awk '
    function printlist()
    {
        sub( ", $", "", list );
        printf( "%sfruit %s\n", last, list );
        list = "";
    }

    {
        x = $0;
        sub( "fruit.*", "", x );
        gsub( ".*fruit ", "", $0 );
        if( list && x != last )
            printlist();
        list = list $0 ", ";
        last = x;
    }
    END {
        if( list )
            printlist();
    }
 ' input-file >output-file