Bacteriological Analysis of Alfalfa Seeds and Sprouts Using Disinfectants for Sanitization

Abstract

Alfalfa sprouts are an important element in ready-to-eat vegetables for making a salad. This food item poses a potential and relatively high risk of food-borne illnesses due to the fact that it is ready to be used, and its exposure to poor sanitary conditions during both seed and sprout production. In addition, the conditions for seed germination as well as for sprouting are characterized by warm temperature, high humidity, and readily available nutrients. All of these conditions facilitate the growth of the microorganisms adhering to the seeds. In this study, refrigerated alfalfa sprouts from some domestic supermarkets in northern Taiwan were sampled; and the microbiological analysis showed these food samples to be negative for three types of pathogenic bacteria, while the total plate count (TPC) and coliform count were higher than 8 and 5 log CFU/g, respectively. In the experiments of chemical disinfectants including 0.5% H2O2, 100ppm available chlorine (NaOCl), 100 ppm ClO2 (Clean Good), and 75% ethanol as well as 50 and 70℃ sterile water, their effects on the bacterial load of alfalfa sprouts and on the germination rate of alfalfa seeds were tested. Among the chemicals, 100 ppm available chlorine, 75% ethanol, and 0.5% H2O2 could effectively reduce TPC by ＞1.5 log CFU/g of alfalfa seeds, while both 75% ethanol at 70℃ and 0.5% H2O2 at 50℃ displayed a negative impact on the germination rate of alfalfa seeds. During the process of seed germination and sprouting, both the TPC and the coliform count increased 3-4 log CFU/g of alfalfa sprouts. For freshly harvested alfalfa sprouts on which the TPC and the coliform count were initially 8.8 and 6.6 log CFU/g, respectively, a single chemical disinfection with acidified 60 ppm ClO2 (Clean Good), 60 ppm ClO2, 50 ppm available chlorine, or 50 ppm H2O2 reduced the TPC and the coliform count by only 0.9-2.2 and 0.2-1.0 log CFU/g, respectively. The cause of the poor efficacy of chemical disinfectants was due to the fact that a washing procedure with any single disinfectant could not completely sanitize or get rid of the alfalfa seed coating of bacterial contamination. In contrast, a three-stage washing treatments in a manner of sequential disinfection (NaOCl→Clean Good→electrolyzed oxidizing water) under ultrasonic enhancement could reduce 4.5 log CFU/g for TPC and 3.5 log CFU/g for coliform count, and eliminated Salmonella typhimurium, Escherichia coli O157: H7, and Listeria monocytogenes (at 3.0 log CFU/g each) inoculated onto alfalfa sprouts.