3

I was discussing with a friend about my smoothies consumption and he argued that putting them in the fridge to consume them the next day was not good as the vitamin level/effect drops quickly.

Question

  • Does the vitamins' effect drop as quickly as he implies?
  • If so, does putting smoothies in the fridge hasten the effect?
  • 2
    Don't have enough of a biology/chemistry background to say something meaningful on the first question, but as to the second - cooling things slows down most biological processes, which is why it helps to preserve food. There isn't anything magical about vitamins that would suffer the reverse effect. – Shadur Oct 19 '16 at 6:59
  • Notability example – Oddthinking Oct 19 '16 at 8:10
  • The claim seems more centered around vitamins degrading over time once the smoothie is made, so the suggestion seems to be more about saving some for the next day than the fridge, specifically, causing the vitamins to degrade. Or was your friend specific that he/she felt the cooler temperatures were the cause? – PoloHoleSet Oct 19 '16 at 14:53
7

I would not worry.

Most vitamins are very stable. Vitamin C can oxidize, a little, over about a week, but overall vitamins are retained in large percentages, over months, even at room temperature.

More in particular, your question is very wide so I will only give a general answer based on this USAID study, but there are different reasons why vitamins degrade (heat, light, oxidation, reduction, enzymes...) and different concentrations in smoothies to start with. Overall, vitamins are sensitive to external conditions:

Sensitivity of Vitamins

Reading the study, vitamin C is the least stable vitamin typically found in fruits

Ascorbic acid (vitamin C) is easily destroyed during processing and storage through the action of metals such as copper and iron. Both exposure to oxygen and prolonged heating in the presence of oxygen destroy ascorbic acid; thus, the stability of vitamin C in fortified foods depends on the product, processing method, and type of packaging used. Vitamin C retention in fortified foods and beverages stored for 12 months at room temperature ranges from 75 to 97 percent (Table 6)

But, as you can see, a large proportion of vitamin C is retained over a year in juices at room temperature.

Stability of Vitamin C

  • 1
    Storing a juice for a year certainly means a sealed package and pasteurization (or similar preserving techniques) and is very different from storing in a more-or-less open container in the fridge. – cbeleites supports Monica Oct 22 '16 at 14:02
1

According @Sklivvz' reference, vitamin C is typically the least stable vitamin.

I found a Study on the Kinetics of Vitamin C Degradation in Fresh Strawberry Juices that reports halflife for storage at 8 °C of 4:47 and 5:36 h for juice prepared without and with additional sugar, respectively - I assume that the former number is more relevant for people thinking about healthy nutrition.

This means that after 24 h (5 halflifes), you'd expect about 3 % of vitamin C remaining.

Degradation is slowed down by cooling (the paper gives kinetics also for 28 °C).


Additional "anecdata": This agrees well with a labwork practicum experiment in analytical chemistry I used to supervise where the students consistently found substantial loss of vitamin C in orange juice standing for a few hours at room temp compared to both the freshly prepared juice and juice prepared from peeled orange sectors that were left at room temperature (though I don't have the values at hand).


However, I agree with @sklivvz that you don't need to worry too much: while we humans have not much vitamin C storage (compared to say, vitamin D)* getting a bit more and less on alternating days is not going to be a concern. And anyways, eating an additional fresh orange on those days will get you almost your whole DRI.

* update: Matissek and Baltes: Lebensmittelchemie, 8th ed, Springer Spektrum lists both vitamin C and D in the 2-4 months reserve capacity (humans) category (table 3.3, p 45).

They also state (p. 605) that after destruction of the cell walls, fruits undergo rapid enzymatic degradation, but do not give quantitative information on freshly prepared juices. They explain, however, that fruit juice (in particular the unfiltered varieties ("naturtrüb") usually undergo heat treatment to inactivate enzymes.

  • 2
    I'm just curious what the reason is that vitamin C was lost in the juice in just a number of hours but apparently not in the fruit itself – Tom Oct 23 '16 at 1:56
  • @Tom: The "destruction" of vitamin C is actually oxidation (by oxygen from air) - vitamin C is an anti-oxidant. Our explanation was that as long as the cellwalls are intact, they keep the interior of the cell separated from oygen from air. Although we never performed experiments to check that explanation, there is more evidence pointing in that direction: if you cut an apple, the brown surface color that forms is due to iron being oxidized to Fe³⁺. This happens only at the surface that is exposed to air - i.e. where cell walls are cut. – cbeleites supports Monica Oct 24 '16 at 14:01
  • @Tom: turns out, this is textbook knowledge. See update of answer. – cbeleites supports Monica Oct 24 '16 at 14:23

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .