Takako Yamazaki

Sequential analysis of masseter activity patterns during chewing in healthy males

Abstract The present study examined sequential changes in masseter activity patterns observed during chewing of four different agar samples in eight healthy young males. Two parameters, T50 and D50, were specifically used for evaluation of the activity patterns of individual bursts. Statistical significances were detected in regression coefficients (21.9% of 32 trials) and Spearman’s rank correlation coefficients (28.1%) between the calculated T50 values and chewing cycles, whereas no significant differences among the four agar samples were found. Three (I–III) types of activity patterns of masseter bursts during chewing sequences were classified by the D50 values, which were derived from the T50 values. The three types physiologically corresponded to incrementing (Type I), decrementing (Type III) and mixed discharge patterns (Type II). The classification of activity patterns suggested the usefulness of D50 values in the sequential analysis of masseter activity patterns.

Differential sweetness of commercial sour liquids elicited by miracle fruit in healthy young adults

Miracle fruit (Synsepalum dulcificum) contains the glycoprotein miraculin which turns a sour taste into a sweet one. Chemical analyses and sensory evaluation experiments were conducted to examine the sweetening effect of miracle fruit with regard to five different commercial sour liquids which were diluted until they were subjectively equally sour. HPLC-based analyses revealed that (1) the predominating acids in two and three of the liquids were citric acid and acetic acid, respectively and (2) all five liquids contained fructose and glucose. Healthy young adults (eight males and 10 females) in the sensory evaluation experiments were asked to chew a miracle fruit and apply their saliva to the oral mucosae. They were asked to score the sweetness elicited by the five liquids relative to a sucrose standard at 0, 15, 25 and 35 min thereafter. The citric acid-based liquids were perceived as being sweeter than the acetic acid-based liquids at all timepoints. Thus, commercial sour liquids that mainly contain citric acid are more effective than acetic acid-based liquids in eliciting a perception of sweetness after the miracle fruit application, while the sugars in the liquids seemed to play a minimal role as determinants of sweetness.

Synchronization of masseter activity patterns between the right and left sides during chewing in healthy young males

Abstract Masseter activity patterns during chewing, which were quantitatively assessed using T50 values, were compared between the right and left sides of healthy young males. Surface electromyograms were recorded from both masseters, and each participant was asked to chew four different agar samples at his own pace across two separate sessions. The four agar samples, each possessing differing textural properties, consisted of two normal and two distinctive agar varieties. The Pearson’s correlation coefficient was calculated for each pair of T50 values to evaluate the degree of synchronization of activity patterns between both masseters. A three-way analysis of variance revealed significant main effects of the ‘participant’ and ‘experimental session’ factors, but not of the ‘test food’. The number of significant coefficients increased stepwise by increasing the number of chews per sequence. These results suggest the importance of the initial stages of chewing sequences in facilitating the synchronization of bilateral masseter activity patterns.