Abstract:

E. coli secretes β-galactosidase under the induction of isopropyl-β-D-thiogalactopyranoside (IPTG). The
β-galacosidase catalyzes chlorophenol ReD-β-D-galactopyranoside (CPRG) to form chlorophenol red (CPR) along with
a color reaction. Based on the significant correlation between intensity of the color change from the reaction and the
concentration of E. coli, a photoelectric sensor for detecting E. coli was developed. The results showed that the optimal
pH for the reaction system was 7.5 and the optimal time for enzymatic reaction was 4 h. The logarithm value of bacterial
concentration in samples presented a significant correlation with the reflected light signal value (R = －0.98944, P ＜ 0.01),
the linear equation was Y = 1426.10485 － 97.23368X. The detection limit was 104 CFU/mL. The photoelectric sensor based
on color reaction can provide a quick, simple and cheap way to detect E. coli in food samples and therefore deserves further
development and application.

Key words: E.coli；photoelectronic sensor；&beta, -galactosidase；photoelectric test strip