For the record, I do not buy most of my fruit and vege at a supermarket. I chose to buy such at either fruit and vege markets or independent grocers.
One must also realise that post harvesting can have a significant impact on the nutritional value of produce after harvesting.
It is possible that fresh fruit and vegetables sold at a farmer’s markets may have less nutritiinal value than that sold elsewhere… either fresh or procesed (frozen or canned). This can especially the case if the produce is not stored in a cool environment (inc. refrigerated). If the produce is stored at room temperature, exposed to higher temperatures such as on display outdoors, potentially in high light/sunlight, such can quickly degrade the nutrient value of the produce. Believing that farmer’s market produce is better is problematic and in fact may be proven not to be the case. The same applies to supermarket and other retail outlets.
There are to many variable for the consumer to determine whether the product is in fact fresh and whether it has a high nutritional value, similar to that at harvest or through better handling and storage processes.
This summary of research papers provides some information on this…
