Gluten Index for Wheat Products: Main Variables in Affecting the Value and Nonlinear Regression Model

A gluten index test was recently introduced as a quicker method to measure wheat processing quality in comparison with the classical instrumental methods, such as a mixograph and farinograph. It is also a criterion defining whether the gluten quality is weak, normal, or strong. The gluten index test has gained wide acceptance as a method of determining gluten strength and is used in international trade specifications. The innovation of this work was to: (a) collect published data regarding the values of gluten index and form a database; (b) investigate the impact of variables, such as genotype, glutenin, and gliadins subunits, the level of nitrogen fertilization, irrigation, the protein content of flour, damages on crop and addition of enzymes, on the value of the gluten index aiming the comprehension of their interaction; (c) establish a relationship between gluten index and the two predictor variables, nitrogen fertilization level and protein content. The results suggested that the above variables have a contrary effect on the value of the gluten index, even for the same treatment of definite wheat genotype, which leads us to the conclusion that additional variables must account for defining the gluten index value. Out of all interactions between the experimental variables and gluten index, only nitrogen fertilization level and protein content were found to be significant, having a power law nonlinear relationship.