Effect of relative humidity on shrinkage and color changes in dehydrated strawberry

Abstract

Dehydrated fruits are prone to discoloration during storage. Many natural pigments are unstable in dried fruits, and brown pigments can be formed. The rate of physical and chemical changes in dried vegetables and food models is slow in the glassy state. At temperatures above the glass transition, in addition to decreasing viscosity and increasing rate, other changes such as crystallization and structural collapse affect the rate of discoloration (Karmas et al. 1992). Diffusion-controlled chemicalreactions are particularly dependent on translational diffusivity of the reactants (or on the viscosity of the matrix material) and are thus susceptible to the physical state of the system (Slade et al. 1995). It has been shown that matrix collapse caused by storage above the glass transition temperature (Tg) or by mechanical compression and porosity (Burin et al. 2004; White and Bell 1999) affected browning rates, indicating that besides water content, system structure plays a relevant role.Color and size changes affect fruit appearance and organoleptic quality and may be an indication of decreased nutritional and functional properties of foods. Food discoloration can occur homogeneously, but most often, heterogeneous distribution of color is observed. Color meters typically claim to measure the average color of the food material?s surface exposed to the measuring window of the instrument (Balaban 2008). However, many food products, such as strawberry slices, show heterogeneous color distribution. While averaging is acceptable for uniformly colored surfaces (Briones and Aguilera 2005; Mendoza et al. 2006; Venir et al. 2007; Acevedo et al. 2008a, b), when the colors change with location or are non-homogeneous, averaging may result in inaccurate color determination (Balaban 2008). The objective of this work was to assess the effect of relative humidity (RH) on color alterations and shrinkage in freeze-dried strawberry slices.