Vitamin C, (5R)-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxyfuran-2(5H)-one, is a very powerful antioxidant present in fruits and vegetables and an ingredient in many supplements. It is important for the work of the immune system, which stimulates the activity of leukocytes and increases the concentration of interferon. Increased interferon concentrations result in the secretion of thymus hormones and the production of antibodies. It participates in the metabolism of fatty acids and the synthesis of carnitine and collagen. It also helps in the formation of erythrocytes, participates in the absorption of iron and the transformation of folic acid into its active form, 5-methyltetrahydrofolic acid. Fresh fruits and vegetables have the highest concentration of vitamin C, and food processing reduces its concentration because it is easily soluble in water, photosensitive and susceptible to oxidation. It is extremely unstable and loses its characteristics and its concentration decreases at high temperatures (thermal decomposition of vitamin C) and long-term storage. In this paper, iodometric titrations were used to determine the effect of storage and type of processing on the concentration of ascorbic acid in fruits and fruit products. The method is simple and practical for the rapid determination of vitamin C. The values collected were compared with the USDA database to determine how applicable used method was for that purpose. The method is good in our case if the sample solutions are lighter in colour so the colour change to dark blue is easily noticeable. For darker coloured samples, it is more difficult to determine the end point of the titration. The results of this study indicate that the content of vitamin C is much lower in fruit products than in fresh fruit. Reduction of vitamin C content in plant materials is caused by preparation, heat treatment and long-term storage of food.