The satiety center and feeding center adjust appetite and control diet behavior . Histamine, which is an antifeedant, was found to be secreted by mastication, i.e. chewing stimulation by the genetically obese animal the Zucker rat. In our previous study, the effect of mastication was examined using a chewing gum, and from the result, it was suggested that mastication is associated with the central nervous system. In the present study, for the purpose of examining the relationship between mastication and insulin secretion, food of the same energy but with different hardness was given to the following subjects.
The subjects were 25 healthy females aged 18 to 24 years and were instructed to masticate ordinary food and crushable food. They were grouped into a high mastication group and low mastication group after evaluating their ability to masticate using a mastication test gum . Blood was collected from the cubital vein 4 times in total, at fasting state and 30, 60 and 120 minutes after meal, and the blood glucose and plasma insulin levels were measured. As a result of analysis of the blood glucose and plasma insulin levels classified by the ability to masticate in the ordinary food intake group and the crushable food intake group, no statistically significant difference was observed. In the high mastication group, the blood glucose and plasma insulin levels were analyzed statistically between the ordinary food intake group and crushable food intake group, but no significant difference was observed. However, when the blood glucose and plasma insulin levels between the ordinary food intake group and the crushable food intake group were analyzed in the low mastication group, it was found that the plasma insulin level 30 minutes after meal was higher in the crushable food intake group than in the ordinary food intake group with a statistically significant difference. No glucose tolerance abnormality or insulin resistance was detected from the subjects. In the low mastication group, therefore, it was thought that stimulation by mastication was conveyed to the central nervous system because of the ingestion of crushable food, and the secretion volume of insulin increased with a significance difference .

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The objective of this study was to clarify the influence of food firmness in cooked rice on mastication. We prepared four rice samples by cooking with different water contents (1 .2, 1.5, 3.0 and 10.0-times water to rice weight). The firmness of cooked rice samples were evaluated using a rheometer. We used electromyography (EMG) to record both sides of the masseter and temporal muscle activities while young female subjects masticated 5 g of each sample and 10 g of the softest rice gruel. Firmer rice samples required more chews, longer mastication time, and greater EMG amplitude. Consequently, the firmer samples exhibited more muscle activity and longer total EMG-burst duration until swallowing. Mastication of 10 g gruel (× 10.0 water) resulted in 1.4-fold values in the number of chews, mastication time, and total muscle activity compared to 5 g gruel. These findings suggest that rice firmness affects mastication more than the bolus amount of cooked rice. Our results suggest that ingesting small amount of gruel more frequently requires more mastication than taking large bolus to reduce the number of boli.

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The relationship between the rheological properties of xanthan gum (0.6, 1.2, 2.0%) and the palatability of the minced carrots with the xanthan gum was examined by steady shear viscosity, dynamic viscoelasticity measurements, and sensory evaluation. As has been reported previously, aqueous solutions of xanthan gum showed shear thinning flow and weak gel behavior. Adding xanthan gum reduced the number and the time for chewing of minced carrots. The number and the time for chewing of minced carrots with xanthan gum by the aged panel were more than those of the young panel. The number and the time for chewing of minced carrots with 0.6% xanthan gum by the young panel were less than those with 1.2% xanthan gum, while those with 1.2% xanthan gum by the aged panel were least. The young panel evaluated that minced carrots with 0.6% xanthan gum was stickier, of better mouthfeel, easy to be swallowed, and better in taste than those without xanthan gum, while minced carrots with 2.0% xanthan gum were felt remained in the mouth after swallowing and difficult to be swallowed, and bad in taste. The aged panel judged that minced foods with xanthan gum were sticky, easy to be swallowed, easy to be eaten and better in taste than those without xanthan gum. They also evaluated that minced carrots with 1.2% xanthan gum were better than others. The difference between the most palatable xanthan concentrations for young and aged panels was observed. These results suggest that the rheological properties of xanthan gum make minced carrots more palatable and easy to masticate and swallow.

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Objective: The purpose of this study was to describe meal form, general conditions, and maximal tongue pressure of elderly care recipients in a nursing home and evaluate the utility of tongue pressure measurement for selecting suitable meal form.
Subjects and methods: Sixty-six residents (21 male and 45 female; over 65 years of age) in a nursing home in Hiroshima Prefecture took part in this study. The residents and their families were informed about the purpose and method of this study and gave their consent. General conditions including activities of daily living (ADL) and standardized level of independence for demented elderly, oral status, form of daily meal and maximum voluntary tongue pressure (MVTP) were examined.
Results: The number of subjects who could eat boiled rice, rice porridge, minced meal, or mashed meal was 29, 14, 19, and 4 respectively. Between these groups, there were no statistical differences in age and gender distribution. As general condition fell, the proportion of subjects who ate softer meal increased (p < 0.01). Furthermore, statistical analysis with logistic regression showed significant association between MVTP and meal form after adjustment for general conditions (p <0.05).
Conclusion: Beside the assessments of general condition, maximum tongue pressure measurement could have clinical utility for appropriate meal form selection for the elderly care recipients.

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The purpose of this experiment was to clarify the change of brain blood flow when chewing chewing-gum using NIRS (near infrared spectroscopy).
Twenty healthy subjects in their twenties were asked to chew chewing-gum on their habitual chewing side and on their non-habitual chewing side for 1 minute respectively, and the order was random. The brain blood flow was recorded using NIRS. The measurement was performed about 7 sessions; before chewing (rest), during chewing, and 1, 2, 3, 4, and 5 minutes after chewing. Measuring probe was attached on the skin over the cortical masticatory area. The change in blood flow in the brain caused by chewing was investigated using repeated measures ANOVA. Next the amount of change in blood flow was compared between the habitual side chewing and the non-habitual side chewing using paired t-test.
The brain blood flow increased for both habitual and non-habitual chewing sides during mastication and decreased gradually after mastication and returned the condition prior to the mastication (habitual chewing side; F=127.0, non-habitual chewing side; F=92.9, p<0.01). When comparing the session prior to mastication with all the other sessions significant differences were found except with the session 5 minutes after mastication. In 18 out of 20 cases the amount of change in blood flow was larger for the habitual chewing side than for the non-habitual chewing side and a statistically significant difference was found (t = 3.78, p <0.01).
From these results it was suggested that mastication activated brain activities and that the habitual chewing side had a stronger effect than the non-habitual chewing side.

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