University of Arkansas, Fayetteville


Consumption of raw or lightly cooked alfalfa sprouts has been a concern of the U.S. Food and Drug Administration (FDA) in recent years due to connections between sprouts and foodborne illnesses. Researchers have identified, contaminated seeds as the primary source of alfalfa sprouts contamination. Contamination of alfalfa seeds can originate in the field, harvesting, storing, or sprouting. Two pathogens of particular concern on alfalfa seeds are Escherichia coli 0157:H7 (E. coli) and Salmonella. These pathogens are capable of producing biofilms that provide protection for individual cells and allow for survival in otherwise hostile environments, including some disinfectant washes. Other factors that contribute to contamination are the crevices of the seed surface, which provide opportunities for the protection of organisms. Various disinfection options have been evaluated and the use of a 20,000 ppm calcium hypochlorite ( Ca( OCl)2)) solution is the most effective disinfectant for satisfying the requirements of Task 2. Continued outbreaks of food poisoning indicate current disinfecting procedures are inadequate. In an effort to improve disinfection procedures, three bench scale apparatuses were constructed and tested to provide options for the commercial range of seed sanitation rates (from about 75 to 600 lb/week). Experiments were conducted to determine the disinfecting effectiveness of the apparatuses, as well as the current sanitization practices in industry. Experiments included dye removal tests where non-uniform dye removal indicated ineffective contacting. Similar experiments were performed using E. coli inoculating and post-contacting culturing. One bench scale apparatus constructed was a model of the rotary drums widely used in industry. After a 30 minute treatment in the rotary drum, the seeds were found to be free of dye, indicating good contacting. The seeds were also sprouted showing sanitation did not damage the seeds. However, due to the capital expense of $14,000, the drum is not a viable option for small-scale sprout producers. For sprout growers who currently own rotary drums, drum use is recommended for seed sanitation. Another bench scale apparatus was designed to improve the current industry practice of hand dunking seed-filled mesh draw-string bags. Through experimentation, it was determined . the current hand dunking procedure, with little or no agitation, produces inadequate, non-uniform contact of the seeds and sanitizer. Therefore, the hand dunking procedure was modified to include agitation to effectively suspend the seeds throughout the bag to obtain good contact of the sanitizer solution with the seeds. The agitation-in-bag method is recommended for use in small volume sprout facilities, which currently employ the hand dunking procedure for sanitizing. A modest investment of $113 is needed to implement the agitation-in-bag sanitizing method. Since no additional operating costs are accrued in implementation, no incremental costs are required. Finally, an auger system was designed to sanitize one ton per hour of alfalfa seeds. The one ton per hour rate exceeds the demand of any individual sprout producer. Thus, the auger system is applicable to a partnership of sprout growers. Individual sprout growers within the mung bean industry, with much larger production volumes than the alfalfa industry, could economically use the auger system. However, the auger system can be scaled to sanitize any feed rate. A 1 3/8" diameter, 4' long auger bench scale model was constructed and tested at 4.5 lbs/hr rate with a contact time of 15 minutes. Scale-up of this bench scale sanitizer to a 2000 lb/hr rate requires a 16" diameter by 20' auger. The entire full-scale sanitizing system, which includes a vibrating screen washer, will handle 5,000,000 lb/yr of seeds, operating 8 'hr/day, with a capital investment of $227,000 and an incremental operating cost (primarily labor) of $214,000/yr.