Effect of Pullulan Coating on Postharvest Quality and Shelf-Life of Highbush Blueberry (Vaccinium corymbosum L.)

Formulations based on pullulan and a derivative as coating material for the food sector

Carboxymethylated derivatives of pullulan (PU) were synthesized and evaluated as coating for the postharvest preservation of blueberries. Carboxymethylpullulan was obtained by etherification reaction with the substitution degrees of 0.52, 0.34, and 0.26 for CMP1, CMP2, and CMP3 respectively. Infrared spectroscopy and nuclear magnetic resonance results showed characteristic signals of the carbonyl group belonging to the carboxymethyl group. Thermal analysis showed that CMP1, CMP2, and CMP3 derivatives presented thermal stability values of 209.91 C, 214.73 C, and 225.52 °C, respectively, and were lower with respect to PU with Td of 238.84 °C. Furthermore, an increase in the glass transition temperature due to carboxymethylation was determined. The chemical modification decreased the contact angle with respect to PU (71.34°) with values for CMP1, CMP2, and CMP3 of 39.89°, 53.72° and 60.61°, respectively. The carboxymethylation also increased the water vapor permeability and mechanical properties of the films. In addition, it was found that the CMP molecules affected the optical properties. The application of CMP-based coatings reduced the mass loss and ripening rate of blueberries compared to native pullulan, therefore, packaging from CMP molecules could be used as a coating capable of delaying ripening and extending the shelf life of fruits.

Antimicrobial screening of pecan shell extract and efficacy of pecan shell extract-pullulan coating against Listeria monocytogenes, Salmonella enterica, and Staphylococcus aureus on blueberries

Pecan shell is considered an agricultural waste; however, it contains various bioactive compounds with potential inhibitory effect against microorganisms. This study evaluated the antimicrobial efficacy of pecan shell extract (PSE) in vitro using disc-diffusion method and in vivo on blueberries as an antimicrobial coating using pullulan. For in vitro study, 5 and 10 % of aqueous (A-PSE) or ethanol pecan shell extract (E-PSE) incorporated into pullulan film were tested against different bacterial and fungal strains. Pullulan film disc was used as control. The diameter of growth inhibition (mm) around discs was measured. For in vivo study, PSE-P (5 % w/v aqueous pecan shell extract+5 % w/v pullulan), P (5 % w/v pullulan) or control (water) were spray coated on blueberries inoculated (∼5 log CFU/g) with Listeria monocytogenes, Salmonella enterica or Staphylococcus aureus; and stored at 4 °C, 50 ± 10 % RH for 15 days. The effect of antimicrobial coating against pathogens and its impact on quality during storage were determined. A-PSE and E-PSE films were more effective against Gram-positive bacteria and showed no antifungal effect at tested concentrations when evaluated in vitro. Immediately after coating on blueberries, PSE-P significantly reduced Listeria monocytogenes by 2 log CFU/g and lowered survival until day 5 than control or P. Native aerobic microbial population was reduced (P < 0.05) by 0.7 log CFU/g immediately after coating. PSE-P coating or storage time had no significant effect (P > 0.05) on the survival of S. enterica, S. aureus and native fungal population. PSE-P maintained the firmness of blueberry with no significant effect on its color, TSS, and pH during 15 days storage. PSE-P significantly reduced (P < 0.05) the spoilage rate by 21 % than control (28.5 %) and P (37 %); and minimized (P < 0.05) weight loss during storage. Pecan shell extracts show promise as a potential antimicrobial compound whose application on various food products or packaging material could be further explored.

Effect of Gaseous Ozone and Storage Time on Polyphenolic Profile and Sugar Content in Fruits of Selected Vaccinium corymbosum L. Genotypes

One of the best sources of antioxidant and health-promoting bioactive substances is the fruit of V. corymbosum. A potent oxidizing agent, ozone (O3), can effectively eliminate bacteria. The application of ozone gas to V. corymbosum fruit during storage had a favorable impact on the fruit's phenolic component and sugar content in the current investigation. After 7 days of storage, phenolic content in all highbush blueberry cultivars and clones tested increased on average by 28.60%, including anthocyanins by 34%. After 14 days of storage, an average increase of 16.50% in phenolic compounds was observed, including a 20.53% increase in anthocyanins. Among all the tested varieties, clone BOR-21 treated with a dose of 0.01 mL·L-1 ozone for 30 min after 14 days had the highest TPC-143.73 mg·100 g-1 f.w. The sugar content of berries treated with a dose of 0.01 mL·L-1 ozone for 30 min, on day 7 and day 14 of storage increased by 9.2% and 6.3%, respectively. On day 7, the highest amount of total sugar (22.74 g·100 g-1) was observed in Duke cultivar after being exposed to 0.01 mL·L-1 ozone for 15 min. The ozonation treatments enhanced the fruit's saturation with nutrients, which raises the fruit's value as food.

Effect of Surfactant Formula on the Film Forming Capacity, Wettability, and Preservation Properties of Electrically Sprayed Sodium Alginate Coats

Surfactants are always added to coating formulations to ensure good adhesion of edible coatings to a product's surface and to maintain freshness. In this study, the effects of the mix surfactants Tween 20 and Span 80 with different hydrophile-lipophile balance (HLB) values on the film-forming ability, wettability, and preservation capacity of blueberry sodium alginate coating were investigated. The results indicated that Tween 20 obviously ensured favorable wettability and improved the uniformity and mechanical properties of the resulting film. While the addition of Span 80 reduced the mean particle size of the coating, enhanced the water resistance of the film, and helped to reduce blueberry weight loss. A sodium alginate coating with low viscosity and medium HLB could better inhibit the galactose, sucrose, and linoleic acid metabolism of blueberries, reduce the consumption of phenols, promote the accumulation of flavonoids, and thus display superior coating performance. In summary, sodium alginate coating with medium HLB had comprehensive advantages in film-forming ability and wettability and was conducive to the fresh-keeping role.

The strategic applications of natural polymer nanocomposites in food packaging and agriculture: Chances, challenges, and consumers' perception

Natural polymer-based nanocomposites have received significant attention in both scientific and industrial research in recent years. They can help to eliminate the consequences of application of petroleum-derived polymeric materials and related environmental concerns. Such nanocomposites consist of natural biopolymers (e.g., chitosan, starch, cellulose, alginate and many more) derived from plants, microbes and animals that are abundantly available in nature, biodegradable and thus eco-friendly, and can be used for developing nanocomposites for agriculture and food industry applications. Biopolymer-based nanocomposites can act as slow-release nanocarriers for delivering agrochemicals (fertilizers/nutrients) or pesticides to crop plants to increase yields. Similarly, biopolymer-based nanofilms or hydrogels may be used as direct product coating to extend product shelf life or improve seed germination or protection from pathogens and pests. Biopolymers have huge potential in food-packaging. However, their packaging properties, such as mechanical strength or gas, water or microbial barriers can be remarkably improved when combined with nanofillers such as nanoparticles. This article provides an overview of the strategic applications of natural polymer nanocomposites in food and agriculture as nanocarriers of active compounds, polymer-based hydrogels, nanocoatings and nanofilms. However, the risk, challenges, chances, and consumers' perceptions of nanotechnology applications in agriculture and food production and packaging have been also discussed.

Investigations into Determinants of Blueberry Coating Effectiveness

Coatings have been investigated as a means of slowing weight loss and helping to preserve quality in blueberries but reported results have been inconsistent with the inadequate presentation of the impact of coatings on blueberry appearance. In this study, we compare the ability to limit weight loss, along with the effect on appearance, of several previously studied coatings for blueberries and attempt to identify reasons why coatings have not been more successful in limiting weight loss in blueberries. In a two-year study, coatings were applied either as a spray or a dip, depending on the nature of the coating, and included 1% chitosan (CH) with and without either 1% or 2% oleic acid (OA), 1% Semperfresh (SF), 2% sodium caseinate (SC), and carnauba wax (CAR). None of the coatings reduced weight loss in either year of the study and sometimes enhanced it. CH, CH + OA, CAR, and SF greatly altered the appearance of the berries by removing all or a part of the waxy bloom. SC also did this to some degree but was generally better at maintaining the natural appearance. It was found that coating application did not effectively limit weight loss through either the cuticle or stem end of the blueberries. Loss of the bloom on the blueberry surface, confirmed visually and by scanning electron microscopy, occurred during coating application, but was found to not influence coating effectiveness. Using CH + OA as an example, it was found that increasing the amount of handling during the drying process significantly increased subsequent weight loss relative to blueberries with minimal handling. This indicates that careful handling during the coating process is important for coating success.

Chemical Structures, Properties, and Applications of Selected Crude Oil-Based and Bio-Based Polymers

The growing perspective of running out of crude oil followed by increasing prices for all crude oil-based materials, e.g., crude oil-based polymers, which have a huge number of practical applications but are usually neither biodegradable nor environmentally friendly, has resulted in searching for their substitutes-namely, bio-based polymers. Currently, both these types of polymers are used in practice worldwide. Owing to the advantages and disadvantages occurring among plastics with different origin, in this current review data on selected popular crude oil-based and bio-based polymers has been collected in order to compare their practical applications resulting from their composition, chemical structure, and related physical and chemical properties. The main goal is to compare polymers in pairs, which have the same or similar practical applications, regardless of different origin and composition. It has been proven that many crude oil-based polymers can be effectively replaced by bio-based polymers without significant loss of properties that ensure practical applications. Additionally, biopolymers have higher potential than crude oil-based polymers in many modern applications. It is concluded that the future of polymers will belong to bio-based rather than crude oil-based polymers.

Recent Advancements of Polysaccharides to Enhance Quality and Delay Ripening of Fresh Produce: A Review

The freshness of fruits and vegetables plays a significant role in consumers' decision to purchase a product at the supermarket. Fresh-cut products are the latest trend in fulfilling society's restless needs, and the food industry is faced with the challenge of maintaining the quality of fresh produce. The food industry is concerned with the natural maturation and degradation of fruits and vegetables, primarily due to enzymatic reactions. It has been demonstrated that polysaccharide coatings effectively preserve the freshness of these products, extending their shelf life depending on the preservation method used. This review informs readers about the different types of polysaccharides and their novel applications as natural food preservatives in the past five years (2018-2022). The key findings summarized the properties of the antimicrobial agent, the molecular mechanism of action, coating methods, and formulation for the preservation approach. Additionally, we discuss the scientific factors influencing polysaccharide processing and preservation efficacy, allowing it to be used in post-harvest management.

Application of a MOGA Algorithm and ANN in the Optimization of Apple Drying and Rehydration Processes

The aim of the study was to estimate the optimal parameters of apple drying and the rehydration temperature of the obtained dried apple. Conducting both processes under such conditions is aimed at restoring the rehydrated apple to the raw material properties. The obtained drying parameters allow the drying process to be carried out in a short drying time (DT) and at low energy consumption (EC). The effect of air velocity (vd), drying temperature (Td), characteristic dimension (CD), and rehydration temperature (Tr) on rehydrated apple quality was studied. Quality parameters of the rehydrated apple as: color change (CC), mass gain ratio (MG), solid loss ratio (SL), volume gain ratio (VG) together with DT and EC were taken into consideration. The artificial neural network was used for modeling of rehydrated apple quality parameters, DT, and EC. A multi-objective genetic algorithm was developed in order to optimize parameters of the drying and rehydration processes. The simultaneous minimization of CC, SL, DT, EC, and the maximization of MG and VG were considered with the following drying and rehydration processes parameters: Td: 50–70 °C, vd: 0.01–2 m/s, Tr: 20–70 °C. The best solution has been found at drying temperature 56.1 °C, air velocity 1.3 m/s, characteristic dimension 2.0 mm, and rehydration temperature 59.2 °C. This apple drying and rehydration resulted in MG = 3.51, SL = 0.57, VG = 4.77, CC = 11.2, DT = 5.4 h, EC = 159.8 GJ/kg. The parameters of apple drying and rehydration processes can be recommended for the industry application.

Fabrication and characterization of Pickering emulsion gels stabilized by zein/pullulan complex colloidal particles

BACKGROUND

Zein particles are unsuitable as stabilizers of Pickering emulsions because of their high hydrophobicity. However, few studies have reported on the use of a strong hydrophilic neutral polysaccharide to regulate its wettability. In this work, zein/pullulan complex particles (ZPPs) were formulated by an anti-solvent method to fabricate Pickering emulsions.

RESULTS

The presence of pullulan increased the size, decreased the zeta, and provided excellent resistance to the gravitational separation of zein. Scanning electron microscopy (SEM) revealed that the shape of zein particles changed from spherical as they became aggregated ZPP nanoparticles. Fourier transform infrared (FTIR) spectroscopy indicated that the flocculation phenomenon of ZPPs was related to the hydrogen bond between zein and pullulan. Moreover, the hydrophobicity of zein was modified by hydrophilic pullulan to endow the ZPPs with nearly neutral wettability when the mass ratio was 15:1, allowing for the preparation of stable Pickering emulsions. In contrast to zein, the ZPPs contributed to building a compact interface layer around the droplets and smaller emulsion droplets. Under a certain ZPP concentration, the size and viscosity of emulsion increased with an increase in the oil volume fraction, indicating that the Pickering emulsions stabilized by ZPPs showed better stability against coalescence. Confocal laser scanning microscopy (CLSM) revealed that the ZPPs constructed a dense filling layer on the surface of oil droplets, thus further emphasizing that ZPPs can potentially be used in fabricating Pickering emulsion gels.

CONCLUSION

Zein/pullulan complex particles are an excellent Pickering emulsion gel stabilizer that can be used in the delivery system of bioactive substances in food formulations. © 2020 Society of Chemical Industry.

Shelf-life, quality, safety evaluations of blueberry fruits coated with chitosan nano-material films

Chitosan coating (B/CH) in addition with nano-material films as silicon (B/CH/Nano-SiO₂) and titanium (B/CH/Nano-TiO₂) dioxides were developed and applied to detect potential changes on fresh blueberry fruits in commercial storage temperature. Physical, mechanical parameters (weight loss, decay rate, colour index and firmness), phytochemical contents (ascorbic acid, acidity, soluble solids concentration, titratable acidity, and repining index), phenolic enzymes (peroxidase and polyphenoloxidase), pigments (anthocyanin) and microbiological analysis (mesophilic aerobic, yeasts and molds populations) were detected every other day until the end of the experiment. Nano-coating based on (Nano-TiO₂) established the most suitable values for weight loss (2.22%), titratable acidity (0.45% citric acid), and repining index. (B/CH/Nano-TiO₂) reported a gradual increase in polyphenoloxidase and peroxidase enzyme activities (659.45 U/min g) and (20.39 U/min g), respectively. While, (B/CH/Nano-SiO₂) established the slightest change in acidity (2.61), anthocyanin (105.19 cyanidin-3-O-glucoside mg/100 g FW) and minimized the growth of mesophilic aerobic, yeasts, and molds populations (3.73–3.98 log CFU/g), respectively. (B/CH) films maintained lightness (6.80% loss) and recorded the highest ascorbic acid content (7.34 g/100 g FW). Therefore, chitosan nano-material films can maintain nutrients and control the microbial growth for extending the shelf life of fresh blueberry fruits.

Reducing Meat Perishability through Pullulan Active Packaging

The provision of safe products from the meat industry has been considered as the major source of protein for maintaining human health. Meat-borne outbreaks are mainly due to Salmonella typhimurium (S. typhimurium), Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Clostridium perfringens (C. perfringens), reducing the shelf life and consumer demands. A variety of vulnerable substances, including cholesterol oxidation products (COPs), are generated by the oxidation of meat induced by the microbial infestations. The use of certain biodegradable active packaging, including pullulan active packaging, is being focused by the meat industry due to their safety, stability, and negligible health risks. The potential of pullulan active packaging, incorporated with silver nanoparticles and essential oils, against E. coli, S. typhimurium, Mycoplasma, and other bacterial species is exclusive. Similarly, maintenance of organoleptic properties of meat with nominal oxidative rancidity and limited human health issues can be acquired by pullulan active packaging.

Characterization of Starches Isolated from Colombian Native Potatoes and Their Application as Novel Edible Coatings for Wild Andean Blueberries (Vaccinium meridionale Swartz)

Andean blueberry is a promissory fruit native to South America. The current work aimed to characterize starches isolated from Colombian native potatoes and to evaluate the effect of the application of starch edible coatings on the changes in the physicochemical quality parameters of the Andean blueberry during storage. Starches were isolated from three different potatoes varieties (pacha negra, mora, and alcarrosa) and characterized. Then, starch-based coatings were applied to Andean blueberries, and the changes in their quality parameters were monitored during 12 days of storage. Despite the phenotypical differences in the starch sources used, starches were similar in terms of their granule morphology, amylose content (~19%), crystallinity degree (~46%), and thermal properties. Coatings were able to reduce the gaseous exchange of the fruit, and, thus, the respiration rate of all coated blueberries was ~27% lower compared to the uncoated fruits (p < 0.05) at the end of the storage. While the application of starch coatings did not prevent water loss, all samples reached water loss of up 20%. Besides, the coated fruits showed soluble solids contents ~14% higher compared to the control one, as well as better bright and firmness. The new edible coatings can help add value to the Andean blueberry.

Application of Pullulan and Chitosan Multilayer Coatings in Fresh Papayas

In this work, some multilayer coatings (two-layer, four-layer or six-layer) based on pullulan and chitosan for protecting papayas were prepared by the layer-by-layer technique. The papayas were coated by immersion and stored at 25 °C, 50% relative humidity or up to 14 days. Uncoated and monolayer-coated papayas were used as controls. The pullulan/chitosan coatings decreased the papaya weight loss, softening, color change (b*, ΔE), and pH, retarded the fall of titratable acidity and vitamin C, and maintained respiratory rate and soluble solid contents. Sensory quality evaluation demonstrated that pullulan/chitosan coatings effectively preserved papaya flavor and overall acceptance. In general, the four-layer coatings provided the best fruit preservation. In conclusion, multilayer pullulan/chitosan coatings are efficient in maintaining the post-harvest quality and prolonging the shelf life of fresh papaya.

Pullulan – Biopolymer with Potential for Use as Food Packaging

The materials used in food packaging based on non-biodegradable synthetic polymers pose a serious threat of pollution to the environment. Hence, research is now focused on developing eco-friendly and biodegradable packaging obtained from natural polymers. Pullulan is a microbial exopolysaccharide, obtained on a commercial scale by the yeast-like fungus Aureobasidium pullulans. It is a water-soluble, non-toxic and non-mutagenic edible biopolymer with excellent film-forming abilities and adhesive properties. Furthermore, pullulan presents great potential to fabricate thin, transparent, odorless and tasteless edible films and coating used as packaging material. This review article presents an overview on the basic mechanical and barrier properties of a pullulan-based film. It also describes the modification methods applied in order to obtain multifunctional materials in terms of satisfactory physico-mechanical performance and antimicrobial activity for food packaging.

Thermal Stabilization of Viral Vaccines in Low-Cost Sugar Films

Most currently available vaccines, particularly live vaccines, require the cold chain, as vaccine efficacy can be significantly hampered if they are not stored in a temperature range of 2-8 °C at all times. This necessity places a tremendous financial and logistical burden on vaccination programs, particularly in the developing world. The development of thermally stable vaccines can greatly alleviate this problem and, in turn, increase vaccine accessibility worldwide. In this paper, we detail a simple and cost-effective method for stabilizing live vaccines that uses FDA-approved materials. To this end, we dried enveloped DNA (Herpes Simplex Virus type 2) and RNA (Influenza A virus) viral vaccines in a pullulan and trehalose mixture. The results of these studies showed that the live-attenuated HSV-2 vaccine retained its efficacy for at least 2 months of storage at 40 °C, while the inactivated influenza vaccine was able to retain its immunogenicity for at least 3 months of storage at 40 °C. This work presents a simple approach that allows thermo-sensitive vaccines to be converted into thermo-stable vaccines that do not require refrigeration, thus contributing to the improvement of vaccine deployment throughout the world.

Ready-to-use thermally stable mastermix pills for molecular biology applications

Rolling circle amplification (RCA), polymerase chain reaction (PCR), and loop-mediated isothermal amplification (LAMP), are powerful tools that can be used for gene manipulation, pathogen detection, and infectious disease diagnostics. However, these techniques require trained personnel, as the pipetting steps involved can lead to contamination and, consequently, erroneous results. Furthermore, many of the reagents used in molecular biology are thermally labile and must be kept within a cold-chain. In this article, we present a simple and cost-effective method that allows molecular biology reagents to be thermally stabilized into ready-to-use mastermixes via drying in pullulan and trehalose films. Our experimental results demonstrate that this method is capable of preserving the activity of RCA, PCR, LAMP, ligase, polynucleotide kinase, and Klenow fragment mastermixes for at least 3 months at ambient conditions. Thus, stabilizing reagents via drying in pullulan and trehalose film may allow for a drastic reduction in the number of pipetting steps and the elimination of the need for a cold chain. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2764, 2019.

Statistical Optimization of Medium for Pullulan Production by Aureobasidium pullulans NCPS2016 Using Fructose and Soybean Meal Hydrolysates

Pullulan, with its excellent characteristics of film-forming, water solubility, and biodegradability, is attracting more and more attention in agricultural products preservation. However, high pullulan production cost largely restricts its widely application due to its low production. In order to improve pullulan production by Aureobasidium pullulans NCPS2016, the medium was optimized using single factor experiment and response surface methodology. Based on the single factor experiments, the contents of soybean meal hydrolysates (SMHs), (NH₄)₂SO₄, and K₂HPO₄·3H₂O were considered to be main factors influencing the extracellular polysaccharide (EPS) production, and were further optimized by Box⁻Behnken design. The optimal content of SMHs of 7.71 g/L, (NH₄)₂SO₄ of 0.35 g/L, and K₂HPO₄·3H₂O of 8.83 g/L were defined. Finally, EPS production of 59.8 g/L was obtained, 39% higher in comparison with the production in the basal medium. The purified EPS produced by NCPS2016 was confirmed to be pullulan. This is the first time fructose is reported to be the optimal carbon source for pullulan production by Aureobasidium pullulans, which is of great significance for the further study of the mechanism of the synthesis of pullulan by NCPS2016. Also, the results here have laid a foundation for reducing the industrial production cost of pullulan.