Desenvolvimento de biopolímeros ativos de isolado proteico de soro de leite e micropartícula de lignina para aplicação em alimentos

Abstract

In this work, an active biopolymer of whey protein isolate (WPI) and lignin microparticle (LMP) was developed. WPI was used as a polymeric base with glycerol as plasticizer and LMP as reinforcement and antioxidant material. In the first stage of the study, LMP was produced and characterized by the analysis of X-ray diffraction (XRD), zeta potential, infrared (FTIR), particle size, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), content phenolic compounds and antioxidant potential. In the second stage, LMP was added in different concentrations to WPI films produced by casting and the biopolymers were characterized in terms of structural (XRD and FTIR), morphological (SEM), physical (TGA and differential scanning calorimetry - DSC, mechanical properties, water vapor barrier and color) and antioxidant activity. In the last stage, antioxidant analyzes of the active biopolymers and the application of the films in ground meat (Biceps femoris) were carried out in order to evaluate the ability to prevent lipid oxidation of meat by active films, through the analysis of identification of volatile compounds by gas chromatography (GC-MS), thiobarbituric acid reactive species index (TBARS) and color (L*, a*, b*, C*, h), during storage at 4ºC ± 1°C for 4 days. The results of first stage showed that there was no change in the chemical nature of lignin after its size was reduced in LMP. In addition, the decrease in particle size reduced the zeta potential of the lignin suspension, increasing dispersion and thermal stability, there was exposure of a greater number of phenolic compounds with increased concentration of total phenolic compounds and antioxidant activity, confirming the potential for use of LMP in active biopolymers. The second stage demonstrated that the addition of LMP also preserved the chemical bonds present in the films, however there was a reduction in the crystallinity index of films, characteristic of the LMP. Intermediate concentrations of LMP (at 0.25 and 0.50% w/w) promoted good dispersion of LMP over the surface and interior of the films. Such dispersion allowed better thermal resistance (increase in Tg and temperature of onset degradation), increase in mechanical properties and water vapor barrier. The addition of LMP also allowed the formation of darker, reddish and transparent films and kept the antioxidant activity observed for LMP. Third stage shows that there is a trend towards a increase in antioxidant activity of films with an increase concentration of LMP. There was a decrease in TBARS index with storage time. In addition, the identification of 30 phenolic compounds in meat samples, 7 of which were present at all times and sampling: pentadecane, octadecane, hexanal, heptanal, octanal, nonanal of decanal, with a decrease in the areas of the relative peaks - hexanal, heptanal, octanal and decanal of the samples stored in the active films. The color of the meat showed an expected behavior ranging from bright red to brown during storage, with no difference between treatments. It is suggested that the addition of 0.50% (w/w) of LMP is the ideal concentration for its performance as reinforcement and antioxidant material in WPI films produced by casting.