Effect of cold plasma and ultrasound pretreatments on the chemical compositions and antioxidant properties of the hydroalcoholic extract of Quince leaves

Introduction:
Several studies have showed that quince tree is a good and low-cost natural source of phenolic acids and flavonoids, which are potent antioxidants. These compounds could provide a chemical basis to some health benefits claimed for quince leaf and fruit in folk medicine. It is well known that quince fruit shows antioxidant effects which result from the presence of a number of polyphenolic substances, e.g. flavonoids quercetin, rutin, kaempferol etc. and also from increased levels of vitamin C. Different parts of quince (fruit, seeds and leaves) have been used as traditional remedies for cardiovascular diseases, cough, bronchitis, nausea, fever, diarrhea, constipation, hemorrhoids, diabetes, and hypertension. Total phenolic content of quince leaves varied from 4.9 to 16.5 g/kg dry matter. Moreover, organic acids composition of quince leaf was investigated; quinic acid (72.2%) and citric acid (13.6%) were the major acidic components (Oliveira et al., 2008). However, the obtained results showed higher total concentrations of phenolics in quince leaves than in pulps, peels and seeds (Oliveira et al., 2008). Costa et al. (2009) studied the methanolic extract from quince leaf and reported 5-Ocaffeoylquinic acid as the major phenolic compound. Antibacterial effects of aqueous and organic quince leaf extracts on gram-positive and gram-negative bacteria were also investigated. The obtained results had indicated that ethanolic quince leaf extract had the greatest effect on gram-negative and gram- positive bacteria. Also, the aqueous extract showed the lowest effect on tested bacteria (Semnani et al., 2017). During the last few decades, many researches have been carried out to identify suitable methods for extraction with high efficiency and environmental friendliness. Moreover, nowadays, special attention has been paid to plants that are a rich source of natural antioxidants and bioactive properties, one of these plants is the quince leaves. Due to quince leaf extract is rich of a phenolic and antioxidant compounds, it can be used as a natural antioxidant and be a good substitute for synthetic antioxidants.
Material & methods: In this research, the aim was to investigate the effect of cold plasma (CP) and ultrasound (US) pretreatments on the chemical compositions and antioxidant properties of the hydroalcoholic extract of the quince leaves. In order to improve the performance of quince leaves, cold plasma pretreatment (5, 10 and 15 min) and ultrasonication (20 and 30 min) was used at different times, separately. Three samples of crushed quince leaves were subjected to CP pretreatment with a pressure of 500 mTorr, a voltage of 2.1 kV and a current of 90 mA at different times of 5, 10, and 15 minutes. Also, three other samples of grounded leaves that were mixed with 80% ethanol were subjected to probed US pretreatment with a power of 300 w and a frequency of 24 kHz at different times of 10, 20, and 30 minutes. In this research, the samples of the quince leaves were pretreated with CP and US, and after extracting the leaves extracts and its concentration, the amount of total phenolic compounds, antioxidant activity, total chlorophyll, carotenoid and color indices of the treated and control samples were investigated.
Results and discussion: The obtained results showed that both CP and US processes caused a significant increase (P<0.05) in the amounts of phenolic and antioxidant compositions, total chlorophyll and carotenoid. In agreement with this study, Bao et al. (2020a) reported the effect of CP treatment to improve the extraction of phenolic and antioxidant compounds from tomato pulp; their results showed that CP treatment increased the antioxidants of tomato pulp extract. The radicals generated by CP disintegrate the cellular tissue and plant cell walls which reduce the space barrier for molecules to transport, and increase the release of free phenolics in the cell vacuole and cytoplasm into the solvent. Active plasma species have also the potential to break covalent bonds, thus releasing phenolic compounds that covalently bind to cell wall polysaccharides, which leads to higher extraction efficiencies. CP treatment also facilitates the extraction of free phenolic antioxidants in the solvent (Bao et al. 2020b). Ultrasonic-assisted extraction is one of the most inexpensive, rapid, simple and efficient techniques compared with conventional extraction, and has been applied to extract bioactive compounds from different materials owing to its high reproducibility at shorter time, simplified manipulation, significant reduction in solvent consumption and temperature, and lower energy input (Liu et al., 2013). The color indices L*, a*, b* decreased significantly (P<0.05) compared to the control as a result of cold plasma pretreatment, but had not differ significantly compared to the control due to ultrasound pretreatment. According to this study,Sanai et al. (1398) reported that the effect of cold plasma (gas type) on any of the curcuma longa color indices was not significant, while with increasing plasma duration the mean of all three color indices decreased. There were significant differences (P<0.05) between 15 and 25 minutes.
Conclusion: In overall, based on the results of this research, cold plasma pretreatment can be a better and more efficient method than ultrasound-assisted to extract bioactive compounds and replacement of conventional thermal methods. Also, this present study shows that quince leaves are promising sources of valuable compounds and may be used to produce functional foods as well as for medical purposes.