## 4 Discussion
[35], who studied starch-based snacks, concluded that sodium diffusion from high to low NaCl layers reduces the initial concentration ratios, so high concentration gradients must be applied while maintaining a low overall NaCl content. Moreover, to reduce the diffusion effects, configuration patterns other than layer configurations can be used, where concentrated spots are site-specifically introduced in the matrix without salt addition [35]. The food matrix is one of the factors involved in sodium release and the consequent saltiness perception. The interaction of sodium with food matrix components is crucial for saltiness perception. An increased protein content in meat reduces the sodium availability, while water improves the salinity perception [36]. The data on protein-based products are limited. To the best of our knowledge, no other authors have studied multilayered beef patties. Previous research was performed on a model of layered pork sausages. An inhomogeneous sodium chloride distribution in sausage formulations with various layers was perceived as saltier than homogeneous sausage formulations at the same sodium chloride concentration [12]. In other studies, a heterogenous salt distribution was achieved in beef frankfurter by placing NaCl in the edible coating and reducing the salt content by over 50% while maintaining the saltiness intensity. Such sausages had higher consumer acceptability and purchase intention than traditional sausages with added salt [19]. A saltiness contrast may also be elicited by modifying the size of the salt crystals, e.g., from 0.2-0.4 mm (regular) to 3 mm, as most regular-sized NaCl crystals are swallowed without the consumer noticing the salty taste [36]. [PERSON] et al. [20] found that coated 3 mm sized salt crystals in a reduced-sodium beef patty (0.7%) can achieve a saltiness comparable to table salt (1%). Low-sodium-chloride (0.7%) patties with 100% 3 mm salt crystals were perceived as being 20% saltier compared to a regular control patty and 34% saltier compared to a regular low-salt patty. However, unsalted meat patties struggle to entrap water and fat, causing cooking loss and affecting the meat texture and juiciness. Large-sized NaCl crystals cause incomplete solubilisation in the mouth, suggesting reduced-size alternatives for sodium reduction in meat products [36]. In our study, a saltiness enhancement via an inhomogeneous salt distribution was found by trained sensory panellists, while the consumers did not clearly perceive a difference between the samples. We believe that differences between analytical tests (trained sensory panels) and affective (consumer) responses may arise from the sensitivity of trained sensory panellists. In the analytical measurement, selected, sensory-screened, experienced, and well-trained panellists were used, while the consumer test involved regular burger eaters. The consumers were not aware that the study was focused on saltiness perception, while the professional panellists were trained using four samples of varied salt concentrations. Hence, their attention could be focused on other burger traits that diminished the perceived differences in saltiness. When the scores were converted to a rank-based variable and habitual salt intake was considered, subjects with a high dietary salt intake assessed a lower saltiness of HM 0.7% compared to the HT-L-IN sample. Insignificant differences in the consumer perceptions of saltiness may result from the measurement tool used. Many approaches have been proposed by various authors. Some authors reported contrast-induced saltiness enhancement involving trained or only sensory-screened panellists using mainly visual analog scales [7; 11; 15; 17] or a paired comparison test, 2-AFC [35]. Saltiness assessment in consumer tests conducted by other authors was performed using various methods, i.e., category scale [15], 2-AFC [12], and VAS [16; 19]. In a recent study by [PERSON] et al. [37], the visual analog scales and ranking methods were compared to evaluate odour-induced saltiness enhancement (OISE).