How to get child of child in firebase

hello
i want to show a child of child in ionic ng-for from FirebaseListObservable

i tried this but i get error
i want to get one form catlogy array

image


 <ion-item *ngFor=" let item of assets | async " >
            <h4 style="text-align: center;"> {{item.name}}</h4>
       <h4 style="text-align: center;">  {{item.desc}}</h4>
             <h4 style="text-align: center;">  {{item.price}}</h4>
       <h4 style="text-align: center; color:blue;">  {{item.catlogy.one}}</h4>

           </ion-item>

hello please help me