66 Chemische Verfahrenstechnik
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The packaging of fresh meat has been studied for decades, leading to improved packaging types and conditions such as modified atmosphere packaging (MAP). While commonly used meat packaging uses fossil fuel-based materials, the use of biodegradable packaging materials for this application has not been studied widely. This study aimed at evaluating the sustainability of biodegradable packaging materials compared to established conventional packaging materials through analyses of the quality of freshly packaged pork. The quality was assessed by evaluating sensory aspects, meat color and microbiological attributes of the pork products. The results show no significant differences (p > 0.05) in ground pork and pork loin stored in biodegradable MAP (BioMAP) and conventional MAP for the evaluated sensory attributes, meat color or total bacterial count (TBC) over extended storage times. The data suggest that BioMAP could be a viable alternative to MAP using conventional, fossil fuel-based materials for the storage of fresh meats, while simultaneously fulfilling the customers’ wishes for a more environmentally friendly packaging alternative.
Polymer materials that regulate the relative humidity in their environment are relevant for applications in the packaging and building sectors. By integration of salts in polymer structures, such materials are able to absorb and desorb high amounts of water vapor. In this study, films of polylactic acid and polypropylene with dispersed calcium chloride (2 and 4 wt %) were produced and biaxially stretched to induce the formation of cavities. The resulting cavities in these films account up to 10 vol % and are able to contain emerging calcium chloride solution formed by water vapor absorption. These films absorb reversibly up to 15 wt % water vapor at 75% relative humidity at 23 °C. This absorption behavior is described by effective diffusion and effective sorption coefficients. Using a simple model, the effective water vapor diffusion coefficient of these films can be estimated from the permeation coefficient of the polymer and the sorption coefficient of the absorber.
The oxygen permeability of films is relevant for packaging related and technical applications. An increasingly used test method for the measurement of oxygen permeability is the optical test method, because it allows a simple and cost-efficient measurement setup. This method is based on optical chemical sensors. However, not much is known about its validity. Therefore, method validation is necessary which is subject of this study. The optical method is compared with the carrier gas method for a variety of film samples. In the tested permeability range of 0.5–2500 cm3 (STP)·(m2 d bar)−1 both methods deviated less than 20% for zero and 50% relative humidity.
Oxygen scavengers are used in food packaging to protect oxygen-sensitive food products. A mixture of gallic acid (GA) and sodium carbonate was used as an oxygen scavenger (OSc) in bio-based multilayer packaging films produced in a three-step process: compounding, flat film extrusion, and lamination. We investigated the film surface color as well as oxygen absorption at different relative humidities (RHs) and temperatures, and compared the oxygen absorption of OSc powder, monolayer films, and multilayer films. The films were initially brownish-red in color but changed to greenish-black during oxygen absorption under humid conditions. We observed a maximum absorption capacity of 447 mg O2/g GA at 21 °C and 100% RH. The incorporation of GA into a polymer matrix reduced the rate of oxygen absorption compared to the GA powder because the polymer acted as a barrier to oxygen and water vapor diffusion. As expected, the temperature had a significant effect on the initial absorption rate of the multilayer films; the corresponding activation energy was 75.4 kJ/mol. Higher RH significantly increased the oxygen absorption rate. These results demonstrate for the first time the production and the properties of a bio-based multilayer packaging film with GA as the oxygen scavenger. Potential applications include the packaging of food products with high water activity (aw > 0.86).
Water loss, gain or transfer results in a decline in the overall quality of food. The aim of this study was to form a uniform layer of sodium alginate-based edible coating (1.25% sodium alginate, 2% glycerol, 0.2% sunflower oil, 1% span 80, 0.2% tween 80, (w/w)) and investigate the effects on the water barrier characteristics of fresh-cut cantaloupe and strawberries. To this end, a uniform and continuous edible film formation was achieved (0.187 ± 0.076 mm and 0.235 ± 0.077 mm for cantaloupe and strawberries, respectively) with an additional immersion step into a calcium solution at the very beginning of the coating process. The coating application was effective in significantly reducing the water loss (%) of the cantaloupe pieces. However, no significant effect was observed in water vapor resistance results and weight change measurements in a climate chamber (80%→60% relative humidity (RH) at 10 °C). External packaging conditions (i.e., closed, perforated, and open) were not significantly effective on water activity (aw) values of cantaloupe, but were effective for strawberry values. In general, the coating application promoted the water loss of strawberry samples. Additionally, the water vapor transmission rate of stand-alone films was determined (2131 g·100 µm/(m2·d·bar) under constant environmental conditions (23 °C, 100%→50% RH) due to the ability to also evaluate the efficacy in ideal conditions.
Achieving high quality of a coated food product is mostly dependent on the characteristics of the food material to be coated, the properties of the components in the coating solution, and the obtained coating material. In the present study, usability and effectiveness of various components as well as their concentrations were assessed to produce an effective coating material. For this purpose, different concentrations of gelling agent (sodium alginate 0–3.5%, w/w), plasticizers (glycerol and sorbitol (0–20%, w/w), surfactants (tween 40, tween 80, span 60, span 80, lecithin (0–5%, w/w), and vegetable oils (sunflower oil, olive oil, rapeseed oil (0–5%, w/w) were used to prepare edible coating solutions. Formulations were built gradually, and characteristics of coatings were evaluated by analyzing surface tension values and its polar and dispersive components, emulsion droplet size, and optical appearance in microscopic scale. The results obtained showed that 1.25% sodium alginate, 2% glycerol, 0.2% sunflower oil, 1% span 80, and 0.2% tween 40 or tween 80 can be used in formulation to obtain an effective coating for hydrophobic food surfaces. Three formulations were designed, and their stability (emulsion droplet size, optical characteristics, and creaming index) and wettability tests on strawberry showed that they could be successfully used in coating applications
The water vapour transmission rate (WVTR) of packaging materials and edible coatings is one of their critical parameters for the shelf life of many food products. The water vapour transmission rates of flat bodies such as films are determined by permeation measurements which are a steady-state method. Another method is based on water vapour sorption measurements which is a non-steady-state method. It can be used only for mono-material flat bodies. It allows using smaller sample areas compared to permeation measurements. However, not much is known about how well both methods correlate with each other. Therefore, the aim of this study was to compare the WVTR results of different materials determined by both methods. The results of both methods differed by up to factor of three, measured at identical samples. In a few cases the difference was up to factor five. The exact reasons for these differences are unknown. Nonetheless, the water vapour sorption method is a suitable method to determine the magnitue of order of the water vapour transmission rate but not its exact value.
Alginate is a naturally occurring polysaccharide used in the bio industry. It is mainly derived from brown algae species. Alginate-based edible coatings and films attract interest for improving/maintaining quality and extending the shelf-life of fruit, vegetable, meat, poultry, seafood, and cheese by reducing dehydration (as sacrificial moisture agent), controlling respiration, enhancing product appearance, improving mechanical properties, etc. This paper reviews the most recent essential information about alginate-based edible coatings. The categorization of alginate-based coatings/film in food packaging concept is formed gradually with the explanation of the most important titles. Emphasis will be placed on active ingredients incorporated into alginate-based formulations, edible coating/film application methods, research and development studies of coated food products and mass transfer and barrier characteristics of the alginate-based coatings/films. Future trends are also reviewed to identify research gaps and recommend new research areas. The summarized information presented in this article will enable researchers to thoroughly understand the fundamentals of the coating process and to develop alginate-based edible films and coatings more readily.
Edible coating based on sodium alginate solution was applied to fresh‐cut cantaloupe melon by dipping and vacuum impregnation coating methods. One aim of this work is to produce more technical information concerning these conventional and novel coating processes. For this purpose, the effect of various coating parameters (dipping time, draining time, time length of the vacuum period, vacuum pressure, atmospheric restoration time) with several levels on physical quality parameters (percentage of weight gain, color, and texture) of noncoated and coated samples were determined in order to define adequate coating process parameters to achieve a successful coating application. Additionally, the effects of dipping and vacuum impregnation processes were compared. Both processes improved the firmness of the melon pieces. However, vacuum impregnation application had higher firmness and weight gain results, and had significant effect (P < 0.05) on color (lower luminosity, higher redness, yellowness, and chroma values). Experimental results affirm that vacuum impregnation method can be used successively to improve mechanical and structural properties of food products.
The relative humidity level in the immediate vicinity of objects such as foods and technical items has an influence on transpiration and undesired relative humidity dependent reactions on their surfaces such as water vapour condensation, chemical reactions and microbial growth. Desirable are therefore materials that regulate the relative humidity to predefined levels in closed spaces such as in packagings and also in housing spaces. Such materials should be able to adjust the surface humidity of objects via water vapour diffusion in the gas phase without being in direct contact. A strategy to create such humidity regulating materials is the use of substances that absorb and desorb high amounts of water vapour, such as sodium chloride. Sodium chloride (NaCl) particles absorb water vapour at a relative humidity above 75% at 23 degrees C and then they form NaCl solution. NaCl solution desorbs water vapour when the relative humidity in the immediate vicinity decreases below the equilibrium relative humidity of that salt solution. Therefore, this system is able to regulate the relative humidity in its immediate vicinity. A strategy to provide free space in polymeric structures for the NaCl solution is the creation of cavities by foaming and stretching. However, only little knowledge exists about the influence of the combination of both processes on the functional properties of humidity regulating films with salt as active substance. Hence, the aim of this study was to investigate how and to which extend foaming and/or stretching affects the functional properties, i.e. water vapour sorption and mechanical properties, of polypropylene (PP) films containing NaCl particles. For this study, foamed and non-foamed PP with 3 and 6 weight-% NaCl were extruded into films. In the next step, some of these samples were biaxially stretched and their structures, water vapour absorption, porosities and mechanical strengths were analysed. The only-foamed films had a porosity of 0.3, the porosity of only-biaxially stretched films was between 0.1 and 0.2. The porosity increased to 0.7 when the films were first foamed and stretched afterward. Foamed and then stretched films with 6 wt.-% NaCl absorbed a high amount of water vapour from air with a value of 0.8 g H2O/g film at 97% relative humidity. Stretching of filled and non-filled foamed films also resulted in higher mechanical strength of the pure matrix polymer in comparison to the pure matrix polymer of non-stretched films. By the results of this study is shown that humidity regulating films with high water vapour sorption capacity can be produced via extrusion, foaming and stretching processes which are established processes in the polymer industry.