Effect of pulsed electric fields pretreatment on juice expression and quality of chicory

Highlights

• Pulsed electric fields (PEF)-assisted pressing (P) for extraction of chicory juice was studied.

• Juice expression yield and pressing kinetic rate were enhanced after PEF pretreatment.

• PEF-P and P-PEF-P modes resulted in an increase of 9% higher than P mode.

• Cake mixing and smaller cossettes favored to extraction of chicory juice.

• PEF-P treated smaller chicory cossettes has lower turbidity and higher inulin content.

Abstract

This study investigates the effects of pulsed electric fields (PEF) and freeze thawing (FT) pretreatments on juice yield and quality from chicory by pressing (P). The four different modes (P, PEF-P, FT-P and P-PEF-P) were compared. The effects of pressing mode, PEF conditions, cossettes size on the juice yield, and total soluble matter (°Bx), conductivity, pH, turbidity in expressed juices were evaluated. The pressing kinetics for different modes were also investigated. For studied modes, the highest juice yield and kinetic rate were obtained for FT-P mode, the lowest was P mode. PEF-P and P-PEF-P modes resulted in the same juice yield, an increase of 9% higher than P mode. A 600 V/cm of intensity and 0.2 s duration were optimal PEF conditions with desired energy consumption. Moreover, cake mixing and relative small-sized cossettes allowed improving juice yield assisted by PEF-P mode. Quality analysis showed that expressed juice from smaller cossettes by PEF-P mode has lower turbidity and higher inulin content.

Introduction

Chicory is an agricultural residue whose roots contain a high inulin content (≈ 40%) (Chinyelu, Karabo, & Chilaka, 2017; Perovi, Aponjac, Koji, Krulj, & Ili, 2020). Inulin is a popular polysaccharide-based nutraceutical, and it has been associated in fat replacement, calorie reduction and health keeping (Chaito, Judprasong, & Puwastien, 2016; Maumela, Rensburg, Chimphango, & Grgens, 2019). Currently, chicory roots are grown commercially for inulin production, besides its high content of inulin, it contains regular root and good tolerance to cold (Zhu et al., 2016).

The industrial production of inulin from chicory consists mainly on two steps: extraction and purification (Zhu et al., 2016). The extraction of juice is a crucial step influencing all the transformation process for production of inulin. Because large amount of inulin existed in chicory root can transfer into the juice during the process of extraction. Zhu et al. (Zhu et al., 2013) have also reported that the extracted chicory juice contain 9–11% of inulin and 8.5–12% soluble matter content (°Bx). Furthermore, they have demonstrated a good linear correlation between the inulin content and the value of °Bx in the extracted chicory juice. The value of °Bx in extracted juice can be roughly considered as the content of inulin during the extraction process (Zhu, Bals, Grimi, & Vorobiev, 2012).

Traditionally, chicory roots are firstly cut into homogeneous slices, then inulin-containing juice is produced through diffusion of slices using water at 70–80 °C during 1–2 h (Zhu et al., 2012). This thermal diffusion leads to the breakage of cellular membranes and tissue denaturation, making intensive inulin transfer into the chicory juice. However, high temperature and prolonged duration also leads to impurities release into the extracted juice resulting in complicated juice purification. Besides to the extraction by solvent (diffusion), extraction by pressure (pressing) is another important technique widely used for inulin-containing juice production (Yu, Gouyo, Grimi, Bals, & Vorobiev, 2016). Such treatment can damage cell walls of chicory tissues (Grimi, Praporscic, Lebovka, & Vorobiev, 2007). The intracellular juice, which is initially bounded inside cellular chicory tissue, can be expressed after the cell rupture. Since pressing is a kind of extraction technology without solvent usage, it may be a promising technology to produce the undiluted juice and the high nutritional valued pulp. However, the usual pressing equipment produces rather turbid and impure juices, and their further clarification is required (Grimi et al., 2007).

In this line, alternative extraction techniques assisted by enzymes (Sherpa, 2011; Stein-Chisholm, Finley, Losso, & Beaulieu, 2017), freezing thawing (Nadulski et al., 2016; Nadulski, Grochowicz, Sobczak, & Panasiewicz, 2015), ultrasound-assisted extraction (Lin et al., 2019), or pulsed electric fields (PEF) (Grimi, Mamouni, Lebovka, Vorobiev, & Vaxelaire, 2011; Grimi et al., 2007; El Kantar et al., 2018) are also developed. Several studies have shown the positive effect of PEF treatment on both juice yield and juice quality (Grimi, Lebovka, Vorobiev, & Vaxelaire, 2009; El Kantar et al., 2018; Loginova, Shynkaryk, Lebovka, & Vorobiev, 2010; Mhemdi, Bals, Grimi, & Vorobiev, 2012). These authors confirmed the juice extracted alternatively, with PEF treatment, contain less impurity than juice obtained by using conventional methods. PEF causes a temporary or complete electroporation of cell membranes increasing the membrane permeability and facilitating the passage of intracellular components to the surrounding juice (Yu et al., 2016). Especially in our previously study, the PEF has been applied to assist diffusion of inulin from chicory roots at moderate temperature (Zhu et al., 2012). A 600 V/cm of PEF intensity and a 10 ms of PEF duration were evidenced to decrease diffusion temperature from 75 °C to 60 °C with comparable inulin juice yield and purity. Additionally, the effects of PEF assisted pressing on apple juice yield, turbidity and phenolic content was investigated by (Grimi et al., 2011). In their study, efficiency of the PEF application for acceleration of the juice extraction and improvement in qualitative characteristics of the PEF-expressed juices was demonstrated.

The extraction efficiency of juice from different sizes of chicory cossettes can be improved by using PEF assisted pressing protocols. However, to the best of our knowledge, such studies on chicory roots are scarce at the present. The main aim of this work was to study the impact of different individual and combined PEF and pressing protocols on extraction efficiency of juice from different sizes of chicory cossettes. Freeze thawing pretreatment was used as a maximal conference due to its complete cell denaturation. The data were compared for four different protocols (pressing, PEF-pressing, freeze thawing-pressing and pressing-PEF-pressing). The pressing kinetics and juice quality (total soluble matter, conductivity, pH and turbidity) were also investigated in this work. Attention was also focused on the effects of electrical parameters (electric field intensity, PEF treatment duration) on the ratio of juice yield to energy consumption.