foods Article The Quality of Red Bell Pepper Subjected to Freeze-Drying Preceded by Traditional and Novel Pretreatment Katarzyna Rybak 1, * , Artur Wiktor 1 , Dorota Witrowa-Rajchert 1 , Oleksii Parniakov 2 and Malgorzata Nowacka 1   Citation: Rybak, K.; Wiktor, A.; Witrowa-Rajchert, D.; Parniakov, O.; Nowacka, M. The Quality of Red Bell Pepper Subjected to Freeze-Drying Preceded by Traditional and Novel Pretreatment. Foods 2021, 10, 226. https://doi.org/10.3390/foods 10020226 Received: 1 December 2020 Accepted: 19 January 2021 Published: 22 January 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences—SGGW, 02-787 Warsaw, Poland; artur_wiktor@sggw.edu.pl (A.W.); dorota_witrowa_rajchert@sggw.edu.pl (D.W.-R.); malgorzata_nowacka@sggw.edu.pl (M.N.) 2 Elea Vertriebs-und Vermarktungsgesellschaft mbH, Prof. von Klitzing Str. 9, 49610 Quakenbrück, Germany; o.parniakov@elea-technology.com * Correspondence: katarzyna_rybak@sggw.edu.pl; Tel.: +48-22-593-7574 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: red bell pepper; blanching; pulsed electric field; ultrasound; hybrid treatment; shock freezing; vacuum freezing; freeze-drying 1. Introduction Red bell pepper is a very popular vegetable, which can be eaten raw, cooked, as a pickle, paste, or sauce. As a result of its high rate of perishability, it is processed in order to extend its shelf life. In the food industry, red bell pepper is usually added in dried form as a spice or flavor ingredient [1,2]. Furthermore, bell pepper and its extracted compounds can be used as a coloring agent for food and cosmetics [3,4], pharmaceuticals, and nutraceuticals [5]. However, nowadays, dried fruits and vegetables consumed as a snack are becoming highly popular [6–8]. Drying is the oldest method of food preservation and one of the most frequently used processing techniques that enable fruits and vegetable surplus to be handled during its season [9,10]. The most often utilized method of drying is convective drying, but the quality of a product usually is not satisfactory due to the loss of thermolabile compounds and structural changes, which occur during an elongated exposure of the plant tissue to high temperatures [7,11,12]. Furthermore, drying is considered to be one of the most energy-consuming processes due to the change in the state of water from liquid to gas phase. It is estimated that drying uses between 12 and 20% of the total energy consumed by the food industry [13]. To maintain the high quality of the dried fruits and vegetables freeze-drying (lyophilization) process can be applied. This process is known as the best method for preserving the nutritional value, color, bioactive compounds as well as structure of raw material due to low temperature, reduced pressure, and lack of air during the process [4,8,14]. However, freeze-drying is a very long and expensive process. Furthermore, Foods 2021, 10, 226. https://doi.org/10.3390/foods10020226 https://www.mdpi.com/journal/foods