Orderby with *ngFor array

Question

I made the following structure in my json file with Firebase Real Time Database to work on Composer and his Compositions:

I have the following service that give me the data of one composer with his composition

getComposerWithKey(key: string): Observable<Composer> {
const memberPath = `composer/${key}`;
this.composer = this.db.object(memberPath)
  .snapshotChanges().map(action => {
    const $key = action.payload.key;
    const arrcompositions = action.payload.val().compositions?Object.entries(action.payload.val().compositions):null;
    const data = { 
      $key,
      arrcompositions,
      ...action.payload.val() };
    return data;
  });
return this.composer
}

Now I can get the composer info with a list of his compositions with the ngFor directive :

<mat-list-item *ngFor="let composition of composer.arrcompositions">
    {{ composition[1] }}
</mat-list-item>

My problem is that I can't order the compositions in alphabetic order. I tried to use the ngx-order-pipe but I don't know how to precise the value used to order

<mat-list-item *ngFor="let composition of composer.arrcompositions | orderBy: 'composition[1]'">
{{ composition[1] }}

This obviously doesn't work...