Although, answer is already accepted, but I want to give solution to this problem if you do not want to use [(ngModel)] two way data binding and want to break it down. Complete working example can be founded in this StackBlitz Link
In your HTML File we use [value] as default value setters.
<mat-select [value]="defaultSelectedOption" id="status" (selectionChange)="onChange($event)">
<mat-option *ngFor="let food of foods" [value]="food.value">
{{food.viewValue}}
</mat-option>
</mat-select>
<br> <br> <div>
<span> Default selected and changable value is :<strong> {{defaultSelectedOption}}</strong> </span>
</div>
Class file is..
defaultSelectedOption = '';
foods: Food[] = [
{value: 'steak-0', viewValue: 'Steak'},
{value: 'pizza-1', viewValue: 'Pizza'},
{value: 'tacos-2', viewValue: 'Tacos'}
];
ngOnInit(){
this.defaultSelectedOption = this.foods[1].value;
}
onChange(eventValue){
this.defaultSelectedOption= eventValue.value;
}