Hello I would like to set the Description for magento products using data collected from Amazon api. I am calling the API and would like to get the xml response into magento description. I have some code prepared :

    <?php
     require('../AmazonApi.php');
     require_once ('../app/Mage.php');
     Mage::app();

     //Create API access object
     $public_key = '*************';
     $secret_key = '*************';
     $associate_tag = '**********-21';
     $amazon_api = new AmazonAPI($public_key, $secret_key, $associate_tag);


    $products = Mage::getModel('catalog/product')
    ->getCollection()
    ->addAttributeToSeleXct('asin')
    ->addAttributeToSelect('description')
    ->load($productId);
    
    //Array of request parameters
    foreach($products as $product)
    {
    $asin = $product->getAsin();
    $product->setDescription($response);
    $product->save();
    $params_array = array(
	'Operation' => 'ItemLookup',
	'IdType' => 'ASIN',
	'ItemId' => $asin ,
	'ResponseGroup' => 'Tracks');

    // returns a list of items for the search query 'Slow Magic'
    $response = $amazon_api->sendRequest($params_array);

    foreach ($response as $restponse)
    {
    sleep(1);
    }

    echo '<pre>';
    print_r($response);
    echo '</pre>';
    }

    foreach($parsed_xml->OperationRequest->Errors->Error as $error){
     echo "Error code: " . $error->Code . "\r\n";
     echo $error->Message . "\r\n";
     echo "\r\n";
     }
I am getting the data by calling the api however it doesn't save it into magento product description.