Sodium Bisulfate vs Sodium Bisulfite
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:
$$\ce{2 NaHSO3 -&gt; Na2S2O5 + H2O }$$
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.