Osorio, Samara Dias

Santana, Ruth Marlene Campomanes

English

Lume 5.8

INFLUENCE OF PH ON THE HYGROSCOPICITY OF BLENDS OFGELATIN AND POTATO SKIN STARCHSamara D. Osorio¹*, Ruth M. C. Santana¹1 - Department of Materials, Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazilsamara.osorio@ufrgs.brAbstract - Biodegradable blends of agricultural origin are exciting alternatives to conventional polymers from fossilsources. In addition, the use of organic waste, such as potato skin, is a way to develop products with higher added value,contributing to the environment. Thus, in this work, starch (A) was extracted from potato skins to produce blends, inwhich commercial gelatin (G) was also used as raw material. The G/A blends (50:50) were made via casting at thenatural pH 5 of the filmogenic solution and neutral pH, which are later submitted to the contact angle and moistureanalyses.The results showed that the mixture showed a hydrophobic trend, with greater stability to moisture at acidicpH.Keywords: Blend, starch, gelatin, pH, hygroscopicity.IntroductionDisposable plastic packages, usually products of petrochemical origin, are considered anenvironmental problem due to their chemical inertness and low-density characteristics, whichgenerate large volumes, and can take more than hundreds of years to degrade [1]. And, even whendegraded, plastics are still present as smaller parts invisible to the naked eye, called microplastics,which contributes to being one of the leading environmental problems today [2]. Given this, thesearch for more sustainable alternatives has been growing, in which biodegradable polymers aregaining more and more space in research and the market [3]. Among the new materials studied inthe literature, biodegradable polymers of agricultural, microbiological, and biotechnological originhave been attracted attention [4].Polysaccharides, proteins, and lipids are some materials derived from agricultural origin thatstand out, mainly due to their availability, low toxicity, biodegradability, filmogenic characteristics,in addition to their low cost [4]. In general, pure films based on starch or protein, such as gelatin, donot show very encouraging results due to the hydrophilic character of these polymers [5]. For thisreason, polymer blends emerge as an exciting alternative to improve the properties of pure filmssince it is possible to make the combined use of polymers, with the advantages of each of thecomponents [6-10]. Thus, the resulting blend basically depends on its composition, interactions, andprocessing method [8].In Brazil, potatoes are planted and harvested throughout the year based on demand and thecountry's appropriate weather conditions [11]. Despite being the fourth food source of humanity[12], this polysaccharide can present, in harvest times, a total produced much higher thanconsumed, generating an oversupply and consequently transforming it into organic waste. Thelatter, in turn, has enormous potential, as it is formed by starch, cellulose, hemicellulose, lignin, andimpurities [13], and can be used in the production of new products with higher added value [14].Thus, the objective of this work was to produce blends of gelatin and starch extracted from potatoProceedings of the 16th Brazilian Polymer Conference (16° CBPOL), October 24-28, 2021, Ouro Preto-MG, Brazil 948skins, in the proportion 50:50, at natural and neutral solutions pHs. This work also assesses theeffect of this pH variation on the hygroscopic properties of the blend.ExperimentalIn this work, commercial gelatin type B and starch extracted from potato skins (Solanumtuberosum) were used as polymeric matrix components. Glycerol was used as a plasticizer, water asa solvent, and sodium hydroxide (NaOH) 2 M as pH adjuster.Starch extraction began with washing the potato skin in running water and sodiumhypochlorite (NaClO), at a concentration of 20 mg/L, for 10 min. It is then followed by amechanical process of grinding, filtering, and decanting, based on the method used by Fernandes[15] and Mahecha [16]. The extracted (hydrated) starch stayed in an environment with a controlledtemperature of 60 ºC for 24 h so that the water would evaporate, leaving only the starch.The blends were obtained by Casting, in triplicate, in which the individual filmogenicsolutions were produced. The gelatin solution was obtained by hydrating 10 g of gelatin in 100 mLof distilled water for 1 hour. The starch solution was prepared using 3 g of starch in 100 mL ofdistilled water. These solutions were heated at 85 °C individually for 10 minutes for gelatin and 3minutes for starch, followed by the addition of the plasticizer. It was added 20 % of glycerolconcerning the dry mass of the raw materials under magnetic stirring until homogenization. Then,the volumetric mixture of the solutions was performed, using 15 mL of gelatin solution and 15 mLof starch solution, forming the blend. PH was adjusted when necessary The 50:50 mixture washomogenized for 15 min at 85 °C, distributed in 25 cm x 18 cm plates, placed in a laboratory ovenat 30 °C for 24 h to form the films, and finally to a desiccator for another 24 h.Film thicknessThe average thickness of each blend considers three measurements that were performed atdifferent and random points of the films using a micrometer, Mainard brand, and model M-73010.Contact angleA camera provided with focus adjustment and light source was used to project the images,following an adaptation of the ASTM D 7334-08 standard [17]. Samples with 5 cm x 2.5 cm werepreviously stored in a desiccator 1 h before testing. Then, the films were positioned 3 mm awayfrom the syringe needle tip, which contained deionized water. Ten drops of deionized water weredripped on each sample, photographed 3 seconds after application to assess the stability of thematerial. The measurements were performed in triplicate, using the Surftens software.MoistureA saline solution saturated with sodium chloride (NaCl) with a relative humidity of 75%,following the ASTM E 104-02 [18], was used to determine the moisture of the blends. Samples of 2cm x 2.5 cm, in triplicate, were placed in the laboratory oven at 60 °C for 1 h and then in thedesiccator for 24 h. After the first weighing, the samples were placed in previously weighedcontainers, whose saline solution was already prepared in accordance with the standard above.These containers were kept in the laboratory oven at 30°C throughout the test. The sample masswas monitored for a total period of 99 h, and the moisture calculation was made based on the massdifferences.Digital microscopeThe film surface images were obtained by a digital microscope, brand Cityhua, with 1000 x.Results and DiscussionProceedings of the 16th Brazilian Polymer Conference (16° CBPOL), October 24-28, 2021, Ouro Preto-MG, Brazil 949Thickness and contact angleTable 1 shows the results for the average thickness of the plasticized gelatin/starch blendsand the contact angle values obtained.Table 1. Average thickness and contact angle of gelatin/starch blendsBlend G/A50:50pH Average thickness (µm) Contact angle (º)G/A - 5 5 60 ± 5 91.12 ± 1.27G/A - 7 7 52 ± 8 91.38 ± 2.30It was possible to observe that the blends did not show a significant variation in thicknessaccording to changes in pH. Al-Hassan and Norziah [8] found similar thickness values, between 50and 70 µm, for starch/gelatin blends.Also reported by Acosta et al. [9], in plasticized films ofcassava starch and bovine gelatin.According to the contact angle results obtained, it was noted that the blends presentedhydrophobic characteristics since the values were higher than 90º [19]. Similar results were reportedby Nunes [20], in starch blends with tilapia and bovine gelatin. Likewise, Zhang et al. [10] observedthat their blends of corn starch and commercial gelatin had angles around 110º for all studiedblends. Fig. 1 shows the drops formed in the G/A blends, both rounded, indicating theirhydrophobicity and corroborating the numerical data found.Figure 1. Images of droplets formed on G/A films at pH 5 and 7 (from left to right)The contact angle indicates the material's wettability and, according to Nunes [20], it can beinfluenced by the presence of polar and non-polar groups on the surface, as well as by the material'sporosity and surface roughness. In addition to other factors such as swelling or deformation whenabsorbing moisture. In this way, the material is said to be suitable or not for a particular application.Thus, it can be seen that the studied blends did not present a less polished, rough appearance, whichcould arise due to the presence of fibers and even impurities in the potato skins, as well as notexhibiting insoluble gelatin particles. Furthermore, no significant difference was observed in thecontact angle values at pH 5 and 7.It is noteworthy that the standard deviation values, shown in Table 1, were more accentuatedat neutral pH, which may be related to obtaining a lower quality blend at this pH. Fig. 2 depicts theblends at pH 5 and 7. It was noticed that there was a more apparent phase separation at neutral pH,which consequently can compromise the execution of the proposed analyses and the results.Proceedings of the 16th Brazilian Polymer Conference (16° CBPOL), October 24-28, 2021, Ouro Preto-MG, Brazil 950Figure 2. Surface images of G/A films at pH 5 and 7 (from left to right) under a microscope (1000 x)According to Liu et al. [7], this phase difference may suggest that the blends are immiscible,although compatible, also reported by Acosta et al. [9] and Zhang et al. [10]. This result is possiblyassociated with the type of interactions, attractive or repulsive, carried out between gelatin andstarch, as well as the drying conditions [9]. Another possible explanation is that these zones ofdiscontinuity occurred due to the absence of strong interactions between starch and gelatin, asmentioned by Zhang et al. [10] and Su et al. [21]. According to Su et al. [21], gelatin carboxylgroups ionize at pH above the isoelectric point (pI) of the protein, as pH 7 studied in this work,resulting in a large electrostatic repulsive force that limits the interactions between gelatin andstarch. A fact that probably occurred based on the microstructures obtained.MoistureFig. 3 illustrates the mass gain in the blends as a function of time. It is noticeable that theblend at pH 5 (G/A-5) was more stable, showing less sensitivity to moisture. On the other hand,when neutralizing the pH of the blend (G/A-7), it proved to be more unstable and obtained aconsiderable gain in mass (approximately between 6 h and 21 h of testing). This result may berelated to the pH in the pI of the protein, since at this point the charges are in equilibrium, resultingin lower solubility [21]. This explains the lower humidity at pH 5, since the gelatin used in theproduction of the blends was of bovine origin, with a pI between pH 4.6 and 5.2 [22]. Differentfrom when at pH values above or below pI, as with this the protein will have an excess positive ornegative charge, which favors its interaction with water [21], as observed for pH 7.Figure 3. Moisture of gelatin/starch blends as a function of timeSimilar results were obtained by Fakhouri et al. [6], who developed blends of corn starchand gelatin, plasticized with glycerol, at acid pH. Furthermore, Fakhouri and colleagues verifiedthat their films had the potential for application as fruit coatings, being completely soluble in acidicmedium and, therefore, would be dissolved entirely when a subject ingests the fruit.Proceedings of the 16th Brazilian Polymer Conference (16° CBPOL), October 24-28, 2021, Ouro Preto-MG, Brazil 951ConclusionsThis work aimed to investigate the influence of pH on the hygroscopic properties ofgelatine/starch blends. Through experiments of contact angle and moisture, hydrophobiccharacteristics and lower moisture in acidic pH were observed. Thus, at pH 5, the mixture showedpromise for future investigations.AcknowledgementsI thank the Laboratory of Polymeric Materials (LAPOL) and the Federal University of RioGrande do Sul (UFRGS) for the infrastructure to carry out this work. And also to theCNPq/Universal and FAPERGS/PqG projects for their financial assistance.References1. Q. Wu; L. Zhang. Industrial & Engineering Chemistry Research, v. 40, p. 1879–1883, 2001.2. M. L. Picchio et al. Food Hydrocolloids, v. 84, p. 424–434, 2018.3. G. F. Brito et al. Revista Eletrônica de Materiais e Processos, v. 6, n. 2, p. 127-139, 2011.4. S. S. Farias et al. Geonorte, v. 7, n. 26, p. 61-77, 2016.5. M. A. S. P. Nur Hazirah; M. I. N. Isa; N. M. Sarbon. Food Packaging Shelf Life, v. 9, p. 55–63,2016.6. F. M. Fakhouri. et al. Postharvest Biology and Technology, v. 109, p. 57-64, 2015.7. X. Liu et al. Chinese Journal of Polymer Science, v. 32, n. 1, p. 108-114, 2014.8. A. A. Al Hassan;  M. H. Norziah. Food Hydrocolloids, v. 26, n. 1, p. 108-117, 2012.9. S. Acosta et al. Food Hydrocolloids, v. 49, p. 135-143, 2015.10. N. Zhang et al. Carbohydrate Polymers, v. 92, p. 455– 461, 2013.11. M. C. C. Silva; P. C. R. Fontes; G. V. Miranda. Horticultura Brasileira, v. 27, n. 1, p. 017-022,2009.12. A. C. Ávila et al. Horticultura Brasileira, v. 27, n. 4, 2009.13. E. Dinand; H. Chanzy; M. R. Vignon. Cellulose, v. 3, p. 183–188, 1996.14. T. T. Garmus et al. Revista Brasileira de Tecnologia Agroindustrial. v. 3, n. 3, p. 56-65, 2009.15. A. F. Fernandes. Dissertação de Mestrado, Universidade Federal de Lavras, 2006.16. M. M. A. Mahecha. Dissertação de Mestrado, Universidade Estadual de Campinas, 2009.17. American Society for Testing Materials. ASTM D77334-08 Standard Practice for SurfaceWettability of Coatings, Substrates and Pigments by Advancing Contact Angle Measurement, 3 p.,Reapproved 2013.18. American Society for Testing Materials. ASTM E104-02 Standard Practice for MaintainingConstant Relative Humidity by Means of Aqueous Solutions, 5 p., 2002.19. P. V. P. Huillca. Dissertação de Mestrado, Universidade de São Paulo, 2015.20. Y. L. Nunes. Dissertação de Mestrado, Universidade Federal do Rio Grande do Norte, 2014.21. R. Su et al. Journal of Polymer Science: Part B: Polymer Physics, v. 47,  p. 239–247, 2008.22. E. A. Baldwin; R. Hagenmaier; J. Bai. Edible coatings and films to improve food quality, 2ªedição.CRC Press, USA, p. 1-460, 1994.Proceedings of the 16th Brazilian Polymer Conference (16° CBPOL), October 24-28, 2021, Ouro Preto-MG, Brazil 952

Influence of pH on the hygroscopicity of blends of gelatin and potato skin starch

https://lume.ufrgs.br/bitstream/10183/256478/1/001165009.pdf

Influence of pH on the hygroscopicity of blends of gelatin and potato skin starch

Abstract

Similar works

Full text

Available Versions

Lume 5.8