Custom component property that is not a trait

I would like to create a custom component with a property that will be updated by specific code, but I don't want this property to be visible and updatable as a trait; let say my property is called "ebTesto", I wrote a plugin function like that:

function addComponentX(editor, options){
	const COMPONENT_TYPE = 'eb-componentx';
	editor.DomComponents.addType(COMPONENT_TYPE, {
		isComponent: function(el) {
			if(el.getAttribute && el.getAttribute('data-gjs-type') ==COMPONENT_TYPE) {
				return {type:COMPONENT_TYPE};
			}
		 },		      	
		 model: {
		      defaults: {
			      ebTesto: 'Ciao',
			      tagName: 'div',
			      components: [
					{
						type:'text',
						content: 'Title component X',
						removable: false
					}
				]						
			},
			ebTesto: 'Ciao'				
		}		      	
	});
	editor.BlockManager.add(COMPONENT_TYPE, {
		    label: 'Component X',
		    category: 'EB',
		    attributes: {class:'eb-componentx-block'},
		    content: `<div class="eb-componentx" data-gjs-type="${COMPONENT_TYPE}"></div>`
      });
}

I expected to find my new property in the "gjs-components" part of the stored JSON, but this is what I got:

[
  {
    "type": "eb-componentx",
    "classes": [
      "eb-componentx"
    ],
    "components": [
      {
        "type": "text",
        "removable": false,
        "content": "Title component X"
      }
    ]
  }
]

Maybe I'm trying the wrong way? Has anyone ever had a similar need? Thanks for your help!