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Abstract
In recent years, folates have come into focus due to their protective role against child birth defects, for example, neural tube defects. In addition, folates may have a protective role to play against coronary heart disease and certain forms of cancer. During the last few years most countries have established increased recommended intakes of folates, for example, between 300–400μg per day for adults. This review of folates in milk and dairy products compares some recent data based on high pressure liquid chromatography (HPLC) analyses and radioprotein-binding assays, with previous data based on microbiological assays. All three methods show similar ranges for folates in cow’s milk, 5–10μg per 100g, the variation being due to seasonal variations. Data on folates in fermented milk (buttermilk and yogurt) are also similar for these methods. Different starter cultures, however, might explain some of the variations in folate content and folate forms. Most cheese varieties contain between 10μg and 40μg folate per kg, with slightly higher values for whey cheese. Ripened soft cheeses may contain up to 100μg folate per 100g. Most previous and recent studies using HPLC indicate that 5-methyl-tetrahydrofolate (5-methyl-THF) is the major folate form in milk, but more studies are needed concerning folate forms in other, especially fermented dairy products. Relatively new data on actual concentrations in different dairy products show folate-binding proteins (FBP) to occur in unprocessed milk, but also in pasteurised milk, spray-dried skim milk powder and whey. In contrast, UHT milk, fermented milk and most cheeses only contain low levels or trace amounts.
- ATCC = American Type Culture Collection
- DNA = deoxyribonucleic acids
- ELISA = enzyme-linked immunosorbent assay
- FBP = folate binding protein(s)
- HPLC = high performance liquid chromatography
- MA = microbiological assay
- RPBA = radio protein binding assay
- RDI = recommended dietary intake
- RNA = ribonucleic acids
- THF = tetrahydrofolate
- UHT = ultra high temperature
Key teaching points:
• The last decade has recognised health benefits of folates regarding their prevention of neural tube defects in babies and occlusive vascular diseases caused by elevated plasma homocysteine, their link to mental fitness and possibly some forms of cancer in adults.
• When publishing the dietary reference intakes (DRI) in 1998, the US Food and Nutrition Board included the concept of these possible health-protective effects of folates by increasing recommendations for adults to 400μg/day from the previous 200μg/day. The fact that the average daily intake of folate among Western populations is generally lower than these recently set recommendations, emphasizes the need for a critical evaluation of the dietary sources of folates.
• The low concentrations of folates occurring in foods, along with a great number of unstable chemical forms of this vitamin, make analysis of dietary folates very demanding. A continuously up-dating and re-evaluation of folate figures currently present in food tables and data bases and mainly based on microbigical assay, are absolutely necessary. Recently developed, more specific and carefully validated methodology, for example, HPLC and protein-binding methods, should be used.
• Milk and especially fermented dairy products like yogurt, buttermilk and different varities of cheeses are already recognised as good dietary sources of folates. More quality-assured methodology in up-dating folate concentrations in the whole set of dairy products, especially those based on fermentation, would probably strengthen their significance further as folate sources.
• Raw and pasteurised milk contain folate binding proteins (FBP). Thermal treatments above pasteurisation generally denaturate FBP. To what extent this denaturation of FBP will affect the retention of folates during processing and storage of dairy products need further investigation. Likewise the role of intact FBP for the bioavailability of dairy folates should be paid more attention.
• In order to judge which foods are good or bad sources of folates, we need to have validated figures on the absorption and bioavailability of food folates. Still reliable data concerning to what extent dietary folates actually are absorbed are incomplete, mainly owing to lack of suitable methodology for studies on humans. However, such work is in progress.
Key teaching points:
• The last decade has recognised health benefits of folates regarding their prevention of neural tube defects in babies and occlusive vascular diseases caused by elevated plasma homocysteine, their link to mental fitness and possibly some forms of cancer in adults.
• When publishing the dietary reference intakes (DRI) in 1998, the US Food and Nutrition Board included the concept of these possible health-protective effects of folates by increasing recommendations for adults to 400μg/day from the previous 200μg/day. The fact that the average daily intake of folate among Western populations is generally lower than these recently set recommendations, emphasizes the need for a critical evaluation of the dietary sources of folates.
• The low concentrations of folates occurring in foods, along with a great number of unstable chemical forms of this vitamin, make analysis of dietary folates very demanding. A continuously up-dating and re-evaluation of folate figures currently present in food tables and data bases and mainly based on microbigical assay, are absolutely necessary. Recently developed, more specific and carefully validated methodology, for example, HPLC and protein-binding methods, should be used.
• Milk and especially fermented dairy products like yogurt, buttermilk and different varities of cheeses are already recognised as good dietary sources of folates. More quality-assured methodology in up-dating folate concentrations in the whole set of dairy products, especially those based on fermentation, would probably strengthen their significance further as folate sources.
• Raw and pasteurised milk contain folate binding proteins (FBP). Thermal treatments above pasteurisation generally denaturate FBP. To what extent this denaturation of FBP will affect the retention of folates during processing and storage of dairy products need further investigation. Likewise the role of intact FBP for the bioavailability of dairy folates should be paid more attention.
• In order to judge which foods are good or bad sources of folates, we need to have validated figures on the absorption and bioavailability of food folates. Still reliable data concerning to what extent dietary folates actually are absorbed are incomplete, mainly owing to lack of suitable methodology for studies on humans. However, such work is in progress.
The financial support to Karin Forssén by the Swedish Dairy Association (Svensk Mjölk AB) and to Cornelia Witthöft by the EC (Marie Curie TMR grant) is gratefully acknowledged.
