The Sulphur Response in Wheat Grain and Its Implications for Acrylamide Formation and Food Safety.

Sarah Raffan,Nigel G Halford,Joseph Oddy

doi:10.3390/ijms21113876

Sarah Raffan, Nigel G Halford + Show 1 more

Open Access

https://doi.org/10.3390/ijms21113876

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Abstract

Free (soluble, non-protein) asparagine concentration can increase many-fold in wheat grain in response to sulphur deficiency. This exacerbates a major food safety and regulatory compliance problem for the food industry because free asparagine may be converted to the carcinogenic contaminant, acrylamide, during baking and processing. Here, we describe the predominant route for the conversion of asparagine to acrylamide in the Maillard reaction. The effect of sulphur deficiency and its interaction with nitrogen availability is reviewed, and we reiterate our advice that sulphur should be applied to wheat being grown for human consumption at a rate of 20 kg per hectare. We describe the genetic control of free asparagine accumulation, including genes that encode metabolic enzymes (asparagine synthetase, glutamine synthetase, glutamate synthetase, and asparaginase), regulatory protein kinases (sucrose nonfermenting-1 (SNF1)-related protein kinase-1 (SnRK1) and general control nonderepressible-2 (GCN2)), and basic leucine zipper (bZIP) transcription factors, and how this genetic control responds to sulphur, highlighting the importance of asparagine synthetase-2 (ASN2) expression in the embryo. We show that expression of glutamate-cysteine ligase is reduced in response to sulphur deficiency, probably compromising glutathione synthesis. Finally, we describe unexpected effects of sulphur deficiency on carbon metabolism in the endosperm, with large increases in expression of sucrose synthase-2 (SuSy2) and starch synthases.

Highlights

Sulphur nutrition has been known to affect cereal crop yield and grain quality for many years
The effect of sulphur availability on yield and protein content of wheat grain has been the subject of extensive study for several decades (see [2], for Starch synthases are encoded by multigene families and there are both soluble and granule-bound forms of the enzyme (SS and GBSS, respectively) [85]
In the RNA-seq data [52], SS1 genes were identified on chromosome 7; SSII on chromosomes 1, 6, and 7; GBSSI genes on chromosomes 1 and 7; and GBSSII genes on chromosome 2

Summary

Introduction

Sulphur nutrition has been known to affect cereal crop yield and grain quality for many years. Is required for farmers to achieve optimum yield and protein content in wheat, with UK farmers applying 250–300 kg of nitrogen per hectare to breadmaking wheat. The authors of that study noted that sulphur deficiency had become much more widespread in agricultural land in western Europe towards the end of the 20th Century. This was caused in part, ironically, by the huge decrease in atmospheric sulphur deposition that had been achieved in that period, with the switch to low-sulphur fuels such as natural gas and the fitting of coal- and oil-burning power stations with pre- and post-combustion systems for removing sulphur. We describe evidence that sulphur deficiency has unexpected but substantial effects on genes involved in the regulation of carbon metabolism and starch synthesis

The Discovery of Acrylamide in Food

Findings

Conclusions