Protein-based Coatings Research Articles

Biocompatibility Studies of Functionalized Regioregular Poly(3‐hexylthiophene) Layers for Sensing Applications

There is a significant medical and biological need for cheap disposable analytical sensing devices, which can be used in clinical settings or medical research. Organic electronics based on polymeric materials, being suitable for large-area, low-cost, flexible, and maybe even disposable electronics, could satisfy this need in a very elegant way. Unfortunately, the ensurance of biocompatibility and biofunctionalization of conducting and semiconducting polymers is still often lacking. In the present study, we concentrate on one of the most promising polymeric materials, regioregular poly(3-hexylthiophene) (P3HT), being both a reasonably conducting and optically active polymer. To overcome biocompatibility problems, protein-based coatings and oxygen-plasma treatments are performed to enable growth of adherent living cells on those modified surfaces. For our studies, the polymer material is spun or casted onto glass substrates under an inert nitrogen atmosphere. The toxic solvents are removed by thermal treatment with subsequent application of the coating or functionalizing materials. Cell-growth studies and adhesion experiments on the modified P3HT thin-film layers are carried out with mouse fibroblasts. This work demonstrates the biocompatibility and biofunctionalization of an active semiconducting organic polymer, hence opening new possibilities in the realization of biomedical test systems based on organic biosensors in life sciences.

Protein hydrophobic dressing on seeds aiming at the delay of undesirable germination

Polymer seed-coatings have been largely tested as an alternative method for preventing diseases and have the potential to be used to control undesirable germination and thereby increasing seed storage. Amongst these, the protein-based coatings can be applied with advantage of forming stable biodegradable and hydrophobic films. Due to their chemical structure, protein dressings act as efficient barriers for water uptake, even when seeds are unavoidable exposed to a moist environment. In this work, the effect of hydrophobic dressings was tested on the germination rate of sugar beet (Beta vulgaris L.) and broccolis (Brassica oleraceae var italic L.) seeds under laboratorial condition. Zein, natural maize (Zea mays L.) proteins extracted from gluten meal, was used as precursor polymers to form the coatings. Seeds were dressed by direct submersion into a zein/ethanol formulation of zein concentration of 3.0 g L-1, followed by natural air drying. The resultant coating has elevated the hydrophobic feature due to the high content amino acids present in the structure of the zein. For both types of seeds an overall delay in sprouting and germination was observed, with a more accentuated reduction on sugar beet germination percentage after eleven days of measurements. The effect on germination rates is understood as the efficiency of the zein coating to form a physical barrier preventing water permeation into the seeds.

Protein-based coatings on peanut to minimise oil migration

Abstract Soy protein isolate (SPI) or calcium caseinate (CC)-based coatings were applied on peanuts as a barrier of oil migration, and their efficiency was evaluated. These coatings induced a decrease of oil migration as compared to the uncoated peanuts. Subsequently, three polysaccharides were individually added to the coating solution to prevent oil migration further. The incorporation of carboxymethylcellulose (CMC) with SPI and CC coating solutions significantly (p ⩽ 0.05) decreased the migration of oil as compared to the coatings without CMC. The addition of pectin seemed unfavourable because it enhanced the migration of oil. Starch in SPI-based coating solution helped to decrease the oil migration, but it did not affect the migration level in samples treated with CC solution. The results from size-exclusion chromatography showed strong cross-links by glutaraldehyde and transglutaminase treatments in SPI and CC-based coating solutions. A strong cross-linking in protein-based coating correlated closely with a reduction in oil migration. For both proteins, the cross-linking by transglutaminase was most efficient for improving the effectiveness of coating. This study demonstrated that our protein-based coatings can be effectively implemented to food industry for better quality of peanut products.

Effect of whey protein- and hydroxypropyl methylcellulose-based edible composite coatings on color change of fresh-cut apples

Edible composite coatings were prepared from whey protein isolate (WPI), whey protein concentrate (WPC) or hydroxypropyl methylcellulose (HPMC) as the hydrophilic phase, and beeswax (BW) or carnauba wax (CarW) as the lipid phase. Apple pieces were coated with the emulsion coatings and weight loss and color (CIELAB color parameters, L*, a*, b*, and browning index (BI)) were measured during storage. Results show that apple pieces coated with whey protein-based coatings had higher L*-, and lower b*-, a*-, and BI-values than HPMC-based coated and uncoated apple pieces, which indicate that whey proteins exert an antibrowning effect. Coatings containing BW were more effective in decreasing enzymatic browning than coatings containing CarW. The sensory panel differentiated samples coated with whey protein-based coatings from samples coated with HPMC-based coatings. However, differences due to lipid type were less evident at the end of the storage time. Coating application did not reduce weight loss in fresh-cut apples, probably due to the high relative humidity of the product.

Evaluation of Mechanical and Barrier Properties of Protein Coatings on Shell Eggs

Development of a coating material for shell eggs is important because of economic loss from shell damage and decline in interior egg quality. Studies were done to evaluate the interior quality (moisture loss, Haugh unit, and pH) and shell properties (strength, thickness, morphology, and color) of uncoated eggs and eggs coated with mineral oil or with solutions of egg albumen, soy protein isolate, wheat gluten, or corn zein. Coated shell eggs were evaluated during 1, 3, 5, 7, 10, 14, 21, and 28 d of storage at room temperature. Eggshells coated with corn zein solution exhibited the least moisture loss and the strongest shell strength. Light microscopy depicted a more compact structure of eggshells coated with corn zein solution. Shell eggs coated with corn zein exhibited the lowest moisture loss and maintained a higher Haugh unit than eggs coated with other treatments. Results also indicated that the protein-based coatings, corn zein and wheat gluten, added strength to the shell, which, in turn, served as a protective barrier.