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In the UK at present, one of the examination boards has set a "controlled assessment" (an experiment that pupils do at school under exam conditions) that involves testing a hypothesis that vitamin C is removed from fruit juice by heating it (i.e. in the pasteurisation process).

I am massively skeptical about this. The teacher guidance suggests "Treating fresh orange juice in boiling water for between 10 and 30 mins gives an easily measurable decrease in vitamin C levels". Leaving aside that this hardly represents a simulation of the pasteurisation process(!), does anybody know of any solid, academic studies of the effect of pasteurisation on the vitamin C content of fruit juice? I have tried (as a scientist, but non-biologist) my usual routes to reliable information and they fail miserably - the www is full of crackpots on this one.

As a follow-up to that, is it not the case anyway that the oxidation of the orange juice when it is boiled in this experiment, plus simple exposure to light could also be responsible for any decrease in vitamin C observed?

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  • $\begingroup$ Orange juice is pasteurized!? That's unheard of (for me, at least). $\endgroup$ – user19679 Dec 10 '15 at 20:21
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Hodgins AM, Mittal GS, Griffiths MW. 2002. Pasteurization of Fresh Orange Juice Using Low-Energy Pulsed Electrical Field. J Food Sci 67(6):2294-2299

This is a study of non-thermal food preservation, but it cites two studies that measured ascorbate loss from pasteurisation. I can't cite the studies directly because I can't find them online. According to these authors, they reported losses of 7.0-15.0% and 18.0% after 95°C for 15s. This is high compared to the pulsed electrical field method.

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Yeom HW, Streaker CB, Zhang QW, Min DB. 2000. Effects of Pulsed Electric Fields on the Quality of Orange Juice and Comparison with Heat Pasteurization. J Agric Food Chem 48(10):4597-4605

This study compared ascorbate loss during storage after PEF or thermal treatment. While no difference was observed when stored at 22°C, PEF treated orange juice maintained significantly higher ascorbate concentration than thermally treated orange juice when stored at 4°C. The authors attribute this to the "higher processing temperature".

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They also say (and reference other studies):

Ascorbic acid is a typically heat sensitive nutrient. High temperatures during processing and storage cause loss of ascorbic acid.

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  • $\begingroup$ Thanks for this. The comment at the end is a bit puzzling. Table 3 appears to show that even pasteurisation at temperatures higher than normal (95 vs 72) does not decrease the vitamin C content by more than 20%. I am going to follow this up on Chemistry SE and see if I can find out what is going on. $\endgroup$ – Rob Jeffries Jan 15 '15 at 8:55
  • $\begingroup$ @RobJeffries Does 20% hold some special significance? $\endgroup$ – canadianer Jan 15 '15 at 9:00
  • $\begingroup$ No, I was just rounding up 18% from Table 3. I suppose if I was writing the paper I would argue this demonstrates that it is not especially heat sensitive. I also see from the graph that there is very little difference (none at 22C) between the Heat and PEF curves until you get beyond 40 days storage. So whilst the storage temperature seems important, the processing bit seems much less so. $\endgroup$ – Rob Jeffries Jan 15 '15 at 9:11

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