Four different matrices without peanuts

The number of chews (H(3) =16.819, P<0.005), the chewing time (H(3) = 14.154, P<0.005) and mastication frequency (H(3) = 11.172, P<0.05) were significantly different between matrices (Table 7-4). The gelatine gel was chewed the greatest number of times and for the longest period (15.5 chews on average), and the brownie was chewed the least number of times and the shortest period (9.5 chews on average). The number of chews and chewing time is vastly shorter when peanuts were not included inside the matrices, despite the same volumes being served.

Table 7-4: Mastication of four different matrices with peanuts removed: Parameters of mastication (mean±SE).

Matrix Number of chews Chewing time (s) Mastication frequency (s-1) Scone 11.5±0.8 a 8.45±0.61 ac 1.36±0.02 a Gelatine gel (200 bloom) 15.5±0.6 b 10.94±0.50 b 1.42±0.03 a Brownie 9.5±0.3 c 7.15±0.33 a 1.33±0.04 ab Chocolate 11.8±0.6 a 10.01±0.50 cb 1.19±0.05 b

Different letters (a & b) down each column indicate a significant statistical difference after pair wise Kruskal-Wallis tests (P<0.05).

Matrix containing peanuts Number of chews Chewing time (s) Mastication frequency (s-1) d50 b % Peanut weight retention (drywt/dry wt) Volume of peanuts in bolus (mm3) Scone 25.8±1.8 18.27±1.42 a 1.42±0.02 a 1.22±0.04 1.17±0.02 21.47±1.29 1460±90 Gelatine gel (200 bloom) 24.3±2.0 17.40±1.35 a 1.40±0.02 a 1.18±0.03 1.22±0.05 28.23±2.04 1620±70 Brownie 20.3±1.0 14.19±0.74 b 1.43±0.02 a 1.20±0.02 1.28±0.03 25.53±1.54 1550±60 Chocolate 23.3±1.5 19.33±1.11 a 1.21±0.03 b 1.26±0.02 1.26±0.03 25.35±1.92 1480±40

7.4 Discussion

7.4.1 Peanuts embedded inside four different matrices

Results showed that different matrices were being processed differently in the mouth (chewing time and mastication frequency were significantly different, and differences were seen in the number of chews despite a lack of significance) (Table 7-3). However, as the properties of the internal peanut piece were kept constant, no differences in the properties of the bolus were found in terms of d50, broadness (b), volume retention, or weight retention of peanut particles.

This shows that the significant differences in d50 in Chapter 6 resulted from differences in properties of the peanut pieces inside the matrix (i.e moisture), rather than from differences the matrices may have on manipulating the d50 required to form a swallow- safe bolus. Hence these results suggest that despite differences in chewing behaviour and physical properties of the matrix, the peanut particles needed to be reduced to a similar particle size distribution no matter which matrix it is inside. The difference in chewing behaviour but similarity in particle size in the bolus indicates the matrices may be influencing the selection of peanut particles between the molars.

The influence the matrix has on the broadness (b) value of the peanut particle size distribution inside the bolus remains unclear. Chapter 6 suggested the matrix may cause differences in the broadness of the distribution, however the differences are not significant is this study. Further investigation is undertaken in Chapters 8-10.

The similarity in peanut particle size outcome somewhat challenges previous literature surrounding a swallow-safe bolus. Boluses are believed to be safe for swallowing once particles reach a certain size distribution and degree of lubrication (where both variables vary between foods) (Hutchings and Lillford, 1988), and the bolus reaches a maximum degree of cohesion (Prinz & Lucas, 1997). Different matrices are likely to induce different rheological properties (such as lubrication and cohesion) in the food bolus, however this has not induced differences in the size of peanut particles between matrices.

One possible explanation for the similarity in particle size outcome is that receptors inside the mouth can precisely detect the texture and size of the peanut particles within all the different matrices. Such acute detection of particles may mean that differences in cohesion or lubrication of the surrounding matrix are largely irrelevant in determining final peanut particle size. In the test foods used, the size of particles may also be the priority in preparing a swallow safe bolus, and the cohesion or lubrication of the surrounding matrix is not deemed as important. Receptors on the tongue and oral mucosa can detect single particles as small as 2 mm (Ringel & Eawonski, 1965; Lucas, 2004), and the threshold discrimination on teeth is reported to be as small as 8-15 µm by some authors (Utz 1983 in Lucas, 2004). Furthermore, particles as small as 2 µm (Engelen et al., 2005a) to 10 µm (Imai et al., 1995) can influence textural sensations.

It is also feasible that the peanut particles are treated independently from the matrix during mastication. Peanuts could be isolated or removed from the matrix early in the chewing sequence, and could be broken down and determined suitable for swallowing separately of the matrix. In this case peanut particles may be stored in a different part of the oral cavity (a different compartment) than the matrix during the chewing sequence, where the matrix and peanuts are returned separately between the molars for communition. Flynn (2010) presented a hypothesis that mastication occurs within a multi-compartment system where particles are stored in at least one compartment (i.e the tongue), but can settle in a separate compartment (i.e around the cheek or the sides of the molars).

7.4.2 Four different matrices without peanuts

Mastication of matrices without peanut pieces showed that the presence of peanuts greatly increases the time and number of chews spent chewing the same initial volume of food (Table 7-3 and Table 7-4). The presence of peanuts in a system may increase the mastication required to prepare the bolus for swallowing because peanuts are a hard and crunchy material (Young & Schadel, 1990) in comparison to the matrices.

Some differences in chewing trends can also be seen between the two trials (in terms of which matrix was chewed for the longest time and greatest number of chews). Most

notably, the scone is chewed for a longer period of time and for a greater number of chews than the gelatine gel when peanuts were present, where as the opposite was found without peanuts in the matrices. This suggests a small interaction in chewing behaviour between peanuts and matrices.

7.5 Conclusion

When peanuts of identical physical properties where manually inserted into different food matrices and masticated, differences in chewing behaviour were observed between matrices, however the particle size distribution of the peanut particles in the bolus was similar. Weight and volume retention of peanuts the bolus after mastication were not influenced by the type of matrix. When the matrices (of an identical initial volume) were masticated without peanuts, the number of chews and chewing time was greatly reduced.

Chapter 8 : Identification of parameters to