if(isnumber(search("word *";B1);sheet!$A$1) with no characters preceding "word"

I use if(isnumber(search("word *";B1));sheet1!$A$1) functions a lot to find specific words after which a random word follows (that's why I use the wildcard "*"). I use this to automatically provide categories from sheet1!. But now I need to find a word in cell B1 which doesn't have any word before it. But it should still be possible to have characters after the word in cell B1. So is there a way to incorporate the lack of characters before B1 in this function?