There are no tab characters in that line. Presumably due to a cut/paste issue. Can you try again to get the tabs in there? And also show the output you expect vs the output you are getting?

my $var='474627    asidase ta sidase ala,"lpha-D- ctoside gtohydrolase
+","razyme","arazyme    (enz Corp)","Melie","lagal","idase bta",    ru
+g    00103';
my @each=split(/(?<!,)\t/,$var);

for my $eachvar(@each)
    {
       print "$eachvar\n";
     }
[download]

This is the output i get

474627
asidase ta
sidase ala,"lpha-D- ctoside gtohydrolase","razyme","arazyme
(enz Corp)","Melie","lagal","idase bta",        rug
00103
[download]

This is the output i expect

474627
asidase ta
sidase ala,"lpha-D- ctoside gtohydrolase","razyme","arazyme    (enz Co
+rp)","Melie","lagal","idase bta",
rug
00103
[download]

So in addition to ignoring a tab after a comma, you also want to ignore tabs within quoted strings. This revises the original spec just a bit.

Do you really require both of these things? Or is the real requirement only the latter (ignore tabs within strings), and the original example just happened to have been derived from a string with a comma-tab?

Also, I get this output, different from yours. (no tab after 'ta') (And you have a comma-tab, just before 'rug', that you do want to split.)

474627
asidase ta sidase ala,"lpha-D- ctoside gtohydrolase","razyme","arazyme
(enz Corp)","Melie","lagal","idase bta",        rug
00103
[download]