check if ingredient exist

I have 3 tables the Ingredient(ingredient_id,name),Category(category_id,name) and category_ingredient(ingredient_id_category_id).

category

I want to be able to add an ingredient and get the number of its specified category in the category table and pass to other table category_ingredient(this table gets the IDs of the ingredient and also the ID its specified category). and that is not the problem because my code works on that. But my problem now is that I have no condition when my ingredient exist. What I want to happen is when ingredient exist, I can no longer add it so that my ingredient will not be redundant in my ingredient table and i can only get its ID and the ID of its category so that it will pass to my table category_ingredient.

Here's my code:

   <?php echo form_open('dashboard/uploadIngredients', 'class="form-horizontal" enctype="multipart/form-data"'); ?>
        <div class="form-group">
            <div class="col-sm-10">

                <select required class="form-control" name="ingredient_category">

                    <option value="" selected disabled>Select Ingredient Category</option>
                <option value="All">All</option>
                <?php foreach($this->products_model->getCategory() as $row): ?>
                    <option value="<?php echo $row->category_id ?>"><?php echo $row->name; ?></option>
                <?php endforeach; ?>
                </select>

            </div>
        </div>
        <div class="form-group">
            <div class="col-sm-10">
                <textarea class="form-control" name="ingredients" rows="5" placeholder="Ingredients (EX. onion, oil, pasta)" required></textarea> 
            </div>
        </div>

        <div class='form-group'>
            <div class="col-sm-10">
                <button class="btn btn-lg btn-positive" type="submit"><i class="glyphicon glyphicon-ok"></i> Save Ingredient</button>
            </div>
        </div>
    <?php echo form_close(); ?>

CONTROLLER:

public function uploadIngredients() {

    foreach(explode(',', $this->input->post('ingredients')) as $key => $value)
    {
        $saveData[] = array('ingredient_id' => null,
                            'name'  => trim($value)
        );  
    }

    $ingredient_id = $this->products_model->saveIngredients($saveData); 
    foreach (explode(',', $this->input->post('ingredient_category')) as $key => $value)
    {
     foreach ( $ingredient_id as $key => $str ){
        $joinData[] = array(
                            'ingredient_id'     => $str,
                            'category_id'       => intval($value)
        );
}
        //var_dump($joinData); die();
        $this->products_model->saveCategoryIngredients($joinData);

        redirect('dashboard/add_ingredients');
        }


}

MODEL:

 public function saveIngredients($ingredient_id)
{
    foreach($ingredient_id as $row => $value) {
        $query=$this->db->where('ingredient_id', $value->ingredient_id);
            $this->db->insert('ingredient', $value);
            $insert_id[] = $this->db->insert_id();  
    }


    return $insert_id;
}