food chemistry - Sodium Bisulfate vs Sodium Bisulfite

I'm wanting to do a follow up to this Q&A on the cooking stack regarding browning avocados. I specifically want to expand my experiment to include the options in Wayfaring Stranger's Answer. Unfortunately, I managed to get the wrong stuff, and shipping rules make exchanging it problematic.

I am the proud owner of $500~\mathrm{g}$ of sodium bisulfate ($\ce{NaHSO4}$), instead of sodium bisulfite ($\ce{NaHSO3}$).

Dammit Jim! I'm a cook not a chemist!

What I have learned is that that both compounds are used as food additives towards the same end, and that my stuff has a slightly higher LD50. That's it.

Can anyone advise as to substituting my compound for the other? I'm not interested in tasty guacamole at this point, I'm really only looking at browning. If I'm trying to more or less duplicate the more successful experiments of the University of Florida, should I start with the same ratios? Or more or less of the additive? I can get sodium metabisulfite (also an anti-oxidant food additive) locally, if that would be a better option.

EDIT: So far, answers have all been consistent in that I have a half-kilo of white powder that is useless to me. I will make a trip to the wine-making shop and acquire some sodium metabisulfite. That still leaves me with the question of how much? The University of Florida got the results I'd like to duplicate with $30~\mathrm{mg}$ of sodium bisulfite per $100~\mathrm{g}$ of avocado. Should I start with the same ratio of sodium metabisulfite?

Answer

• Sodium bisulphate (NaHSO₄): an acid


• Sodium bisulphiTe (NaHSO₃): an antioxidant


• Sodium metabisulphiTe (Na₂S₂O₅): another antioxidant

In short, bisulphate and bisulphite are not interchangeable, but bisulphite and metabisulphite are.

Sodium metabisulphite is prepared from sodium bisulphite via dehydration, as in this equation: $$\ce{2 NaHSO3 -> Na2S2O5 + H2O }$$ It's reversible in aqueous solution. The assumption that 30 mg of metabisulphite contain the same amount of sulphite as 30 mg of bisulphite is OK, the error is small, about 10 %. The correct amount would be 27 mg of metabisulphite.

You'd ask yourself if pasteurization (75 deg. C, 30 seconds) would work to deactivate the polyphenoloxidase without affecting flavour too much.

I'd also suggest searching Pubmed (it's a decent alternative to commercial citation databases) for such keywords as "polyphenol oxidase" (that's the enzyme that causes browning), "inhibition" and "sulfite".

If you want hands-on answers I'd suggest going to the library and get (via interlibrary loan) a copy of this paper: Plant Foods Hum Nutr. 1995, 47, 245-56, "The control of polyphenol oxidase activity in fruits and vegetables. A study of the interactions between the chemical compounds used and heat treatment."

From the abstract: ... Interactions between the use of ascorbic acid, citric acid, EDTA, sodium metabisulphite and heat treatment (70 degrees C for 2 min) in the control of PPO activity were studied in avocado ..., banana ..., apple ..., pear ..., peach ..., potato ..., eggplant ..., mushroom ... and hearts-of-palm ... . The results demonstrated that PPO of avocado and eggplant was most resistant to inhibition by the methods used. ... The results indicated that, with the exception of PPO from avocado, the most adequate alternative method to substitute for the use of SO2 in the control of PPO was a combination of ascorbic acid, citric acid and heat treatment.

This shows that how to get on top of browning while still having a presentable product is a tough problem and an active area of research. Also, avocado seems a specially hard case.