Demo:

Code:

We can use the beforeFlip() function to reset the flipbook zoom, when flipbook starts to flip.

<script>
jQuery(function(){

    DFLIP.defaults.beforeFlip = function(flipbook){
    
        flipbook.zoomValue =1;
        flipbook.zoom(-1);
    
    }

});
</script>

For WordPress, please read on 
How to add Custom Code to WordPress Pages