In food processing, health professionals and and health conscious individuals are trying their best to avoid food nutrient loss. The thing is, commodity nutrient conservation should start while the plant is being cultured, before it start bearing, while developing food parts, during harvesting and after. So in short, it should be done it all stages before it reaches the human mouth.
Some species produce more Vitamins than others. I think it would be best to choose high yielding variety that produce appreciable amount of Vitamins.
Higher light intensity encourage more Vitamin C production. It usually comes with high temperatures and should be within the plant tolerable limit.
High rates of Nitrogen fertilizers reduces Vitamin C, for fruit and vegetables. This reminds me that too much of anything is no good.
Less frequent irrigation increased Vitamin C. This is odd. To think that it is washed away by too much water during period of plant development.
Harvesting and after….
Loss is accelerated by high temperature and longer storage period. So better keep it cold and consume it as soon as possible.
Cold storage is good but do not set it to too low to reach the point of chilling injury. Loss occurs when chilling injury occurs.
Bruising, mechanical injuries and trimmings are detrimental to Vitamin C retention. Take good care to avoid damages and too much trimmings.
One kGy or lower irradiation have no significant effects. However, it was not mentioned whether application of large doses have.
Modified Atmosphere storage of reduced O2 or up to 10% CO2 is beneficial. Higher carbon dioxide levels accelerate Vitamin C loss.
Here comes the cooking part. Do it in the shortest possible way. Induction and microwave cooking methods are preferred. Opt for half-cooked dishes. If fruits and veggies can be eaten as is, then do.
How vitamin C loss was studied by Sueng K. Lee and Adel A Kader on their study entitled “Preharvest and Postharvest factors influencing Vitamin C content of horticultural crops.