Evaluation of Anthocyanin Content, Color Stability, and Antibacterial Activity of Purple Corn Extract for Application in Colorimetric Sensors

¹ Department of Industrial Chemistry, Faculty of Applied Science, King Mongkut’s University of Technology North Bangkok, Wongsawang, Bangsue, 10800 Bangkok, Thailand
² The Petroleum and Petrochemical College, Chulalongkorn University, Phyathai Road, Pathumwan, 10330 Bangkok, Thailand
³ The Center of Excellence on Petrochemical and Materials Technology, Chulalongkorn University, Pathumwan, 10330 Bangkok, Thailand

^* Corresponding author: saowapa.t@sci.kmutnb.ac.th

Abstract

In recent years, increasing attention has been paid to plant-derived compounds as natural alternatives to synthetic chemicals in food, cosmetic, and healthcare applications. Purple corn (Zea mays L.) has attracted considerable interest due to its high anthocyanin content, which not only imparts a vibrant color but also exhibits antioxidant and antibacterial properties. This study aimed to evaluate the multifunctional potential of purple corn extract as both a natural pH indicator and an antibacterial agent. Anthocyanins were extracted from purple corn and analyzed using UV-Visible spectrophotometry. The extracts were tested in buffer solutions across a pH range of 2.0–12.0. The extracts color exhibited distinct transitions: reddish-purple under acidic conditions (pH 2.0–6.0), grayish-purple under neutral to slightly basic conditions (pH 7.0–9.0), and bluish-green under alkaline conditions (pH 10.0–12.0). Despite these variations, the maximum absorbance was observed at 520 nm, particularly at pH 1.0 and 4.5, where measurements were conducted for anthocyanin. FTIR spectroscopy confirmed the presence of functional groups including hydroxyl, alkyl, alkene, and aromatic ring, which are characteristic of phenolic and anthocyanin compounds. Quantitative analysis showed that total anthocyanin content peaked at 177.10 ± 24.68 mg/L, corresponding to increased extract concentrations. Antibacterial activity was assessed against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) using serial dilution method. The extract demonstrated bactericidal properties at concentrations ranging from 7.0–14.0 %w/v. Overall, the study highlights the potential of purple corn extract as a natural, eco-friendly pH-sensitive dye with significant antibacterial activity, suitable for application in food packaging, cosmetics, and biomedical fields.