Desenvolvimento e caracterização de filmes biopoliméricos compostos majoritariamente por galactomananas recuperadas da borra de café

Abstract

Coffee is one of the most popular beverages in the world with strong cultural and social impacts. In 2017/2018, world coffee production was approximately164,99million bags of 60 kg, and consequently, more than 2 billion tons of by-products were concomitantly produced, such as husk, mucilage, parchment, coffee silverskin and spent coffee grounds (SCG). The main waste produced in the processing of coffee is SCG, which is rich in organic compounds such as fatty acids, caffeine, amino acids, polyphenols and especially polysaccharides, which enable potential applications. Galactomannans are the most abundant polysaccharides in SCG, presenting a low degree of branching and a high degree of polymerization, which enables excellent emulsifying and stabilizing properties. In view of the aforementioned, SCG is a potential alternative source for the production of biofilms, which have received attention in recent years, especially due to the large environmental impacts caused by synthetic packaging. Thus, the objective of this work was to develop a biopolymeric film comprised mostly of galactomannans recovered from spent coffee grounds by alkaline and enzymatic treatment. Initially, the effects of three distinct pretreatments to remove lignin from SCG were studied, one with alkaline peroxide solution, the other with alkaline solution and the last with alkaline potassium permanganate solution assisted by ultrasound. All pretreatments resulted in considerable removal of lignin, with the remaining lignin content in the range of 6-11%. The delignified materials were submitted to enzymatic treatment using commercial cellulase enzymes produced by Trichoderma reesei ATCC 26921. In order to optimize the hydrolytic process, different concentrations of SCG, cellulase and incubation times were evaluated, as well as the combination of extraction methods assisted by techniques such as ultrasound, autoclave, and microwave. Characterization of the delignified material was performed before and after the enzymatic treatment. Furthermore, the galactomannan-rich delignified material was used to produce biofilms, as well as the material after enzymatic treatment. The biofilms produced with the delignified coffee grounds and the cellulose-depleted galactomannan-rich fractions were similar in physical appearance and texture. However, they were different in relation to water vapor permeability, glass transition temperature and mechanical properties. Thus, the partial removal of the cellulose allowed for the formation of a more rigid film than that with the cellulose due to the strong interactions between the galactomannan chains. The different characteristics of this film allow for potential applications such as water filtration membranes, bioactive membranes and seedling packaging.