Nauka Przyroda Technologie

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1 206 Tom 0 Nauka Przyroda Technologie Zeszyt 4 #48 ISSN DOI: Dział: Nauki o Żyności i Żyieniu Copyright Wydanicto Uniersytetu Przyrodniczego Poznaniu TERESA WITCZAK, ANNA STĘPIEŃ, MARIUSZ WITCZAK, SŁAWOMIR PIETRZYK 2, AGATA BEDNARZ, ADAM FLORKIEWICZ 3 Department of Engineering and Machinery in Food Industry University of Agriculture in Krako 2 Department of Food Analysis and Quality Assessment University of Agriculture in Krako 3 Department of Catering Technology and Consumption University of Agriculture in Krako SORPTION PROPERTIES OF MODIFIED POTATO STARCH * WŁAŚCIWOŚCI SORPCYJNE MODYFIKOWANEJ SKROBI ZIEMNIACZANEJ Summary Background. Starch is one of the biopolymers most commonly used in the food industry. In its native form its applications are limited. In contrast, its structure is relatively readily modified using various methods, producing starch derivatives of greatly diverse properties. The primary methods used to change characteristics of starch include acetylation and oxidation. Thus obtained ra materials are used as food additives. Stability of these ra materials and food products to a considerable extent depends on their composition and parameters characterizing storage facilities, i.e. relative humidity and temperature. One of the methods to specify adequate ambient conditions is based on ater activity supplemented by sorption isotherms. As a result studies investigating correlations beteen ater activity and moisture content are of importance for the optimization of storage conditions and design of certain food processing procedures. For this reason the aim of this study as to assess the effect of modification (oxidation, acetylation and their combination) on sorption properties (described based on sorption isotherms) of potato starch. Material and methods. Analyses ere conducted on potato starch and its derivatives produced by acetylation, oxidation and co-modification (acetylation coupled ith oxidation). Starch as oxidized using sodium chlorate (I), hile acetylation as run using anhydrous acetic acid. Sorption isotherms ere determined by the static desiccator method. Results ere described applying selected mathematical methods equipped ith physical interpretations (BET and GAB) and empirical models (Halsey, Osin, Henderson, Pelega, Leicki, Blahovec-Yanniotis). Calculations ere made using non-linear estimation. * The project as financed from funds of the National Science Centre allocated on the poer of decision no. DEC-203/09/B/NZ9/078.

2 2 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of Results. The greatest ater absorbability as found for native potato starch. Modifications caused a decrease in the amount of adsorbed ater vapour, dependent on the applied modification. Acetylation resulted in significantly greater reduction of the amount of adsorbed ater vapour in comparison to oxidation. Oxidation had a slight effect on sorption properties. The loest hygroscopicity as recorded for co-modified starch, hich resulted from the overlapping effect of oxidation and acetylation, reducing the capacity to adsorb ater vapour. Four of the applied mathematical models (Pelega, Leicki, GAB and Blahovec-Yanniotis) adequately reflected the course of isotherms and ere characterized by comparable accuracy. Water contents in the monolayer ranged from to (the BET model) and from to 0.00 (the GAB model). Based on the model proposed by Blahovec and Yanniotis it as found that modifications led to a decrease in the share of adsorbed ater and an increase in the share of free ater available for soluble components. Conclusions. Sorption isotherms for all tested starch forms (native and modified) had a sigmoid shape. Analyzed modifications led to a decrease in starch hygroscopicity, ith acetylation causing a markedly greater reduction of ater vapour adsorbability in comparison to oxidation. Among the eight mathematical models used to describe sorption properties the Pelega model proved to be the best, although three other (the Leicki, GAB and Blahovec-Yanniotis models) described experimental data ith comparable accuracy. In most cases chemical modification of starch resulted in a reduced monolayer absorbability. An exception in this respect as connected ith the value established based on the GAB model for oxidized starch. The results may be used to optimize storage conditions and to design products containing starch and its derivatives. Key ords: potato starch, modification, sorption properties, acetylation, oxidation Introduction Among numerous starch modification methods (Pietrzyk et al., 203; Tharanathan, 2005; Witczak et al., 206a) a significant role is played by oxidation and acetylation. As a result of oxidation carboxyl and/and aldehyde groups are substituted in starch. The number of these groups is influenced by such factors as the type of applied oxidant, reaction conditions as ell as the botanical provenance of biopolymer. The oxidation reaction leads to a decrease of molecular mass and contents of substances accompanying starch such as fats, protein and phosphorus. The internal and external structure of starch grains ere changed. All these factors affect ater binding capacity and thus also sorption characteristics of starch (Pietrzyk et al., 2006). In turn, acetylated starch is produced in the reaction ith acetic acid, its anhydride or their mixture (Tegge, 200). At present a large variety of acetylated starch preparations are available for applications not only in food production, but also in the textile, pharmaceutical and biodegradable packaging industries (Golachoski et al., 205). Properties of acetylated starch preparations depend on the type of starch, esterifying agent, reaction medium and reaction conditions (ratios of substrates, ph, temperature, catalyst, reaction time, pressure, etc.) (Golachoski et al., 205). Stability of food products to a considerable extent is determined by interactions beteen ater and their other components (Sablani et al., 2004). To characterize these interactions and define product stability the concept of ater activity is applied, hich value is connected ith microbial groth, fat oxidation, enzymatic activity, etc. In turn, the relationship of ater activity and its content in the product expressed in sorption

3 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of 3 isotherms are used to design and control food production processes (Sablani et al., 2004). The aim of this study as to assess the effect of modification (oxidation, acetylation and their combination) on sorption properties (described using sorption isotherms) of potato starch. Material and methods Material Analyses ere conducted on potato starch (SZ) produced by AVEBE (Holland), oxidized potato starch (SZu), acetylated potato starch (SZa) and co-modified potato starch (SZau). Starch as oxidized using sodium chlorate (I) in 40% aqueous starch suspension according to Forssell et al. (995) at a temperature of 20 ±2 C. Starch suspension as mixed in an alkaline medium (ph = 0.0) for 50 min. Next the reaction mixture as neutralized ith M H 2SO 4 solution to ph = 7.0. The amount of NaOCl used in oxidation as equivalent to 20 g Cl/kg starch. Folloing neutralization starch as rinsed, dried at room temperature for 48 h, comminuted and sieved through mechanical screens (mesh size 0.2 mm). Acetylation as run folloing the methodology proposed by Mężyński (972) in an aqueous starch suspension. A batch of 200 g starch (in terms of dry mass) as placed in a reactor and supplemented ith distilled ater to 560 g. The ph value of the suspension (ph 8 9) as regulated using 2% NaOH solution. Next 5 cm 3 anhydrous acetic acid as added mixing gently ith constant velocity of cm 3 /min together ith 2% NaOH solution in order to adjust ph of the mixture to 8 9. Folloing the introduction of acetic anhydride the suspension as mixed for 5 min and subsequently it as acidified ith 0% HCl to ph The produced starch as separated in a filter funnel ith the sintered disc, rinsed ith distilled ater to remove reagent residue, dried at max. 30 C and screened. Efficiency of oxidation and acetylation as assessed by determining the contents of carboxyl groups (ISO 24) and acetyl groups (Wurzburg, 964). Obtained preparations contained 0.50% carboxyl groups (oxidized potato starch) and.270% (acylated potato starch) as ell as.474% acetylated groups (oxidized acetylated potato starch). Sorption isotherms Native potato starch and modified starches ere subjected to freeze drying in a lyophiliser (LAB CONCO Free Zone 6) and stored for to eeks over P 2O 5 for force drying. Next sorption isotherms ere determined using the static desiccator method (Witczak et al., 206b). Analytical samples of the preparation (approx. 0.5 g) ere stored at 25 C over saturated saline solutions of varying ater activity ranging from 0. to 0.9 until equilibrium moisture content as reached. Analyses ere performed in to replications. Modelling and statistical analyses Sorption isotherms ere described using eight models (Table ). To of them, i.e. BET and GAB, are based on the theory of adsorption and are physically interpretable.

4 4 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of Table. Sorption models used in this study Tabela. Modele sorpcyjne ykorzystane pracy Model BET (Brunauer et al., 938) Blahovec-Yanniotis (Blahovec and Yanniotis, 2009) GAB (Guggenheim, 966; Anderson, 946; de Boer, 953) HALSEY (Halsey, 948; Iglesias and Chirife, 976) HENDERSON (Henderson, 952) LEWICKI (Leicki, 998) OSWIN (Osin, 946) PELEG (Peleg, 993) u = Equation Rónanie u0 C a ( a ) ( + ( C ) a ) a a u = + a + ba a2 b2a u = u0 C K a ( K a ) ( K a + C K a ) S n u ln a = ln u = P u = F ( a ) m G H ( ) ( ) a + a z a u = h a D E u = A a + B a u equilibrium ater content (g H 2O per g d.m.), a ater activity, u 0 monolayer ater content (g H 2O per g d.m.), C, a, b, a 2, b 2, K, S, n, m, P, F, G, H, h, z, A, D, B, E constants of respective equations. u rónoagoa zaartość ilgoci (g H 2O g s.m.), a aktyność ody, u 0 zaartość ody monoarstie (g H 2O g s.m.), C, a, b, a 2, b 2, K, S, n, m, P, F, G, H, h, z, A, D, B, E stałe odpoiednich rónań. The other models represent empirical dependencies and they are applied mainly to reliably reflect experimental data. Sorption models ere fitted using the non-linear estimation module (the Marquardt-Levenberg method) of the Statistica 9.0 softare package (Statsoft, Inc., USA). The coefficient of determination R 2 and the root mean square (RMS) ere used as assessment criteria (Ciurzyńska and Lenart, 200). Results and discussion Sorption isotherms Figure presents sorption isotherms of tested starches. The greatest ater absorbability as recorded for potato starch. Modifications caused a decrease in adsorbed ater vapour. The analyzed isotherms ere sigmoid in shape, hich classifies them to type II

5 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of Equilibrium ater content (g H2O per g d.m.), u Rónoagoa zaartość ilgoci, u (g H2O g s.m.) Peleg Model Model Pelega Leicki Model Model Leickiego GAB Model Model GAB Water activity Aktyność ody, a 0.30 Equilibrium ater content (g H2O per g d.m.), u Rónoagoa zaartość ilgoci, u (g H2O g s.m.) Peleg Model Model Pelega Leicki Model Model Leickiego GAB Model Model GAB Water activity Aktyność ody, a Fig.. Sorption isotherms of analysed starches ( potato starch, acetylated potato starch, oxidized potato starch, acetylated and oxidized potato starch) Rys.. Izotermy sorpcji badanych skrobi ( skrobia ziemniaczana, skrobia ziemniaczana acetyloana, skrobia ziemniaczana utleniona, skrobia ziemniaczana acetyloana i utleniona) isotherms according to the classification proposed by Brunauer et al. (938). These results are consistent ith those recorded previously for native and modified starches of various botanical origin (Al-Muhtaseb et al., 2004a; Pałacha and Chrzanoski, 203).

6 6 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of Sorption properties of tested starches depended on the applied modification. Acetylation caused a significantly greater decrease in the amount of adsorbed ater vapour in comparison to oxidation. Oxidation had a limited effect on sorption properties. Hoever, as a result the loest hygroscopicity as found for co-modified starch, hich results from the overlapping effect of oxidation and acetylation, reducing the capacity to adsorb ater vapour. Hoever, this effect as not additive. At loer values of ater activity this decrease as smaller than the total decrease resulting from oxidation and acetylation, hile at higher values it as greater than that for the sum of single modifications. The smallest capacity to adsorb ater vapour for acetylated starch as also reported by Pałacha and Chrzanoski (203) hen comparing sorption properties of potato starch and modified starches. According to Al-Muhtaseb et al. (2004b), potato starch shos higher values of heat of adsorption and desorption in comparison to other starches. According to those authors this suggests that potato starch is more polar on the surface and thus bond energy of ater molecules on the starch surface is greater. Hoever, it needs to be remembered that the starch granules have a complex structure, composed of amorphous and crystalline zones. The former may be plasticized by ater, hile the latter are relatively resistant to the action of ater vapour (Fornal et al., 202, Al- -Muhtaseb et al., 2004b). Thus ater binding capacity to a considerable degree depends on the degree of crystallinity and position of the above-mentioned structures in relation to one another. Observed dependencies ere described using selected mathematical models (Table ). Equation parameters are given in Table 2. Most applied models correctly described the course of sorption isotherms. In this respect the Halsey and BET models ere least accurate. Slightly higher RMS values in relation to the other models ere also obtained for the Osin and Henderson model. In turn, the Pelega, Leicki, GAB and Blahovec-Yanniotis models reflected the course of the isotherms ith comparable accuracy (RMS ranging from 4.39% to 5.35%). A similar dependency, although ith loer RMS values, as obtained by Pałacha and Chrzanoski (203). According to those authors ater vapour adsorption isotherms for starch ere best described by the model proposed by Pelega. Similar conclusions ere earlier reached by Al-Muhtaseb et al. (2004a) hen determining sorption isotherms for potato starch at various temperatures. To basic models of sorption isotherms are referred to as BET and GAB. The GAB model is based on the theory of multiple layer adsorption. Its parameters are physically reliable and in contrast to the BET model (being its modification) it may be applied ithin a broader range of ater activity values ranging from 0 to 0.9. Both these models make it possible to calculate ater contents in the monolayer. In the analyzed case this content ranged from to (BET) and from to 0.00 (GAB). These values ere slightly higher than those reported by Pałacha and Chrzanoski (203), amounting for potato starch to (BET) and (GAB). Hoever, these differences may be ascribed to the variability of properties in the case of potato starch. Values of constants C and K for the GAB model ere found ithin the ranges described by Leicki (997). According to that author, the value of the C constant should be greater than 5.67, hile that of the K constant should be ithin the range of 0.24 to. Otherise this model does not produce the sigmoid shape or it leads to high discrepancies (the error exceeding 5.5%) beteen the actual ater content in the monolayer and that calculated based on the above-mentioned model (Leicki, 997).

7 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of 7 Table 2. Parameters of sorption models Tabela 2. Parametry modeli sorpcyjnych Model Parameter Parametr SZ (PS) SZa (PSa) SZu (PSo) SZau (PSao) BET u 0 0,080 0,0740 0,0789 0,0738 C 9,86 9,26 20,44 20,9 R 2 0,976 0,977 0,978 0,977 RMS 9,23 9,9 8,86 9,02 GAB u 0 0,0987 0,0960 0,00 0,0962 C 7,2 3,90 5,47 4,50 K 0,724 0,72 0,74 0,77 R 2 0,997 0,997 0,997 0,997 RMS 5,35 4,93 4,82 4,79 OSWIN h 0,40 0,32 0,40 0,33 z 0,36 0,324 0,35 0,320 R 2 0,993 0,990 0,99 0,989 RMS 7,6 8,25 7,8 7,99 PELEG A 0,202 0,8 0,96 0,77 D 0,534 0,523 0,525 0,500 B 0,57 0,46 0,47 0,45 E 5,742 4,40 4,875 4,5 R 2 0,997 0,997 0,997 0,997 RMS 4,89 5,3 4,82 5,06 LEWICKI F 0,267 0,26 0,274 0,262 G 0,90 0,85 0,80 0,8 H 0,602 0,667 0,637 0,658 R 2 0,997 0,996 0,997 0,995 RMS 4,98 5,6 4,82 5,5 HALSEY S 0, ,0047 0, ,00389 n 2,55 2,49 2,56 2,53 R 2 0,962 0,954 0,956 0,953 RMS 2,0 2,9 2,34 2,59 HENDERSON P 28,87 28,25 28,9 29,97 m,93,86,93,89 R 2 0,994 0,995 0,995 0,995 RMS 6,7 6,02 5,73 5,99 BLAHOVEC- -YANNIOTIS a,5,7,0,08 b 7,59 9,94 8,56 0,38 a 2 20,64 5,9 6,60 4,52 b 2 6,82,6 2,6 0,4 R 2 0,996 0,995 0,996 0,995 RMS 4,39 4,82 4,46 4,79 In the ater activity range of 0 to W zakresie aktyności ody od 0 do 0,43.

8 8 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of Values of the C constant obtained for the BET and GAB models ere greater than those in a study by Pałacha and Chrzanoski (203), hile they ere similar to those reported by Al-Muhtaseb et al. (2004a) for potato starch. In turn, the K constant had loer values in comparison to both these studies. An interesting model is provided by a dependence presented by Blahovec and Yanniotis (2009). That equation as applied ith satisfactory results to describe sorption in such food products as starch, fruit, vegetables, etc. (Blahovec and Yanniotis, 2009; Červenka et al., 202). According to the assumptions of this model, the total ater content in the product at a specific activity may be divided into ater hich is sorbed by insoluble components and hich forms the monolayer, and ater available for soluble components. Such a dependence is presented in Figure 2. As it may be seen, the content of ater participating in dissolution is slight at lo activities and it increases gradually, reaching high values at high activities. Chemical modification caused a reduction of the share of adsorbed ater and an increase in the amount of ater available for soluble components Equilibrium ater content (g H2O per g d.m.), u Rónoagoa zaartość ilgoci, u (g H2O g s.m.) Water activity Aktyność ody, a Fig. 2. Bound ater (solid symbols) and unbound ater (open symbols) determined on the basis of the Blahovec-Yanniotis model ( potato starch, acetylated potato starch, oxidised potato starch, acetylated and oxidised potato starch) Rys. 2. Woda ziązana (pełne symbole) i nieziązana (puste symbole) yznaczona na bazie modelu Blahoveca-Yanniotisa ( skrobia ziemniaczana, skrobia ziemniaczana acetyloana, skrobia ziemniaczana utleniona, skrobia ziemniaczana acetyloana i utleniona)

9 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of 9 Conclusions. The course of isotherms for all the tested starches (native and modified) as sigmoid, corresponding to type II isotherms according to the classification presented by Brunauer et al. 2. All tested modifications led to a decrease in starch hygroscopicity, ith acetylation causing a markedly greater loss of ater vapour absorbing capacity in comparison to oxidation. 3. Of the eight analyzed models that proposed by Pelega proved to be the best, although three other (Leicki, GAB and Blahovec-Yanniotis) described experimental data ith similar accuracy. 4. In most cases chemical modification resulted in a decrease in monolayer capacity. An exception in this respect as found for the value determined from the GAB model for oxidized starch. References Al-Muhtaseb, A. H., McMinn, W. A. M., Magee, T. R. A. (2004a). Water sorption isotherms of starch poders. Part : Mathematical description of experimental data. J. Food Eng., 6, 3, Al-Muhtaseb, A. H., McMinn, W. A. M., Magee, T. R. A. (2004b). Water sorption isotherms of starch poders. Part 2: Thermodynamic characteristics. J. Food Eng., 62, 2, Anderson, R. B. (946). Modifications of the Brunauer, Emmett and Teller equation. J. Am. Chem. Soc., 68, 4, Blahovec, J., Yanniotis, S. (2009). Modified classification of sorption isotherms. J. Food Eng., 9,, de Boer, J. H. (953). The dynamical character of adsorption. Oxford: Clarendon Press. Brunauer, S., Emmett, P. H., Teller, E. (938). Adsorption of gases in multimolecular layers. Am. Chem. Soc. J., 60, Červenka, L., Kubínová, J., Juszczak, L., Witczak, M. (202). Moisture sorption isotherms and glass transition temperature of elecampe (Inula helenium L.) and burdock (Arctium lappa L.) roots at 25 C. Food Sci. Technol. Int., 8,, 8 9. Ciurzyńska, A., Lenart, A. (200). Rehydration and sorption properties of osmotically pretreated freeze-dried straberries. J. Food Eng., 97, 2, Fornal, J., Sadoska, J., Błaszczak, W., Jeliński, T., Stasiak, M., Molenda, M., Hajnos, M. (202). Influence of some chemical modifications on the characteristics of potato starch poders. J. Food Eng., 08, 4, Forssell, P., Hamunen, A., Autio, K., Suortti, T., Poutanen, K. (995). Hypochlorite oxidation of barley and potato starch. Starch/Stärke, 47, 0, Golachoski, A., Zięba, T., Kapelko-Żeberska, M., Drożdż, W., Gryszkin, A. M., Grzechac, M. (205). Current research addressing starch acetylation. Food Chem., 76, Guggenheim, E. A. (966). Applications of statistical mechanics. Oxford: Clarendon Press. Halsey, G. (948). Physical adsorption on non-uniform surfaces. J. Chem. Phys., 6, Henderson, S. M. (952). A basic concept of equilibrium moisture. Agric. Eng., 33, Iglesias, H. A., Chirife, J. (976). Prediction of the effect of temperature on ater sorption isotherms of food materials. Int. J. Food Sci. Technol.,, 2, ISO 24:996 (996). Modified starch Determination of carboxyl group content of oxidized starch. Genève: ISO.

10 0 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of Leicki, P. P. (997). The applicability of the GAB model to food ater sorption isotherms. Int. J. Food Sci. Technol., 32, 6, Leicki, P. P. (998). A three parameter equation for food moisture sorption isotherms. J. Food Process Eng., 2, 2, Mężyński, L. (972). Acetyloanie skrobi. Przem. Chem., 5, 5, Osin, C. R. (946). The kinetics of package life. III. The isotherm. J. Chem. Technol. Biotechnol., 65, 2, Pałacha, Z., Chrzanoski, P. (203). Badanie procesu adsorpcji i desorpcji ody ybranych skrobi. Post. Tech. Przet. Spoż.,, Peleg, M. (993). Assessment of a semi-empirical four parameter general model for sigmoid moisture sorption isotherms. J. Food Process Eng., 6,, Pietrzyk, S., Fortuna, T., Soa, M. (2006). Wpły katalizatoró na efektyność procesu utleniania skrobi i jej łaściości fizykochemiczne. Żyn. Nauka Technol. Jakość, 47, 2, Pietrzyk, S., Juszczak, L., Fortuna, T., Królikoska, K. (203). Wpły kompleksoania skrobi utlenionych składnikami mineralnymi na ich łaściości reologiczne. Żyn. Nauka Technol. Jakość, 88, 3, Sablani, S. S., Kasapis, S., Rahman, M. S., Al-Jabri, A., Al-Habsi, N. (2004). Sorption isotherms and the state diagram for evaluating stability criteria of abalone. Food Res. Int., 37, Tegge, G. (200). Skrobia i jej pochodne. Krakó: Polskie Toarzysto Technologó Żyności, Oddział Małopolski. Tharanathan, R. N. (2005). Starch value addition by modification. Crit. Rev. Food Sci. Nutr., 45, 5, Witczak, M., Ziobro, R., Juszczak, L., Korus, J. (206a). Starch and starch derivatives in glutenfree systems a revie. J. Cereal Sci., 67, Witczak, T., Witczak, M., Socha, R., Stępień, A., Grzesik, M. (206b). Candied orange peel produced in solutions ith various sugar compositions: sugar composition and sorption properties of the product. J. Food Process Eng., on-line. DOI: 0./jfpe.2367 Wurzburg, O. B. (964). Acetylation. In: R. L. Whistler, R. J. Smith, J. N. BeMiller, M. L. Wolfrom (eds.), Method in carbohydrate chemistry (pp ). Ne York: Academic Press. WŁAŚCIWOŚCI SORPCYJNE MODYFIKOWANEJ SKROBI ZIEMNIACZANEJ Streszczenie Wstęp. Skrobia należy do najczęściej ykorzystyanych przemyśle spożyczym biopolimeró, jednak formie natynej ma ograniczone zastosoanie. Jej budoa spraia, że stosunkoo łato ulega różnorodnym modyfikacjom, proadzącym do postania jej pochodnych o bardzo zróżnicoanych łaściościach. Do podstaoych metod stosoanych celu zmiany charakterystyki skrobi należą acetylacja i utlenianie. Uzyskiane dzięki temu suroce są stosoane jako dodatki do żyności. Stabilność tych surocó oraz produktó spożyczych z ich udziałem silnie zależy od ich składu oraz parametró charakteryzujących miejsce przechoyania ilgotności zględnej i temperatury. Jedna z metod określania łaściych arunkó charakteryzujących otoczenie opiera się na pojęciu aktyności ody, a następnie izotermach sorpcji. Spraia to, że badania proadzące do poiązania aktyności i zaartości ody są ażne z punktu idzenia optymalizacji arunkó przechoyania oraz projektoania niektórych procesó przetórsta żyności. Celem niniejszej pracy była zatem ocena płyu modyfikacji (utlenianie, acetylacja oraz ich połączenia) na łaściości sorpcyjne (opisane z ykorzystaniem izoterm sorpcji) skrobi ziemniaczanej.

11 Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of Materiał i metody. Badaniom poddano skrobię ziemniaczaną oraz jej pochodne uzyskane yniku acetylacji, utleniania oraz podójnej modyfikacji acetylacji i utleniania. Utlenianie skrobi proadzono z zastosoaniem chloranu (I) sodu, a acetylację z ykorzystaniem bezodnika kasu octoego. Izotermy sorpcji yznaczono metodą statyczno-eksykatoroą. Uzyskane yniki opisano ybranymi modelami matematycznymi, posiadającymi interpretację fizyczną (BET i GAB), oraz empirycznymi (Halseya, Osina, Hendersona, Pelega, Leickiego, Blahovca- -Yanniotisa). Obliczenia ykonano z ykorzystaniem estymacji nielinioej. Wyniki. Najiększą zdolnością absorpcji ody charakteryzoała się natyna skrobia ziemniaczana. Modyfikacje poodoały spadek ilości adsorboanej pary odnej, zależny od rodzaju zastosoanej modyfikacji. Acetylacja poodoała istotnie iększe ograniczenie ilości adsorboanej pary odnej niż utlenianie. Utlenianie płyało na łaściości sorpcyjne nieznaczny sposób. Najmniejszą higroskopijnością charakteryzoała się skrobia podójnie modyfikoana, co ynikało z nakładania się efektu utleniania i acetylacji, zmniejszającego zdolność adsorpcji pary odnej. Cztery z zastosoanych modeli matematycznych (Pelega, Leickiego, GAB oraz Blahovca-Yanniotisa) dobrze odzierciedlały przebieg izoterm, z podobną dokładnością. Zaartość ody monoarstie zmieniała się zakresie od 0,0738 do 0,080 (model BET) oraz od 0,0960 do 0,00 (model GAB). Na podstaie modelu Blahovca i Yanniotisa stierdzono, że modyfikacje proadziły do spadku udziału ody adsorboanej i ziększenia udziału ody dostępnej dla składnikó rozpuszczalnych. Wnioski. Izotermy sorpcji szystkich badanych skrobi (natynej i modyfikoanych) charakteryzoały się sigmoidalnym kształtem. Analizoane modyfikacje proadziły do spadku higroskopijności skrobi, przy czym acetylacja poodoała zdecydoanie iększy spadek zdolności adsorboania pary odnej niż utlenianie. Z ośmiu modeli matematycznych zastosoanych do opisu łaściości sorpcyjnych za najlepszy uznano model Pelega, chociaż trzy inne (Leickiego, GAB oraz Blahovca-Yanniotisa) opisyały dane eksperymentalne z podobną dokładnością. W iększości przypadkó modyfikacja chemiczna skrobi proadziła do zmniejszenia pojemności monoarsty. Wyjątek stanoiła artość yznaczona z modelu GAB dla skrobi utlenionej. Uzyskane yniki mogą zostać ykorzystane do optymalizacji arunkó przechoyania i projektoania produktó z udziałem skrobi i jej pochodnych. Słoa kluczoe: skrobia ziemniaczana, modyfikacja, łaściości sorpcyjne, acetylacja, utlenianie Corresponding address Adres do korespondencji: Teresa Witczak, Katedra Inżynierii i Aparatury Przemysłu Spożyczego, Uniersytet Rolniczy im. Hugona Kołłątaja Krakoie, ul. Balicka 22, Krakó, Poland, t.itczak@ur. krako.pl Accepted for publication Zaakceptoano do opublikoania: For citation Do cytoania: Witczak, T., Stępień, A., Witczak, M., Pietrzyk, S., Bednarz, A., Florkieicz, A. (206). Sorption properties of modified potato starch. Nauka Przyr. Technol., 0, 4, #48. DOI: /J.NPT