Effects of pulsed electric field and subcritical water on the extraction of valuable compounds from carrot leaves

Abstract

In New Zealand and many other countries, carrot leaves are considered an agricultural residue. However, carrot leaves are rich in bioactive compounds such as polyphenols that are essential micronutrients for human wellbeing. This study investigates the extraction of polyphenols and luteolin (flavonoid) from carrot leaves using Subcritical water (SCW) and Pulsed Electric Field (PEF) extraction methods. SCW has the ability to behave as low polar solvent to enhance extraction of organic compounds while PEF has the ability to disintegrate the cells increasing diffusion of bioactives from the cellular matrix. SCW was investigated at different temperatures (110 – 230 °C), times (0 - 114 min) and solid liquid ratios (15 and 35 g/L). Whereas PEF was studied while varying the electric field strength (5- 25 kV/cm) and treatment time (0 –710 μs). The effect of the parameters of each method were analysed and also compared with conventional hot water extraction (HWE) and Soxhlet extraction (SE) methods for particles of less than 100 μm. Accordingly, it was revealed that TPC and luteolin content obtained with SE was16.45 GAE mg/g dw and 0.336 mg/g dw, respectively. Moreover, extraction of TPC from carrot leaf using SCWE has an increasing trend with temperature and resulted in a value of 42.83 GAE mg/g dw at 210 °C/ 113.5 min. However, luteolin content using SCWE behaved differently where increase of temperature was inversely affected. HWE studies revealed the presence of an optimum luteolin content (0.768 mg/g dw) at 120 °C for 10 min while further increase in time resulted in lower values. On the other hand, PEFE enhanced the extraction of TPC and luteolin with the increase of Electric Field Strength (EFS) and treatment time. PEF at 15 kV/cm, 500 Hz 710 μs resulted in TPC value of 33.27 GAE mg/g dw whereas PEF conditions of 25 kV/cm, 500 Hz for 551 μs gave a luteolin content of 0.344 mg/g dw. Further, it was shown that TPC and luteolin extracted from carrot leaves using these technologies are higher than that from other agricultural residues including onion or mango peel, grape pomace and peanut hulls. In conclusion, SCW and PEF are two technologies that have shown enhanced extraction abilities than conventional technologies and carrot leaves could be a potential source for extraction of polyphenol and luteolin in a NZ context. Moreover it is recommended to do further studies on finding the optimum parameters and also antioxidant properties of carrot extract to make the study more comprehensive and of commercial value.