Reliability in viscosity measurement of thickening agents for dysphagia management: Are results obtained by cone-and-plate rheometers reproducible between laboratories?

Viscosity measurement using a cone-and-plate rheometer is considered to provide an objective and reliable evaluation of thickening agents for dysphagia management. Here, we showed its measurement uncertainty in the context of an inter-laboratory study. Eight test samples (i.e., four viscosity standard liquids, one xanthan gum reagent powder, and three commercial thickening agent powders) were distributed to 10 laboratories in a blinded manner. According to the same standard operating procedure, each laboratory dissolved the xanthan gum or thickening agents at four concentrations (0.5-4.0 g/100 g) and then measured their viscosity (35-803 mPa∙s). As for the viscosity of the standard liquids, the grand means were 98-100% of the certified values, and the relative standard deviations for repeatability (RSDr ) and reproducibility (RSDR ) were ca. 1% and ca. 5%, respectively, suggesting good accuracy in the measurement process. On the other hand, as for the viscosity of the thickening agents, RSDr and RSDR were ca. 2-6% and ca. 5-8%, respectively; however, heterogeneity in the preparation process comprising a manual dissolving step may increase these to near 60%. Furthermore, RSDr and RSDR of estimated additive concentrations to achieve targeted viscosities (50-500 mPa∙s) based on concentration-viscosity curves were ca. 1-3% and ca. 3-5%, respectively, with a few exceptions. These findings suggest that a strictly standardized procedure provides reliable data on the viscosity measurements for thickening agents.

[Method Verification for Vitamin D Analysis in Processed Foods Based on the Analytical Manual for the Standard Tables of Food Composition in Japan 2015 (Seventh Revised Edition)].

Considerable amounts of processed foods contain vitamin D (ergocalciferol (D2) and cholecalciferol (D3)) as food additives. For field surveys on food additives, the analytical method for vitamin D should be well-validated. However, the current official method in Japan cannot separately determine the concentrations of D2 and D3, whereas the method for the Standard Tables of Food Composition in Japan 2015 (STFC method) can. Therefore, in this study, we verified the applicability of the STFC method to processed foods. During the course of this research, we added some improvements to the original method. Spike and recovery experiments using vegetable juice, soymilk, and corn flakes as food matrices showed that the recovery rates (relative standard deviation) of D2 and D3 were 103-112% (4.7-12.6%) and 102-109% (2.4-21.8%), respectively, at the estimated method limit of quantification (EMLOQ) level; and 100-110% (4.0-7.4%) and 102-105% (3.8-4.8%), respectively, at 10 times the EMLOQ level. These results indicated that accuracy and precision of the modified STFC method were enough to determine dietary D2 and D3 as endogenous nutrients and/or food additives, and suggested that this method is appropriate for analyzing vitamin D concentrations in processed foods.

Tandem Cation/Anion Exchange SPE Cartridge Method for Sample Desalting for HPLC Analysis of Soluble Dietary Fiber: Development and Inter-laboratory Validation.

In HPLC analyses of soluble dietary fiber, desalting processes using open, mixed-bed ion-exchange columns are time-consuming and labor-intensive. We developed and validated a simple desalting method using tandem cation/anion exchange SPE cartridges. We found that combining Bond Elut Jr SCX (upstream) and Bond Elut PSA (downstream) cartridges provided adequate desalting of test solutions. The developed method was then validated in an inter-laboratory study. Five test samples were prepared by mixing food matrixes with purified soluble dietary fiber and treated to generate solutions to test the desalting process. These solutions were then analyzed by eight different laboratories. The results demonstrated that the developed method is simple and reliable for desalting samples containing 140 to 945 mg/100 mL of soluble dietary fiber in preparation for HPLC analysis of soluble dietary fiber.