Organic Acid and Hypochlorite Treatments for Sprouts

Organic Acid and Hypochlorite Treatmentsfor Sprouts; Efficacy of Novel Organic Acid and Hypochlorite Treatments forEliminating Escherichia Coli O157:H7 from Alfalfa Seeds Prior to Sprouting
July 28 2000
International Journal of Microbiology 58: 73-82
M. M. Lang, B.H. Ingham, S.C. Ingham
Reprinted from International Journal of Microbiology, volume 58, M. M.
Lang, B.H. Ingham, S.C. Ingham,

ABSTRACT(Reformatted so that people other than nurds can read it)

Thisstudy investigated novel two-step organic acid/hypochlorite treatments asalternatives to 20,000 ppm active chlorine (from calcium hypochlorite) foreliminating Escherichia coli O157:H7 from alfalfa seeds prior to sprouting.Commercially available alfalfa seeds were inoculated with a five-strain E. coliO157:H7 mixture and dried to attain ca. 106 CFU/g of seeds. Seeds then underwentone of several soak treatments including:

1) 5%(v/v) lactic acid for 10 min at 42C,

2) 5%acetic acid (v/v) for 10 min at 42C,

3)2.5% lactic acid for 10 min at 42C followed by 2,000 ppm active chlorine (fromcalcium hypochlorite) for 15 min at 25C,

4) 5%lactic acid for 10 min at 42C followed by 2000 ppm active chlorine for 15 min at25C, or

5)20,000 ppm active chlorine for 15 min at 25C.

Eachtreatment reduced numbers of inoculum cells by about 6.0 log10 CFU/g asdetermined by plating on Sorbitol MacConkey agar (SMac). Plating onnon-selective Brain Heart Infusion agar (BHI) showed that treatments 1 – 4reduced counts by 2.3 – 4.1 log10 CFU/g, thus indicating a large proportion ofinjured cells.

Successivelactic acid and hypochlorite treatments (treatments 3 and 4) were more lethalthan either organic acid alone (treatments1 and 2).

Nosurviving cells were detected on SMac or BHI following treatment with 20,000 ppmactive chlorine (treatment 5).

Regardlessof the previous treatment, E. coli O157:H7 counts increased to 107 – 108 CFU/gduring sprouting. Germination of seeds was not adversely affected by any of thetreatments (germination > 90%).

Resultsof this study show that:

a)non-lethal cell injury must be considered when evaluating interventiontreatments against E. coli O157:H7 on alfalfa seeds,

b)reductions of 2 – 4 log10 CFU/g can be attained without using 20,000 ppm activechlorine,

c)successive lactic acid and hypochlorite treatments have greater lethality thanorganic acid treatments alone, and

d)none of the treatments tested can prevent regrowth of surviving E. coli O157:H7during sprouting.

BarbaraIngham has generously offered to send a reprint of this article to anyone whowould like a copy.  She can be reached at