RESUMEN
This paper proposes to apply a postharvest environmental stress to red apples, Malus domestica, variety Red Delicious in order to increase the polyphenols compounds (PP) content in their peels. The possibility of enhancing extractable PP provides a useful alternative for the use of discarded crops in the food industry. A great increase in PP was observed in response to light damage produced by the environmental stress applied in this work. Flavonols > anthocyanins > flavanols > dihydrochalcones > phenolic acids is the order in PP content. The interaction of the extracted PP from unstressed and stressed apple peels with beta-lactoglobulin (ß-LG) was characterized. A PP/ß-LG complex which was formed with one single binding site in the protein was determined. The interaction was spontaneous and enthalpy driven. PP extracted from unstressed samples had greater affinity for the protein than PP extracted from stressed samples, possibly due to the polar characteristic of anthocyanins. The results of this last study could provide a better understanding of the interaction between PP and ß-LG to incorporate them into functional foods.
RESUMEN
Solid sodium alginate was dissolved into chicken stock in order to give a final alginate concentration of 0.9 percent (w/v). Calcium ions present in chicken stock were enough to induce ionic gelation. After drying, Fourier transform infrared spectroscopy, thickness and mechanical properties of films obtained were determined. Calcium alginate-chicken stock films were heated at 130 °C for different times between 0 and 15 min. Mechanical and optical studies, differential scanning calorimetry, visual aspect and scanning electron microscopy were carried out to describe physicochemical properties of heat treated films. Heating developed a maroon ochre color and increased the brittleness (crispness) of the films related to the intensity of the treatment. Differential scanning thermometry and study on appearance of the films suggested that Maillard reactions may be responsible for the observed changes. Maillard reactions mainly occurred between reducing sugar monomers and free amino groups of gelatin peptides present in the chicken stock, and between alginate and gelatin peptides to a lesser extent. In addition, the plasticizing effect of fat added with chicken stock was also studied. These studies suggest a potential use of heat treated chicken stock films as a substitute of roasted chicken skin.