Thermal stability of anthocyanin extract of Hibiscus sabdariffa L. in the presence of beta-cyclodextrin

The thermal stability of anthocyanin extract isolated from the dry calyces of Hibiscus sabdariffa L. was studied over the temperature range 60-90 degrees C in aqueous solutions in the presence or absence of beta-cyclodextrin (beta-CD). The results indicated that the thermal degradation of anthocyanins followed first-order reaction kinetics. The temperature-dependent degradation was adequately modeled by the Arrhenius equation, and the activation energy for the degradation of H. sabdariffa L. anthocyanins during heating was found to be approximately 54 kJ/mol. In the presence of beta-CD, anthocyanins degraded at a decreased rate, evidently due to their complexation with beta-CD, having the same activation energy. The formation of complexes in solution was confirmed by nuclear magnetic resonance studies of beta-CD solutions in the presence of the extract. Moreover, differential scanning calorimetry revealed that the inclusion complex of H. sabdariffa L. extract with beta-CD in the solid state was more stable against oxidation as compared to the free extract, as the complex remained intact at temperatures 100-250 degrees C where the free extract was oxidized. The results obtained clearly indicated that the presence of beta-CD improved the thermal stability of nutraceutical antioxidants present in H. sabdariffa L. extract, both in solution and in solid state.     

Effects of soil application of olive mill wastewaters on the structure and function of the community of arbuscular mycorrhizal fungi

Recycling of olive mill wastewaters (OMW) into agricultural soils is a controversial issue since benefits to soil fertility should counterbalance potential short-term toxicity effects. We investigated the short-term effects of OMW on the soil-plant system, regarding the diversity, structure and root colonization capacity of arbuscular mycorrhizal (AM) fungi and the respective growth response of Vicia faba L, commonly used as green manure in olive-tree plantations. A compartmentalized pot system was used that allowed the establishment of an AM fungal community in one compartment (feeder) and the application of three OMW dose levels in an adjacent second compartment (receiver). At 0, 10, and 30 days after OMW treatment (DAT), V. faba pre-germinated seeds were seeded in the receiver compartment. At harvest, shoot and root dry weights, AM fungal root colonization, soil hyphal length and P availability were recorded in the receiver compartment. In addition, OMW effects on AM fungal diversity in plant roots were studied by DGGE. A transient effect of OMW application was observed; plant growth and AM fungal colonization were initially inhibited, whereas soil hyphal length was stimulated, but in most cases differences were absent when seeding was performed 30 DAT. Similarly, changes induced in the structure of the root AM fungal community were of transient nature. Cloning and sequencing of all the major DGGE bands showed that roots were colonized by Glomus spp. The transient effects of OMW on the structure and function of AM fungi could be attributed to OMW-derived phytoxicity to V. faba plants or to an indirect effect via alteration of soil nutritional status. The high OMW dose significantly increased soil P availability in the presence of AM fungi, suggesting efficient involvement of AM fungi in organic-P minerilization. Overall our results indicate that soil application of OMW would cause transient changes in the AM fungal colonization of V. faba plants, which, would not impair their long-term plant growth promoting ability.