Characteristics of Acetylated Banggai Yam Starch on pH and Concentration of Anhydride Acetic
If’all1,2*, Asriani Hasanuddin3, Abdul Rahim4, Syahraeni Kadir4
1 Agricultural Doctoral Program, Tadulako University, City of Palu, Indonesia
2 Agricultural Product Technology Study Program, Alkhairaat University, City of Palu, Indonesia
3 Animal Husbandry Study Program, Tadulako University City of Palu, Indonesia
4 Agrotechnology Study Program, Tadulako University, City of Palu, Indonesia
Abstract
The Banggai yam starch, like other native starches, has a weakness that can reduce the use of the starch in the food industry. Therefore, it is necessary to improve physicochemical properties by modifying Banggai yam starch. This study aimed to obtain the influence of pH dispersion (7, 8, 9 and 10) and acetic anhydride concentration (6, 9, 12 and 15% v/b) in the acetylation process of Banggai yam starch. In addition, to determine the characteristics of the Banggai acetylated starch, which include percentage of acetyl, degree of substitution, water and oil holding capacity, swelling power, solubility, acetyl group binding and crystallinity of Acetylated banggai yam starch. The optimum acetylation was achieved at pH dispersion 9 and with acetic anhydride concentration of 15%. High degree of substitution (DS) of acetylated banggai yam starch had high water and oil holding capacity, swelling power and solubility with values of 29.97%, 30.16%, 1.91 g/g, and 34.35% respectively.
Keywords: acetylated banggai yam starch, pH, acetic anhydride concentration, degree of substitution
INTRODUCTION
Banggai yam starch is a potential carbohydrate substitute food source in Central Sulawesi because it has a high amylose content of 26.98-31.02% (Lebot et al., 2006), a stable structure at high temperatures and low pH (Mali et al., 2006), and hypoglycemic (Chen and Lin, 2007). Starch is widely used in the food industry as an ingredient in processed products (eg sauces, soups, snacks, bread) as a gelling agent, stabilizing, thickening, binding, modificating the textures and as a bulking agent. Starch is uniquely varied in physicochemical, functional and structural properties between and within botanical species, and even when the same plant cultivars grow under different environmental conditions.
Among starch, yam is preferred because it has a glycemic index (IG) of 22.4 and is categorized as a food item with a low GI value (<55), as a substitute for gluten-free flour which is safe for diabetics and autistic consumption. In addition, yam contains nutrients and functional components such as mucin, dioscin, allantoin, choline, and essential amino acids. Purple yam (D. alata L) also contains a lot of anthocyanins (Fang et al., 2011). Yam (D. alata L) contains mucus which influences the physicochemical properties (Yeh et al., 2009).
One way to increase the added value of starch is to modify the starch to obtain properties suitable for a particular application (Palguna et al., 2014). Classified starch modification techniques into 4 groups namely: (i) chemical modification; (ii) physical modification; (iii) enzymatic modification; and (iv) biotechnology modification (Kaur et al., 2012). Chemical modification has the greatest effect on the functional properties of starch.
One chemical modification of starch is esterification. Esterification of starch is the reaction to form ester bonds between carboxylic acids and starch. Modification of starch by esterification can increase the stability and starch resistance of retrogradation (Xie and Liu, 2004). Modification of starch by esterification is expected to improve the characteristics of starch, such as hydrophobic and crystallinity. The process of chemical modification of starch with esterification of citric acid can increase levels of resistant starch (Mei et al., 2015).
The chemical modification process of starch is influenced by several factors, namely granule composition, granule structure, chemical parameters, and reaction conditions. Reaction conditions include pH, type and concentration of salts which inhibit swelling, solvents, temperature and reaction time. The double modification by acetylation and "butyrylization" is expected to produce starch acetate which has a functional effect on human health because it has a high resistant starch (RS) content. RS is resistant to digestive enzymes fermented by colon bacteria that produce short-chain fatty acids as a source of energy in the colon, reduce cholesterol, bile acids, and formation of gallstones, prevent colon cancer, prostate cancer, colonic inflammation and as anti-carcinogenic (Bajka et al., 2010). As with other types of native starch, Banggai yam starch has weaknesses that can reduce the use of starch in the food industry. The purpose of this study was to improve physicochemical properties by modifying Banggai yam starch. The purpose of this study was to obtain the influence of pH dispersion (7, 8, 9 and 10) and acetic anhydride concentration (6, 9, 12 and 15% v/b) in the Banggai yam starch acetylation process. In addition, to determine the characteristics of Acetylated banggai yam starch, namely the percentage of acetyl, degree of substitution, water and oil binding capacity, swelling capacity, solubility, acetylated group binding and crystallinity of Acetylated banggai yam starch.
MATERIALS AND METHODS Materials
Banggai yam starch used was from Banggai Island Regency. The chemicals for the acetylation process were acetic anhydride, 3% NaOH, 0.5 N HCl, 96% ethanol, 0.5 M KOH, indicators of phenolphthalein, destilled water, and chemicals used for analysis.
Acetylation of Banggai Yam Starch
Modification of Banggai yam starch with acetic anhydride was performed according to a method by Chi et al., (2008) (Rahim et al., 2016). This study used a completely randomized design (CRD) of two factors, namely pH (7, 8, 9 and 10) and acetic anhydride concentration (6, 9, 12 and 15% v/b). This study was replicated 2 times so there were 4 x 4 x 2 = 32 experiments. The synthesis of the Acetylated banggai yam starch was performed by dispersing Acetylated banggai yam starch into 225 ml of distilled water and stirred with a magnetic stirrer for one hour at room temperature. After that, the acetate anhydride concentration of 6, 9, 12 and 15% (v/b) was added. Then, the suspension was added a 3.0% NaOH solution until the pH according to the treatment (7, 8, 9 and 10) at room temperature for 50 minutes. After that, the pH of the suspension was reduced to 4.5 using 0.5 N HCl solution. After there was a deposition, washing was carried out to free the acid residues. The next process was sedimentation and washing with distilled water three times and ethanol once, then drying with an oven at 50 oC for 20 hours.
Determination of Percentage of Acetyl and Degree of Substitution
Percentage of acetyl was determined by using titration method ((Singh et al., 2004). A 1.0 gram Acetylated banggai yam starch was placed into 250 ml erlemeyer 50 ml 75% ethanol was added. The starch dispersion is heated and agitated at 50 oC in a water bath for 30 minutes and then cooled at room temperature. After chilling, 40 mL 0.5 M KOH was added and shaken using a shaker for 30 minutes at room temperature. The excess alkali was titrated using 0.5 M HCI solution and phenolphthalein as an indicator until there was no pink color. As a blank, Banggai yam native starch was used. If W = the weight of the substituent bound which replaced the hydrogen group in the OH group (% by weight), M = substituent molecular weight (acetyl group = 0.043), W/M = number of substituent moles, 1 x W/M = total hydrogen weight (% ), 162 = molecular specific weight of glucose (anhydrous, C6H10O5 and (100–W x W/M)/162 = unit weight of glucose, then:
% acetyl (W) = [(Blank−Sample )mL x M HCI x 0.043 x 100]
Dry weight of sample (g)
HCl was used for blank titration and samples in ml of HCl, while the sample was in dry weight (grams).
To calculate DS, the following formula was used:
DS = 162 W
100 M−(M−1)W
FTIR Spectra Analysis
The FTIR spectrum of native starch and acetylated/butyrated starch was measured by using the KBr method (Pushpamalar et al., 2006). The sample was mixed with KBr with a ratio of starch/KBr = 1:4. The mixture was compressed to obtain a transparent pellet and then the sample was identified by infrared light with a spectrometer (MIDAC, prospect 269, Costa Mesa, CA USA). Each spectrum was analyzed in a range of 400-4000 cm resolution-1.
X-ray Diffractometry Analysis
X-ray crystallinity of native starch and acetylated starch diffraction was measured using the method (Miao et al., 2011). X-ray analysis was performed by using an X-ray diffractor PRO Pert-X-ray (PANalytical, Almelo, Netherlands) which was operated on 40 kV, 30 mA, and radiation of Cu Kα (λ = 1.5406). Starch samples were packed square (15x10 mm, thickness 0.15 cm) and scanned at a speed of 2d/min at a diffraction angle (20) from 3d to 70d at room temperature. Crystallinity was calculated according to the following equation:
Xc = 𝐴𝑐 𝐴𝑎 + 𝐴𝑐
Where Xc is crystalline, Ac is the Crystal region and Aa is the amorphous region on the X-ray diffractogram.
Water and Oil Holding Capacity
Water/oil holding capacity (WHC/OHC) of acetylated starch. Twenty-five millimeters of distilled water or olive oil were added to 250 mg of a dry sample, stirred and left at room temperature for 1 hour.
After it was centrifuged, the residue was weighed, WHC and OHC were calculated as g of water or oil per g of dry sample.
Swelling power and solubility
Swelling power and solubility were determined using a method by (Adebowale et al., 2009). Starch was suspended with distilled water (1%, w/v) with weighted test tubes (W1). Then it was heated at 80oC for 30 minutes, then cooled to room temperature. After that, it was centrifuged at 3400 rpm for 15 minutes until residues and supernatants were separated. The residue and water that was retained after centrifugation was then weighed (W2). Starch swelling (based on dry weight was determined as follows):
Swelling power (g/g) = 𝑊2−𝑊1
𝑠𝑎𝑚𝑝𝑙𝑒 𝑤𝑒𝑖𝑔ℎ𝑡
The supernatant (5 mL) was dried to a constant weight at 110oC. The residue after the supernatant was dried, it showed the amount of starch dissolved in water (%).
RESULTS AND DISCUSSION Degree of Substitution
The analysis of variance showed that there was no interaction between pH and acetic anhydride concentration on the degree of substitution of Acetylated banggai yam starch. The acetic anhydride concentration had a significant influence on the degree of substitution of Acetylated banggai yam starch but pH dispersion had no significant influence on the degree of substitution of Acetylated banggai yam starch which can be seen in Figure 1.
Figure 1. Degree of substitution of Acetylated banggai yam starch as a result of synthesis with different pH dispersions and acetic anhydride concentrations. Different letters for each DS of Acetylated banggai yam starch showed significant differences (p<0.05).
Acetyl group binding
Acetate fixation pattern in Banggai yam starch was determined by using FTIR spectrometer on frequency of 400-4000 cm-1. Acetyl group binding occurs in OH groups of C2, C3 or C6 of starch molecules. If the group interacts with the ester group, it will cause changes in the absorption band of the FTIR spectrum produced. FTIR spectrum of native Banggai yam starch and DS of Acetylated banggai yam starch at various concentrations of acetic anhydride and pH can be seen in Figure 2.
Figure 2. FTIR spectrum of native starch (d) and Banggai yam acetylatedstarches prepared by reaction with 15% (sb) acetic anhydride for 50 min at pH 9 (a), with 9% (sb) acetic anhydride at pH 10 (b), and with 6% (sb) acetic anhydride at pH 9 (c)
In Figure 2, it can be seen the results of the analysis of the infrared spectrum on acetylated starch which shows that there was a change in chemical structure compared to native starch. The infrared
0.147b
0.087a
0.231a
0.125a 0.079b
0.116a
0.183a 0.169a
0.054b
0.173a 0.183a
0.250a
0.125b
0.151a
0.209a 0.227a
0 0.05 0.1 0.15 0.2 0.25 0.3
6 9 12 15
Degree of Subtitution (DS)
Concentration Acetic Anhydride (%)
BNJ α 0,05 = 0.11
pH 7 pH 8 pH 9 pH 10
spectrum of native starch showed a wave frequency of 3000-3500 cm-1 which can be likened to a stretch of the -OH and -CH functional groups (Sánchez-Rivera et al., 2013). The infrared spectrum of Acetylated banggai yam starch in addition to showing the -OH and -CH functional groups, also it shoed strong absorption at the peak of the wave in 1750 cm-1. The peak at 1750 cm-1 wave was a characteristic of the ester (C = O) functional group that indicates the acetylation reaction. The acetylation reaction was indicated by the binding of the acetyl functional group into the starch compound which changes the chemical structure. The acetyl group binding in the starch granules was characterized by an increase in the intensity of the wave peak at 1750 cm-1 and a decrease in the intensity of the peak frequency of the wave at 3000-3600 cm-1 or in other words C = O (the acetyl group) increased, while the -OH group (the acetyl group) decreased. According to (Xu et al., 2004) the acetyl group in the starch molecule is exchanged by the acetyl group, which can cause damage to the crystal starch granules.
Crystallinity
The crystallinity of the starch granules can be seen using the X-ray diffraction pattern method and can be determined by the integration of curves under the peak of the amorphous and crystalline regions.
The peak intensity of the X-ray diffraction produced on the curve is related to the crystalline region within the granular starch. XRD pattern of native Banggai yam starch and DS of Acetylated banggai yam starch at various concentrations of acetic anhydride and pH can be seen in figure 3. The results of the study showed that the native Banggai yam starch and S of Acetylated banggai yam starch had crystalline type B.
The results showed that acetylation was not able to change the crystal type of Banggai yam starch because the number of substituted acetyl groups in the starch molecule was still low. Other results also explained that the esterification reaction was unable to change the type of starch crystalline.
Figure 3. X-ray diffract grams and crystallinity of native (a), and acetylated Banggai yam starches with different DS: 0.054 (b), 0.151 (c), and 0.250 (d)
The results showed that the degree of crystallinity of Acetylated banggai yam starch was lower than native Banggai yam except in Banggai acetylated starch yam with moderate DS. The Acetylated banggai yam starch had weak intra and inter molecular bonds, so it was easy to experience crystalline damage in the acetylation process. This decrease in crystallinity is caused by the intermission of inter and intra-molecular hydrogen bonds due to the acetylation process. According to (Sha et al., 2012) the degree of crystallinity of the rice acetylated starch granules was lower than the native rice starch due to the acetylation process. Whereas in Acetylated banggai yam starch with moderate DS was stronger against the acetylation treatment so it did not suffer crystalline damage. The physical shape of the yam starch
12,24 (d), 16,84 (c) 12,16 (b), 12,93 (a)
granule is semicrystalline consisting of crystalline units and amorphous units. Crystal unit is more resistant to strong acids and enzymes, while the amorphous unit is volatile to strong acids and enzymes.
The diffraction pattern known as A, B, C represents the specific diffraction angle caused by the double helix in the amylopectin bonding chain (Parker and Ring, 2001). Crystallinity patterns as interplanar space bases and the relative intensity of X-ray diffraction lines (Tester et al., 2004). These diffraction patterns give polymorphic forms such as types A, B and C. Type C polymorphic is considered to be a type with the intermediate crystalline form between type A and B (Tester et al., 2004).
The hydrolysis treatment causes damage to the structure of the starch in the amorphous region, but hydrolysis with a long time will also damage the crystalline area. The Banggai yam starch which was hydrolyzed by acetic anhydride for 50 minutes resulted in a decrease in crystallinity because hydrolysis had damaged the crystalline structure of the starch. The precipitation process causes a peak in the crystallinity pattern to fall so that the peak point almost disappears. Changes in crystallinity in nanocrystalline tapioca due to the presence of crystallized short-chain amylose and form a double helix structure, resulting in changes in the granular starch and a decrease in the degree of crystallinity. The process of acetylation in native Banggai yam starch can slightly reduce the crystallinity of the starch, but there was not much difference in the pattern of crystallinity. The peak in the crystallinity pattern did not change and remains at 12°, 15°, 16°, and 45°.
Acetic anhydride which causes a substitute reaction for the replacement of OH groups in the starch also leaves residues in the form of acetic acid which can increase the crystallinity of the starch, because the acid can degrade the amorphous regions of the starch. Acid hydrolyzed starch will slightly increase the degree of crystallinity (Wang et al., 2003). The increase in the degree of crystallinity is due to the tendency of acids to attack amorphous regions. Acid hydrolysis does not only attack amorphous regions, but also crystalline regions, where acid will initially attack amorphous regions which are more easily degraded due to loose structures (Bertoft, 2004).
Water dan oil holding capacity
The results of the analysis of variance showed that there was an interaction between pH and acetic anhydride concentration water dan oil holding capacity acetylated banggai yam starch. Acetic anhydride concentration and pH had significant influence on water dan holding capacity of Acetylated banggai yam starch, which can be seen in Figure 4 .
Figure 4. Effects of DS on the water and oil holding capacities of Acetylated banggai yam starch. Figures in the graph followed by the same letter showed no significant difference at p < 0.05
24.192b 28.435a 28.514a 29.970a
23.799c
27.592b 28.405a 30.167a
- 5.000 10.000 15.000 20.000 25.000 30.000 35.000
- 5.00 10.00 15.00 20.00 25.00 30.00 35.00
Native Starch DS 0,054 DS 0,151 DS 0,250
OHC (%)
WHC (%)
Degree of Substitution
BNJ α 0,05 = 2.35 (WHC), 2.20 (OHC)
WHC OHC
Based on the graph above, the average WHC and OHC of Acetylated banggai yam starch had greater WHC and OHC compared to native proud yam starch. The increase in WHC and OHC occurs with increasing degrees of substitution. The ability of water absorption in starch is influenced by hydroxyl groups found in starch molecules. If the number of hydroxyl groups in starch is very large then the ability of water absorption is very large, also influenced by the size of the granules and chemical characteristics.
Similarly, the ability of oil absorption, caused by starch granules become damaged, so that the granules stretch and facilitate the oil to tightly bond with the granules caused by protein on the surface of the granular starch. This protein can form a complex with starch, where the starch-protein complex can provide a place for the binding of oil. The ability of starch to absorb oil is determined by the fat and fiber content in the starch. Fat forms a hydrophobic layer on the surface of the starch granules. The increase in WHC and OHC is caused by changes in geometric and acetate functional groups in starch molecules that have the ability to hold water and oil. The ability to absorb water and oil in starch shows hydrophilic and hydrophobic properties. This is caused by the number of substituted hydroxyl groups (hydrophilic). This results in a hydrophobic increase from starch. The binding capacity of the oil to the starch is influenced by the presence of protein on the surface of the starch granules that can form complexes which can make the oil bound to the starch, also related to the amylose contained in the starch.
Swelling power and solubility
The analysis of variance showed that there was an interaction between pH and acetic anhydride concentration on swelling power and solubility. The treatment of acetic anhydride concentration and pH had no significant influence on swelling power and solubility of the acetylated starch, which can be seen in Figure 5.
Figure 5. Effects of DS on the swelling power and solubility of acetylated banggai yam starch. Figures in the graph followed by the same letter showed no significant difference at p < 0.05
Based on Figure 4, the average value of swelling power was 1.52-1.91 g/g and the solubility was 31.28-34.35%. The acetylation process increases swelling power which associated with the hydrolysis of the starch that degrades the crystalline area in the Acetylated banggai yam starch. The increase in swelling power was caused by a disturbed crystalline starch structure that causes water molecules to form bonds with amylose and amylopectin through hydrogen bonds. The substitution of acetyl groups makes water easy to enter the amorphous and weakens hydrogen bonds between starch molecules and water molecules form hydrogen bonds with starch granules (Betancur and Chel, 1997). The increase in swelling power was due to the weak hydrogen bonds in the acetylated starch molecule making it easier for water to enter the starch granules. The more substituted groups, the weaker the hydrogen bonds, so that the
1.519b 1.603b 1.614b
1.914a
20.388b
31.287a 32.946a 34.355a
- 5.000 10.000 15.000 20.000 25.000 30.000 35.000 40.000
- 0.500 1.000 1.500 2.000 2.500
Native Starch DS 0,054 DS 0,151 DS 0,250
Solubility (%)
Swelling power (g/g),
Degree of Substitution
BNJ α 0,05 = 0.25 (Swelling power), 9.32 (Solubility) Swelling power
Solubility
crystalline structure trasnforms into amorphous. In general, the increase in DS caused the increase in swelling power and solubility of acetylated starch or in other words, acetylated starch with a DS value of 0.250 (on average there were 2 acetyl groups per 10 anhydroglucose unit in the starch molecule) which had higher solubility levels. The increase in the concentration of acetic anhydride and pH can increase the DS of acetylated starch, the increase in DS can increase the swelling power and solubility of acetylated starch. An increase in swelling power and solubility caused by the substitution of acetyl groups into hydroxyl groups that can weaken hydrogen bonds between starch molecules. The higher the concentration of acetic anhydride, the more acetyl groups diffuse and adsorb on the surface of the starch.
The increase in swelling power was due to the weak hydrogen bonds in the acetylated starch molecule making it easier for water to enter the starch granules. The more substituted groups, the weaker the hydrogen bonds, so that the crystalline structure trasnforms into amorphous. The substitution of acetyl groups in the Banggai yam starch was weakened the hydrogen bonds in the starch molecule so that water was easier to penetrate into the starch granules and causes amylose out of the granules, which caused the solubility value to increase, but after 50 minutes the solubility value decreased.This was caused by the number of substituted hydroxyl (hydrophilic) groups. This caused an increase in the hydrophobic of starch which can ultimately reduce the solubility of starch in water.
The increase in the concentration of acetic anhydride and pH can increase the DS of acetylated starch, the increase in DS can increase the swelling power and solubility of acetylated starch. An increase in swelling power and solubility caused by the substitution of acetyl groups into hydroxyl groups that can weaken hydrogen bonds between starch molecules.
CONCLUSION
The maximum percentage of acetyl and degree of substitution were achieved at pH dispersion 9 and with acetic anhydride concentration of 15%, with values of 6.21% and 0.25, respectively. Physical, chemical and functional characteristics of acetylated starch were influenced by the value of DS. The high DS of acetylated starch had high water and oil holding capacity, swelling power and solubility with values of 29.97%, 30.16%, 1.91 g/g, and 34.35% respectively.
ACKNOWLEDGEMENT
Our gratitude to the Ministry of Research, Technology and Higher Education which have supported the funding through the Basic Research scheme with Contract Number: 100/SP2H/LT DRPM/2019 Dated March 21, 2019.
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