A Maria lava a ameixa antes de a comer.

In European Portuguese, it is very common to use the definite article before a person's name: a Maria, o João, a Ana.

So A Maria is not unusual or extra-emphatic here; it is just a normal Portuguese way of saying Maria in many contexts in Portugal.

A few notes:

• It is especially common in speech.
• It is less likely in some very formal styles.
• This is a noticeable difference from English, where we normally say just Maria, not the Maria.

That a is also the definite article, but here it goes with the noun ameixa.

• a ameixa = the plum
• ameixa is a feminine singular noun
• so the article is a

So in this sentence:

• A Maria = article + name
• a ameixa = article + noun

They look the same, but they are doing different jobs.

Lava is the conjugated form of the verb lavar in the present indicative, 3rd person singular:

• eu lavo
• tu lavas
• ele/ela lava

Since the subject is A Maria (she), the verb must be lava.

So:

• A Maria lava... = Maria washes...

Antes de means before when it is followed by a verb in the infinitive.

So:

• antes de comer = before eating
• antes de sair = before leaving
• antes de dormir = before sleeping

In this sentence, antes de a comer means before eating it.

This is a very common Portuguese structure:

• antes de + infinitive

After the preposition de in antes de, Portuguese normally uses the infinitive.

That is why you get:

• antes de comer not
• antes de come not
• antes de comeu

This works much like English before eating or before she eats, but Portuguese often prefers the infinitive structure here.

That a is not an article. It is a direct object pronoun meaning it, referring to a ameixa.

So:

• a ameixa = the plum
• a = it (feminine singular direct object)

So antes de a comer literally works like:

• before eating it

This pronoun is feminine singular because ameixa is feminine singular.

Because this a is a pronoun, not an article.

Portuguese contracts de + a into da when a is an article or similar word:

• de + a casa → da casa

But here, the a is the object pronoun it, so there is no contraction:

• antes de a comer ✔
• antes da comer ✘

This is a very common learner question because the words look identical, but grammatically they are different.

In European Portuguese, when an infinitive comes after a preposition such as de, it is very common for the object pronoun to come before the infinitive:

• antes de a comer
• de o fazer
• para me ajudar

So antes de a comer is a very natural European Portuguese pattern.

You may also see forms like comê-la in other contexts, and sometimes in other varieties or more formal styles, but for Portuguese from Portugal, antes de a comer is very normal.

Yes. That is perfectly correct.

Compare:

• antes de a comer = before eating it
• antes de comer a ameixa = before eating the plum

The difference is mainly that the first version uses a pronoun instead of repeating the noun.

Using the pronoun is natural when the object has already been mentioned.

Mostly because of meaning and context.

Grammatically, both Maria and ameixa are feminine singular, so the pronoun a could in theory match either one. But in this sentence, the thing that is washed and then eaten is clearly the plum, not Maria.

So Portuguese relies on normal real-world logic here:

• Maria washes the plum
• then she eats it

That makes a naturally refer to a ameixa.

No. They look the same, but they have three different functions:

• A Maria → definite article before a person's name
• a ameixa → definite article before a noun
• de a comer → direct object pronoun meaning it

So one short sentence gives you three different uses of a:

1. article with a name
2. article with a noun
3. object pronoun

That is one reason this sentence can look confusing at first, even though the grammar is completely normal.