Interactions of Opuntia ficus-indica with Dactylopius coccus and D. opuntiae (Hemiptera: Dactylopiidae) through the Study of Their Volatile Compounds.

Opuntia ficus-indica has always interacted with many phytophagous insects; two of them are Dactylopius coccus and D. opuntiae. Fine cochineal (D. coccus) is produced to extract carminic acid, and D. opuntiae, or wild cochineal, is an invasive pest of O. ficus-indica in more than 20 countries around the world. Despite the economic and environmental relevance of this cactus, D. opuntiae, and D. coccus, there are few studies that have explored volatile organic compounds (VOCs) derived from the plant-insect interaction. The aim of this work was to determine the VOCs produced by D. coccus and D. opuntiae and to identify different VOCs in cladodes infested by each Dactylopius species. The VOCs (essential oils) were obtained by hydrodistillation and identified by GC-MS. A total of 66 VOCs from both Dactylopius species were identified, and 125 from the Esmeralda and Rojo Pelón cultivars infested by D. coccus and D. opuntiae, respectively, were determined. Differential VOC production due to infestation by each Dactylopius species was also found. Some changes in methyl salicylate, terpenes such as linalool, or the alcohol p-vinylguaiacol were related to Dactylopius feeding on the cladodes of their respective cultivars. Changes in these VOCs and their probable role in plant defense mechanisms should receive more attention because this knowledge could improve D. coccus rearing or its inclusion in breeding programs for D. opuntiae control in regions where it is a key pest of O. ficus-indica.

Modification of solubility and heat-induced gelation of amaranth 11S globulin by protein engineering.

The primary structure of amaranth 11S globulin (Ah11S) was engineered with the aim to improve its functional properties. Four continuous methionines were inserted in variable region V, obtaining the Ah11Sr+4M construction. Changes on protein structure and surface characteristics were analyzed in silico. Solubility and heat-induced gelation of recombinant amaranth 11S proglobulin (Ah11Sr and Ah11Sr+4M) were compared with the native protein (Ah11Sn) purified from amaranth seed flour. The Ah11Sr+4 M showed the highest surface hydrophobicity, but as consequence the solubility was reduced. At low ionic strength (µ = 0.2) and acidic pH (<4.1), the recombinant proteins Ah11Sr and Ah11Sr+4 M had the highest and lowest solubility values, respectively. All globulins samples formed gels at 90 °C and low ionic strength, but Ah11Sn produced the weakest and Ah11Sr the strongest gels. Differential scanning calorimetry analysis under gel forming conditions revealed only exothermic transitions for all amaranth 11S globulins analyzed. In conclusion, the 3D structure analysis has revealed interesting molecular features that could explain the thermal resistance and gel forming ability of amaranth 11S globulins. The incorporation of four continuous methionines in amaranth increased the hydrophobicity, and self-supporting gels formed had intermediate hardness between Ah11Sn and Ah11Sr. These functional properties could be used in the food industry for the development of new products based on amaranth proteins.