Većina zamrznute hrane još je sigurna.

Croatian does not have articles like the or a/an.
So Većina zamrznute hrane još je sigurna is perfectly normal without any separate word for the.

If English uses the here, Croatian usually just leaves it unspoken and lets context do the work.

Većina means most or the majority.

Grammatically, it is a noun, not just an adverb or determiner. Its dictionary form is većina, and it is feminine singular.

Because it is a noun meaning the majority of, it is followed by another noun in the genitive:

• većina hrane = most of the food
• većina ljudi = most of the people

Because većina requires the genitive.

So the basic form:

• zamrznuta hrana = frozen food
  changes to:
• zamrznute hrane = of frozen food

Both words change because the adjective must agree with the noun:

• zamrznuta → zamrznute
• hrana → hrane

Here they are both feminine singular genitive.

Croatian often treats food as an uncountable mass noun: hrana.

So većina zamrznute hrane literally means something like most of the frozen food. That is very natural in Croatian.

If you wanted to emphasize separate food items or products, you might use a different noun, for example:

• većina zamrznutih proizvoda
• većina zamrznutih namirnica

But with hrana, singular is normal.

Because it has to match hrane.

The adjective zamrznut changes its ending to agree with the noun in:

• gender
• number
• case

Here hrane is:

• feminine
• singular
• genitive

So the adjective is also:

• feminine
• singular
• genitive

That gives zamrznute hrane.

Because the grammatical subject is većina, and većina is feminine singular.

So Croatian treats the sentence as:

• Većina ... je sigurna
  not
• Većina ... su sigurne

The adjective sigurna agrees with većina, not with the idea of many pieces of food.

For the same reason: većina is singular.

Even though most feels plural in English, Croatian usually uses singular agreement with većina:

• Većina ljudi je došla.
• Većina hrane je sigurna.

So je is the normal form here.

Here još means still.

So the idea is:

• it was safe before
• it remains safe now

In other contexts, još can also mean more, another, or be part of other expressions, but in this sentence it clearly means still.

Croatian word order is fairly flexible, and short forms like je often stay near the front of the clause.

The given order, još je sigurna, is very natural and keeps još closely tied to the idea of still safe.

You may also hear:

• Većina zamrznute hrane je još sigurna.

That is also understandable and natural. The difference is mostly about rhythm and emphasis, not basic meaning.

It can mean both, depending on context.

The adjective siguran / sigurna / sigurno can mean:

• safe
• sure
• certain

But with food, the meaning is clearly safe:

• safe to keep
• safe to use
• safe to eat

So here sigurna does not mean confident or certain. It means not dangerous / still okay.

The main special letters here are:

• ć in većina: a soft ch-like sound
• ž in zamrznute: like the s in measure
• š in još: like sh in ship

A rough English-style approximation would be:

• Većina ≈ VEH-chee-na
• zamrznute ≈ zam-RZ-noo-teh
• hrane ≈ HRA-neh
• još ≈ yosh
• je ≈ yeh
• sigurna ≈ see-GOOR-na

The cluster hr in hrane is pronounced, and zamrznute has a consonant-heavy middle that may take practice.