The impact of pulsed electric field treatment on selected bioactive compound content and color of plant tissue

Abstract

Abstract The aim of this study was to analyze the impact of pulsed electric field treatment on selected bioactive compound content and color of plant tissue. For this purpose apple and carrot tissues were treated by pulsed electric field (PEF) at 0, 1.85, 3, 5 kV/cm and 0, 10, 50 and 100 pulses which corresponded to the specific energy input of 0–80 kJ/kg. The electroporation efficiency was assessed by the means of electrical conductivity (EC) measurement. Immediately and 60 min after the PEF application the optical properties of both materials were measured and compared. Moreover, the total carotenoid content was determined in the case of carrot, whereas in the case of apple the free radical scavenging activity and the total polyphenol content was examined. The highest EC values were observed when 30 and 40 kJ/kg were delivered to the carrot and apple samples, respectively. The total color change (ΔE) of carrot tissue as a result of PEF treatment was smaller (ΔE0min = 1.64–5.51; ΔE60min = 1.33–3.91) than in the case of apple samples (ΔE0 = 0.48–7.20; ΔE60 = 1.25–21.87) which could be linked to the different chemical compositions of these raw materials. The application of PEF at 1.85 kV/cm regardless of the applied pulse number increased the total carotenoid content (TCC) up to 11.34%. In turn, the maximal increase of total polyphenolic content (TPC) and antioxidant activity (EC50) in the case of apple tissue was observed for samples treated by 10 pulses at 1.85 kV/cm. The utilization of 3 kV/cm decreased the TCC up to 25.33% whereas the application of PEF at 5 kV/cm and 100 pulses decreased the TPC and EC50 up to 35.93 and 32.95%, respectively. The research indicated that PEF can be used to enhance the extractability of bioactive compounds from plant tissue and to modify its color. Industrial relevance The paper discusses the impact of PEF treatment on bioactive compound concentration in apple and carrot tissues. Moreover, it deals with the color changes after the PEF treatment. Due to the fact, that pulsed electric field could be applied to the processes which depend on the heat and/or mass transfer such data should be considered of great importance. Firstly, the bioactive compounds (e.g., polyphenols, carotenoids) are very important regarding both their nutritional value and technological functionality (antioxidant properties, coloring agent production, etc.). Moreover, the PEF treatment efficiency depends on many different factors linked to the raw material properties and to the treatment protocol and conditions. This paper demonstrates that it is possible to improve the extractability of the carotenoids or polyphenols by PEF application. However, incorrectly selected PEF treatment parameters can result in the decrease of the bioactive compounds content in the solid material, as described and discussed more deeply in the paper. Color is one of the most important quality parameters. Especially that it is directly perceived by the consumers. As it can be read in the paper pulsed electric field treatment could be used to modify the color of plant tissue before any further processing. Such data is also important considering the minimal process food, which PEF could be involved in (e.g., special minimal process food for elderly people). In the presented experiment the color has been measured directly after the PEF application and after 60 min of it. Such information could be beneficial when considering the proper time interval between particular technological steps (when PEF is applied). i.e. the phenomena that the color change after PEF is accelerating (in the case of apple tissue) should be considered before other processing. The vast majority of publications present this kind of data regarding juices. In our study more complicated matrix is discussed. Thus, the paper, according to the best knowledge of authors, is the first which discusses the impact of PEF treatment on bioactive compound concentration of solid-like, plant material — such often used as a raw material in many different food applications (e.g., yogurt or smoothie ingredient) or further processed (e.g., dried or frizzed).