Asparagine, problem in the production of many foods
Asparagine is an important reserve substance in many plant seeds, which provides sufficient nitrogen during germination. However, asparagine can also become a problem in the production of many of our foods. We often use plant seeds as the basis for our diet and heat or roast them to produce tasty foods (e.g.: baked goods, muesli, beer, coffee, whiskey, nuts, marshmallows). Unfortunately, the amino acid asparagine reacts preferentially when heated (>140°C) with many sugars (reducing carbohydrates, e.g. glucose, fructose, lactose), which are usually present in excess in the seed, to form acrylamide (Maillard reaction), which is neurotoxic and carcinogenic works [1]. The EU has therefore set guideline values for acrylamide:
from REGULATION (EU) 2017/2158:
The following guideline values apply to acrylamide in food in accordance with Article 1 paragraph 1:
| Food | standard value [µg/kg] |
|---|---|
| French fries (ready to eat) | 500 |
| Potato chips made from fresh potatoes and potato dough Other potato products made from potato dough | 750 |
| soft bread | |
| a) Wheat-based bread | 50 |
| b) Soft bread other than wheat-based bread | 100 |
| Breakfast cereals (excluding porridge) | |
| Bran products and whole grains, puffed grains | 300 |
| Wheat and rye based products | 300 |
| Corn, oat, spelt, barley and rice based products | 150 |
| Cookies and waffles | 350 |
| Crackers, excluding potato/potato based crackers | 400 |
| Crispbread | 350 |
| Gingerbread | 800 |
| Roasted coffee | 400 |
| Instant coffee (soluble coffee) | 850 |
| coffee agents | |
| a) Coffee substitutes made exclusively from grain | 500 |
| b) coffee essence exclusively from chicory | 4000 |
| c) Coffee agent from a mixture of grain and chicory | 500-4000 |
| Infant food, processed cereal-based food for infants and young children, excluding biscuits and rusks | 40 |
| Biscuits and rusks for babies and toddlers | 150 |
What can be done to comply with the guidelines?
Heating or roasting is decisive for the formation of acrylamide. This explains the high standard values that are given to dry baked goods. Bread is our predominant food and requires heating. Therefore, it is advisable to use grains with low asparagine content. The asparagine content in flour depends on many factors: type of plant, soil fertilization (especially sulphur), climate (stress factor: drought) or milling process (ash content, whole grain to refined flour). Curtis et al. (2018) recommend determining the asparagine content of wheat varieties [2].
In order to comply with the guide values, attempts are also made to reduce the asparagine content before baking. This is possible by adding the enzyme asparaginase, which breaks down existing asparagine into the amino acid aspartate. Asparaginase is produced on an industrial scale. This allows the formation of acrylamide to be reduced by up to 90% [3]. But if you don't want to use a recombinantly produced enzyme, you can try asparaginase-producing yeast or bacterial strains (sourdough).
By determining the asparagine content in the flour or measuring the asparaginase, we can help to find decision criteria to minimize the formation of acrylamide during baking.
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[1] IAC MONOGRAHS ON THE EVALUATION OF CARCINOGENIC RISKS TO HUMAS (1994) Vol. 60 IARC, Lyon [2] Curtis et al. (2018) Effects of variety, year of cultivation and sulphur supply on the accumulation of free asparagine in the grain of commercial wheat varieties. Food Chemistry 239: 304-313. [3] Kumar et al. (2014) Reduction of Acrylamide Formation in Sweet Bread with L-Asparaginase Treatment Food Bioprocess Technol 7:741–748
