Combined treatment to inactivate pathogens in red pepper

Researchers said the combined intervention has important implications for food safety since spices such as powdered red pepper are added to a variety of foods with minimal processing.

Super-heated steam and exposure to ionizing radiation have been used to decontaminate spices but the former brings about loss of sensory properties and change of colour and the high moisture content aids mould growth.

The latter, involving treatment with gamma-rays, X-rays, and electron beam exposure is effective but also subject to oxidation and degradation of colour or aromatic component concerns.

Bacterial strains​

Three bacterial strains of E. coli O157:H7 and S. Typhimurium were stored at -80 °C in 0.7 ml of Tryptic Soy Broth (TSB) and 0.3 ml of 50% glycerol.

Working cultures were streaked onto Tryptic Soy Agar (TSA), incubated at 37 °C for 24 hours and stored at 4 °C.

When UV-C irradiation was applied at 20.4 kJ/m2 without raising the temperature (25 °C), reduction levels of E. coli O157:H7 and S.​ Typhimurium were 0.22 and 0.29 log CFU/g.

Reductions of E. coli O157:H7 were 0.88 and 1.23 log CFU/g when treated at 55 and 65 °C, and S.​ Typhimurium, were 0.85 and 1.29 log CFU/g, respectively.

When treated at 40.8 kJ/m2 the number of surviving cells exposed to UV-C irradiation treatment alone were slightly reduced independent of UV-C radiation dose.

Combined treatment effect​

Combined treatment with mild heating at 65 °C reduced the surviving numbers of each pathogens by 2.88 and 3.06 log CFU/g.  

“The inactivation effect on powdered red pepper when treated at different UV-C irradiation doses (20.4 and 40.8 kJ/m2) at room temperature (25 °C) was very minor with differences of less than 0.5 log CFU/g,”​ said the researchers.

The synergistic effect was observed with increasing temperature, they added.

“It is more effective to combine ultraviolet radiation with mild temperature heating for inactivation of ​E. coli​ O157:H7 and ​S.​ Typhimurium than to treat with UV-C irradiation alone.” ​

A constant UV intensity (3.40 mW/cm2) of the emitting lamps was applied to samples for five and 10 minutes at 25, 35, 45, 55, and 65 °C.

Source: Food Control

Online ahead of print, DOI: 10.1016/j.foodcont.2014.08.025​

“Inactivation of foodborne pathogens in powdered red pepper (​Capsicum annuum​ L.) using combined UV-C irradiation and mild heat treatment”​

Authors: Ho-Lyeong Cheon, Joo-Yeon Shin, Ki-Hwan Park, Myung-Sub Chung, Dong-Hyun Kang