Glycemic Index. I am working with a manufacturer who wants the glycemic index of various types of tortillas. (There is only the glycemic index published for a wheat tortilla).

The glycemic index values that are in the software were adapted from a table that was published in the American Journal of Clinical Nutrition in 2002. The article was published by the Brand-Miller research group. Matching database foods with foods listed in the article involved matching the exact food name and the carbohydrate content. Since glycemic index is affected by so many other factors (eg: fiber, citrus, fat), we only used table matches that could be applied to exact (or near exact) database matches. 

Our software calculates the average glycemic index from a list of items. This is a documented practice in the literature, although there are different schools of thought on how valid this is. This method would not consider how non-glycemic index items (like fat and citrus) affect the whole. Glycemic index values on food packages in Australia are always determined in a lab. There is a web site that may list more glycemic index values than what we have in the software, that you many find interesting:

http://www.glycemicindex.com/