Loss of vitamins due to blending of selfmade smoothies

Question

I (CF, pancreas insufficiency, much sport) pay a lot attention to my nutrition. However, as I have hardly any appetite on “real” food during the summer, I live preferably on self-made smoothies. My favorites are: 500ml certified raw milk, 1 banana, ½ mango, ¼ pineapple or apricots (about 500 kcal) or 300ml puree of carrots with 2 bananas (about 300 kcal) and a pinch of salt and curcuma each. I buy the certified raw milk at an organic food store (so hygienically o.k.) in order to strengthen my immune system and above all because it tastes better and I tolerate it also better compared to the normal homogenized milk. I also grew up with fresh milk, so there should not be any concerns.
Now I have read, that blending (mixing is also a sort of blending) leads to a loss of vitamins in the food. Unfortunately I only found this single sentence on this topic.
Therefore these are my two questions:
1. Is it really true that mixing causes a loss of vitamins? If yes, how high is this loss?
2. Are the protein and fat of the certified raw milk also destroyed due to mixing and does it then resemble to the fat respectively protein of the homogenized milk?
Many thanks for your answer,
Yours sincerely,
A CF patient

Answer

Dear CF patient,
to your first question: due to blending you increase the surface of action for bacteria, but also for oxygen, so that more oxygen-sensitive vitamins and enzymes are oxidized (destroyed). Furthermore, you foam up the smoothie by blending, so that additional oxygen is mixed in. However, the oxidation is time dependent. In case you prepare the smoothie rapidly and drink it immediately, the loss of vitamins is moderate.
To your second question: Blending with the hand-held blender does not lead to changes of milk fat and protein, as can be found in homogenized milk, as this procedure is done under very high pressure. More likely, specific enzymes in the fruit lead to a change of the ingredients. The enzyme bromelain from the pineapple is for example able to split the milk protein in smaller particles (proteases).
In case you place value on intact protein structures in the certified raw milk, I recommend to you either to prepare the smoothie without certified raw milk and to drink the raw milk purely at another time or to prepare your smoothie with raw milk however without pineapple, papaya, kiwi, mango and figs as these fruits contain proteases. I hope to have answered your question hereby,
Yours sincerely,
Suzanne van Dullemen

02.08.2012