INTRODUCTION: The production of sufficient saliva is indispensable for good chewing. Recent research has demonstrated that salivary flow rate has little influence on the swallowing threshold. OBJECTIVES: The hypothesis examined in the present study was that adding fluids to foods will influence chewing physiology. Materials and METHODS: Twenty subjects chewed on melba toast, cake, carrot, peanut and Gouda cheese. They also chewed on these foods after addition of different volumes of water or alpha-amylase solution. Jaw muscle activity, number of chewing cycles until swallowing and chewing cycle duration were measured. Repeated measures analysis of variance was applied to test the null hypothesis that there would be no statistically significant difference among the results obtained for the various food types and fluids. Subsequently, contrasts were determined to study the levels of intra-subjects factors (food type and fluid volume). Linear regression was used to determine the changes in muscle activity and cycle duration as a function of the chewing cycles. RESULTS: Fluid addition significantly decreased muscle activity and swallowing threshold for melba, cake and peanut (p<0.05). The effect of alpha-amylase in the solutions was similar to that of water (p>0.05). Doubling the volume of tap water had a greater effect. CONCLUSIONS: Fluid addition facilitated chewing of dry foods (melba, cake), but did not influence the chewing of fatty (cheese) and wet products (carrot). This study is relevant to improve patients' life quality and the management of chewing and feeding disorders caused by hyposalivation.

O objetivo deste estudo foi determinar a relação entre o fluxo salivar e características de diferentes alimentos. Avaliou-se a taxa de secreção salivar em 16 indivíduos saudáveis, sem estimulação, na estimulação com Parafilm e na mastigação de alimentos naturais (torrada com e sem margarina e 3 volumes de bolo industrial). Determinou-se também a velocidade, o tempo de mastigação, o número de ciclos mastigatórios até o limiar da deglutição. As características físicas dos alimentos foram quantificadas através da experimentação força-deformação. Os resultados mostraram que a média em que a falha mecânica ocorreu foi 1,86 ± 0,24 N para o bolo industrial e 16,3 ± 1,3 N para a torrada. Os fluxos salivares obtidos sem estimulação e com a estimulação pelo Parafilm foram significativamente menores (P < 0,001) que os fluxos salivares obtidos na mastigação dos alimentos naturais. Não houve diferença significativa no fluxo salivar entre os alimentos naturais. Os fluxos salivares obtidos sem estimulação, com estimulação pelo Parafilm e na mastigação dos vários alimentos foram significantemente correlacionados (P < 0,05). Não houve diferença significativa na velocidade da mastigação entre os alimentos. O número de ciclos mastigatórios e o tempo de mastigação até o limiar da deglutição dependeram do tipo e do volume do alimento.

The aim of the present study was to determine the relationship between the flow rate of saliva and characteristics of the food. Therefore, we determined the rate of saliva secretion in 16 healthy subjects in rest and while chewing natural and artificial foods (toast with and without margarine, three sizes of breakfast cake, and Parafilm). We also determined the chewing rate, number of chewing cycles until swallowing, and time until swallowing. The physical characteristics of the foods were quantified from force-deformation experiments. The results showed that the average at which mechanical failure occurred (yield force) was 1.86 ± 0.24 N for the breakfast cake and 16.3 ± 1.3 N for the melba toast. The flow rates obtained without stimulation and with Parafilm were significantly lower (P < 0.001) than the flow rates obtained from chewing food. No differences in flow rate occurred between the natural foods. The flow rates of the saliva as obtained without stimulation, with Parafilm stimulation, and with chewing on the various foods were significantly correlated (P < 0.05). There were no significant differences in chewing rate among the foods. The number of chewing cycles and the time until swallowing significantly depended on the type or volume of the food.