Characterization of time-series fluorescence properties of bean sprouts during storage using excitation emission matrix and fluorescence imaging

Abstract

Soybean (Glycine max (L.) Merr.) and mung bean (Vigna radiata L.) are popular varieties of bean sprouts, which are used in various Asian cuisines. The freshness of bean sprouts reduces at fast rate during storage. Hence, determining index of monitoring the state of sprouts is required to prevent unnecessary food loss, which is also linked to economical loss. The aim of this study is to reveal fluorescence characteristic of bean sprouts and investigate its potentiality for tracking the freshness state of bean sprouts. The fluorescence spectroscopy and imaging were used. For fresh bean sprouts, the Excitation–Emission Matrix (EEM) showed two fluorescence regions: Excitation (Ex) 270–300 nm with Emission (Em) 300–400 nm and Ex 300–350 nm with Em 400–450 nm, which are suspected to be amino acids and vitamins, respectively. When browning process started, the new fluorescence region occurred at Ex 400–450 nm with Em 450–550 nm. Consistent with EEM, under 365 nm, bean sprouts initially had blue fluorescence emission, and later changed to green when they start spoiling. However, due to higher emission, 420 nm-excitation wavelength was preferable for detecting browning part. With these basic fluorescence information, further application on inspecting both physical change and chemical change of bean sprouts can be easily established.