Isolation and Identification of Polyphenols From Fresh Sweet Sorghum Stems and Their Antibacterial Mechanism Against Foodborne Pathogens

Abstract

As a C4 energy crop widely planted all over the world, sweet sorghum is mainly used in sugar making and brewing. Fresh sweet sorghum stalks contain many natural ingredients that have antioxidant properties and can significantly inhibit the growth of foodborne pathogens. In this study, the polyphenols in sweet sorghum were extracted by acid ethanol and ion precipitation, and the types of polyphenols were determined by HPLC-MS. The polyphenol content in fresh sweet sorghum stalks was 5.77 mg/g after process optimization with 18 types of phenolic acids identified. The extract had a total antioxidant capacity of 9.4 μmol Trolox/mL. Polyphenol extract of sweet sorghum displayed antibacterial activity against Staphylococcus aureus, Escherichia coli, Listeria spp., and Salmonella spp. The extract increased the conductivity of cell suspensions by destroying the membrane structure, resulting in leakage of cell electrolytes. Changes in bacterial morphology and internal structure were indicated. The data describe an optimized process to extract polyphenols from sweet sorghum stalks and the methodology to identify the major components within the extract. The data provide a novel option for the comprehensive utilization of fresh sweet sorghum stalks.

Polyphenolic compounds in the combat of foodborne infections – An update on recent evidence

“…Chen et al. [ 18 ] investigated the potential value of polyphenolic extract from fresh sorghum stalks as a natural anti-oxidant and anti-bacterial agent. Polyphenols were extracted from sweet sorghum and further identified.…”

“…The conductivity of the bacterial culture medium increased significantly within 1 h, but hardly changed between 1 and 7 h, suggesting that polyphenols affect the integrity of bacterial membranes and cause leakage of cell electrolytes. In conclusion, sweet sorghum polyphenolic extract has been shown to be rich in phenolic compounds and to exert both, strong anti-oxidant capacity and anti-bacterial activity [ 18 ].…”

“…It was found that the TPC expressed as gallic acid equivalents (GAE) was highest in the acidified methanolic extract (AME) at 26.8 mg g −1 , although the total phenolic mass fraction expressed as GAE on a dry matter (DM) basis was only 7.4 ± 0.7 mg g −1 . The anti-bacterial activity against S. aureus NCDC 109 and E. coli ATCC 5922 was measured by agar well diffusion assay, in contrast to the previous study [ 18 ] which used flow cytometry to determine the anti-bacterial efficacy against the selected pathogens. The concentration of all added extracts was kept uniformly at 12 mg mL −1 .…”

“…Complete inhibition of S. aureus was observed at a MIC of 1.1 mg mL −1 , while E. coli was inhibited only at a concentration of 2.2 mg mL −1 [ 19 ]. The authors of both studies [ 18 , 19 ] concluded that the polyphenolic extracts from sorghum bran and stalks were significantly more effective against Gram-positive than against Gram-negative bacteria, which may be due to the fact that the polyphenols disrupt the integrity of the bacterial cell membrane structure [ 18 , 19 ].…”

Honokiol inhibits Botryosphaeria dothidea, the causal pathogen of kiwifruit soft rot, by targeting membrane lipid biosynthesis

“…The relative conductivity was calculated using the formula , where C t represents the treatment conductivity, C t0 represents the control conductivity, and C t1 represents the lethal treatment conductivity. Referring to the method of Chen et al ., 17 the leakage of nucleic acids, proteins, and potassium (K) ions at different concentrations of honokiol (0, 10, 50, and 90 μg mL −1 ) were determined at 30, 60, 120, 240, and 360 min, respectively.…”