Ecomaterials Based on Food Proteins and Polysaccharides

Prevention of Chilling Injury in Pomegranates Revisited: Pre- and Post-Harvest Factors, Mode of Actions, and Technologies Involved

The storage life of pomegranate fruit (Punica granatum L.) is limited by decay, chilling injury, weight loss, and husk scald. In particular, chilling injury (CI) limits pomegranate long-term storage at chilling temperatures. CI manifests as skin browning that expands randomly with surface spots, albedo brown discoloration, and changes in aril colors from red to brown discoloration during handling or storage (6-8 weeks) at <5-7 °C. Since CI symptoms affect external and internal appearance, it significantly reduces pomegranate fruit marketability. Several postharvest treatments have been proposed to prevent CI, including atmospheric modifications (MA), heat treatments (HT), coatings, use of polyamines (PAs), salicylic acid (SA), jasmonates (JA), melatonin and glycine betaine (GB), among others. There is no complete understanding of the etiology and biochemistry of CI, however, a hypothetical model proposed herein indicates that oxidative stress plays a key role, which alters cell membrane functionality and integrity and alters protein/enzyme biosynthesis associated with chilling injury symptoms. This review discusses the hypothesized mechanism of CI based on recent research, its association to postharvest treatments, and their possible targets. It also indicates that the proposed mode of action model can be used to combine treatments in a hurdle synergistic or additive approach or as the basis for novel technological developments.

Synthesis and Characterization of Chanar Gum Films

New polysaccharides are being intensely studied as sources of edible materials, with potential application in food packaging systems, eco-materials and the pharmaceutical industry. This investigation aimed to develop biopolymer films based on the polysaccharides obtained from chañar (CH) fruit (Geoffrea decorticans). The resulting polysaccharides, from hydrothermal extraction (CHT) and acid extraction (CHA) were hydrodynamically characterized, with density, viscosity, and diffusion coefficient measurements to obtain their properties in an aqueous solution (intrinsic viscosity, shape factor, partial specific volume, hydration value, molecular weight, and hydrodynamic radius). The polysaccharides films (CHTF and CHAF) were characterized with SEM/EDX, DSC, TGA-DTG, FTIR, DRX, mechanical tests, water vapor permeation, colorimetry, antioxidant capacity, and biodegradability, to determine potential applications based on these properties. The results indicated that the extraction method affects the hydrodynamic properties of the obtained polysaccharide. They differ in molecular weight, and RH of CHT was greater than CHA. Both gums were quasi-spherical, and the νa/b value of CHT was more than CHA. The films properties did not present significant differences in most cases. SEM micrographs illustrate that CHAF presents a much rougher surface. The results of the mechanical analysis show that CHTF has better mechanical properties, it has higher elongation at break and tensile strength, with a Young Modulus of 2.8 MPa. Thermal analysis indicates good thermal stability of the films until about 150 °C. The degradation study shows that CH films are biodegradable in a 35 day range. The study of this properties is critical to demonstrate the functionality of biopolymers and their application. The obtained results represent an advantage and evidence that chañar is an interesting source for extract polysaccharides with film forming properties.

Approaches in Animal Proteins and Natural Polysaccharides Application for Food Packaging: Edible Film Production and Quality Estimation

Natural biopolymers are an interesting resource for edible films production, as they are environmentally friendly packaging materials. The possibilities of the application of main animal proteins and natural polysaccharides are considered in the review, including the sources, structure, and limitations of usage. The main ways for overcoming the limitations caused by the physico-chemical properties of biopolymers are also discussed, including composites approaches, plasticizers, and the addition of crosslinking agents. Approaches for the production of biopolymer-based films and coatings are classified according to wet and dried processes and considered depending on biopolymer types. The methods for mechanical, physico-chemical, hydration, and uniformity estimation of edible films are reviewed.

Glutamic Acid as Repeating Building Block for Bio-Based Films

Commercial inexpensive preparations of poly-γ-glutamic acid were used to obtain films made with a polypeptide constituted by a single repeating unit. The homopolymer was characterized by ¹H-NMR spectroscopy and thermogravimetry, as well as by zeta potential and Z-average measurements. Manipulatable materials were obtained by casting film-forming solutions prepared at pH values between 3.0 and 4.0 and containing extensively dialyzed samples of the commercial product. The analysis of the mechanical properties highlighted a marked extensibility and plasticity of the films obtained without plasticizer, even though the addition of low amounts of glycerol (1–4%) was able to further increase these features. The characterization of poly-γ-glutamic acid molecular species, performed by membrane ultrafiltration and size-exclusion chromatography, coupled with triple-detection analysis of the obtained fractions, suggested that biopolymer chain length is responsible not only for its capacity to form film, but also for conferring to the films different features depending on the homopolymer molecular weight.

Biodegradable films based on fruit puree: a brief review

The production of fruit-film packaging has attracted increasing attention in scientific research due to the packaging's environmentally friendly, nontoxic, and edible characteristics. The development of alternative packaging contributes to both minimizing the environmental impacts caused by the large consumption of non-biodegradable plastics and favoring the reduction of postharvest loss/waste of fruit. In addition, these fruit films have the potential to be functional packages due the presence of antioxidant and antimicrobial compounds that can migrate to the food matrix, acting as natural additives. The use of fruit puree to develop biodegradable films can be simpler and more practical than the developed of films from fruit flour or extracts, reducing the time, energy, and resources necessary to prepare the film-forming solution. A better understanding of the mechanical properties, bioactive compounds, and potential applications is interesting in terms of prospecting new specific ways to produce and use these films. In this study, we briefly review the general aspects of fruit puree films, highlighting their characterization for use as food packaging.

On the thermal behavior of protein isolated from different legumes investigated by DSC and TGA

BACKGROUND

Pea, lentil, faba bean, chickpea and bean proteins are potentially renewable raw materials for bioplastic production that can be obtained from agricultural waste. Plastics are usually processed under heating, and thus thermal stability is a mandatory requirement for the application. In this study, the thermal behavior of several legume protein isolates at different purity degrees was investigated.

RESULTS

The thermal stability of proteins extracted from legumes was maximum for chickpeas and minimum for beans and decreased with decreasing protein purity in the range 30-88%. A similar dependence on purity was observed for the glass transition temperature. On the contrary, the denaturation temperature was found not to depend on sample purity and origin and was lower than the degradation temperature only in the case of protein samples with purity higher than 60%.

CONCLUSION

Proteins from legumes are suitable to produce thermoplastic biopolymeric materials if isolated at purity higher than 60%. In fact, under this circumstance, they can be denaturized without degrading and thus are suitable for extrusion processing. © 2018 Society of Chemical Industry.

The effect of shear history on urea containing gliadin solutions

Currently, a substantial amount of research is devoted to gluten bioplastics. A promising processing route towards composites and films uses solutions of reduced gliadin. The addition of sufficient urea allows the preparation of highly concentrated gliadin solutions without an anomalous rheology. This is investigated in this paper by thixotropy experiments on gliadin solutions. These solutions show a balance between structural build-up due to molecular interactions and structural break-down induced by shear flow. Because of this, such protein solutions should be prepared with great caution. To assure a rheology suitable for processing, a shear history and a sufficient amount of added urea to disrupt molecular interactions are crucial.

Characterization of agar/soy protein biocomposite films: Effect of agar on the extruded pellets and compression moulded films

Agar/soy protein biocomposite films were successfully processed by extrusion and compression moulding, obtaining transparent and homogeneous films. The conformational changes occurred during the extrusion process and the effect of agar on the final properties were analyzed. As shown by differential scanning calorimetry (DSC) and specific mechanical energy (SME) values, during the extrusion process protein denatured and unfolded protein chains could interact with agar. These interactions were analyzed by Fourier transform infrared spectroscopy (FTIR) and the secondary structure was determined from the amide I band. Those interactions were supported by the decrease of film solubility. Furthermore, the good compatibility between agar and soy protein was confirmed by the images from scanning electron microscopy (SEM).