Genetic and environmental factors controlling acrylamide formation in wheat products

Acrylamide forms from free asparagine and reducing sugars during cooking and products derived from the grain of cereals, including wheat and rye, contribute a large proportion of total dietary intake. In this study, free amino acid concentrations were measured in the grain of wheat varieties Spark and Rialto and four doubled haploid lines from a Spark × Rialto mapping population. The parental and doubled haploid lines had differing levels of total free amino acids and free asparagine in the grain, with one line (SR3) consistently being lower than either parent for both of these factors. Sulphur deprivation led to huge increases in the concentrations of free asparagine and glutamine, and statistical analysis showed clear separation of the grain samples as a result of treatment (environment, E) and genotype (G), and provided evidence of G × E interactions. Low grain sulphur and high free asparagine concentration were closely associated with increased risk of acrylamide formation. G, E and G × E effects were also evident in grain from six varieties of wheat grown at field locations around the UK in 2006 and 2007. Free amino acid and sugar concentrations were also measured in the grain of a range of rye varieties grown at locations in Hungary, France, Poland and the United Kingdom and harvested in 2005, 2006 and 2007. The data showed free asparagine concentration to be the main determinant of acrylamide formation in heated rye flour, as it is in wheat. Free asparagine concentration was shown to be under genetic, environmental and integrated (G × E) control. The same was true for glucose, whereas maltose and fructose were affected mainly by environmental factors while sucrose was largely under genetic control.

Free asparagine concentration was closely associated with bran yield, while sugar concentration was associated with low Hagberg falling number. Rye grain was found to contain much higher concentrations of free proline than wheat grain and less acrylamide formed per unit of asparagine in rye than wheat flour. Matrix-assisted laser desorption/ionization mass spectrometric (MALDI-MS) imaging was used to visualize free asparagine distribution in wheat grain. In grain produced under full nutrition, free asparagine was localized mainly in the embryo (bran fraction) while in grain grown in the absence of sulphur it accumulated throughout the grain, notably at high levels in the endosperm (white flour fraction). Field trials with 130 doubled haploid lines and their parent varieties, Spark and Rialto, were carried out over three years and significant progress was made towards the identification of quantitative trait loci (QTL) controlling asparagine accumulation. The data indicate that progress in reducing the risk of acrylamide formation in processed wheat and rye products could be made immediately through the selection and cultivation of low free asparagine varieties and that further genetically-driven improvements should be achievable. Environmental factors, including agronomy, are also important, and even moderate sulphur deprivation should be avoided in wheat.