The influence of Aloe Vera gel incorporation on the

Research Article Received: 12 June 2017

Revised: 3 December 2017

Accepted article published: 27 January 2018

Published online in Wiley Online Library:

(wileyonlinelibrary.com) DOI 10.1002/jsfa.8915

The influence of Aloe vera gel incorporation on the physicochemical and mechanical properties of banana starch-chitosan edible films Magda I Pinzon,a* Omar R Garciaa and Cristian C Villab* Abstract BACKGROUND: Aloe vera (AV) gel is a promising material in food conservation, given its widely reported antimicrobial and antioxidant activity; however, its application in the formation of edible films and coatings has been small owing its low film-forming capability. The aim of this study was to investigate the physicochemical properties of film-forming solutions and films prepared using unripe banana starch–chitosan and AV gel at different AV gel concentrations. RESULTS: Our results showed that AV gel considerably affected the rheological and optical properties of the edible coatings, mainly due to increased amounts of solids brought by the AV gel. Film-forming capacity and physicochemical properties were also studied; most of the film properties were affected by the inclusion of AV gel, with decreased water vapor permeability, tensile strength and elongation at break. Fourier transform infrared studies showed that the inclusion of AV gel disrupts the interaction between starch and chitosan molecules; however, further studies are needed to fully understand the specific interactions between the components of AV gel and both starch and chitosan molecules. CONCLUSION: Our results suggest that the addition of AV gel creates a crosslinking effect between the phenolic compounds in AV gel and starch molecules, which disrupts the starch–chitosan interaction and greatly affects the properties of both the film-forming solution and edible films. © 2018 Society of Chemical Industry Keywords: Aloe vera gel; chitosan; banana starch; edible films

INTRODUCTION Edible coatings can be defined as thin layers of edible materials formed directly on a food product, usually by immersion of the food product into a solution of the coating material. On the other hand, an edible film is a pre-formed thin layer made of edible materials that are first molded as solid sheets and then applied as a wrapping on the food product.1,2 It has been demonstrated that both edible films and coatings can contribute to extending the shelf life of fresh fruits and vegetables by reducing moisture and solids migration, gas exchange respiration and oxidative reaction rates.1–4 Also, they have shown the capability to carry different active ingredients such as colorants, flavors, nutrients, and anti-browning and antimicrobial agents that can extend shelf life and reduce pathogen growth on food surfaces.5–7 These characteristics have made edible films and coatings one of the main research topics in food science in recent years. Edible films and coatings can be made from a vast array of materials, including carbohydrates, proteins, lipids or multicomponent blends. Among carbohydrates, native and modified starches are considered among the most promising materials because of their availability, price and good film-forming ability.8–10 Currently, increasing demand exists for starches with specific properties that have triggered the search for novel sources. An interesting source of starch are bananas (Musa paradisiaca), an important food crop J Sci Food Agric (2018)

extensively grown in tropical and subtropical regions around the world; unripe bananas have approximately 36% starch content and are easily available in local markets.11 Banana starch is known for its higher amylose content than potato, corn and wheat starch, and for its resistance to hydrolysis.12,13 Starch coatings tend to be odorless, tasteless, colorless, non-toxic, as well as semipermeable to moisture, gases (carbon dioxide and oxygen) and flavor components.8 Nevertheless, starch-based edible coatings have shown high water solubility and poor water vapor barrier due to their hydrophilicity.7,14 A compound that can be added to starch-based coatings is chitosan, a natural carbohydrate polymer obtained by deacetylation of chitin from the shells of crustaceans, such as crabs and shrimps.

∗

Correspondence to: MI Pinzon or CC Villa, Carrera 15 Calle 12 Norte, Universidad del Quindío, Armenia, Quindío, Colombia. E-mail: [email protected] (Pinzón); [email protected] (Villa)

a Programa de Ingeniería de Alimentos, Facultad de Ciencias Agroindustriales, Universidad del Quindío, Armenia, Quindío, Colombia b Programa de Química, Facultad de Ciencias Básicas y Tecnologías, Universidad del Quindío, Armenia, Quindío, Colombia

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© 2018 Society of Chemical Industry

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MI Pinzon, OR Garcia, CC Villa

Studies have shown the effect of chitosan addition to starch-based edible films and coatings, which mostly increases antimicrobial activity and changes mechanical proprieties (tensile strength and percentage of elongation).5,7,15–20 In recent years, Aloe vera gel has been studied as a potential component in edible films and coatings, which can extend the shelf life of different fruits and vegetables. The AV gel consists of approximately 99.5% water and 0.5% solids, which include polysaccharides (mainly cellulose, hemicellulose, glucomannan and mannose derivate), vitamins, minerals, enzymes, organic acids and phenolic compounds.21–23 For years, AV has been used for medical purposes as an anti-inflammatory agent and in the treatment of skin burns, frostbite and psoriasis, among others.24,25 On the other hand, the antimicrobial and anti-inflammatory effects of AV gel have been well established.26 In the food industry, the main use of AV has been as a source of functional foods, mainly in drinks and beverages.24 Aloe vera gels have been used as edible coatings by themselves or as additives to other coat-forming compounds (shellac, gelatin, chitosan and pectin) in the preservation of different fruits and vegetables. The results of these studies have indicated that AV reduces respiration rate, ethylene production, weight loss and softening, while maintaining other parameters, such as color and firmness.23,24,27–36 In this work, we studied the effect on the physicochemical, rheological, color and film-forming properties of AV gel incorporation on banana starch–chitosan film-forming solutions and edible films with potential use in the food industry.

2002). The starch presented the following composition: dry matter, 906 g kg−1 ; amylose, 303 g kg−1 ; protein, 3 g kg−1 ; fats, 4 g kg−1 ; ash, 1 g kg−1 .

MATERIALS AND METHODS Materials Low-molecular-weight chitosan with acetylation degree ≥75% (Sigma-Aldrich), food-grade sorbitol and citric acid (Tecnas, Colombia) were used. The AV gel was obtained from AV leaves purchased at local markets in Armenia, Colombia. Green bananas (Musa paradisiaca L.), known in Colombian local markets as platano guayabo, were purchased at local markets in Armenia, immediately after harvest in the month of July of 2015 (unripe with green skin). Unripe bananas were selected as their starch content is much higher than in ripe bananas. Starch isolation Banana starch (Musa paradisiaca L.) was isolated according to the procedure described by Espinosa-Solis et al.,37 with some modifications. Samples of green banana were peeled using a kitchen knife and cut into 2 cm slices and immediately dipped in citric acid solution (20 g L−1 ) for 5 min and blended for 2 min. The homogenate was then sieved and washed through screens (20, 40 and 60 US mesh) until the deionized wash water was free from solutes and suspended solids. The solution was left to decant for 8 h. The white starch sediments were dried in a Digitronic JP Selecta hot-air oven at 40 ∘ C for 48 h. The solids were ground with a pestle and passed through a sieve (100 US mesh), and placed in a sealed container and stored at room temperature until required. A compositional analysis of the isolated starch was carried using the following methods: dry matter by AOAC method 934.06 (AOAC, 1990);38 amylose content was determined using the colorimetric method proposed by Williams et al. (1970);39 protein analysis was carried out using method 960.52 (AOAC, 2002);40 fat content was determined using method 960.39 (AOAC, 2002) and crude ash content was determined using method 923.03 (AOAC,

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Aloe vera gel preparation Aloe vera leaves were washed with tap water, rinsed with distilled water and dried with a paper towel. Thereafter, the outer green skin layer was removed with a knife. The resulting AV parenchyma (AV gel) was washed with distilled water (40 ∘ C), dried using paper towels and blended for 3 min; it was then filtered using a cheesecloth in a vacuum to discard solid residues arising from cell walls. A compositional analysis of the obtained AV gel was carried out using the following methodology: dry matter by the AOAC method 934.06 (AOAC, 1990); protein analysis was carried using method 960.52 (AOAC, 2002); fat content was determined using method 960.39 (AOAC, 2002), and crude ash content was determined using method 923.03 (AOAC, 2002); titratable acidity expressed as malic acid was measured using method 942.15 (AOAC, 1990); total sugar content was measured using the anthrone method. AV gel presented the following composition: dry matter, 29.2 g kg−1 ; protein, 1.3 g kg−1 ; fat, 0.3 g kg−1 ; ash, 1.5 g kg−1 ; malic acid, 1 g kg−1 ; total sugars, 310 mg kg−1 of dry matter. Film-forming solutions preparation An appropriate amount of banana starch was dispersed in a sorbitol–water solution. This suspension was heated on a hotplate at 80 ∘ C with constant stirring for 45 min to accomplish complete gelatinization. An appropriate amount of chitosan was dispersed in 2% citric acid under gentle stirring at 35 ∘ C. The suspension was filtered through a cheesecloth to eliminate all the insoluble material. The edible coatings were obtained by adding the chitosan–citric acid solution to the gelatinized plantain starch–sorbitol suspensions and, when required, an appropriate amount of AV gel. The edible coatings were homogenized with magnetic stirring (1200 rpm) for 30 min. All the edible coatings studied have final component concentrations of plantain starch, 30 g L−1 ; chitosan, 20 g L−1 ; sorbitol, 10 g L−1 ; and different AV gel concentrations (100, 200, 300, 500 g L−1 ). Characterization of the film-forming solution Water activity (aw ) values were obtained using a Pawkit Decagon meter. Edible coating pH values were measured using a Methrohm 704 pH meter, previously calibrated. Dry matter content of the starch–chitosan–AV film-forming solutions was determined at 70 ∘ C by weight difference using a Precisa 301 M Swiss Quality Precisa Ha 300 infrared moisture meter analyzer. The rheological characterization of starch–chitosan and AV edible coatings was performed with an Anton Paar MCR 301 series rheometer using a parallel plate system (50 mm diameter) at 25 ∘ C. Rotational mode was used to investigate the time-related behavior of the starch–chitosan edible coatings at different AV concentrations. All the solutions studied were mathematically modeled with the Ostwald equation (Eqn (1)): 𝜏 = k𝛾 n

(1)

where 𝜏 is the shear stress, k is the consistency coefficient, 𝛾 . is the shear rate and n is the flow behavior index. Viscoelastic behavior of the edible coatings as a function of AV gel concentration was studied by performing dynamic assays. The linear viscosity range


J Sci Food Agric (2018)

Influence of Aloe vera gel incorporation on banana starch–chitosan edible films was determined in a stress sweep experiment (0–20 Pa) at constant frequency (1 Hz). Also, frequency sweeps (0.1–10 Hz) were performed at constant stress. Storage modulus (G′ ), loss modulus (G′′ ), tangent phase angle (tan 𝛿 = G′′ / G′ ) and the complex shear stress (G*) were obtained. Rheological (rotational and dynamic) tests were performed in triplicate for each solution. Color analysis of the starch–chitosan solutions (CIE lab color parameters L*, a* and b*, and total color difference, ΔE) was performed using a HunterLab ColorQuest XE spectrophotometer with D65 illuminant and 10∘ observer and a black tile background. Transparency of the starch–chitosan solutions as a function of AV concentration was measured as described by Mali et al.,41 using a Hewlett Packard UV–visible spectrophotometer (HP-8453 model). A 1% (w/v) film-forming solution was heated for 30 min (98 ∘ C) and cooled to room temperature, then transmittance (%T) at 650 nm was determined. All analyses were made in triplicate. Film-forming capability and film properties The film-forming capacity of the edible coatings was evaluated using the casting method. Approximately 20 g of the suspensions was cast onto Petri dishes (diameter 8.1 cm), dried in a hot-air oven at 70 ∘ C for 3 h and then maintained at 25 ∘ C until constant weight. Films were removed from the Petri dishes and stored at controlled temperature (25 ∘ C) and humidity (60%). Film thickness was measured using a Fowler electronic micrometer (0–25.4 mm) with 1.27 𝜇m precision. Ten measurements were taken in random locations of each film and the mean value was reported; all analyses were made in three different films. All measurements were made in triplicate. Transparency was studied via the Kubelka-Munk theory42 using the reflectance values of the films obtained in a HunterLab ColorQuest XE spectrophotometer with D65 illuminant and 10∘ observer at 𝜆 = 560 nm. The measurements were performed using black and white backgrounds. Film transparency is affected by the absorption (K) and dispersion (S) coefficients, both calculated using Eqn (2): )2 ( 1 − R∞ K (2) = S 2R∞ where R∞ is the reflectance of an infinitely thick layer of film. R∞ is calculated using Eqns (3), (4) and (5) in terms of the reflectance (R) of the film backed by a known reflectance background (Rg ). Rg corresponds to the reflectance of a totally white tile (HunterLab ColorQuest XE Instrument Standard: X = 80.27; Y = 85.18; Z = 90.14). R0 is the reflectance of the film with an ideal black background; a and b are mathematical terms used to facilitate the calculation of R∞ : R∞ = a − b (3)

a=

1 2

( ) R0 − R + Rg R+ R0 Rg b=

√

(4)

(a2 − 1)

(5)

Internal transmittance (T i ) was calculated using Eqn (6): √ ( )2 a − R0 − b2 Ti =

(6)

Edible film CIE L* a* b* values were obtained using a HunterLab ColorQuest XE spectrophotometer with D65 illuminant and 10∘ observer against a white tile background. J Sci Food Agric (2018)

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Water vapor permeability (WVP) was performed according to the ASTM E96-05 method. Films were placed in permeation cells and maintained in a controlled humidity cabinet at 65% relative humidity and 25 ∘ C for 48 h. The permeation cells were weighted at 1 h intervals during 8 h. WVP (g m−1 s−1 Pa−1 ) was calculated using the thickness of each film studied. Film solubility in water was measured using the method described by Shi et al.43 with some modifications. 2 cm × 2 cm pieces of each film were kept in a desiccator containing concentrated sulfuric acid until constant weight; then they were submerged in water with constant stirring at 25 and 95 ∘ C. After 6 h the film pieces were taken out and dried at 105 ∘ C until constant weight. Mechanical properties of the starch–chitosan–AV films were measured using a TA-XT Plus Stable Microsystems Texturometer with a tension grip system A/TG. Film samples were cut (2 × 7 cm). Tensile strength (TS; MPa) and elongation at break (%E) values were obtained. A 50 mm initial grip and a test speed of 5 mm s−1 were used. Fourier transform infrared (FTIR) spectra of the films were recorded using an attenuated total reflection (ATR) method in an IR Prestige 21 Shimadzu spectrophotometer. 200 scans were performed in the 4000–1000 cm−1 region. The thin films were applied directly onto ZnSe ATR Cell. Statistical analysis All experiments were carried out in triplicate and results were analyzed by multifactor analysis of variance with 95% significance level using Statgraphics® Plus 5.1. Multiple comparisons were performed through 95% least significant difference (LSD) intervals.

RESULTS AND DISCUSSION Physiochemical analysis Table 1 shows the mean values and standard deviations for the dry matter content, water activity (aw ) and pH of the starch–chitosan edible coatings with different concentrations of AV gel. As noted in Table 1, the incorporation of AV gel increased dry matter content (%) of the starch–chitosan edible coatings from 2.92 ± 0.1 to 3.15 ± 0.8 at 100 g L−1 AV gel concentration. Nevertheless, further increase of the AV gel concentration did not affect (P < 0.05) dry matter content values of the edible coatings. Table 1 also shows that increased AV gel concentration did not significantly affect aw values of the starch–chitosan film-forming solution; both of these results could be attributed to the small dry matter content of pure AV gel, which is only 1.3 ± 0.3%. Finally, Table 1 shows a decrease in the pH values of the starch–chitosan film-forming solutions with increased AV gel concentration. It has been reported27 that organic acids are responsible for up to 22% of the dry matter content of AV gel; thus adding AV gel to the starch–chitosan film-forming solutions increases their total acid content and lowers pH values. Rheological characterization Table 2 shows the rheological parameters obtained from rotational assays of the film-forming solutions at different AV gel concentrations. All solutions were adjusted to the Ostwald model exhibiting a pseudo-plastic shear thinning behavior (n < 1). Although, in general, the flow behavior of the film-forming solutions did not change with increased AV gel concentration, significant differences (P < 0.05) were present in the flow behavior index (n) as it was reduced considerably with the added AV gel. As shown in



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AV (g L-1 ) 0 100 200 300 500 AV gel

Dry Matter (g kg-1 )

aw

29 ± 1a 31 ± 1b 32 ± 1b 32 ± 01b 32 ± 5b 13 ± 3c

0.96 ± 0.01a 0.97 ± 0.02a 0.97 ± 0.02a 0.97 ± 0.02a 0.97 ± 0.01a 0.98 ± 0.01a

pH 4.1 ± 0.1a 4.1 ± 0.1a 3.9 ± 0.1b 3.8 ± 0.2b 3.8 ± 0.1b 3.8 ± 0.1b

(A) 1

Elastic modulus, G' (Pa)

Table 1. Dry matter content (g kg−1 ); water activity (aw ) and pH values of the banana starch–chitosan film-forming solutions at different concentrations of AV gel (g L−1 )


0,1

0,01

Means with different letters are significantly different in their respective column (P < 0.05). 1E-3 0,1

Table 2. Effect of increasing AV gel (g L−1 ) on the rheological properties of banana starch–chitosan film-forming solutions

0 100 200 300 500 AV gel

𝜂 ap (Pa s) (100 s−1 )

k (Pa s)n

n

0.36 ± 0.02a 0.33 ± 0.03a 0.33 ± 0.02a 0.23 ± 0.05b 0.11 ± 0.03c 0.01 ± 0.02f

1.11a 1.42b 1.75c 2.51d 2.54d 0.43e

0.68a 0.63a 0.58b 0.51b 0.48c 0.34d

R2 0.993 0.997 0.998 0.999 0.995 0.999

Means with different letters are significantly different in their respective column (P < 0.05).

Table 2, n values decrease from 0.68 to 0.48, indicating a more pseudo-plastic behavior of the film-forming solutions with the added AV gel. As shown in Table 2, the n values of AV gel are lower than all the film-forming solutions studied, indicating that as AV gel concentration is increased it becomes the main driving force in their rheological behavior. It has been reported44–46 that the pseudo plastic behavior of AV gel samples can be attributed to the presence of small bioactive molecules polymers (mostly acemannan), so as AV gel concentration increases in the film-forming solution the effect of the bioactive polymers is increased. This is also reflected in the consistency values (k) of the film-forming solutions. As shown in Table 2, k values increased as the AV gel concentration was increased – an expected behavior due to decreased n values and the increasing concentration of soluble solids. Finally, Table 2 shows the decrease of the apparent viscosity (𝜂 app ) from 0.33 Pa s (solutions without AV gel) to 0.11 Pa s (AV 500 g L−1 ) (P < 0.05). It has been reported that in starch–chitosan solutions the hydrogen bond interaction between the molecules plays an important factor in their rheological behavior and that interaction can be disrupted by the addition of different molecules.47 It is possible to think that as AV gel concentration increases in the film-forming solutions the different organic compounds disrupt the banana starch–chitosan interaction, leading to aggregates with smaller molecular weight and thus a reduction in 𝜂 app values. Figure 1 shows the elastic (A) and viscous (B) modulus of the banana starch–chitosan–AV gel film-forming solutions as a function of frequency. Table 3 shows the viscoelastic parameters of the film-forming solutions at different AV gel concentrations obtained from oscillatory assays, values taken at 100 rad s−1 . All the starch–chitosan–AV gel film-forming presented a viscous fluid behavior because all the viscous module values were larger than


10

100

Frequency (rad s–1)

(B)

Viscous modulus, G'' (Pa)

AV (g L−1 )

1

10

1

0,1

0,01

1E-3 0,1

1

10

100

Frequency (rad s–1)

Figure 1. Changes in the (A) elastic and (B) viscous modulus as a function of frequency of the banana starch–chitosan–AV gel film-forming solutions at different AV gel concentrations (g L−1 ). ( ) 0; ( ) 100; ( ) 200; ( ) 300; ( ) 500; ( ) AV gel.

those obtained for the elastic modulus (G′′ > G′ ). The difference between both modules increased as the AV gel concentration increased; for example, at 100 g L−1 AV gel the viscous module was almost nine times higher than the elastic one, and at 300 g L−1 the difference was 17 times higher. This is also evident as the damping factor (tan 𝛿) increases considerably as the AV gel concentration was increased. As the damping factor is expressed as tan 𝛿 = G′′ / G′ , it was expected that as the elastic modulus increased with respect of the viscous modulus the damping increased considerably. Table 3 also shows the values of the complex viscosity (G*) of the banana starch–chitosan–AV gel film-forming solutions. As shown in Table 3, G* values decreased from 5.51 to 0.36 Pa s. A similar trend was observed in the 𝜂 app values, shown in Table 2. The decrease in G* and 𝜂 app values as AV gel concentration was increased indicates that adding AV gel makes the film-forming solutions less viscous. Color characterization Color parameters L*, a* and b* of the starch–chitosan film-forming solutions as a function of AV gel are shown in Table 4. The L* values



Influence of Aloe vera gel incorporation on banana starch–chitosan edible films

Table 3. Viscoelastic properties of the banana starch–chitosan film-forming solutions as a function of AV gel concentration (g L−1 ). G′ and G′′ values taken at 100 rad s−1 AV (g L−1 )

G′ (Pa)

G′′ (Pa)

tan 𝛿

0 100 200 300 500 AV gel

0.724a 0.518b 0.378c 0.010d 0.002e 0f

5.47a 4.63b 3.81c 1.68d 1.31e 0.36f

7.55a 8.93b 10.08c 16.8d 52e 50000f

|G*| (Pa s) 5.51 4.66 3.82 1.69 1.31 0.36


Table 4. Color parameters and transparency (%T) of the banana starch–chitosan film-forming solutions at different AV gel concentrations (g L−1 ) AV (g L−1 ) 0 100 200 300 500

L*

a*

b*

ΔE

32.94 ± 0.4a 35 ± 1.2b 35.25 ± 0.8b 35.59 ± 0.4b 35.76 ± 1.1b

−0.06 ± 0.01a −0.09 ± 0.02 a −0.20 ± 0.04b −0.24 ± 0.1b −0.41 ± 0.1c

−0.11 ± 0.2a −0.41 ± 0.4b −0.73 ± 0.4b −0.83 ± 0.5b −1.44 ± 0.2c

– 1.10a 1.46a 1.81a 2.28b

T(%) 15.23a 7.48b 6.78c 5.63d 3.23e


increased from 32.94 to 35 with 10% addition of AV gel, indicating a more luminous solution. Nevertheless, the increased AV gel concentration from 100 to 500 g L−1 did not significantly change (P > 0.05) the L* values of the edible coating solutions. Both the a* and b* parameters with the first addition of AV gel (100 g L−1 ) showed a significant change (P < 0.05) from −0.06 to −0.09 and from −0.11 to −0.41, respectively. Another significant change was observed when the AV gel was increased to 500 g L−1 , with −0.41 for the a* parameter and −1.44 for the b* parameter; this change is reflected by an increase (P < 0.05) in the total color difference (ΔE), as shown in Table 4. Although the statistical results show a difference in the color parameters of 100 and 500 g L−1 with film-forming solutions with respect to coatings with no added AV gel, these changes were not visually significant. Table 4 also shows the transparency values of the film-forming solutions (T%). As shown in the table, transparency values of the film-forming solutions decreases considerably as AV gel concentration is increased. This behavior can be attributed to the increasing concentration of solids (organic acids and small dispersed bioactive polymers present in AV gel) in the film-forming solutions as AV gel is added. Film-forming capability and physicochemical characterization Thickness As seen in Table 5, AV gel concentration significantly (P < 0.05) affects the thickness of the films formed by the starch– chitosan–AV gel film-forming solutions, so that as AV gel concentration increased from 0 to 500 g L−1 , film thickness increased from 59.3 ± 0.2 𝜇m to 174.5 ± 1.5 𝜇m, respectively. It has been established that film thickness depends on the film composition24,48 ; thus it is possible to think that the dry matter increase observed J Sci Food Agric (2018)

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in the film forming solutions as a function of AV gel concentration (Table 1) is related to film thickness. Nevertheless, as shown in Table 1, AV gel concentration did not have a significant effect on the film’s dry matter content (P > 0.05). On the other hand, Silva-Weiss et al.47 reported that the addition of polyphenolic compounds to starch–chitosan blends films have a crosslinking effect that leads to increasing thickness. A similar behavior was observed by Gutiérrez and González49 in banana flour–AV edible films, attributed to the crosslinking effect of the polyphenolic compounds in AV gel with starch molecules. Mechanical properties Previous reports16 show that films made from starch–chitosan blends have higher elongation values than films made from either starch or chitosan alone, and that those values are affected by adding other components to the blend. Table 5 shows the tensile strength values (TS) of the starch–chitosan–AV gel edible films with different AV gel concentrations. As shown in Table 5, TS values did not significantly change (P > 0.05) with 100 g L−1 gel concentration; nevertheless, at higher concentrations these values decrease considerably from 9.7 ± 1.2 MPa at 100 g L−1 to 4.6 ± 0.4 MPa at 500 g L−1 . A similar behavior was observed in elongation at break values (%E), as shown in Table 5. Film %E was reduced as AV gel concentration increased from 30.3 ± 0.5% in films without AV gel to 10.4 ± 0.4% in films with 500 g L−1 AV gel concentration; however, the 0% and 10% films did not show a significant difference (P > 0.05). Khoshgozaran-Abras et al.24 observed that including AV gel in chitosan films has a threshold of 20%, after which TS and %E values decrease considerably, mainly attributed to the high moisture content of the AV gel, which has low plasticizing effect. These reports are consistent with Gutiérrez and González,49 who showed that the increasing concentration of polyphenolic compounds due to AV gel increasing concentration in banana flour–glycerol–AV gel films has a crosslinking effect between starch molecules, leading to more rigid films. Unripe banana starch is known for its high amylose content,12,37,50 which could lead to a strong interaction with chitosan molecules and thus a low %E of the edible films that is improved by adding sorbitol as plasticizer agent. It seems that the addition of AV gel has a crosslinking effect that lessens the plasticizing effect of sorbitol, thereby reducing the %E and TS values of the films. However, it seems to be a 100 g L−1 threshold in which the AV gel did not have a significant effect in the mechanical properties of the edible films studied. As mentioned before, the dry matter of AV gel is a complex mixture of glucomannan, amino acids and organic acids that creates a heterogeneous and complex matrix that may create specific interactions with both starch and chitosan molecules, which could contribute to the lessening of the plasticizing effect of sorbitol, but this needs further study to be completely understood. WVP and water solubility (WS) It has been established that edible film WVP depends to a large extent on the film composition, mainly on the ratio of hydrophilic and non-hydrophilic groups in the film, given that this ratio defines the film’s interaction with water.31,51 Table 5 shows the WVP of the starch–chitosan–AV gel films at different AV gel concentrations. As shown in Table 5, the addition of AV gel decreases the WVP values of the edible films from 2.85 ± 0.8 (109 (g Pa−1 s−1 m−1 )) in films without AV gel to 1.99 ± 0.2 (109 (g Pa−1 s−1 m−1 )) at 500 g L−1 . However, up to a 200 g L−1 threshold there was no significant difference (P > 0.05) between the values. Khoshgozaran-Abras et al.24



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Table 5. Thickness, mechanical properties, water vapor permeability (WVP) and water solubility (WS) of the banana starch–chitosan edible films at different AV gel concentrations (g L−1 ) WS (%) AV (g L−1 )

Thickness(𝜇m)

E(%)

TS(MPa)

0 100 200 300 500

59.3 ± 0.2a 73.5 ± 0.5b 81.4 ± 1.2c 135.4 ± 1.3d 174.5 ± 1.5e

30.3 ± 0.5a 29.5 ± 0.3a 23.4 ± 0.2b 16.3 ± 0.3c 10.4 ± 0.4d

10.5 ± 0.5a 9.7 ± 1.2ab 8.3 ± 0.8b 5.4 ± 0.5c 4.6 ± 0.4d

WVP × 109 (g Pa−1 s−1

25 ∘ C

m−1 )

2.85 ± 0.8a 2.45 ± 0.4a 2.44 ± 0.3a 2.11 ± 0.2b 1.99 ± 0.2b

95 ∘ C

35.3 ± 0.8a 36.3 ± 0.7ab 38.3 ± 0.8bc 40.3 ± 0.4c 45.2 ± 1.2d

37.3 ± 0.4a 38.3 ± 0.6a 40.1 ± 0.8c 42.4 ± 0.6d 48.3 ± 0.7e


Table 6. Color and transparency (K/S) values of the banana starch–chitosan edible films with different AV gel concentrations (g L−1 ) AV g L−1 0 100 200 300 500

L*

a*

b*

ΔE

40.90 ± 0.3a 40.72 ± 0.5a 40.46 ± 0.4 ab 40.24 ± 0.6 ab 39.37 ± 0.2b

−0.03 ± 0.01a −0.05 ± 0.02a −0.07 ± 0.02a −0.07 ± 0.03a −0.10 ± 0.05a

0.63 ± 0.02a 0.65 ± 0.04a 0.66 ± 0.04a 1.35 ± 0.02b 1.48 ± 0.03c

0.18 0.44 0.98 1.75

K/S 0.19 ± 0.04a 0.21 ± 0.02ab 0.25 ± 0.05 ab 0.3 ± 0.04b 0.42 ± 0.03c


reported that adding AV gel only significantly decreased the WVP values of the chitosan film at 50% concentration; those results were explained as the possible interaction between the AV gel components and chitosan molecules, which reduces the availability of the hydrophilic groups in chitosan to interact with water, reducing the WVP of the films. As previously explained, it is likely that the presence of AV gel disrupts the starch–chitosan by a crosslinking effect with the starch molecules, reducing the availability of the hydrophilic groups in starch and reducing the films’ WVP. Table 5 also shows the WS values of the starch–chitosan–AV gel films at 25 and 100 ∘ C. WS increased with AV gel concentration at both temperatures. Usually, edible films with low WVP tend to have a low WS, so it was expected that as the WVP values of the banana starch–chitosan–AV gel edible films decreased their WS also decreased. Nevertheless, it is necessary to note that most of the components of the AV gel (sugars, organic acids, amino acids) have a high WS, so they could be easily solubilized from the edible films, increasing their WS.

Color and transparency Color and transparency of edible films and coatings is an important factor in their application at industrial level; colorless and transparent films and coatings are preferred. Table 6 shows the L*, a*, b* and ΔE of the starch–chitosan–AV gel films. Color parameters of the edible films are only significantly affected (P < 0.05) at AV gel concentrations higher than 200 g L−1 ; this is especially notorious with a decrease in L* values and an increase in b* values, although none of those changes were visually significant. On the other hand, transparency values (K/S) were significantly affected (P > 0.05) by the AV gel concentration, mainly at concentrations above 300 g L−1 . The increase in K/S values can be interpreted as a reduction in film transparency, a behavior that can be attributed to increased solid content of the films due to higher amounts of AV gel.


FTIR spectral analysis FTIR spectroscopy was used to characterize the effect of AV gel incorporation in the interactions between banana starch and chitosan in the edible films. The FTIR results of banana starch, chitosan, banana starch/chitosan and banana starch–chitosan–AV gel edible films are shown in Fig. 2. For the banana starch edible films (Fig. 2A) the broad band at 3320 cm−1 was attributed to the vibrational stretches of the starch O—H groups. The 2905 cm−1 peak corresponds to C—H stretching, while the 1607 and 1400 cm−1 peaks correspond to the O—H of water. The chitosan edible film spectra (Fig. 2B) showed a broad band at 3363 cm−1 that corresponds to the O—H groups of chitosan and citric acid molecules in the film, while the peak at 2937 cm−1 was attributed to C—H stretching. The bands at 1583 and 1359 cm−1 were attributed to the N—H stretching of amide I and amide III, respectively. The peak at 1703 cm−1 can be attributed to the stretching of the citric acid’s carboxyl groups. It has been reported16,52 that the hydrogen bonding between the N—H and O—H groups of the chitosan and starch molecules shift the position of the chitosan amino group stretching. In the banana starch–chitosan edible films (Fig. 2C), the N—H stretching of amide I and amide III shifted to 1625 and 1430 cm−1 , respectively, while the intensity of amide I decreases; these changes indicate the starch–chitosan hydrogen bond interaction. Those two bands (amide I and amide II) shift again when AV gel is added to the edible film composition, indicating a change in the interaction between the starch and chitosan molecules. As shown in Fig. 2(D), the N—H stretching of amide I and amide III appears at 1617 and 1400 cm−1 , shifting to a lower wavenumber than in the banana starch–chitosan edible films (Fig. 2C), probably due to the crosslinking effect of the phenolic compounds in AV gel and starch molecules. On the other hand, Gutiérrez and González49 reported that the crosslinking of the AV gel phenolic compounds and starch molecules reduces the intensity of the O—H stretching band; a similar behavior is shown in Fig. 2,



Influence of Aloe vera gel incorporation on banana starch–chitosan edible films

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REFERENCES 1617 3265

1530

2914

1400

% Transmittance

(D)

3328

1625

2914 2914

(C)

1528 1430

3368 2937 1703 1583

(B)

3320

1607

2905

1528 1400

(A) 3600

1359

3200

2800

2400

2000

1600

1200

-1

Wavenumber (cm ) Figure 2. FTIR spectra of (A) starch; (B) chitosan; (C) starch–chitosan; (D) starch–chitosan–AV gel (300 g L−1 ) edible films.

as the intensity of that band is reduced in films with AV gel (Fig. 2D).

CONCLUSION The results presented in this paper indicate that adding AV gel to unripe banana starch–chitosan film-forming solutions has a considerable influence on the properties of the edible films obtained. This effect can be attributed to the different solids present in the AV gel. Rheological properties of the filmogenic solutions are affected as their pseudo-plastic behavior increases, while their apparent viscosity and elastic modulus values decrease. Our results suggest that the addition of AV gel creates a crosslinking effect between the phenolic compounds in AV gel and starch molecules, which affect the physicochemical and mechanical properties of the edible films formed by banana starch–chitosan–AV gel edible solutions. However, further studies concerning the specific interactions between the many components of AV gel and starch and chitosan molecules are needed.

ACKNOWLEDGEMENTS The authors want to thank Vicerrectoria de Investigaciones from Universidad del Quindio for the financial support of this work through Proyecto de Investigaciones 746. They also want to thank Facultad de Ciencias Agropecuarias, Programa de Quimica and FEDEPLATANO for their support. J Sci Food Agric (2018)

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