nutrient loss in vegetables

[Forbes-Ewan, Chris]

> -----Original Message-----

> From:	Ruhs, Barbara [SMTP:BRuhs at doe.mass.edu]

> Sent:	Saturday, April 08, 2000 2:04 AM

> To:	Public Health Nutrition Discussion and Information Group

> Subject:             FW: nutrient loss in vegetables

> 

Last year, the Australian nutritionists network (Nutnet) compiled a
'frequently asked question' (FAQ) on a subject related to this. The FAQ is
below my signature block. If you would like to see any of the other 25 or so
completed FAQs (with a new one being finalised each month) they can be
accessed through:

www.nutritionaustralia.org

Click on Food Facts and then on Frequently Asked Questions.

Chris Forbes-Ewan

Senior Nutritionist
Defence Nutrition Research Centre
76 George St
Scottsdale  Tas  7260
Australia

Phone:	Int + 61 3 6352 6607	(03 6352 6607 within Australia)
Fax: 	Int + 61 3 6352 3044	(03 6352 3044 within Australia)

E-mail:	chris.forbes-ewan at dsto.defence.gov.au

The views expressed in this message are those of the author and do not
necessarily represent the position of the Defence Science and Technology
Organisation or of the Australian Department of Defence.



Question: How nutritious are commercially-frozen vegetables compared to
fresh vegetables?

Answer:

Freezing is a very efficient method of preserving the nutritional value,
texture and flavour of many vegetables. Most vitamins will keep well in
frozen vegetables. Carotene (a compound that is converted to vitamin A in
the body) may actually be better preserved in frozen produce because
packaging keeps the vegetables away from light (which destroys carotene).
For example, frozen peas typically have about 60% more carotene than 'fresh'
peas (that have been exposed to light during their trip to the market and
while awaiting sale). 

Some losses of vitamin C and folate (also known as folic acid) occur during
commercial freezing. About 25% of the vitamin C, and perhaps a greater
percentage of the folate, will be lost during the blanching process that
precedes commercial freezing. A smaller quantity (perhaps 10%) of the
thiamin (formerly called vitamin B1) will be lost during blanching. Little
further loss occurs during the time the food is kept frozen, provided that
it has been stored properly (-18 degrees C for no more than six months).

However, the vitamin losses associated with blanching and the
thawing/cooking process are similar to those that occur during normal
cooking of fresh vegetables. This means that, provided they have been 
stored and then cooked properly, frozen vegetables provide similar levels 
of nutrition to fresh vegetables. It is also worth noting that for cooking 
both frozen and fresh vegetables, microwave cooking and steaming are 
both superior (in terms of retaining nutritional value) than boiling in a 
large volume of water. 

Other vitamins are generally fairly heat stable and are largely retained
during the blanching process and subsequent period of frozen storage, or are
not found in significant quantities in vegetables anyway. Nutrients other
than vitamins are not significantly affected by the freezing process.

In Australia it is recommended that people eat seven serves of fruits and
vegetables each day, with five of these being vegetables. Some people find
it inconvenient to prepare fresh vegetables. This can lead to a reduction in
their intake of vegetables generally. Therefore, frozen vegetables (which
are already washed, peeled and sliced or diced) can be a useful way of
encouraging greater intake of these highly nutritious foods.

To retain the maximum nutritional value, texture and flavour of frozen
vegetables (and of most other frozen foods) the following is recommended by
the CSIRO Division of Food Research:
Collect your frozen foods last at the supermarket and take them home in
insulated containers.
Put frozen food in a freezer maintained at about -18 degrees C as soon as
you arrive home.
Frozen storage for no more than about six months is recommended for most
vegetables.
Steam or microwave frozen (and fresh) vegetables to retain a high proportion

of the vitamins. 
If cooking frozen food in boiling water, the food should be taken directly
from the freezer and placed in water that has already come to the boil. 
Boil vigorously until ready, and then serve immediately (ie, do not leave
the food 'simmering' for long periods).
Do not use saucepans or other utensils made from copper or brass. 
Cooking utensils made from glass, stainless steel, aluminium or enamel do
not affect the nutritional content.