Nutritional difference - freeze dried and Dehydrated food

[Mutley]

Just listened to a hiking podcast, where it was claimed Freeze Dried food retains 90% plus of its nutritional value whereas home dehydrated food only retains 60%. I have scoured for confirmation online but all I could find, was dehy does loose vitamins A and E during the drying process.

From a very amateur perspective, both methods remove water from the food, but the macronutrients should not change, as you are not removing any fats, carbs or protein during drying.

This really concerns me as losing 40% of a food’s nutrition is a huge issue.

Any thoughts/comments ?

[CraigVIC]

Tim's a member isn't he? You could ask him for a source.

[Mutley]

Do you know Tim’s user name ?

[CraigVIC]

'Tim-Australian hiker'

[Mutley]

Thanks Craig, Just Pm’d Tim

[Mark F]

The question I have is what is meant by nutritional value. I can accept that there may be a reduction in some vitamins but calories and minerals etc are unlikely to be affected. Given that most freeze dried meals as well as most dehydrated foods are cooked at 100 degrees Centigrade or more before drying I would expect most break down of vitamins etc would occur in the cooking, not in the dehydrating process which is at around 50 degrees. I suspect any effect is due to oxidation.

I expect there may be a differential loss of some nutrients depending on the drying technique but whether this is of any consequence to ones health is I suspect *&^%$#!. There is a massive difference between a statistically significant difference and an observable difference in health outcomes.

[ribuck]

Here are two scholarly articles from the Journal of Food Science Technology:

https://www.ncbi.nlm.nih.gov/pmc/articl ... cle_10.pdf
"Recent advances in drying and dehydration of fruits and vegetables: a review"
It says "The retention of vitamin C in freeze-dried products is significantly higher than that of oven and sun-dried products".

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3722389/
"Retention of nutrients in green leafy vegetables on dehydration"
They measured the retention of nutrients in five types of vegetables after oven-drying for 10 to 12 hours at 60 Celsius. They found that "retention of ascorbic acid was 1–14%, thiamine 22–71%, total carotene 49–73% and β—carotene 20–69% respectively, of their initial content. Dialyzable iron and calcium in the fresh vegetables ranged between 0.21–3.5 mg and 15.36–81.33 mg/100 g respectively, which reduced to 0.05–0.53 mg and 6.94–58.15 mg/100 g on dehydration." Dialyzable means being in a form which can pass through a membrane. So dehydrating does remove most of the Vitamin C (ascorbic acid), and significant amounts of some other vitamins and minerals.

The following article, from the Journal of Molecular Biology...
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5297706/
...states that "during convective drying, the oxidation processes caused by hot air results in significant chemical alterations in the profile and the content of the thermolabile biologically active compounds".

So if you like lots of Vitamin C in your food, go for the freeze-dry rather than the dehydrated vegetables.

All of the papers speak very positively about freeze-drying. It seems the biggest problem is that it's a high-cost way to preserve food. The papers have lots of references, and apart from the Green Leafy Vegetables paper they are literature reviews, which means you will need to go to the references for the original experimental data.

[ribuck]

... the macronutrients should not change, as you are not removing any fats, carbs or protein during drying ...

Correct.

[Turfa]

Even if there is a difference between dehydrated and freeze-dried, does it really matter over the course of a walking trip ?

If you were living off the stuff permanently then perhaps it would make a difference, but for a weekend, week or even several week trip, are you really going to suffer from some kind of vitamin/mineral deficiency ???

[Mark F]

I quickly perused the first two papers mentioned. The first doesn't really address any pre-drying cooking while the second does but only looks at the combined effects of both the blanching (5 minutes of steam) and the drying without separating out the effects of each process. I have always heard (hearsay, no evidence) that cooking reduces the vitamin content of food so I would expect that part of the reduction in nutritional value is due any cooking prior to dehydration.

As I believe none of us have suffered from scurvy or beriberi on a trip I will continue to eat my dried fruit and home cooked dehydrated meals without fear and not rush to pay extravagant prices for usually over salted freeze dried food. For those who are concerned there are always multi vitamin tablets.

[Moondog55]

Don't forget the "Tang" it and similar fruit flavoured drinks are loaded with VitC. As for the other micro nutrients I do think it pays a part in metabolisation of the simple carbohydrates I tend to overload on when walking so I often ad a HighB tablet, what ever stress formula is on special if I haven't added extra already to my Kram bars

[ribuck]

Mark F, Vitamin C oxidises in contact with warm air. There is some loss during cooking, but much more will be lost during air-drying.

Home-dehydrated food tastes better, for sure. It's also less expensive and the packaging is much less than the foil pouches of freeze-dri.

During May I walked for 22 days, and developed no food cravings whatsoever. Previously, on every extended trip of a week or more I would end up with a massive craving for fruit and salad.

I suspect the lack of cravings this time was due to a good vitamin intake. I had Back Country freeze-dri every night, and a Cliff bar (which has supplementary vitamins) every day, and also plenty of fatty food with its fat-soluble vitamins.

A good approach might be to home-dehydrate your meals without vegetables, then add Campers Pantry freeze-dried vegetables to the resultant mix. Needs some experimentation.

[Mark F]

Ribuck - Every year I do a couple of walks of 10 to 20 days and I agree with you about cravings at the end but for me they tend towards fried food/pastry/beer and salad. I find a multivitamin every couple of days and inclusion of things like orange juice and canned fruit in food drops keeps me relatively happy. I do miss the texture/mouth appeal of a salad but I don't think it has much to do with a lack of vitamins. I also find the idea of paying $25-$30 per kilo (fresh weight) for veges a bit daunting let alone $16 per evening meal (about $340 for your 22 day walk)

[Orion]

I suspect the lack of cravings this time was due to a good vitamin intake. I had Back Country freeze-dri every night, and a Cliff bar (which has supplementary vitamins) every day, and also plenty of fatty food with its fat-soluble vitamins.

While that's a tempting hypothesis I'm skeptical that one has cravings for specific micronutrients. It reminds me of a pregnant woman who insisted to me that she craved ice cream because of the calcium it contained, as opposed to the fat and sugar. Curiously she had no interest in bone meal, egg shells, antacid tablets, or chalk.

If it's true one craves vitamins instead of high quality food that happens to contain vitamins you'd think there would be experimental evidence for it. Is there?