Could they have meant "effect" in the sense of bringing about a result? Seems like they could have based on context.

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Note added at 3 mins (2020-05-08 13:02:10 GMT)
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I don't think "effect to" is grammatical regardless, but it looks like they could have been going for that meaning, anyway.

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Note added at 5 mins (2020-05-08 13:04:18 GMT)
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Oh, and in this case, your guess of "break down [into]" *could* be a possibility.

English term (edited): could additively affect

Not my subject, hence the 3, but the following (also by a Japanese writer) makes more sense to me:

The concentration of ethyl isovalerate showed relatively good correlation with isovaleric acids derived from hops
http://www.researchgate.net/publication/338139006_Behaviour_...

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Note added at 20 mins (2020-05-08 13:18:52 GMT)
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You can see how the translator wrongly arrived at "could additively affect". The more hops, and thus isometric acids, the more ethyl isovalerate.

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Note added at 22 mins (2020-05-08 13:20:51 GMT)
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If it's the same author, that makes it MORE likely that my answer is correct. He's saying the same thing in two different ways.

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Note added at 23 mins (2020-05-08 13:21:29 GMT)
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So make it a 4, not a 3.

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Note added at 24 mins (2020-05-08 13:23:16 GMT)
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Sorry, that was an autocorrect error. Isovaleric, not isometric.

In fermentation there are cascades of reactions where each product of a singular reaction yields to another product where the final product in this case is “ethyl isovalerate.”
Ethyl isovalerate is an organic compound that is the “ester” formed from ethyl alcohol and isovaleric acid.
Normally esters are derived from a carboxylic acid (such as 3-Methylbutanoic also known as isovaleric acid) and an alcohol (such as ethanol).
Thus formation of isovaleric acid and ethanol during fermentation process could yield to “ehyl isovalerate.”
In other words the use “affect” is not equivalent to breakdown.

In my professional opinion the authors’ use of phrase “...could additively affect to ethyl isovalerate.” perhaps can be rephrased as “...during fermentation process ethyl isovalerate is expected to form and its amount should be proportional to isovaleric acid that was produced during this metabolic process.”

As for the next sentence “...However, it was interesting to note that *no correlation between isobutyric acid and ethyl isobutyrate* was found (Figure 3).” this is interesting because if you have a carboxylic acid (such as isobutyric acid) and an alcohol it is expected to find ethyl isobutyrate in this mixture. However they did not find any! Perhaps this is the difference between simple one to one chemical reaction vs a complex metabolic process.

FYI i am not here to argue about the errors in the use of the language. Instead as a fellow biochemist i am providing “an explanation” about their description of defined chemical reaction.