A survey on anthocyanins stability extracted from red cabbage with high voltage electrical discharge and pulsed electric fields using natural deep eutectic solvents

Abstract

Abstract Introduction and objective Red cabbage is a functional food rich in bioactive compounds such as anthocyanins, polyphenols, flavonoids, vitamins, and minerals. It is considered an anthocyanin-rich vegetable with more than 30 anthocyanin structures. Red cabbage anthocyanins have health-promoting effects, including hepatoprotective, cardioprotective, renoprotective, and cholesterol-lowering activities. The extraction of plant materials is the best method for obtaining bioactive phytonutrients, which is usually done using two classical and modern methods. In extraction methods, selecting an appropriate solvent compatible with the target chemical is crucial. Among various extraction solvents, natural deep eutectic solvents (NADES) are preferred over organic solvents due to their low toxicity, suitable stability, and low volatility and vapor pressure. In addition to the type of solvent, implementing the extraction method using modern methods to reduce the extraction time and preserve the original structure of the food is another goal of developing extraction methods. This research aims to optimize the extraction of anthocyanins and polyphenols from red cabbage using pulsed electric field (PEF) and high voltage electrical discharge (HVED) pretreatments, along with solid-liquid extraction with NADES. Additionally, the study intends to examine the antioxidant properties, thermal and storage stability of the resulting extract.

Materials and methods In the first phase of the study, red cabbage extract was extracted using five different NADES (glucose, choline chloride and citric acid as hydrogen bond acceptors, lactic acid, oxalic acid, glycerol and ethylene glycol as hydrogen bond donors) and the best one was selected based on the total anthocyanin content. Then, the best extraction conditions with NADES were obtained based on the parameters of water and extraction solvent ratio, extraction solvent volume, stirring type, stirring time and temperature and based on the total anthocyanin content. Total polyphenol content, antioxidant property, thermal and storage stability were measured for the samples. In the second phase of the study, to investigate the effect of PEF and HVED pretreatments on extraction efficiency, two parameters of electrical pulse number and voltage were optimized based on the total anthocyanin content. In the final stage, the extraction efficiency of bioactive compounds in samples pretreated with PEF and HVED and solid-liquid extraction with NADES was measured based on the total anthocyanin content. Finally, the tests performed in the first phase were repeated. Results The highest anthocyanin, polyphenol, and antioxidant content was obtained during extraction by NADES of choline chloride: oxalic acid and water with a volume ratio of 1:3, in a volume of 8 mL, under ultrasonic agitation at 60°C for 120 min. Pretreatment with HVED with 17 electrical pulses and 100 V voltage yielded the highest total anthocyanin content compared to pretreatment with PEF with 222 electrical pulses and 100 V voltage. Pretreatment with HVED and NADES extraction yielded the highest anthocyanin, polyphenol, and antioxidant content. With increasing temperature from 60 to 90°C, the anthocyanin content decreased by 29.18%. Also, the samples were 1.8 times more stable during 60 days of storage at refrigerated temperature than 60 days of storage at ambient temperature. Conclusion Overall, the findings indicated that red cabbage extract obtained using NADES as the extraction solvent and HVED as an enhanced, green, and non-thermal extraction method resulted in improved yield of bioactive compounds, antioxidant properties, as well as thermal stability and shelf life of the extracts. Keywords: High voltage electrical discharge, Pulsed electric field, Anthocyanins, Natural deep eutectic solvents, Extraction