ORAL SOMATOSENSORY FUNCTION AND THE PERCEPTION OF CHOCOLATE PARTICLE SIZE
Open Access
- Author:
- Breen, Scott Patrick
- Graduate Program:
- Food Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 23, 2018
- Committee Members:
- John E Hayes, Thesis Advisor/Co-Advisor
Nicole Michele Etter, Committee Member
Gregory Ray Ziegler, Committee Member - Keywords:
- Chocolate
Oral Somatosensation
Psychophysics
Particle Size - Abstract:
- Texture is a sensory property that plays a strong role in liking or rejection of many foods; however, the mechanisms of oral texture perception remain poorly understood. Particle size and particle size distribution (PSD) are fundamental characteristics of food products which can have a large influence on texture. For example, in chocolate, a semi-solid suspension of fine particles from cocoa and sugar that are dispersed in a continuous fat phase, the PSD directly influences the overall viscosity and mouthfeel. Orofacial somatosensation arises from multiple afferent nerves which are essential for achieving rapid and accurate motor outputs, like speech and swallowing, and may play a role in texture detection mechanisms. To date, no work has been done to measure human somatosensory function on lingual (tongue) surfaces as they relate to the detection of particle size in a food product. Here, I measured the just noticeable difference (JND) for particle size in melted dark chocolate and assessed two conceptually distinct measures of oral somatosensory function – oral point pressure sensitivity and surface roughness discrimination – and tested the relationship between these phenotypes. Cocoa liquor and sugar mixtures were refined to twelve different particle sizes and combined with cocoa butter and soy lecithin to create dark chocolate samples with a fat content of ~32%. To estimate JND values for particle size in four series of samples, naïve participants evaluated pairs of samples in a 2-alternative forced choice (2-AFC) task. Detection and discrimination threshold estimates for oral pressure point sensitivity were measured with Von Frey Hair (VFH) monofilaments (8mg to 10g) and discrimination threshold estimates for surface roughness were measured with stainless steel blanks ground to different levels of roughness (Ra; 0.535-0.722 m), both by using staircase procedures. Two commercial samples of dark chocolate differing in mean particle size (19 and 26 m) were evaluated for differences in grittiness via a 2-AFC task. The JND for D90 (90% of particles smaller than) particle size was fairly constant for the first three series (~5m) but increased with increasing particle size to ~10m. The Weber Fraction (K) was roughly constant: approximately K = 0.2 for the particle size range (~20-80 m) studied here. Consistent with prior work, the responses of participants were characterized by high (RHi) and low (RLo) sensitivity groups for roughness; observed variation in point pressure sensitivity allowed participants to be grouped into high (PPHi) and low (PPLo) sensitivity groups. However, there was no significant relationship between the two oral phenotypes. Across all participants, the group successfully discriminated between two chocolates differing in particle size (i.e. 19 versus 26 m), but this effect was driven almost entirely by those more sensitive to pressure from VFH: 17 out of 20 of the PPHi group significantly identified the grittier chocolate, versus chance performance (12/24) for PPLo. No effect was seen for roughness sensitivity on perception of chocolate particle size. This work suggests differences in oral somatosensory function may influence perception of food texture. Additional research is needed to further characterize texture detection mechanisms in the mouth and their relationship to food texture.