Antimicrobial plastic film: Physico-chemical characterization and nisin desorption modeling

Antimicrobial active films represent an innovative concept in food packaging, developed to answer to consumer's expectation for better microbiological safety. In this study, the growth of pathogenic micro-organisms on the surface of food is proposed to be controlled by coating, on the surface of polyethylene/polyamide/polyethylene film (PE/PA/PE), a film-forming solution containing Nisaplin, a commercial form of bacteriocin produced by Lactococcus lactis subsp. lactis: nisin. The bioactivity of these multi-layer films coated with Nisaplin loaded HydroxyPropylMethylCellulose film is based on the release of this antimicrobial molecule towards a food simulant. Nisin mass transfer was studied and modeled, for different operating conditions, generally encountered in food products. pH didn't seem to interfere with nisin release kinetics, while the variation of NaCl concentration between 0.8% and 3.2% decreased the desorption coefficient (k_d) by 18% and the temperature increase from 10 °C to 28 °C resulted in an increase of k_d from 1.78 × 10^? 2 m s^? 1 to 2.10 × 10^? 2 m s^? 1. Coating of PE/PA/PE film with this antimicrobial layer induced little mechanical properties modifications without compromising industrial applications. Water barrier capacity was not altered.Industrial relevanceThis paper concerns active packaging, considered as a new approach to preserve food shelf life. Active packaging is a real gain for plastic and Food industrials. Coating was used to obtain antimicrobial packaging. The impact of coating on film characteristics is investigated.Also, antimicrobial agent desorption is determined during storage conditions.     

Evaluation of biodegradable film packaging to improve the shelf-life of Boletus edulis wild edible mushrooms

The objective of this work was to evaluate the effect of poly(lactic acid) (PLA) based biodegradable film packaging combining 0.5% nisin antimicrobial polypeptide on the physicochemical and microbial quality of Boletus edulis wild edible mushrooms stored at 4 ± 1 °C. The experiment was set up by packaging mushrooms with extruded PLA films containing 0, 7.5, and 15 wt.% triethyl citrate plasticizer. The low-density polyethylene (LDPE) film was used as the control. Mushrooms stored in PLA films containing 7.5 and 15 wt.% plasticizer provided better retention of quality characteristics and received higher sensory ratings compared to mushrooms stored in pure PLA film and LDPE film. Samples with these two treatments underwent minimal changes in texture, PPO activity, total bacteria count, and sensory attributes. Results suggest that nisin in combination with plasticized PLA film has the potential to maintain B. edulis wild edible mushroom quality and extend its postharvest life to 18 days.Industrial relevanceB. edulis is one of the most commercialized mushrooms worldwide. However, as with all fresh mushrooms, there are severe preservation problems. Extruded PLA films containing triethyl citrate plasticizer plus antimicrobial agent nisin proved to be a suitable technology for mushroom conservation. This material exhibits an environmental-friendliness potential and a high versatility in food packaging.     

Conductive plastic film electrodes for Pulsed Electric Field (PEF) treatment—A proof of principle

Nowadays Pulsed Electric Field (PEF) treatment of food needs to be performed prior to packaging, either hygienic or aseptic packaging is necessary. New techniques for PEF treatment after packaging can be considered when plastic conductive (film) electrodes can be integrated within the package, so that the package and the product can be treated as a whole. This paper describes a newly developed treatment chamber, which can be used to test the ability of any arbitrary plastic packaging film to be used as electrodes for PEF treatment. Tests with a flexible commercially available electrically conductive copolymer film showed that reduction of Lactobacillus plantarum by PEF was possible. This heat sealable film obeys the mechanical properties of a polymer; however it has an electrical conductivity of 0.75 S m^? 1 and approximately 2.3% of the surface area is electrically conductive. The maximum obtained inactivation was 2.1 log₁₀ with a specific energy of 17 J ml^? 1. The microbial experiments gave a consistent outcome compared with finite element simulations and with models from literature. Further research to reach real pasteurisation levels is needed as well as issues concerning utilisation of these film electrodes.Industrial relevanceStainless steel electrodes, which are widely used as electrode material for Pulsed Electric Field (PEF) treatment systems, have as main disadvantage that they exhibit certain wear. This article showed that polymer composites can be considered as electrode material for newly to be developed PEF treatment concepts. With extensive research on food grade composite films the integration of cheap disposable plastic electrodes in food packages comes within reach.     

Monitoring nisin desorption from a multi-layer polyethylene-based film coated with nisin loaded HPMC film and diffusion in agarose gel by an immunoassay (ELISA) method and a numerical modeling

Polyethylene-based films coated with nisin loaded HPMC films were put in contact with food simulants, i.e. agarose gels with 5 or 30% (w/w) fat. Nisin desorption from the multi-layer films and diffusion in agarose gels were monitored by ELISA (Enzyme Linked ImmunoSorbent Assay). The data obtained after 2 or 6 days of contact between antimicrobial films and agarose gels were employed to determine nisin mass transfer by numerical modeling following Fick's second law. The values were in the range from 0.87 × 10^? 3 m s^? 1 to 4.30 × 10^? 3 m s^? 1 and 6.5 × 10^? 11 m² s^? 1 to 3.3 × 10^? 10 m² s^? 1, for nisin apparent desorption and diffusion coefficients, respectively. The diffusion process was governed by interactions between food matrix simulant and nisin. Moreover, it was observed that the polymer in the coating did not modify plastic film initial mechanical resistance and water vapor permeability.Industrial relevanceThis paper concerns active packaging, considered as a new approach to preserve food shelf life. Active packaging is a real gain for plastic and Food industrials. The paper deals with coating as a manner to activate packaging. The impact of coating on film properties is investigated.Also, predictive models are proposed to determine antimicrobial agent desorption and diffusion during some storage conditions.     

Migration of α-tocopherol from LDPE films to corn oil and its effect on the oxidative stability

The migration of α-tocopherol (α-T) from low density polyethylene (LDPE) films, added with 20 (film A) and 40 mg g^?1 (film B) to corn oil for 12 weeks at 5, 20 and 30 °C was determined. A LDPE film added with no α-T was used as control (film C). Diffusion coefficient (D) values for the film A system were 1.4 × 10^?11, 7.1 × 10^?11 and 30.3 × 10^?11 cm² s^?1 at 5, 20 and 30 °C, respectively. Meanwhile, D values for the film B system were 1.3 × 10^?11, 9.6 × 10^?11 and 51.1 × 10^?11 cm² s^?1 at the same temperatures. The activation energy (E_a) for the diffusion of α-T was 126.5 (film A) and 105.9 kJ mol^?1 (film B). The effect of the migration of α-T on the oxidative stability of corn oil was evaluated by monitoring hexanal content by solid phase micro-extraction (SPME) and gas chromatography. The hexanal content in the oil showed that both films added with α-T resulted suitable to maintain the oxidative stability of the oil for about 16 weeks at 30 °C, compared to 12 weeks for the oil in contact with the film C.     

Time–temperature study of the kinetics of migration of DPBD from plastics into chocolate,chocolate spread and margarine

Migration of low molecular weight substances into foodstuffs is a subject of increasing interest and an important aspect of food packaging because of the possible hazardous effects on human health.The migration of a model substance (diphenylbutadiene) from low-density polyethylene (LDPE) was studied in foodstuffs with high fat contents: chocolate, chocolate spread and margarines (containing 61% and 80% fat).A simplifying mathematical model based on Fick’s diffusion equation for mass transport processes from plastics was used to derive effective diffusion coefficients which take also kinetic effects in the foods into account and to determine partition coefficients between plastic and food. With this model migration levels obtainable under other storage conditions can be predicted. The effective diffusion coefficients for both margarines stored at 5 °C (3.0–4.2 × 10⁻¹⁰ cm² s⁻¹) and at 25 °C (3.7–5.1 × 10⁻⁹ cm²  s⁻¹) were similar to each other, lower than for chocolate spread stored at 5 °C (9.1 × 10⁻¹⁰ cm² s⁻¹) and higher than the diffusion coefficient for chocolate stored at 25 °C (2.9 × 10⁻¹⁰ cm² s⁻¹). Good agreement was found between the experimental and the estimated data, allowing validation of this model for predicting diffusion processes in foodstuffs with high fat contents.     

Effect of active and modified atmosphere packaging on quality retention of dark chocolate with hazelnuts

The present study investigated the effect of active and modified packaging as well as packaging material oxygen permeability on quality retention of dark chocolate with hazelnuts. Dark chocolate was packaged in: a) polyethylene terephthalate//low density polyethylene (PET//LDPE), and b) polyethylene terephthalate coated with SiOx//low density polyethylene (PET-SiOx//LDPE). Samples were packaged either under, vacuum or N₂ or with an oxygen absorber and stored in the dark at 20 °C for a period of 12 months. “Commercial” control samples for comparison purposes consisted of chocolate packaged in aluminum foil in air while “model” control samples used for sensory evaluation consisted of chocolate packaged in glass jars and stored at ? 18 °C. Quality parameters monitored were: peroxide value, hexanal content, color, fatty acid composition and volatile compounds. Of the sensory attributes color, texture, odor and taste were evaluated. PV ranged between 0.80 for fresh dark chocolate with hazelnuts and 6.51 meq O₂/kg chocolate fat for commercially packaged samples after 12 months of storage. Respective values for hexanal were 0.53 and 7.56 mg/kg. % Saturated fatty acids (SFA) increased with a parallel decrease in monounsaturated fatty acids (MFA) and polyunsaturated fatty acids (PUFA) after 12 months of storage mainly in least protected samples (commercial package). Likewise, after 12 months of storage an increase in concentration of aldehydes, ketones, alcohols and alkanes (p < 0.05) with a parallel decrease in pyrazines where observed especially in case of least protected products after 6 and 12 months of storage. In general after 12 months of storage chocolate showed whitening of the surface resulting to an increase in L* and a* values (p < 0.05) and a decrease in b* value. Dark chocolate with hazelnuts retained acceptable quality for ca. 8 months in commercial packages. For samples packaged in PET//LDPE irrespective of storage atmosphere the shelf life was 8 to 9 months and for samples packaged in PET-SiOx//LDPE irrespective of storage atmosphere the shelf life was 11 months. Finally for samples packaged with an oxygen absorber irrespective of packaging material the shelf life was at least 12 months.Industrial relevanceChocolate packaged with an oxygen absorber in a barrier packaging material will maintain its aroma, taste and nutritional quality substantially longer than other packaging methods.     

Inactivation effect of dielectric barrier discharge plasma against foodborne pathogens on the surfaces of different packaging materials

The usefulness of dielectric barrier discharge (DBD) plasma for surface disinfection of the common food packaging materials, namely glass, polyethylene, polypropylene, nylon, and paper foil was evaluated. DBD plasma was generated by applying a pulsed DC voltage of 10 kV and at a power of 208 W. The separation distance between the electrodes was 2.65 mm. On exposure of food pathogens-loaded packaging materials to the plasma, > 4 log/cm² reduction (99.99%) in viable cell counts of Escherichia coli O157:H7 was observed in 10 min. The other two tested pathogen strains, Salmonella typhimurium and Staphylococcus aureus, were inactivated in the range 3.0–3.5 log/cm². The inactivation pattern of the pathogens fitted well to the log-linear and tail model. Compared to unexposed packaging materials, no significant (p > 0.05) changes in the surface temperatures, optical characteristics, tensile strengths, and strain-induced deformation were observed for the DBD plasma-exposed materials. Therefore, the DBD plasma can be used to disinfect surfaces of different food packaging materials harboring moderate levels of bacterial contaminants without adversely affecting their physicomechanical properties.Industrial relevanceTraditionally, dry heat, steam, UV light and chemicals like ethylene oxide and hydrogen peroxide have been used as surface sterilants and disinfectants for packaging materials in the food industry. However, certain limitations have motivated the search for new approaches. Cold plasma technology is an emerging, green process for surface sterilization. The DBD plasma was found to be effective in reducing the bacterial food pathogens on different food packaging materials. As the technology is simple and scalable, it can be readily applied industrially.     

Sensory methods and electronic nose as innovative tools for the evaluation of the aroma transfer properties of food plastic bags

Despite the key role of the sensory quality for food acceptance, the aroma transfer properties of food packaging materials have not yet been studied using sensory approaches. This research investigated the suitability of sensory and electronic nose methods to evaluate the aroma transfer properties of plastic materials that come in contact with food. Four (W, X, Y, and Z) commercial freezer bags (polyethylene) for domestic uses were compared. The degree of the aroma transfer through the materials was estimated as the sensory contamination of an odor absorber food (bread) by an odor releaser food (onion), separated by the bags and stored under frozen conditions. Bread samples were analyzed by means of an electronic nose, and 42 assessors used three different sensory methods (triangle, scoring, and partial sorted Napping tests). From the triangle test, none of the plastic bags acted as a complete aroma barrier, showing a sensory contamination of bread stored in all four materials. Partial sorting Napping results clearly described the sensory contamination of bread as “onion flavor”, due to the aroma transfer from the odor releaser food to the odor absorber food through the plastic bag. Scoring tests showed significant (p < 0.0001) differences of aroma transfer properties among the plastic bags, revealing the highest aroma permeation for W (3.1 ± 0.1), the lowest aroma transfer for X and Y (2.0 ± 0.1), and intermediate aroma transfer properties for Z (2.6 ± 0.1). Electronic nose data were in good agreement with the sensory responses, and a high correlation with the scoring data was observed (R² = 0.988). The presented approaches had suitable results to provide meaningful information on the aroma transfer properties of freezer plastic bags, and could advantageously be applied in the future for analyzing other finished food containers (e.g. plastic trays, boxes, etc.) or packaging materials of a different nature (multilayer plastic films, biodegradable materials, composites, etc.).     

Detection of pyrrolizidine alkaloids in commercial honey using liquid chromatography–ion trap mass spectrometry

Pyrrolizidine alkaloids (PAs) are known secondary plant metabolites which can cause hepatotoxicity in both humans and livestock. PAs can be consumed through the use of plants for food, medicinal purposes and as contaminants of agricultural crops and food. PA contaminated grain has posed the largest health risk, although any PA contamination in our food chain should be recognised as a potential health threat. For this purpose, retail honeys were tested by LC–MS/MS. The method allows for specific identification of toxic retronecine and otonecine-type PAs by comparison to reference compounds via a spectral library. In total, 50 honey samples were matched to the reference spectra within a set of tolerance parameters. Accurate data analysis and quick detection of positive samples was possible. Positive samples contained an average PA concentration of 1260 μg kg^?1 of honey. Good linear calibrations were obtained (R² > 0.991). LOD and LOQ ranged from 0.0134 to 0.0305 and 0.0446 to 0.1018 μg mL^?1, respectively.     

Effect of the ripening time under vacuum and packaging film permeability on processing and quality characteristics of low-fat fermented sausages

The effect of vacuum ripening of low-fat fermented sausages packaged in films with different permeabilities on their microbiological, physicochemical and sensorial characteristics was studied. High-fat control sausages were produced with 30% initial fat and low-fat sausages with 10% initial fat. The low-fat sausages were separated into: (a) non-packaged (control) and (b) packaged under vacuum on 7th, 12th and 17th day of processing, remaining under vacuum during the ripening period for 21, 16 and 11 days, respectively, in three different oxygen (100, 38 and ⩽ 5 cm³/m²/24 h/1 atm) and water vapour (4.5, <2.5 and 1 g/m² 24 h) permeability plastic bags. Vacuum packaging reduced (p < 0.05) the weight loss, the hardness and extent of lipid oxidation in the sausages, increased (p < 0.05) their lightness, but had no effect (p > 0.05) on the redness, compared to the control sausages. Packaging low-fat fermented sausages under vacuum for the last 11 days of ripening in packaging film with high permeability increased (p < 0.05) the lactic acid bacteria count. The same product packaged in film with medium permeability had a higher (p < 0.05) Micrococcaceae count and the same (p > 0.05) hardness and overall acceptability as the high-fat control sausages. A ripening time of 11 days and the medium packaging film permeability were the most appropriate conditions for the vacuum packaging of low-fat fermented sausages.     

Incorporation of partially purified hen egg white lysozyme into zein films for antimicrobial food packaging

Lysozyme, partially purified from hen egg white by precipitation of non-enzyme protein with ethanol and lyophilized after dialysis, was incorporated into zein films. The recovery and specific activity of the enzyme after partial purification varied between 45% and 72% and 2173 and 3448 U/mg, whereas the activity of the lyophilized enzyme varied between 2900 and 3351 U/mg. The partially purified enzyme was very stable and lost almost no activity in lyophilized form or in zein films stored at −18 and 4 °C for up to 8 and 4 months, respectively. During partial purification and in zein film preparation, ethanol treatment caused 123–137% and 132–315% activation of the enzyme, respectively. In zein films incorporated with 187–1318 U/cm² (63–455 μg/cm²) lysozyme, the release rates at 4 °C, changed between 7 and 29 U/cm²/min, increased at high lysozyme concentrations. Zein films incorporated with partially purified lysozyme showed antimicrobial effect on Bacillus subtilis and Lactobacillus plantarum. By the addition of disodium EDTA, the films also became effective on Escherichia coli. The results of this study showed that the partially purified lysozyme may be used in antimicrobial packaging to increase food safety.     

Anthocyanin infused watermelon rind and its stability during storage

Anthocyanins from Garcinia indica Choisy was impregnated in watermelon rind (WMR) through osmotic dehydration. The impregnation of anthocyanin was enhanced by application of pretreatments like vacuum and sonication (from 24 to 32 mg/100 g). Application of pretreatment during impregnation changes the tissue architecture of the WMR which helps in retaining the infusate during candy making process. The developed product from WMR was highly acceptable w.r.t. texture, taste and appearance. Moisture sorption study indicated that the WMR product was quite stable at ambient temperature upto 75% RH. Storage of the sample in LDPE (low density polyethylene pouches) and PET/LDPE (Polyethylene terephthalate/low density polyethylene pouches) did not show any significant difference in moisture content, anthocyanin degradation, texture, taste and appearance of the product. The WMR product was stable for 90 days at ambient storage conditions.Industrial relevanceThe knowledge provided by this work may be useful the development of new product (watermelon candy) from watermelon rind impregnated with anthocyanin. The extent and rate of infusion of anthocyanin was enhanced by application of pretreatments like vacuum and sonication. The developed product had highly acceptable texture, taste and appearance. The product was quite stable at ambient temperature upto 75% RH in LDPE (low density polyethylene pouches) and PET/LDPE (Polyethylene therapthalate/low density polyethylene pouches) pouches without significant difference in moisture content, anthocyanin degradation, texture, taste and appearance of the product. The WMR product was stable for 90 days at ambient storage conditions. This technique may be helpful in producing foods with enriched bioactive compounds, besides providing diversified products in terms of taste and nutrition.     

Antimicrobial activity of whey protein based edible films incorporated with oregano,rosemary and garlic essential oils

The use of edible films to release antimicrobial constituents in food packaging is a form of active packaging. Antimicrobial properties of spice extracts are well known, however their application to edible films is limited. In this study, antimicrobial properties of whey protein isolate (WPI) films containing 1.0–4.0% (wt/vol) ratios of oregano, rosemary and garlic essential oils were tested against Escherichia coli O157:H7 (ATCC 35218), Staphylococcus aureus (ATCC 43300), Salmonella enteritidis (ATCC 13076), Listeria monocytogenes (NCTC 2167) and Lactobacillus plantarum (DSM 20174). Ten millilitres of molten hard agar was inoculated by 200 μl of bacterial cultures (colony count of 1 × 10⁸ CFU/ml) grown overnight in appropriate medium. Circular discs of WPI films containing spice extracts, prepared by casting method, were placed on a bacterial lawn. Zones of inhibition were measured after an incubation period. The film containing oregano essential oil was the most effective against these bacteria at 2% level than those containing garlic and rosemary extracts (P < 0.05). The use of rosemary essential oil incorporated into WPI films did not exhibit any antimicrobial activity whereas inhibitory effect of WPI film containing garlic essential oil was observed only at 3% and 4% level (P < 0.05). The results of this study suggested that the antimicrobial activity of some spice extracts were expressed in a WPI based edible film.     

Kinetic desorption models for the release of nanosilver from an experimental nanosilver coating on polystyrene food packaging

To predict the kinetic desorption of silver from an experimental nanosilver coated polystyrene food packaging material into food simulants (0, 1, 2 and 3% acetic acid (HAc) in distilled water (dH₂O)) at 4 temperatures (10, 20, 40 and 70 °C), 5 sorption models were examined for their performance. A pseudo-second order kinetic sorption model was found to provide the best prediction of an unseen desorption validation dataset with R² = 0.90 and RMSE = 3.21. Poor predictions were witnessed for desorption at 70 °C, potentially due to re-adsorption of the silver back onto the polystyrene substrate, as shown in the kinetic migration experiments. Similarly, the temperature dependence of the desorption rate constant was satisfactorily described using the Arrhenius equation with the exception of the 70 °C scenario. The use of sorption models identified scenarios that may limit human exposure to nanosilver migrating from this experimental nanocoating, i.e. low temperature applications.Industrial relevanceThe use of antimicrobial packaging has the potential to reduce food spoilage and risk from pathogenic microorganisms while reducing food waste by extending the shelf life of food products. Coating of antimicrobial silver nanoparticles (AgNPs) to polymer surfaces is a highly advantageous technology as microbial contamination predominantly occurs on the surface of fresh and processed food products. However, uncertainty related to the potential release of nanoparticles from food packaging materials, subsequent potential human exposure and toxicology is a barrier to the uptake of these novel materials. In the European Union, where the safety assessment of these materials is stringent, mathematical models used to predict the worst case migration of nanoparticles from food packaging materials have supported the acceptance of some nanomaterials for use in food packaging. The performance of a number of desorption models was evaluated to predict the release of AgNPs from AgNP coated polystyrene. The model identified factors that influenced migration and possible industrial applications for the developed material to minimise human exposure. The study highlights the potential benefits of using predictive models to assess migration of NPs from polymers into food simulants instead of time consuming and expensive migration studies.     

Effect of mechanical,barrier and adhesion properties on oxygen plasma surface modified PP

In this work, the Polypropylene (PP) film was surface modified by Oxygen plasma treatment and the effect of mechanical, barrier and adhesion properties was studied. The PP film was plasma treated with various RF power settings of 7.2 W, 10.2 W and 29.6 W in various time intervals of 60 s, 120 s, 180 s, 240 s and 300 s. To characterize the wettability, the contact angle was measured and the surface energy values were estimated with different test liquids. The generation of oxygen functional groups on the surface of plasma modified PP and the surface change characterization were observed by attenuated total reflection-Fourier transform infrared spectroscope (ATR-FTIR) and they resulted in wettability improvement. The roughness of the PP film and the surface morphology were analyzed by Atomic Force Microscopy (AFM). It was found that the roughness value increased from 1.491 nm to 7.26 nm because of the increase of treatment time and RF power. The PP crystallinity structure of the untreated and treated PP was evaluated by X-ray diffraction analysis (XRD). The bond strength of the untreated and surface modified films were measured by T-peel test method. For the untreated and oxygen plasma treated sample, the mechanical properties like Tensile Strength and the barrier properties like oxygen transmission rate (OTR), Water vapor transmission rate (WVTR) were also calculated. From the results, the tensile strength reduced from 6 MPa to 1.350 MPa because of polypropylene etching and degradation. The OTR increased from 1851.2 to 2248.92 cc/m²/24 h and the Water vapor transmission rate increased from 9.6 to 14.24 g/m²/24 h.Industrial RelevancePlasma technology applied to packaging and printing industry is a dry, environmentally- and worker-friendly method to achieve surface alteration without modifying the bulk properties of different materials. In particular, atmospheric non-thermal plasmas are suited because most are heat sensitive polymers and applicable in continuous process. In the last years plasma technology has become a very active, high growth research field, assuming a great importance among all available material surface modifications in packaging industry.     

Extension of the display life of lamb with an antioxidant active packaging

Fresh lamb steaks were treated with three different preparations of natural antioxidants: one group was packaged with a rosemary active film, the second group was packaged with an oregano active film, and the third group was sprayed on the meat surface with a rosemary extract before packaging in a high-oxygen atmosphere. Samples were stored under illumination at 1 ± 1 °C for 13 days. Metmyoglobin formation, lipid oxidation (TBARS), instrumental colour (CIE a¹), psychrotrophic bacterial counts (PCA), sensory discolouration and off-odour were determined. The use of a rosemary extract, a rosemary active film or an oregano active film resulted in enhanced oxidative stability of lamb steaks. Active films with oregano were significantly more efficient than those with rosemary, exerting an effect similar to that of direct addition of the rosemary extract; in fact, they extended fresh odour and colour from 8 to 13 days compared to the control.     

Effect of process variables on the drying rate of mango pulp by Refractance Window

Refractance Window (RW) process is considered a novel and promising drying method, which uses hot water in contact with a polyester film (Mylar) at its bottom face to heat up and dry out a solution spread on the film surface. The aim of this study was to investigate the effect of process variables on the RW drying of mango pulp: water temperature (75, 85 and 95 °C), product thickness (2, 3 and 5 mm) and radiant source (transparent and painted Mylar film). Films' transmissivities to infrared radiation were determined and the drying kinetics of mango pulp with the nine possible pairs of layer thickness and water temperature were assessed. Mylar film was partially transparent to infrared radiation, while the black film (Mylar painted) blocked all infrared radiation emitted from the hot water. RW evaporation capacity was up to 10 kg m^− 2 h^− 1 (pulp with 2 mm, water at 95 °C), indicating a very efficient drying process. RW is more efficient than black film process for pulp thickness up to 3 mm. In fact, this study clearly established that radiative heat transfer contributes to less than 5% of the total amount of energy delivery to food during the RW drying process.     

Use of activated carbon for removing phenylalanine from reconstituted skim milk powder hydrolysates

With the aim of preparing dietary supplements for phenylketonurics, the activated carbon was used in this work to remove phenylalanine (Phe) from skim milk powder enzymatic hydrolysates. Six hydrolysates were prepared, using a protease from Aspergillus oryzae (AO), isolated or in association with papain (PA). Different conditions were tested for removing Phe, and the best one showed to be the use of a activated carbon:casein ratio of 118 (g) and a temperature of 25 °C, which produced 96–99% of Phe removal. Among the hydrolytic conditions employed, the association of AO with PA (1 h, 1 g of enzyme/100 g of substrate and 4 h, 2 g of enzyme/100 g of substrate, respectively) led to the lowest absolute value for the final Phe concentration (0.060×10⁻⁴ mg/100 mg of protein).     

Use of hyperspectral imaging for evaluation of the shelf-life of fresh white button mushrooms (Agaricus bisporus) stored in different packaging films

The shelf life of mushrooms packaged using different polymer top-films (PVC, PET with different levels of perforations) was investigated using hyperspectral imaging (HSI). Packaged mushrooms were stored at 4 ± 0.2 °C for 14 days and weight loss, Hunter L, a, b values, maturity index and in-pack gas composition (% CO₂ and O₂) were also measured. The results obtained showed that the PET film perforated with small holes (1 mm in diameter) was generally superior in terms of maintaining overall mushroom quality. Regression models were built to correlate HSI data with measured quality parameters. Prediction maps were generated from hyperspectral data to show the model performance at pixel level. Results presented in this work show hyperspectral imaging can be used to evaluate the effect of different packaging systems on mushroom quality and that perforated PET packaging film is a viable alternative to the conventional PVC packaging, facilitating an increase in shelf life from 10 to 14 days.Industrial relevanceThe present study demonstrates HSI can be used for rapid evaluation of mushroom quality facilitating non-destructive evaluation of the effect of packaging systems on mushroom shelf-life. In addition, this work suggests an effective packaging solution to extend shelf life of mushrooms during storage. The proposed solution potentially improves the packaging recyclability as the same polymer material (PET) is used for the tray and top film, compared to conventional mushroom packaging where PVC is used for the top film and polypropylene (PP) for the tray.