private function getFulltextFilter(\Magento\Framework\Api\Search\SearchCriteriaInterface $searchCriteria)
    {
        $queryText = null;

        foreach ($searchCriteria->getFilterGroups() as $filterGroup) {
            foreach ($filterGroup->getFilters() as $filter) {
                if ($filter->getField() == "search_term") {
                    $queryText = $filter->getValue();
                }
            }
        }

        return $queryText;
    }