Structural features and water sorption isotherms of carrageenans: A prediction model for hybrid carrageenans

Carbohydrate Polymers 180 (2018) 72–80

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Structural features and water sorption isotherms of carrageenans: A prediction model for hybrid carrageenans María D. Torres, Francisco Chenlo, Ramón Moreira

MARK

⁎

Department of Chemical Engineering, Universidade de Santiago de Compostela, rúa Lope Gómez de Marzoa, Santiago de Compostela, E-15782, Spain

A R T I C L E I N F O

A B S T R A C T

Keywords: Adsorption Caurie model Desorption Moisture content Water activity

Experimental: water adsorption and desorption isotherms of kappa/iota-hybrid carrageenan (KIC) extracted from Mastocarpus stellatus red seaweed as well as commercial kappa-carrageenan (KC) and iota-carrageenan (IC) were obtained at several temperatures (5, 25, 45, 65 °C). Spectroscopic and X-ray diffraction techniques allowed identifying the fundamental composition of above biopolymers. Crystallinity values (%) followed the order IC (25.4 ± 0.6) > KIC (9.3 ± 0.4) > KC (4.8 ± 0.2), which nicely matched with the hygroscopic properties of the tested biopolymers (KC > KIC > IC) at each temperature. Sulphate content and sulphation degree of KIC were also intermediate. The experimental sorption data were successfully fitted using the two-parameter Caurie model, selected following a statistical analysis. A prediction model to estimate the KIC water sorption isotherms based on its individual disaccharides units content (% mol) (kappa- (73 ± 4) and iota- (27 ± 4)) and including the temperature effect was successfully developed.

1. Introduction The hygroscopic nature of the biopolymers is a relevant aspect on moisture, texture or quality of foodstuffs, since the biopolymers tend to develop physical and chemical changes strongly dependent on their temperature/moisture history (Rosell, Collar, & Haros, 2007). Nowadays, the use of alternative biopolymers as gelling, thickening or stabilising agents rises in several food (Larotonda, Torres, Gonçalves, Sereno, & Hilliou, 2015) and non-food (Jonathan & Karim, 2016) applications to achieve determined themo-rheological properties of final products. Namely, the food industry requests biopolymers as solid powders that are incorporated to various solid or liquid materials during processing (Imeson, 2010). The understanding of water sorption characteristics among biopolymers and atmosphere is essential for the suitable process conditions selection owing to physicochemical characteristics, microbial safety or other features dependents on water activity (Bahloul, Boudhrioua, & Kechaou, 2008; Chenlo, Moreira, Prieto, & Torres, 2011). The experimental water sorption isotherms can be obtained by the determination, usually at atmospheric pressure, of the equilibrium moisture content and the water activity at fixed temperature. These isotherms can be gotten either for water adsorption or desorption procedures by increasing or decreasing the sample water activity. Both processes are not completely reversible (Bonilla, Azuara, Beristain, & Vernon-Carter, 2010). Water sorption isotherms are notably

⁎

influenced by the biopolymer structure or state (i.e. crystal, an ordered molecular lattice, or amorphous, lacking in molecular order). In simplest terms, amorphous non crystalline materials are more hygroscopic since can hydrogen-bond water internally, non just on the surface which is the only way water can interact with a perfect crystal (Labuza, Knnane, & Chen,1985). In the bibliography, it can be found numerous empirical and semi-empirical models that allow establishing mathematical correlations between the equilibrium moisture content and the water activity and are commonly evaluated by the fitting of the experimental data sets; see as e.g. a recent comprehensive review (Willems, 2015). Another option is estimate the water activity, at each temperature and moisture content, from fundamental laws and empirical relationships using estimation algorithms based on materials chemical composition (Moreira, Chenlo, & Torres, 2009), which would be of great interest, since the current literature displays relevant discrepancies between different experimental water sorption isotherms for certain products as well as reduce time in the experimental determination. Carrageenans are sulphated galactans isolated from red seaweeds (Gigartinales, Rhodophyta), which have been ever more employed in industrial applications as gelling, thickening, texturing or stabilising agents. The main commercial carrageenans are usually divided into kappa- and iota- carrageenans. Kappa-carrageenan strands are less oriented and less crystalline that the salts of iota-carrageenan with glass transition temperatures between 160.8 and 89.5 °C (10% and 50%,

Corresponding author. E-mail addresses: [email protected] (M.D. Torres), [email protected] (F. Chenlo), [email protected] (R. Moreira).

http://dx.doi.org/10.1016/j.carbpol.2017.10.010 Received 12 July 2017; Received in revised form 20 September 2017; Accepted 2 October 2017 Available online 07 October 2017 0144-8617/ © 2017 Elsevier Ltd. All rights reserved.

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water and selected by their colour (reddish) and size (∼ 20 cm) before being processed in order to get the KIC gum employed as raw material as previously described in detail (Torres, Chenlo, & Moreira, 2017). Concisely, the seaweeds were dried (temperature of 35 °C, initial load density of 1.5 ± 0.1 kg/m2, air velocity of 2 m/s and relative humidity of 30%) in a pilot-scale tray dryer (Angelatoni Challenge 250, Italy). Then, dried seaweeds were milled (weight-average particle size, Dw (μm) 77.5 ± 0.4) using an ultra-centrifugal mill with an internal sieve of 200 μm (ZM200 Retsch GmbH, Germany) and equilibrated at room temperature with an atmosphere generated by a saturated solution of Mg(NO3)2 (water activity, aw ∼ 0.55). Subsequently, equilibrated seaweed powders were stored at 4 °C in vacuum sealed bags until its utilization to ensure adequate post- harvest preservation until KIC extraction. The KIC extraction was carried out at least in triplicate using a set of optimized parameters get in an earlier work (Azevedo et al., 2015). Briefly, dried seaweed powders (1.5 g) were soaked in 100 mL of distilled water (90 °C for 2 h). Then, suspensions were cooled to 55 °C and treated for 1 h with stirring with α-amylase (1 mg/g algal material; amyloglucosidase from Aspergillus niger, Fluka Biochemika) in order to digest any floridean starch existent. Afterwards, samples were heated to 80 °C to simplify the centrifugation (3000 rpm for 10 min). Supernatants were precipitated in 2.5 vols of ethanol (96%) and precipitates were filtered through cotton clothes, washed twice with ethanol and oven dried (50 °C for 24 h).

respectively) (Mahmood, Rahman, & Yee, 2014). Commonly, carrageenophyte seaweeds do not produce these pure carrageenans, but rather a range of hybrid structures (Pereira, Amado, Critchley, van de Velde, & Ribeiro-Claro, 2009). A specific type of hybrid carrageenans is kappa/iota-hybrid carrageenans (KIC). Particularly, those KIC extracted from underexploited algal resources as Mastocarpus stellatus red seaweeds would contribute to meet the growing demand for biopolymers with specific physicochemical and mechanical features to be used in food, biomedical or pharmaceutical applications (van de Velde, 2008; Yan et al., 2012). KIC are natural polyelectrolyte copolymers consistent in blocks of kappa-carrageenan (alternating sequences of 3-linked β-D-galactopyranose bearing a sulphate group on the fourth carbon of the sugar ring (G4S) and 4-linked α-D-anhydrogalactopyranose (DA)) and blocks of iota-carrageenan (alternating sequences of G4S and 4-linked α-D-anhydrogalactopyranose with a sulphate group on the second carbon of the anhydro ring (DA2S)) (Azevedo, Torres, Sousa-Pinto, & Hilliou, 2015). The kappa-/iota- ratio, the length of the block or the relative content of more sulphated carrageenan units notably depend on family and life stage of the seaweeds (Bixler & Porse, 2011). It is well-known that the carrageenans quality can be influenced by numerous aspects such as the season of harvest (Azevedo et al., 2015), the seaweed maturity state (Hilliou et al., 2012) or the post-harvest storage (van de Velde, 2008). In this context, the knowledge of the carrageenans sorption behaviour is a critically relevant step in the industrial processing to select more appropriately the drying and storage conditions. This knowledge is also relevant to reduce the impact of an inappropriate equipment use which could change the quality of the raw material and increase the operation costs (Williams, 2007). In the past decade, some studies have been made concerning the sorption properties of different galactomanans such as guar gum (Vishwakarma, Shivhare, & Nanda, 2011), locust bean gum (Wang & Somasundaran, 2007) or carrageenan gum films (Larotonda et al., 2015) and other hydrocolloids such as carboxymethyl cellulose, tragacanth or xanthan (Torres, Moreira, Chenlo, & Vázquez, 2012). Nevertheless, scarce information restricted to specific temperatures is available in the bibliography on water sorption characteristics of selected biopolymers. In this context, the main objective of this work is to get the experimental water adsorption and desorption isotherms of different types of carrageenans (kappa-, iota- and kappa/iota-hybrid carrageenan), over a wide range of water activities and temperatures of interest. The particular objectives include: (i) the determination of some chemical characteristics of the tested biopolymers relevant on the hygroscopic behaviour; (ii) the experimental water sorption data fitting using Caurie model and (iii) the prediction of the kappa/iota-hybrid carrageenan water sorption isotherms from the individual water sorption isotherms of kappa- and iota- carrageenans.

2.3. Spectroscopic measurements The kappa/iota fractions and purity of the samples were determined using Fourier Transform Infrared Attenuated Total Reflectance (FTIRATR) and Nuclear Magnetic Resonance (NMR) analysis. FTIR-ATR spectra of sample materials (i.e. KIC, KC and IC) were recorded on a Varian 670-IR spectrometer at room temperature in the range between 500 and 1500 cm−1, following the procedure described in detail elsewhere (Pereira et al., 2009), for the qualitative characterization of the tested hydrocolloids. 1H NMR spectroscopy of the above materials was conducted on a Varian Unity plus 300 spectrometer operating at 300.13 MHz for the quantitative determination of the carrageenan fractions. The molar fractions of the carrageenan repeating units (κ and ι) are calculated as the integrated intensity of the corresponding 1H NMR peak (5.09 and 5.5 ppm, respectively) over the sum of the integrated intensities of all assigned carrageenan anomeric protons (Azevedo et al., 2015). The degree of sulphation (i.e. the relation of sulphate to total carbohydrate) was also estimated from infrared spectroscopy according to Rochas, Lahaye, and Yaphe (1986). Note here that the sulphate content was estimated by the widely used barium chloride precipitation method (Jackson and McCandless, 1978), after sulphate hydrolysis by 1N HCl at 100 °C for 4 h as reported elsewhere (Villanueva, Mendoza, Rodriguez, Romero, & Montaño, 2004).

2. Materials and methods 2.1. Raw materials Fresh Mastocarpus stellatus seaweeds (moisture content of 67.9 ± 2.5%, wet basis, AOAC, 2000) were gently provided by Conservas Mar de Ardora Company (Ortigueira, A Coruña, Spain). The tested hydrocolloids were kappa/iota-hybrid carrageenan (KIC) extracted from above seaweeds, and commercial kappa-carrageenan (KC) (Sigma-Aldrich, St. Louis, MO) and iota- carrageenan (IC) (Sigma-Aldrich, St. Louis, MO) with weight-average molar masses (Mw) of 2.20 106, 2.31 106 and 1.32 106 g/mol, respectively, determined by gel permeation chromatography as previously detailed (Torres, Hallmark, & Wilson, 2014).

2.4. X-ray diffraction measurements The crystalline structure analysis of KIC, KC and IC was conducted at room temperature on a Philips diffractomer using CuK-alpha radiation (λ: 0.154 nm) operating at 40 KV and 20 mA. The samples were scanned through the 2θ (diffraction angle) from 2 to 50° at a scanning rate of 8°/min. Note here that samples used for crystallinity measurements were those equilibrated at intermediate water activities (aw ∼ 0.55, Mg(NO3)2). The relative crystallinity degree was calculated following the method reported elsewhere (Correia, CruzLopes, & Beirão-da-Costa, 2012), which takes into account the amorphous and crystallized area on the X-ray diffractogram. The measurements were made at least in duplicate.

2.2. Biopolymer extraction Mastocarpus stellatus seaweeds were cautiously washed with fresh 73

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Fig. 1. FTIR-ATR spectra of kappa/iota-hybrid carrageenan (KIC) extracted from Mastocarpus stellatus red seaweed, commercial kappacarrageenan (KC) and commercial iota-carrageenan (IC). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

determination coefficient (R2), the root mean squared error (RMSE), Eq. (2), and the mean relative deviation (MRD), Eq. (3):

2.5. Water sorption isotherms Experimental water adsorption and desorption isotherms of KIC, KC and IC were determined in triplicate at four temperatures (5, 25, 45 and 65 °C) and different water activities within the range of 0.10-0.86 using a static gravimetric method based on dispositive (Evans & Cristhfield, 1933). Firstly, samples were placed into an environment of approximately 8% (NaOH) and 100% (H2O) relative humidity for a couple of weeks in order to ensure the adsorption and desorption processes, respectively. Afterwards, small samples (around 0.5 ± 0.1 g) were placed in sealed jars, which were provided with different water saturated salt solutions to generate atmospheres with different relative humidity, until equilibrium was achieved. Samples were weighed at regular intervals until constant weight ( ± 0.0005 g) in an analytical balance (Denver Instruments SI-234, Germany). The saturated salt solutions used (LiCl, MgCl2, Mg(NO3)2, NH4NO3, NaCl and KCl) were prepared following Greenspan’s recommendations (Greenspan, 1977). Small amounts of crystalline thymol were placed into the jars at water activity, aw, higher than 0.5 in order to avoid microbial growth. The average time of samples equilibration was around 3 months. Several models to fit the experimental equilibrium moisture content, X (kg water (kg d.b.)−1), at different water activity, aw, were tested. Caurie model (Caurie 1970), Eq. (1), was selected as the most adequate model fitting all experimental isotherms of tested hydrocolloids, after the corresponding statistical analysis of fit goodness.

1 ⎤ X= exp ⎡a w ln (A) − ⎢ 4.5XS ⎥ ⎦ ⎣

⎡1 RMSE = ⎢ N ⎣

MRD =

1 N

1/2

N

∑ i= 1

N

∑

⎤ (X exp − X cal)2⎥ ⎦

(2)

X exp − X cal

i= 1

X exp

(3)

being N the samples numbers and Xexp and Xcal the experimental and calculated equilibrium moisture content, respectively. R2, RMSE and MRD coefficients may be combined into the following performance index, ϕ, Eq. (4), where higher ϕ values indicate a better adequacy of the model to describe the experimental behaviour:

φ=

R2 (RMSE)(MRD)

(4)

Moreover, a series of statistical indices (γ, χ and zr), reported elsewhere (Ruiz-López & Hernan-Lara, 2009; Moreira, Chenlo, Torres, & Prieto, 2017) to determine whether a given model should be used to fit the experimental data, were also used here in order to verify the satisfactory selection of Caurie model for tested isotherms. The model discrimination procedure can be summarised as follows: reject any model where γ < 1, χ2 > 5.99 and zr > 1.96. Differences between means of the values of the Caurie model parameters for all water sorption isotherms were identified by onefactor analysis of variance (ANOVA), followed by the Scheffé test, considering significant p-values ≤ 0.05 (IBM SPSS Statistics 22.0.0). 2

(1) −1

where A (−) and XS (kg water (kg d.b.) ) are the corresponding Caurie parameters. Note here that A corresponds to the antilog of the magnitude of the gradient and Xs, the safe moisture content, has been related to the maximum food stability under the process/storage conditions (Caurie 1970; Vega-Gálvez, López, Ah-Hen, Torres, & LemusMondaca, 2014).

3. Results and discussion 3.1. Chemical characteristics Fig. 1 displays the FTIR-ATR spectra of extracted kappa/iota-hybrid carrageenan (KIC) compared with those of commercial kappa- (KC) and iota- (IC) carrageenans. As expected, KC spectra exhibited the main commercial kappa-carrageenan features: a relatively strong band around 845 cm−1 which is related to D-galactose-4-sulphate (G4S) and

2.6. Statistical analysis The fit goodness of tested models was determined based on the 74

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another strong band at approximately 930 cm−1 ascribed to 3,6-anhydro-D-galactose (DA). IC spectra also showed the two aforementioned bands together with a characteristic band (around 805 cm−1) of the iota-carrageenan which indicates the presence of a sulphate group on the second carbon of the anhydro ring (DA2S). In this context, KIC spectra indicated that extracted biopolymer exhibits kappa- and iotacarrageenan disaccharide units in their backbone, with bands at 805 cm−1 (DAS2) and 845 cm−1 (G4S). The two bands intensity ratio can be employed to deduce the iota/kappa hybridisation degree (Hilliou et al., 2012). The presence of DA in KIC is confirmed by a welldefined band at approximately 930 cm−1. All tested carrageenans showed a wide band at approximately 1240 cm−1 assigned to the S]O stretching vibration of the sulphated groups, which is related to the biopolymer sulphate amount. These FTIR-ART spectra nicely match with those previously reported for different pure and hybrid carrageenan types extracted from different red algae (Pereira et al., 2009). Hence, above spectra confirm that Mastocarpus stellatus red seaweed is basically a carrageenophyte from which kappa/iota-hybrid carrageenans can be isolated as reported elsewhere (Azevedo et al., 2015), even when biopolymer isolation is carried out without alkali pre-treatment. The molar fractions of the kappa- and iota- carrageenan disaccharide units in tested KIC samples, defined as the integrated intensity of the corresponding 1H NMR peak over the sum of the integrated intensities of all assigned carrageenan anomeric protons, were 73 ± 4 and 27 ± 4, respectively (Fig. 2). These values are consistent with those previously reported for kappa/iota-hybrid carrageenan extracted from Mastocarpus stallatus seaweeds with alkali extraction procedures (Azevedo et al., 2015; van de Velde, Pereira, & Rollema, 2004). In 1H NMR spectra of KIC, the absence of any peak at 1.44 and 5.35 ppm also indicated that this biopolymer is free of impurities as pyruvate and floridean starch (Pereira & van de Velde, 2011). A negligible signal (∼5.15 ppm) was observed a bit downfield from the anomeric proton of DA of kappa-carrageenan, suggesting very small amount of impurities (< 1.5%) coming from the extraction procedure. In this context, isolated KIC was employed without further purification, since KIC samples are basically pure with minor pigment content as previously identified by detailed 1H NMR spectroscopic analysis (Azevedo et al., 2015). Sulphate analysis indicated that KIC (20.7 ± 0.3) exhibited intermediate sulphate content (%) between IC (27.8 ± 0.2) and KC (18.9 ± 0.1). These values are consistent with those (between 15 and 40%) previously reported for hybrid carrageenans extracted from

Mastocarpus stellatus (Gómez-Ordoñez, Jiménez-Escrig, & Rupérez, 2014) and other carrageenans extracted from different red seaweeds (Villanueva et al., 2004). Concerning the degree of sulphation, it should be indicated that the experimentally obtained data for IC (1.97 ∼ 2.0), KIC (1.15) and KC (0.98 ∼ 1.0) nicely match with those theoretical reported elsewhere (Rochas et al., 1986). The crystallinity values (%) obtained from X-ray diffraction for IC, KIC and KC were 25.4 ± 0.6, 9.3 ± 0.4 and 4.8 ± 0.2, respectively. These results suggest that the KIC crystallinity degree could be acceptably estimated (around 10.4%) by means of the molar fractions of the kappa- and iota- carrageenan disaccharide units present in assayed KIC samples above indicated. These results nicely match with those previously reported elsewhere (Michel, Nyval-Collen, Barbeyron, Czjzek, & Helbert, 2006), where iota carrageenan, the galactan so far most fully characterized in the solid state, particularly, as oriented fibres, is well-known as more crystalline structure than the kappa- one which has been identified as an almost amorphous biopolymer. The magnitudes of crystallinity for commercial tested carrageenans are consistent with those previously reported in the literature (Rane, Savadekar, Kadam, & Mashke, 2014). The authors are not aware that these crystallinity values had been previously reported for KIC. 3.2. Water sorption isotherms Fig. 3 gathers the experimental water (a) adsorption and (b) desorption isotherms for extracted KIC at tested temperatures. In all cases, the equilibrium moisture content rose with increasing water activity at each temperature and dropped with increasing temperature at fixed water activity. All tested isotherms were type II following Brunauer’s classification. The above observed thermal behaviour confirms that at the largest temperatures the water molecules activation changes to larger levels of energy, the links get less stable and break away from the biopolymer water binding sites, whence the equilibrium moisture content drop (Chenlo et al., 2011; Velázquez-Gutiérrez et al., 2015). Similar hygroscopic trends were identified for water (a) adsorption and (b) desorption sorption isotherms of commercial KC and IC (Fig. 4) when compared with those obtained for KIC, although exhibiting larger and lower hygroscopic characteristics, respectively. These carrageenans have two major characteristic functional groups, the anhydro (KC > KIC > IC) and sulphate groups (IC > KIC > KC), in different content as indicated above. As it is well-known, following the index of hydrophilicity of functional groups, the sulphate group exhibits much higher Fig. 2. 1H NMR spectrum of kappa/iota-hybrid carrageenan (KIC) extracted from Mastocarpus stellatus red seaweed. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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Fig. 3. Water (a) adsorption and (b) desorption isotherms of kappa/ iota-hybrid carrageenan (KIC) at different temperatures: (squares) 5, (circles) 25, (diamonds) 45 and (triangles) 65 °C. Lines correspond to Caurie model (Eq. (1)).

explain by its ionic character that carboxymethyl cellulose exhibits large values of equilibrium moisture content. Comparing water adsorption and desorption isotherms at each temperature, it was noticed that KIC, KC and IC exhibited hysteresis cycles in the water activity range from 0.3 to 0.86. In all cases, the largest differences between adsorption and desorption processes were observed at 5 °C, decreasing with increasing temperature. These results could be related to the process of solubility of some compounds in water promoted by temperature and structural changes (Bell & Labuza, 2000). This thermal impact on hysteresis cycles has been previously found for red seaweeds as Gracilaria chilensis with high polysaccharides content (Lemus et al., 2008), starchy flours (Moreira, Chenlo, Torres, & Prieto, 2010) or different types of leaves (Bahloul et al., 2008), suggesting that the hysteresis phenomenon could depend on temperature. Experimental water adsorption and desorption data for KIC, KC and

values than those reported elsewhere for the anhydro (38.7 vs 1.3) (Mitsuiki, Yamamoto, Mizuno, & Motoki, 1998). Thus it can be estimated that the hydrophilicities of these biopolymers increase in order IC > KIC > KC, which means that the water-binding capacities of IC seem to be higher. Nevertheless, the observed hygroscopic trend (KC > KIC > IC) is consistent with the obtained crystallinity data (IC > KIC > KC), since biopolymers containing less crystalline fraction are expected to be more hygroscopic. Briefly, the surface of the crystal is flat with minimal pores and water primary interacts with the polar groups on the crystalline surface (Mahmood et al., 2014). The equilibrium moisture content values for KIC, KC and IC are larger than those found for carrageenan gum films (Larotonda et al., 2015) and other galactomanans like guar gum (Vishwakarma et al., 2011), but in the same range as those reported for other hydrocolloids as carboxymethyl cellulose (Torres et al., 2012). Latter authors stated that the substitution degree of hydroxyl groups by carboxymethyl groups 76

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Fig. 4. Water (a) adsorption and (b) desorption isotherms of k/i-hybrid carrageenan (KIC) (grey) and commercial kappa- carrageenan (KC) (black) and iota- carrageenan (IC) (white) at maximum and minimum tested temperatures: (squares) 5 and (triangles) 65 °C. Dashed lines correspond to proposed model (Eq. (5)).

IC were satisfactorily fitted by means of Caurie model, Eq. (1), throughout the whole range of water activities. This model was selected based on the suitable values got for several statistical parameters (RuizLópez & Hernan-Lara, 2009) such as R2 (> 0.976), RMSE (< 0.025), MRD (< 0.087), Φ (> 2428), γ (> 8.65 104), χ2 (< 4.35), zr (< 0.993) (Table 1). The corresponding values of the Caurie model parameters for adsorption and desorption isotherms for KIC, KC and IC are summarised in Table 2. For all tested biopolymers, A parameter increased with increasing temperature, whereas Xs parameter showed the opposite trend. Note here that A parameter is related to the variation of the moisture content with water activity. The results showed that A values were approximately duplicated with temperature increasing from 5 to 65 °C. These values allow the evaluation of the wellknown effect of water activity on moisture content, which is more

Table 1 Statistical parameters for goodness assessment of non-linear fitting with Caurie model for experimental data of tested hydrocolloids. Samples

Statistical parameters R2

Adsorption

Desorption

KIC KC IC KIC KC IC

0.978 0.976 0.985 0.996 0.993 0.993

RMSE 0.022 0.025 0.018 0.016 0.018 0.014

MRD 0.087 0.083 0.072 0.068 0.070 0.063

Φ 2428 2493 2719 3608 3456 3490

γ 8.65 9.26 3.53 4.21 1.02 9.46

4

10 104 105 108 106 105

χ2

zr

4.35 4.26 3.06 2.01 2.94 2.98

0.993 0.989 0.802 0.523 0.791 0.752

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Table 2 Parameters for Caurie model (Eq. (1)) of kappa/iota-hybrid carrageenan (KIC) isolated from Mastocarpus stellatus red seaweed, commercial kappa-carrageenan (KC) and iota-carrageenan (IC) at several temperatures. Biopolymer

Parameter

Adsorption

Desorption

5 °C KIC

KC

IC

A (−) XS (kg water (kg d.b.)−1) A (−) XS (kg water (kg d.b.)−1) A (−) XS (kg water (kg d.b.)−1)

25 °C d

45 °C c

65 °C b

5 °C a

25 °C d

45 °C

65 °C

97.2 ± 4.5 0.051 ± 0.001a

130.6 ± 3.6 0.046 ± 0.001b

181.1 ± 3.8 0.041 ± 0.001c

223.5 ± 6.3 0.037 ± 0.001d

35.7 ± 0.8 0.068 ± 0.001a

45.5 ± 0.4 0.063 ± 0.001b

49.9 ± 1.5 0.055 ± 0.002c

61.0 ± 1.4a 0.047 ± 0.001d

100.9 ± 4.1d 0.053 ± 0.001a

145.5 ± 4.2c 0.049 ± 0.001b

200.4 ± 3.1b 0.043 ± 0.001c

244.6 ± 3.4a 0.039 ± 0.001d

38.9 ± 0.9d 0.073 ± 0.001a

51.3 ± 0.7c 0.068 ± 0.001b

54.9 ± 1.7b 0.061 ± 0.001c

67.2 ± 1.3a 0.051 ± 0.002d

78.25 ± 2.3d 0.049 ± 0.001a

122.9 ± 4.1c 0.044 ± 0.001b

169.0 ± 1.8b 0.039 ± 0.001c

206.1 ± 1.3a 0.035 ± 0.001d

33.5 ± 0.5d 0.063 ± 0.001a

39.1 ± 0.7c 0.060 ± 0.001b

46.1 ± 1.8b 0.051 ± 0.002c

60.3 ± 1.1a 0.043 ± 0.001d

E XS KC; IC = XS 0exp ⎡ aX ⎤ ⎣ RT ⎦

pronounced at high temperature. Overall, considering Xs as the safe moisture content, the determination of these values for adsorption and desorption processes allow the determination of the range of water activity for safe storage conditions. Particularly, the safe aw ranges at common storage temperatures for KC were between 0.12 and 0.27 at 5 °C and from 0.15 to 0.31 at 25 °C. For IC, these values ranged between 0.22 and 0.35 at 5 °C and from 0.24 to 0.40 at 25 °C. The above thermal dependence of the parameters is consistent with that previously reported for different foodstuffs with high sugar content (Panchev, Slavov, Nikolova, & Kovacheva, 2010; Vega-Gálvez, Palacios, & LemusMondaca, 2008). As expected from experimental data trends, A and Xs presented the following order KC > KIC > IC at constant temperature. Previous works suggested that this hygroscopic behaviour could also be related with the biopolymer molecular weight, since different carboxymethyl cellulose (Imeson, 2010) and polyethylene glycol (Baird, Olayo-Valles, Rinaldi, & Taylor, 2010) samples with different degrees of substitution and molecular weights; exhibiting a variety of watersorption behaviours. This hypothesis jointly the crystallinity features aforementioned could support the general hygroscopic trends observed in this manuscript for tested carrageenans. The magnitudes of these values are within the range of those found for other foodstuffs rich in carbohydrates (Pallavi, Chetana, Ravi, & Reddy, 2015). Data are presented as mean ± standard deviation. Data values in a row (adsorption and desorption independently) with different superscript letters are significantly different at the p ≤ 0.05 level.

c

b

(7)

being A0 and XS0 (kg water (kg d.b.)−1) the corresponding Arrhenius parameters, Eai are the corresponding activation energies (J/mol), R the gas constant (J/(K mol)−1) and T the absolute temperature (K). The analysis of the Eai values indicated that, in all cases, the dependence of A parameter with temperature was larger than XS and more pronounced in the water adsorption isotherms. This thermal effect was strong for KC. The combined effect on both parameters is related to the shift of the safe range towards higher water activity in the case of IC. Fig. 4 displays representative predicted water (a) adsorption and (b) desorption isotherms of KIC at maximum and minimum tested temperatures, as representative of tested systems, compared with those data obtained experimentally for KIC, KC and IC at the same temperatures. The largest differences between experimental and estimated isotherms were observed for adsorption process at the lowest temperature (5 °C). In all cases, the experimental water adsorption (R2 > 0.981 RMSE (< 0.026), MRD (< 0.082), Φ (> 2124), γ (> 2.01 104), χ2 (< 4.91), zr (< 0.943)) and desorption (R2 > 0.989, RMSE (< 0.018), MRD (< 0.072), Φ (> 2641), γ (> 3.42 105), χ2 (< 3.79), zr (< 0.883)) isotherms of extracted KIC were adequately estimated from the corresponding individual water sorption isotherms of commercial kappa and iota carrageenans at each temperature. These results indicate that it is possible to predict adequately the water sorption behaviour of KIC from their disaccharide units in a wide range of temperatures. The good reproducibility of the model is still surprising considering the differences between commercial and extracted carrageenans, even though it represents an interesting achievement that should be corroborated with other carrageenans. Above outcomes also suggests that the crystallinity of KIC samples could be indirectly estimated throughout the proposed model since knowing the hygroscopic properties could be estimated the corresponding kappa- and iota- carrageenan content and then predicted the crystallinity values. Even though, similar procedures were used to satisfactorily predict the water desorption isotherms of sucrose from water desorption isotherms of its individual monomers (glucose and fructose) from 20 to 65 °C (Moreira et al., 2017).

3.3. Prediction water sorption isotherms of kappa/iota-hybrid carrageenan Analysing Caurie model parameters, Eq. (1), and taking into account molar fractions of the carrageenan repeating units calculated by 1 H NMR and the corresponding molecular weights determined by GPC, the following mass fractions (0.83 and 0.17) can be determined for KC and IC, respectively. Adding these factors to the Caurie model parameters, a nice prediction model for KIC hygroscopic properties can be established for adsorption and desorption processes at each temperature.

1 ⎤ XKIC = exp ⎡a w ln (0.83AKC + 0.17AIC ) − ⎢ 4.5(0.83XS KC + 0.17XS IC) ⎥ ⎦ ⎣

4. Conclusions (5) Water sorption behaviour of tested biopolymers was influenced by molar fractions of the kappa (KC) and iota (IC) carrageenan repeating units and crystallinity. Hybrid carrageenan (KIC) exhibited intermediate hygroscopic characteristics between KC and IC at each tested temperature. Water sorption isotherms of KIC were adequately estimated from water sorption isotherms of its disaccharides units (kappa and iota) from proposed model including the temperature effect. The experimental equilibrium moisture content data of assayed biopolymers were nicely fitted using the Caurie model. Further work should be

where, XKIC is the equilibrium moisture content for KIC samples and AKC, AIC, XsKC and XSIC the corresponding Caurie parameters for kappa and iota carrageenan, respectively. The influence of temperature on above proposed model parameters (Eq. (5)) can be successfully calculated (R2 > 0.978) by Arrhenius-type equations (Table 3):

E AKC; IC = A0 exp ⎡ aA ⎤ ⎣ RT ⎦

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Table 3 Parameters for Eqs. (6–7) corresponding to the dependence on proposed model (Eq. (5)) with temperature. Biopolymer

KC IC

Adsorption

Desorption

A0 (−)

EaA/R (K)

XS0 (kg water (kg d.b.)−1)

EaX/R (K)

A0 (−)

EaA/R (K)

XS0 (kg water (kg d.b.)−1)

EaX/R (K)

11097 ± 111 19714 ± 205

–1305 ± 53.2 –1526 ± 22.4

0.10 ± 0.01 0.07 ± 0.01

459.2 ± 9.8 529.5 ± 8.7

665.1 ± 10.6 815.5 ± 23.2

−779.3 ± 15.4 −896.7 ± 9.2

0.12 ± 0.01 0.10 ± 0.01

478.6 ± 12.3 543.6 ± 10.4

on the synthesis and thermal properties of carrageenan ester. Journal of Physical Science, 25, 123–138. Michel, G., Nyval-Collen, P., Barbeyron, T., Czjzek, M., & Helbert, W. (2006). Bioconversion of red seaweed galactans: a focus on bacterial agarases and carrageenases. Applied Microbiology and Biotechnology, 71, 23–33. Mitsuiki, M., Yamamoto, Y., Mizuno, A., & Motoki, M. (1998). Glass transition properties as a function of water contente for various low-moisture galactans. Journal of Agricultural and Food Chemistry, 46, 3528–3534. Moreira, R., Chenlo, F., & Torres, M. D. (2009). Simplified algorithm for the prediction of water sorption isotherms of fruits: vegetables and legumes based upon chemical composition. Journal of Food Engineering, 94, 334–343. Moreira, R., Chenlo, F., Torres, M. D., & Prieto, D. M. (2010). Water adsorption and desorption isotherms of chestnut and wheat flours. Industrial Crops and Products, 32, 252–257. Moreira, R., Chenlo, F., Torres, M. D., & Prieto, D. M. (2017). Statistical criteria for modelling of water desorption isotherms of sugars: estimation of sucrose hygroscopic properties from glucose and fructose data. Advances in Food Science and Engineering, 1, 18–27. Pallavi, B. V., Chetana, R. C., Ravi, R., & Reddy, S. Y. (2015). Moisture sorption curves of fruit and nut cereal bar prepared with sugar and sugar substitutes. Journal of Food Science and Technology, 52, 1663–1669. Panchev, I. N., Slavov, A., Nikolova, Kr., & Kovacheva, D. (2010). On the water-sorption properties of pectin. Food Hydrocolloids, 24, 763–769. Pereira, L., & van de Velde, F. (2011). Portuguese carrageenophytes: carrageenan composition and geographic distribution of eight species (Gigartinales, Rhodophyta). Carbohydrate Polymers, 84, 614–623. Pereira, L., Amado, A. M., Critchley, A. T., van de Velde, F., & Ribeiro-Claro, P. J. A. (2009). Identification of selected seaweed polysaccharides (phycocolloids) by vibrational spectroscopy (FTIR-ATR and FT-Raman). Food Hydrocolloids, 23, 1903–1909. Rane, L. R., Savadekar, N. R., Kadam, P. G., & Mashke, S. T. (2014). Preparation and characterization of k-carrageenan/nanosilica biocomposite film. Journal of Materials, 2014, 736271. Rochas, C., Lahaye, M., & Yaphe, W. (1986). Sulfate content of carrageenan and agar determined by infrared spectroscopy. Botanica Marina, XXIX, 335–340. Rosell, C. M., Collar, C., & Haros, M. (2007). Assessment of hydrocolloid effects on the thermo-mechanical properties of wheat using the Mixolab. Food Hydrocolloids, 21, 454–462. Ruiz-López, I. I., & Hernan-Lara, E. (2009). Statistical indices for the selection of food sorption isotherms models. Drying Technology, 27 [726–238. Torres, M. D., Moreira, R., Chenlo, F., & Vázquez, M. J. (2012). Water adsorption isotherms of carboxymethyl cellulose, guar, locust bean: tragacanth and xanthan gums. Carbohydrate Polymers, 89, 592–598. Torres, M. D., Hallmark, B., & Wilson, D. I. (2014). Effect of concentration on shear and extensional rheology of guar gum solutions. Food Hydrocolloids, 40, 85–95. Torres, M. D., Chenlo, F., & Moreira, R. (2017). Thermal reversibility of kappa/iota-hybrid carrageenan gels extracted from Mastocarpus stellatus at different ionic strengths. Journal of the Taiwan Institute of Chemical Engineers, 71, 414–420. Vega-Gálvez, A., Palacios, M., & Lemus-Mondaca, R. (2008). Moisture sorption isotherms and isosteric heat determination in chilean papaya (Vasconcellea pubescens). Quimica Nova, 31, 1417–1421. Vega-Gálvez, A., López, J., Ah-Hen, K., Torres, M. J., & Lemus-Mondaca, R. (2014). Thermodynamic properties, sorption isotherms and glass transition temperature of cape gooseberry (Physalis peruviana L.). Food Technology and Biotechnology, 52, 83–92. Velázquez-Gutiérrez, S. K., Figueira, A. C., Rodríguez-Huezo, M. E., Román-Guerrero, A., Carrillo-Navas, H., & Pérez-Alonso, C. (2015). Sorption isotherms, thermodynamic properties and glass transitiontemperature of mucilage extracted from chia seeds (Salvia hispanica L.). Carbohydrate Polymers, 121, 411–419. Villanueva, R. D., Mendoza, W. G., Rodriguez, M. R. C., Romero, J. B., & Montaño, M. N. E. (2004). Structure and functional performance of gigartinacean kappa-iota hybrid carrageenan and solieriacean kappa-iota carrageenan blends. Food Hydrocolloids, 18, 283–292. Vishwakarma, R. K., Shivhare, U. S., & Nanda, S. K. (2011). Moisture adsorption isotherms of guar (Cyamposis tetragonoloba) grain and guar gum splits. LWT- Food Science and Technology, 44, 969–975. Wang, J., & Somasundaran, P. (2007). Study of galactomannose interaction with solids using AFM: IR and allied techniques. Journal of Colloid and Interface Science, 309, 373–383. Willems, W. (2015). A critical review of the multilayer sorption models and comparison with the sorption site occupancy (SSO) model for wood moisture sorption isotherm analysis. International Journal of the Biology, 69, 67–75. Williams, P. A. (2007). Handbook of industrial water soluble polymers. Oxford: Blackwell Publishing Ltd.

carried out to extend the proposed estimation model and selection statistical criteria to water sorption isotherms from other natural hybrid carrageenans including lamda-, mu-, nu-, among others. Acknowledgements The authors acknowledge the financial support to the Consellería de Cultura, Educación e Ordenación Universitaria da Xunta de Galicia (ED431B). We also would like to thank the use of RIAIDT-USC analytical facilities for FTIR-ATR, 1HNMR and X-ray diffraction tests. Spain, as sponsor country. References AOAC (2000). Official methods of analysis. Washington DC: Association of Official Analytical Chemists. Azevedo, G., Torres, M. D., Sousa-Pinto, I., & Hilliou, L. (2015). Effect of pre-extraction alkali treatment on the chemical structure and gelling properties of extracted hybrid carrageenan from Chondrus crispus and Ahnfeltiopsis devoniensis. Food Hydrocolloids, 50, 150–158. Bahloul, N., Boudhrioua, N., & Kechaou, N. (2008). Moisture desorption-adsorption isotherms and isosteric heats of sorption of Tunisian olive leaves (Olea europaea L.). Industrial Crops and Products, 28, 162–176. Baird, J. A., Olayo-Valles, R., Rinaldi, C., & Taylor, L. S. (2010). Effect of molecular weight, temperature: and additives on the moisture sorption properties of polyethylene glycol. Journal of Pharmaceutical Sciences, 99, 154–168. Bell, L. N., & Labuza, T. P. (2000). Moisture sorption: practical aspects of isotherm measurement and use. Minnesota: American Association of Cereal Chemists. Bixler, H. J., & Porse, H. (2011). A decade of change in the seaweed hydrocolloids industry. Journal of Applied Phycology, 23, 321–335. Bonilla, E., Azuara, E., Beristain, C. I., & Vernon-Carter, E. J. (2010). Predicting the suitable storage conditions for spray-dried microcapsules formed with different biopolymer matrices. Food Hydrocolloids, 24, 633–640. Caurie, M. (1970). A new model equation for predicting safe storage moisture levels for optimum stability of dehydrated foods. Journal of Food and Technology, 5, 301–307. Chenlo, F., Moreira, R., Prieto, D. M., & Torres, M. D. (2011). Desorption isotherms and net isosteric heat of chestnut flour and starch. Food and Bioprocess Technology, 4, 1497–1504. Correia, P., Cruz-Lopes, L., & Beirão-da-Costa, L. (2012). Morphology and structure of chestnut starch isolated by alkali and enzymatic methods. Food Hydrocolloids, 28, 313–319. Evans, W. D., & Cristhfield, C. L. (1933). Water absorption. Journal of Research of the National Bureau of Standards, 11, 147–152. Gómez-Ordoñez, E., Jiménez-Escrig, A., & Rupérez, P. (2014). Bioactivity of sulfated polysaccharides from the edible red seaweed Mastocarpus stellatus. Bioactive Carbohydrates and Dietary Fibre, 3, 29–40. Greenspan, L. (1977). Humidity fixed points of binary saturated aqueous solutions. Journal of Research of the National Bureau of Standards Section A, 81, 89–102. Hilliou, L., Larotonda, F. D. S., Abreu, P., Abreu, M. H., Sereno, A. M., & Gonçalves, M. P. (2012). The impact of seaweed life phase and post-harvest storage duration on the chemical and rheological properties of hybrid carrageenans isolated from Portuguese Mastocarpus stellatus. Carbohyd Polymers, 87, 2655–2663. Imeson, A. (2010). Food stabilisers, thickeners and gelling agents. United Kingdom: WileyBlackwell. Jackson, S. G., & McCandless, E. L. (1978). Simple, rapid: turbidometric determination of inorganic sulfate and/or protein. Analytical Biochemistry, 90, 802–808. Jonathan, G., & Karim, A. (2016). 3D printing in pharmaceutics: a new tool for designing customized drug delivery systems. International Journal of Pharmaceutics, 499, 376–394. Labuza, T. P., Knnane, A., & Chen, J. Y. (1985). Effect of temperature on the moisture sorption isotherm and water activity shift of two dehydrated foods. Journal of Food Science, 50, 385–392. Larotonda, F. D. S., Torres, M. D., Gonçalves, M. P., Sereno, A. M., & Hilliou, L. (2015). Hybrid carrageenan-based formulations for edible film preparation: benchmarking with kappa carrageenan. Journal of Applied Polymer Science, 42263–42273. Lemus, R., Pérez, M., Andrés, A., Roco, T., Tello-Ireland, C. M., & Vega-Gálvez, A. (2008). Kinetic study of dehydration and desorption isotherms of red alga Gracilaria. LWTFood Science and Technology, 41, 1592–1599. Mahmood, W. A. K., Rahman, M. M., & Yee, T. C. (2014). Effects of reaction temperature

79

Carbohydrate Polymers 180 (2018) 72–80

M.D. Torres et al.

data of carrageenans. Carbohydrate Research, 339, 2309–2313. van de Velde, F. (2008). Structure and function of hybrid carrageenans. Food Hydrocolloids, 22, 727–734.

Yan, H., Cai, B., Cheng, Y., Guo, G., Li, D., Yao, X., et al. (2012). Mechanism of lowering water activity of konjac glucomannan and its derivatives. Food Hydrocolloids, 26, 383–388. van de Velde, F., Pereira, L., & Rollema, H. S. (2004). The revised NMR chemical shift

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