Physicochemical properties, rheology and degree of esterification of ...

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Physicochemical properties, rheology and degree of esterification of passion fruit (Passiflora edulis f. Flavicarpa) peel flour

Emanuela M Coelho1,2, Luciana C de Azevêdo1*, Arão C Viana1, Ingrid G Ramos2, Raquel G Gomes3, Marcos dos S Lima1, Marcelo A Umza-Guez2

1

Department of Food Technology, Federal Institute of Sertão Pernambucano, BR 407,

Km 08 Jardim São Paulo, Zip Code: 56314-520, Petrolina, Pernambuco, Brazil. 2

Department of Food Science, Federal University of Bahia, Av Ademar de Barros, s/n,

Campus Ondina, Zip Code: 40170-115, Salvador, Bahia, Brazil. 3

State University of Maringa, Av Colombo, 5790, Cidade Universitária, Zip Code: 12

13 97020-900, Maringá, Paraná, Brazil.

2

Department of Science in Food, Federal University of Bahia, Av Ademar de Barros, s/n, Campus Ondina, Zip Code: 40170-115, Salvador, Bahia, Brazil. *Corresponding author, Phone number +55 87 2101 4330 E-mail: [email protected]

ABSTRACT BACKGROUND: The peel of yellow passion fruit is as an agroindustrial waste of great environmental impact, representing more than 50% of the total weight of the fruit. For this reason, and also considering its importance as a source of functional components such as pectin, this organic waste is increasingly attracting the attention of researchers. The aim of this study was to investigate the physicochemical composition and physical properties of this material, which may be of interest to the food industry.

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/jsfa.8451

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RESULTS: We obtained two samples of passion fruit peel flour applying different processes: flour without treatment (FWOT) and flour with treatment by maceration

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(FWT). It was found that the flour samples contain, respectively, 372.4g Kg-1 and 246.7 Kg-1 of soluble fiber and, according to the FTIR analysis, this material corresponds to high and low methoxyl pectins, respectively. CONCLUSION: The flour obtained by maceration (FWT) offers greater benefits for industrial use, with 60% less tannins and greater thermal stability. In addition, this sample does not reabsorb moisture as easily, although FWOT also shows potential for use in dietary products. Considering the pseudoplastic properties of the flours, the application of both samples could be expanded to many industrial sectors.

Keywords: Chemical composition, methoxylation, rheological properties, waste.

INTRODUCTION The yellow passion fruit (Passiflora edulis f. flavicarpa) is native to Brazil and this species is well known worldwide, being commonly used in food products.¹ Most of the production of yellow passion fruit is intended for the preparation of soft drinks, mainly juices and nectars, and approximately 54,000 tons of by-products, including seeds and peel, are generated annually.²


Passion fruit peel has been studied for medicinal purposes, for instance, aiding a reduction in cholesterol and controlling body weight gain.3-4 It is also a

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potential source of dietary fiber with functional properties5 and has been studied due to its water retention, swelling and fat retention capacity.6 Furthermore, it is reported in the literature that the characteristics of passion fruit peel flour are suitable for obtaining biofilms with properties similar to those obtained with starch, and thus this peel flour represents an option for use in the food industry.7 According to Lopez-Vargas et al.2, the main chemical constituent of passion fruit peel is dietary fiber, especially pectin. Pectin is widely used in the food industry, mainly as a gelling agent in the preparation of jams, jellies and confectionery. Pectin can be classified based on the degree of esterification: high methoxyl content (degree of methoxylation > 50%) or low methoxyl content (degree of methoxylation < 50%).8 Several authors have described various methods for the extraction of pectin from passion fruit peel with a view to possible industrial applications.8-11 However, a study conducted by Coelho et al.12 showed that, due to its technological properties, flour produced from passion fruit peel has the potential for direct application in food, as a replacement for commercial colloids such as guar gum, xanthan gum, carrageenan and pectins. Based on the same study, it is evident that passion fruit peel flour can act as a stabilizer, emulsifier, gelling agent and thickener. In this context, studies need to be carried out to characterize passion fruit peel flour in order to identify possible industrial applications. In this regard, the aim of this study was to produce flour samples from the peel of yellow passion fruit. Physicochemical and rheological studies were performed to identify the compounds associated with the technological properties and compare the flour samples with commercial pectins of high and low methoxylation.


MATERIALS AND METHODS

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Raw material Samples of fully mature yellow passion fruit (Passiflora edulis f. flavicarpa) were purchased in September and October 2014, at the produce market in Juazeiro, Bahia, Brazil. According to the climatic data for the region during the harvest season, the rainfall was 5.2 mm in September 2014, with average temperatures of 26.3 to 27.3 °C, relative humidity of 56 to 53 %, radiation of 553.9 to 525.9 ly/day, and insolation of 9.3 to 8.8 hours, measured at the Mandacaru weather station (Juazeiro, Bahia, Brazil, 09º24'S, 40º26'W ). Preparation of passion fruit peel flour samples In order to facilitate the use of passion fruit peel in food formulations, two flour samples were prepared with this material. One sample consisted of ‘flour with treatment’ (FWT), obtained with the application of soaking in water for 12 h, through a methodology described by Oliveira et al13, and the other consisted of ‘flour without treatment’ (FWOT). To obtain the flour, the shells were cut into strips around 1 cm in length and airdried with forced air circulation (Meloni - PE 30 Classic Electric, Brazil) at 50 °C until constant weight. The samples were then crushed and sieved to obtain particles of 0.15 mm, which were ground for future analysis.

Particle size analysis For the determination of the particle size, 100 g of FWOT and FWT flour samples were sieved for 30 min with a frequency of 15 rpm in a vibrating screen shaker (AG-37/13 Bronzinox, Brazil) and with 28, 48, 60, 65, 80 and 100 meshes


corresponding to openings of 0.60, 0.30, 0.25, 0.21, 0.18 and 0.15 mm, respectively.

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The mass retained on each sieve was then weighed and the percentage calculated.14

Classic Analysis The two flour samples (FWT and FWOT) were subjected to tests to determine the following parameters: pH, titratable acidity (TA), moisture content by drying at 105 °C, fixed mineral residue (dry ash) by calcination in a muffle furnace at 550 °C, total protein content by the Kjeldahl method using a nitrogen distiller, lipids by the Soxhlet method, and total soluble and insoluble fiber by the enzymatic-gravimetric method. All of these parameters were determined based on the methods described by the Association of Official Analytical Chemists.15 The total tannin content was determined by the FolinDenis method16 and the pectin content by the Rangana method.17 The water activity content (aw) was measured by direct reading, using a portable water activity meter (Aqualab, Brazil).

Determination of sugars and acids by high performance liquid chromatography The acids and sugars were determined simultaneously by high performance liquid chromatograph (HPLC) on an Agilent Technologies chromatograph (model 1260, Infinet, USA) equipped with an autosampler, diode array detector (DAD) and refractive index (RI) detector, according to the methodology described in the Analysis of Carbohydrates Alcohols and Organic Acids produced by Agilent Technologies.18 Acids were determined was using the DAD detector at a wavelength of 210 nm. The column used was a Hi-Plex H 300 x 7.7 mm (Agilent Technologies, Santa Clara, USA). The furnace temperature was 70 °C, the injection volume of pre-diluted sample was 10 uL, the flow rate was 0.5 ml min -1 and the total run time was 20 min. The liquid


phase was isocratic ultrapure water acidified with sulfuric acid (4 mM L

-1

).

The validation parameters determined were R², limit of detection (LOD), limit of

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quantification (LOQ), precision and linear working range. The values set for each parameter are shown in Table 1.

Determination of esterification degree of pectin in passion fruit peel flour The degree of esterification (DE) of the pectinic material in the FWT and FWOT flour samples was determined by Fourier transform infrared (FTIR) spectroscopy using the methodology proposed by Monsoor.19 A Perkin Elmer FTIR spectrometer (Spectrum Two, USA) was used in transmittance mode (% T) and the analysis was carried out in the range of 4000-400 cm

-1

with the accumulation of 8 scans and a

resolution of 1 cm -1. The spectra were obtained with KBr pellets containing 10% of the sample (FWOT or FWT). The results were compared with the spectra obtained for pure standards of high methoxyl (HMP) and low methoxyl (LMP) pectin samples (INS 440) obtained from CPKelco (Atlanta, USA). Equation 1 was used to calculate the degree of esterification (DE) of the samples under study: DE =

(

)

100

(Eq. 1)

Where APGCE = peak area of esterified carboxyl groups and APGCNE = peak area of non-esterified carboxyl groups. Peaks in the range of 1760-1745 cm

-1

indicate

the esterified carboxyl groups (COO-R) and those in the range of 1640 to 1620 indicate the non-esterified carboxyl groups (COO-).

Thermogravimetric Analysis (TGA)


The thermal stability of the flour samples (FWOT and FWT) was evaluated on a Perkin Elmer thermogravimetric analyzer (model Pyris 1), in a previously calibrated

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thermobalance using an oxidizing synthetic air atmosphere with a flow rate of 30 mL min

-1

(sheath gas) and N2 at 10 mL min

-1

(purge gas) in the samples. For comparison

purposes, commercial samples of pectin (HMP and LMP) were also analyzed. Approximately 5 mg of the samples were heated in an open platinum crucible. The analysis was performed in triplicate, in the temperature range of 25-900 °C at a heating rate of 10 °C min -1. The weight loss versus temperature data were plotted to obtain the thermogravimetric (TG) curves.

Derivative thermogravimetric (DTG) curves were

constructed using the software OriginLab® (Northampton, USA).

Rheological Analysis The rheological behavior of the flour (FWT and FWOT) and commercial pectin (HMP and LMP) samples was determined in a cone and plate rheometer (Thermo Scientific, model MARS III) at 25 °C in triplicate. The ascendant and descendant curves were obtained using a shear gradient of 0 to 700 s for 30 s with a cone/plate spindle. To classify the rheological behavior of the samples, shear stress versus viscosity curves were generated using the power law rheological model.

Adsorption curves for flour samples To evaluate the water resorption capacity, small amounts of flour were placed in different hermetically sealed environments, according to the scheme published by Souza.20 Six salt solutions were used to reproduce different humidity conditions (lithium chloride, magnesium chloride, sodium chloride, ammonium sulfate, potassium chloride and barium chloride). The samples remained at room temperature (25 °C) until


a moisture equilibrium was reached between the internal environment and the sample. The powder equilibrium moisture content (dry basis) was obtained from the ratio

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between the weight of water at equilibrium and the dry weight.

Statistical analysis The results obtained in the physicochemical analysis were tabulated and compared using the Student t-test (5% probability of error) using the SPSS Version 17.0 statistical package for Windows (SPSS, Chicago, USA).

RESULTS AND DISCUSSION Particle size analysis The flour samples (FWT and FWOT) showed a heterogeneous granulometric behavior. The highest percentages of retention for both flours were obtained on the 48 mesh screen (0.30 mm) and the last with particles less than 0.15 mm, summing to 62.3 and 59.4% for FWT and FWOT, respectively. Heterogeneous particle size characteristics for passion fruit peel flour have also been reported by Leoro et al.21. In this study, the flour samples were standardized using the sieve of mesh 100 to obtain particles smaller than 0.15 mm, since this provided samples with the aspect of a very fine powder, facilitating their mixing with other substances. Palacios-Fonseca, Vazquez-Ramos & Rodríguez-García22 reported that the particle size of flour after grinding has a strong influence on its functionality in food products. It can also affect the quality and taste of the final products.23 Thus, a more uniform particle size allows the preparation of a final product with better sensory quality, particularly, texture, taste and visual appearance.


Classic analysis of passion fruit flour The physical and chemical compositions of the passion fruit peel flour samples

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are shown in Table 2. The values for the titratable acidity and contents of ash, protein, lipids, soluble fiber, pectin and tannins differed significantly and were lower for the FWT compared to FWOT. The lower values observed for the FWT may be associated with leaching during the sample maceration treatment because, according to Perez & Sanchez,24 during the washing of products rich in fiber, soluble compounds, including some hemicelluloses and pectins, are leached out. The values obtained for total fiber in the flour (FWOT = 613.2 g Kg-1 and FWT = 676.0 g Kg-1) are in line with those observed in other studies reported in the literature. 1, 2, 5, 8, 25

The concentrations of insoluble fiber in the FWOT and FWT samples were

considered high (385.0 and 509.0 g Kg-1, respectively), suggesting that there is a considerable amount of cellulose and hemicellulose, as observed by Oliveira et al.8 In agreement with Nascimento et al.7 who found that pectin is the major component of soluble fiber, it was observed in this study that of the 164.0 and 220.0 g Kg-1 of the soluble fiber, respectively, in the FWT and FWOT flour samples, 135.0 and 164.0 g Kg1

represented material composed of pectins. Some studies have associated beneficial health effects, such as a reduction in

LDL and increase in HDL cholesterol levels and weight gain control, with the soluble fiber component of passion fruit flour.3, 4 This is therefore a functional constituent. Regarding the organic acids determined by HPLC, citric and malic acids were present in the flour in amounts ranging, respectively, from 5.58 to 6.32 and 21.03 to 23.84 mg g -1. Sugars, glucose and fructose were present in amounts ranging from 44.49 to 49.06 and 65.34 to 68.67 mg g -1, respectively. On characterizing the lyophilized passion fruit pulp, the main compounds found were glucose, fructose and citric and


malic acids,26 suggesting that these are the main components of these metabolites

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present in passion fruit.

Spectrometric profile and determining the degree of esterification of pectins in the samples The FTIR spectra obtained for FWT and FWOT are shown in Fig.1a and are compared with the spectra for commercial pectins (HMP and LMP). No differences were observed in the spectra for the FWOT and FWT samples, suggesting that the maceration treatment of the peel with water did not alter the chemical structure of the FWT sample. Likewise, the spectral bands at 3600 and 2500 cm -1 for the FWOT, FWT, HMP and LMP samples showed similar behavior, characteristic of pectin, according to Abid et al.27 who reported that regions around 3309 cm -1 correspond to the absorption caused by O-H stretching due to inter and intramolecular hydrogen bonds of the galacturonic acid polymer. As can be seen in Fig.1b, absorbance bands were observed for the FWT and FWOT flour samples at 1745 and 1615 cm -1, and the HMP and LMP samples at 1747 and 1631 cm -1. These data indicate that the material present in the flour samples is similar to that of the commercial pectins, since the spectral region between 1800 and 1500 cm-1 relates to carboxylic acids and carboxylic esters, which are the key functional groups responsible for the characteristics of pectin. 27 The results for the study on the degree of esterification (DE) of the commercial pectin and flours samples are shown in Table 3. The analysis shows that the untreated passion fruit peel flour (FWOT) has a low degree of esterification (37.8%) and can be classified as a low methoxyl pectin (LMP), that is, it has a DE of < 50%. This is


advantageous in relation to the manufacture of diet products, allowing a product with low sugar to gel content.28 On the other hand, after the treatment the flour showed a

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greater degree of esterification (61.3%), being classified as a high methoxyl pectin (HMP), which increases its ability to form a gel. This pectin class has the same industrial value, but the types of potential application differ, since it requires a significant amount of sugar to form a gel, and its most appropriate use is therefore in the development of products that require high sugar content. 28 The degree of esterification is thus associated with the carboxylic groups of the main chain of galacturonic acid being esterified with methyl and acetyl groups and it is related to the technological features of pectin, with respect to the ability to form a gel. This parameter is a very important factor in determining the quality of pectin.8 Thus, DE analysis was fundamental in the classification of the esterification of the flour. In the literature, values similar to those obtained for the FWT sample are reported for the degree of esterification of pectin extracted from passion fruit peel.9-11 The literature reports various methods for the extraction and purification of pectin from passion fruit peel, since this affects the way it is marketed.8-11 However, Coelho et al.12 found that passion fruit peel flour in the form in which it is obtained can be used in foods that benefit from its thickening and gelling properties, as well as is action as an emulsifier and stabilizer. The same authors report that treated and untreated passion fruit peel flours have technological properties similar to various colloids, such as guar gum, carrageenan, xanthan gum and pectins (LMP and HMP). Thus, analysis of the degree of esterification verifies the link between the FWT and FWOT flour samples and HMP and LMP, demonstrating advantages of the use of a flour derived from industrial waste as a low-cost product.


Thermogravimetric analysis The thermogravimetric (TG) and derivative thermogravimetric (DTG) curves

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verified the thermal stability of the pectin (HMP and LMP) and the flour (FWT and FWO) samples, as can be observed in Fig. 2a. The contours of the curves for HMP and LMP were similar, showing two thermal events. The first event occurred in the region of 25-170 °C, which is associated with the elimination of water, as the temperature was increased, from the OH bonds present in the pectin structure and compounds of low molecular weight in the sample.7 The second thermal event corresponds to decomposition of the polysaccharide which, as shown in the DTG curve, occurs in two steps for the HMP and one step for the LMP, with decomposition in the region of 200-320 °C. Similar events were observed by Combo et al.,29 who analyzed beet pectin. The DTG thermal profile for the passion fruit flour samples (FWOT and FWT) showed a thermal event related to dehydration from ambient temperature to 145 °C, related to the same event observed for the pectin samples. The second thermal event observed in the DTG profile, which occurs between approximately 148-190 °C, is not observed for the the pectin samples and thus it can be assigned to the decomposition of another substance present in the passion fruit peel flour, such as sugars and hemicellulose.7 The thermal stability results for the commercial pectin and flour samples, determined by the Tonset of the decomposition event, can be observed in Table 4. It was found that the LMP showed higher thermal stability than the HMP. The FWT sample showed behavior similar to the HMP, but FWOT showed lower thermal stability. These results are not consistent with those reported by Combo et al.29 and Einhorn-Stoll, Kunzek & Dongowski,30 which could be due to structural differences between the


samples. Thermal stability is influenced by the degree of methoxylation, the molecular weight of the substituents present and the physical condition resulting from the

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extraction30. Wenjun et al.31 report that pectins which are resistant to high temperatures offer benefits in the food industry. The thermal events occurring at between 400-850 °C in the case of the pectins and between 375-720 °C for the flour samples showed slow weight loss, which is probably associated with the decomposition of the carbon chains of the pectins.31

Rheological Analysis Fig. 3a shows the apparent viscosity curves as a function of shear stress for the flour (FWT and FWOT) and commercial pectin (HMP and LMP) samples. All of these samples showed pseudoplastic behavior, as the viscosity decreases with increasing shear rate. Thus, they demonstrate the behavior of non-Newtonian fluids, that is, non-linear shear stresses arising from structural changes caused by the shear gradient applied, where the first gums involved probably have highly coiled long chains in the relaxed state. After exposure to shear stress the chains can uncoil and become aligned in the direction of the shear, releasing water molecules involved in the dissolution of the gums. Similar behavior was observed by Nascimento, Calado e Carvalho7 who evaluated the use of solutions of passion fruit peel flour in the preparation of biofilms and obtained good results for viscosity. However, the continuous shear analysis revealed that the rheological flow behavior of the gums had distinct characteristics, as can be observed in Fig. 3b and Fig. 4a. The FWT, FWOT and HMP gums showed much a more pronounced pseudoplastic flow behavior than the LMP gum, with distinct values for the consistency index, yield


value, and thixotropic area and coefficient. This may be due to an increased entanglement of the chains and greater resistance to deformation.32

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The flow properties observed in each rheogram were evaluated considering the consistency index K (viscosity) and flow behavior index n. This approach also verified that the FWT, FWOT and HMP gums showed similar characteristics and good firmness. Since the values for the flow behavior index were less than 1, these materials can be classified as pseudoplastic or plastic; however, considering that the results were positive they can be considered as plastic.33 It can be noted from the rheograms that after the application of force there was not a thixotropic interval between the ascending and descending curves, proving again that there was no release of water (syneresis) from the structure of the passion fruit peel flour samples. This indicates that this material has well branched and coiled chains (i.e. a high degree of methoxylation). Due to the form of branching in the polysaccharide structure, water trapping occurs, leading to a more or less gelatinous medium. Due to their uniform and firm characteristics, the flour samples investigated could be applied to improve the viscosity and appearance of different products, making them more homogeneous. The action of acidity and sugar leads to the protonation of ionized carboxyl groups and dehydration of the pectin micelle, allowing the approximation and bonding of molecules and the formation of a hydrocolloid characteristic.34

Moisture adsorption capacity of flour samples The samples showed a variation in the moisture adsorption capacity, with linear behavior up to aW = 0.5. Above this value, exponential behavior was observed,


indicating a strong moisture adsorbing characteristic (Fig. 5a), due to the presence of sugars in the composition. Under more extreme conditions of ambient humidity, the

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FWOT sample adsorbed up to 32.71%, while only 24.84% was adsorbed by the FWT sample. In a study on dehydrated passion fruit peel, other researches observed similar behavior in relation to this hygroscopic characteristic, indicating that this product requires considerable care during handling and storage in environments with humidity higher than 50%, to avoid humidification, deterioration caused by undesirable reactions and the proliferation of microorganisms. It is clear, however, that the adsorption capacity decreases when the shells undergo a pre-treatment, as in the case of the FWT sample.

CONCLUSIONS Flours produced from passion fruit peel, through drying with forced air circulation, contained substantial amounts of soluble solids, minerals, protein, lipids, fiber and pectin, with values similar to those reported in the literature. The main sugars present were glucose and fructose while the major organic acids were citric and malic. The application of a pre-treatment through soaking (FWT) resulted in a decrease in tannins and other compounds. Fiber and pectin were constituents of the flour samples with notably high values. FTIR analysis of the flour samples showed that the pectin content corresponded to high and low methoxyl pectins, suggesting that they offer nutritional benefits and have potential for use in food products as a replacement for commercial additives, aimed at enhanced viscosity, gelification or emulsion stabilization.


The thermogravimetric curves showed that the treated (FWT) flour had greater thermal stability compared to the untreated (FWOT) flour. Furthermore, the treated

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sample showed pseudoplastic flow behavior similar to that of commercial pectins and can thus be applied in polymeric films in the chemical industry in general.

ACKNOWLEDGEMENTS The authors would like to acknowledge the Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq for granting a scholarship.

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properties. Food Chem, 215: 318–325 (2017). 28. Kastner H, Kern K, Wilde R, Berthold A, Einhorn-Stoll U and Drusch S. Structure formation in sugar containing pectin gels – Influence of tartaric acid content (pH) and cooling rate on the gelation of high-methoxylated pectin. Food Chem 144: 4449 (2014). 29. Combo AMM, Aguedo M, Quiévy N, Danthinec S, Goffin D, Jacquet N, Blecker C, Devaux J and Paquot, M. Characterization of sugar beet pectin-derived oligosaccharides obtained by enzymatic hydrolysis. Int J Biol Macromol, 52: 148-156 (2013). 30. Einhorn-Stoll U, Kunzek H and Dongowski G. Thermal analysis of chemically and mechanically modified pectins. Food Hydrocolloids, 21 (7): 1101-1112 (2007). 31. Wenjun W, Ma X, Jiang P, Hu L, Zhi Z, Chen J, Ding T, Ye X and Donghong L. Characterization of pectin from grapefruit peel: A comparison of ultrasoundassisted and conventional heating extractions. Food Hydrocolloids 61: 730 – 739 (2016). 32. Carvalho FC, Calixto G, Hatakeyama IN, Luz GM, Gremiao MPD and Chorilli M. Rheological, mechanical, and bioadhesive behavior of hydrogels to optimize skin delivery systems. Drug Dev Ind Pharm, 39 (11): 1750-1757 (2013). 33. Schnaare RL, Block LH and Rohan LC. Rheology. In: Remington. The Science and practice of pharmacy 21: 338-358. Philadelphia: Lippincontt Willians & Wilking. (2005).


34. Siqueira BSS, Alvez LD, Vasconcelos PN, Damiani C and Soares Junior MS. Pectina extraída de casca de pequi e aplicação em geléia light de manga, Rev

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Bras de Fruticultura 34 (2): 560-567 (2012).

Figure captions Figure 1. (a) FTIR spectra for the treated (FWT) and untreated (FWOT) passion fruit peel flour samples compared with commercial low and high methoxyl pectins (LMP and HMP). (B) Absorbance spectra for the FWT and FWOT samples in the region of 1500-1 to 850 cm-1. Figure 2. Thermogravimetric (TG) and derivative thermogravimetric (DTG) curves for (a) high (HMP) and low (LMP) methoxyl pectins and (b) passion fruit peel flour samples without (FWOT) and with (FWT) treatment. Experimental conditions: sample mass approximately 5 mg, synthetic air flow 40 ml min-1, heating rate 10 °C min-1 . Figure 3. Viscosity versus shear rate for solutions of high (HMP) and low (LMP) methoxyl pectins and of treated (FWT) and untreated (FWOT) passion fruit peel flour. Figure 4. Shear stress x shear gradient for solutions of high (HMP) and low (LMP)methoxyl pectins and treated (FWT) and untreated (FWOT) passion fruit peel flour samples. Figure 5. Moisture sorption isotherm for the treated (FWT) and untreated (FWOT) passion fruit peel flour samples at 25 °C.


Table 1. Method validation parameters for determination of acids and sugars in the FWT and FWOT samples. Compounds

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R2 Organic Acids 0.9996 Citric 0.9999 Malic 0.9999 Tartaric 1.0000 Acetic 1.0000 Lactic Sugars 0.9999 Glucose 0.9999 Fructose 0.9982 Maltose 0.9999 Rhamnose

Validation parameters Range LOD LOQ RSD (g.L-1) (g.L-1) (g.L-1) 0.0021 0.0070 0.0260 0.0030 0.0200

0.0960 0.0260 0.0710 0.0080 0.0560

0.0090 0.0030 0.0070 0.0010 0.0050

0.025-5.0 0.025-5.0 0.025-5.0 0.010-2.0 0.025-5.0

0.0210 0.0500 0.0370 0.044

0.1030 0.1990 0.1140 0.1510

0.0120 0.0210 0.0110 0.0150

0.010-20.0 0.010-20.0 0.025-5.0 0.025-5.0

R2 – linear correlation coeficient; LOD – Detection limit; LOQ – Quantification limit; RSD – residual standard deviation.


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Table 2. Mean values obtained in the determination of the physical and chemical composition of passion fruit peel flour samples (FWOT = untreated flour and FWT = treated flour). Flours Variables FOWT FWT a pH 4.25 ± 0.0 4.30a ± 0.00 aW 0.36a ± 0,0 0.34a ± 0.00 a Soluble solids (°brix) 28.0 ± 0.0 27.8a ± 0.0 Titratable acidity (g.kg-¹) 6.53a ± 0.12 4.65b ± 0.12 Moisture (g.kg-¹) 64.0a ± 0.20 65.3a ± 0.40 a Ash (g.kg ¹) 71.4 ± 0.20 69,20b ± 0.30 Protein (g.kg-¹) 38.5a ± 0.30 25.40b ± 0.70 a Lipids (g.kg ¹) 8.50 ± 0.00 6.90b ± 0.00 Total fiber (g.kg-¹) 613.2b ± 6.50 676.0a ± 7.60 Insoluble fiber (g.kg-¹) 384.8b ± 11.70 509.2a ± 5.50 Soluble fiber (g.kg ¹) 220.0a ± 11.30 169.8b ± 13.4 Pectin (g.kg-¹) 164.2a ± 4.50 135.5b ± 5.2 a Tannin (g.kg ¹,Tanic acid) 7.30 ± 0.00 4.30b ± 0.00 OrganicAcids (mg.g-1 of sample) Citric 6.32a ± 0.00 5.58b ± 0.00 Malic 21.03b ± 0.00 23.84a ± 0.00 Tartaric ND ND Acetic ND ND Lactic ND ND -1 Sugars (mg.g of sample) Glucose 49.06a ± 0.03 44.49b ± 0.00 Fructose 68.67a ± 0.04 65.34b ± 0.00 Maltose ND ND Rhamnose ND ND

* Averages followed by the same letter are not statistically different from each other. Tukey's test was applied at the level of 5 % probability. * ND = Not Detected


Table 3. Degree of esterification for commercial high (HMP) and low (LMP) methoxyl

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pectin and treated (FWT) and untreated (FWOT) passion fruit peel flour samples. Sample

Esterification Degree (ED) (%)

LMP

31.2

HMP

63.7

FOWT

37.8

FWT

61.3


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Table 4. Results obtained from the TG curves. Sample

Thermo stability* (oC)

Tendset of the decomposition event (oC)

Content (%)

HMP LMP FWOT FWT

229.5 238.8 162.3 164.1

167.4 176.2 130.2 145.2

5.4 7.2 7.8 7.8


Tendset of the coal decomposition event 790.6 833.9 659.2 719.4

Dry ashes (%) 4.8 4.4 13.3 9.0

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Figu ure 1. (a) FT TIR spectraa for the treeated (FWT T) and untreeated (FWO OT) passionn fruit peel flour sampples comparred with co ommercial low l and hig gh methoxy yl pectins (LMP ( and H HMP). (B) Absorbancce spectra for fo the FWT T and FWO OT samples in the region of 15000-1 to 850 cm m-1.


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Figu ure 2. Therm mogravimettric (TG) annd derivativve thermogravimetric (D DTG) curvees for (a) hhigh (HMP) and low (LMP) meethoxyl pecctins and (bb) passion fruit peel flour sampples withoutt (FWOT) and a with (F FWT) treatm ment. Experrimental co onditions: saample -1 masss approximaately 5 mg, synthetic aiir flow 40 ml m min , heaating rate 100 °C min-1 .


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Figu ure 3. Viscosity versuus shear ratte for soluttions of higgh (HMP) and low (L LMP) methhoxyl pectin ns and of treeated (FWT) and untreaated (FWOT T) passion fruit f peel floour.


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Figu ure 4. Shear stress x shear grradient for solutions of high (H HMP) andd low T) and untreeated (FWO OT) passionn fruit (LMP)metthoxyl pecttins and treated (FWT peel flour samples.


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Figu ure 5. Moissture sorption isotherm m for the trreated (FW WT) and unntreated (FW WOT) passiion fruit peeel flour sam mples at 25 °C. °
