An Investigation of the Influence of Age and Saliva Flow on the Oral Retention of Whey Protein and Its Potential Effect on the Perception and Acceptance of Whey Protein Beverages

Abstract

Protein fortified products are regularly recommended to older adults to improve nutritional status and limit sarcopenia. However protein fortification can elicit negative sensory attributes such as mouthdrying. Sensitivity to mouthdrying can increase with age, yet the influence of saliva flow and mucoadhesion remain uncertain. Here, two studies tested different whey protein beverages (WPB); 22 healthy younger volunteers completed a pilot and 84 healthy volunteers from two age groups (18–30; 65+) completed the main study. In both studies salivary flow rates (mL/min) were measured and saliva samples were collected at time intervals post beverage consumption to measure mucoadhesion to the oral cavity, where protein concentration was analysed by Bradford Assay. Volunteers rated perception and acceptability of WPBs in the main study. WPB consumption resulted in significantly increased protein concentration (p < 0.0001) in saliva samples compared with a control whey permeate beverage. Older adults had significantly lower unstimulated saliva flow (p = 0.003) and significantly increased protein concentration (p = 0.02) in saliva samples, compared with younger adults. Heating of WPB significantly (p < 0.05) increased mouthdrying and thickness perception and reduced sweetness compared with unheated WPB. Mucoadhesion is concluded to be a true phenomenon in WPBs and increases with age.

Influence of Age and Individual Differences on Mouthfeel Perception of Whey Protein-Fortified Products: A Review

“…For example, a previous in vitro study has shown that, despite being washed with artificial saliva, proteins remained on the buccal mucosa or tongue apex (with proteins bound to the oral mucosa) [ 131 ]. Indeed, more recently, our research group confirmed in a human oral retention study that protein does adhere to the oral cavity post WPB consumption to a greater extent [ 89 ]. Although whey proteins have a high nutritional value, they become unstable when heated, resulting in protein denaturation and aggregation, which influences the structure and stability of the protein [ 132 ].…”

“…Table 2. Commonly proposed causes of whey protein beverage (WPB) derived mouthdrying adapted from Norton et al [89] and associated limitations [135][136][137][138][139][140]. Cakes and biscuits [90], WPB [83,86,91,92,[123][124][125][126][140][141][142], rye bread and cream cheese [94] o…”

“…Whey protein-fortified products typically have poor consumer acceptance and this has been linked to both undesirable taste and aroma attributes, as well as negative mouthfeel attributes, such as a build-up of mouthdrying, mouthcoating, chalky, metallic and filming, associated with repeated consumption [ 81 , 83 , 84 , 85 , 86 , 87 , 88 ]. Mouthdrying has been perceived by consumers in two different whey protein-fortified food matrices [ 89 , 90 ]. For example, within a liquid model, beverages fortified with whey protein were associated with mouthdrying, low liking scores and presence of off flavours [ 83 , 89 , 91 , 92 ].…”

“…Mouthdrying has been perceived by consumers in two different whey protein-fortified food matrices [ 89 , 90 ]. For example, within a liquid model, beverages fortified with whey protein were associated with mouthdrying, low liking scores and presence of off flavours [ 83 , 89 , 91 , 92 ]. Within a solid model, snacks (such as cakes, muffins, biscuits and rye bread) fortified with whey protein were perceived as mouthdrying and/or had a dry texture and reduced liking [ 90 , 93 , 94 ].…”

“…Currently, the majority of the literature, as outlined in Table 3 a–c has focused on using in vivo and physiochemical analysis to understand the proposed mechanisms of whey protein-derived mouthdrying alongside collecting sensory data. Key limitations are, however, associated with these methods: (1) researchers are only able to provide correlations between potential underpinning mechanisms and sensory data, and therefore, are unable to prove relationships; (2) a lack of research involving the human mouth, apart from the oral retention method developed by our research group [ 89 , 134 , 136 ]; (3) the ongoing challenge of quantifying mouthdrying using a ‘physical measure’ at the same time as scoring mouthdrying perception within products; (4) there is no defined mouthdrying threshold test to quantify individual sensitivity; (5) few studies have explored the role of individual differences on mouthdrying using consumers. Despite mouthdrying sensations being present in different whey protein-fortified food matrices, the majority of cited studies which have investigated mouthdrying in the solid food matrices have only used sensory methods ( Table 3 a–c) [ 90 , 93 , 94 ].…”