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Article

A Comparative Study on the Development of Bioactive Films Based on β-glucan from Spent Brewer’s Yeast and Pomegranate, Bilberry, or Cranberry Juices

by
Ionut Avramia
* and
Sonia Amariei
Faculty of Food Engineering, Stefan cel Mare University of Suceava, 720229 Suceava, Romania
*
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(5), 2807; https://doi.org/10.3390/app13052807
Submission received: 7 January 2023 / Revised: 16 February 2023 / Accepted: 20 February 2023 / Published: 22 February 2023
(This article belongs to the Special Issue Plants, Lichens, Fungi and Algae Ingredients for Nutrition and Health)
Browse Figures
Versions Notes

Abstract

:
This study provides new insight into developed bioactive films. The development of film-forming solutions from different fruit juices has demonstrated a major impact of bioactive compounds in film formulation, from smart packaging to bioactive packaging that releases the compounds from the oral solution at the same time as the packaged product. There were significant influences among independent parameters such as yeast β-glucan, gelling agent, fruit juice, or surfactant for each individual film. However, in this study, it was found that the amount of juice was the most significant factor in assigning their properties to all three types of films made of different juices (pomegranate, bilberry, and cranberry). Properties such as WVTR through the film varied within quite wide limits between 3.2562 and 32.1869 g/h·m2, while their solubilization time started from a few seconds for a complete dissolution or ensured only partial dissolution after 10 min of stirring (in the case of films made of β-glucan and cranberry juice). Therefore, natural biopolymer-based films developed with excellent water vapor barrier properties and improved solubility have a huge potential for application as packaging materials for dry powdered such as pharmaceuticals.

1. Introduction

From antibacterial properties to UV radiation protection, bioactive films are used in a wide range of applications [1,2], including for the antioxidant properties by supplementing compounds such as naphtho-γ-pyrone in film-forming solutions (FFSs) based on yeast cell walls [3] to the use of edible films as carriers of bioactive compounds [4] or the incorporation of lactic acid bacteria (LAB) producing bacteriocins into edible whey protein films for antimicrobial properties [5] and up to product packaging materials that dissolves into the oral solution formed with the product [6,7].
A new possibility for the development of bioactive films is the incorporation of different types of fruit juices into the film-forming solution to impart antioxidant and antimicrobial properties [8,9]. Suitable matrices of FFS can be represented by yeast cell walls [3,10] or β-glucans extracted by purification from the cell walls, with immunostimulatory effect.
The bioactivity of films developed from juices, compared to edible films, consists mainly of the high content of tannins and polyphenols such as in the following: pomegranate juice (Punica granatum L.) ellagitannins between 2010 and 6420 mg/L (up to 103 mg/L ellagic acid) and gallic acid up to 8.55 mg/L [11,12,13]; up to a 444.5 mg/100 g of anthocyanins in bilberry juice (Vaccinium myrtillus L.) and 65 mg/100 mL flavonols [14,15]; or about 59 compounds identified by Vilkickyte et al., (2022) in lingonberry (Vaccinium vitis-idaea L.) including quercitin, catechins, flavonols, and a phenolic content up to a total of 760 mg/100 g fresh weight [16,17].
With the synergistic action of pomegranate, bilberry, and cranberry juices, along with β-glucans from yeast, it confers antioxidant and antidiabetic properties, as well as immunomodulatory activity [17,18,19,20,21]. For example, in bilberries, it has been found that due to anthocyanosides, in case of vascular complications the fruit is used instead of leaves. For a daily intake of 25% anthocyanosides from the fruit extract, doses of up to 240–480 mg per day have been established [22]. In the case of cranberries, a consumption of 240 mL cranberry juice (45.7 mg polyphenols) daily for a period of 12 weeks was beneficial in the control of type II diabetes [21]. Vascular functions can also be visibly improved after a month of consumption of cranberry due to the high content of polyphenols (especially proanthocyanidins type A, anthocyanins, flavonols, and phenolic acids) [23]. Besides bilberry-derived bioactive compounds with hypoglycemic activity, pomegranate juice is also particularly valuable and can be used in the management of diabetes complications from vasoprotective effect to reduction in serum glucose levels. In a communication on how pomegranate juice acts on glucose metabolism, Carlos et al. (2022) summarized in a table up to 10 case reports on the effect of pomegranate juice in type II diabetes. These includes blood glucose reduction after consuming 200 mL for 4 days while another report revealed that after 4 weeks the PON1, an HDL-associated enzyme increased, helping to reduce total cholesterol [24]. Films developed from pomegranate extract, in addition to the antioxidant and antimicrobial activity, were shown to improve mechanical properties, thermal stability, and inhibited the activity of Penicillium digitatum [25].
β-glucans are described as high molecular weight polymers of glucose that can be isolated from oats, plants, bacteria, fungi, and yeast [26]. Depending on the source of origin, they can play roles ranging from dietary fiber (as in the case of β-glucans from oats) to anti-cancer, anti-inflammatory, and immune system stimulating roles (β-glucans from mushrooms and yeast) [27]. The benefits of using β-glucans isolated from yeast cells can be attributed to the ability to stimulate both the innate and acquired immune systems [28,29]. The valorization of spent brewer’s yeast through the extraction of β-glucans has a high economic potential, is well documented in the literature and promotes the circular economy [30,31]. Previously films made from yeast β-glucan were made for the improved mechanical properties given by the β-1,3/1,6 structure of glucans [32].
Fruit juices and β-glucan are incorporated into film-forming solution so it presents the active agents as components of films. Once they dissolve in the oral solution, it releases the active ingredients. Of course, some studies point out that the addition of bioactive compounds to the film-forming solution, without prior encapsulation of the active agent, will lead in a reduction in effectiveness and deterioration of bioactivities [33]. Regarding β-glucans, they are used especially in dry form in order to support the overall immune function [34] while studies on juices have shown that drying up to 80 °C maintains vitamins, antioxidant activity, and anthocyanins content in the same parameters as in the case of lyophilization [35,36].
The potential applications of β-glucan/juice-based films as packaging agents for pharmaceutical dry powders were investigated due to the antioxidant, immunostimulant, and antidiabetic properties. In this context, the present research was carried out to evaluate the bioactive films made of β-glucan and the three types of fruit juices in terms of uniformity of film thickness, moisture vapor transmission rate, water vapor permeability, and dissolution time.

2. Materials and Methods

2.1. Raw Materials and Chemicals

Pomegranate juice (BioAgros, Pella, Greece) (dw. 12.42%, pH = 3.03), bilberry juice (Vaccinium myrtillus L.) (dw. 11.5%, pH = 3.3), and cranberry juice (dw., 6.85%) were purchased from a local supermarket. β–glucan was extracted by the alkaline-acid method from spent brewer’s yeast provided by the SC. Bermas SA. brewery (Suceava, Romania). The alkaline process involved treating the autolyzed cells in a ratio of 1 to 5 (w/v) with a 1.5 N NaOH solution (at 90 °C for 2 h). The pellet resulted after centrifugation was treated with 1 N hydrochloric acid at 75 °C for 2 h for the elimination of amorphous substances. The β-glucans obtained were centrifuged, washed with distilled water and stored in the refrigerator until use. Chemical reagents from film composition were: Sodium alginate, Product No. 9180.1 (Carl Roth, Karlsruhe, Germany), Glycerin, Product No. G7893 (Sigma-Aldrich, St. Louis, MO, USA, ACS reagent ≥99.5%), Soybean oil (oil of genetically unmodified soybeans, Dachim SRL, Cluj, Romania).

2.2. Film Preparation and Casting

The film-forming solution was made in the following order. First, β-glucans were added up to a total content of 1.5 g dry weight (dw.), then the gelling agent (sodium alginate) was added in an amount of maximum 1 g while the various fruit juices were calculated in order a total amount of solid substance to not exceed 6 g in FFS. To this composition glycerin was also added as a plasticizer as 25% of the total solids while the 2% soybean oil was added for the bilberry and cranberry juice films. The film-forming solution was made up with distilled water at volume of 150 mL. The stirring time to homogenize was 30 min at 80 °C, then FFS was casted onto petri dishes and subjected to drying process for 48 h at 40 °C [37,38]. The overall chart flow is shown in Figure 1.
The development of β-glucan and pomegranate juice-based films was carried out according to an experimental design involving 15 experiments with three different levels for β-glucan, pomegranate juice, and sodium alginate (0.5–1.5 g; 10–30 mL and 0.2–0.6 g). In the case of films containing bilberry juice and cranberry juice, the incorporation of soybean oil was considered in order to observe changes in dissolution time. In the 7 samples of bilberry juice films, the sodium alginate remained constant at 0.8 g, while in the case of the cranberry juice films, the amount of SA was increased to 1 g due to increased juice content (between 36 and 43 g juice corresponding to 2.5–3 g dw.). The amount of yeast β-glucan did not exceed 1.5 g in all film-forming solutions.

2.3. Methods

2.3.1. Thickness

Thickness was determined with the thickness gauge PosiTector 6000 (DeFelsko, Ogdensburg, NY, USA). On each film, on the surface to be analyzed, such as WVTR or WVP, thickness was measured in ten different locations. The average of ten determinations (μm) was used in establishing the film properties.

2.3.2. Water Vapor Transmission Rate (WVTR)

WVTR tests (g/h · m2) were measured using the dry cup method according to the ASTM E96/96M method [39]. Circular pieces of the films were sealed horizontally on polystyrene petri dishes containing approximately 10 g of CaCl2 as the desiccant. The cups (with an internal 0% RH) were placed in an environmental chamber with a saturated solution of NaCl at the bottom, providing a 75% RH. The WVTR of the films was calculated by dividing the slope (the weight gain versus time) to the area of exposed film using the following equation:
W V T R = ∆ W ∆ t × A   ( g / h · m 2 )
where ∆ W/ ∆ t is the slope (g/h) and A represents the area exposed to the water vapor flux (m2).
The weight of the cups was measured every 8 h within 72 h. A number of ten data points over the 72 h time was provided for accurate information about the amount of water gain.

2.3.3. Water Vapor Permeability (WVP)

WVP describes how easily a film is penetrated by water vapor and was calculated by dividing the WVTR to water vapor partial pressure across the film and multiplying by the thickness of the film. The water vapor permeability at the specific RH chamber the follows the next equation:
W V P = W V T R × L ∆ p   ( g · m m / kPa · h · m 2 )
where WVTR is the water vapor transmission rate, L is the film thickness (in mm), and ∆ p is the water vapor partial pressure across the film (kPa) which is calculated according to:
∆ p = S · R 1 − R 2   ( kPa )
where S is the saturation vapor pressure of the water (3.1687 kPa), R1 is the RH inside the desiccator, and R2 is the RH inside the cup filled with CaCl2.

2.3.4. Dry Weight Determination

The percentage dry weight content was determined gravimetrically by referring to the dry substances which has held in an oven at 105 ± 1 °C. Samples were dried for at least 24 h followed by cooling in desiccator prior to weighing [40].

2.3.5. Dissolution Time

The film samples were cut into squares of 2 × 2 cm, immersed in 50 mL of distilled water, and then vigorously shaken. The dissolution time was determined when the film dissolved and no visible fragments were found in suspension. The dissolution time (min) was recorded using a chronometer [41].

2.3.6. Scanning Electron Microscopy (SEM)

SEM images were recorded by using a scanning electron microscope (VEGA II LMU, Tescan, Brno, Czech Republic). For higher depth of field, a secondary electron detector was used at an accelerating voltage of 30 kV.

2.3.7. Optical Properties of the Film Samples

The absorption and transmission spectra in the 200–800 nm region of bioactive films was investigated by means of a UV-Vis-NIR Shimadzu 3600 spectrophotometer (Tokyo, Japan). Each sample (1 × 4 cm) was placed directly in the side of spectrophotometer cell and an empty cell was used as reference. The ability to block UV radiation is crucial for materials used in food packaging. UV penetration into food can cause unwanted chemical changes, such as the creation of unpleasant odors, by forming free radicals and their derivatives. By reducing the amount of light that passes through the packaging, the rate at which photo-oxidation occurs in food products can be slowed down [42].

2.3.8. Statistical Analysis of the Results

The data was processed by using XLSTAT software for Excel 2022 version (Addinsoft, New York, NY, USA). Significant differences between samples were considered at p < 0.05 by applying Tukey test.

3. Results

The order of development and examination of β-glucan-based films from yeast was as follows. First, 15 films were developed from β-glucan and pomegranate juice following a Box–Behnken optimization of response surface methodology. After identification of the optimal composition and validation of the data by laboratory tests on the developed films, acceptable properties for packaging products of powdery nature were observed [37]. The standard errors of the design are shown in Figure 2. As a result of the preceding analysis results, it was decided, in order to facilitate rapid dissolution, to use a surfactant at a concentration of 2% (soybean oil) in the development of the β-glucan and bilberry juice films [38]. For a comparative study, it was considered to make four control films without soybean oil. In the last stage of the research, the amount of solids in the FFS of films designed with β-glucan and cranberry juice was increased to 5 g, with the use of soybean oil in half of the samples, keeping the plasticizer at 25% of the total solids and increasing the gelling agent (sodium alginate) to 1 g in each film. For statistical analysis, data were determined in triplicate, the exception was the determination of the thickness, which was measured in 10 points for the accuracy of measurements.
Figure 2 shows the standard error of the design of the 15 experimental runs. The largest standard errors at the edges of the design space were found between the parameters β-glucan and pomegranate juice, respectively, and β-glucan and sodium alginate. Therefore, based on the figure, the measured root mean square error of the design space were relatively low, with values between 0.5 and 1.2 suggesting the model is expecting to provide reasonable prediction.

3.1. The Gelling Agent Characterization in Order to Obtain the Film-Forming Solution

Extremely important in making films is the sizing of the gelling agent so that the film-forming solution (FFS) is not too viscous. An instability of the polymer solution can occur by the deviation from the Cox–Merz rule which is attributed to high content of sodium alginate. Mancini et al., (1996) by investigating polymeric alginate solutions, concluded that, to fit into a pseudoplastic behavior, sodium alginate solutions should be between 0.125 and 1.5% (w/v) (on a temperature range of 5–35 °C) [43]. Thus, for the preparation of the films, the highest amount of sodium alginate used was 1 g in 150 mL of film-forming solution, an amount that would comply with the Cox–Merz rule and corresponding to a maximum of 0.66% (w/v). For data veracity, a separate solution with the highest amount of sodium alginate of 1 g in 150 mL of distilled water was subjected to rheological analysis (Haake Mars 40 rheometer, ThermoHaake, Germany, plate-plate geometry, 80/40 mm, 2 mm distance between plates). The results of the analysis are highlighted in Figure 3a,b by flow curves.
As can be seen in Figure 3a, the viscosity profile of the polymer solution (blue flow curve) is a descending one, as the applied shear stress increased (non-Newtonian behavior), in the first 0.1 s a steep decrease in the viscosity value was observed. On return, by decreasing the shear rate, the viscosity remained constant without any dilatancy. This pseudoplastic behavior leading to fluidization of the polymer system upon shear is particularly important in the dosing and dispersion of ingredients in a FFS when it is subjected to mixing, having an influence on film formation. From the rheological analysis we can conclude that the sodium alginate solution obeys the Cox–Merz rule, where the viscosity (η, mPas) is dependent on the shear rate (ɤ, 1/s) [44]. Studies of film-forming solutions with sodium alginate as gelling agent and pullulan (another type of glucan) it has been observed an overlapping of the pullulan chains with the formation of a transient network while the polymer chains of sodium alginate adopted a cross-linked network [45]. Further, Figure 3b gives details of the elastic modulus and viscous modulus of the sodium alginate solution. As can be seen, the viscous modulus (G”) exhibited values significantly higher than the elastic modulus (G’) until the end of the linear viscoelastic range (LVR), indicating that the polymer solution exhibits a viscous character. Both moduli (G’ and G”) are a function of frequency (Hz), and by gradually increasing both with frequency, information about the structure of the polymer gel is provided. Thus, at low frequencies (10−1 Hz) the polymer chains had more time to relax and form entangled chains but with increasing frequency towards 10 Hz the alginate chains unravel into random anchors [46].

3.2. Film Thickness

The thickness of the films was mostly influenced by the amount of dry matter in the film-forming solution. As can be seen in Figure 4, the optimization process of the pomegranate juice films, nor the addition of soybean oil to the bilberry or cranberry juice films, did not show a significant influence on the thickness, which was below 150 μm. Generally, edible films intended for packaging are within the thickness values between 31.2 μm [47] and 300 μm [48] with an average around 150 μm in order to achieve a uniform distribution of compounds from the FFS stage [49,50,51]. The maximum and minimum values are found in films with the highest amount of juice and solids with a peak at 147.3 μm in Sample 11 and, respectively, the lowest value at a low amount of solids at Sample 2 with 64.4 μm containing 0.5 g BG, 0.4 g SA, 1.24 g PJ.
Figure 4b presents a cross-section image taken with the scanning electronic microscope (SEM). This technique is also often found in the scientific literature for film thickness measurement, although it is usually used for thin films [52,53]. Moreover, the uniform surface structure of the top of the film demonstrates good compatibility between β-glucan, sodium alginate and juice. In the cross-section, there are no pores or transverse microcracks, indicating a homogeneous interaction between the plasticizer and the polymers.

3.3. Water Vapor Transmission Rate (WVTR)

The barrier capacity of the film expressed by the amount of water vapor that can permeate per one unit of material area for certain time is particularly important in packaging (and especially for dry products that can absorb moisture from the external environment). The following figure shows the tendency of the rate of the water permeating through the film which occurs when water vapor diffuses from a higher partial pressure to a lower partial pressure [54]. From Figure 5, it can be observed with red line the WVTR trend of the film samples. In the case of the film optimization process of β-glucan (BG), sodium alginate, and pomegranate juice, high values can be observed. Of course, the highest value of all three types of films developed from different juices was found in this case at Sample 3 with 32.1896 g/h · m2 having 0.5 g β-glucan content, 0.4 g sodium alginate (SA), and 30 mL (3.73 g dw.) pomegranate juice (PJ) [37]. From Sample 17, an abrupt decrease in the WVTR values was observed for the bilberry- and cranberry-based films. The lowest value of WVTR was found in the Sample 19 with 3.2562 g/h · m2 containing 1 g BG, 0.8 SA, 20 g bilberry juice (BJ) [38]. In the case of films made of β-glucan/cranberry juice, with the highest amount of dry weight and the highest sodium alginate content, a minimum WVTR value of 7.6918 g/h · m2 was identified. A drop in the WVTR values it could also be observed by the addition of soybean oil to the films based on bilberry and cranberry juices (Sample 18, 23, 25 and 27), compared to control samples (Sample 17, 22, 24 and 26). In all analyzed samples the amount of β-glucan no more than 1.5 g (dry weight) was added in the film-forming solution and varied at 0.5, 1 and 1.5 g. Sodium alginate did not exceed 1 g and the amount of plasticizer (glycerin) was 25% of total solids. However, such large differences between WVTR values (from 32.1896 to 3.2562 g/h · m2) can only be explained by the change in juice in FFS.

3.4. Water Vapor Permeability (WVP)

The WVP results of the films (Figure 6a) showed values between 0.1057 and 1.8657 g · mm/kPa · h · m2. A fairly strong positive relationship with a correlation coefficient of 0.8 was observed between WVP values and film thickness. The lowest value found in Sample 17 showed a thickness of 66.43 μm while the highest vapor flux through the film was found at Sample 11 with 147.3 μm thickness made of 30 mL PJ (3.73 g dw.), 1 g BG, 0.6 g SA [37]. The WVP results of the β-glucan/cranberry juice films (between 0.3523 and 0.3782 g · mm/kPa · h · m2) are higher than β-glucan/bilberry juice films but in comparison with the scientific literature, Severo et al., (2021) after the development of films based on cranberry extract and chitosan for the antibacterial properties found values between 3.71 and 4 ( × 10−12 mol · m/m2 · s · Pa) [51]. Owning that 1 mole of water weighs 18.01 g we can deduce that the values found for WVP by the authors were between 0.2405 and 0.2593 g · mm/kPa · h · m2, close to our values. Azeredo et al., 2016 determined that a high pomegranate juice content in films will increase WVP values due to the plasticizing effect of sugars by adding significant amounts of juice and decreasing the concentration of the polymer matrix that weakens the films. The highest value found in that study was 10.91 g · mm/kPa · h · m2 [55]. Of course, by all of three types of films made, it was found that the highest value of WVP was found in films based on pomegranate juice with 1.8657 g · mm/kPa · h · m2 and 30 mL juice added. An innovative aspect that improved water vapor permeability was the addition of β-glucans to the films of various juices. It was observed in previous studies on films made of β-glucan/pullulan that the WVP values does not exceed 1.2 g · mm/kPa · d · m2 [56]. In addition, films made of cranberry pomace extract, low methoxyl pectin, and glycerin showed increased values of 68.5 g · mm/kPa · d · m2 (2.85 g · mm/kPa · h · m2) compared to our samples that included β-glucans [57].
Based on the five stages for the gas transport described by Crank and Park (a diffusion surface layer of the side with higher concentration of penetrants, the absorption of the gas, diffusion the gas through the polymer of a certain thickness, desorption of the gas to the side with lower concentration of penetrant and diffusion of the gas [58]) in films based on pomegranates, bilberries, and cranberries juice, the composition and thickness of the layer are the only parameters that differs, whereas the rest of the parameters such as the surface of the film and the pressure on the two layers remained the same.
However, another factors that affects the WVP values between samples are represented by the integrity of the film, hydrophilic-hydrophobic ratio, crystalline–amorphous ratio, or the polymeric chain mobility [60]. In the present study, in all 27 samples the FFS was a homogeneous mixture and the films showed uniformity, without coarse particles or air bubbles in the mass of the film. The plasticizer with the hydrophilic nature (glycerin) was kept at 25% from total solids while the addition of soybean oil did not show linear association with WVP (r = 0.09). The main use of glycerin was to impart flexibility and enhance toughness for films. In the absence of a plasticizer, the longitudinal microcracks visible in the cross-section of Figure 6b can initiate and over time it can lead to film breakage [61,62].

3.5. Dissolution Time

Depending on the destination of the packaged product, the films must fit within a certain time of solubilization to allow the release of the contents from the package. In the present study, films were intended for the packaging of dry powdered products that dissolves in the oral solution, thus the dissolution time must be as short as possible. As can be seen in Figure 7, the optimization process of β-glucan/pomegranate juice films managed to provide an optimal time of 4.5 min (Sample 16), taking into account a high content of juice compounds (1.74 g dw.), low WVTR, and WVP values.
On the other hand, in the case of β-glucan/bilberry juice films, if a surfactant was added to the film-forming solution, a halving in the dissolution time was found from the 1.45 min in Sample 22 to 0.55 min at Sample 23 which contains a surplus of only 0.092 g soybean oil (2% of total solids) [38]. Besides soybean oil, the amount of bilberry juice had a significant influence (p < 0.05) on the dissolution time. The blend compatibility of the natural compounds from the fast-dissolving film, the non-toxic, non-irritating and hydrophilic nature of juices make developed films an advantageous alternative to release the drugs [63]. Interestingly, in the case of β-glucan/cranberry, even after 10 min of shaking, a complete dissolution was not achieved. The use of soybean oil was also taken into account but without visible results. One possible explanation is that the gelling agent was increased to 1 g (SA) in all samples and the juice that was added at 36.49 and 43.79 g CJ (6.85% w/w) to reach 5 g of total solids in FFS. Another explanation could be the newly formed intermolecular bonds between polymer chains or the interaction between polyvalent cations from juice (such as calcium) that forms strong gels up to insoluble polymers [64,65].

3.6. Color and Optical Properties of the Film Samples

The color of the films is largely derived from the color of the juices introduced into the FFS. Only in the case of films made from bilberry juice there is an exception where the pH influences color changes because of the anthocyanins [66]. This property is widely used to the intelligent films for detection the food freshness [67,68].
As can be seen in Figure 8d–f, optical properties in the UV-VIS region were recorded for the representative samples. In the 200–400 nm region, the transmission was close to zero, sign that ultraviolet radiation was blocked by the film. With increasing the wavelength, transmittance increases and visible radiation penetrates through the film. It should be noted that, due to the intense red coloring given by the anthocyanin pigments such as cyanidins and peonidins from cranberry, a peak can be seen in the 500–600 nm region downward in the transmission of radiation in the visible range (arrow marked with 1 in Figure 8f). This shows us that films developed from β-glucan/cranberry juice absorb to some extent the green radiation of the visible spectrum.

4. Conclusions

Bioactive films based on β-glucan and pomegranate, bilberry, or cranberry juice have been successfully developed. The results obtained in the order of film development (pomegranate, bilberry, and cranberry) showed differences in WVTR, WVP, solubilization time, and color.
The rheological study on the polymeric solution of sodium alginate (gelling agent) revealed a pseudoplastic behavior, leading to fluidization of the polymer system. This non-Newtonian behavior is particularly important in the dosing and dispersion of ingredients in a film-forming solution when subjected to mixing.
Film thickness was dependent on the amount of solids introduced into the film-forming solution as well as whether a constant layer thickness was maintained during casting. No more than 6 g of solids were added to the film-forming solution and the casting was conducted uniformly to obtain films below 200 μm thickness.
As the amount of sodium alginate increases, the WVTR decreases, but it increases when a higher concentration of juice was added. The hydrophobic nature of soybean oil decreases WVTR values to a small extent. In the case of the films with the highest amount of sodium alginate (1 g), a minimum WVTR of 7.6918 g/h · m2 was found, while the highest value of 32.1896 g/h · m2 was identified at a value of 0.4 g of SA and 30 mL of juice.
WVP was dependent on film thickness. The lowest WVP value was found in bilberry juice-based films (0.1057 g · mm/kPa · h · m2) followed by cranberry juice (0.3523 g · mm/kPa · h · m2) and finally in pomegranate juice-based films.
The addition of soybean oil to bilberry juice films reduces the dissolving time by half. The most noticeable effect of increasing the amount of sodium alginate and juice was to reduce solubility that has been found in films made from cranberry juice. Fast-dissolving films showed stability against water vapor, acceptable thickness, and no visible cracks in the film mass
Considering the results of the current study, the amount of juice and gelling agent are an important factor in attributing the physicochemical properties to bioactive films.

Author Contributions

Conceptualization, S.A. and I.A.; methodology, I.A. and S.A.; software, I.A.; validation, S.A. and I.A.; formal analysis, I.A.; investigation, I.A.; resources, S.A.; writing—original draft preparation, I.A.; writing—review and editing, I.A.; visualization, I.A.; supervision, S.A.; project administration, S.A.; funding acquisition, S.A. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by Ministry of Research, Innovation and Digitalization within Program 1—Development of national research and development system, Subprogram 1.2—Institutional Performance—RDI excellence funding projects, under contract no. 10PFE/2021.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study can be provided on request.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Figure 1. Flowchart of the production of bioactive β–glucan/juice films.
Figure 1. Flowchart of the production of bioactive β–glucan/juice films.
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Figure 2. 3-D surface plot of the standard errors of the design of experiments.
Figure 2. 3-D surface plot of the standard errors of the design of experiments.
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Figure 3. (a) Rheological behavior of sodium alginate solution, η−viscosity function, mPas; r−shear stress, Pa; ɤ−shear rate, 1/s; (b) Elastic modulus (G’) and viscous modulus (G”) in scan tests as a function of frequency (Hz).
Figure 3. (a) Rheological behavior of sodium alginate solution, η−viscosity function, mPas; r−shear stress, Pa; ɤ−shear rate, 1/s; (b) Elastic modulus (G’) and viscous modulus (G”) in scan tests as a function of frequency (Hz).
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Figure 4. Film thickness. (a) The thickness of the films related to the composition of the FFS; (b) 2-D SEM image of a cross-section film made from BG, SA and PJ. Values followed by different letters are significantly different at p < 0.05.
Figure 4. Film thickness. (a) The thickness of the films related to the composition of the FFS; (b) 2-D SEM image of a cross-section film made from BG, SA and PJ. Values followed by different letters are significantly different at p < 0.05.
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Figure 5. (a) WVTR tendency of the β-glucan, sodium alginate and juices films; (b) Experimental model of dry cup with CaCl2 as desiccant according to ASTM (4 mm air gap). Values followed by different letters are significantly different at p < 0.05.
Figure 5. (a) WVTR tendency of the β-glucan, sodium alginate and juices films; (b) Experimental model of dry cup with CaCl2 as desiccant according to ASTM (4 mm air gap). Values followed by different letters are significantly different at p < 0.05.
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Figure 6. (a) Water vapor pressure tests of the films; (b) Cross-section SEM of a film obtained and the diffusion zones, adapted after [59]. Values followed by different letters are significantly different at p < 0.05.
Figure 6. (a) Water vapor pressure tests of the films; (b) Cross-section SEM of a film obtained and the diffusion zones, adapted after [59]. Values followed by different letters are significantly different at p < 0.05.
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Figure 7. (a) Dissolution time of the films; (b) Image of suspended β-glucan/cranberry juice particles in solution after dissolution tests. Values followed by different letters are significantly different at p < 0.05.
Figure 7. (a) Dissolution time of the films; (b) Image of suspended β-glucan/cranberry juice particles in solution after dissolution tests. Values followed by different letters are significantly different at p < 0.05.
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Figure 8. (a−c) Images of the films made of pomegranate, bilberry and cranberry juice; (d−f) Optical properties of the β−glucan/ juice films.
Figure 8. (a−c) Images of the films made of pomegranate, bilberry and cranberry juice; (d−f) Optical properties of the β−glucan/ juice films.
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Avramia, I.; Amariei, S. A Comparative Study on the Development of Bioactive Films Based on β-glucan from Spent Brewer’s Yeast and Pomegranate, Bilberry, or Cranberry Juices. Appl. Sci. 2023, 13, 2807. https://doi.org/10.3390/app13052807

AMA Style

Avramia I, Amariei S. A Comparative Study on the Development of Bioactive Films Based on β-glucan from Spent Brewer’s Yeast and Pomegranate, Bilberry, or Cranberry Juices. Applied Sciences. 2023; 13(5):2807. https://doi.org/10.3390/app13052807

Chicago/Turabian Style

Avramia, Ionut, and Sonia Amariei. 2023. "A Comparative Study on the Development of Bioactive Films Based on β-glucan from Spent Brewer’s Yeast and Pomegranate, Bilberry, or Cranberry Juices" Applied Sciences 13, no. 5: 2807. https://doi.org/10.3390/app13052807

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