Abstract
This study investigates the influence of the surface free energy (SFE) on the adhesion behaviour between wheat dough and bakery-relevant food processing surfaces. In doing so, the contact time and production-related changes of the adhesive and the adherend were taken into account. The adhesion measurements were conducted by means of previously developed methods (modified Chen/Hoseney, contact time measuring cell), whereby the force required for separating the dough from the surface after processing-relevant contact times was determined applying a texture analyzer. The SFE was determined by contact angle measurements. The SFE values for the examined materials are ranged between 5.5 ± 0.81 and 42.7 ± 0.88 mN/m. A strong linear correlation between the SFE of the bakery surfaces and their adhesion to dough could be determined after a certain contact time (≥ 1 min) (r = + 0.96 for surfaces with Sa > 20 μm; r = + 0.94 for surfaces with Sa < 20 μm). Bakery surfaces with energy values σsolid surface, total > 30 mN/m including a polar content indicated a strong interaction with wheat dough, which was confirmed by high adhesion values. Production-related changes to the processing surfaces showed a great impact on the adhesion behaviour: e.g. the abrasion of proofing cloths caused a higher amount of protruding fibres, which operate as a separating layer, resulting in a decrease of dough adhesion even after long contact times. The results in this study emphasize the importance of the SFE in the development of processing surfaces for the baking industry.
Highlights
Adhesiveness can be a desirable as well as undesirable product property of foods
During the production of baking goods, dough usually comes in contact with several different food contact materials such as stainless steel during the kneading process, with conveyor belts of different coatings during the transportation, with proofing trays which are often made of textile proofing cloths, and with baking foils
The roughness values of the stainless steel samples and the conveyor belts made of thermoplastic polyurethane (TPU), PVC, and thermoplastic polyolefin (TPO) are in a similar range between Sa = 1.21–2.85 μm, those of the baking foils at Sa = 10.21 μm for PTFE baking foils, and Sa = 18.89 μm for silicone baking foils
Summary
Adhesiveness can be a desirable as well as undesirable product property of foods. The adhesiveness of dough during the processing usually leads to negative consequences such as production disruptions, loss of dough, and cleaning operations due to adhering dough residues on the processing surfaces. The surface properties of, e.g., proofing cloths or conveyor belts are modified through the use of release flour, adhering dough residues, or abrasion of the materials through cleaning processes (including brushing) that can highly influence the surface structure (Moeller et al, 2017) and SFE of such materials. Such changes of the processing surfaces through the practical use must be considered in the examinations of the effect of the SFE on the adhesion behaviour of dough
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