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Exploiting Process Factors to Reduce Acrylamide in Cereal-based Foods

Project Code: C03032

31/05/2005

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Hamlet, C ;
Brewing Research International
Baxter, D;
RHM Technology
Sadd, P;
Brewing Research International
Slaiding, I;
RHM Technology
Liang, L;
Brewing Research International
Muller, R;
RHM Technology
Jayaratne, S;
Brewing Research International
Booer, C

BACKGROUND

Since the discovery that the human population is regularly exposed to acrylamide through the consumption of cooked foods, research efforts have focussed primarily on those foods displaying some of the highest levels of acrylamide formed, i.e. potato based products. It has been proposed that the formation of acrylamide during cooking involves the Maillard reaction and that the amount of acrylamide formed in foods is the net result of reactions leading to both formation and degradation of this compound (Wedzicha et al. 2005). Several research groups have examined the formation of acrylamide in model systems involving amino acids and simple sugars (Mottram et al. 2002; Stadler et al. 2002; Becalski et al. 2003, Zyzac et al. 2003).

Asparagine (Asn), which is an abundant free amino acid in potato products, has emerged as a key precursor, and it is the reaction of this amino acid with carbonyl sources, such as simple reducing sugars, that is believed to be the key acrylamide forming reaction in cooked foods. It is also known that Asn is relatively abundant in cereal crops such as barley, rye and wheat. However in contrast to potato based foods, where changes in reducing sugar levels are believed to be the dominant variable (Becalski et al., 2004), there is little understanding of how the natural variation in Asn (and sugar levels) and the effects of processing, influence acrylamide formation in cereal-based foods and beverages.

APPROACH

This project was undertaken collaboratively by two food industry research centres, Brewing Research International (BRi) and RHM Technology Ltd (RHMT). The study comprised five main activities: extension of analytical methods for acrylamide and key precursors in foods; a survey of acrylamide in products and key precursors in raw materials; development of model systems and predictive models; the relationship between key precursors in the raw materials, processing factors and acrylamide levels formed in foodstuffs; and mitigation and the impact on other process contaminants, e.g. 3-monochloropropanediol (3-MCPD). The aim of the study was to deliver recommendations on how to achieve minimal acrylamide levels in commercial and domestically prepared cereal-based foods and beverages.

The individual objectives were as follows:

Develop/extend analytical methods for acrylamide and key precursors in foodstuffs
Examine the relationship between key precursors in raw materials and acrylamide levels in foods
Develop simplified food products/systems and establish the conditions of formation and removal of acrylamide
Determine the effect of compositional and process factors on levels of acrylamide in the simplified food products
Explore methods of adjusting amino acid profiles i.e. yeast metabolism
Develop mathematical models to predict formation and ways of reducing acrylamide levels
Produce a report with recommendations on how to achieve minimal acrylamide levels in cereal foodstuffs

OUTCOME/KEY RESULTS OBTAINED

Analytical method developments

An improved (rapid, sensitive, robust) method for the determination of acrylamide in heavily processed cereal products using GC/MS/MS
A new procedure for the analysis of free amino acids in cereal products by HPLC/FLD

Survey data

Bakery products/ingredients

Highest levels of acrylamide are seen in browned biscuits
- o Degree of browning is not a good guide
Commercial bread crusts can contain relatively high levels of acrylamide, but whole product levels are much lower
Levels in cakes are low, even in the crust
There is some evidence for ginger and ammonium enhancing acrylamide formation
- The effect of ammonium was confirmed by experiment
Asn levels in wheat:
- Can double within and between cultivars
- No link with protein or total free amino acid levels
- Order in flours: cake<biscuit<white bread<wholemeal bread
Levels of simple sugars in wheat vary little
- Individual sugar levels are as variable within as between wheat cultivars

Brewing and malting

Heat-treated cereals and malted cereals can contain relatively high levels of acrylamide.
Highest acrylamide levels are generally found in cereal products with a moderate colour.
Very dark cereal products contain lower levels of acrylamide
Beverages made with cereal-based raw materials containing acrylamide generally contain only low levels of acrylamide.
- This is largely due to dilution but there may also be some losses during processing

Model system work

Bakery products/ingredients

Levels of acrylamide are limited by amino acids running out as well as direct decay of both amino acids and acrylamide
The levels of Maillard products do not necessarily align with acrylamide levels; low moisture is more important for acrylamide
- These findings are very significant for biscuits
Simple sugars are not the main carbonyl sources in wheat
- Starch and oligosaccharides inferred to be the major carbonyl precursors
Acrylamide levels broadly follow free Asn levels in wheat and nonyeasted dough samples
During proving, yeast:
- Preferentially removes Asn
  - This effect diminishes as the recipe become more commercial, i.e. with added fat, vinegar and improver
- Rapidly consumes sucrose and releases fructose

Brewing and malting

Levels of acrylamide are closely related to total heat input.
That relationship is similar regardless of how heat input is measured (i.e. whether it is measured as maximum temperature, heat energy, or time above a certain temperature)
In some circumstances, it appears that acrylamide can be formed below 100°C.
Loss of acrylamide begins to exceed formation at temperatures above approximately 140°C
Acrylamide formation is related to colour generation, but, as with bakery products, product colour alone is a poor guide to acrylamide level
Cereal type appears to have little effect on acrylamide levels. An exception to this may be where the heating time is very short, such that the speed with which the product can equilibrate to the applied temperature is rate limiting for acrylamide formation
There is some evidence that acrylamide may be removed by yeast during fermentation, but more work is required to confirm this
Both formation and degradation of acrylamide occur at lower temperatures than for 3-MCPD

Options for reduction (benefit/risk)

Bakery products/ingredients

Calcium supplementation appears to have promise as an amelioration route
- Surface application via pan release agent may have potential for bread products
- Direct supplementation of dough recipe may have potential for biscuit products
Optimisation of temperature and moisture control
- Changes of this type pose no risk of increased levels of other contaminants such as 3-MCPD
Phytic acid supplementation can significantly reduce acrylamide
- Nutritional implications (mineral availability)
- May not be effective in leavened products (metabolised by yeast)
Amino acid supplementation has a modest effect on acrylamide in dough (dilution effect)
- May be more effective as a surface application (concentration effect), but
  - Cysteine has adverse effects on dough rheology
  - Impact of added amino acids on the generation of other contaminants is not known
Low pH is beneficial for reducing acrylamide
- pH is limited by natural dough pH buffering
- Low pH promotes 3-MCPD formation
High addition rates of bakers yeast can further reduce Asn precursor levels in dough
- Selection of low CO2 gassing bakers yeast variants may permit process optimisation
- Impact on product quality unknown
- Can increase 3-MCPD production (from increased glycerol)
Reduce ammonium based raising agent levels in biscuit products
- Replacements e.g. sodium (bicarbonate) have nutritional and quality implications (leavening ability)
- May increase 3-MCPD levels

Brewing and malting

On the pilot scale, application of calcium salts to unkilned malt can reduce acrylamide formation during subsequent heat treatment and should be tested on the commercial scale
There is some evidence that extending stewing times may reduce acrylamide levels in crystal malts without adversely affecting other parameters, however, more work needs to be done to confirm this.
It may be possible to remove acrylamide by fermentation with yeast but more work would be required to explore this.

Final report

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