## 4 Discussion
In a similar way, PIPs are involved in the immune response and oral homeostasis; thus, their increase after chewing CS could also be related to their involvement in the protection of mucosal surfaces from increased chewing activity. Regarding PIPs, in a previous study using 2-DE analysis to evaluate the impact of rice and bread mastication on the salivary proteome, the authors also found increases in two and one spot of PIP after rice and bread mastication, respectively [16], which is consistent with the present results. Finally, decreased levels of serum albumin and regions of slgA due to CS mastication were observed. slgA is involved in oral immune response functions, while serum albumin is associated with protective and maintenance functions in the oral cavity [34]. The impact of chewing on those proteins has been poorly investigated. In the case of slgA, different effects (increase, decrease, or no effect) of mastication have been reported when evaluating their concentration in saliva by ELISA [15]. In humans, slgA secretion has been reported to increase with chewing compared to resting levels [35], but in our previous study, a decrease in chains of slgA with bread and rice mastication was observed, which was explained by the gustatory stimulation that chewing involves, together with the mechanical stimulation [16]. Nevertheless, there are also reports of increased slgA secretion induced by gustatory stimuli [36], highlighting that the effect of food chewing and oral processing on slgA and salivary proteins needs to be better understood. In 2002, [PERSON] and [PERSON] reviewed the neural control of slgA secretion, from which the authors concluded that both parasympathetic and sympathetic nervous system activation results in slgA increases in saliva, although the effects of the two branches of the autonomic nervous system have different strengths [37]. The authors also state that the effect of autonomic innervation in the secretion of this protein is different from the one at the level of salivary proteins stored in acinar cell granules. As such, it is possible that the decrease observed in slgA chains after chewing CS does not represent a true decrease in the slgA concentration in saliva, but rather a lower proportion of this protein in relation to other salivary proteins. In fact, for electrophoretic separation, the same amount of total protein was used for all samples, independently of whether some samples had a higher total protein concentration than others, allowing only a comparison of the proportions among salivary proteins between treatments and not the absolute amounts of those proteins in saliva. The increased proportion of some immunoglobulins (the Ig kappa chain C region) might, at first sight, appear contradictory to the decreased proportion of slgA chains with CS chewing. However, the Ig chain that is observed to increase after CS chewing is a light chain (kappa light chain). Whereas heavy chains are specific and determine the class of an immunoglobulin, the same light chains can be present in all Ig classes. Hence, the increase in the kappa light chain proportion after chewing the carrot that required a higher mastication effort may indicate a higher passage of Ig from blood sources to the saliva (e.g., [PERSON] et al. (2020) [38], and for more details about Ig in saliva, please see [PERSON], 2013 [39]).