Culinary processing is an integral part of food preparation, affecting not only sensory properties but also the biological activity of nutrients. This study investigates how different thermal treatments of sardines (Sardina spp.) and sprats (Sprattus spp.)—rich sources of polyunsaturated fatty acids with proven anti-inflammatory and probiotic-modulating effects—influence the adhesion of selected probiotic strains to intestinal epithelial cells.

Samples of sardines and sprats were subjected to boiling, steaming, frying, and baking, with raw samples serving as controls. All samples were then digested using the standardised INFOGEST in vitro digestion protocol. After digestion, the samples were incubated with FITC-labelled probiotic strains (Lactobacillus brevis, Lacticaseibacillus rhamnosus, and Lactobacillus gasseri) on two epithelial co-culture models: Caco-2 + HT29 and Caco-2 + HT29-MTX. Adhesion was quantified via fluorescence measurement after washing off non-adherent bacteria.

The results showed that adhesion capacity was significantly influenced not only by the bacterial strain and cell model but, most notably, by the type of heat treatment. L. rhamnosus exhibited the highest adhesion, particularly on the Caco-2 + HT29 model, with increases exceeding 100% for raw sardine digests and nearly 95% for boiled samples compared to controls. In contrast, L. gasseri showed the lowest adhesion levels across all conditions, while L. brevis displayed moderate responses (e.g., over 50% increase with baked sprats and over 40% decrease with baked sardines).

Gentler cooking methods, such as boiling and steaming, enhanced bacterial adhesion, likely due to reduced protein denaturation and limited oxidation. These findings confirm the strain-specific nature of adhesion and highlight the importance of appropriate culinary processing for preserving the probiotic potential of foods. This knowledge may contribute to the development of functional foods aimed at supporting gut health.