| Synthetic antioxidants are commonly applied in foods to inhibit lipid oxidation, being consumed in appreciable quantities by humans. However, the use of such synthetic antioxidants has been associated with potential health risks resulting in their strict regulations in food applications. Consequently, there is a practical need for the development of natural antioxidants from plant as effective alternatives in the prevention of food deterioration. Black currant is rich in variety of bioactive components, such as vitamins, phenolics and phenolic acid; it is a good source of natural antioxidants, in addition, it possesses the potential health benefit, such as anticancer and scavenging radicals in vivo. The objectives of this research were to prepare black currant extract with high anthocyanins content and antioxidant activity, and evaluate its antioxidant activity and stability. The antioxidant effects of black currant in pork patties and salad dressing were evaluated. In addition, its antiproliferative ability on gastric cancer SGC-7901cells and the protective effect on human embryonic lung fibroblast cells MRC-5damage by H2O2were also investigated.1. The optimal extract condition for preparing black currant extract was determined by single factor experiment. The black currant extract with high anthocyanins and antioxidant activity was extracted with40%ethanol for2h which was then concentrated by rotary vacuum evaporator at40℃. The total anthocyanins content and phenolic content of the concentrated black currant extract were4.1mg/mL and12.2mg/mL, respectively.2. Compared with0.01%BHA and0.01%ascorbic acid,25mg/mL black currant extract exhibited higher reducing power,1,1-diphenyl-2-picrylhydrazyl (DPPH),2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and superoxide radicals scavenging activity, but lower hydroxyl radical scavenging activity (P<0.05).3. The stabilities of anthocyanins in black currant extract and the antioxidant activity of black currant extract were investigated.(1) The black currant extract containing100mg/mL anthocyanins was heated at60℃,80℃and100℃for1-5h and the anthocyanins content and antioxidant activity were evaluated.A reduction of anthocyanins content was observed during heating which followed first-order reaction kinetics. The reaction rate constant increased and the half-time decreased with the increasing heating temperature. The activation energy of the thermal degradation of anthocyanins was71.97KJ/mol. The DPPH, ABTS, superoxide and hydroxyl radicals scavenging activity and reducing power were also decreased with increasing heating temperature and time. (2) The black currant extract containing100mg/mL anthocyanins’was placed in outdoor natural light, in indoor natural light and in dark for25d and the anthocyanins content and antioxidant activity were evaluated. The anthocyanins content decreased during storage as:outdoor light> indoor light> dark. The degradation of anthocyanins followed first-order reaction kinetics. The highest reaction rate constant and the lowest half-time were observed when the black currant extract was exposed to outdoor natural light, which were higher and lower than that of the black currant extract stored in indoor natural light and in dark, respectively. The DPPH, ABTS, superoxide and hydroxyl radicals scavenging activity and reducing power were also decreased (outdoor light> indoor light> dark).(3) The black currant extract at pH3-7was stored for15days in indoor natural light. The black currant extract exhibited different color at various pH and the maximum absorption wavelength shift to red at high pH. The black currant extract showed the stable antioxidant activity at low pH which decreased a lot at high pH during storage.4. The pork patties added with5,10and20g/kg black currant extract were stored at4℃for9days and the TBARS value, carbonyl content, sulfydryl content and color were determined. The black currant extract treatments significantly decreased the TBARS value and carbonyls conformation, reduced the sulfhydryl loss of pork patties in a dose-dependent manner, which showed the black currant extract had a significant inhibition to lipid and protein oxidation. The black currant extract treated patties showed significant higher redness (P<0.05) than control.5. The salad dressing added with2.5g/kg,5g/kg and10g/kg black currant extract were stored at25℃for6weeks and the POV value, TBARS value, viscosity and red color were determined. The black currant extract treatments significantly decreased the POV value and TBARS value to inhibited lipid oxidation. The salad dressing added with black currant extract showed lower viscosity and higher red color than control. Most of the anthocyanins and phenolics in black currant extract were present in the aqueous phase to inhibit lipid oxidation in salad dressing.6. The black currant extract inhibited the proliferation of SGC-7901cells in a dose-and time-dependent manner, and the IC5o were12.7,10.2and9.0mg/mL for12,24and48h, respectively. Morphologic observations with inverted and fluorescence microscopes yielded vivid evidence of cell shrinkage, formation of cytoplasmic filaments, condensation of nuclear chromatin, and cell apoptosis in the presence of black currant extract. Flow cytometric analysis also showed that black currant extract treatment resulted in marked reductions of viable cells.7. The black currant extract could protect the human embryonic lung fibroblast cells MRC-5from H2O2induced cytotoxicity. The black currant extract treated cells showed higher cell viability; and the morphologic observations and flow cytometric analysis confirmed the reduction of apoptosis cells. The cytoprotective effect of black currant extract was associated with the decreases in the MDA level and increases in the GSH, SOD and CAT activity in treated MRC-5cells. |
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