Abstract
Asparagine is the predominant free amino acid in potato tubers and the present study aimed to establish whether it is imported from the leaves or synthesised in situ. Free amino acid concentrations are important quality determinants for potato tubers because they react with reducing sugars at high temperatures in the Maillard reaction. This reaction produces melanoidin pigments and a host of aroma and flavour volatiles, but if free asparagine participates in the final stages, it results in the production of acrylamide, an undesirable contaminant. 14CO2 was supplied to a leaf or leaves of potato plants (cv. Saturna) in the light and radioactivity incorporated into amino acids was determined in the leaves, stems, stolons and tubers. Radioactivity was found in free amino acids, including asparagine, in all tissues, but the amount incorporated in asparagine transported to the tubers and stolons was much less than that in glutamate, glutamine, serine and alanine. The study showed that free asparagine does not play an important role in the transport of nitrogen from leaf to tuber in potato, and that the high concentrations of free asparagine that accumulate in potato tubers arise from synthesis in situ. This indicates that genetic interventions to reduce free asparagine concentration in potato tubers will have to target asparagine metabolism in the tuber.
Highlights
Interest in the synthesis, transport and accumulation of free amino acids, free asparagine, has been stimulated in recent years by the discovery of acrylamide in common, plant-derived foods (Tareke et al 2002)
The food industry has devised many strategies for reducing acrylamide formation by modifying food processing, and in Europe this has resulted in a significant downward trend for mean levels of acrylamide in potato crisps from 763 ppb in 2002 to 358 ppb in 2011, a decrease of 53 % (Powers et al 2013)
Day temperature was maintained at 18 °C and night temperature at 16 °C; supplementary lighting was used to provide the plants with a 16-h day
Summary
Transport and accumulation of free amino acids, free asparagine, has been stimulated in recent years by the discovery of acrylamide in common, plant-derived foods (Tareke et al 2002). The FAO/WHO Expert Committee on Food Additives has recommended that dietary exposure to acrylamide should be reduced (Joint FAO/WHO Expert Committee of Food Additives 2011) and the European Commission issued ‘indicative’ levels of acrylamide in food in early 2011 (European Food Safety Authority 2011a). The food industry has devised many strategies for reducing acrylamide formation by modifying food processing (compiled in a ‘Toolbox’ produced by Food Drink Europe: http:// www.fooddrinkeurope.eu/uploads/publications_documents/ Toolboxfinal260911.pdf), and in Europe this has resulted in a significant downward trend for mean levels of acrylamide in potato crisps from 763 ppb in 2002 to 358 ppb in 2011, a decrease of 53 % (Powers et al 2013)
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