Abstract
Exploring new sources of polyphenols with biological activities that work against human diseases is the target of natural product studies. This study determined the polyphenol composition of the bark of Malus species M. baccata var. gracilis (Rehder) T.C.Ku and M. toringoides (Rehder) Hughes, using high-performance liquid chromatography with a diode-array detector (HPLC-DAD) analysis. The antiproliferative, cytotoxic, antioxidant and antimicrobial applications of these extracts, as well as the identified phenol, were studied. The HPLC-DAD analysis confirmed three polyphenols in the extracts out of the 21 screened compounds: protocatechuic acid, gallic acid, and catechin. The major constituents in M. baccata and M. toringoides were protocatechuic acid, at 3.16 and 7.15 mg 100 g−1 dry weight (DW), respectively, and catechin, at 5.55 and 6.80 mg 100 g−1 DW, respectively. M. baccata and M. toringoides bark extracts showed antioxidant activities using 2,2-diphenyl-1-picrylhydrazyl (DPPH), β-carotene bleaching, and ferric-reducing antioxidant power (FRAP) assays, which were attributed to the dominance of protocatechuic acid. The highest antiproliferative and cytotoxic effects were against Jurkat cells. Against MCF-7 and Hela cells, there was necrotic cell accumulation in the early apoptotic as well as the late apoptotic phase. The bark extracts showed noticeable antibacterial effects against Listeria monocytogenes, Bacillus cereus, and Escherichia coli. Protocatechuic acid showed comparable results to bark extracts. There were antifungal effects against Aspergillus ochraceus, A. niger, and Candida albicans, and the activities were higher than the commercial reagent. M. baccata and M. toringoides could be considered as a new source of phenolic acids, including protocatechuic acid with anticancer, antibacterial antifungal, and antioxidant-promising effects.
Highlights
The least significance difference (LSD) was determined using SPSS software. This is the first report investigating the phenolic profile of M. baccata bark
This is the first report on the antiproliferative, cytotoxic, antioxidant, antibacterial, and antifungal effects of M. baccata and M. toringoides bark extracts
Out of the 21 screened, the high-performance liquid chromatograph (HPLC) study revealed the availability of three different polyphenols: protocatechuic acid, gallic acid, and catechin
Summary
Polyphenol groups (e.g., phenolic acids) are important secondary plant metabolites that contain a large group of compounds with extremely important pharmacological applications.Processes 2020, 8, 283; doi:10.3390/pr8030283 www.mdpi.com/journal/processesThey are widely used for the control of neurodegenerative diseases [1], cancers [2,3,4,5], inflammation cardiovascular health [6,7], type 2 diabetes [8], obesity [9], insect control [10], antibacterial agents [11,12], antioxidants [13], food processing, and the production of functional foods [14]. Polyphenol groups (e.g., phenolic acids) are important secondary plant metabolites that contain a large group of compounds with extremely important pharmacological applications. They are widely used for the control of neurodegenerative diseases [1], cancers [2,3,4,5], inflammation cardiovascular health [6,7], type 2 diabetes [8], obesity [9], insect control [10], antibacterial agents [11,12], antioxidants [13], food processing, and the production of functional foods [14]. Polyphenols are abundant in plants, and specific phenols have strong anticancer activities [15]. Phenolic acids are an important group of phenols as they act as antioxidant agents and have, for example, anticancer and antimicrobial properties [3,23,24,25,26,27]
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