Dinu, Vlad
(2020)
Flavour-saliva interactions: implications of submaxillary mucin and α-amylase.
PhD thesis, University of Nottingham.
Abstract
During food ingestion, a large proportion of the aroma and taste compounds remain trapped in the food bolus and are therefore not available for perception. These compounds serve no functional benefit as flavourings and may also have negative health impacts (e.g.hypertension through high levels of salt, diabetes from excess of sugar ) to the consumer. Understanding the interactions underpinning the partitioning of aroma and taste compounds from the bolus during oral processing is required to mitigate these adverse effects. Therefore, the focus of this study is on the interactions between functional food ingredients (dietary acidity, salt, polyphenols, polysaccharide mucoadhesives) and two of saliva’s most abundant macromolecules, salivary mucin and α-amylase.
Firstly, the macromolecular hydrodynamic integrity of glycoproteins was assessed as a function of pH and ionic strength, as a way of understanding the effects of dietary acid and salt, and evaluate any resulting changes in the aroma release profile. An increase in acidity and saltiness impacted the native state of mucin and α-amylase, through charge shielding effects and aggregation phenomena. Protein interactions with pH and ionic strength are suggested to be, at least in part, responsible for the enhanced flavour perceived in acidic and salty foods. Then, green tea was investigated for its ability to interact with whole human saliva as a means of developing a platform for analysing interactions with food in their native dilute states. The green tea polyphenol epigallocatechin gallate (EGCG) interacted with low molecular weight components in saliva and was found to be an essential step in the formation of green tea aroma.
The development of new mucoadhesive biopolymers for oral processing formulations has received great attention in recent years for enhancing the release of flavour in food. The addition of pullulan to saliva was identified to result in the formation of lower molecular weight and lower viscosity fragments via salivary α-amylase hydrolisis. This property was correlated to an enhanced release of aroma and salt. To address issues associated with the rapid ingestion, a cationic pullulan analogue was developed to aid in its adhesion to submaxillary mucins. Dimethylaminoethyl pullulan (DMAE-Pullulan) was synthesised for the first time, and shown to bind to submaxillary mucin, and also degraded by salivary α-amylase. In addition, an in-vitro mucus-like biomimetic was developed for evaluating mucoadhesion and flavour retention by immobilising mucin glycoproteins in calcium alginate gels. This resulted in the formation of bead structures containing mucin and mucin aggregates both on and within the calcium-alginate matrix. Polysaccharides of different ionic properties were tested for their ability to retain flavour compounds onto the surface of the mucus like mimetic. It was found that mucins were the predominant driving force in the interaction with the polymers, with positively charged species showing the highest retention (electrostatic interactions).
Findings from these investigations also added to our current understanding of the interactions between salivary proteins and aroma compounds. Current evidence suggests that high concentrations (>1 %), of aroma compounds i.e. ketones, aldehydes and phenols, can affect the hydrodynamic integrity of proteins. These changes are suggested to directly impact on the structure and function of mucosal proteins.
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