Why does pre-frozen Kale/spinach loose 90% nutrition?

I read that boiled fresh kale has 350% vitamin A, but I know of 2 brands of frozen kale that say 35%. How can Kale loose 90% of the nutrition when frozen? My freezer is like a time machine to me; what I put in comes out just the same/similar. If I buy fresh kale and freeze it, will it loose 90% of the nutrition in a week? If not, why do the bags say 35%? Thanks for any answer, I have eye, digestive, and money problems so it’s important I don’t have to pay 10 times as much for A and eat 10 times the food… Thanks…

I highly doubt the quoted vitamin A differential.

Frozen veggies may actually contain more of certain nutrients than fresh offerings:

*"Most frozen produce is picked at peak season and then immediately frozen to retain nutrients and freshness. Fresh produce from faraway places, on the other hand, loses some of its nutrient value while traveling and then sitting on a shelf for days or longer. But the amount of nutrient loss varies greatly depending on the type of produce, says Jeff Blumberg, professor of nutrition science and policy at Tufts University.

“If you are looking at something like fresh spinach, you are losing up to half the folates after about eight days,” Blumberg says."*

The article makes the point that if you get the recommended number of servings of fruits and vegetables, fresh vs. frozen is not nutritionally important (though taste and texture are a different story).

[wrote the following before reading Jack’s post]
On a 2nd glance, the main nutrition data site on the web (can I mention basic websites here?) lists 350%+ for both boiled fresh/raw kale, and boiled frozen kale. Frozen is actually higher at 380%. Why do these bags say 35%? It’s not just this I’ve seen similar with other vegetables (spinach…) Thx…

OK but which one’s right, then? My bagged spinach says a fourth of the A that nutritiondata.com says. How can it be drastically different? Who is wrong, or is the truth in the middle?

I think answers depend on what products are involved and who’s doing the analyzing (while searching earlier I found one site claiming frozen spinach had something like 80% more vitamin A than fresh, which sounds dubious too).

OK but which one’s right, then? My bagged spinach says 1/4 the A that nutritiondata.com says. Which is right, or are both wrong?

First of all, check your serving sizes. If they’re by volume, like, “1 cup”, then a serving of fresh, raw kale is going to be a considerably smaller amount of kale than 1 cup of frozen chopped kale. That stuff loses a lot of volume when frozen and then thawed. What you want is a weight based serving size, like 100g or something, if you’re going to directly compare nutrition data.

I double checked the amount by grams. The frozen spinach bag is still 1/4 of what nutritiondata.com says…

The kale is blanched and chopped prior to freezing. Vitamin A has some temperature instability when heated. Also, some kale juice is lost during processing.

You should use your website for both the raw kale and the frozen kale. They show the frozen has 40% the vitamin A per unit weight as fresh.

Vegetables don’t come out of a factory; they come out of the ground and different soils, climate, time of harvest and zillion other factors affect the nutritional value.

Nutritiondata (and all online nutrition calculators) draw from USDA tables that portray average nutrition from a set of samples, whereas a product sold in stores must display actual nutrition for the contents of the package.

Whether it is because of depleted soil, a bad growing year, poor processing, or less-than-ideal harvest conditions, it’s impossible to know why your spinach has less nutrition than average. But where FDA-required package nutrition and USDA tables conflict, the package labeling is more correct with respect to the contents of the package you’re about to eat.

Frozen produce is often some of the best you can buy, short of daily-picked from a farmer’s stand. It’s the cream of the crop in appearance and often grown to be frozen, meaning that it is a strain that has better qualities than shipping resistance. It’s often flash-frozen as soon as it can be picked, washed and (if necessary) de-hulled. Cooked properly, it’s not only the best-tasting and often highest in retained nutrition, but indistinguishable from fresh.

Which is not to say that all vegetables freeze equally well. But on the whole, if truly fresh isn’t available, my next choice for most bush vegetables is frozen.

Nutritiondata does indeed match up with the USDA’s dataset. And the packages of commercial products are reporting significantly less Vitamin A than the USDA and nutritiondata say should be there. The discrepency is not explained by loss from freezing as noted in posts above. But it does not fit. I do not think that Hello Again’s explanation is completely correct.

Here are the labelling rules.

Manufacturers need to have a testing protocol but not for each batch. And they will be spot checked. When spot checked they must be 80% or greater of the amount of vitamins on the label.

My guess is that the manufacturers know that there is variation about the mean and err way low to avoid testing out of compliance ever. So say 50% even though on average it is over 500% per 30 calorie serving … the consumer is going to care?

Has the OP just considered taking a multivitamin instead?

(runs away)

This is probably correct. When I said the labelling is the more accurate of the two, I was thinking about the fact that not every batch is actually tested, but that spot tests must show 80% of the labelled value. I didn’t follow that to the logical conclusion that in a spot-testing environment, under-reporting would be the norm.