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Progress in starch modification in the last decade
Food Hydrocolloids 26 (2012) 398e404
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Progress in starch modification in the last decade Bhupinder Kaur, Fazilah Ariffin, Rajeev Bhat, Alias A. Karim* Food Biopolymer Research Group, Food Technology Division, School of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 3 September 2010 Accepted 17 February 2011
Modification of starch is carried out to enhance the positive attributes and eliminate the shortcomings of the native starches. Modification of starch is an ever evolving industry with numerous possibilities to generate novel starches which includes new functional and value added properties as a result of modification and as demanded by the industry. In this paper, we will highlight the many current methods that have been discovered in starch modification which includes four broad areas that are chemical, physical, enzymatical and genetical modification. Ó 2011 Published by Elsevier Ltd.
Keywords: Modification of starch Chemical Physical Enzymatic Genetic/biotechnology
1. Introduction Starch is made up of two fractions: amylose which is made up of essentially a-(1 / 4) D-glucopyranosyl units and amylopectin which is made up of a large number of short chains linked together at their reducing end side by a a-(1 / 6) linkage (Biliaderis, 1998). Starch affects texture, viscosity, gel formation, adhesion, binding, moisture retention, film formation and product homogeneity. It is used mainly in soups, sauces and gravies, bakery products, dairy confectionery, snacks, batters and coatings and meat products (Davies, 1995). Non-food applications of starch include in the field of pharmaceuticals, textiles, alcohol-based fuels and adhesives. New uses of starch include low-calorie substitutes, biodegradable packaging materials, thin films and thermoplastic materials with improved thermal and mechanical properties (Biliaderis, 1998). Modification of starch was carried out to overcome shortcomings of native starches and increase the usefulness of starch for industrial applications. Native starches when cooked can easily retrograde and there is a gelling tendency of pastes besides easily undergoing syneresis. Therefore starch modification not only decreases retrogradation, gelling tendencies of pastes and gel syneresis but also improves paste clarity and sheen, paste and gel texture, film formation and adhesion (BeMiller, 1997). Modification of starches has brought about an evolution of new processing technologies and market trends. These highly functional derivatives have been tailored to create competitive advantage in a new product, improve product aesthetics, simplify product proclamation, lower recipe/
* Corresponding author. Tel.: þ60 4 653 2221; fax: þ60 4 657 3678. E-mail address: [email protected] (A.A. Karim). 0268-005X/$ e see front matter Ó 2011 Published by Elsevier Ltd. doi:10.1016/j.foodhyd.2011.02.016
production costs, increase product all through, eliminate batch rejects, ensure product consistency and extend shelf-life whilst clearly making starch relevant in all stages of a food product’s lifecycle (Murphy, 2000; Wurzburg, 1986). Modification of starch is an ongoing process as there are numerous possibilities. There is a huge market for the many new functional and added value properties resulting from these modifications. Over the last few decades, starch has been modified by various methods to achieve functionalities suitable for various industrial applications. Basically there are four broad based kinds of modifications; chemical, physical, enzymatical and genetical. A number of review articles (BeMiller, 1997; Jobling, 2004; Tharanathan, 2005) on the subject of starch modification are available. However, within the last decade there has been intense interest among researchers to develop novel methods of starch modification with more emphasis on enzymatic, physical and genetic modifications. Therefore this paper was written to bring forward all the new modifications that have taken place in the last decade. 2. Chemical modification Chemical modification of starch involves the polymer molecules of the starch granule in its native form. Modification is generally achieved through derivatization such as etherification, esterification and crosslinking, oxidation, cationization and grafting of starch. However, there has been dearth of new methods in chemical modifications as this kind of modification gives rise to issues concerning consumers and the environment. There has been a trend to combine different kinds of chemical treatments to create new kinds of modifications. Similarly, chemical methods have been combined
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with physical modifications such as microwave, radiation and extrusion to produce modified starch with specific functional properties. Overall advantages of these modifications were to shorten the time of modification and increase production. Some of the recent chemical modifications that have been studied are summarised in Table 1.
2.1. Starch esters Development of new methods to produce hydrophobic starch has been carried out in the last decade to produce hydrophobic starch as an alternative to the process patented by National Starch and Chemical Corporation. Modification of maize and cassava starch with microwave radiation was used to esterify free fatty acids with lipase as catalyst. The free fatty acids were obtained from recovered coconut oil which was hydrolysed with lipase. A DS (degree of substitution) of 1.1 was obtainable using microwave radiation for esterification with hydrolysed coconut oil and DS 0.33 when palmitic acid was the acyl donor. These modified starches have potential uses in the surface coating materials and biomedical materials applications (Rajan, Prasad, & Abraham, 2006; Rajan, Sudha, & Abraham, 2008). Hydrophobically modified starch was prepared by enzyme-catalyzed reaction of starch and alkenyl ketene dimer (AKD), which is a fatty acid residue. Enzymes used were lipases from Pseudomonas sp. and Pseudomonas fluorescens. This modified starch can be used as an ingredient in applications where high solution viscosity and hydrophobic interactions are required for example as paint thickener, construction material, emulsion stabiliser and emulsifier in cosmetics (Qiao, Gu, & Cheng, 2006). Selective esterification of starch nanoparticles was done using Candida antarctica Lipase B (CAL-B) in its immobilized and free forms as catalyst. Acylation reactions were made accessible for the starch nanoparticles by formation of Aerosol-OT (AOT, bis(2-ethylhexyl) sodium sulfosuccinate) to stabilise the microemulsions. Acylations of 3-caprolactone (CL), vinyl stearate, and maleic anhydride were obtained when AOT-coated dispersions of starch nanoparticles in toluene were exposed to physically immobilized CAL-B (Novozym 435). The modified starch nanoparticles were found to retain their nanodimensions upon the removal of the surfactant when dispersed in DMSO or water (Chakraborty, Sahoo, Teraoka, Miller, & Gross, 2005).
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2.2. Dual modifications Starch modification using a combination of chemical and physical or chemical and enzymatical methods have grown rapidly. A combined method of modification using crosslinking and phosphorylation on rice starch, provided modified rice starch with good freeze-thaw stability (Deetae et al., 2008). Crosslinking of tapioca starch with sodium trimetaphosphate in the presence of osmotic-pressure enhancing salts caused an increase in the peak and final viscosity with a decrease in breakdown. Enhancement of osmotic pressure increases the activity of the crosslinking agent (Varavinit, Paisanjit, Tukomane, & Pukkahuta, 2007). Starch-based hydrogels were prepared by UVinduced polymerization of acryloylated starch with zwitterionic monomer 3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate (DMAPS). A unique salt-tolerant swelling behaviour was observed for this modified starch (Li & Zhang, 2007). Starch modified through esterification with ferulic acid giving rise to starch ferulate showed lower viscosity, higher water holding capacity and much less retrogradation during low temperature storage compared to native starch (Ou, Li, & Yang, 2001). Microwave-assisted esterification to produce starch maleate using the dry method had a reaction efficiency of up to 98% and a reaction time of under 5 min. This is thought to be an efficient method in esterifying starch (Xing, Zhang, Ju, & Yang, 2006). The high efficiency in producing succinylated cassava starch with microwave assistance was also observed by Jyothi, Rajasekharan, Moorthy, and Sreekumar (2005). This is a good method to decrease the use of chemicals to enhance production. Microwave and ultrasound irradiation was used for the esterification of carboxymethyl cold-water-soluble potato starch with octenylsuccinic anhydride. They were positively able to shorten the esterification time from a few hours to a few minutes. The derivatives displayed excellent emulsifying and surfactant performance properties (Cí zová, Sroková, Sasinková, Malovíková, & Ebringerová, 2008). Karim, Sufha, and Zaidul (2008) prepared modified corn and mung bean starch using a dual modification process, whereby the native starch was treated to partial enzymatic hydrolysis using a mixture of fungal a-amylase and glucoamylase followed by hydroxypropylation with propylene oxide. The resultant modified starch proved to have significantly different functional properties compared to hydroxypropyl starch prepared with untreated native starch. 2.3. Other methods
Table 1 Recent chemical modification of starch. Chemical modification
References
Microwave radiation with lipase as catalyst Hydrophobic reaction of starch and alkenyl ketene dimer Esterification of starch nanoparticles with lipase as a catalyst Dual modified crosslink-phosphorylated Crosslinking coupled with osmotic pressure Starch-based hydrogels prepared by UV photopolymerization Starch esterified with ferulic acid Microwave-assisted synthesis of starch maleate and starch succinates Microwave and ultrasound irradiation Hydroxypropylation and enzymatic hydrolysis Ozone-oxidised starch
Rajan et al. (2006, 2008) Qiao et al. (2006) Chakraborty et al. (2005) Deetae et al. (2008) Varavinit et al. (2007) Li and Zhang (2007) Ou et al. (2001) Xing et al. (2006); Jyothi et al. (2005) Cí zová et al. (2008) Karim et al. (2008) Kesselmans and Bleeker (1997); An and King (2009); Chan et al. (2009)
The process of ozonation, oxidises starch and is a powerful oxidant as it has an extra oxygen atom. During the ozonation process the carboxyl and carbonyl contents were found to increase with the time of exposure to ozone. There was a difference in the extent of starch oxidation among starches from different sources (Chan, Bhat, & Karim, 2009). Ozonated starches were found useful as thickening agents whereas those treated in the presence of amino acids were suitable alternatives to highly chemically oxidised starch (An & King, 2009). Ozone is a clean and powerful oxidant and leaves no residues behind unlike hypochlorite oxidation process where large amount of salts are produced (Kesselmans & Bleeker, 1997). 3. Physical modification Physical modification can be safely used as a modification process in food products as it does not involve any chemical presence. There has been a wave of new methods in the physical
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modification of starches. Some of the new physical modifications that have been investigated in the last decade are given in Table 2. “Osmotic-pressure treatment” (OPT) was carried out in the presence of high salt solutions (Pukkahuta, Shobsngob, and Varavinit, 2007). Starch solution was suspended in sodium sulphate to obtain a uniform starch suspension and heat distribution. The potato-starch treated changed from a B to a A type after treatment with the gelatinization temperatures increasing significantly. A uniform heat distribution is provided for using this method as compared to heat-moisture treatment and modified starch is able to be produced in a large scale. Deep freezing and thawing of moistened starch increased the ska, Krok, & Tomasik, 2000) crystallinity of the granules (Szymon ska, Krok, but multiple deep freezing and thawing (Szymon Komorowska-Czepirska, & Re˛ bilas, 2003) caused an irreversible disruption of the crystalline order. Iterated syneresis was similar to multiple deep freezing and thawing. The freezing and thawing was repeated until the moisture content in the solid phase was less than 20%. All modified starches showed a change towards B-type X-ray diffraction pattern indicating a disruption of the crystalline prop erty (Lewandowicz & Soral-Smietana, 2004). Again as there are no chemicals involved then there is no concern for the effect on the environment and safety issues to be addressed. The instantaneous controlled pressure drop, DIC, process involves a short pressurisation obtained as a result of injection of saturated steam at a fixed pressure and predetermined time before it drops towards vacuum (Maache-Rezzoug et al., 2009; Zarguili, Maache-Rezzoug, Loisel, & Doublier, 2006). Gelatinization transition temperatures and enzymatic hydrolysis increased whereas gelatinization enthalpy decreased after treatment. The use of friction, collision, impingement, shear and other mechanical actions to alter the crystalline structures and properties of the starch granule refers to mechanical activation or micronization. This process causes large particles to crush to form smaller particles whereas the tiny particles agglomerate and form large particles. The gelatinization temperature and viscosity is decreased for the treated sample (Che, Li, Wang, Chen, & Mao, 2007; Huang, Lu, Li, & Tong, 2007). A non-thermal food preservation method, pulsed electric field (PEF) technology has been used to study the effect of the treatment on starch. Re-arrangement and destruction of starch molecules were observed as well as a decrease in gelatinization properties, viscosity and crystallinity (Han, Zeng, Zhang, & Yu, 2009). The solubility, gel consistency and clarity of starches decreased with increase of exposure time to corona electrical discharges (Nemtanu & Minea, 2006). Thermal inhibition of starch is done by dehydrating starch until it is anhydrous (<1% moisture) and treating it to a temperature of
Table 2 Recent methods of physical modification of starches. Physical modification
References
Osmotic-pressure treatment Deep freezing Multiple deep freezing and thawing Instantaneous controlled pressure drop (DIC) process Mechanical activation-with stirring ball mill Micronization in vacuum ball mill Pulsed electric fields treatment Corona electrical discharges Thermally inhibited treatment (dry heating) Iterated syneresis Superheated starch
Pukkahuta et al. (2007) ska et al. (2000) Szymon ska et al. (2003) Szymon Zarguili et al. (2006); Maache-Rezzoug et al. (2009) Huang et al. (2007) Che et al. (2007) Han et al. (2009) Nemtanu and Minea (2006) Chiu et al. (1998); Lim et al. (2002) Lewandowicz and Soral-Smietana (2004) Steeneken and Woortman (2009)
100 C or greater for a period of time enough to inhibit starch. An alkaline condition enhanced the effect of heating. Pastes formed from theses starches had increased resistance to viscosity breakdown and a non-cohesive texture (Chiu, Schiermeyer, Thomas, & Shah, 1998). Thermal inhibition with ionic gums had sodium alginate, CMC and xanthan behaving as crosslinking agents and were able to form graft copolymers through ester formation (Lim, Han, Lim, & BeMiller, 2002). Superheated starches were prepared by heating a starch solution to a temperature between 180 and 220 C to produce spreadable particle gels with spherulite morphology and creamlike texture upon cooling. Dry superheated starches mixed with cold water are able to give immediate gel-like texture (Steeneken & Woortman, 2009). Extrusion heating (EH) and fluidized bed heating (FBH) was used on amaranth starch-rich fraction. EH caused a high degree of granule disruption and almost complete loss of crystallinity whereas FBH saw some loss of crystallinity but granule integrity was preserved (González, Carrara, Tosi, Añón, & Pilosof, 2007). 4. Enzymatic modification Enzymatic modification has mainly used hydrolyzing enzymes in its modification and one of its products is syrup be it glucose syrup or high fructose corn syrup. With research, there are more enzymes being identified for use in modification of starch. The use of amylomaltases (EC 2.4.1.25) to modify starches is expected to find applications in the food industry as a plant and chemical free alternative to gelatine (Euverink & Binnema, 1998). Starch treated with a-1,4ea-1,4 glucosyl transferases also known as amylomaltases is used in forming a thermoreversible gel. This is done by breaking an a-1,4 bond between two glucose units to subsequently make a novel a-1,4 bond. These enzymes are found in the Eukarya, bacteria and archaea representatives. The enzyme used has to be free of enzymatic components that can cause undesirable damage to the starch molecule. The starches that can be used for modification should contain amylose such as potato, maize, wheat, rice and tapioca starch. The average molecular weight, reducing power and branching percentage remain unchanged from the starting material. It is believed a mutual rearrangement between the starch molecules has occurred without an increase in oxidation-sensitive places or parts having reducing activity. Little or no retrogradation occurs. This modified starch can be used in foodstuffs, cosmetics, pharmaceutics, detergents, adhesives and drilling fluids. It is also a good source of plant-derived substitute for gelatine except that it forms a turbid gel whereas gelatine gels are transparent (Euverink & Binnema, 1998; Kaper, van der Maarel, Euverink, & Dijkhuizen, 2003; van der Maarel et al., 2005). Similar work was also done by Oh, Choi, Lee, Kim, and Moon (2008) on granular corn starch. The thermodynamics of this gelatine-like starch-based system was studied by Hansen, Blennow, Pedersen, and Engelsen (2009). An amylomaltase-modified potato starch has been used as a fat replacer and enhancer of creaminess in yoghurt (Alting et al., 2009). In the study by Hansen, Blennow, Pedersen, Nørgaard, and Engelsen (2008) on gel texture formed in the modification of potato, high-amylose potato, maize and pea starch with amylomaltase (AM) isolated from the hyperthermophilic bacterium Thermus thermophilus, there was an improvement in gel texture compared to the parent starch. All the modified starches showed broadened amylopectin chain length profiles. Fig. 1 shows a schematic representation of the reaction taking place. A putative glycogen branching enzyme (GBE) was cloned and expressed from Streptococcus mutans, thereafter known as SmGBE. This enzyme differs from the first bacterial GBE group in that it is
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Fig. 1. Schematic representation of the enzymatic conversion of potato-starch-derived amylose and amylopectin into ATS by amylomaltase. Reprinted from Alting et al. (2009), Copyright (2009) with permission from Elsevier.
encoded with four highly conserved regions of the a-1,4-GBE family and does not have the extra N-terminal stretch. SmGBE is able to modify starches and produce shorter branches with more branched structure compared to native starch. Starch retrogradation is also retarded with enzyme reaction due to low temperature storage (Kim, Ryu, Bae, Huong, & Lee, 2008). Cyclomaltodextrinase (CDase; EC 3.2.1.54), isolated from alkalophilic Bacillus sp. I-5 (CDase I-5) was used to modify rice starch to produce low-amylose starch products. The amylose content was found to have decreased significantly from 28.5 to 9% while there was no significant change in the side chain length distribution of the amylopectin. Storage of the modified rice starch at 4 C for 7 days, showed that the retrogradation rate had significantly retarded compared to the control sample (Auh et al., 2006). As GI (glycemic index) in foods is related to diabetes, prediabetes, cardiovascular disease and obesity (Ludwig, 2002) it is becoming important to have more low GI foods to control these diseases. One of the methods is to produce foods containing starch that is digested slowly. There was a significant reduction of rapidly digested starch by 14.5%, 29.0%, 19.8%, and 31.0% for maize starch modified with b-amylase, b-amylase and transglucosidase, maltogenic a-amylase, and maltogenic a-amylase and transglucosidase, respectively. An increase in the starch branch density and crystalline structure in the modified starches was thought to contribute to the slow digestion (Ao et al., 2007). In the reaction of glucoamylase (1,4-a-D-glucan glucohydrolase, EC 3.2.1.3) with starch, 8e32% of the D-glucose remains inside the granule during the early stages of the reaction, but over 80% of the D-glucose is found in the reaction supernatant outside the granule during the later stages of the reaction. Kim and Robyt (1999) reacted glucoamylase with waxy maize, maize and amylomaize-7 starches to retain 100% of the D-glucose produced inside the granule by controlling the length of time of the reaction and the type of starch. The amount of water used in the reaction was also decreased to an amount equal to the weight of starch which gave a solid-granule reaction system. The amount of water used was enough for hydrolysis to take place, but the solid granules did not allow diffusion of the D-glucose. The starch granules containing D-glucose, rapidly diffuse out the D-glucose when suspended in water. Besides this the same authors (Kim & Robyt, 2000) worked with cyclomaltodextrin glucanosyltransferase (CGTase, EC 2.4.1.19) in the presence of isoamylase to produce cyclodextrins (CDs) with
a maximum yield of 3.4 and 100% retention inside waxy maize starch granules. Cyclomaltodextrins are also formed in situ, with the retention of CDs in the granule and this leads to the production of a new material that has properties of starch granules and cyclomaltodextrins. Formation of complexes of organic molecules with cyclomaltodextrins provides stabilisation of light, heat and oxygen-sensitive materials in the starch granules and also a mechanism for their slow release besides providing special tastes, odors and flavours to the starch granules. 5. Genetic/biotechnology modification The advancement of genetic engineering technologies has made the genetic modification of starch in planta possible by targeting the enzymes of the starch biosynthetic pathway. This transgene technology has a potential to produce novel starches which can reduce or eliminate the use of environmentally hazardous post-harvest chemical and enzymatic modification (Davis, Supatcharee, Khandelwal, & Chibbar, 2003). The activity of these enzymes affects the reactivity, functionality, applicability in food processing and food applications of these modified starches therein enabling a market for “niche” products. Genetic modification can be carried out by the traditional plant-breeding techniques or through biotechnology (Johnson, Baumel, Hardy, & White, 1999). The genetic modification that is carried out uses the methods as shown in Fig. 2.Some of the modification of starches that has been done genetically are shown in Table 3. The data in the table has been adapted from Jobling (2004). Repression of GWD (starch phosphorylating enzyme R1) was used in the alteration of specific structural motifs of potato starch (Viksø-Nielsen, Blennow, Jørgensen, Jensen, & Møller, 2001). An Escherichia coli glg B encoding a glycogen branching enzyme from a patatin promoter onto potato lines was done by Wischmann et al. (2005). Starch containing amylopectin molecules with a relatively higher number of amylopectin branches and higher amount of short amylopectin chains with lower content of phosphate was obtained. This starch also gave rise to hard and adhesive gels. AGPase (ADP-glucose pyrophosphorylase) was used as a catalyst to increase the total cassava root biomass by 2.6 fold (Ihemere, AriasGarzon, Lawrence, & Sayre, 2006). When a full length cDNAs encoding a second starch branching enzyme (SBE A) isoform was isolated and an antisense SBE A RNA was generated on transgenic
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Fig. 2. Modification of starch and their end-uses. The makeup, modification and levels of starch can be manipulated via genetic and biochemical means. The resulting changes can alter the properties and applications of starch. Note: the text shades used in the modification portion correspond to those found under end-uses. An arrow pointing upwards indicates an increase in the level of an enzyme; an arrow pointing downwards indicates a decrease in the level of an enzyme; a plus symbol indicates the addition of reactive groups. Abbreviations: DBE, debranching enzyme; GBSSI, granular-bound starch synthase I; SBE, starch branching enzyme; SBE A, class A SBE; SS, starch synthase. Reprinted from Slattery, Kavakli, and Okita (2000), Copyright (2000) with permission from Elsevier.
potato plants, a complete reduction in SBE A was observed. The composition and structure of the potato starch was completely altered in that the average chain length of amylopectin was greater. This caused an increase in the apparent amylose content and higher
levels of phosphorous was observed too (Jobling et al., 1999). Similar observation had been detected by Safford et al. (1998). Potato starches of low SBE values showed an increase of up to 5 C in DSC peak temperature and viscosity onset temperature. This was
Table 3 Genetic modification of starch. Modified
Starch
Enzyme
Properties
Reference
Amylose-free waxy
Maize-commercial, barley, sorghum, amaranth, wheat, sweet potato, potato
Crossing partial waxy mutants, Inhibition of GBSS
-
Gelatinises easily, Clear paste, Stabiliser, thickener, Emulsifier, Improved freeze-thaw stability
Potato
Inhibition of GBSS, SS II, SS III
Sharma, Sissons, Rathjen, and Jenner (2002); Ishada, Miura, Noda, and Yamauchi (2003); Kimura et al. (2001); Noda et al. (2002); Zheng and Sosulski (1998); Jobling, Westcott, Tayal, Jeffcoat, and Schwall (2002); Fulton et al. (2002); Jobling (2004)
Maize-commercial (50, 70, 90% amylose), cereals, potato,
Mutation of SBE IIb, Inhibition of SBE I & SBE II for amylose 60% and greater, Inhibition of SBE II for still higher amylose content, SS IIa is missing
-
High gelling strength Film forming ability Resistant starch Adhesive
Bird, Brown, and Topping (2000); Jobling et al. (1999, 2003); Schwall et al. (2000); Morell et al. (2003)
High-amylose starch
Barley sex6 mutant
- Starch does not swell when heated to 100 C - Increased short chains in amylopectin - Lower gelatinization temperature
Altered amylopectin structure
Potato Rice
SS II and SS III isoforms inhibited
- Low gelatinization temperatures (<50 C)
Edward et al. (1999); Umemoto, Yano, Satoh, Shomura, and Nakamura (2002)
Phosphate content
Potato
Inhibition of GWD
- Performance of potato starch does not correlate directly with phosphate level
Lorbeth, Ritte, Willmitzer, and Kossmann (1998); Ritte et al. (2002); Blennow, Hansen, et al. (2003); Blennow, Bay-Smidt, Leonhardt, Bandsholm, and Madsen (2003)
Granule size and number
Cereal
Isoamylase
- Effects granule number and form
Burton et al. (2002); Dinges, Colleoni, James, and Myers (2003)
Abbreviations: GBSS-granular-bound starch synthase; SS-starch synthase; SBE-starch branching enzyme; GWD- a-glucan water dikinase.
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speculated to be due to an alteration in amylopectin branch patterns. Three mutagenised grains of the diploid oat, Avena strigosa Schreb, was identified: mutants lam-1, lam-2 and sga-1. lam-1 and lam-2 lacked in GBSS activity and amylose component therefore representing mutations of the waxy type. The nature of mutation in sga-1 is yet to be discovered (Verhoeven, Fahy, Leggett, Moates, & Denyer, 2004). 6. Conclusions and future outlook The challenges involved in starch modification involve modification of starch that is safe to the consumer and kind to the environment. The physical, enzymatic and genetic modification of starch has been most promising with a large number of newer methods in starch modification. Osmotic-pressure treatment, multiple deep freezing and thawing as well as ozone-oxidised starch modification are capable of producing a variety of starches with numerous properties that will be applicable in the food industry. The use of amylomaltases in producing thermoreversible gel is a breakthrough in having an alternative product for gelatine and products using gelatine. However, certain issues need to be considered before amylomaltase-modified starch can find application as a gelatin alternative. As pointed out by Hansen et al. (2008), the textural profile of starch gels was very different from gelatin. The elasticity of gelatin gels was much higher, making them firmer than starch gels. In addition, amylomaltase-modified starches formed opaque gels, while gelatin gels were fully transparent. Therefore, Kaper et al. (2005) suggested that amylomaltasemodified starch should not be regarded as a replacement for gelatin but rather as an extension of the variety of available gelling products with their own specific applications. Products using dual or more modification processes are also being looked at for forming new novel products with conventional and non-conventional properties. Genetic modification has come a long way and now there is a greater understanding of biosynthesis pathway of starch making it easier to be manipulated. Starch modification has come a long way since it was first carried out in the 1800s. As with any modification, the possibilities are numerous with starch modification but there should be an eye on the safety and health measurements taken for consumers and the environment. Acknowledgments Dr. Bhupinder Kaur is the recipient of USM Post-Doctoral Fellowship in Research. References Alting, A. C., van de Velde, F., Kanning, M. W., Burgering, M., Mulleners, L., Sein, A., et al. (2009). Improved creaminess of low-fat yoghurt: the impact of amylomaltase-treated starch domains. Food Hydrocolloids, 23, 980e987. An, H. J., & King, J. M. (2009). Using ozonation and amino acids to change pasting properties of rice starch. Journal of Food Science, 74, 278e283. Ao, Z., Simsek, S., Zhang, G., Venkatachalam, M., Reuhs, B. L., & Hamaker, B. R. (2007). Starch with a slow digestion property produced by altering its chain length, branch density, and crystalline structure. Journal of Agricultural and Food Chemistry, 55, 4540e4547. Auh, J.-H., Chae, H. Y., Kim, Y.-R., Shim, K.-H., Yoo, S.-H., & Park, K.-H. (2006). Modification of rice starch by selective degradation of amylose using alkalophilic Bacillus cyclomaltodextrinase. Journal of Agricultural and Food Chemistry, 54, 2314e2319. BeMiller, J. N. (1997). Starch modification: challenges and prospects. Starch/Stärke, 49, 127e131. Biliaderis, C. G. (1998). Structures and phase transitions of starch polymers. In R. H. Walter (Ed.), Polysaccharide association structures in food (pp. 57e168). New York: Marcel-Dekker, Inc.
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Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd
Progress in starch modification in the last decade Bhupinder Kaur, Fazilah Ariffin, Rajeev Bhat, Alias A. Karim* Food Biopolymer Research Group, Food Technology Division, School of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 3 September 2010 Accepted 17 February 2011
Modification of starch is carried out to enhance the positive attributes and eliminate the shortcomings of the native starches. Modification of starch is an ever evolving industry with numerous possibilities to generate novel starches which includes new functional and value added properties as a result of modification and as demanded by the industry. In this paper, we will highlight the many current methods that have been discovered in starch modification which includes four broad areas that are chemical, physical, enzymatical and genetical modification. Ó 2011 Published by Elsevier Ltd.
Keywords: Modification of starch Chemical Physical Enzymatic Genetic/biotechnology
1. Introduction Starch is made up of two fractions: amylose which is made up of essentially a-(1 / 4) D-glucopyranosyl units and amylopectin which is made up of a large number of short chains linked together at their reducing end side by a a-(1 / 6) linkage (Biliaderis, 1998). Starch affects texture, viscosity, gel formation, adhesion, binding, moisture retention, film formation and product homogeneity. It is used mainly in soups, sauces and gravies, bakery products, dairy confectionery, snacks, batters and coatings and meat products (Davies, 1995). Non-food applications of starch include in the field of pharmaceuticals, textiles, alcohol-based fuels and adhesives. New uses of starch include low-calorie substitutes, biodegradable packaging materials, thin films and thermoplastic materials with improved thermal and mechanical properties (Biliaderis, 1998). Modification of starch was carried out to overcome shortcomings of native starches and increase the usefulness of starch for industrial applications. Native starches when cooked can easily retrograde and there is a gelling tendency of pastes besides easily undergoing syneresis. Therefore starch modification not only decreases retrogradation, gelling tendencies of pastes and gel syneresis but also improves paste clarity and sheen, paste and gel texture, film formation and adhesion (BeMiller, 1997). Modification of starches has brought about an evolution of new processing technologies and market trends. These highly functional derivatives have been tailored to create competitive advantage in a new product, improve product aesthetics, simplify product proclamation, lower recipe/
* Corresponding author. Tel.: þ60 4 653 2221; fax: þ60 4 657 3678. E-mail address: [email protected] (A.A. Karim). 0268-005X/$ e see front matter Ó 2011 Published by Elsevier Ltd. doi:10.1016/j.foodhyd.2011.02.016
production costs, increase product all through, eliminate batch rejects, ensure product consistency and extend shelf-life whilst clearly making starch relevant in all stages of a food product’s lifecycle (Murphy, 2000; Wurzburg, 1986). Modification of starch is an ongoing process as there are numerous possibilities. There is a huge market for the many new functional and added value properties resulting from these modifications. Over the last few decades, starch has been modified by various methods to achieve functionalities suitable for various industrial applications. Basically there are four broad based kinds of modifications; chemical, physical, enzymatical and genetical. A number of review articles (BeMiller, 1997; Jobling, 2004; Tharanathan, 2005) on the subject of starch modification are available. However, within the last decade there has been intense interest among researchers to develop novel methods of starch modification with more emphasis on enzymatic, physical and genetic modifications. Therefore this paper was written to bring forward all the new modifications that have taken place in the last decade. 2. Chemical modification Chemical modification of starch involves the polymer molecules of the starch granule in its native form. Modification is generally achieved through derivatization such as etherification, esterification and crosslinking, oxidation, cationization and grafting of starch. However, there has been dearth of new methods in chemical modifications as this kind of modification gives rise to issues concerning consumers and the environment. There has been a trend to combine different kinds of chemical treatments to create new kinds of modifications. Similarly, chemical methods have been combined
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with physical modifications such as microwave, radiation and extrusion to produce modified starch with specific functional properties. Overall advantages of these modifications were to shorten the time of modification and increase production. Some of the recent chemical modifications that have been studied are summarised in Table 1.
2.1. Starch esters Development of new methods to produce hydrophobic starch has been carried out in the last decade to produce hydrophobic starch as an alternative to the process patented by National Starch and Chemical Corporation. Modification of maize and cassava starch with microwave radiation was used to esterify free fatty acids with lipase as catalyst. The free fatty acids were obtained from recovered coconut oil which was hydrolysed with lipase. A DS (degree of substitution) of 1.1 was obtainable using microwave radiation for esterification with hydrolysed coconut oil and DS 0.33 when palmitic acid was the acyl donor. These modified starches have potential uses in the surface coating materials and biomedical materials applications (Rajan, Prasad, & Abraham, 2006; Rajan, Sudha, & Abraham, 2008). Hydrophobically modified starch was prepared by enzyme-catalyzed reaction of starch and alkenyl ketene dimer (AKD), which is a fatty acid residue. Enzymes used were lipases from Pseudomonas sp. and Pseudomonas fluorescens. This modified starch can be used as an ingredient in applications where high solution viscosity and hydrophobic interactions are required for example as paint thickener, construction material, emulsion stabiliser and emulsifier in cosmetics (Qiao, Gu, & Cheng, 2006). Selective esterification of starch nanoparticles was done using Candida antarctica Lipase B (CAL-B) in its immobilized and free forms as catalyst. Acylation reactions were made accessible for the starch nanoparticles by formation of Aerosol-OT (AOT, bis(2-ethylhexyl) sodium sulfosuccinate) to stabilise the microemulsions. Acylations of 3-caprolactone (CL), vinyl stearate, and maleic anhydride were obtained when AOT-coated dispersions of starch nanoparticles in toluene were exposed to physically immobilized CAL-B (Novozym 435). The modified starch nanoparticles were found to retain their nanodimensions upon the removal of the surfactant when dispersed in DMSO or water (Chakraborty, Sahoo, Teraoka, Miller, & Gross, 2005).
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2.2. Dual modifications Starch modification using a combination of chemical and physical or chemical and enzymatical methods have grown rapidly. A combined method of modification using crosslinking and phosphorylation on rice starch, provided modified rice starch with good freeze-thaw stability (Deetae et al., 2008). Crosslinking of tapioca starch with sodium trimetaphosphate in the presence of osmotic-pressure enhancing salts caused an increase in the peak and final viscosity with a decrease in breakdown. Enhancement of osmotic pressure increases the activity of the crosslinking agent (Varavinit, Paisanjit, Tukomane, & Pukkahuta, 2007). Starch-based hydrogels were prepared by UVinduced polymerization of acryloylated starch with zwitterionic monomer 3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate (DMAPS). A unique salt-tolerant swelling behaviour was observed for this modified starch (Li & Zhang, 2007). Starch modified through esterification with ferulic acid giving rise to starch ferulate showed lower viscosity, higher water holding capacity and much less retrogradation during low temperature storage compared to native starch (Ou, Li, & Yang, 2001). Microwave-assisted esterification to produce starch maleate using the dry method had a reaction efficiency of up to 98% and a reaction time of under 5 min. This is thought to be an efficient method in esterifying starch (Xing, Zhang, Ju, & Yang, 2006). The high efficiency in producing succinylated cassava starch with microwave assistance was also observed by Jyothi, Rajasekharan, Moorthy, and Sreekumar (2005). This is a good method to decrease the use of chemicals to enhance production. Microwave and ultrasound irradiation was used for the esterification of carboxymethyl cold-water-soluble potato starch with octenylsuccinic anhydride. They were positively able to shorten the esterification time from a few hours to a few minutes. The derivatives displayed excellent emulsifying and surfactant performance properties (Cí zová, Sroková, Sasinková, Malovíková, & Ebringerová, 2008). Karim, Sufha, and Zaidul (2008) prepared modified corn and mung bean starch using a dual modification process, whereby the native starch was treated to partial enzymatic hydrolysis using a mixture of fungal a-amylase and glucoamylase followed by hydroxypropylation with propylene oxide. The resultant modified starch proved to have significantly different functional properties compared to hydroxypropyl starch prepared with untreated native starch. 2.3. Other methods
Table 1 Recent chemical modification of starch. Chemical modification
References
Microwave radiation with lipase as catalyst Hydrophobic reaction of starch and alkenyl ketene dimer Esterification of starch nanoparticles with lipase as a catalyst Dual modified crosslink-phosphorylated Crosslinking coupled with osmotic pressure Starch-based hydrogels prepared by UV photopolymerization Starch esterified with ferulic acid Microwave-assisted synthesis of starch maleate and starch succinates Microwave and ultrasound irradiation Hydroxypropylation and enzymatic hydrolysis Ozone-oxidised starch
Rajan et al. (2006, 2008) Qiao et al. (2006) Chakraborty et al. (2005) Deetae et al. (2008) Varavinit et al. (2007) Li and Zhang (2007) Ou et al. (2001) Xing et al. (2006); Jyothi et al. (2005) Cí zová et al. (2008) Karim et al. (2008) Kesselmans and Bleeker (1997); An and King (2009); Chan et al. (2009)
The process of ozonation, oxidises starch and is a powerful oxidant as it has an extra oxygen atom. During the ozonation process the carboxyl and carbonyl contents were found to increase with the time of exposure to ozone. There was a difference in the extent of starch oxidation among starches from different sources (Chan, Bhat, & Karim, 2009). Ozonated starches were found useful as thickening agents whereas those treated in the presence of amino acids were suitable alternatives to highly chemically oxidised starch (An & King, 2009). Ozone is a clean and powerful oxidant and leaves no residues behind unlike hypochlorite oxidation process where large amount of salts are produced (Kesselmans & Bleeker, 1997). 3. Physical modification Physical modification can be safely used as a modification process in food products as it does not involve any chemical presence. There has been a wave of new methods in the physical
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modification of starches. Some of the new physical modifications that have been investigated in the last decade are given in Table 2. “Osmotic-pressure treatment” (OPT) was carried out in the presence of high salt solutions (Pukkahuta, Shobsngob, and Varavinit, 2007). Starch solution was suspended in sodium sulphate to obtain a uniform starch suspension and heat distribution. The potato-starch treated changed from a B to a A type after treatment with the gelatinization temperatures increasing significantly. A uniform heat distribution is provided for using this method as compared to heat-moisture treatment and modified starch is able to be produced in a large scale. Deep freezing and thawing of moistened starch increased the ska, Krok, & Tomasik, 2000) crystallinity of the granules (Szymon ska, Krok, but multiple deep freezing and thawing (Szymon Komorowska-Czepirska, & Re˛ bilas, 2003) caused an irreversible disruption of the crystalline order. Iterated syneresis was similar to multiple deep freezing and thawing. The freezing and thawing was repeated until the moisture content in the solid phase was less than 20%. All modified starches showed a change towards B-type X-ray diffraction pattern indicating a disruption of the crystalline prop erty (Lewandowicz & Soral-Smietana, 2004). Again as there are no chemicals involved then there is no concern for the effect on the environment and safety issues to be addressed. The instantaneous controlled pressure drop, DIC, process involves a short pressurisation obtained as a result of injection of saturated steam at a fixed pressure and predetermined time before it drops towards vacuum (Maache-Rezzoug et al., 2009; Zarguili, Maache-Rezzoug, Loisel, & Doublier, 2006). Gelatinization transition temperatures and enzymatic hydrolysis increased whereas gelatinization enthalpy decreased after treatment. The use of friction, collision, impingement, shear and other mechanical actions to alter the crystalline structures and properties of the starch granule refers to mechanical activation or micronization. This process causes large particles to crush to form smaller particles whereas the tiny particles agglomerate and form large particles. The gelatinization temperature and viscosity is decreased for the treated sample (Che, Li, Wang, Chen, & Mao, 2007; Huang, Lu, Li, & Tong, 2007). A non-thermal food preservation method, pulsed electric field (PEF) technology has been used to study the effect of the treatment on starch. Re-arrangement and destruction of starch molecules were observed as well as a decrease in gelatinization properties, viscosity and crystallinity (Han, Zeng, Zhang, & Yu, 2009). The solubility, gel consistency and clarity of starches decreased with increase of exposure time to corona electrical discharges (Nemtanu & Minea, 2006). Thermal inhibition of starch is done by dehydrating starch until it is anhydrous (<1% moisture) and treating it to a temperature of
Table 2 Recent methods of physical modification of starches. Physical modification
References
Osmotic-pressure treatment Deep freezing Multiple deep freezing and thawing Instantaneous controlled pressure drop (DIC) process Mechanical activation-with stirring ball mill Micronization in vacuum ball mill Pulsed electric fields treatment Corona electrical discharges Thermally inhibited treatment (dry heating) Iterated syneresis Superheated starch
Pukkahuta et al. (2007) ska et al. (2000) Szymon ska et al. (2003) Szymon Zarguili et al. (2006); Maache-Rezzoug et al. (2009) Huang et al. (2007) Che et al. (2007) Han et al. (2009) Nemtanu and Minea (2006) Chiu et al. (1998); Lim et al. (2002) Lewandowicz and Soral-Smietana (2004) Steeneken and Woortman (2009)
100 C or greater for a period of time enough to inhibit starch. An alkaline condition enhanced the effect of heating. Pastes formed from theses starches had increased resistance to viscosity breakdown and a non-cohesive texture (Chiu, Schiermeyer, Thomas, & Shah, 1998). Thermal inhibition with ionic gums had sodium alginate, CMC and xanthan behaving as crosslinking agents and were able to form graft copolymers through ester formation (Lim, Han, Lim, & BeMiller, 2002). Superheated starches were prepared by heating a starch solution to a temperature between 180 and 220 C to produce spreadable particle gels with spherulite morphology and creamlike texture upon cooling. Dry superheated starches mixed with cold water are able to give immediate gel-like texture (Steeneken & Woortman, 2009). Extrusion heating (EH) and fluidized bed heating (FBH) was used on amaranth starch-rich fraction. EH caused a high degree of granule disruption and almost complete loss of crystallinity whereas FBH saw some loss of crystallinity but granule integrity was preserved (González, Carrara, Tosi, Añón, & Pilosof, 2007). 4. Enzymatic modification Enzymatic modification has mainly used hydrolyzing enzymes in its modification and one of its products is syrup be it glucose syrup or high fructose corn syrup. With research, there are more enzymes being identified for use in modification of starch. The use of amylomaltases (EC 2.4.1.25) to modify starches is expected to find applications in the food industry as a plant and chemical free alternative to gelatine (Euverink & Binnema, 1998). Starch treated with a-1,4ea-1,4 glucosyl transferases also known as amylomaltases is used in forming a thermoreversible gel. This is done by breaking an a-1,4 bond between two glucose units to subsequently make a novel a-1,4 bond. These enzymes are found in the Eukarya, bacteria and archaea representatives. The enzyme used has to be free of enzymatic components that can cause undesirable damage to the starch molecule. The starches that can be used for modification should contain amylose such as potato, maize, wheat, rice and tapioca starch. The average molecular weight, reducing power and branching percentage remain unchanged from the starting material. It is believed a mutual rearrangement between the starch molecules has occurred without an increase in oxidation-sensitive places or parts having reducing activity. Little or no retrogradation occurs. This modified starch can be used in foodstuffs, cosmetics, pharmaceutics, detergents, adhesives and drilling fluids. It is also a good source of plant-derived substitute for gelatine except that it forms a turbid gel whereas gelatine gels are transparent (Euverink & Binnema, 1998; Kaper, van der Maarel, Euverink, & Dijkhuizen, 2003; van der Maarel et al., 2005). Similar work was also done by Oh, Choi, Lee, Kim, and Moon (2008) on granular corn starch. The thermodynamics of this gelatine-like starch-based system was studied by Hansen, Blennow, Pedersen, and Engelsen (2009). An amylomaltase-modified potato starch has been used as a fat replacer and enhancer of creaminess in yoghurt (Alting et al., 2009). In the study by Hansen, Blennow, Pedersen, Nørgaard, and Engelsen (2008) on gel texture formed in the modification of potato, high-amylose potato, maize and pea starch with amylomaltase (AM) isolated from the hyperthermophilic bacterium Thermus thermophilus, there was an improvement in gel texture compared to the parent starch. All the modified starches showed broadened amylopectin chain length profiles. Fig. 1 shows a schematic representation of the reaction taking place. A putative glycogen branching enzyme (GBE) was cloned and expressed from Streptococcus mutans, thereafter known as SmGBE. This enzyme differs from the first bacterial GBE group in that it is
B. Kaur et al. / Food Hydrocolloids 26 (2012) 398e404
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Fig. 1. Schematic representation of the enzymatic conversion of potato-starch-derived amylose and amylopectin into ATS by amylomaltase. Reprinted from Alting et al. (2009), Copyright (2009) with permission from Elsevier.
encoded with four highly conserved regions of the a-1,4-GBE family and does not have the extra N-terminal stretch. SmGBE is able to modify starches and produce shorter branches with more branched structure compared to native starch. Starch retrogradation is also retarded with enzyme reaction due to low temperature storage (Kim, Ryu, Bae, Huong, & Lee, 2008). Cyclomaltodextrinase (CDase; EC 3.2.1.54), isolated from alkalophilic Bacillus sp. I-5 (CDase I-5) was used to modify rice starch to produce low-amylose starch products. The amylose content was found to have decreased significantly from 28.5 to 9% while there was no significant change in the side chain length distribution of the amylopectin. Storage of the modified rice starch at 4 C for 7 days, showed that the retrogradation rate had significantly retarded compared to the control sample (Auh et al., 2006). As GI (glycemic index) in foods is related to diabetes, prediabetes, cardiovascular disease and obesity (Ludwig, 2002) it is becoming important to have more low GI foods to control these diseases. One of the methods is to produce foods containing starch that is digested slowly. There was a significant reduction of rapidly digested starch by 14.5%, 29.0%, 19.8%, and 31.0% for maize starch modified with b-amylase, b-amylase and transglucosidase, maltogenic a-amylase, and maltogenic a-amylase and transglucosidase, respectively. An increase in the starch branch density and crystalline structure in the modified starches was thought to contribute to the slow digestion (Ao et al., 2007). In the reaction of glucoamylase (1,4-a-D-glucan glucohydrolase, EC 3.2.1.3) with starch, 8e32% of the D-glucose remains inside the granule during the early stages of the reaction, but over 80% of the D-glucose is found in the reaction supernatant outside the granule during the later stages of the reaction. Kim and Robyt (1999) reacted glucoamylase with waxy maize, maize and amylomaize-7 starches to retain 100% of the D-glucose produced inside the granule by controlling the length of time of the reaction and the type of starch. The amount of water used in the reaction was also decreased to an amount equal to the weight of starch which gave a solid-granule reaction system. The amount of water used was enough for hydrolysis to take place, but the solid granules did not allow diffusion of the D-glucose. The starch granules containing D-glucose, rapidly diffuse out the D-glucose when suspended in water. Besides this the same authors (Kim & Robyt, 2000) worked with cyclomaltodextrin glucanosyltransferase (CGTase, EC 2.4.1.19) in the presence of isoamylase to produce cyclodextrins (CDs) with
a maximum yield of 3.4 and 100% retention inside waxy maize starch granules. Cyclomaltodextrins are also formed in situ, with the retention of CDs in the granule and this leads to the production of a new material that has properties of starch granules and cyclomaltodextrins. Formation of complexes of organic molecules with cyclomaltodextrins provides stabilisation of light, heat and oxygen-sensitive materials in the starch granules and also a mechanism for their slow release besides providing special tastes, odors and flavours to the starch granules. 5. Genetic/biotechnology modification The advancement of genetic engineering technologies has made the genetic modification of starch in planta possible by targeting the enzymes of the starch biosynthetic pathway. This transgene technology has a potential to produce novel starches which can reduce or eliminate the use of environmentally hazardous post-harvest chemical and enzymatic modification (Davis, Supatcharee, Khandelwal, & Chibbar, 2003). The activity of these enzymes affects the reactivity, functionality, applicability in food processing and food applications of these modified starches therein enabling a market for “niche” products. Genetic modification can be carried out by the traditional plant-breeding techniques or through biotechnology (Johnson, Baumel, Hardy, & White, 1999). The genetic modification that is carried out uses the methods as shown in Fig. 2.Some of the modification of starches that has been done genetically are shown in Table 3. The data in the table has been adapted from Jobling (2004). Repression of GWD (starch phosphorylating enzyme R1) was used in the alteration of specific structural motifs of potato starch (Viksø-Nielsen, Blennow, Jørgensen, Jensen, & Møller, 2001). An Escherichia coli glg B encoding a glycogen branching enzyme from a patatin promoter onto potato lines was done by Wischmann et al. (2005). Starch containing amylopectin molecules with a relatively higher number of amylopectin branches and higher amount of short amylopectin chains with lower content of phosphate was obtained. This starch also gave rise to hard and adhesive gels. AGPase (ADP-glucose pyrophosphorylase) was used as a catalyst to increase the total cassava root biomass by 2.6 fold (Ihemere, AriasGarzon, Lawrence, & Sayre, 2006). When a full length cDNAs encoding a second starch branching enzyme (SBE A) isoform was isolated and an antisense SBE A RNA was generated on transgenic
402
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Fig. 2. Modification of starch and their end-uses. The makeup, modification and levels of starch can be manipulated via genetic and biochemical means. The resulting changes can alter the properties and applications of starch. Note: the text shades used in the modification portion correspond to those found under end-uses. An arrow pointing upwards indicates an increase in the level of an enzyme; an arrow pointing downwards indicates a decrease in the level of an enzyme; a plus symbol indicates the addition of reactive groups. Abbreviations: DBE, debranching enzyme; GBSSI, granular-bound starch synthase I; SBE, starch branching enzyme; SBE A, class A SBE; SS, starch synthase. Reprinted from Slattery, Kavakli, and Okita (2000), Copyright (2000) with permission from Elsevier.
potato plants, a complete reduction in SBE A was observed. The composition and structure of the potato starch was completely altered in that the average chain length of amylopectin was greater. This caused an increase in the apparent amylose content and higher
levels of phosphorous was observed too (Jobling et al., 1999). Similar observation had been detected by Safford et al. (1998). Potato starches of low SBE values showed an increase of up to 5 C in DSC peak temperature and viscosity onset temperature. This was
Table 3 Genetic modification of starch. Modified
Starch
Enzyme
Properties
Reference
Amylose-free waxy
Maize-commercial, barley, sorghum, amaranth, wheat, sweet potato, potato
Crossing partial waxy mutants, Inhibition of GBSS
-
Gelatinises easily, Clear paste, Stabiliser, thickener, Emulsifier, Improved freeze-thaw stability
Potato
Inhibition of GBSS, SS II, SS III
Sharma, Sissons, Rathjen, and Jenner (2002); Ishada, Miura, Noda, and Yamauchi (2003); Kimura et al. (2001); Noda et al. (2002); Zheng and Sosulski (1998); Jobling, Westcott, Tayal, Jeffcoat, and Schwall (2002); Fulton et al. (2002); Jobling (2004)
Maize-commercial (50, 70, 90% amylose), cereals, potato,
Mutation of SBE IIb, Inhibition of SBE I & SBE II for amylose 60% and greater, Inhibition of SBE II for still higher amylose content, SS IIa is missing
-
High gelling strength Film forming ability Resistant starch Adhesive
Bird, Brown, and Topping (2000); Jobling et al. (1999, 2003); Schwall et al. (2000); Morell et al. (2003)
High-amylose starch
Barley sex6 mutant
- Starch does not swell when heated to 100 C - Increased short chains in amylopectin - Lower gelatinization temperature
Altered amylopectin structure
Potato Rice
SS II and SS III isoforms inhibited
- Low gelatinization temperatures (<50 C)
Edward et al. (1999); Umemoto, Yano, Satoh, Shomura, and Nakamura (2002)
Phosphate content
Potato
Inhibition of GWD
- Performance of potato starch does not correlate directly with phosphate level
Lorbeth, Ritte, Willmitzer, and Kossmann (1998); Ritte et al. (2002); Blennow, Hansen, et al. (2003); Blennow, Bay-Smidt, Leonhardt, Bandsholm, and Madsen (2003)
Granule size and number
Cereal
Isoamylase
- Effects granule number and form
Burton et al. (2002); Dinges, Colleoni, James, and Myers (2003)
Abbreviations: GBSS-granular-bound starch synthase; SS-starch synthase; SBE-starch branching enzyme; GWD- a-glucan water dikinase.
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speculated to be due to an alteration in amylopectin branch patterns. Three mutagenised grains of the diploid oat, Avena strigosa Schreb, was identified: mutants lam-1, lam-2 and sga-1. lam-1 and lam-2 lacked in GBSS activity and amylose component therefore representing mutations of the waxy type. The nature of mutation in sga-1 is yet to be discovered (Verhoeven, Fahy, Leggett, Moates, & Denyer, 2004). 6. Conclusions and future outlook The challenges involved in starch modification involve modification of starch that is safe to the consumer and kind to the environment. The physical, enzymatic and genetic modification of starch has been most promising with a large number of newer methods in starch modification. Osmotic-pressure treatment, multiple deep freezing and thawing as well as ozone-oxidised starch modification are capable of producing a variety of starches with numerous properties that will be applicable in the food industry. The use of amylomaltases in producing thermoreversible gel is a breakthrough in having an alternative product for gelatine and products using gelatine. However, certain issues need to be considered before amylomaltase-modified starch can find application as a gelatin alternative. As pointed out by Hansen et al. (2008), the textural profile of starch gels was very different from gelatin. The elasticity of gelatin gels was much higher, making them firmer than starch gels. In addition, amylomaltase-modified starches formed opaque gels, while gelatin gels were fully transparent. Therefore, Kaper et al. (2005) suggested that amylomaltasemodified starch should not be regarded as a replacement for gelatin but rather as an extension of the variety of available gelling products with their own specific applications. Products using dual or more modification processes are also being looked at for forming new novel products with conventional and non-conventional properties. Genetic modification has come a long way and now there is a greater understanding of biosynthesis pathway of starch making it easier to be manipulated. Starch modification has come a long way since it was first carried out in the 1800s. As with any modification, the possibilities are numerous with starch modification but there should be an eye on the safety and health measurements taken for consumers and the environment. Acknowledgments Dr. Bhupinder Kaur is the recipient of USM Post-Doctoral Fellowship in Research. References Alting, A. C., van de Velde, F., Kanning, M. W., Burgering, M., Mulleners, L., Sein, A., et al. (2009). Improved creaminess of low-fat yoghurt: the impact of amylomaltase-treated starch domains. Food Hydrocolloids, 23, 980e987. An, H. J., & King, J. M. (2009). Using ozonation and amino acids to change pasting properties of rice starch. Journal of Food Science, 74, 278e283. Ao, Z., Simsek, S., Zhang, G., Venkatachalam, M., Reuhs, B. L., & Hamaker, B. R. (2007). Starch with a slow digestion property produced by altering its chain length, branch density, and crystalline structure. Journal of Agricultural and Food Chemistry, 55, 4540e4547. Auh, J.-H., Chae, H. Y., Kim, Y.-R., Shim, K.-H., Yoo, S.-H., & Park, K.-H. (2006). Modification of rice starch by selective degradation of amylose using alkalophilic Bacillus cyclomaltodextrinase. Journal of Agricultural and Food Chemistry, 54, 2314e2319. BeMiller, J. N. (1997). Starch modification: challenges and prospects. Starch/Stärke, 49, 127e131. Biliaderis, C. G. (1998). Structures and phase transitions of starch polymers. In R. H. Walter (Ed.), Polysaccharide association structures in food (pp. 57e168). New York: Marcel-Dekker, Inc.
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