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Retention of aroma compounds by corn, sorghum and amaranth starches
Food Research International 54 (2013) 338–344
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Retention of aroma compounds by corn, sorghum and amaranth starches Wioletta Błaszczak a,⁎, Tamara A. Misharina b, Dimitrios Fessas c, Marco Signorelli c, Adrian R. Górecki a a b c
Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Tuwima Str. 10, 10-748 Olsztyn, Poland The Emmanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygina 4, Moscow 119991, Russia DeFENS, University of Milan, Via Celoria 2, 20133 Milano, Italy
a r t i c l e
i n f o
Article history: Received 13 March 2013 Accepted 7 July 2013 Keywords: Retention Aroma compounds Starch GC DSC
a b s t r a c t The presented study addressed assays of odorant retention from an essential oil mixture by native corn, sorghum and amaranth starches using capillary gas chromatography (GC) and differential scanning calorimetry (DSC). The essential oil mixture consisted of 30 main compounds, including monoterpene and sesquiterpene hydrocarbons, alcohols, ketone, phenols and ester. The native starches were characterized for their chemical composition (amylose, protein, and surface lipids content), surface properties (surface area, pore diameter), and microstructure (SEM). The starches were mixed with odorants, stirred intensively, and stored at room temperature in the dark for 2 days (reference sample), 3 and 7 months. The chemical properties of odorants, their composition in the mixture as well as starch surface properties were observed to affect the retention of aroma compounds upon storage. Irrespective of starch botanical origin, a significant loss was noticed in monoterpene hydrocarbons throughout the storage period. Alcohols, ketone, phenols and sesquiterpene hydrocarbons were highly retained on amaranth and sorghum starches upon 3 months of storage. However, after prolonged storage their retention diminished, especially in the case of amaranth starch. The DSC results obtained for stored corn and sorghum starches with odorants demonstrated an extra endothermic contribution, which indicated that the aroma compounds were highly retained by the gelatinized starch matrixes. Furthermore, the odorants showed ability to interact with the solubilized amylose. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction The encapsulation of aroma compounds is used to entrap volatile and labile flavorings into a carrier in order to protect them from evaporation and/or degradation as well as from off-flavor development upon storage (Baranauskiene, Bylaite, Zukauskaite, & Venskutonis, 2007; Partanen, Ahro, Hakala, Kallio, & Forssel, 2002). The mechanism of protection and release of the encapsulated compounds would differ between the various carriers. The encapsulation wall system is often based on polymers with hydrophilic and/or hydrophobic groups that display the ability to form a network-like matrix (Baranauskiene et al., 2007). Starch and its derivatives are widely used not only as thickeners, stabilizers, and gelling and texturing agents but also as carriers of aroma compounds. The nature of some starches, their granule size, shape, specific area, porosity, crystalline or amorphous character, etc., and the composition of starch–polysaccharide matrices were found to play a major role in binding the volatile substances (Boutboul, ⁎ Corresponding author. Tel.: +48 895234615; fax: +48 895240124. E-mail addresses: [email protected] (W. Błaszczak), [email protected] (T.A. Misharina), [email protected] (D. Fessas), [email protected] (M. Signorelli), [email protected] (A.R. Górecki). 0963-9969/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodres.2013.07.032
Giampaoli, Feigenbaum, & Ducruet, 2002; Baranauskiene et al., 2007; Savary, Lafarge, Doublier, & Cayot, 2007; Zafeiropoulou, Evageliou, Gardeli, Yanniotis, & Komaitis, 2010). The binding of flavorings to starch is known as inclusion complex formation through the hydrophobic bonding in the amylose helix and/or polar interaction that involve hydrogen bonds between hydroxyl groups of starch and the odorant (Arvisenet, Voilley, & Cayot, 2002; Boutboul et al., 2002). The binding of low molecular compounds to starch might also be based on their non-specific sorption to the starch powders or to granule agglomerates (Conde-Petit, Escher, & Nuessli, 2006; Misharina, 2004). These porous structures of corn starch treated with glucoamylase revealed a high ability to retain peppermint oil (Zhao, Madson, & Whistler, 1996). The porous starch granules were found to retain 29% of the oil after standing in the open air for two months, while only 12% of oil remained on native starches after three days of storage in an open dish. Corn and barley starches subjected to succinylation were deemed promising carriers of volatile meat flavor compounds (Jeon, Vasanthan, Temelli, & Song, 2003). Over a 4-week storage period, flavor retention by these starches was higher than by β-cyclodextrin which is commonly used for encapsulation. It was also noted that hydrophobically-modified starches were used as shell materials in spray drying to encapsulate up to 50% of flavor compounds (Baranauskiene et al., 2007). The emulsifying starch (HiCap)
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was found to be an effective heat-stable matrix for encapsulating caraway oil (Partanen et al., 2002). Studies on starch type effect on the retention of aroma compounds from strawberry showed that corn starch (Amilogel G) was the best carrier for the majority of the compounds analyzed (Vidrith, Zlatic, & Hribar, 2009). The retention of aroma compounds on cross-linked waxy corn starch and/or polysaccharide gel was ascribed to the physicochemical interaction between the low molecular compounds and gel components (Savary et al., 2007). Apart from the structural and physicochemical characteristics of the polymer matrix, the efficiency of aroma compound retention was also related to their structure and chemical properties (Misharina, 2004). This author studied also the storage-related changes in the retention of different aroma compounds on dry corn starch and proved that the corn starch prevented volatile component oxidation during storage. The small pores, noted in literature as ‘pin holes’ were found on the granule surface of native sorghum starch using different microscopy techniques. It was suggested that these structures were openings to channels, with diameter from 5 to 400 nm, connecting an internal cavity at the granule hilum to the external surface (Fannon, Gray, Gunawan, Huber, & BeMiller, 2003; Perez, Baldwin, & Gallant, 2009; Singh, Sodhi, & Singh, 2010). It is likely that the pores and channels, naturally formed on the granule surface, allow some molecules with low molecular weight to directly access to the granule interior. However, the exact nature of the interaction between ligands (i.e. aroma compounds) and granule surface of native sorghum starch remains unknown since this topic is scarce in literature. Amaranth starch was also found to demonstrate a unique character of granules with respect of their size and surface properties. These starch granules appeared as small (up to 2.0 μm) (Kong, Corke, & Bertoft, 2009), and they tend to form large aggregates (up to 80 μm in size) (Mariotti, Lucisano, Pagani, & Perry, 2009). The literature data showed that the specific surface area of amaranth starch was significantly higher compared to that calculated for native potato starch or maize starch (Marcone, 2001; Sujka & Jamroz, 2009; Szymonska & Wodnicka, 2005), but on the other hand the specific surface area was also affected by other factors (Boutboul et al., 2002). A stable pore structure was found to be critical to provide a high surface area including the interiors and outer regions of the microspheres (Glenn et al., 2010). For sorghum and amaranth starches demonstrate unique surface properties, they might be considered as interesting material for odorant retention (Fannon et al., 2003). Bearing this in mind, in this study the ability of corn, sorghum and amaranth starches to retain aroma compounds was studied in relation to surface characteristics, thermal properties, and microstructure of starch. 2. Materials and methods 2.1. Plant material and starch isolation The seeds of plant species Amaranthus cruentus L. were donated by the Metro Industrial Centre “Szarłat” s.c. (Łomża, Poland), and sorghum Sorghum grains bicolor (v. Rona 1) were purchased from the Kutno-Centre for Sugar Beet Breeding in Straszkow, Poland. Commercial maize starch was donated by the Department of Food Concentrates in Poznan, the Institute of Agricultural and Food Biotechnology, Poland. The starch from amaranth seeds was isolated and purified according to the method developed by Walkowski, Fornal, Lewandowicz, and Sadowska (1997). Since the amaranth starch granules naturally form agglomerates varying in diameter, the isolated starch granules were sieved through a screen with a mesh of 350 — in order to unify their diameter. The isolation procedure described by Olayinka, Adebowale, and Olu-Owolabi (2008) was used to obtain starch from sorghum grains.
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2.2. Characteristics of essential oil mixture components The experiment was conducted with the aroma mixture comprising 30 main compounds, including monoterpene and sesquiterpene hydrocarbons, alcohols, ketones, phenols and ester (Table 1). All of them are constituents of commonly applied seasonings, and widely occur in a number of food products. The aroma mixture was prepared by mixing the essential oils of black pepper (1 mL), caraway (1 mL), coriander (1 mL), oregano (1 mL), and ginger (1.5 mL). The essential oils were purchased from Plant Lipids, Ltd, India. The composition of the analyzed essential oil mixtures (μg/50 mg) was determined by GC with internal standard — n-tridecane (Fluka, 99.5%) (Table 1). The hydrophobic properties of odorants were analyzed according to the method proposed by Griffin, Wyllie, and Markham (1999) by determining the octanol (Sigma-Aldrich, 99%) — water partition coefficient for terpenoids (Log Kow) with the use of reversed-phase high-performance liquid chromatography (Table 1). 2.3. Starch characterization Protein and moisture content of the analyzed starches were determined with standard AOAC methods (AOAC 1990a, 1990b). The amylose content of amaranth, sorghum and corn starches was assayed according to the method proposed by Morrison and Laignelet (1983). Surface lipids were defined as the lipid fraction extracted from the granule surface by cold solvent and was determined according to Kaukovirta-Norja, Reinikainen, Olkku, and Laakso (1997). The surface lipids were extracted by n-propanol (Sigma-Aldrich, 99.7%) — water Table 1 Composition of a model essential oil mixture. Compound Monoterpene hydrocarbons 1 α-Tujene 2 α-Pinene 3 Camphene 4 Sabinene 5 β-Pinene 6 β-Myrcene 7 α-Phellandrene 8 3-Carene 9 α-Terpinene 10 р-Cymene 11 Limonene 12 γ-Terpinene
Log Kow
Content in mixture (g/100 g)
4.38 4.25 4.10 4.38 4.36
0.32 3.96 1.20 2.20 2.35 0.88 0.02 1.90 1.10 4.80 15.70 1.60
4.44
4.16
Alcohols, 13 14 15 16 17 18 19 20
ketone, phenols Linalool Camphor α-Terpineol Terpinene-4-ol Carveol Carvone Thymol Carvacrol
3.50 2.74 3.28 3.26 3.12 2.74 3.30 3.49
15.40 1.02 0.26 0.02 0.29 11.40 0.60 11.80
Ester 21
Neryl acetate
3.98
0.60
Sesquiterpene hydrocarbons 22 α-Cubebene 23 β-Elemene 24 Caryophyllene 25 β-Selinene 26 β-Bisabolene 27 β-Sesquiphellandrene 28 α-Curcumene 29 Zingiberene 30 Caryophyllene oxide
6.33
1.00 0.36 5.80 0.58 1.80 3.10 2.54 6.80 0.60
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mixture (3:1, v/v) at ambient temperature for 30 min at a solid to solvent ratio of 1:10 (w/v). Extracts were combined, organic solvent was evaporated and the resultant products were lyophilized. The specific surface area, mesopore volume and average pore diameter were estimated using low-temperature nitrogen adsorption (ASAP 2405, Micrometrics Inc., USA). Isotherms were plotted for high-purity nitrogen adsorption at a temperature of 77.3 K. The monolayer capacity was calculated on the basis of adsorption isotherm (Brunauer, Emmett, & Teller, 1938) from five measurement points in the relative pressure range p/p0 0.006–0.2. Prior the measurements, starch samples were dried for 25 h in vacuum at 100 °C, automatically desorbed and flushed with pure helium. Pore characteristics were determined according to Barrett, Joyner, and Hallenda (1951). Samples were analyzed in triplicate. 2.4. Sample preparation Starch samples (5 g) were placed into flasks (50 mL) and 250 mg of an odorant mixture (50 mg/g) was added to the starches. The samples with the odorants were stirred intensively for 2 h, the flasks were closed using a cellulose stopper, and stored at room temperature in the dark for 2 days (reference sample), 3 and 7 months.
the first DSC heating run, which corresponds to the apparent heat capacity Cp(T) of the sample to obtain the trend of the excess (with re−1 −1 spect to the trend prior gelatinization) heat capacity, Cex g p (T) / J K (per gram of dry matter) and then evaluate the enthalpy drop ΔH through a straightforward integration of the corresponding trace. Each run was repeated at least twice. The actual dry mass of such samples was determined at the end of the DSC run by weighing the pierced cell kept at 105 °C for about 5 h. 2.7. Scanning electron microscopy The starch granules (powders) were deposited on the specimen holder using cuprum tape, and coated with gold in a vacuum evaporator (JEE 400, JEOL). The specimens were viewed in a JEOL JSM 520 scanning electron microscope at the accelerating voltage of 10 kV. 2.8. Statistical analysis The statistical analysis of results was carried out with Statistica ver. 5 (StatSoft, USA) software using variance analysis ANOVA supplemented by the Duncan multiple range test (General Convention and Statistics, Statistica for Windows, 2nd Edition, 209 StatSoft Inc.).
2.5. Capillary gas chromatography (GC) 3. Results and discussion 1.00 g of the sample (reference and stored) placed in a 5-mL glass tube and 2 mL of diethyl ether (Sigma-Aldrich, 99.7%) were added, the mixture was shaken for 0.5 h, and then 1 μL of n-tridecane (Fluka, 99. 5%) was added. The ether layer with extracted substances was separated by centrifugation (8000 g for 20 min) and analyzed by GC. Analyses of ether extracts of essential oils and the control sample were carried out using a Kristall 2000 M chromatograph (Russia) with a flame ionization detector and an SPB-1 fused silica capillary column (50 m × 0.32 mm, phase layer 0.25 μm). The column temperature was programmed from 60 to 250 °C with the speed of 8 °C/min at detector and injector temperature of 250 °C. The rate of helium flow through the column was 1.5 mL/min. The volume of the injected sample was 1–2 μL. The components of the essential oil mixture were identified based on retention indexes. Each sample was analyzed 3–4 times. The amount of substance unbound by starch and remaining in the aqueous phase was calculated from the ratio of substance peak areas and an internal standard. The amount of bound substances was calculated as the difference between the amount of the substance in the initial dispersions and the amount determined in the aqueous phase after centrifugation. The residual substance was determined with a maximum measurement error no more than 5% relative. The retention of odorant mixture components was expressed as a ratio of odorant determined in the reference sample (1.0) to the odorant amount determined after storage (3 and 7 months). 2.6. DSC analysis A PerkinElmer Diamond with 60 μL sealed cells was used to investigate starch gelatinization in excess of water (humidity 70%). The reference cell contained a suitable amount of distilled water. Measures were carried out in a temperature range of 20–150 °C at 2.0 °C min−1 scanning rate. Indium was used for calibration. The typical sample mass was 30 mg. The raw data were processed with the dedicated software IFESTOS which was assembled by the authors for handling raw calorimetric data according to the suggestions by Barone, Del Vecchio, Fessas, Giancola, and Graziano (1993), and Fessas and Schiraldi (2000). The base-line chosen to work out a given DSC trace was the trend extrapolated from the DSC record of the immediate re-heating run. It was subtracted from the record of
3.1. Retention of odorants by starches The retention values of individual odorants determined for the 2-day-stored starch powders (reference sample) ranged from 0.99 to 1.0. They indicated that none of the analyzed compounds, that formed the essential oil mixture, was lost during this period of storage. After 3 months of storage, the ability of corn, sorghum and amaranth starches to retain odorants from the essential oil mixture was observed to vary (Table 2). Amaranth starch demonstrated the highest average retention values for the analyzed groups of odorants (monoterpene and sesquiterpene hydrocarbons, alcohols, ketone, phenols or ester) compared to the corn and sorghum starches (Table 3). After 3 months of storage, retention of the majority of individual compounds from the groups of alcohols, ketone, phenols and sesquiterpene hydrocarbons by amaranth starch did not change for amaranth starch compared to the reference sample. Such individual compounds as linalool, camphor, and carvacrol were also highly retained by the amaranth starch. The retention values obtained for α-curcumene and caryophyllene oxide exceeded 1.0, whereas retention of zingiberene and caryophyllene by the amaranth starch was significantly lower compared to the initial values. This could result from zingiberene and caryophyllene oxidation to α-curcumene and caryophyllene oxide, respectively (Misharina, 2002). Such a relationship between the retention values of caryophyllene and caryophyllene oxide as well as zingiberene and α-curcumene was also noted for all samples analyzed throughout the storage period (3 and 7 months). In contrast to amaranth starch, sorghum starch manifested a significantly lower ability to retain the monoterpene and sesquiterpene hydrocarbons after 3 months of storage (Tables 2 and 3). γ-Terpinene was found to be retained at the lowest level (0.06) compared to the other compounds from the monoterpene hydrocarbon group. The high retention value obtained for p-cymene could be due to γ-terpinene oxidation. In turn, alcohols, ketone, phenols and ester as well as the majority of sesquiterpene hydrocarbons were highly retained on the sorghum starch upon 3 months of storage. Among all the analyzed starches, the corn starch revealed the weakest ability to retain alcohols, ketone, phenols, ester and sesquiterpene hydrocarbons throughout the storage period.
W. Błaszczak et al. / Food Research International 54 (2013) 338–344 Table 2 Retention of odorant mixture components by starches after 3 and 7 months of storage at room temperature. Compound
Retention on dry starch 3-month storage Corn
7-month storage
Sorghum
Amaranth
Corn
Sorghum
Amaranth
Monoterpene hydrocarbons α-Tujene 0.154 α-Pinene 0.146 Camphene 0.186 Sabinene 0.274 β-Pinene 0.267 β-Myrcene 0.337 α-Phellandrene 0.154 3-Carene 0.349 α-Terpinene 0.169 р-Cymene 0.617 Limonene 0.456 γ-Terpinene 0.152
0.224 0.207 0.255 0.377 0.357 0.504 0.192 0.454 0.231 0.816 0.577 0.069
0.510 0.480 0.531 0.643 0.625 0.780 0.769 0.720 0.600 0.835 0.793 0.776
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.021 0.013 0.000
0.000 0.000 0.000 0.010 0.010 0.025 0.000 0.025 0.000 0.152 0.086 0.000
0.000 0.000 0.000 0.011 0.010 0.050 0.000 0.049 0.000 0.192 0.120 0.030
Alcohols, ketone, phenols Linalool 0.829 Camphor 0.793 α-Terpineol 0.833 Terpinene-4-ol 0.771 Carveol 0.356 Carvone 0.874 Thymol 0.919 Carvacrol 0.877
0.879 0.867 0.938 1.000 1.000 0.932 1.000 0.954
0.989 0.966 1.000 1.000 1.000 1.000 1.000 0.989
0.720 0.608 0.800 0.743 0.333 0.940 0.838 1.000
0.811 0.779 0.816 1.000 1.000 0.904 1.000 0.986
0.676 0.615 0.640 1.000 0.849 0.755 1.000 0.844
Ester Neryl acetate
0.780
0.848
0.906
0.712
0.809
0.702
Sesquiterpene hydrocarbons α-Cubebene 0.817 β-Elemene 0.893 Caryophyllene 0.774 β-Selinene 0.411 β-Bisabolene 0.835 β-Sesquiphellandrene 0.829 α-Curcumene 1.687 Zingiberene 0.394 Caryophyllene oxide 0.916
0.895 1.000 0.859 0.458 1.000 0.926 2.107 0.368 1.602
1.000 1.000 1.000 0.557 1.000 1.000 1.068 0.911 1.200
0.815 0.969 0.603 0.335 0.980 0.873 2.510 0.080 3.029
0.926 0.994 0.728 0.435 1.000 0.929 2.867 0.035 2.878
0.698 0.869 0.722 0.312 0.772 0.724 1.412 0.391 1.236
Statistically significant differences were found in monoterpene hydrocarbon retention by the analyzed starches between storage periods (3 and 7 months) (Tables 2 and 3). Such compounds as α-tujene, α-pinene, camphene, α-phellandrene, and α-terpinene were completely lost after the 7-month storage — irrespectively of starch origin. In addition, a significant reduction was noticed in retention values of ester (Neryl acetate) between the storage periods. The retention values noted for carvacrol, carvone, β-elemene, and β-bisabolene on 7-month-stored corn starch were higher than the values obtained for 3-month-stored corn starch. In view of literature data, this might be ascribed to the structural changes of these odorants that proceed during their storage in the presence of other organic compounds (Misharina, 2002, 2004). Table 3 Retention of odorant groups by starches. Starch
Storage (months)
Monoterpene hydrocarbons
Alcohols, ketone, phenols
Ester (Neryl acetate)
Sesquiterpene hydrocarbons
Corn
3 7 3 7 3 7
0.272* 0.003* 0.355* 0.026* 0.672* 0.039*
0.842 A 0.807 a 0.946 B 0.912 b 0.993* B 0.797* a
0.780* A 0.712* a 0.848 AB 0.809* b 0.906* B 0.702* a
0.844* A 0.910* b 0.956 B 0.962 b 0.998* C 0.761* a
Sorghum Amaranth
A a A ab B b
Asterisk indicates statistically significant differences between storage months for starches of different botanical origin separately, capital and small letters indicate differences (uniform Duncan's groups) between starch of different origins after 3 and 7 months of storage, respectively.
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The sorghum starch demonstrated significantly higher average retention values of alcohols, ketone, phenols, ester and sesquiterpene hydrocarbons after 7 months of storage compared to corn and amaranth starches. Among sesquiterpene hydrocarbons, the retention of β-bisabolene remained unchanged after the storage period. In turn, a high retention value was noted for β-elemene. A significant decrease was observed in the retention of alcohols, ketone, phenols and sesquiterpene hydrocarbons by amaranth starch between 3 and 7 months of storage. The retention of terpinene-4-ol and thymol on amaranth starch did not change upon 7 months of storage, whereas the retention values noted for linalool, camphor and α-terpineol were distinctly lower compared to those obtained after 3 months of storage.
3.2. Effect of structure and surface properties of granules on odorant retention In order to characterize the surface properties of starches, the specific surface area and average pore diameter of granules were estimated using low-temperature nitrogen adsorption. While corn and sorghum starches demonstrated similar values of surface area, the values of average pore diameter determined for their granules varied significantly (Table 4). The SEM observations of corn starch (Fig. 1A) indicated that the granules were 6–14 μm with a slightly polygonal shape. The granules of corn starch varied also in surface morphology. Some of them appeared smooth, while others demonstrated a rough surface with distinct crater-like structures. It is generally known that the craterlike structures were formed upon starch synthesis in the kernel and resulted from the pressing of protein bodies into the soft, at that moment, starch granule (Haros, Blaszczak, Perez, Sadowska, & Rosell, 2006). This was also the case for sorghum starch (Fig. 1B). In addition, the SEM inspection showed explicitly the presence of small pores ‘pin holes’/capillaries on the starch granule surface. Those structures appeared on individual granules in the number of 30–50, providing access to the granule interior. The depth of those pores probably affected the value of average pore diameter to a significantly greater extent than in the case of corn starch. The amaranth starch was characterized by the highest values of surface area and average pore diameter compared to corn and sorghum starches. Considering the microscopic observations, it needs to be pinpointed that the physical properties determined for amaranth starch should be attributed to the agglomerates formed by granules (Fig. 1C) rather than to a single granule (Fig. 1D). The amaranth agglomerates were 20–60 μm large with an irregular shape, and were composed of hundreds of granules. Their surface was rough with multiple air spaces between the adhering granules, whereas the individual granules of amaranth starch were 0.8– 1.2 μm in size and had a polygonal shape and a smooth surface. In view of the above, the diminished retention of aroma compounds by the stored corn starches was, probably, due to the fact that most of the odorants were adsorbed on the granule's surface, owing to which they were more susceptible to vaporization/oxidation (Varavinit, Chaokasem, & Shobsngob, 2001; Wasserman, Misharina, & Yuryev, 2002) compared to the odorants trapped inside pores and/or capillaries of sorghum starch. As demonstrated in previous studies, the porous starches might prevent oxidation and transformation of volatile components during storage (Misharina, 2004; Zhao et al., 1996). The retention of aroma compounds by the matrices was also shown to depend on surface composition, i.e. presence of lipids and/or proteins (Seuvre, Philippe, Rochard, & Voilley, 2006). However, in the present study the retention of aroma compounds on the analyzed starches (corn, sorghum and amaranth) was triggered by the chemical properties of individual
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Table 4 Chemical, morphological, and thermodynamic characteristics of starches. Corn
Sorghum
Amaranth
Chemical analysis of starch (g/100 g) Moisture Amylose content Protein Surface lipid
10.50 ± 0.04 20.57 ± 0.31 0.44 ± 0.07 0.24 ± 0.07
12.80 ± 0.04 19.19 ± 0.11 0.78 ± 0.00 0.45 ± 0.07
10.50 ± 0.06 – 0.78 ± 0.00 0.16 ± 0.01
Physical properties of granules BET surface area (m2/g) Average pore diameter by BET (Å)
0.4635 48.9633
0.4911 80.0930
3.4062 104.2441
Gelatinization enthalpy (ΔH) of starch–odorant systems Native starch (ΔH, J g−1) Starch–odorants stored for 3 months (ΔH, J g−1) Starch–odorants stored for 7 months (ΔH, J g−1)
15 ± 1 18 ± 1 20 ± 1
16 ± 1 19 ± 1 22 ± 1
16 ± 1 15 ± 1 11 ± 1
odorants and surface properties of granules rather than by the presence of non − starch constituents on their surface (Table 4). 3.3. Thermal analysis of starch stored with odorants DSC measurements were also performed to assess the strength of interactions and the influence of aroma compounds retained in the starch matrices in respect of starch gelatinization properties. Thermograms obtained for the corn starch systems were presented in Fig. 2A. The main low-temperature peak (57–77 °C), observed in the thermogram of native corn starch, was attributed to amylopectin gelatinization. The consecutive broad peak (80–95 °C) is not clearly defined. Most likely it depicts the transition resulting
from the dissociation of the amylose–lipid complex. Worthy of notice is that the cooperativity and the temperature of such transition depend on system humidity (Fessas & Schiraldi, 2000). The results obtained for corn starches stored with odorants for 3 months and 7 months indicate that the heating of granules with the essential oil mixture caused an increase in the enthalpy values for the low-temperature peak (starch gelatinization region) (Table 4). This extra endothermic contribution might correspond to the energy required to displace aroma compounds adsorbed on the surface of starch granules during starch gelatinization. If so, the extra enthalpy would reflect the strength of such retention. Its value shows a kinetic evolution that can be matched with diffusion processes, which are affected by peculiarities (pores, cavities, etc.) of the granule structure.
Fig. 1. SEM images of native starch granules: A — corn; B — sorghum; C, D — amaranth.
W. Błaszczak et al. / Food Research International 54 (2013) 338–344
A
5.0
Cp ex / J g -1
4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 20
40
60
80
100
120
T /°C
B
5.0
Cp ex / J g -1
4.0 3.0
1.0
4. Conclusions
0.0
-2.0 20
40
60
80
100
120
80
100
120
T /°C 5.0 4.0
Cp ex / J g -1
process of the system (Table 4). In the case of the 7-month storage time, a strong variation was observed in the thermogram. In-depth analysis of a thermogram profile suggests the occurrence of exothermic effects (aggregations) that are concomitant with the gelatinization process rather than the destabilization of starch granules. We hypothesize that such aggregation phenomena could be triggered by the significant decrease in odorants in the starch matrix after 7 months of storage, which in turn might change the hydration properties of the system. In conclusion, in this case, there is no evidence of a particular complexation/interaction between the aroma compounds and the amaranth starch, and the retention properties might mostly depend on the large surface area exposed. The data obtained from DSC analysis confirm the findings presented in the preceding paragraphs, although only in a qualitative sense. A more precise estimation would indeed require much more information about such factors as: chemical properties of odorants, the overall exposed granule surface, defects and pore conformation and distribution, as well as the total amount of the odorants per gram of the samples investigated (Misharina, 2002; Wasserman et al., 2002).
2.0
-1.0
C
343
3.0 2.0 1.0 0.0 -1.0 -2.0 20
40
60
T /°C Fig. 2. Thermograms of corn (A), sorghum (B), and amaranth (C) starches: native (—); 3 months stored (–); 7 months stored (⋯).
Furthermore, it was observed that exothermic signals appeared in the amylose transition region, which indicated that crystallization and eventually melting occurred during heating, and suggested further interactions of aromatic compounds with amylose. A similar phenomenon was observed for the sorghum starch systems (Fig. 2B) in terms of amylopectin gelatinization. Higher enthalpy values obtained for sorghum-odorant systems, heated in an excess of water, implied stronger retention of aroma compounds on the granules than in corn starch stored with odorants (Table 4). Due to high humidity, the transition of amylose–lipid complexes was not tangible in the thermograms obtained. However, in the case of sorghum starch stored with odorants for 7 months, strong disturbances (almost random in the profile but present in all replicas) were noted in this temperature region, which may correspond to the phenomena observed for corn starch. Thermograms obtained for amaranth systems (Fig. 2C) were biphasic, which indicated different stability of granules distributed in a bulk sample. Storage of starch with the aroma compounds for 3 months did not seem to affect considerably the overall gelatinization
The corn, sorghum and amaranth starches demonstrated different abilities to retain aroma compounds from the essential oil mixture upon 3 and 7 months of storage. The retention of aroma compounds from the group of monoterpene hydrocarbons on the stored starches was the lowest, compared to such groups of odorants as: alcohols, ketone, phenols and sesquiterpene hydrocarbons. The overall exposed surface and/or pores distribution found for aggregates of amaranth starch make it the most promising for odorant retention during 3-month storage. However, the sorghum and corn starch should be recommended for the prolonged period of storage. An increase in melting enthalpy noted for both these starches and the appearance of exothermic signals in the amylose transition region indicated that the odorants were strongly retained in the gelatinized starch matrix, and additionally showed ability to interact with hydrated and solubilized amylose. Summarizing, the overall retention of odorants by starches resulted from various factors, with the key ones including: composition and chemical properties of aroma compounds, morphology and surface characteristics of starch granules. Acknowledgments The study was financed by a grant from the Ministry of Science and Higher Education (Grant No. N N312 101938). References AOAC (1990a). Official method of analysis, protein (15th ed.)Arlington, USA: Association of Official Analytical Chemistry, 781. AOAC (1990b). Official method of analysis, ash and moisture content (15th ed.) Arlington, USA: Association of Official Analytical Chemistry, 777. Arvisenet, G., Voilley, A., & Cayot, N. (2002). Retention of aroma compounds in starch matrices: Compositions between aroma compounds toward amylose and amylopectin. Journal of Agricultural and Food Chemistry, 50, 7345–7349. Baranauskiene, R., Bylaite, E., Zukauskaite, J., & Venskutonis, P. R. (2007). Flavor retention of peppermint (Mentha piperita L.) essential oil spray-dried in modified starches during encapsulation and storage. Journal of Agricultural and Food Chemistry, 55, 3027–3036. Barone, G., Del Vecchio, P., Fessas, D., Giancola, C., & Graziano, G. (1993). Theseus: A new software package for the handling and analysis of thermal denaturation data of biological macromolecules. Journal of Thermal Analysis, 39, 2779–2790. Barrett, E. P., Joyner, L. G., & Hallenda, P. H. (1951). The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms. Journal of the American Chemical Society, 73, 373–381. Boutboul, A., Giampaoli, P., Feigenbaum, A., & Ducruet, V. (2002). Influence of the nature and treatment of starch on aroma retention. Carbohydrate Polymers, 47, 73–82. Brunauer, S., Emmett, P. H., & Teller, E. (1938). Adsorption of gases in multimolecular layers. Journal of the American Chemical Society, 62, 723.
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Conde-Petit, B., Escher, F., & Nuessli, J. (2006). Structural features of starch-flavor complexation in food model system. Trends in Food Science & Technology, 17, 227–235. Fannon, J. E., Gray, J. A., Gunawan, N., Huber, K. C., & BeMiller, J. N. (2003). The channels of starch granules. Food Science and Biotechnology, 12, 700–704. Fessas, D., & Schiraldi, A. (2000). Starch gelatinization kinetics in bread dough: DSC investigations on ‘simulated’ baking processes. Journal of Thermal Analysis and Calorimetry, 61, 411–423. Glenn, M. G., Klamczynski, P. A., Woods, F. D., Chiou, B. S., Ortis, J. W., & Iman, H. S. (2010). Encapsulation of plant oils in porous starch microspheres. Journal of Agricultural and Food Chemistry, 58, 4180–4184. Griffin, S., Wyllie, S. G., & Markham, J. (1999). Determination of octanol-water partition coefficient for terpenoids using reversed-phase high-performance liquid chromatography. Journal of Chromatography. A, 864, 221–228. Haros, M., Blaszczak, W., Perez, O. E., Sadowska, J., & Rosell, C. M. (2006). Effect of ground corn steeping on starch properties. European Food Research and Technology, 222, 194–200. Jeon, Y. -J., Vasanthan, T., Temelli, F., & Song, B. -K. (2003). The suitability of barley and corn starches in their native and chemically modified forms for volatile meat flavour encapsulation. Food Research International, 36, 349–355. Kaukovirta-Norja, A., Reinikainen, P., Olkku, J., & Laakso, S. (1997). Starch lipids of barley and malt. Cereal Chemistry, 74, 733–738. Kong, X., Corke, H., & Bertoft, E. (2009). Fine structure characterization of amylopectins from grain amaranth starch. Carbohydrate Research, 344, 1701–1708. Marcone, M. F. (2001). Starch properties of Amaranthus pumilus (seabeach amaranth): A threatened plant species with potential benefits for the breeding/amelioration of present Amaranthus cultivars. Food Chemistry, 73, 61–66. Mariotti, M., Lucisano, M., Pagani, A., & Perry, K. W. Ng (2009). The role of corn starch, amaranth flour, pea isolate and psyllium flour on the rheological properties and the ultrastructure of gluten-free doughs. Food Research International, 42, 963–975. Misharina, T. A. (2002). Sorption of monoterpenoids and sesquiterpenoids by natural polysaccharides. Applied Biochemistry and Microbiology, 38, 480–486. Misharina, T. A. (2004). Retention of essential oil components sorbed by native cornstarch during storage. Applied Biochemistry and Microbiology, 40, 104–107. Morrison, W. R., & Laignelet, B. (1983). An improved procedure for determining apparent and total amylose in cereal and other starches. Journal of Cereal Science, 1, 9–20.
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Retention of aroma compounds by corn, sorghum and amaranth starches Wioletta Błaszczak a,⁎, Tamara A. Misharina b, Dimitrios Fessas c, Marco Signorelli c, Adrian R. Górecki a a b c
Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Tuwima Str. 10, 10-748 Olsztyn, Poland The Emmanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygina 4, Moscow 119991, Russia DeFENS, University of Milan, Via Celoria 2, 20133 Milano, Italy
a r t i c l e
i n f o
Article history: Received 13 March 2013 Accepted 7 July 2013 Keywords: Retention Aroma compounds Starch GC DSC
a b s t r a c t The presented study addressed assays of odorant retention from an essential oil mixture by native corn, sorghum and amaranth starches using capillary gas chromatography (GC) and differential scanning calorimetry (DSC). The essential oil mixture consisted of 30 main compounds, including monoterpene and sesquiterpene hydrocarbons, alcohols, ketone, phenols and ester. The native starches were characterized for their chemical composition (amylose, protein, and surface lipids content), surface properties (surface area, pore diameter), and microstructure (SEM). The starches were mixed with odorants, stirred intensively, and stored at room temperature in the dark for 2 days (reference sample), 3 and 7 months. The chemical properties of odorants, their composition in the mixture as well as starch surface properties were observed to affect the retention of aroma compounds upon storage. Irrespective of starch botanical origin, a significant loss was noticed in monoterpene hydrocarbons throughout the storage period. Alcohols, ketone, phenols and sesquiterpene hydrocarbons were highly retained on amaranth and sorghum starches upon 3 months of storage. However, after prolonged storage their retention diminished, especially in the case of amaranth starch. The DSC results obtained for stored corn and sorghum starches with odorants demonstrated an extra endothermic contribution, which indicated that the aroma compounds were highly retained by the gelatinized starch matrixes. Furthermore, the odorants showed ability to interact with the solubilized amylose. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction The encapsulation of aroma compounds is used to entrap volatile and labile flavorings into a carrier in order to protect them from evaporation and/or degradation as well as from off-flavor development upon storage (Baranauskiene, Bylaite, Zukauskaite, & Venskutonis, 2007; Partanen, Ahro, Hakala, Kallio, & Forssel, 2002). The mechanism of protection and release of the encapsulated compounds would differ between the various carriers. The encapsulation wall system is often based on polymers with hydrophilic and/or hydrophobic groups that display the ability to form a network-like matrix (Baranauskiene et al., 2007). Starch and its derivatives are widely used not only as thickeners, stabilizers, and gelling and texturing agents but also as carriers of aroma compounds. The nature of some starches, their granule size, shape, specific area, porosity, crystalline or amorphous character, etc., and the composition of starch–polysaccharide matrices were found to play a major role in binding the volatile substances (Boutboul, ⁎ Corresponding author. Tel.: +48 895234615; fax: +48 895240124. E-mail addresses: [email protected] (W. Błaszczak), [email protected] (T.A. Misharina), [email protected] (D. Fessas), [email protected] (M. Signorelli), [email protected] (A.R. Górecki). 0963-9969/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodres.2013.07.032
Giampaoli, Feigenbaum, & Ducruet, 2002; Baranauskiene et al., 2007; Savary, Lafarge, Doublier, & Cayot, 2007; Zafeiropoulou, Evageliou, Gardeli, Yanniotis, & Komaitis, 2010). The binding of flavorings to starch is known as inclusion complex formation through the hydrophobic bonding in the amylose helix and/or polar interaction that involve hydrogen bonds between hydroxyl groups of starch and the odorant (Arvisenet, Voilley, & Cayot, 2002; Boutboul et al., 2002). The binding of low molecular compounds to starch might also be based on their non-specific sorption to the starch powders or to granule agglomerates (Conde-Petit, Escher, & Nuessli, 2006; Misharina, 2004). These porous structures of corn starch treated with glucoamylase revealed a high ability to retain peppermint oil (Zhao, Madson, & Whistler, 1996). The porous starch granules were found to retain 29% of the oil after standing in the open air for two months, while only 12% of oil remained on native starches after three days of storage in an open dish. Corn and barley starches subjected to succinylation were deemed promising carriers of volatile meat flavor compounds (Jeon, Vasanthan, Temelli, & Song, 2003). Over a 4-week storage period, flavor retention by these starches was higher than by β-cyclodextrin which is commonly used for encapsulation. It was also noted that hydrophobically-modified starches were used as shell materials in spray drying to encapsulate up to 50% of flavor compounds (Baranauskiene et al., 2007). The emulsifying starch (HiCap)
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was found to be an effective heat-stable matrix for encapsulating caraway oil (Partanen et al., 2002). Studies on starch type effect on the retention of aroma compounds from strawberry showed that corn starch (Amilogel G) was the best carrier for the majority of the compounds analyzed (Vidrith, Zlatic, & Hribar, 2009). The retention of aroma compounds on cross-linked waxy corn starch and/or polysaccharide gel was ascribed to the physicochemical interaction between the low molecular compounds and gel components (Savary et al., 2007). Apart from the structural and physicochemical characteristics of the polymer matrix, the efficiency of aroma compound retention was also related to their structure and chemical properties (Misharina, 2004). This author studied also the storage-related changes in the retention of different aroma compounds on dry corn starch and proved that the corn starch prevented volatile component oxidation during storage. The small pores, noted in literature as ‘pin holes’ were found on the granule surface of native sorghum starch using different microscopy techniques. It was suggested that these structures were openings to channels, with diameter from 5 to 400 nm, connecting an internal cavity at the granule hilum to the external surface (Fannon, Gray, Gunawan, Huber, & BeMiller, 2003; Perez, Baldwin, & Gallant, 2009; Singh, Sodhi, & Singh, 2010). It is likely that the pores and channels, naturally formed on the granule surface, allow some molecules with low molecular weight to directly access to the granule interior. However, the exact nature of the interaction between ligands (i.e. aroma compounds) and granule surface of native sorghum starch remains unknown since this topic is scarce in literature. Amaranth starch was also found to demonstrate a unique character of granules with respect of their size and surface properties. These starch granules appeared as small (up to 2.0 μm) (Kong, Corke, & Bertoft, 2009), and they tend to form large aggregates (up to 80 μm in size) (Mariotti, Lucisano, Pagani, & Perry, 2009). The literature data showed that the specific surface area of amaranth starch was significantly higher compared to that calculated for native potato starch or maize starch (Marcone, 2001; Sujka & Jamroz, 2009; Szymonska & Wodnicka, 2005), but on the other hand the specific surface area was also affected by other factors (Boutboul et al., 2002). A stable pore structure was found to be critical to provide a high surface area including the interiors and outer regions of the microspheres (Glenn et al., 2010). For sorghum and amaranth starches demonstrate unique surface properties, they might be considered as interesting material for odorant retention (Fannon et al., 2003). Bearing this in mind, in this study the ability of corn, sorghum and amaranth starches to retain aroma compounds was studied in relation to surface characteristics, thermal properties, and microstructure of starch. 2. Materials and methods 2.1. Plant material and starch isolation The seeds of plant species Amaranthus cruentus L. were donated by the Metro Industrial Centre “Szarłat” s.c. (Łomża, Poland), and sorghum Sorghum grains bicolor (v. Rona 1) were purchased from the Kutno-Centre for Sugar Beet Breeding in Straszkow, Poland. Commercial maize starch was donated by the Department of Food Concentrates in Poznan, the Institute of Agricultural and Food Biotechnology, Poland. The starch from amaranth seeds was isolated and purified according to the method developed by Walkowski, Fornal, Lewandowicz, and Sadowska (1997). Since the amaranth starch granules naturally form agglomerates varying in diameter, the isolated starch granules were sieved through a screen with a mesh of 350 — in order to unify their diameter. The isolation procedure described by Olayinka, Adebowale, and Olu-Owolabi (2008) was used to obtain starch from sorghum grains.
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2.2. Characteristics of essential oil mixture components The experiment was conducted with the aroma mixture comprising 30 main compounds, including monoterpene and sesquiterpene hydrocarbons, alcohols, ketones, phenols and ester (Table 1). All of them are constituents of commonly applied seasonings, and widely occur in a number of food products. The aroma mixture was prepared by mixing the essential oils of black pepper (1 mL), caraway (1 mL), coriander (1 mL), oregano (1 mL), and ginger (1.5 mL). The essential oils were purchased from Plant Lipids, Ltd, India. The composition of the analyzed essential oil mixtures (μg/50 mg) was determined by GC with internal standard — n-tridecane (Fluka, 99.5%) (Table 1). The hydrophobic properties of odorants were analyzed according to the method proposed by Griffin, Wyllie, and Markham (1999) by determining the octanol (Sigma-Aldrich, 99%) — water partition coefficient for terpenoids (Log Kow) with the use of reversed-phase high-performance liquid chromatography (Table 1). 2.3. Starch characterization Protein and moisture content of the analyzed starches were determined with standard AOAC methods (AOAC 1990a, 1990b). The amylose content of amaranth, sorghum and corn starches was assayed according to the method proposed by Morrison and Laignelet (1983). Surface lipids were defined as the lipid fraction extracted from the granule surface by cold solvent and was determined according to Kaukovirta-Norja, Reinikainen, Olkku, and Laakso (1997). The surface lipids were extracted by n-propanol (Sigma-Aldrich, 99.7%) — water Table 1 Composition of a model essential oil mixture. Compound Monoterpene hydrocarbons 1 α-Tujene 2 α-Pinene 3 Camphene 4 Sabinene 5 β-Pinene 6 β-Myrcene 7 α-Phellandrene 8 3-Carene 9 α-Terpinene 10 р-Cymene 11 Limonene 12 γ-Terpinene
Log Kow
Content in mixture (g/100 g)
4.38 4.25 4.10 4.38 4.36
0.32 3.96 1.20 2.20 2.35 0.88 0.02 1.90 1.10 4.80 15.70 1.60
4.44
4.16
Alcohols, 13 14 15 16 17 18 19 20
ketone, phenols Linalool Camphor α-Terpineol Terpinene-4-ol Carveol Carvone Thymol Carvacrol
3.50 2.74 3.28 3.26 3.12 2.74 3.30 3.49
15.40 1.02 0.26 0.02 0.29 11.40 0.60 11.80
Ester 21
Neryl acetate
3.98
0.60
Sesquiterpene hydrocarbons 22 α-Cubebene 23 β-Elemene 24 Caryophyllene 25 β-Selinene 26 β-Bisabolene 27 β-Sesquiphellandrene 28 α-Curcumene 29 Zingiberene 30 Caryophyllene oxide
6.33
1.00 0.36 5.80 0.58 1.80 3.10 2.54 6.80 0.60
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mixture (3:1, v/v) at ambient temperature for 30 min at a solid to solvent ratio of 1:10 (w/v). Extracts were combined, organic solvent was evaporated and the resultant products were lyophilized. The specific surface area, mesopore volume and average pore diameter were estimated using low-temperature nitrogen adsorption (ASAP 2405, Micrometrics Inc., USA). Isotherms were plotted for high-purity nitrogen adsorption at a temperature of 77.3 K. The monolayer capacity was calculated on the basis of adsorption isotherm (Brunauer, Emmett, & Teller, 1938) from five measurement points in the relative pressure range p/p0 0.006–0.2. Prior the measurements, starch samples were dried for 25 h in vacuum at 100 °C, automatically desorbed and flushed with pure helium. Pore characteristics were determined according to Barrett, Joyner, and Hallenda (1951). Samples were analyzed in triplicate. 2.4. Sample preparation Starch samples (5 g) were placed into flasks (50 mL) and 250 mg of an odorant mixture (50 mg/g) was added to the starches. The samples with the odorants were stirred intensively for 2 h, the flasks were closed using a cellulose stopper, and stored at room temperature in the dark for 2 days (reference sample), 3 and 7 months.
the first DSC heating run, which corresponds to the apparent heat capacity Cp(T) of the sample to obtain the trend of the excess (with re−1 −1 spect to the trend prior gelatinization) heat capacity, Cex g p (T) / J K (per gram of dry matter) and then evaluate the enthalpy drop ΔH through a straightforward integration of the corresponding trace. Each run was repeated at least twice. The actual dry mass of such samples was determined at the end of the DSC run by weighing the pierced cell kept at 105 °C for about 5 h. 2.7. Scanning electron microscopy The starch granules (powders) were deposited on the specimen holder using cuprum tape, and coated with gold in a vacuum evaporator (JEE 400, JEOL). The specimens were viewed in a JEOL JSM 520 scanning electron microscope at the accelerating voltage of 10 kV. 2.8. Statistical analysis The statistical analysis of results was carried out with Statistica ver. 5 (StatSoft, USA) software using variance analysis ANOVA supplemented by the Duncan multiple range test (General Convention and Statistics, Statistica for Windows, 2nd Edition, 209 StatSoft Inc.).
2.5. Capillary gas chromatography (GC) 3. Results and discussion 1.00 g of the sample (reference and stored) placed in a 5-mL glass tube and 2 mL of diethyl ether (Sigma-Aldrich, 99.7%) were added, the mixture was shaken for 0.5 h, and then 1 μL of n-tridecane (Fluka, 99. 5%) was added. The ether layer with extracted substances was separated by centrifugation (8000 g for 20 min) and analyzed by GC. Analyses of ether extracts of essential oils and the control sample were carried out using a Kristall 2000 M chromatograph (Russia) with a flame ionization detector and an SPB-1 fused silica capillary column (50 m × 0.32 mm, phase layer 0.25 μm). The column temperature was programmed from 60 to 250 °C with the speed of 8 °C/min at detector and injector temperature of 250 °C. The rate of helium flow through the column was 1.5 mL/min. The volume of the injected sample was 1–2 μL. The components of the essential oil mixture were identified based on retention indexes. Each sample was analyzed 3–4 times. The amount of substance unbound by starch and remaining in the aqueous phase was calculated from the ratio of substance peak areas and an internal standard. The amount of bound substances was calculated as the difference between the amount of the substance in the initial dispersions and the amount determined in the aqueous phase after centrifugation. The residual substance was determined with a maximum measurement error no more than 5% relative. The retention of odorant mixture components was expressed as a ratio of odorant determined in the reference sample (1.0) to the odorant amount determined after storage (3 and 7 months). 2.6. DSC analysis A PerkinElmer Diamond with 60 μL sealed cells was used to investigate starch gelatinization in excess of water (humidity 70%). The reference cell contained a suitable amount of distilled water. Measures were carried out in a temperature range of 20–150 °C at 2.0 °C min−1 scanning rate. Indium was used for calibration. The typical sample mass was 30 mg. The raw data were processed with the dedicated software IFESTOS which was assembled by the authors for handling raw calorimetric data according to the suggestions by Barone, Del Vecchio, Fessas, Giancola, and Graziano (1993), and Fessas and Schiraldi (2000). The base-line chosen to work out a given DSC trace was the trend extrapolated from the DSC record of the immediate re-heating run. It was subtracted from the record of
3.1. Retention of odorants by starches The retention values of individual odorants determined for the 2-day-stored starch powders (reference sample) ranged from 0.99 to 1.0. They indicated that none of the analyzed compounds, that formed the essential oil mixture, was lost during this period of storage. After 3 months of storage, the ability of corn, sorghum and amaranth starches to retain odorants from the essential oil mixture was observed to vary (Table 2). Amaranth starch demonstrated the highest average retention values for the analyzed groups of odorants (monoterpene and sesquiterpene hydrocarbons, alcohols, ketone, phenols or ester) compared to the corn and sorghum starches (Table 3). After 3 months of storage, retention of the majority of individual compounds from the groups of alcohols, ketone, phenols and sesquiterpene hydrocarbons by amaranth starch did not change for amaranth starch compared to the reference sample. Such individual compounds as linalool, camphor, and carvacrol were also highly retained by the amaranth starch. The retention values obtained for α-curcumene and caryophyllene oxide exceeded 1.0, whereas retention of zingiberene and caryophyllene by the amaranth starch was significantly lower compared to the initial values. This could result from zingiberene and caryophyllene oxidation to α-curcumene and caryophyllene oxide, respectively (Misharina, 2002). Such a relationship between the retention values of caryophyllene and caryophyllene oxide as well as zingiberene and α-curcumene was also noted for all samples analyzed throughout the storage period (3 and 7 months). In contrast to amaranth starch, sorghum starch manifested a significantly lower ability to retain the monoterpene and sesquiterpene hydrocarbons after 3 months of storage (Tables 2 and 3). γ-Terpinene was found to be retained at the lowest level (0.06) compared to the other compounds from the monoterpene hydrocarbon group. The high retention value obtained for p-cymene could be due to γ-terpinene oxidation. In turn, alcohols, ketone, phenols and ester as well as the majority of sesquiterpene hydrocarbons were highly retained on the sorghum starch upon 3 months of storage. Among all the analyzed starches, the corn starch revealed the weakest ability to retain alcohols, ketone, phenols, ester and sesquiterpene hydrocarbons throughout the storage period.
W. Błaszczak et al. / Food Research International 54 (2013) 338–344 Table 2 Retention of odorant mixture components by starches after 3 and 7 months of storage at room temperature. Compound
Retention on dry starch 3-month storage Corn
7-month storage
Sorghum
Amaranth
Corn
Sorghum
Amaranth
Monoterpene hydrocarbons α-Tujene 0.154 α-Pinene 0.146 Camphene 0.186 Sabinene 0.274 β-Pinene 0.267 β-Myrcene 0.337 α-Phellandrene 0.154 3-Carene 0.349 α-Terpinene 0.169 р-Cymene 0.617 Limonene 0.456 γ-Terpinene 0.152
0.224 0.207 0.255 0.377 0.357 0.504 0.192 0.454 0.231 0.816 0.577 0.069
0.510 0.480 0.531 0.643 0.625 0.780 0.769 0.720 0.600 0.835 0.793 0.776
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.021 0.013 0.000
0.000 0.000 0.000 0.010 0.010 0.025 0.000 0.025 0.000 0.152 0.086 0.000
0.000 0.000 0.000 0.011 0.010 0.050 0.000 0.049 0.000 0.192 0.120 0.030
Alcohols, ketone, phenols Linalool 0.829 Camphor 0.793 α-Terpineol 0.833 Terpinene-4-ol 0.771 Carveol 0.356 Carvone 0.874 Thymol 0.919 Carvacrol 0.877
0.879 0.867 0.938 1.000 1.000 0.932 1.000 0.954
0.989 0.966 1.000 1.000 1.000 1.000 1.000 0.989
0.720 0.608 0.800 0.743 0.333 0.940 0.838 1.000
0.811 0.779 0.816 1.000 1.000 0.904 1.000 0.986
0.676 0.615 0.640 1.000 0.849 0.755 1.000 0.844
Ester Neryl acetate
0.780
0.848
0.906
0.712
0.809
0.702
Sesquiterpene hydrocarbons α-Cubebene 0.817 β-Elemene 0.893 Caryophyllene 0.774 β-Selinene 0.411 β-Bisabolene 0.835 β-Sesquiphellandrene 0.829 α-Curcumene 1.687 Zingiberene 0.394 Caryophyllene oxide 0.916
0.895 1.000 0.859 0.458 1.000 0.926 2.107 0.368 1.602
1.000 1.000 1.000 0.557 1.000 1.000 1.068 0.911 1.200
0.815 0.969 0.603 0.335 0.980 0.873 2.510 0.080 3.029
0.926 0.994 0.728 0.435 1.000 0.929 2.867 0.035 2.878
0.698 0.869 0.722 0.312 0.772 0.724 1.412 0.391 1.236
Statistically significant differences were found in monoterpene hydrocarbon retention by the analyzed starches between storage periods (3 and 7 months) (Tables 2 and 3). Such compounds as α-tujene, α-pinene, camphene, α-phellandrene, and α-terpinene were completely lost after the 7-month storage — irrespectively of starch origin. In addition, a significant reduction was noticed in retention values of ester (Neryl acetate) between the storage periods. The retention values noted for carvacrol, carvone, β-elemene, and β-bisabolene on 7-month-stored corn starch were higher than the values obtained for 3-month-stored corn starch. In view of literature data, this might be ascribed to the structural changes of these odorants that proceed during their storage in the presence of other organic compounds (Misharina, 2002, 2004). Table 3 Retention of odorant groups by starches. Starch
Storage (months)
Monoterpene hydrocarbons
Alcohols, ketone, phenols
Ester (Neryl acetate)
Sesquiterpene hydrocarbons
Corn
3 7 3 7 3 7
0.272* 0.003* 0.355* 0.026* 0.672* 0.039*
0.842 A 0.807 a 0.946 B 0.912 b 0.993* B 0.797* a
0.780* A 0.712* a 0.848 AB 0.809* b 0.906* B 0.702* a
0.844* A 0.910* b 0.956 B 0.962 b 0.998* C 0.761* a
Sorghum Amaranth
A a A ab B b
Asterisk indicates statistically significant differences between storage months for starches of different botanical origin separately, capital and small letters indicate differences (uniform Duncan's groups) between starch of different origins after 3 and 7 months of storage, respectively.
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The sorghum starch demonstrated significantly higher average retention values of alcohols, ketone, phenols, ester and sesquiterpene hydrocarbons after 7 months of storage compared to corn and amaranth starches. Among sesquiterpene hydrocarbons, the retention of β-bisabolene remained unchanged after the storage period. In turn, a high retention value was noted for β-elemene. A significant decrease was observed in the retention of alcohols, ketone, phenols and sesquiterpene hydrocarbons by amaranth starch between 3 and 7 months of storage. The retention of terpinene-4-ol and thymol on amaranth starch did not change upon 7 months of storage, whereas the retention values noted for linalool, camphor and α-terpineol were distinctly lower compared to those obtained after 3 months of storage.
3.2. Effect of structure and surface properties of granules on odorant retention In order to characterize the surface properties of starches, the specific surface area and average pore diameter of granules were estimated using low-temperature nitrogen adsorption. While corn and sorghum starches demonstrated similar values of surface area, the values of average pore diameter determined for their granules varied significantly (Table 4). The SEM observations of corn starch (Fig. 1A) indicated that the granules were 6–14 μm with a slightly polygonal shape. The granules of corn starch varied also in surface morphology. Some of them appeared smooth, while others demonstrated a rough surface with distinct crater-like structures. It is generally known that the craterlike structures were formed upon starch synthesis in the kernel and resulted from the pressing of protein bodies into the soft, at that moment, starch granule (Haros, Blaszczak, Perez, Sadowska, & Rosell, 2006). This was also the case for sorghum starch (Fig. 1B). In addition, the SEM inspection showed explicitly the presence of small pores ‘pin holes’/capillaries on the starch granule surface. Those structures appeared on individual granules in the number of 30–50, providing access to the granule interior. The depth of those pores probably affected the value of average pore diameter to a significantly greater extent than in the case of corn starch. The amaranth starch was characterized by the highest values of surface area and average pore diameter compared to corn and sorghum starches. Considering the microscopic observations, it needs to be pinpointed that the physical properties determined for amaranth starch should be attributed to the agglomerates formed by granules (Fig. 1C) rather than to a single granule (Fig. 1D). The amaranth agglomerates were 20–60 μm large with an irregular shape, and were composed of hundreds of granules. Their surface was rough with multiple air spaces between the adhering granules, whereas the individual granules of amaranth starch were 0.8– 1.2 μm in size and had a polygonal shape and a smooth surface. In view of the above, the diminished retention of aroma compounds by the stored corn starches was, probably, due to the fact that most of the odorants were adsorbed on the granule's surface, owing to which they were more susceptible to vaporization/oxidation (Varavinit, Chaokasem, & Shobsngob, 2001; Wasserman, Misharina, & Yuryev, 2002) compared to the odorants trapped inside pores and/or capillaries of sorghum starch. As demonstrated in previous studies, the porous starches might prevent oxidation and transformation of volatile components during storage (Misharina, 2004; Zhao et al., 1996). The retention of aroma compounds by the matrices was also shown to depend on surface composition, i.e. presence of lipids and/or proteins (Seuvre, Philippe, Rochard, & Voilley, 2006). However, in the present study the retention of aroma compounds on the analyzed starches (corn, sorghum and amaranth) was triggered by the chemical properties of individual
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Table 4 Chemical, morphological, and thermodynamic characteristics of starches. Corn
Sorghum
Amaranth
Chemical analysis of starch (g/100 g) Moisture Amylose content Protein Surface lipid
10.50 ± 0.04 20.57 ± 0.31 0.44 ± 0.07 0.24 ± 0.07
12.80 ± 0.04 19.19 ± 0.11 0.78 ± 0.00 0.45 ± 0.07
10.50 ± 0.06 – 0.78 ± 0.00 0.16 ± 0.01
Physical properties of granules BET surface area (m2/g) Average pore diameter by BET (Å)
0.4635 48.9633
0.4911 80.0930
3.4062 104.2441
Gelatinization enthalpy (ΔH) of starch–odorant systems Native starch (ΔH, J g−1) Starch–odorants stored for 3 months (ΔH, J g−1) Starch–odorants stored for 7 months (ΔH, J g−1)
15 ± 1 18 ± 1 20 ± 1
16 ± 1 19 ± 1 22 ± 1
16 ± 1 15 ± 1 11 ± 1
odorants and surface properties of granules rather than by the presence of non − starch constituents on their surface (Table 4). 3.3. Thermal analysis of starch stored with odorants DSC measurements were also performed to assess the strength of interactions and the influence of aroma compounds retained in the starch matrices in respect of starch gelatinization properties. Thermograms obtained for the corn starch systems were presented in Fig. 2A. The main low-temperature peak (57–77 °C), observed in the thermogram of native corn starch, was attributed to amylopectin gelatinization. The consecutive broad peak (80–95 °C) is not clearly defined. Most likely it depicts the transition resulting
from the dissociation of the amylose–lipid complex. Worthy of notice is that the cooperativity and the temperature of such transition depend on system humidity (Fessas & Schiraldi, 2000). The results obtained for corn starches stored with odorants for 3 months and 7 months indicate that the heating of granules with the essential oil mixture caused an increase in the enthalpy values for the low-temperature peak (starch gelatinization region) (Table 4). This extra endothermic contribution might correspond to the energy required to displace aroma compounds adsorbed on the surface of starch granules during starch gelatinization. If so, the extra enthalpy would reflect the strength of such retention. Its value shows a kinetic evolution that can be matched with diffusion processes, which are affected by peculiarities (pores, cavities, etc.) of the granule structure.
Fig. 1. SEM images of native starch granules: A — corn; B — sorghum; C, D — amaranth.
W. Błaszczak et al. / Food Research International 54 (2013) 338–344
A
5.0
Cp ex / J g -1
4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 20
40
60
80
100
120
T /°C
B
5.0
Cp ex / J g -1
4.0 3.0
1.0
4. Conclusions
0.0
-2.0 20
40
60
80
100
120
80
100
120
T /°C 5.0 4.0
Cp ex / J g -1
process of the system (Table 4). In the case of the 7-month storage time, a strong variation was observed in the thermogram. In-depth analysis of a thermogram profile suggests the occurrence of exothermic effects (aggregations) that are concomitant with the gelatinization process rather than the destabilization of starch granules. We hypothesize that such aggregation phenomena could be triggered by the significant decrease in odorants in the starch matrix after 7 months of storage, which in turn might change the hydration properties of the system. In conclusion, in this case, there is no evidence of a particular complexation/interaction between the aroma compounds and the amaranth starch, and the retention properties might mostly depend on the large surface area exposed. The data obtained from DSC analysis confirm the findings presented in the preceding paragraphs, although only in a qualitative sense. A more precise estimation would indeed require much more information about such factors as: chemical properties of odorants, the overall exposed granule surface, defects and pore conformation and distribution, as well as the total amount of the odorants per gram of the samples investigated (Misharina, 2002; Wasserman et al., 2002).
2.0
-1.0
C
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3.0 2.0 1.0 0.0 -1.0 -2.0 20
40
60
T /°C Fig. 2. Thermograms of corn (A), sorghum (B), and amaranth (C) starches: native (—); 3 months stored (–); 7 months stored (⋯).
Furthermore, it was observed that exothermic signals appeared in the amylose transition region, which indicated that crystallization and eventually melting occurred during heating, and suggested further interactions of aromatic compounds with amylose. A similar phenomenon was observed for the sorghum starch systems (Fig. 2B) in terms of amylopectin gelatinization. Higher enthalpy values obtained for sorghum-odorant systems, heated in an excess of water, implied stronger retention of aroma compounds on the granules than in corn starch stored with odorants (Table 4). Due to high humidity, the transition of amylose–lipid complexes was not tangible in the thermograms obtained. However, in the case of sorghum starch stored with odorants for 7 months, strong disturbances (almost random in the profile but present in all replicas) were noted in this temperature region, which may correspond to the phenomena observed for corn starch. Thermograms obtained for amaranth systems (Fig. 2C) were biphasic, which indicated different stability of granules distributed in a bulk sample. Storage of starch with the aroma compounds for 3 months did not seem to affect considerably the overall gelatinization
The corn, sorghum and amaranth starches demonstrated different abilities to retain aroma compounds from the essential oil mixture upon 3 and 7 months of storage. The retention of aroma compounds from the group of monoterpene hydrocarbons on the stored starches was the lowest, compared to such groups of odorants as: alcohols, ketone, phenols and sesquiterpene hydrocarbons. The overall exposed surface and/or pores distribution found for aggregates of amaranth starch make it the most promising for odorant retention during 3-month storage. However, the sorghum and corn starch should be recommended for the prolonged period of storage. An increase in melting enthalpy noted for both these starches and the appearance of exothermic signals in the amylose transition region indicated that the odorants were strongly retained in the gelatinized starch matrix, and additionally showed ability to interact with hydrated and solubilized amylose. Summarizing, the overall retention of odorants by starches resulted from various factors, with the key ones including: composition and chemical properties of aroma compounds, morphology and surface characteristics of starch granules. Acknowledgments The study was financed by a grant from the Ministry of Science and Higher Education (Grant No. N N312 101938). References AOAC (1990a). Official method of analysis, protein (15th ed.)Arlington, USA: Association of Official Analytical Chemistry, 781. AOAC (1990b). Official method of analysis, ash and moisture content (15th ed.) Arlington, USA: Association of Official Analytical Chemistry, 777. Arvisenet, G., Voilley, A., & Cayot, N. (2002). Retention of aroma compounds in starch matrices: Compositions between aroma compounds toward amylose and amylopectin. Journal of Agricultural and Food Chemistry, 50, 7345–7349. Baranauskiene, R., Bylaite, E., Zukauskaite, J., & Venskutonis, P. R. (2007). Flavor retention of peppermint (Mentha piperita L.) essential oil spray-dried in modified starches during encapsulation and storage. Journal of Agricultural and Food Chemistry, 55, 3027–3036. Barone, G., Del Vecchio, P., Fessas, D., Giancola, C., & Graziano, G. (1993). Theseus: A new software package for the handling and analysis of thermal denaturation data of biological macromolecules. Journal of Thermal Analysis, 39, 2779–2790. Barrett, E. P., Joyner, L. G., & Hallenda, P. H. (1951). The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms. Journal of the American Chemical Society, 73, 373–381. Boutboul, A., Giampaoli, P., Feigenbaum, A., & Ducruet, V. (2002). Influence of the nature and treatment of starch on aroma retention. Carbohydrate Polymers, 47, 73–82. Brunauer, S., Emmett, P. H., & Teller, E. (1938). Adsorption of gases in multimolecular layers. Journal of the American Chemical Society, 62, 723.
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