Fiber analysis: Evaluation of screen printing fabric filters bags by three statistical approaches

Measurements of fiber fractions using the Ankom filter bag system, and four types of filter bags were compared with results obtained employing the procedure indicated by the Association of Official Analytical Chemists (AOAC). To assess agreement between procedures, three statistical approaches were used. Twenty-three materials differing widely in cell wall content, and composition were evaluated. Filter bags evaluated were Ankom F57 (porosity: 25 μm), and three types of bags made in our laboratory with polyester screen printing fabric, porosities 45 μm (B120), 36 μm (B140), and 23 μm (B150). Amylase neutral detergent fiber organic matter basis (aNDFom), acid detergent fiber organic matter basis (ADFom), and sulfuric acid lignin (Lignin (sa)) values obtained using crucibles (C) were compared with data obtained using F57, B120, B140 or B150 bags, and fiber values obtained with F57 were compared with data obtained employing B120, B140 or B150 bags. Statistical approaches used were analysis of variance (ANOVA), regression analysis (Deming method), and the Bland–Altman method of differences. In the ANOVA, no differences (P>0.18) were observed, between measurements of aNDFom, ADFom, and Lignin (sa) performed employing the AOAC, or the Ankom procedure using any type of bag. In the regression analysis, in all associations tested, the 0.95 confidence interval of the slope of the regressions contained the value 1, and Pearson correlations (P<0.001) were greater than 0.94. In aNDFom, ADFom, and Lignin (sa) comparisons, five, three, and two of the seven regressions did not include 0 in the 0.95 confidence interval of de intercept. In the Bland–Altman method, proportion of differences between limits of agreement, ranged from 0.91 to 1.0, 0.91 to 0.96, and 0.74 to 0.96, respectively, in aNDFom, ADFom and Lignin (sa) method comparisons. The statistical approaches evaluated, suggested a reasonable degree of agreement between aNDFom, ADFom, and Lignin (sa) measurements performed by the AOAC, and the Ankom Fiber Analyzer procedure, when F57 or B120 bags were used. This would suggest that using these procedures in sequential analysis, it is unlikely to yield erroneous values of the analytes. The Bland–Altman method resulted in a sensitive method, to identify differences among analytical procedures. Results suggest that, in the description of fiber protocols using the Ankom Fiber Analyzer, it is crucial to specifically describe filter bags employed.