Abstract
The generation of value from the strawberry agro-chain requires in some cases the disintegration of the structure and formulation of the fruit, resulting in suspensions that behave as thermodynamically unstable colloidal systems and are affected by various forces, such as Van der Waals, electrostatic, steric, hydration, hydrophobic, and phase separation. The aim of this research was to evaluate the influence of the homogenization process and the concentration of gum arabic (GA) on the stability of strawberry-based suspensions. Strawberries with a 9% solid content were used and a centralized-composite central design was proposed (pressure (P) from 4.14-10.34 MPa), time (t) (3-5 min), and GA (0.2-0.4%)) and the dependent variables zeta potential (ζ), spectral absorption index (R), viscosity (μ), and particle size were evaluated. The ζ potential and R-index were not affected by the homogenization process and GA; the suspension was stabilized by the increase of ζ due to t, the GA effect, and the t-GA interaction. Particle size was affected by P but not by t, whereas GA mainly affected D [3,2], D [4,3], and D90. The results indicate that the homogenization and the use of GA as a hydrocolloid confer chemo-physical stability to the strawberry suspension.
Highlights
The strawberry (Fragaria ananassa) is a fruit comprised of components with important physiological activity: vitamin C, tannins, flavonoids, anthocyanins, catechin, quercetin and kaempferol, organic acids, and minerals (i.e., K, P, Ca, Na, and Fe) (Kallio et al, 2000; Mosquera, 2010; Ribeiro et al, 2018)
Pectins and gum arabic (GA) have carboxyl groups susceptible to ionization that depend on their degree of methoxylation, especially in pectin (McClements, 2009; Alba et al, 2016)
When the strawberry suspension has a pH of 3.5, pectin is negatively charged; because this polyacid has a pKa between 3.5 and 4.0, the predominant species in this pH range is in the form of galacturonate (Croak & Corredig, 2006).This anion charge is in the co-ion layer attached to the interphase of the dispersed particles, while a high density of positive charge contributed by the dissociated ions is located in the double electrical layer or Stern layer
Summary
The strawberry (Fragaria ananassa) is a fruit comprised of components with important physiological activity: vitamin C, tannins, flavonoids, anthocyanins, catechin, quercetin and kaempferol, organic acids (i.e., citric, malic, oxalic, salicylic, and ellagic), and minerals (i.e., K, P, Ca, Na, and Fe) (Kallio et al, 2000; Mosquera, 2010; Ribeiro et al, 2018). In strawberry-based suspensions, the presence of sugars, acids, minerals, and polymers such as structural carbohydrates and pectins, lead to interactions of a repulsive nature and Van der Waals type attraction; as described by DLVO theory, the predominance of repulsive forces in this type of attraction promotes the physical stability of the colloidal system (Missana & Adell, 2000; Coupland & Sigfusson, 2005; McClements, 2007) This electrostatic repulsion is important when the particles approach each other and provide a double electrical layer, effectively becoming the necessary energy barrier to prevent the union between the particles (Dickinson, 2009)
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