Fortification of bread-making flour with thiamin

In January 1991, an amendment to the Australian Food Standards Code made it a legal requirement that bread-making flour contains no less than 6.4 mg/kg of thiamin.

The thiamin content of white and wholemeal flours, before fortification, is 2.0-2.5mg thiamin/kg and 4.5-5.0 mg thiamin/kg respectively. Consequently, additional thiamin must be added to the flour before it is used for making bread.

Why was thiamin fortification required?
Mandatory thiamin fortification of bread-making flour was introduced to reduce the incidence of Wernicke-Korsakoff syndrome (WKS) in Australia. WKS is a degenerative brain disease associated with a high alcohol intake and a diet deficient in thiamin. Australia has a relatively high incidence of WKS compared to other countries.

Thiamin plays a critical role in carbohydrate metabolism. A daily intake of 1.1 mg is recommended for good health in healthy adults since thiamin is not synthesised or stored in the body. The requirement for thiamin is increased for those consuming a diet high in sugar or alcohol.

A short period of low thiamin supply may deplete thiamin reserves which can lead to subclinical thiamin deficiency. Thiamin fortification would help to increase the thiamin reserves of those who eat poorly and hence help to prevent WKS.

In 1987, the NHMRC recommended addition of thiamin to beer and flagon wine to reduce the incidence of WKS. However, since fortification of alcoholic beverages was not practiced in other countries, it was opposed by nutritionists, brewers and anti-alcohol groups. The NHRMC therefore decided that thiamin should be added to bread flour since thiamin fortification of white flour is a common practice in other industrial countries (such as the UK and USA) to restore losses from wheat during milling.

The decision to fortify bread-making flour with thiamin was controversial since at the time, there was little evidence to suggest that such a major public health measure would reduce the prevalence of WKS in Australia. However, dietary surveys suggest that specific groups, including the elderly, at risk of low thiamin intake would also benefit from thiamin fortification of the diet.

Why is bread fortified with thiamin?

Bread is a staple food, consumed by most individuals in the Australian population. The 1983 National Dietary Survey of Adults indicated that unfortified bread and cereals were the major sources of thiamin intake in the Australian diet.

Breads and cereals are considered "thiamin donors" because they supply more than sufficient thiamin to metabolise the kilojoules they provide.

Technical aspects of thiamin fortification

• Thiamin is added to flour as synthetic thiamin mononitrate. The level of addition is approximately 0.5 mg/100 g for white flour and 0.2 mg/100 g for wholemeal flour. To achieve this low level reliably, the thiamin is first mixed with a small amount of flour to form a pre-mix.
• Thiamin is relatively stable at pH 5, the pH of most bread products, but increasingly unstable at high pH.
• Thiamin is sensitive to heat. Loss of thiamin during the baking of bread varies from 5% to 40%, depending on the product (since the majority of thiamin destruction occurs in the crust) and production process used. For instance, a BRI Australia study showed that thiamin losses are greater in Arabic flat breads which are cooked at higher temperatures and have a larger surface area.
• Flour treatment agents commonly applied at the mill have no significant effects on the thiamin content of flour.
• The quantity of thiamin added does not affect the baking properties of the flour.
• Thiamin does not affect the taste, texture or smell of bread.

Effectiveness of thiamin fortification

i.Thiamin content of bread

A national study of the nutrient composition of bread conducted by BRI in 1993/4 showed that the thiamin content of white, mixed grain and wholemeal breads had increased to 0.45 mg/100 g (compared to 0.16 mg/100 g for white and 0.22 mg/100 g for wholemeal breads prior to thiamin fortification)1.

Another study conducted in Victoria in 1993 found that the thiamin content of 15 white bread samples averaged 5.0 mg/kg and 15 samples of wholemeal bread averaged 4.8 mg/kg2.These results suggest compliance with mandatory fortification of thiamin to bread-making flour at the level of 0.64 mg/100 g flour.

In some of these samples, there was a low thiamin content which could be attributed to inadequate mixing of thiamin and flour. It is difficult to obtain a homogenous mix of a small quantity of thiamin and a large quantity of flour.

ii. Thiamin status of Australians

CSIRO nationwide surveys conducted in 1988 and 1993 show that there has been a significant increase in thiamin intake in all sub-groups of the population3. This is likely to be due to thiamin fortification of bread-making flour. Despite a decrease in intake of sliced bread, risk of inadequate intake existed in only 3% of women and 7% of men. It was estimated that without thiamin fortification, 8% women and 21% men would have had intakes below the RDI for thiamin.

The 1995 National Nutrition Survey reported an average intake of 1.4 mg and 1.9 mg in women and men aged more than 19 years respectively. Breads and rolls contributed approximately 20% of total thiamin intake in the Australian diet. More than 90% of Australians in most age and sex sub-groups exceeded the RDI for thiamin.

iii. WKS incidence

Autopsy studies conducted before and after the introduction of mandatory thiamin fortification of bread-making flour show a significant reduction in the prevalence of WKS in Australia. Prior to thiamin fortification of bread-making flour, the incidence of WKS was 2.8% in Perth and 2.1% in Sydney4. From 1996 to 1997, the prevalence of this syndrome in NSW had reduced to 1.1%5. Of the 25 cases identified, 2 were acute cases, 6 were acute-on-chronic cases and 17 chronic cases (reflecting past episodes). The fact that fewer cases of acute WKS were identified suggests that thiamin fortification of bread-making flour may have had an impact on the occurrence of acute cases in Australia. Furthermore, the results of this study may underestimate the beneficial effect of the thiamin fortification as many of the cases of chronic WKS observed in these autopsies may have been present before thiamin fortification.

A retrospective survey of hospital records from 17 major general hospitals in Sydney for cases of WKS suggest a reduction in the incidence of acute WKS as well as in reported deaths from WKS since bread was fortified with thiamin6,7. The average incidence of acute cases of WKS from 1992-1996 was 40% lower than in the 5 years before fortification (1986-1990) but appears to be reaching a plateau of approximately 41 acute cases per year7. However, these results suggests that to achieve elimination of this disease complex, addition of thiamin to beer is required.

References
1. Mugford DC, Griffiths PJ, Walker AR. Nutrient levels in white, mixed grain and wholemeal bread. An Australia-wide survey of breads from different bakeries and different States. Food Australia 1996;48(6):264-269)
2. Menz N et al. Thiamin content of bread sold in Melbourne. Food Australia 1995;47(8):381-384
3. CSIRO Division of Human Nutrition. Food and nutrition in Australia. Does five years make a difference? 1996; Adelaide: CSIRO.
4. Harper C. The incidence of Wernicke's encephalopathy in Australia - a neuropathlogical study of 131 cases. J Neurol Neurosurg Psychiatry 1983;46:593-598
5. Harper CG et al. Prevalence of Wernicke-Korsakoff syndrome in Australia: has thiamine fortification made a difference? MJA 1998;168:542-545
6. Ma J, Truswell AS. Wernicke-Korsakoff syndrome in Sydney hospitals: before and after thiamine enrichment of flour. MJA 1995;163:531-534
7. Rolland S, Truswell AS. Wernicke-Korsakoff syndrome in Sydney hospitals after six years thiamin enrichment of bread. Public Health Nutrition 1998; 1(2):117-122
8. Drew LR, Truswell AS. Wernicke's encephalopathy and thiamine fortification of food: time for a new direction? (editorial) MJA 1998;168:534-535