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Formation of Acrylamide in Food
Lauren Jackson, Ph.D.U.S. Food and Drug Administration
Center for Food Safety and Applied NutritionNational Center for Food Safety & Technology
Summit-Argo, IL
Food Advisory CommitteeContaminants and Natural Toxicants
Subcommittee ACRYLAMIDEDecember 4-5, 2002
OBJECTIVES• Summarize what is known about
mechanisms, precursors and factors that affect acrylamide formation
• Identify the research needs• Discuss the FDA Action Plan for Acrylamide-
FormationUnderstand the conditions that lead to the
formation of acrylamide in foodDevelop methods to prevent or reduce formation
of acrylamide
What is Known About Acrylamide Formation?
• How is acrylamide formed in food? – Precursors– Pathways/mechanisms
• What factors affect acrylamide formation?– Food composition– Processing
Precursors of Acrylamide/Pathways of Formation
• Acrolein
• Acrylic acid
• Amino acids alone
Amino acids + reducing sugars via Maillard browning/Strecker degradation
Acrolein
• Acrolein (2-Propenal)– Structurally similar to
acrylamide– Formed in oil during frying– Also formed from thermal
degradation of starches, sugars, amino acids and proteins
– Disproven as the major acrylamide precursor**
c c Hc
OH
H
H
c c NH2
c
OH
H
H
c c OHc
OH
H
H
(O)
(+NH3)
Acrolein
Acrylamide
Acrylic Acid
Acrylic Acid• Acrylic Acid
– Structurally similar to acrylamide– Formed from thermal
deamination of alpha- and beta-alanine
– Formed from assorted di-acids (malic, tartaric) and amino acids (cysteine, serine)
– Not believed to be the major acrylamide precursor** c c NH
2c
OH
H
H
(+NH3)
Acrylamide
c c OHc
OH
H
H
Acrylic Acid
Amino Acids Alone• Alanine• Asparagine• Glutamine• MethionineAmino acids alone
not believed to be a major pathway in potatoes and grains
Relevance to acrylamide formation in other foods (coffee?) needs to be verified
Stadler et al. Nature Vol 419 3 Oct. 2002, p. 449
H2N
Acrylamide
O NH2
O
OH
H2N
O
NH2
O
OH
R.
Asparagine Glutamine
c c NH2
c
OH
H
H
Amino Acids + Reducing Sugars (Maillard Reaction and Strecker Degradation)
• What are the Maillard and Strecker reactions?– Reaction of amino acids with reducing sugars (glucose,
fructose, ribose etc.) or other source of carbonyls
– Responsible for color and flavor formation in heated foods
• Reasons for suspecting mechanism– Potatoes have a relatively high levels of free amino
acids
– Potatoes and grain products are rich in carbohydrates (possible sources of reducing sugars and carbonyls)
– Acrylamide levels in some foods tend to increase with level of browning
Which Amino Acids Form Acrylamide?Aqueous Model System Studies
Reaction mixture mg acrylamide/
mole amino acid
Asparagine + glucose 221
Glycine + glucose < 0.5
Cysteine + glucose < 0.5
Methionine + glucose < 0.5
Glutamine + glucose 0.5 - 1.0
Aspartic acid + glucose 0.5 - 1.0Conditions: 0.1 mmole amino acid: 0.1 mmole glucose in 100 microliters of 0.5 M phosphate buffer (pH 5.5); 185°C, 20 min.
From: Mottram et al. (2002)
Which Amino Acids Form Acrylamide?Potato Chip Model System Studies
Acrylamide Formation– Potato starch <50 ppb– Potato starch + glucose <50 ppb– Potato starch + asparagine 117 ppb– Potato starch + glucose + asparagine 9270 ppb
Other Amino Acids– Alanine <50 ppb Arginine <50 ppb– Aspartic Acid <50 ppb Cysteine <50 ppb– Lysine <50 ppb Methionine <50 ppb– Threonine <50 ppb Valine <50 ppb– Glutamine 156 ppb Asparagine 9270 ppb
From: Sanders et al. (2002)
15N-acrylamidem/z 73
Unlabeled Acrylamidem/z 72
15N13C13C13C-acrylamidem/z 76
Further Proof of Asparagine as Precursor of Acrylamide:Origin of Nitrogen and Carbons of Acrylamide
From: R.A. Sanders et al. (2002)
CH2
#1)NH2
C
CH2
NH2 CH COOH
O
15 NH2
C
CH2
O
15
CH2
#2)NH2
C
CH2
NH2 CH COOH
O
15
NH2
C
CH2
O
CH2
#3)NH2
C
CH2
NH2 CH COOH
O
15
15
13
13
13
13
NH2
C
CH2
O
15
13
13
13
Mechanisms of Formation:A. Maillard Reaction/Strecker Degradation
Formation of acrylamide after Strecker degradation of asparagine (and methionine) in the presence of dicarbonyls (Maillard browning products)
Heating asparagine with butanedione, instead of glucose, resulted in acrylamide formation
From: Mottram et al. (2002)
Mechanisms of Formation:B. Formation from N-Glycosides
From: Stadler et al. (2002)
N-(D-glucos-1-yl)-L-asparagine
N-(D-fructos-2-yl)-L-asparagine
N-(D-glucos-1-yl)-L-glutamine
N-(D-glucos-1-yl)-L-methionine
Speculated Pathway Bvia Formation of N-Glycosides
From: Stadler et al. (2002)
13051419
14 8.1
0
200
400
600
800
1000
1200
1400
1600N-(D-glucos-1-yl)L-asparagine
N-(D-fructos-2-yl)-L-asparagine
N-(D-glucos-1-yl)-L-glutamine
N-(D-glucos-1-yl)-L-methionine
Conditions: 180°C; 30 min; dry state
Acr
ylam
ide
form
ed(m
icro
mol
e pe
r m
ole
N-g
lyco
side
)
Formation of Acrylamide from Other Amino Acids + Sugars
• Glutamine• Aspartic acid• Cysteine?
• Methionine– believed to be the second most important
precursor amino acid– May form acrylamide via N-glycoside formation as
well as through Maillard/Strecker pathway
May be due to impurities
Which Mechanism(s) Occur in Food?
Foods high in asparagine/sugars tend to have greater acrylamide formation upon cooking
Food % ASN (% of total free
amino acids)
mg ASN/kg food
Levels of acrylamide in food after frying, baking or roasting
Potato 40 940 ++++
Wheat flour
14 167 +++
High protein
rye flour
18 173 +++
Asparagus 30 ? ++
Almonds 34.4 ? ++
Coffee (green)
12 ? ++
Meat < 5 ? N.D. or +
Which Mechanism(s) Occur in Food?• Potatoes: Asparagine/sugar; Maillard browning Strecker degradation
Use of asparaginase to treat potato (mashed) before frying decreased asparagine levels by 95% and acrylamide levels by >99% (Zyzak, 2002; personal communication)
• Grain-based foods: Asparagine/sugars are believed to be precursors and Maillard browning/Strecker degradation are believed to be mechanism- Needs to be verified
• Other foods:– Coffee, chocolate/cocoa, almonds- amino acid/sugar?– Meat- methionine/sugar?
What Factors Affect Acrylamide Formation?
• Food composition – Precursors– pH– Moisture – Other compounds
• Processing conditions– Time– Temperature– Other
What Factors Affect Acrylamide Formation?
• Food composition– Amino acids
• ASN, MET, GLN, ASP, CYS• Other amino acids- LYS
– Sugars• Fructose > glucose > sucrose (Becalski et al, 2002- personal
communication)- aqueous model system• No difference in yield of acrylamide from D-fructose, D-galactose,
lactose or sucrose (Stadler et al., 2002) under pyrolysis conditions
– pH • pH 8.0 > 5.5 > 3.0 (Becalski et al., 2002- personal
communication)
What Factors Affect Acrylamide Formation?
• Food composition– Moisture content
• Effects unclear
– Others• Sulfites- no effect on acrylamide formation in
model systems (Zyzak et al., 2002; Becalski et al., 2002- personal communications)
• Antioxidants- Rosemary extract had no effect on acrylamide production during frying (Becalski et al., 2002)
• Glutathione/cysteine • Fermentation
Processing Conditions• Temperature- Yes
• Time- Yes
What Factors Affect Acrylamide Formation?
Effect of Temperature
• At temperatures 120-170°C, acrylamide levels increase with processing temperature
• Acrylamide forms at 120-140°C
• May degrade at temperatures > 170°C?
From Mottram et al. (2002)
Asparagine/glucose aqueousmodel system (closed)
In simple model systems:
Effect of Temperature
0
500
1000
1500
2000
2500
100 120 140 160 180 200 220
Acr
ylam
ide
(ng
/g)
From: Tareke et al. (2002)
In food:• Boiling and retorting
produce little to no acrylamide
• Frying and baking result in modest to high levels
• Acrylamide levels increase with cooking/processing temperature
Oven-cooked French fries
Oven Temperature (°C)
Effect of Temperature
• Acrylamide levels increased with frying oil temperature
160°C; 4 min27 ppb
170°C; 4 min70 ppb
180°C; 4 min326 ppb
Effect of Time
• Acrylamide levels increased with frying time
3.5min12 ppb
180°C; 3.5 min12 ppb
180°C; 4.0 min46 ppb
180°C; 4.5 min227 ppb
180°C; 5.0 min973 ppb
Summary of Research Findings
1. ASN/reducing sugar are important precursors for forming acrylamide in many foods; other amino acids may be important precursors in some foods
2. The Maillard reaction/Strecker degradation pathway is important in many foods
3. The acrolein pathway is unlikely4. Processing conditions (time/temperature)
are critical to levels of acrylamide in food
What Are the Research Gaps?
1. Measure the levels of free asparagine, other amino acids and reducing sugars in foods on a dry weight basis and correlate levels to acrylamide production during processing/cooking
2. Determine the mechanism(s) of formation of acrylamide in each food category
3. Determine the effects of time, temperature, pH, and moisture on acrylamide formation in various matrices
4. Measure the kinetics of acrylamide inhibition/destruction/scavenging under various reaction/process conditions
FDA Action Plan on Acrylamide: Formation
1. ***Understand the food processing and cooking conditions that affect acrylamide formation, destruction, and inhibition in model systems and in food
• FDA Research CFSAN Exploratory Survey of Acrylamide Levels in U.S.
Foods FDA/NCFST work on effects of processing on acrylamide
formation in food (potato products and baked grain products) and in model systems
• Worldwide Research: WHO/JIFSAN clearing house
CFSAN Exploratory Survey of Acrylamide Levels in U.S. Foods
ppb Acrylamide
0 200 400 600 800 1000 1200 1400
Fo
od
Typ
es
Crackers
Cookies
Coffee
Cocoa
Chips
Chicken
Cereal
Bread
Baby Food
Almonds
FDA Action Plan on Acrylamide: Formation
2. Determine the precursors/mechanisms resulting in acrylamide formation in foods
• FDA Research FDA/NCFST work on verifying precursors/mechanisms in grain
products
• Worldwide Research: WHO/JIFSAN clearing house
3. Understand the role of product composition on acrylamide levels in food
• FDA Research CFSAN Survey of Acrylamide Levels in Food
• Worldwide Research: WHO/JIFSAN clearing house
Research on Acrylamide Worldwide
U.S. - FDA; Food Industry; Trade Organizations; AcademiaCanada - Health CanadaU.K. – Food Standards Agency; Univ. of Reading/Leeds;
Leatherhead; Food Industry, Trade Organizations, AcademiaNetherlands - Dutch Food AuthorityAustraliaFrance - AFSSAGermany - BLL Spain – CNCV/Univ. of Baeares/Rocasolano Institute & FIABNorway - MATFORSKSwitzerland - Government agencies; Nestle Research CentreSweden – Swedish Food Administration; Stockholm Univ.
Next Step
• Study effects of processing time and temperature on formation of acrylamide in a model system and in food
