The influence of the sample preparation of carrots (Daucus carota L. Neptun) on the antioxidant activity and phenolic compounds

Abstract

The growing demand for organic food in the world requires the assessment of the value aspects of food quality, its safety, nutritional content and biological-physiological process.
Fruits and vegetables are good sources of natural antioxidants containing many different antioxidant components. These antioxidants include carotenoids, vitamins, phenolic compounds, flavonoids, dietary glutathione and endogenous metabolites which have been shown to function as singlet and triplet oxygen quenchers, free radical scavengers, peroxide decomposers, enzyme inhibitors, and synergists. Phenolic compounds are found in most fruits and vegetables (Zhang, Hamauzu, 2005). Carrots and their fresh produce (shredded carrots, sliced carrots and carrot juice) may protect humans against certain types of cancer and cardiovascular diseases (Krinsky, Johmson, 2005). Carrots contain mainly hydroxycinnamic acids and derivatives. Among them, chlorogenic acid is a major hydroxycinnamic acid, representing from 42.2% to 61.8% of total phenolic compounds (Wang et al., 2006). In addition to the above mentioned compounds found in natural foods, vitamins C and E, beta-carotene and tocopherol are known to possess antioxidant potential.
The aim of the research was to determine the total antioxidant activity and phenolic compounds which operate as free radical scavengers, peroxide decomposers, enzyme inhibitors and synergists. Carrot breed Neptun was obtained from Lithuanian Institute of Horticulture. Correlations between antioxidant activity and phenolic compounds were determined by using three drying methods (carrots were sliced and dried in desiccator at +40  °C and lyophilised under vacuum conditions (freeze-dried) by –72  °C for sample preparation. Antioxidant activity was determined by using DPPH radicals spectrophotometrically. The influence of drying method was not significant p > 0.05, but solvent concentration showed significant correlation with antioxidant activity and phenolic compound (p < 0.05). Among the weight of raw material and various ratios of methanolic extracts, significantly the best antioxidant activity was shown by 0.5 g and 75% of sliced desiccated, freeze-dried and pressed desiccated samples The total phenolic content of carrot material investigated during this research varied from 0.07 to 0.31 mg/ml of the methanolic carrot extracts and from 1.51 to 7.01 mg / g of dry carrot content, expressed by gallic acid equivalent (GAE). The time effect for DPPH scavenging was significant until 30 min (p < 0.05). If the reaction achieved a plato effect (balance), approx. 80% of antioxidant activity, the time effect was not significant (p > 0.05).