Development of a simple and objective evaluation method for thickened liquids using funnels

Some patients with dysphagia are prone to aspiration of low-viscosity liquids. Thickened liquids are often used in attempts to prevent aspiration. The patients should be given thickened liquids with suitable thickness, and the thickness should be constant at all time. While rotational and cone-and-plate viscometers are used for the evaluation of thickened liquids, they are high-precision and expensive equipment. To control the thickness of liquids, a simple and objective evaluation method is thus necessary. We developed a method to evaluate thickened liquids using funnels, and verified the appropriateness of this method. We measured the outflow times of five thickened liquids through funnels. One of the thickened liquids was a commercially available nutritional supplement, another was made with a thickening agent that contained guar gum, and all others were made with a thickening agent that contained xanthan gum. Four funnels with different stem sizes were tested. We found that the outflow time of thickened liquids through a funnel depended on their viscosities at a shear rate between 10 and 50 s^-1 , when the average inner diameter of the stem was in the range of 5.3-9.0 mm, and the volume of the liquid poured into the funnel was 30 mL. The correlation coefficient between the value of the sensory evaluation and the outflow time of the funnel with an average stem ID of 5.3 mm was 0.946. Therefore, this method may be useful in hospital and nursing home kitchens for evaluating thickened liquids.

The findings of this study will help develop a new method for the evaluation of thickened liquids. Funnels made from polypropylene, which are inexpensive and light, were used in this method. The process for measuring the outflow time of thickened liquids through a funnel is simple, and we can obtain quantitative data that are objective. Even though line spread test (LST) is well known as a simple measurement method, nutritional supplements and liquids thickened using a thickening agent containing guar gum have not been evaluated accurately. The funnel method was found to have a stronger correlation with sensory evaluation compared to LST. This method is useful in hospital and nursing home kitchens for evaluating thickened liquids.