Learn Italian: Non ci sono alcune fragranze scadenti in queste miscele. - There are no poor-quality fragrances in these blends.

The word nessuno is strictly singular. While an English speaker might naturally want to translate "no fragrances" as nessune fragranze, Italian grammar requires you to use the plural of alcuno in negative contexts instead. This is why we use alcune fragranze.

Could we use the singular nessuna instead of the plural alcune in this sentence?

Yes, you could say Non c'è nessuna fragranza scadente. In fact, expressing "there are no [items]" using the singular form with nessuno is much more common in everyday spoken Italian. Using the plural with alcune is grammatically correct but tends to sound a bit more formal or literary.

Doesn't alcune usually mean "some"? Why does it mean "not any" here?

Alcuno generally means "some" in positive sentences, but it acts as the mandatory plural counterpart to nessuno in negative contexts. Because it doesn't carry an inherent negative meaning on its own, it always needs a negative trigger word like non, senza, or mai. Here, the non at the start of the sentence shifts its meaning to "not any".

Does the adjective scadenti mean that the fragrances are expired?