Utilization of quercetin flavonoid compounds in onion (Allium cepa L.) as an inhibitor of SARS-CoV-2 spike protein against ACE2 receptors

The world is facing the spread of a disease called COVID-19 which is referred to as a pandemic. The main problem that causes COVID-19 is the coronavirus, this virus will attack the respiratory system. The coronavirus that is spreading is SARS-CoV-2. SARS-CoV-2 is a virus that belongs to the Betacoronavirus family, which is similar to SARS-CoV and MERS-CoV. Inside the host cell, the spike envelope (S) protein of SARS-CoV-2 can interact with the Angiotensin-converting Enzyme 2 (ACE2) receptor. The penetration of SARS-CoV-2 into the human body can be inhibited by the flavonoid compound quercetin in onion. Onion (Allium cepa L.) contain quercetin compounds with very broad pharmacological effects. The quercetin flavonoid compound in onion was incubated with the COVID-19 vaccine as a representation of SARS-CoV-2. This study aimed to determine the inhibitory activity of Spike protein by quercetin against ACE2 receptors. This study used spectroflourometric analysis to determine the inhibitory activity of Spike protein by quercetin against the ACE2 receptor. Before reaching the spectroflourometric analysis stage, the onion’s maceration stage was carried out with 98% methanol as solvent to obtain flavonoid extract. Furthermore, the determination of the quercetin content was carried out by spectrophotometric analysis using a UV-Vis spectrophotometer. The measurement of quercetin levels used a standard solution of quercetin with a concentration series of 6, 8, 10, 12, and 14 ppm. The absorbance was determined by the measurement results on a UV-Vis spectrophotometer. A standard curve was made to obtain a linear equation that will be used to determine the percent content of quercetin in the sample. Through spectrofluorometric analysis,. This analysis uses excitation wavelengths of 340 nm and 490 nm emission waves using 9.15 nm bandwidth to prevent overlapping. The results of this analysis can be proven by the relative fluorescent units (RFU) of protein S in SARS-CoV-2 which will be higher than that of RFU protein S that has been incubated with quercetin to form a protein complex. This is an indicator of the successful inhibition of spike protein activity by quercetin.