Re Nitrates and vegetables

[Guest guest]

When I first saw the reference to beets and nitrates, I as alarmed

because my family likes pickled beets and we avoid nitrates. So I

began to research this problem. For what is worth I am a librarian

who has access to certain databases, one of which is medline, to which

all of you have access. I will provide the citation and abstract if

it is not too long, otherwise I will summarize. I will continue to

research this as I have time.

 

Gary Oliver

 

Medline references:

 

" Yield and content in nitrates, minerals and ascorbic acid of leeks

and turnips grown under mineral or organic nitrogen fertilizations, "

Plant Foods Human Nutrition, 1987;37(4):321-32.

 

" The influence of mineral NPK fertilizers and organic fertilizers such

as manure compost, woodchip compost and blood meal on the yields and

the nutritive value of leeks and turnips were compared. Fertilizers

were applied on the two crops grown successively in 200-1 containers.

Mineral fertilizers, manure compost and blood meal provided equivalent

vegetable yields. Contents in dry matter, ascorbic acid and minerals

of leeks and turnips were not strongly affected by the different

fertilization regimes. The nitrate content of both crops was

significantly lower under the application of manure compost and

woodchip compost, while mineral fertilizers and blood meal induced

similar, higher nitrate levels. The present work thus provides new

data showing the usefulness of composts in growing vegetables with low

nitrate contents. "

 

" Nitrates, nitrites, and methemoglobinemia, " Environ Res, Vol. 3, p.

484-511, 1970.

 

" Spinach and beets may have fairly high concentrations of nitrate

(1000 ppm and over) in their natural state. Several other vegetables

may show high concentrations on occasion. Cured meats are permitted to

contain up to 200 ppm of nitrate and nitrite. Domestic or commercial

preparations, including baby foods, made from plants with a high

content, are likely to have concentrations that are almost as high.

Monitoring of vegetables or commercial products for their nitrate

content would seem to be impracticable in view of the very large

variability both between and within lots. The nitrate contained in the

raw vegetables may be converted into nitrite by accompanying organisms

in the course of storage for several days, particularly at higher

temperatures. The nitrate content of sterile commercial preparations

may similarly be converted if they are kept for several days after

opening and exposure to contaminating organisms. Cooking may do

something to speed up the rate of conversion of nitrate into nitrite,

but some of the salt content is likely to be leached out in the

cooking water. This removal would, of course, be undone if the cooking

water were subsequently added to the diet. Well waters frequently

exceed the USPHS standard of 10 ppm of nitrate nitrogen (45 ppm of

nitrate). These situations seem to have been of long standing. The

increasing use of nitrogenous fertilizers seems not, so far, to have

affected the levels significantly, except where a previously low water

table rises to mobilize deposited fertilizer (or other nitrogenous

materials). Organisms capable of converting nitrate to nitrite may

occur in the alimentary canal, particularly in the course of digestive

upsets. It is the nitrite derived in any of the above ways, and not

the nitrate, that constitutes a hazard. Absorbed into the blood, it

converts hemoglobin into methemoglobin, destroying its power of

carrying oxygen. This conversion will tend to happen more readily in

infants because of the presence of the more susceptible fetal

hemoglobin and a relative lack of enzymes that reconvert the pigment

to hemoglobin. The cases reported in the USA have been almost

exclusively due to the use of nitrate-containing water, but many cases

have been reported in Europe due to the use of baby food preparations

in which nitrite has been formed from the original nitrate, either in

storage of the vegetable or in preparations kept at room temperature.

The clinical condition, although alarming and potentially fatal, is

fairly easily diagnosed and remedied. The condition can be prevented

by: (a) using only fresh or continuously frozen vegetables in the

domestic preparation of baby food; (b) discarding the cooking water;

© preparing only enough, or opening only enough of a commercial

preparation, for one meal and discarding any remainder; (d) avoiding

the use of water that contains nitrate in the preparation of baby

formulas or food. A possible additional hazard to be considered is the

action of nitrate on secondary amines, also contained in or derived

from certain foods, to form nitrosamines with carcinogenic potentiality. "

 

" Enhanced food quality: Effects of composts on the quality of plant

foods, " COMPOST SCIENCE & UTILIZATION; 1 (1). 1993. 82-100.

 

Conclusion, " Composts significantly reduced nitrates and improved the

nitrate to vitamin C ratio of vegetables. "

 

" Nitrate levels in vegetables that may be eaten raw, " ITALIAN JOURNAL

OF FOOD SCIENCE; 9 (1). 1997. 65-69.

 

Conclusion: " The amount of nitrates detected in commercial lettuce

samples was very high, while lettuce cultivated without fertilizing

contained low amounts. "

 

Academic search premier references:

 

" Determination of nitrates by a novel ion chromatographic method:

occurrence in leafy vegetables (organic and conventional) and exposure

assessment for Italian consumers, " Food Additives & Contaminants;

Sep2003, Vol. 20 Issue 9, p787-793.

 

" A novel ion chromatographic method to detect nitrates in vegetables

was developed, and the nitrate contents in green salad (a mixture of

endive and prickly lettuce), lettuce, chicory, rocket and spinach were

determined from Italian markets in 1996-2002. These leaf vegetables

were included because they are currently supposed to provide most of

the nitrate intake in the typical Italian diet. The highest content of

nitrate was detected in chicory (6250 mg kg -1 ) and rocket (6120 mg

kg -1 ), which are consumed in large quantities in some regions of

Italy. Green salad and lettuce contained less nitrate (highest values

= 4200 and 3300 mg kg -1 , respectively), but because they are

consumed more generally, they provided 60% of the total intake of

nitrates. Only a few samples were above the legal limits, with

seasonal variation. A significantly higher nitrate content was found

in organically grown green salad and rocket than in those

conventionally produced. These data indicate that the average intake

of nitrates from leafy vegetables is below the acceptable daily

intake, i.e. 3.7 mg nitrate ion kg -1 body weight day -1 , but the

total intake should be monitored to protect groups at risk, such as

children and vegetarians. " [ABSTRACT FROM AUTHOR]

[Guest guest]

Wow, I am so glad I responded with what I'd been told about beets,

because now I know so much more on the subject! All of the web links &

articles have been eye-opening. Thanks to everyone.

 

Interestingly, it seems that organic vegetables are generally *lower*

in nitrate, which is the opposite of what I was told. And the fact

that green leafy vegs are higher than beets or carrots was quite the

revelation! Storage, cooking water, all that stuff....just shows that

the truth is out there, in all its confusion and complexity, for anyone

who does the research.

 

In the end, I think we've got to accept that feeding our kids good food

is always the right choice, even if nothing's perfect.

 

Liz