Odilio Benedito Garrido Assis

Zeínas são proteínas de reserva do milho (prolaminas), que podem ser extraídas através de solubilização em meio alcoólico. Essas proteínas são altamente hidrofóbicas, com elevado grau de polimerização. Neste estudo, zeínas do tipo a (massa molecular entre 10 e 22 kDa) foram extraídas do glúten do milho e caracterizadas com respeito às suas principais bandas de absorção espectroscópica na região do infravermelho. Blendas de zeínas com ácido oléico (AO) como plastificante foram avaliadas em diversas proporções e filmes processados por casting sobre superfície apolar. Filmes de zeínas sem plastificante mostraram-se inviáveis para manipulação e medidas, mas a adição de 1 e 2% em massa de AO proporcionou um significativo aumento do módulo de elasticidade, segundo análise realizada por DMA. A presença de plastificante introduz também irregularidades superficiais e leva a uma perda das características hidrofóbicas dessas proteínas.

The combination of carboxymethylcellulose (CMC), cashew tree gum and, glycerol as plasticizer was evaluated in the formation and properties of films processed by casting. CMC acts as both a gelling and film-formation agent, yielding samples with reasonable mechanical properties. Increasing the concentration of CMC increased tensile strength, reduced elongation at break, and decreased wettability of the blended films. Microscopy surface observation shows that plasticizer addition reduces cracks in the films. The combination of cashew gum with CMC increases the hydrophobicity characteristic of the films. The plasticizer, even in small amounts, reduces the hydrophobicity thus increasing surface wettability. This study shows that cashew gum/CMC/glycerol–composed films can be considered as potential materials for technological applications.

Summary: Pure zein films are known to be very hydrophobic, but are inappropriate for edible coating applications because of their brittle nature. In an attempt to improve the flexibility of these coatings, the influence of low concentrations of oleic acid (OA) as a plasticiser on mechanical, topographical and wetting properties of zein thin films was evaluated. Films were first obtained by casting from aqueous ethanol solutions with 4.0% in mass of zein and additions of 0%; 0.25%; 0.50%; and 1.0% (w/w) of OA. The results indicate an improvement in mechanical properties with increasing plasticiser leading to a reduction in the elastic modulus. An increase in the elongation at break has been observed, but with minor influence on tensile strength. All plasticised zein films have similar initial contact angle (approximately 69°) with a time‐dependent receding drop behaviour. An increase in plasticiser concentration increases film’s affinity towards water. As measured by atomic force microscopy, a consistent linear relation (R²=0.991) was estimated between film composition and surface adhesion and consequently on the hydrophilicity. Surface topography also varied with plasticiser addition, becoming smoother as the OA concentration increases. When tested as an edible coating on pears (Pyrus communis L.), a formulation with 0.25% wt of plasticiser achieved the best results in preserving the pear mass as measured during the evaluated storage time (12 days) at room temperature. A 0.5% concentration of plasticiser had no influence and higher amounts resulted in a reduction in fruit protection.

The effectiveness of corn-zein edible coatings in blocking oil oxidation on macadamia nuts was studied by using high-resolution Hydrogen Nuclear Magnetic Resonance (¹H NMR) spectroscopy. Formulations with a zein concentration of 4.0% by weight and oleic acid (OA) as a plasticizer in different proportions were evaluated. Accelerated oxidation was conducted by using an O₂-reactor in a 60C water bath. The oil extracted from the nuts at the beginning of the study and after 10 and 30 days into the experiment were analyzed. Results from the ¹H NMR analysis exhibited that the major products formed by lipid oxidation were conjugated dienes. The coatings were imperceptible to the naked eye, but textural changes were visible under scanning electron microscopy. The best coating formulation was a combination of zein with 0.25% OA, which completely inhibited oxidation. Plasticizer addition of 0.50 and 1.00% wt, however, had a negative effect on the coating's property as a barrier against oxygen, resulting in higher rates of oxidation than in the uncoated samples. PRACTICAL APPLICATIONS Hydrophobic zein-based edible coatings, as used in this study, are capable of acting as barriers against oxygen and water vapor by reducing, or even eliminating, undesirable oxidation in unshelled macadamia nuts during long-term storage. The results of our study have demonstrated the ease of forming stable coatings to reduce oxidative fatty rancidity. The films are invisible to the naked eye and do not produce visible changes in the texture and the color of the coated nuts. This study indicates that zein/oleic acid edible coatings are feasible to use for large-scale applications, providing an alternative way to improve the oxidative stability and eventually to lengthen the shelf life and quality of macadamia nuts.

Image analysis techniques have often been chosen as fundamental tools for evaluating the surface and/or structure of organic and inorganic materials over a broad range of scales. In the study reported, a simple image capture system comprising a commercial desktop scanner combined with free image analysis software was used to evaluate the efficiency of antifungal activity of commercial medium‐molecular‐weight chitosan as an edible coating on sliced apples. Fungal growth rate (predominantly Penicillium sp. and Alternaria sp.) was assessed via images acquired twice daily and binary‐transformed for quantitative analysis. The inhibitory effect of chitosan coating on the mycelial fungi growth on cut apple surfaces was confirmed. Chitosan deposited on glass slides was used to simulate film formation and its structure was characterized using atomic force microscopy, revealing a thin porous formation. Copyright © 2011 Society of Chemical Industry

Alteration in hydrophilicity feature of chitosan films by hexamethyldisilazane (HMDS) cold-plasma treatment is evaluated. All treated films were colorless and transparent with no apparent textural changes. The effect on surfaces was characterized through contact angle measurements, degree of swelling and water vapor permeation. A significant reduction in all of the hydrophilicity parameters was observed. It is assumed that the HMDS treatment forms nonpolar silicone type structures. The goal is to investigate the formation of a stable hydrophobic barrier in order to increase the chitosan films usefulness in packaging applications

Neste trabalho resultados e considerações sobre o uso de vidro reciclado na forma de material granulado, como potencial meio filtrante para remoção de agrotóxicos diluídos em água são apresentados. Para esta avaliação garrafas e vasilhames de vidro transparente foram fragmentados e moídos até partículas com tamanhos inferiores a 1 mm e ensaios de filtração gravitacional realizados em colunas, em escala laboratorial. O herbicida atrazina foi escolhido como contaminante em virtude de ser um composto altamente tóxico e amplamente empregado no Brasil. Análises por cromatografia gasosa indicam a retenção de agrotóxicos pelo meio poroso, em todo o intervalo de concentrações avaliadas (0,5; 1,0; 3,0; 10 e 15 mg L-1). O vidro apresentou-se como material de fácil manuseio e potencialmente atraente para uso como meio coadjuvante em filtragem lenta.