Non voglio troppa maionese nel panino.

In Italian, standard negation is usually formed by putting non directly before the verb.

So:

• voglio = I want
• non voglio = I do not want / I don’t want

This is one of the most basic Italian sentence patterns:

• Non capisco = I don’t understand
• Non so = I don’t know
• Non mangio carne = I don’t eat meat

Voglio is the first person singular form of volere, meaning to want.

The present tense of volere begins like this:

• io voglio = I want
• tu vuoi = you want
• lui/lei vuole = he/she wants
• noi vogliamo = we want
• voi volete = you all want
• loro vogliono = they want

Since the sentence means I don’t want..., voglio is the correct form.

Italian often leaves out subject pronouns when they are already clear from the verb ending.

So:

• Non voglio already means I don’t want
• You do not need to say Io non voglio unless you want emphasis

Compare:

• Non voglio troppa maionese = I don’t want too much mayonnaise
• Io non voglio troppa maionese = I don’t want too much mayonnaise, with extra emphasis on I

This is very common in Italian.

Because troppo is an adjective here, and it must agree with the noun it describes.

The noun is maionese, which is feminine singular, so the adjective must also be feminine singular:

• masculine singular: troppo
• feminine singular: troppa
• masculine plural: troppi
• feminine plural: troppe

Examples:

• troppo pane = too much bread
• troppa maionese = too much mayonnaise
• troppi pomodori = too many tomatoes
• troppe patatine = too many fries

In Italian, when using words like troppo, molto, poco, and similar quantity expressions, you often do not use an article before an uncountable noun.

So:

• troppa maionese = too much mayonnaise
• molta acqua = a lot of water
• poco zucchero = little sugar

This works similarly to English, where you also say too much mayonnaise, not too much the mayonnaise.

Yes, maionese is feminine: la maionese.

You often learn noun gender together with the article:

• il panino
• la maionese

In this sentence, you can also tell from the adjective agreement:

• troppa maionese

Since troppa is feminine singular, it matches a feminine noun.

Nel is a contraction of in + il:

• in + il = nel

So:

• nel panino literally means in the sandwich

Italian often combines prepositions with definite articles:

• in + il = nel
• in + la = nella
• su + il = sul
• a + il = al
• di + il = del

Here, nel panino is natural because you are talking about what is inside the sandwich.

Because Italian usually needs the article in cases where English does not.

English says:

• in the sandwich
• in my sandwich
• in a sandwich

In Italian, when speaking generally about a specific sandwich in the situation, nel panino is natural:

• nel panino = in the sandwich

You cannot normally say in panino here. That sounds incomplete or wrong.

Yes, but the meaning changes slightly.

• troppa maionese = too much mayonnaise
• molta maionese = a lot of mayonnaise

So:

• Non voglio troppa maionese nel panino means you do not want an excessive amount
• Non voglio molta maionese nel panino means you do not want a large amount

In many situations they are close, but troppa has a clearer idea of more than desired.

Because the sentence refers to one sandwich.

• il panino = the sandwich
• i panini = the sandwiches

So:

• nel panino = in the sandwich
• nei panini = in the sandwiches

If you were talking about more than one sandwich, the sentence would need to change, for example:

• Non voglio troppa maionese nei panini

Yes, Italian word order is somewhat flexible, but the original order is very natural.

Standard order:

• Non voglio troppa maionese nel panino

You could also hear:

• Nel panino non voglio troppa maionese

This version gives a little more emphasis to nel panino, as if contrasting it with something else.

Still, for a learner, the original version is the safest and most neutral.

Yes. Maionese is an uncountable noun here, so Italian treats it as singular.

That is why you get:

• troppa maionese
• not troppe maionesi

This is like English:

• too much mayonnaise
• not too many mayonnaises

If you were counting separate units or types, the structure could change, but in normal everyday usage, maionese here is singular and uncountable.

A common polite version would be:

• Non vorrei troppa maionese nel panino

Here, vorrei literally means I would like, and it often sounds softer and more polite than voglio.

Compare:

• Non voglio troppa maionese nel panino = I don’t want too much mayonnaise in the sandwich
• Non vorrei troppa maionese nel panino = I wouldn’t like too much mayonnaise in the sandwich / I’d prefer not to have too much mayonnaise

In restaurants or shops, vorrei is often more courteous.