Energy and Quality Aspects of Freeze-Drying Preceded by Traditional and Novel Pre-Treatment Methods as Exemplified by Red Bell Pepper

Abstract

Freeze-drying is one of the most expensive and most energy intensive processes applied in food technology. Therefore, there have been significant efforts to reduce the freeze-drying time and decrease its energy consumption. The aim of this work was to analyze the effect of pulsed electric field (PEF), ultrasound (US), and hybrid treatment (PEF-US) and compare them with the effect of blanching (BL) on the freeze-drying kinetics, energy consumption, greenhouse gasses emission, and physical quality of the product. The freeze-drying process was applied to red bell peppers after pretreatment operations. Results showed that application of BL, PEF, US, or PEF-US reduces freeze-drying time and decreases energy consumption. Among the tested methods, the combination of PEF performed at 1 kJ/kg and US was the most effective in reduction of greenhouse gas emission. BL samples exhibited the highest porosity, but from a statistical point of view, most of the PEF-US treated materials did not differ from it. The smallest color changes were noted for US pre-treated bell peppers (ΔE = 9.4), whereas BL, PEF, and PEF-US material was characterized by ΔE of 15.2–28.5. Performed research indicates the application of pre-treatment may improve the sustainability of freeze-drying process and quality of freeze-dried bell pepper.

Selected Quality Parameters of Air-Dried Apples Pretreated by High Pressure, Ultrasounds and Pulsed Electric Field—A Comparison Study

“…In the case of sonicated samples, slightly but significantly increased the water vapor adsorption capacity was observed, while for PEF-treated samples, hygroscopic properties did not significantly differ from untreated dried apples. These results are not in line with those of Rybak et al [59], who found that US and PEF employed before freezedrying resulted in an increase of about 42 to 48% in water-vapor adsorption ability. In turn, Zubernik et al [61] reported that air-dried apple adsorbed 2-3.5-times less water vapor when previously subjected to sonication in ethanol solution (up to 3 min), in comparison with dried untreated tissue.…”

“…The possible explanation for these better rehydration properties is that electroporation phenomena caused tissue changes and increased the number of pores. Similar effect was also noticed for PEF-treated red bell pepper with prior freeze-drying [59]. As Parniakov et al [60] stated, PEF application effects shrinkage reduction during the drying process, preserving capillary structures, and affecting rehydration properties.…”

The Influence of Different Pretreatment Methods on Color and Pigment Change in Beetroot Products

“…All samples were measured gravimetrically. About 0.6–1 g of the sample was placed in a dish and dried using the vacuum drying method (Memmert VO400, Schwabach, Germany) under a pressure of 10 mPa in 75 °C for 24 h and constant weight, according to information from Rybak et al [ 46 ] and the AOAC protocol [ 47 ]. Juices were placed on dried filter paper placed in a dish, which prevented the juice from burning.…”

Influence of Fermentation Beetroot Juice Process on the Physico-Chemical Properties of Spray Dried Powder

“…For dry matter determination, the gravimetric method was used. About 0.6–1 g of juice was placed in a dish with filter paper; for powders, 1 g was placed into a dish without filter paper, and dried by vacuum drying method (Memmert VO400, Schwabach, Germany) under the pressure of 10 mPa in 75 °C for 24 h until constant weight, according to information from [ 2 , 52 ]. Measurements were made in triplicate.…”