The important role of salivary α-amylase in the gastric digestion of wheat bread starch

Abstract

The role of salivary α-amylase (HSA) in starch digestion is often overlooked in favour of that of pancreatic α-amylase due to the short duration of the oral phase. Although it is generally accepted that the amylase of salivary origin can continue to be active in the stomach, studies ascertaining its contribution are lacking. This study aimed to address this issue by coupling in vitro oral processing with an in vitro dynamic system that mimicked different postprandial gastric pH reduction kinetics observed in vivo following a snack- or lunch-type meal. The digestion of both starch and protein from wheat bread as well as the interplay between the two processes were studied. We have observed that the amylolytic activity of saliva plays a preponderant role hydrolysing up to 80% of bread starch in the first 30 min of gastric digestion. Amylolysis evolved exponentially and nearly superimposing curves were obtained regardless of the acidification profiles, revealing its high efficiency.

In vitro digestion of bread: How is it influenced by the bolus characteristics?

“…The use of a single subject with consistent mastication behavior as chewing "device" has been reported in previous studies (Freitas et al, 2018;Hutchings et al, 2012). A volunteer (female, 29 years old) having a full dentition and normal occlusion was asked to chew a piece of bread crumb (5 g) until it was ready to be swallowed and then spit out the bolus.…”

“…It is evident that the 1:1 food-to-SSF ratio recommended by the INFOGEST protocol (Minekus et al, 2014) was at least 20% higher than what actually impregnated during in vivo mastication. Other in vitro studies of bread digestion also suggested that the optimal saliva level for wheat bread bolus was 0.5-1.0 mL/g (Bornhorst & Singh, 2013;Freitas et al, 2018). Hence, it was recommended that the level of SSF added should be re-evaluated for the specific food of interest, preferably based on in vivo measured saliva impregnation level.…”

“…A direct link between the oral processing results (e.g., bolus particle size) and nutritional outcomes (e.g., glycemic response) was established in studies of starch-based solid food including rice (Ranawana, Monro, Mishra, & Henry, 2010) and pizza (Zhu, Hsu, & Hollis, 2013). Not surprisingly, oral processing has been increasingly considered as an important factor in understanding food digestibility (Freitas & Le Feunteun, 2019;Freitas, Le Feunteun, Panouillé, & Souchon, 2018).…”

Inhibitory effect of black tea, lemon juice, and other beverages on salivary and pancreatic amylases: What impact on bread starch digestion? A dynamic in vitro study

“…The digestion of starch is initiated in the mouth by salivary αamylase (HSA), which starts hydrolyzing starch molecules (Gropper & Smith, 2013). This enzyme can carry on the amylolytic process in the stomach until it is inactivated by the increasing acidity, between pH 3 and 4 (Freitas, Le Feunteun, Panouille, & Souchon, 2018;Fried, Abramson, & Meyer, 1987). Pancreatic α-amylase and brush-border enzymes then resume amylolysis in the small intestine, where glucose, the final product of starch digestion, is finally absorbed (Gropper & Smith, 2013).…”

Salivary functions in mastication, taste and textural perception, swallowing and initial digestion

“…Salivary α‐amylase is considered to be of minor significance in polysaccharide digestion due to its rapid inactivation in gastric acid and its pH optimum at 6.8, but short‐chain glucose polymers in the diet may stabilise the enzyme and allow maintenance of activity at acid pH during the first period in the stomach (Rosenblum, Irwin, & Alpers, ). Furthermore, a recent study indicates that salivary amylase plays a significant role in gastric digestion as it hydrolyses up to 80% of bread starch in the first 30 min of gastric digestion (Freitas, Le Feunteun, Panouille, & Souchon, ). The activity of salivary α‐amylase may be of importance to patients suffering from chronic pancreatic insufficiency and neonates with insufficient development of the pancreas (Alpers, ).…”