Quality of vegetables may be evaluated in terms of sensorial, chemical
composition, microbial population and nutritional composition.
The USDA- agricultural marketing service addresses issues related
to vegetable quality in their website (http://www.ams.usda.gov/fv/)
Their quality standards can be found at http://www.ams.usda.gov/standards/stanfrfv.htm
The University of California at Davis published "Methods for
Determining Quality of Fresh Commodities," you may see it at: