Characterisation of zein-oleic acid films and applications in fruit coating

Plant protein-based edible films and the effect of phenolic additives

The use of protein-based films in food preservation has been investigated as an alternative to synthetic plastics in recent years. Being biodegradable, edible, natural, and upcycling from food waste/by-products are the benefits of protein-based edible films. Their use ensures food safety as an alternative to synthetic plastics, and their film-forming properties can be improved with the addition of bioactive compounds. This review summarizes the studies on the changes in certain quality parameters of plant protein-based films, including mechanical, physicochemical, or morphological properties with the use of different forms of phenolic additives (pure phenolics, phenolic extracts, essential oils) and their application in foods during storage. Phenolics affect protein film matrix formation by acting as plasticizers or cross-linking agents and confer additional health benefits by providing bioactive properties to protein films. On the other hand, the effects were more pronounced with the use of their oxidized forms or higher concentrations. Consequently, phenolic additives have great potential to improve protein films, but further studies are still required to investigate the effects and mechanisms of phenolic addition to the protein-based films.

Aloe-Based Edible Coating to Maintain Quality of Fresh-Cut Italian Pears (Pyrus communis L.) during Cold Storage

Pear fruits are known for their antioxidant and nutritional characteristics. However, they are very susceptible to rapid decay. Edible coating (EC) represents a good strategy to maintain postharvest quality. The effects of two EC in slowing down the senescence processes in fresh-cut ‘Coscia’ pears were investigated: EC1 (A. vera gel, hydroxypropyl-methylcellulose and pomegranate seeds oil (PSO), EC2 (A. vera gel and hydroxypropyl-methylcellulose). Weight loss, firmness and colour decrease more slowly in both EC-treated than in untreated (CTR) slices; soluble solid content increases faster in CTR, indicating a faster ripening process. The specific investigation of undesired microorganisms did not generate any colony in all analysed samples. Sensory analysis confirmed that the tasters preferred the EC2-treated samples, as they were the only ones that did not show undesirable flavours until the last day of storage.

Packham's Triumph Pears (Pyrus communis L.) Post-Harvest Treatment during Cold Storage Based on Chitosan and Rue Essential Oil

Pears (Pyrus communis L.) cv. Packham’s Triumph are very traditional for human consumption, but pear is a highly perishable climacteric fruit with a short shelf-life affected by several diseases with a microbial origin. In this study, a protective effect on the quality properties of pears was evidenced after the surface application of chitosan-Ruta graveolens essential oil coatings (CS + RGEO) in four different concentrations (0, 0.5, 1.0 and 1.5 %, v/v) during 21 days of storage under 18 °C. After 21 days of treatment, a weight loss reduction of 10% (from 40.2 ± 5.3 to 20.3 ± 3.9) compared to the uncoated pears was evident with CS + RGEO 0.5%. All the fruits’ physical-chemical properties evidenced a protective effect of the coatings. The maturity index increased for all the treatments. However, the pears with CS + RGEO 1.5% were lower (70.21) than the uncoated fruits (98.96). The loss of firmness for the uncoated samples was higher compared to the coated samples. The pears’ most excellent mechanical resistance was obtained with CS + RGEO 0.5% after 21 days of storage, both for compression resistance (7.42 kPa) and force (22.7 N). Microbiological studies demonstrated the protective power of the coatings. Aerobic mesophilic bacteria and molds were significantly reduced (in 3 Log CFU/g compared to control) using 15 µL/mL of RGEO, without affecting consumer perception. The results presented in this study showed that CS + RGEO coatings are promising in the post-harvest treatment of pears.

Simple, Low-Cost and Long-Lasting Film for Virus Inactivation Using Avian Coronavirus Model as Challenge

The COVID-19 infection, caused by SARS-CoV-2, is inequitably distributed and more lethal among populations with lower socioeconomic status. Direct contact with contaminated surfaces has been among the virus sources, as it remains infective up to days. Several disinfectants have been shown to inactivate SARS-CoV-2, but they rapidly evaporate, are flammable or toxic and may be scarce or inexistent for vulnerable populations. Therefore, we are proposing simple, easy to prepare, low-cost and efficient antiviral films, made with a widely available dishwashing detergent, which can be spread on hands and inanimate surfaces and is expected to maintain virucidal activity for longer periods than the current sanitizers. Avian coronavirus (ACoV) was used as model of the challenge to test the antivirus efficacy of the proposed films. Polystyrene petri dishes were covered with a thin layer of detergent formula. After drying, the films were exposed to different virus doses for 10 min and virus infectivity was determined using embryonated chicken eggs, and RNA virus quantification in allantoic fluids by RT-qPCR. The films inactivated the ACoV (ranging from 103.7 to 106.7 EID50), which is chemically and morphologically similar to SARS-CoV-2, and may constitute an excellent alternative to minimize the spread of COVID-19.

Changes in microstructure and rheological properties of konjac glucomannan/zein blend film-forming solution during drying

During film formation at 60 °C, the microstructure and rheological properties of konjac glucomannan (KGM) film-forming solution and KGM/zein blend film-forming solution were investigated. The drying process of film-forming solutions was divided into two stages according to the drying curves. Scanning electron microscopy showed that KGM chains in the blend solution aggregated into thicker chains and formed a molecular network with larger pores. Zein particles grew larger but were homogeneously distributed during drying as observed by confocal laser scanning microscopy. The addition of zein improved the thermal stability of the film-forming solution. As the drying proceeded (up to 8 h), KGM solution exhibited a typical concentrated solution behavior due to molecular entanglement; whereas the blend solution gradually formed a weak gel after 2 h. Complex viscosity data for the film-forming solutions were well-fitted by the power-law model. The information obtained from the study is important for understanding the film-forming mechanism.

Development of Bilayer Biodegradable Composites Containing Cellulose Nanocrystals with Antioxidant Properties

The interest in the development of novel biodegradable composites has increased over last years, and multilayer composites allow the design of materials with functionality and improved properties. In this work, bilayer structures based on a coated zein layer containing quercetin and cellulose nanocrystals (CNC) over an extruded poly(lactic acid) (PLA) layer were developed and characterized. Bilayer composites were successfully obtained and presented a total thickness of approx. 90 µm. The coated zein layer and quercetin gave a yellowish tone to the composites. The incorporation of the zein layer containing CNC decreased the volatile release rate during thermal degradation. Regarding to mechanical properties, bilayer composites presented lower brittleness and greater ductility evidenced by a lower Young’s modulus and higher elongation values. Water permeability values of bilayer composites greatly increased with humidity and the zein coated layer containing quercetin increased this effect. Experimental data of quercetin release kinetics from bilayer structures indicated a higher release for an alcoholic food system, and the incorporation of cellulose nanocrystals did not influence the quercetin diffusion process.

Improvement of post-harvest quality of pear fruit with optimized composite edible coating formulations

Application of edible coatings is a suitable method to maintain the quality and reduce post-harvest losses in fresh vegetables and fruits. Pear fruits being climacteric have a short shelf life, and coating is considered as one of the most popular techniques to prolong its shelf life.The present study evaluates the effect of optimized edible coatings containing soy protein isolate (SPI) in combination with additives like hydroxypropyl methylcellulose (HPMC) and olive oil on 'Babughosha' Pears (Pyrus communis L.) stored at ambient temperature (28 ± 5 °C and 60 ± 10% RH). Four different coatings optimized by response surface methodology study were used in the present experiment. The results of the present study shows that the optimized edible coatings help retain the firmness of fruits and lowered the moisture loss. The tested combination of coating could also withhold the levels of ascorbic acid, chlorophyll and sugar contents in the treated fruits. Activities of enzymes associated with fruit softening (β-galactosidase, polygalacturonase, pectin methyl esterase) showed delayed peaks. Amongst all treatments, T1 (SPI 5.0%, HPMC 0.40%, Olive oil 1%, Potassium sorbate 0.22%) and T2 (SPI 5.0%, HPMC 0.40%, Olive oil 0.98% Potassium sorbate 0.20%) were found to have pronounced effect on retention of nutritional quality in pears. Observations of shelf-life extension established that T2 (SPI 5.0%, HPMC 0.40%, Olive oil 0.98% Potassium sorbate 0.20%) was successful in extending shelf-life of pear fruits up to 15 days, as compared to 8 days for untreated pear fruits.

Coating formation during drying of β-lactoglobulin: gradual and sudden changes

The drying dynamics of protein coatings is of importance for many applications. The main focus of research so far was to investigate macroscopic properties of protein coatings, leaving drying dynamics virtually unexplored. A unique combination of techniques is used to monitor drying of a coating containing the protein β-lactoglobulin. The techniques used cover both macroscopic and microscopic aspects of the drying process. For all water fractions amenable to diffusing wave spectroscopy analysis (xw > 0.2 w/w), the tracer particles diffuse in the coating as in a Newtonian viscous medium. Magnetic resonance imaging shows both protein and water are distributed homogeneously over the coating during drying, up to water fractions above 0.2 w/w. When drying continues to lower water fractions, sudden transitions in drying behavior are observed by both dynamic vapor sorption and IR spectroscopy, which we suggest are due to changes in molecular interactions caused by dehydration of the protein backbone.

Revisão: coberturas comestíveis protetoras em frutas: fundamentos e aplicações

O emprego de coberturas comestíveis na conservação de frutas na condição pós-colheita, sejam intactas ou minimamente processadas, tem sido preconizado como uma tecnologia emergente e de grande potencial, principalmente para aplicações sobre frutas de origem tropical. Diversos biopolímeros têm sido avaliados na formulação dessas coberturas e, neste texto, apresentamos, de forma geral, os principais conceitos físico-químicos envolvidos no processo, com o objetivo de subsidiar uma escolha que possa gerar uma maior eficiência da cobertura formada. Alguns exemplos de aplicação, com base na literatura, são apresentados a título ilustrativo. É importante notar que não há uma cobertura "universal", ou seja, uma formulação que possa ser aplicada a qualquer fruta indiscriminadamente. A escolha do material apropriado dependerá das características da fruta, do biopolímero e dos objetivos almejados para o revestimento.

Propriedades mecânicas e molhabilidade de filmes de zeínas extraídas de glúten de milho

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.

Synthesis, characterization and antibacterial activity of biodegradable films prepared from Schiff bases of zein

Pure zein is known to be very hydrophobic, but is still inappropriate for coating and film applications because of their brittle nature. In an attempt to improve the flexibility and the antimicrobial activity of these coatings and films, Chemical modification of zein through forming Schiff bases with different phenolic aldhydes was tried. Influence of this modifications on mechanical, topographical, wetting properties and antimicrobial activity of zein films were evaluated. The chemical structure of the Schiff bases films were characterized by ATR-FTIR spectroscopy. The results indicate an improvement in mechanical properties with chemically modification of zein to form Schiff bases leading to a reduction in the elastic modulus. An increase in the elongation at break has been observed, but with slight influence on tensile strength. Plasticized zein films have similar initial contact angle (∼40°). An increase in reaction temperature and time increases film's affinity towards water. As shown by contact angle measurements, a noticeable relation was found between film composition and the hydrophilicity. Surface topography also varied by forming Schiff bases, becoming rougher than zein-based films. The antibacterial activities of zein and Schiff bases of zein-based films were investigated against gram-positive bacteria (Listeria innocua, Listeria monocytogenes, Bacillus cereus and Clostridium sporogenes) and gram-negative bacteria (Escherichia coli, Yersinia enterocolitica and Salmonella enterica). It was found that the antibacterial activity of the Schiff bases-based films was more effective than that of zein-based films.