Esther Assor, Jolie Davies-Shaw, Margaret A. Marcon and Farid H. Mahmud
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.