Understanding variation in food oral processing behaviorof consumers differing in age, gender and ethnicity : a physiological perspective

Oral processing behavior is the start of food digestion, with the breakdown of food into smaller particles and the formation of a smooth bolus. This process consist of multiple physiological parameters and product properties all contributing to a smooth oral processing. Physiological parameters are driven by differences in consumer characteristics. Oral processing behavior is known to affect our food intake and it is therefore important to understand the variation and underlying mechanism of oral processing behavior. The research described in this thesis aimed to better understand food oral processing behavior of consumers varying in age, gender and ethnicity based on oral physiology, anatomy and sensory sensitivity. Secondly, this thesis systematically investigates the relationship of oral processing behavior with oral physiology and anatomy.In the first chapters of this thesis the influence of product properties (chapter 2) and consumer characteristics (chapter 3) on the oral processing behavior was investigated. In both chapters oral processing behavior was assessed with video recordings of the consumption behavior of 18 liquid, semi-solid and solid foods. In chapter 2 mechanical and rheological properties were assessed with uniaxial compression and with the use of a rheometer. Product liking, familiarity and frequency of consumption were assessed with the use of questionnaire. Rheological and mechanical properties of all food categories had a large effect on bite size, consumption time and eating rate. Liking, familiarity, and consumption frequency showed to have a relatively smaller impact on oral processing behavior.In chapter 3 oral processing behavior was compared between Dutch, Caucasian adults (18-30 yrs), Chinese, Asian adults (18-30 yrs), Dutch, Caucasian older adults (60-80 yrs), and consumers with mild swallowing problems and/or low mastication efficiency (18-80 yrs). Age, gender and ethnicity influenced oral processing behavior of liquid, semi-solid and solid foods differently. Age, gender and ethnicity had a strong effect on oral processing behavior. Older adults had an increased consumption and lower eating rate compared to adults. Females had smaller bite size and therefore a lower eating rate compared to males. Chinese, Asian consumers had a smaller bite size and lower eating rate compared to Dutch, Caucasian consumers. Consumers with decreased mastication efficiency or mild swallowing problems showed similar oral processing behavior than healthy consumers, probably because reduction in eating capability was limited in the group.To understand the underlying mechanisms of the oral processing behavior, oral physiology and anatomy were quantified of Dutch adults and older adults (chapter 4) and Chinese adults and older adults (chapter 4 & 5). Mastication performance, salivary flow rate (stimulated and unstimulated) and dental status were quantified to characterize oral physiology. Volume of oral cavity, tongue dimensions, facial anthropometry, height and weight were quantified to characterize anatomy. Oral processing behavior of three solid foods (carrot, cheese and sausage) was quantified by video recordings. Age, gender and ethnicity were found to affect oral physiology and anatomy. During ageing, dental status decrease, volume of oral cavity was smaller, head dimensions become smaller. Males had a larger volume of oral cavity and larger head dimensions compared to females. Chinese, Asian consumers were shorter, weigh less, had a lower height:width ratio of the head; had a lower percentage of normal occlusion compared to Dutch, Caucasian consumers. Certain effects of ethnicity on physiology were mediated by age, including saliva flow rate, number of teeth and molars. Several relationships were found between oral processing behavior and oral physiology and anatomy. Body weight and number of teeth had the strongest relationships with oral processing behavior. The results of chapter 4 and 5 suggest oral physiology and anatomy partially explain the variation in oral processing behavior. Other factors, including food habits and culture are suggested to have a stronger influence on oral processing behavior.  Chapter 6 investigated texture and taste sensitivity and consumer phenotype in consumers varying in gender and ethnicity. Texture and taste sensitivity were assessed by a 2-AFC ascending staircase method for thickness (maltodextrin solutions differing in viscosity), firmness (agar gels differing in fracture stress) and sweetness (sucrose solutions differing in concentration) sensitivity. Consumer phenotype was quantified by saliva flow rate, fungiform papillae density (FPD), lingual tactile threshold and PROP taster status. No significant differences were found between Chinese, Asian and Dutch, Caucasian adults in thickness, firmness and sweetness sensitivity and consumer’s phenotyping. Minor differences were found in firmness sensitivity and FPD between gender. Only one out of 15 relationships between sensory sensitivity (thickness, firmness, sweetness) and consumer characteristics (saliva flow rate, FPD, lingual tactile threshold, PROP taster status) was significantly and weakly related suggesting that inter-individual variation in these consumer characteristics was almost unrelated to sensory sensitivity. The results of this chapter indicate that texture (thickness, firmness) and taste (sweetness) sensitivity do not differ between Dutch, Caucasian and Chinese, Asian adults. Saliva flow rate, fungiform papillae density, lingual tactile threshold and PROP taster status do not explain inter-individual variation in sensory sensitivity between these consumers.To conclude, oral processing behavior has been found to be influenced by product properties and consumers characteristics, age, gender and ethnicity. While rheological and mechanical food properties have a large impact on food oral processing behavior, consumer characteristics are a major factor contributing to inter-individual variation in food oral processing behavior. Age, gender and ethnicity had an impact on oral physiology and anatomy. These factors should be taken into account when investigating oral processing behavior and oral physiology and anatomy. Since oral physiology and anatomy only partially explain the variation in oral processing behavior, we suggest other factors such as food habits and culture show a stronger influence on oral processing behavior