array(5) {
  [0]=>
  array(4) {
    [0]=>
    string(2) "21"
    [1]=>
    string(5) "Arroz"
    [2]=>
    string(1) "2"
    [3]=>
    string(5) "15.00"
  }
  [1]=>
  array(4) {
    [0]=>
    string(2) "22"
    [1]=>
    string(6) "Feijão"
    [2]=>
    string(1) "3"
    [3]=>
    string(4) "5.00"
  }
  [2]=>
  array(4) {
    [0]=>
    string(2) "11"
    [1]=>
    string(6) "Cebola"
    [2]=>
    string(1) "3"
    [3]=>
    string(4) "1.00"
  }
  [3]=>
  array(4) {
    [0]=>
    string(2) "21"
    [1]=>
    string(5) "Arroz"
    [2]=>
    string(1) "2"
    [3]=>
    string(5) "15.00"
  }
  [4]=>
  array(4) {
    [0]=>
    string(2) "21"
    [1]=>
    string(5) "Arroz"
    [2]=>
    string(1) "2"
    [3]=>
    string(5) "15.00"
  }
}

function search_in($arr=array(), $str)
{
 foreach( $arr as $key => $value )
 {
  if($value[0] == $str)
   return true
 }
 return false;
}