This method describes how to determine the iodine value of laboratory spent grain.
Starch and β-glucans are the most important substances in malt [1]. The starch granules are generally embedded in a matrix of protein and cell walls, which consist largely of β-glucans. These are exposed to a certain extent during malting. A portion of the starch may be bound by lipids or other molecules, for example with clathrate or other inclusion-type compounds. Linear segments of starch molecules, in particular, can be retrograded and thereby made inaccessible to enzymatic degradation. Furthermore, very small starch granules, the so-called omega granules present in malt, are especially difficult to degrade.
Starch degradation during mashing is dependent on the composition of the grist. It occurs more slowly or progresses to a lesser extent in malt kernels of a smaller diameter, in those with shorter acrospires, in kernels that have failed to germinate, in glassy or partially glassy kernels or in coarse grits [1, 2]. As a rule, if amylolysis is judged to be adequate, then cytolysis and particularly proteolysis are also considered to have progressed satisfactorily [1].
The iodine value of the laboratory spent grains serves as a tool for evaluating of the degree of amylolysis and therefore the malt quality [1, 2, 3, 4], particularly if coarse grist is analyzed. The iodine value of the laboratory spent grains provides important information about the degree of modification, enzyme potential, heterogeneity and processability of the malt.
Barley malt intended for use in beer brewing or elsewhere in the food industry
High-molecular weight dextrins and starch present in the wort extracted from brewery spent grains are precipitated through the addition of ethanol, centrifuged and dissolved in phosphate buffer, followed by the addition of an iodine solution. Depending upon the molecular weight and degree of branching, a red to blue color forms, the intensity of which is measured spectrophotometrically at 578 nm.