STUDENT CONTRIBUTION FEATURE
Individual variability of saliva and the perception of food flavour Words by Xinwei Ruan, Jiaqiang Luo and Dr Kate Howell
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veryone has saliva, which is essential to our physiological processes for digestion, but have you ever wondered what saliva is made of? While human saliva appears similar, its composition between people varies widely. Variation mainly depends on who you are, your diet and your lifestyle. Our saliva is integral in every eating process - to reduce food size, initiate digestion and to perceive the flavour of foods. Therefore, is it possible that our individual variation in saliva composition also makes food taste different to different people? Here, we describe the interindividual variation in human saliva and demonstrate the potential connections to both host factors and sensory perception. Studying various sensory responses potentially allows us to better understand the preferences of consumer groups with diverse salivary compositions and to better design foods for particular audiences.
What is in saliva? Our saliva is approximately 99% water, but the remaining 1% is highly complex, and includes electrolytes, proteins, lipids, sugars, and hormones.1 The small fraction of functional salivary ingredients provides critical support during
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food consumption. For example, one of the most common salivary proteins, mucin, has a lubricating and softening effect on food during chewing. Without lubricating proteins like mucin, it is not possible to swallow solid food. Saliva is important for supporting growth of the oral microbiota and allowing the adhesion of the resident microorganisms. The oral cavity is one of the most complex and clinically relevant habitats in our bodies, colonised by various microbial groups including bacteria, fungi, archaea and viruses. Bacteria are the most abundant microorganisms in saliva as more than 700 bacterial species in the oral cavity have been identified and are supported by saliva as a major energy source.2 Every day, 80 billion bacteria are shed from the surface of the mouth and carried into the digestive tract by swallowing with the help of saliva.3 The salivary microbiome is essential in maintaining host health status through host-microbe interaction. Although the underlying mechanisms by which microbes and host are linked have not been fully understood, emerging evidence shows that the salivary microbiome alters with the changes in health status of the host.
Do we all have the same saliva? Numerous studies have evidenced the inter-individual variations in our saliva. Different people may vary in both the volume of saliva produced and its composition. Similarly, not all bacteria detected from the oral cavities are shared from person to person. Our previous study defined the core membership of healthy human salivary microbiota by re-analysing raw 16S rRNA data from 47 studies. Although the core microbiota is common across the 2,206 saliva samples investigated, they also demonstrated large variabilities among different populations.4 Interestingly, the composition of saliva produced by the same person is also dynamic. For example, the composition of our saliva can be significantly different in the morning and the afternoon. The large variability of salivary composition is attributed to intrinsic personal attributes and lifestyle factors. The intrinsic factors are inherent physiological characteristics such as age, gender, ethnicity, circadian rhythm and genetic characteristics, while lifestyle factors are regarded as extrinsic factors. Some lifestyle habits, such as smoking, drinking alcohol and
