Abstract
Objective: To compare the accuracy of the Osborne calculation for estimating gluten content in food in relation a laboratory (ELISA) based method. Methods: We evaluated 25 commonly consumed gluten-containing food products for ELISA testing of gluten to determine analyzed gluten content. This was compared with calculated gluten content (using the Osborne method) which was determined as 80% of the plant protein content of each food item using nutrition information. Correlation coefficient (r), along with a 95% confidence interval (CI) and Bland Altman plots were used to estimate the level of agreement between calculated and analyzed gluten. Results: A reasonable overall correlation coefficient of r = 0.46 a 95% CI (0.08 – 0.73, R2 = 0.22) was seen. We observed that variability in the Osborne (calculated) and analyzed gluten increased as the average gluten content increased and the average difference was not constant over the range of gluten measurements. In addition, the calculated gluten measure tended to be higher than analyzed and thus overestimated gluten content (net overestimation was 3.3 g (95% CI -4.0 to 10). Stronger correlations were observed in foods with a gluten content that was lower than the total protein content (N=18, r=0.70, 95% CI=0.35 to 0.88, R2 = 0.49). Conclusions: These findings indicate that the Osborne (calculated) to analyzed gluten shows a reasonable correlation in foods with lower gluten content (less than 5 g gluten), and that the Osborne method is a practical way to estimate gluten content.
Highlights
Celiac Disease (CD) is an autoimmune enteropathy characterized by damage to the small intestine [1]
It is appreciated that consuming a diet completely devoid of gluten may be difficult to achieve and that trace amounts of gluten are found in both natural gluten-free, and labeled gluten-free products [4,5,6]
Studies have quantified a select number of products consumed by individuals with CD to be tested for gluten consumption under controlled settings using enzyme linked immunoabsorbent assays (ELISA) [5,7] which is the gold standard test for gluten detection and quantification
Summary
A sample of 25 commonly consumed and readily available glutencontaining products were purchased in October, 2012. 0.25 g of each sample was placed in a sterile disposable 15 ml centrifuge tube, and 2.5 ml cocktail solution (r-Biopharm #R7006) was added and incubated at 50°C for 40 minutes. The dilution factor of the sample extract at this point was 1/500 Another factor of 2 was applied to convert the detected gliadin value to gluten value because it is assumed that the glaidins and glutelins (which together make up the glutens) are roughly in equal proportion. Results from the ELISA analysis were provided in ppm gluten, and converted to grams of gluten per 100 grams of food item. R squared values and regression coefficient estimates, where calculated gluten was used to predict analyzed gluten were conducted. Bland Altman Plots were used to assess the consistency of the difference between calculated and analyzed gluten over all values of average gluten content [(calculated+analyzed)/2] [13,14]
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