## 1 Introduction  
The first step in the digestive process is chewing, which helps to prepare the food for swallowing and further processing in the digestive system. During chewing, the food bolus or food particles are reduced in size, saliva is produced to moisten the food [1], and flavours are released [2]. Salivary proteins, the major organic constituents of saliva, are essential for initiating the digestive process and for modulating the sensory experience of food. In addition, saliva is a highly dynamic system that can be influenced by several factors simultaneously, such as diet patterns [3]. Regarding oral digestion, some salivary proteins and enzymes (e.g., amylase, lipase) play well-known roles in breaking down food nutrients so that they can be easily absorbed in later phases of digestion. During oral processing, nutrients are released from the food matrix as it disintegrates during mastication and bolus formation. In this context, the proteins present in saliva might also modulate the release of nutrients from the food matrix, leading to variations in their subsequent bioavailability during digestion [4; 5; 6]. Additionally, mastication also stimulates the secretion of saliva. Several masticatory muscles (the masseter, temporalis, medial pterygoid, and lateral pterygoid muscles) work together to enable the complex process of chewing by controlling the movement of the temporomandibular joint (TMJ) [7]. Disorders such as bruxism (a rhythmic involuntary movement of the jaw muscles) can impact the dynamics of chewing [8]. In terms of consumption, foods with more fibrous textures or dry foods, for example, often require more effort to break down and may lead to increased saliva production [9; 10]. In addition to the characteristics of food, the shape of food can also influence the oral processing behaviour, energy intake, and metabolism [1; 11; 12; 13]. For instance, [PERSON] and colleagues (2024) showed that carrot strips required a longer chewing time than carrot cubes, with carrot julienne producing more and smaller carrot bolus particles than carrot cubes. Although these differences in oral processing did not affect the amount of carrot nutrients released (\(\beta\)-carotene) [14], less is known about how the shape of foods affects their oral sensory perception and consequent intake behaviour (e.g., food preferences, amount of food eaten). Other authors have also investigated how the consumption of different types and sizes of foods (Melba toast with and without margarine, and three sizes of cake and cheese) affects the salivary flow rate without finding significant differences in this salivary parameter among the different foods and forms [9]. However, despite these interesting studies, the effect of food shape on the salivary proteome is still largely unknown. Differences in salivary secretion due to mastication of foods with different textures or shapes might modify the concentration and composition of proteins in saliva. In a recent systematic review, the impact of mastication on the total protein concentration and levels of different salivary proteins (alpha-amylase, peroxidase, lysozyme, slgA, and mucin concentration) was addressed [15]. The authors found that there is no consensus about chewing impact, as some studies reported no or minimum effect, while others showed an increase and others a decrease in salivary protein amounts. These differences could be due to the different experimental approaches and methods used (analytical procedures, chewing material, etc.). Most of these studies used parafilm, plastic pieces, or gums with different compositions as chewing materials, while only two studies used foods (celery and bread). These studies evaluated the impact of chewing on the activity and/or concentration of specific proteins individually, but they did not consider the complete salivary proteome. In fact, the relationship between different food textures and the salivary proteome has been little explored.