Blocking nonspecific adsorption of native food-borne microorganisms by immunomagnetic beads with ι-carrageenan

We present herein the partitioning characteristics of anti-Salmonella and anti-Escherichia coli O157 immunomagnetic beads (IMB) with respect to the nonspecific adsorption of several nontarget food-borne organisms with and without an assortment of well-known blocking agents, such as casein, which have been shown to be useful in other immunochemical applications. We found several common food-borne organisms that strongly interacted with both types of IMB, especially with anti-Salmonella form (av DeltaG(0) = -20 +/- 4kJmol(-1)) even in the presence of casein [1% (w/v): DeltaG(0) = -18 +/- 3 kJmol(-1); DeltaDeltaG(0) similar to -2kJmol(-1)]. However, when one of the most problematic organisms (a native K12-like E. coli isolate; DeltaG(0) = -19 +/- 2kJmol(-1)) was tested for nonspecific binding in the presence of iota-carrageenan (0.03-0.05%), there was an average decline of ca. 90% in the equilibrium capture efficiency xi (DeltaG(0) = -11 +/- 4kJmol(-1); DeltaDeltaG(0) similar to -8kJmol(-1)). Other anionic polysaccharides (0.1% kappa-carrageenan and polygalacturonic acid) had no significant effect (av DeltaG(0) = -19 +/- 1kJmol(-1); DeltaDeltaG(0) similar to 0kJmol(-1)). Varying iota-carrageenan from 0% to 0.02% resulted in xi significantly diminishing from 0.69 (e.g., 69% of the cells captured; DeltaG(0) = - 19 +/- 3kJmol(-1)) to 0.05 (DeltaG(0) = -11 +/- 2kJmol(-1); DeltaDeltaG(0) similar to -9kJmol(-1)) at about 0.03% iota-carrageenan where xi leveled off. An optimum blocking ability was achieved with 0.04% iota-carrageenan suspended in 100mM phosphate buffer. We also demonstrated that the utilization of iota-carrageenan as a blocking agent causes no great loss in the IMBs capture efficiency with respect to the capture of its target organisms, various salmonellae. Published by Elsevier Ltd.