich fruit is thermally processed, anthocyanins degrade and leach to aqueous packing solution because of its heat sensitivity and water solubility. This study developed an innovative technology through implementing sequential treatments of copigmentation and water‐ and heat‐resistant coating for preventing heat and water degradation of anthocyanins in whole fruit during processing in aqueous media. The developed technology can be practically applied to enhance the quality and health benefits of thermally processed anthocyanin‐rich whole fruit. The technology can not only be utilized to improve existing fruit products, but also develop new and novel fruit products.

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

“…OA (0.25% or 1%, wt/wt wet basis), CS (0.25%, wt/wt wet basis), and CaCl 2 ·2H 2 O (0.5%, wt/wt wet basis) were then added into prepared suspensions and homogenized for 30 min. CNF‐based coating without emulsion (0.75% CNF, 0.5% MeC, and 0.5% CaCl 2 ·2H 2 O, wt/wt wet basis) developed in our previous study (Jung et al, 2022) was used as a control for comparison. For preparing the control, CNF slurry (2.95%, wt/wt wet basis) was diluted with distilled water, homogenized for 1 min, and then mixed with 3% MeC stock solution (wt/wt wet basis) and 0.5% CaCl 2 ·2H 2 O (wt/wt wet basis) and homogenized for 3 min.…”

“…CST of blueberry skins was evaluated on nonwashed, washed by a fresh produce detergent (Environne Purely Essential Fruit & Vegetable Wash, Roseburg, Oregon), and copigmentation‐treated fruit. The copigmentation treatment was adopted from our previous study (Jung et al, 2022). Briefly, fruit was washed by the fresh produce detergent and sequentially treated in 1% (wt/vol) Tween 80, 0.5% (wt/vol) TA, or FA, and 1% (wt/vol) CaCl 2 ·2H 2 O for 10 min, respectively (T80 → TA → CaCl 2 or T80 → FA → CaCl 2 ).…”

“…However, anthocyanins are water soluble and sensitive to heat, pH, and oxygen, thus being easily degraded during the conventional fruit processing, such as canning, freezing, and drying (Oliveira et al, 2010;Routray & Orsat, 2011). To preserve anthocyanins within thermally processed whole fruit packed in aqueous media, such as light sugar solution, authors' research team previously developed an emerging approach through combining copigmentation with phenolic compounds and layer-by-layer (LBL) water-resistant coatings to chemically and physically protect anthocyanins (Jung et al, 2015(Jung et al, , 2018Jung et al, 2022). While the technology successfully preserved anthocyanins during fruit processing, the pigments gradually leached out from fruit into the packing media during long-term ambient storage (Jung et al, 2018(Jung et al, , 2022, which may be caused by the unstable and insufficient moisture barrier of coatings in aqueous packing media and weak adhesion of coatings onto fruit surface.…”

“…and enhanced interaction between fruit surface and coating due to the lower CST of blueberry surface than ST of developed CNF-based emulsion coating. The LBL coating was then applied, which included three steps(Jung et al, 2018): (1) dipping fruit in either CNF-based coating developed from previous study(Jung et al, 2022) with formulation consisting of 0.75% CNF, 0.5% MeC, 0.5% CaCl 2 Á2H 2 O (wt/wt, wet basis as a control), or CNF-based emulsion coating from this study for 10 min, (2) drying coated fruit using a fan under ambient condition, and (3) dipping fruit in 0.5% (wt/vol) sodium alginate bath for 1 min then in 3% (wt/vol) CaCl 2 Á2H 2 O bath for 5 min. The LBL-coated fruit were then transferred into Mason jar and filled with 20% (wt/wt, wet basis) sugar solution at pH 4.2 adjusted by 1% (vol/vol) formic acid at 1:1 ratio of fruit and sugar solution.…”

“…e Based on a t-test (p < 0.05) for comparing CNF-based emulsion coating with the control. f Control: coating formulation from our previous study (0.75% CNF, 0.5% MeC, and 0.5% CaCl 2 Á2H 2 O, wt/wt wet basis;Jung et al, 2022).…”