Adhesion buffer composition
The composition of the incubation buffer used during the
adhesion assay can be expected to exert a major influence
on the adhesion of probiotics and microbes in general. In
particular, the effect of divalent cations such as calcium and
magnesium on in vitro adhesion has been investigated (73).
In some cases, the spent culture supernate was found to be
necessary for adhesion as it contains secreted adhesins (22,
74). In using supernate, the pH of the incubation buffer also
becomes important (75). Particularly when working with
tissue culture cells, the adhesion buffer should be of neutral
pH. Low pH has been observed to affect the viability of
tissue culture cells and thereby gives an aberrant exposure
of potential binding sites on the tissue culture cells (69, 76).
More important for the in vivo situation, however, would be
the influence of the food matrix on adhesion. Exposure to
milk for 1 h has been observed to reduce the adhesive
abilities of selected probiotic lactobacilli significantly; even
the fat content of the milk was found to be of influence (77).
It has also been observed that the presence of fatty acids
affects the in vitro adhesion to immobilized human
intestinal mucus (78). Although food is gradually digested
along the digestive tract, the digesta too are likely to
interfere with adhesion (58). An influence of other food
components has not been reported nor has the influence of
intestinal contents been assessed. Both can be expected to
have a significant impact on the adhesion of probiotics in
vitro. The possible mechanisms whereby food components
affect the adhesion of probiotics have likewise not been
investigated. It can be hypothesized that entrapment in the
food matrix, specific or non-specific binding to or steric
hindrance of adhesins are responsible for the observed
phenomena. Knowledge of these mechanisms is important
in order to optimize the delivery vehicle for probiotics