Pulsed Vacuum Osmotic Dehydration (PVOD) of Fermented Beetroot: Modeling and Optimization by Response Surface Methodology (RSM)

Abstract

Fermented beetroots can be osmotically dehydrated and then dried to make a nutritious snack known as fermented beet chips. To ensure the best product quality, it is necessary to determine optimal parameters of osmotic dehydration. Therefore, the aim of this study was to determine the optimal parameters of pulsed vacuum osmotic dehydration (PVOD) of fermented beetroot slices. The response surface methodology (RSM) was employed to optimize PVOD and improve the efficiency of the process. The experimental parameters considered: (T) processing temperature (20 < T < 40 °C), (SC) sugar concentration (40 < SC < 60%), (VT) vacuum impregnation time (10 < VT < 50 min), and (ST) slice thickness (2 < ST < 6 mm). PVOD was optimized in terms of properties of beetroot tissue (hardness, HT, redness, a*T, water loss, WL, solid gain, SG) and osmotic solution (dry matter content, DMS, redness, a*S). The optimum qualities of beetroot tissue (HT = 202.0 N, a*T = 11.8, WL = 55.5%, SG = 7.1%) and osmotic solution (DMS = 57.3%, a*S = 38.9) were obtained at T = 20 °C, SC = 60%, VT = 10 min, ST = 6 mm and T = 40 °C, SC = 60%, VT = 50 min, ST = 2 mm, respectively. The beet tissue obtained by PVOD in optimal parameters was characterized by 2.58 ± 0.21 kg H2O/kg DM moisture content (MCF), 4.64 ± 0.37 mg GA/g DM total polyphenols (TPC), 2.2 ± 0.2 mg TE/g DM ferric reducing antioxidant power (FRAP), 1125 ± 10 kg/m3 density (ρT), and 4.29 ± 0.24 total color change (ΔE*) compared to material before PVOD. 2D and 3D images of the beetroot surface structure allowed to observe the collapse of the structure and the appearance of a semi-transparent coating (most likely a sugar solution) on the material after PVOD.