The Sense of Taste
The are 5 tastes.  A taste is a sensation created by receptors on the tongue.  The entire flavor of a food is a combination of its taste, smell, texture, temperature, etc.  The 5 tastes are:

Sweet

Salty

Sour

Bitter

Umami (oo-mommy) - the recently recognized 5th taste

 
Umami is a Japanese word for the taste imparted by glutamate in foods.  There is no direct English translation, but it is often described as "meaty", "savory" or "broth-like". Traditionally, glutamate was considered a taste enhancer, e.g. it made the tongue more receptive to other tastes.  However, the Japanese have considered umami a taste for a long time.  Only recently have taste receptors on the tongue been identified, which allowed umami to be officially classified as the 5th taste.  It is a taste that gives many vegetables a "meaty" taste. For example, umami is the "meaty" or "savory" taste of sautéed mushroom, fermented foods and sauces such as soy sauce, or fresh tomatoes. The umami taste is also very high in cheese, shellfish seafood, stocks, broths and chocolate. Another compound that imparts the umami taste is ribonucleic acids. Glutamate and ribonucleic acid may complement each other synergistically to create an enhanced umami taste.
Monosodium glutamate (MSG) is the form of glutamate available for seasoning.  One brand is Accent.  Glutamate is an amino acid.  In its free form, called a salt of glutamic acid (such as monosodium glutamate) it imparts in food the umami taste.  Glutamate is an amino acid that  makes up proteins, but when glutamate is bound in a protein it does not impart the umami taste. 

 
So what does this all mean. Adding a pinch of MSG to your seasoning mix or or directly when cooking foods may generate a more "meaty" or "savory" flavor. Of course another option is to use those foods that are naturally high in glutamate. Use of stocks, broths and tomatoes in cajun cooking maybe one of the secrets of its rich savory flavor. 
  
How about a 6th taste - fat

Now that we're on the subject of tastes, I'd like to add a 6th of my own - fat. That's right, fat as a 6th taste. Yes, I know there are no fat taste receptors so it cannot truly be a taste, but there is absolutely no doubt that fat adds to the unbelievably rich flavor of cajun cooking.   Fat is one of the main ingredients that creates the incredibly rich flavor of crawfish etouffee made with the head fat, a gravy made with smothered pork or whole chicken pieces, a well marbled steak, or anything sautéed in butter.  You know you cannot make a decent brown gravy with lean meat such as venison or round steak.  Ok, so fat is a flavor and not a taste! 
 
©David Wm. Reed