The effect of different cooking methods on folate retention in various foods that are amongst the major contributors to folate intake in the UK diet

Abstract

Folate intake is strongly influenced by various methods of cooking that can degrade the natural forms of the vitamin in foods. The aim of the present study was to determine the effect of different cooking methods on folate retention in various foods that contribute to folate intake in the UK diet. Typical purchasing and cooking practices of representative food folate sources were determined from a questionnaire survey of local shoppers (n 100). Total folate was determined by microbiological assay (Lactobacillus casei NCIMB 10463) following thermal extraction and tri-enzyme (a-amylase, protease and conjugase) treatment in raw foods and after typical methods of cooking. Boiling for typical time periods resulted in only 49 % retention of folate in spinach (191·8 and 94·4 mg/100 g for raw and boiled spinach respectively; P, 0·005), and only 44 % in broccoli (177·1 and 77·0 mg/100 g for raw and boiled broccoli respectively, P, 0·0001). Steaming of spinach or broccoli, in contrast, resulted in no significant decrease in folate content, even for the maximum steaming periods of 4·5 min (spinach) and 15·0 min (broccoli). Prolonged grilling of beef for the maximum period of 16·0 min did not result in a significant decrease in folate content (54·3 and 51·5 mg/100 g for raw and grilled beef respectively). Compared with raw values, boiling of whole potatoes (skin and flesh) for 60·0 min did not result in a significant change in folate content (125·1 and 102·8 mg/100 g for raw and boiled potato respectively), nor was there any effect on folate retention whether or not skin was retained during boiling. These current results show that the retention of folate in various foods is highly dependent both on the food in question and the method of cooking. Thus, public health efforts to increase folate intake in order to improve folate status should incorporate practical advice on cooking.

Determination of folates in vegetables and their retention during boiling

“…A correlation between the folate losses caused by various ways of cooking and the kind of vegetable (peas, broccoli, and potatoes) was recently mentioned by Stea et al (2006). Similar data were published by McKillop et al (2002) for spinach, though a lower retention value was found in broccoli. The results of the present experiments with cauliflower are close to the data published by Melse-Boonstra et al (2002) on the losses found after 8 min blanching.…”

“…Leaching and oxidative degradation represent the main causes of the decrease of folate values in this case and may thus influence the folate intake. Extensive folate losses in the course of spinach and broccoli boiling were found by McKillop et al (2002). Steaming, in contrast, resulted in a minimal decrease of the folate content.…”

Iron and Folate Contents of Tajik Legumes

“…Differences of folate forms from our study compared to other research may be attributed to discarding the soaking and cooking water rather than the destruction of folate forms during cooking [24,36]. However, legumes soaked overnight for 16 h have been shown to have higher folate retentions compared to no presoak or quick soak treatments [24].…”

“…Folate content of the cooking water was not determined in our study. It has been suggested to use the cooking water from legumes for further consumption [36]. In Tajikistan, the most common way of preparing legumes is cooking the legume and using the water as broth for stew, soup or other food items.…”

Serum folate and homocysteine and depressive symptoms among Japanese men and women

“…It should be noted that serum folate concentrations and dietary folate intake were only modestly correlated with each other (Spearman's rank correlation coefficient; 0.21 for men and 0.13 for women). This may be partly accounted for by reporting bias in dietary survey but other factors including cooking method (McKillop et al, 2002) and genetic factor (Bottiglieri, 2005;Gilbody et al, 2007a) should also influence. Specifically, methylenetetrahydrofolate reductase (MTHFR) is involved in folate metabolism (Bottiglieri, 2005;Gilbody et al, 2007a), Serum folate, homocysteine and depression A Nanri et al and those carrying MTHFR 677TT genotype have a lower serum folate compared with those carrying 677CC genotype independent of folate intake (Nishio et al, 2008).…”