Does pasteurization destroy vitamin C?
Both rooibos (Asphalatus linearis) and rosehips (Rosa canina) are often mentioned to contain natural vitamin C. The proposition is just 15 grams of fresh rosehips would get the required daily vitamin C for even the most demanding.
On closer inspection, things look fishy. Many of the more popular products labels do not mention vitamin C at all, neither for rooibos or rosehips. How would the labels omit mention of vitamin C? English wikipedia on rooibos also seems to mention that there is no vitamin C in rooibos tea, and elsewhere claims of rooibos tea vitamin C are linked to one paper, Morton 1983.
So whats vitamin C again and whats it needed for?
Vitamin C as required for humans is thought to be as L-ascorbic acid. In human body, anionic ascorbic acid is transported via SVCT1 and 2, expressed in the skin, most organs and glands. Oxidized ascorbic acid, dehydroascorbic acid is transported by GLUT1 to 4 and 8, and usually DHA presents 1-2% of the total ascorbic acid, and can be recycled back into ascorbic acid by the body. Looks like vitamin C might be important!
In metabolism L-ascorbic acid is an electron donor, a reducing compound. As it oxidizes into Dehydroascorbic acid (DHA), its thought to be able to scavenge harmful "free radicals". Ascorbic acid is required for biosynthesis of collage, L-carnitine and neurotransmitters, and absorption of iron.
Cooking foods with vitamin C destroys more than half
Ascorbic acid in foods is vulnerable to light, oxygen, heat (which nutrient isn't?), and high pH and copper & ferrous salts. Cooking and refrigeration of vegetables typically removes 70-80% of the vitamin C content. Cases of scurvy - a gum disease caused by chronic lack of vitamin C - in hospitals have been attributed to heat-chill cycle during cooking. Milk pasteurization by slow (62,5 C deg) and fast (100 C deg) methods reduced ascorbic acid levels by 26 and 41 percent, respectively.
Rosehip processing, quantified
Leahu et al tested processing rosehip tea, suryp and jam in Romania's Suceava University.
They reported 300-4000 mg/100 g ascorbic acid content in literature, and quantified 415 mg/100 g ascorbic acid content in their samples. Processing & diluting rosehip into tea destroyed almost all vitamin C, down to less than 1 mg/100 g. Rosehip suryp, likely to contain filtered pulp boiled to reduce liquid content, had only few milligrams more vitamin C at 1,5 to 2,2 mg/100 g ascorbic acid content.
Fruit jam, which could be guessed to be rosehip and sugar mixture pasteurized, contained roughly 10% of the original rosehip fruits ascorbic acid at 32 to 37 mg/100 g ascorbic acid.
So heat-treated rooibos or pasteurized rosehip will be low in vitamin C?
Yes, its likely most vitamin C will be destroyed from storage, processing and heat. From the above it might be safe to say its likely that pasteurization combined with boiling tea reduces vitamin C content radically. The reduction is likely to be more than half, and up to 99,9% by the time the tea or rosehip-jam is on the table.
Copyright 2020 Casimir Pohjanraito