Pulsed electric field assisted sunflower oil pilot production: Impact on oil yield, extraction kinetics and chemical parameters

Highlights

• The effect of PEF on oil extraction efficiency was investigated based on pilot mill with continuous-flow material treatment

• Porous volume parameter was firstly discussed during extraction kinetic analysis

• Extraction parameters will be useful when calculating the economic efficiency of PEF application on an industrial scale

Abstract

Sunflower oil pilot-production based on local raw materials assisted by pulsed electric field (PEF), which is produced in terms of oil yield, extraction kinetics and chemical parameters on pilot scale mill with continuous-flow material treatment developed in this work. PEF treatment with electric field strength 7 kV/cm and energy consumption of 6.1 kJ/kg on the sunflower seed increased the value of extraction yield by 2.3%, with respect to a control one. Extraction parameters obtained by pulsed electric field treatment showed that diffusion coefficient, micropore volume, and disintegration index were significantly higher than control ones (on 55.5%, 32.2% and 43% respectively). Furthermore, the use of PEF treatment had minor effects on the main chemical characteristics (acid and peroxide value etc.) and color parameters of the sunflower oil. On the basis of obtained results, it can be concluded that PEF could be a high potential industrial technology to improve enriched in human-health-related compounds of sunflower oil.

Practical applications

The obtained results are relevant for specialists using PEF technologies and developing PEF equipment. The data will also be in demand when calculating the economic efficiency of PEF application on an industrial scale.

Introduction

In comparison with other vegetable oils in recent years, the world production of sunflower oil has increased significantly (Luciana & Petrella, 2014). Due to high nutritional value and valuable chemical composition, sunflower oil is largely used for human consumption both in Russia and in many European countries, India and Turkey and considered to be a great source of proteins and lipids (Ramadan, 2013). Thus, scientific research for a novel sunflower oil production processes that could produce a high yield with high quality products and minimize environment impacts is of great importance (Temelli, 2009).

The main industrial vegetable oil production method is solid-liquid extraction with countercurrent immersion and multi-stage countercurrent irrigation methods (Tasan, Gecgel, & Demirci, 2011). The most industrially used solvent for oil extraction from oil-containing seeds is hydrocarbon solvent - hexane (Topallar, 2000). Solvents as subcritical CO₂, subcritical propane, bio-ethanol, and isopropanol have been proposed as alternative solvents to replace hydrocarbon hexane in oil extraction processing of different oil crops (Nimet et al., 2011; Likozar & Levec, 2014; Baümler, Carrin, & Carelli, 2017; Toda, Sawada, & Rodrigues, 2016). With regard to health and safety, alternative solvents such as ethanol and bio-ethanol show a lower risk than hydrocarbons and unlimitedly dissolve the oils close to boiling temperature, but drastically affected by moisture content.

There are many different ways and methods of extraction process intensification both at the stage of raw material preparation and during the extraction process. Nowadays, the most widely used solution for extraction improvement is to increase temperature level and/or solvents amount. However, increasing temperature and/or solvents amount has a negative effect on the oil quality, thus such methods are limited to sunflower oil production (Bakhshabadi et al., 2017; La et al., 2016). One of the ways to improve oil production efficiency is to apply novel physical methods with efficient solvent.

As a novel industry scale technology pulsed electric field has already been mentioned as an innovative solution for electroporation of oil cells (Eing, Bonnet, Pacher, Puchta, & Frey, 2009; Kotnik et al., 2015) during extraction process. The oil cell membrane can be charged sufficiently using rectangular bipolar or monopolar electrical pulses (millisecond or even microsecond pulse width) to cause a rearrangement of the membrane. The main result of PEF treatment is in micro and nanopores formation (Boussetta, Grimi, & Vorobiev, 2015) with low temperature effects, which is quite important for heat-sensitive materials. According to a sunflower kernel structure shown in Fig. 1, the arrangement of cells has orderly character, cells of the cylindrical extended form, are characterized by distinctly expressed lipidic spherosome and proteinaceous globule diffuse located in a volume of cells and united by a cytoplasmic matrix. For such dielectric material, PEF can be applied only with presoaking and locally concentrated electrically pores can be obtained (Shorstkii, Zherlicin, & Li, 2019).

Crushing and roasting are industrial technological steps assisting to release the oil from solid seeds matrix, but not totally. PEF pre-treatment assist in releasing the oil from lipo-vacuoles of mesocarp cells that have not been disrupted. According to Clef and Kemper (2015) >40% sunflower spherosomes remain undestroyed after crushing and roasting. This limits a residual oil yield in a meal. In a recent study on oil crops (Bakhshabadi, Mirzaei, Ghodsvali, Jafari, & Ziaiifar, 2018) it has been discovered that PEF can damage the structure of oil cells during the process, as well as facilitate the oil extraction without any temperature effects before extraction. Pulsed electric field technology due to the fact that very rapid pulses are applied requires low energy consumption (<10 kJ/kg, see Table 1). An overview of pulsed electric field treatment data of oil crops application for the release of oil yield is presented in Table 1.

From the oil yields data presented in Table 1 and obtained from a wide range of experimental approaches, it can be seen that high oil yields depend directly on specific energy consumption (5–240 kJ/kg). Numerous data obtained by various authors show that an additional pre-treatment destruction of their integrity is a necessary operation for effective oil extraction from oilseeds (Sarkis et al., 2015; Perrier et al., 2017).

Extraction kinetics parameters are very important for PEF-treatment effect analysis, modeling and enhancing extraction processes. The solid-liquid oil extraction process can be considered by two main mechanisms. The first one is washing process, which starts immediately after material and solvent contact and describes the extraction of the oil on the seed surface. The second one is a long time diffusion process. Depending on the amount of intact and damaged cells that remain after pre-extraction preparation steps, such as: crashing and heat-moisture (roasting) treatment, the diffusion process can take place in one or two phases. Thus, raw material preparation (pre-treatment) for cell membrane breakage and pore volume increasing plays one of the most important roles. A mathematical model with two mechanisms has been applied in current study for oil extraction processes from sunflower oil seeds. Another interesting dual-porosity model with parameter - pore surface fraction changes described the behavior of electroporated tissue (Mahnič-Kalamiza & Vorobiev, 2014).

Mass transport is also of significance in light of the intended purpose of PEF treatment application. If PEF treatment is applied to facilitate solute extraction by diffusion (increasing rate, yield, etc.) or to change the permeability of the cell membrane and overall oil material for improving the oil yield, the mass transport processes (both of solutes and liquid) are of primary importance.

In order to expand the scope of application of the PEF treatment on an industrial scale, a clear understanding of the changes in the internal material structure, pore volume, processing efficiency, and extraction kinetics is necessary. The purpose of this work was to determine the efficiency of continuously-flow PEF pretreatment in the oil extraction process from sunflower seeds with an assessment of the extraction kinetic parameters.