Article
J. Korean Soc. Appl. Biol. Chem. 53(3), 337-341 (2010)
Changes in the Residual Chlorine Content of Fresh-cut Lettuce during Storage
Sun-Duk Cho , Min-Sun Chang , Yu-Si Lee , Ji-Hyoung Ha , Gun-Hee Kim , Dong-Ho Bae , Yong-Soo Kim , Myung-Sub Chung , Yong-Mu Kim , Dong-Ho Lee , Sun-Hee Park , and Sang-Do Ha * 1
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Department. of Food & Nutrition, Duksung Women’s University, Seoul 132-714, Republic of Korea Department. of Food Science and Technology, Chung-Ang University, Anseong 456-756, Republic of Korea 3 Department. of Bioscience and Biotechnology, Kon-Kuk University, Seoul 143-701, Republic of Korea 4 Korea Health Development Research Institute, Seoul 156-050, Republic of Korea 5 Food & Drug Administration, Seoul 122-407, Republic of Korea Received January 11, 2010; Accepted March 16, 2010 1
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Efficacies of the amounts and methods for chlorinated water to use in disinfection of lettuce were investigated. Concentrations of total and free chlorine in lettuce samples were measured using a colorimetric reaction with diethyl-p-phenylenediamine (DPD). For measurement of the total amount of residual chlorine remaining on samples of lettuce during storage, 100 mg/L DPD samples were used. The residual chlorine content decreased an initial amount of 14 mg/L and further decreased by 42.9% after three minutes, by 92.9% after ten minutes, and diminished to 4 mg/L after seven hours of storage. Measurements made while applying 200 mg/L chlorinated water showed a similar trend. The change in the amount of free available chlorine in the washing water was determined based on storage period and frequency. While washing, the amount of free available chlorine decreased proportionally with time. Key words: diethyl-p-phenylenediamine disinfection, lettuce, residual chlorine, washing ,
The fresh-cut fruit and vegetable industry has been rapidly growing in the past decade in response to an increased consumer demand for fresh and convenient foods [Garrett, 2002]. Fresh-cut fruits and vegetables are minimally processed products that are subject to cleaning, washing, trimming, coring, slicing, shredding, drying, and packaging [Park et al., 2005b]. Fresh-cut consumption has increased in Japan, Korea, and the USA. Initially, the food service industries serving school meals and restaurants were the main users of fresh-cut products, but consumption has expanded to retail markets in both Korea and Japan [Kim, 2005]. The quality of minimally-processed products quickly deteriorates, particularly in color and texture, as a result of endogenous enzymes, enhanced respiration, and microorganisms, resulting in a reduced shelf-life [Varoquacx *Corresponding author Phone: +82-31-670-4831; Fax: +82-31-675-4853 E-mail:
[email protected] doi:10.3839/jksabc.2010.052
and Wiley, 1994; Goupy et al., 1995]. Fresh-cut fruits and vegetables are more perishable than are whole fruits and vegetables because of exposure of internal tissues at the cut surface. Physical damage at the cut surface accelerates tissue metabolism [Watada et al., 1996], and the larger the size of the cut surface, the greater the risk of microbiological contamination [Kabir, 1994]. With the increase in consumption has come an increase in the frequency of outbreaks of illness associated with raw or minimally-processed fruits and vegetables [Weissinger et al., 2000]. Food safety has become a big issue in Korea with increasing fresh-cut sales in retail markets in the last few years [Park et al., 2005a; Kim, 2007]. Washing is one of the most important steps during the processing of produce since it removes soil and microorganisms from the surfaces [Ruiz-Cruz et al., 2007]. Electrolyzed water, ozone, ultrasound, irradiation, and hot water, and combinations of these sanitizing methods have been used in the fresh-cut industry [Garcia et al., 2003]. Chlorine is normally used for disinfection of cut fruit surfaces by addition of sodium hypochlorite (NaOCl) to the wash water [Soliva-Fortuny and Martin-
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Belloso, 2003]. Chlorine is the most commonly used sanitizing agent in the fresh-cut industry due to its strong antimicrobial activity and low cost [Allende ., 2008]. However, treatment with strong solutions of chlorine may produce harmful by-products, such as chloramines and trihalomethanes, which are deleterious to human health [Gonzalez ., 2004]. The industry is not only searching for more effective sanitizers, but also more environmentally-friendly washing methods. Further practical research on washing techniques is required to develop optimum sanitizing methods for individual freshcut products [Kim, 2007]. This study was designed to develop practical management methods, proper dosages, and appropriate uses of sodium hypochlorite for lettuce, the most popular fresh-cut food in Korea.
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Fig. 1. Change in the residual chlorine content in a sodium hypochlorite solution in a test tube for 7 h. - ○-:
100 mg/L, - ●-: 200 mg/L (data: mean of duplicate experiments, ND:
