The Quality of Red Bell Pepper Subjected to Freeze-Drying Preceded by Traditional and Novel Pretreatment

Abstract

It has been demonstrated previously in the literature that utilization of PEF or a combination of a pulsed electric field (PEF) and ultrasounds (US) can facilitate dehydration processes and improve the quality of dried products even better than the application of thermal methods such as blanching. The aim of the study was to evaluate the quality of red bell pepper subjected to freeze-drying preceded by blanching or PEF or US treatment applied in a single and combined mode. Furthermore, the freeze-drying was preceded by shock freezing or vacuum freezing performed inside the freeze-dryer as a result of pressure drop during the first stage of freeze-drying. All of the analyzed technological variants enhanced the drying kinetics when compared to the intact material. Freeze-dried bell pepper subjected to non-thermal pretreatment exhibited higher vitamin C, total phenolic and carotenoids content than blanched material despite the fact that blanching reduced drying time the most compared to all other analyzed methods.

Keywords: blanching; freeze-drying; hybrid treatment; pulsed electric field; red bell pepper; shock freezing; ultrasound; vacuum freezing.

Figure 1

Photo of lyophilized red bell peppers treaded with traditional treatment (BL_W—blanching in water, BL_S—steam blanching), novel single treatment (US—sonication for 30 min, PEF_1—pulsed electric field with energy input 1 kJ/kg, PEF_3—pulsed electric field with energy input 3 kJ/kg) or novel hybrid treatment (PEF+US, US+PEF), preceded by shock freezing (L) and vacuum freezing (L_VF).

Figure 2

Total sugars content of lyophilized red bell peppers treaded with traditional treatment (BL_W—blanching in water, BL_S—steam blanching), novel single treatment (US—sonication for 30 min, PEF_1—pulsed electric field with energy input 1 kJ/kg, PEF_3—pulsed electric field with energy input 3 kJ/kg) or novel hybrid treatment (PEF+US, US+PEF), preceded by shock freezing (L) and vacuum freezing (L_VF). Data are presented as a mean from 3 repetitions with error bars as a standard deviation (SD), data with different letters differ significantly (Tukey’s HSD, p < 0.05).

Figure 3

Vitamin C content in lyophilized red bell peppers treaded with traditional treatment (BL_W—blanching in water, BL_S—steam blanching), novel single treatment (US—sonication for 30 min, PEF_1—pulsed electric field with energy input 1 kJ/kg, PEF_3—pulsed electric field with energy input 3 kJ/kg) or novel hybrid treatment (PEF+US, US+PEF), preceded by shock freezing (L) and vacuum freezing (L_VF). Data are presented as a mean from 3 repetitions with error bars as a standard deviation (SD), data with different letters differ significantly (Tukey’s HSD, p < 0.05).

Figure 4

Total phenolic content (TPC) in lyophilized red bell peppers treaded with traditional treatment (BL_W—blanching in water, BL_S—steam blanching), novel single treatment (US—sonication for 30 min, PEF_1—pulsed electric field with energy input 1 kJ/kg, PEF_3—pulsed electric field with energy input 3 kJ/kg) or novel hybrid treatment (PEF+US, US+PEF), preceded by shock freezing (L) and vacuum freezing (L_VF). Data are presented as a mean from 3 repetitions with error bars as a standard deviation (SD), data with different letters differ significantly (Tukey’s HSD, p < 0.05).

Figure 5

Total carotenoids content (TCC) in lyophilized red bell peppers treaded with traditional treatment (BL_W—blanching in water, BL_S—steam blanching), novel single treatment (US—sonication for 30 min, PEF_1—pulsed electric field with energy input 1 kJ/kg, PEF_3—pulsed electric field with energy input 3 kJ/kg) or novel hybrid treatment (PEF+US, US+PEF), preceded by shock freezing (L) and vacuum freezing (L_VF). Data are presented as a mean from 3 repetitions with error bars as a standard deviation (SD), data with different letters differ significantly (Tukey’s HSD, p < 0.05).

Figure 6

Antioxidant activity expressed as EC50 (the effective concentration of the sample, which can decrease the concentration of 1,1-diphenyl-2-picrylhydrazyl radical—DPPH^• or 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonate) radical cation—ABTS^•+ by 50%) of lyophilized red bell peppers treaded with traditional treatment (BL_W—blanching in water, BL_S—steam blanching), novel single treatment (US—sonication for 30 min, PEF_1—pulsed electric field with energy input 1 kJ/kg, PEF_3—pulsed electric field with energy input 3 kJ/kg) or novel hybrid treatment (PEF+US, US+PEF), preceded by shock freezing (L) and vacuum freezing (L_VF). Data are presented as a mean from 3 repetitions with error bars as a standard deviation (SD), data with different letters lowercase and uppercase differ significantly for L and L_VF, respectively (Tukey’s HSD, p < 0.05).