title: Viscosity of dysphagia-oriented cold-thickened beverages: effect of setting time at refrigeration temperature.
abstract: BACKGROUND
  Although extensive literature is available on the viscosity of thickened beverages with food thickeners, no attempt has been made to study the effect of setting time on the viscosity of pudding-like cold-thickened beverages with xanthan gum (XG)-based thickeners by using a rheometer. In particular, it is of considerable practical importance to investigate the effect of setting time on their viscosity at 5°C because some cold-thickened beverages will be prepared in the kitchen in bulk and stored at 5°C before serving or consuming rather than serving immediately upon mixing with thickeners.
  
  
  OBJECTIVE
  To examine the effect of different setting times (15-120 min) on the viscosity of cold-thickened beverages prepared with various XG-based food thickeners, and also to compare the viscosity differences among the various cold beverages and XG-based food thickeners in beverage-thickener mixture systems.
  
  
  METHODS
  Four commercially available XG-based food thickeners (A-D) and three cold beverages (water, orange juice and milk) were used for the preparation of cold-thickened beverages. The thickened sample was portioned into six samples for the designated setting times and then stored at 5°C over setting time. Their apparent viscosity (η(a,50)) at 50 s(-1) was measured using a rheometer.
  
  
  RESULTS
  The largest increases in η(a,50) values for thickened beverages, except for water, were observed at 15 min (p < 0.05), showing a pudding-like fluid, and at longer time periods their η(a,50) values gradually increased or were constant with an increase in setting time. The percentage increase in viscosity values at different setting times (15-120 min) as compared with the control (0 min) was less pronounced in the thickened orange juice and milk samples with thickener A over setting time, indicating that the thickened beverages with thickener A had more stable structure compared with those with other thickeners (B-D) over time. Statistical analysis showed that changes in the viscosity of cold-thickened beverages over setting time are greatly influenced by the type of beverages and thickeners.
  
  
  CONCLUSIONS
  Cold-thickened beverages should be carefully prepared with instant commercial XG-based food thickeners because they produced different thickening patterns over setting time which clinicians must consider for a safe and easy swallowing. The information presented in this study will provide both clinicians and patients with additional knowledge to prepare cold-thickened beverages with the corrected viscosity for safe swallowing.
authors.affiliation: Department of Food Science and Biotechnology, Dongguk University, Seoul, Korea.
authors.forename: Sung-Gun
authors.initials: SG
authors.lastname: Kim
authors.forename: Byoungseung
authors.initials: B
authors.lastname: Yoo
mesh_terms: D001628:Beverages; D003080:Cold Temperature; D003680:Deglutition Disorders / Q000178:diet therapy*; D005503:Food Additives; D006801:Humans; D011135:Polysaccharides, Bacterial; D012034:Refrigeration; D014783:Viscosity
chemical_list: D005503:Food Additives; D011135:Polysaccharides, Bacterial; C002563:xanthan gum
keywords: dysphagia; food thickener; setting time; viscosity; xanthan gum