Notes on Starch
by Eben van Tonder
1 August 2020
I group information I am using and would like to use on starch in this section. It particularly relates to its use in cooked sausage production.
In reality, starches are nothing more than chains of sugar molecules strung together. This is a simple and well designed system for the plant to store energy. The main places where we find starch in plants are in the seeds and roots and this makes sense because it is exactly here where the most energy are required.The seeds need the energy fro starch for germination. The starch continue to be the source of energy till the leaves appear and it can generate its energy through photosynthesis. In the same way, the roots needs to continue to grow and and transport fluids and nutrients which is the role of the energy stored in starch in the plant roots. Starch are made up from basically two molecules, namely amylose which is straight chain sugar molecules and amylopectin which is branched-chain sugar molecules. Starch is then basically these two molecules packed into discrete granules. The starch in each plant differs in its percentage composition of amylose and amylopectin which is what gives the different starches different functional characteristics, in the first place for the plant, but then also for us as food scientists. (education.com)
There is more to starch than just this, but no less and as far as its functional characteristics are concerned which we are interested in, these are the main compositional qualities which we must remember.
It is useful to know a bit more about the composition of starch before we look at functionality and interaction with other constituents in a complex system like a sausage batter, lets look more closely at its structure.
When we said that starch is chains of simple sugars, this should tell us that we are dealing with monosaccharides and we know that many monosaccharides which form a large molecule is called a polysaccharide. The simple sugars are sugars like glucose. The polysaccharide that is mainly responsible for structure is cellulose. For the storage and regulation of energy, the plant uses similar polysaccharides that in combination are referred to as starch. Amylopectin is the the major constituent in most starches while amylose is the minor constituent. We said that starches are present as granules which can be described as intramolecularly hydrogen-bonded polymer aggregates. By weight, starch is the second most abundant polysaccaride in a plant. (Carraher, 2003) The most abundant polysaccharide is cellulose. The latest literature define starch as “2 polymers of D-glucose: the lightly branched amylose with a small number of long glucan chains, and the highly branched amylopectin, which contains many clusters of short chains.” (Wang, 2015)
The majority starched produced for commercial purposes are made from corn, white potatoes, wheat, rice, barely, millet, cassava, tapioca, arrowroot, and sorghum. Amylopectin, which is sometimes called the B fraction, is usually the major type of starch present in grains. However, amylose, which is sometimes called the A fraction, is present exclusively in a recessive strain of wrinkled pea. The percentage of composition of amylopectin and amylose differ for every plant and is also dependent on the usual weather, age, and soil conditions. Carraher (2003) notes that “amylose serves as a protective colloid.” As a result, an amylose/ amylopectin mix as its found in native starch, it forms a suspension in cold water. When poured into hot water, the suspension produces a paste (Carraher, 2003)
Lets look deeper into our simplified definition at the start of that amylose is straight chain sugar molecules and amylopectin is branched-chain sugar molecules. We drill down into this a bit with the help of Carraher (2003). “While cellulose can be considered a highly regular polymer of D-glucose with the units linked through a β-1,4 linkage, amylose is a linear polysaccharide with glucose units linked in an α-1,4 fashion while amylopectin contains glucose units with chains of α-1,4 glucopyranosyl units but with branching occurring on every 25–30 units, with the chainbranch occurring from the 6 position. While this difference in orientation in how the glucose units are connected appears small, it causes great differences in the physical and biological properties of cellulose and starch. For instance, humans contain enzymes that degrade the α-glucose units of starch allowing it to be metabolized as a major food source but we are not able to convert the β unit, found in cellulose, into glucose so that wood and other cellulose-intensive materials are not food sources for us. Also, the individual units of cellulose can exist in the chair conformation with all of the substituents equatorial, yet amylose must either have the glucosyl substituent at the 1 position in an axial orientation or exist in a nonchair conformation” (Carraher, 2003) In general, native starches contains between 20% and 30% amylose, although most pulse starches have higher amylose content. (Wang, 2015)
“Amylose typically consists of over 1000 D-glucopyranoside units. Amylopectin is a larger molecule containing about 6000 to 1,000,000 hexose rings essentially connected with branching occurring at intervals of 20–30 glucose units. Branches also occur on these branches giving amylopectin a fan or treelike structure similar to that of glycogen. Thus, amylopectin is a highly structurally complex material. Unlike nucleic acids and proteins where specificity and being identical are trademarks, most complex polysaccharides can boast of having the “mold broken” once a particular chain was made so that the chances of finding two exact molecules is very small.” (Carraher, 2003) “An interesting feature of amylose is its ability to form molecular complexes with variety of compounds, such as aliphatic alcohols, lipids, and iodine. This is the result of the ability of the amylose molecule to adopt a single helical conformation, creating an internal helical space where hydrophobic molecules, or hydrophobic side chains of molecules, can be located as ligands.” (Ottenhof, 2004)
The form that we encounter native starch in is mostly in semi-crystalline granules with a complex hierarchical structure. Look at the image below from Wang (2015).
From the image above you can see how starch granules are in general consists of “an amorphous bulk core area surrounded by concentric semi-crystalline growth rings alternating with amorphous growth rings. The amorphous core, as observed by scanning electron microscopy (SEM) and transmission electron microscopy(TEM), is composed mainly of amylose and amylopectin chains disordered at the reducing end (Wang and Copeland 2012). The size of the amorphous core is related to the amylose content of starch; waxy maize starch granules had the smallest core compared.” (Wang, 2015)
“An important characteristic of amylose is its ability to form a blue-coloured solution in the presence of iodine. The formation of this complex has been widely employed for the detection of starch in general and amylose in particular. The iodine atoms are believed to lie along the hollow core of the amylose. While amylopectin also interacts with iodine, it does so much more weakly giving a reddish-purple complex.” (Carraher, 2003)
Functional Properties of Starch
Both the quality and nutritional properties of starch depends on its processing/ cooking and subsequent storage. These impacts on the functional properties of starch and it involves:
- water uptake,
- granule swelling,
- formation of a viscoelastic paste during heating,
- followed by reassociation of dispersed starch chains on cooling, and
- formation of a gel.
The properties above are used to control:
- mouth-feel, and
- shelf-life of the finished products
(The above from Wang, 2015)
The most basic difference between starch granules of different botanical origins are, as we have discussed before, the percentage of amylose and amylopectin which gives rise to different functional properties. These are however not always constant per botanical variant and factors such as weather causes differences in this composition, even among the same botanical variant. Amylose and amylopectin, even from the same botanical variant is also not exactly identical and this may or may not have an impact on the functional characteristics important to us in sausage formulations.
Ottenhof (2004) reports, for example, that the number of chains found per amylose molecule depends on the botanical source, with wheat starch having -2 and potato starch -7 chains on average (Takeda et al., 1984). The degree of polymerization (DP) of amylose will also vary depending on its botanical source, where values of 570 have been reported for wheat amylose, and much larger values of 4920 for potato amylose (Takeda etal., 1984). In work carried out by Roger and Colonna (1996) on corn starch, it was concluded, however, that the presence of the branches in the amylose did not significantly alter the solution behaviour, which was similar to that of linear chains.”
In the case of amylopectin, chain length distribution varies according to the botanical source which again impacts on the starch properties. (Cornejo-Ramírez, et al., 2018)
Gelatinization is the the irreversible loss of the molecular order of starch granules (crystallinity).” It is considered a glass transition from an ordered initial state to a disordered final state, usually resembling a “melting” process, that requires water and heat. In the cooking or baking process, it’s the stage where starch granules swell and absorb water, becoming functional.” (bakerpedia.com)
Carraher (2003) gives us a more detailed description of the subject. “Starch granules are insoluble in cold water.” Remember that they form a suspension which is defined as heterogeneous mixture in which the solute particles do not dissolve, but get suspended throughout the bulk of the solvent, left floating around freely in the medium. When heated in water, starch granules become hydrated, swell, and are transformed into a paste. Upon heating it in water, the structure of the granule start to collapse due to the following events:
- the crystallites melt,
- the double helices unwinds,
- the hydrogen bonds break. (Wang, 2014)
“These changes are collectively referred to as starch gelatinization.” (Wang, 2014) Swelling is “first reversible until gelatinization occurs, at which point the swelling is irreversible. At this point the starch loses its birefringence, the granules burst, and some starch material is leached into solution. As the water temperature continues to increase to near 100 deg C, a starch dispersion is obtained. Oxygen must be avoided during heating or oxidative degradation occurs. Both amylose and amylopectin are then water-soluble at elevated temperatures. Amylose chains tend to assume a helical arrangement giving it a compact structure. Each turn contains six glucose units.” (Carraher, 2003)
A starch basically forms a gel by creating a matrix that slows the movement of water molecules, thus increasing the viscosity. (Allan, 2019) “The amylose and amylopectin fractions start to solubilize at 158°F (70°C) and 194°F (90°C), respectively. These fractions become loose and eventually become more reactive and prone to enzyme attack (especially amylases). The following schematic representation shows how the mode of starch granules swelling and loss of birefringence.” (bakerpedia.com)
We will see later that greater amounts of water will lower the gelation temperature. This is true if we only consider the effect of water. Much of the water in finely comminuted meat pasts are bound. The presence of any dissolved solids and other compounds of low molecular weight including salts, sugars, amino acids and alcohols (e.g. polyols and glycerol) which will lower the amount of free or unbound water will result in higher temperatures for starch gelatinization. Certain formulations, low in water, may therefore never attain complete gelatinization. This leads me to consider the option of creating a separate starch/ water mixture in the same way as we create soy, collagen and fat pasts.
Remember that we can interfere in the gelling action through various means. One is through mechanical action. For thickening to begin, for example in corn starch, it must be cooked to 95 deg C (203 deg F). A gel is formed as a matrix is created that slows the movement of the water molecules and increases the viscosity. In a sauce, it thickens rapidly at this point and will turn from opaque to transparent. Because of the structure of the sauce, if one would continue to stir it, it will thin again as the matrix is disrupted and the setting process is interfered with. (Accidental Scientist)
When you use starch in the creation of a separate get for use as a component in sausage production, prevent gelatinization before mixing is complete. If the network that is created which traps the liquid are broke during chopping if a hot paste has been created the paste will thin.” (The Accidental Scientist)
The following gerenal temperatures apply for gelatinization.
It is important to remember that during gelatinization, the starch absorbs free water. The starch gel coagulates with the protein matrix and increases the viscosity of the batter to form a firm structure, essential for a proper sausage or polony texture. (Bakingpedia)
The flexibility of amylose and its ability to take on different conformations are responsible for the initial rapid recrystallization upon cooling in a process called retrogradation. Retrogradation was discovered in 1852 (Boussingault, 1852). It was discovered very early that the two polysaccharides amylose and amylopectin play different roles in this process.
This initial rapid stage is followed by a slow recrystallization of amylopectin molecules. Retrogradation is an ongoing process. (Wang, 2014) The rate of cooling has a determinant effect of syneresis. “Slow cooling allows the chains to align to take advantage of inter- and intrachain hydrogen bonding, squeezing out the water molecules, leading to precipitation of the starch. This process gives retrograded starch, either in the presence of amylose alone or combined in native starch, which is generally difficult to redisperse. Rapid cooling of starch allows some inter- and intrachain hydrogen bonding, but also allows water molecules to be captured within the precipitating starch allowing it to be more easily redispersed.” (Carraher, 2003)
“Most uses of starch make use of the high viscosity of its solutions and its gelling characteristics. Modification of starch through reaction with the hydroxyl groups lowers the gelation tendencies decreasing the tendency for retrogradation.” (Carraher, 2003)
“It will be incorrect to think of retrogradation of simply the reversal of the initial processing. Amylose is without a clearly defined shape or form (amorphous) in native starch but during retrogradation, it crystalizes first. The initial treatment plays a significant role in retrogradation, as is typical in crystallization. The other significant factor is the presence of other polymers.” (Wang, 2014)
Amylose retrogradation determines the initial hardness of a starch gel and the stickiness and digestibility of processed foods. The long-term development of gel structure and crystallinity of processed starch, which are
involved in the staling of bread and cakes, are considered to be due to retrogradation of amylopectin (Tran and others 2001; Gray and BeMiller 2003; Fadda and others 2014).
– Which starch forms the strongest gel under retrogradation?
Waxy starch are varieties of commercially available starch composed almost entirely of amylopectin molecules. This gives rise to retrogradation of nonwaxy starch with both amylose and amylopectin or of the newly developed waxy varieties.
The more productive focus of study related to gelation of starches in sausages is possibly not to look at gelatinization, but to retrogradation. Ibanez et al (2007) in investigating the gelatinization and pasting properties of waxy and non‐waxy rice starches notes that “previous studies on the effect of amylose content on gelatinization and pasting properties of starches from different botanical origins have yielded inconsistent results. Potential reasons include variations in the botanical source of the starch, the starch isolation method,
and climate and soil conditions during grain development. Despite huge progress in quantifying the functional characteristics of waxy starch and non-waxy starch, as Ibanez et al develops in their paper in relation to rice, we have seen the futility of developing a theoretical model to predict the behavior of the starch in sausage production as we explained in, Interaction of Starch with Soy and other ingredients in Fine Emulsion Meat Pastes. We are we are dealing with complex and mixed gels.
It may be more productive to focus attention on retrogradation. Wang (2014) explains it as follows. “For nonwaxy starch, retrogradation results in the transformation of a starch paste into a firm gel consisting of a 3-dimensional network. Waxy starch pastes on retrogradation form a soft gel, which contains aggregates but no network (Tang and Copeland 2007).” (Wang, 2014) This makes waxy starched undesirable for frankfurter/ Hungarian/ Russian/ Polony production and starches with high amylose content is preferred since “stronger starch gels are associated with a higher amylose content (Ishiguro and others 2000). . . Amylose-based networks are considered to provide starch gels with elasticity and strength against deformation (Miles and others 1985b; Tang and Copeland 2007), whereas soft gels containing aggregates in the absence of networks display easier penetrability and greater stickiness and adhesiveness. The reduced availability of amylose for intermolecular hydrogen-bonding disrupts long-range interactions within the gel resulting in decreased cohesiveness of the structure.” (Wang, 2014)
Starches and Gelatin: Heating and Re-Heating
The gel melts evenly upon re-heating, unlike starches. The gel of every starch melts differently upon re-heating. The starches cook up, the starch grains break open and the starch leaks into solution. When this cools, it crystallizes into a less soluble form. Re-heating thus results in a solution which is uneven in texture.” (Allan, 2019) This becomes a major factor in a Post Pack Patriation system for treating the sausages before boxing and distribution which is preferred in Africa with its challenges in chilled distribution. “Carrageenans or pectins can be added to overcome this.” (Allan, 2019)
It is a useful analytical tool to take two components or even characteristic variables such as different particle sizes and water content and compare the different functionalities. To evaluate more than two at a time becomes complex. Still, the fact is that we can not consider starch and their gelatinization in isolation from other components in the mix.
“Meat batters are “a complex system which contains many types of proteins, lipids and ingredients (salts, nitrites, sugars, etc.). Finely-comminuted meat products can be classified as multicomponent gels. Tolstoguzov and Braudo (1983) defined three types of multicomponent gels, filled mixed and complex.” (Foegeding, 1988)
“In filled gels (see below, a), one macromolecule is forming the gel matrix while the other molecules are acting as fillers within the interstitial spaces. The filler molecules can affect certain textural properties and/or water binding. A filled gel would form when starch or a non-gelling protein is added to meat batters (Foegeding and Lanier, 1987).” (Foegeding, 1988)
“A complex gel has a matrix produced by interactions among more than one component (see below, b). For example, fibrinogen interacts with myosin during gelation and this would result in a complex gel when blood plasma is added to comminuted meats (Foegeding et al., 1987).” (Foegeding, 1988)
“Mixed gels (see below, C) are those in which the gelling macro-molecules independently form two or more three-dimensional networks without interactions among the polymers. The formation of mixed gels in meat batters would require independent gelation within different fractions of muscle proteins, or addition of a non-meat gelling agent. From the limited data available, it was suggested that mixed and complex gels have the potential to produce textural characteristics which cannot be achieved with either component individually (Tolstoguzov and Braudo, 1983).” (Foegeding, 1988)
Gel Formation in Meat Batter
“Heating meat batters causes structural changes in the muscle proteins which favor intermolecular protein interactions. Protein aggregation progresses to gelation under favorable conditions. The transformation from a raw batter to a gel can be determined by changes in the viscoelastic properties. The shape of the force-deformation curve from small, nondestructive strains can be used to determine the amount of energy lost during deformation (Montejano et al., 1983). In a perfectly elastic system, all the energy of deformation is recovered after the force is removed, 0% energy loss. The energy of deformation in a viscous system would be lost as heat, 100% energy loss. Frankfurters have a major transition in energy loss at 45°C to 55°C (see figure below) that indicates the change from a viscous (raw) batter to a gelled (elastic) cooked product (Saliba et al., 1987). The rigidity (shear modulus) of meat batters starts to increase at 58°C to 60°C and continues to increase from 60°C to 70°C (Fig. 2). The increase in rigidity can be viewed as development of the gel matrix structure. The reason for the time-temperature delay between energy loss and rigidity has not been determined. For example, it is not known if rigidity would incease at 50°C if a meat batter was held isothermally (at a constant temperature).” (Foegeding, 1988)
“The effects of heat can be studied by heating for various time-temperature combinations and evaluating the cooled product. Textural and water-holding properties of meat batters processed under these conditions reflect changes due to heating and cooling. The gelation of meat batters between 40°C and 50°C can be observed by increases in the textural properties of hardness (force at the end of a compression), force to fracture (force required for initial failure) and shear stress at failure (Patana-Anake and Foegeding, 1985; Singh et al, 1985; Foegeding and Ramsey, 1987). In contrast, the water-holding ability does not change between 40°C and 50°C (Patana-Anake and Foegeding, 1985; Whiting, 1984). Between 50°C and 60°C, major changes take place. The textural properties of hardness, force to fracture and shear stress increase while the shear strain at failure (deformability) decreases (Patana-Anake and Foegeding, 1985; Singh et al., 1985; Foegeding and Ramsey, 1987). The water-holding properties also change. Moisture is released during heating (Patana-Anake and Foegeding, 1985; Whiting, 1984) or, in batters which do not have cooking losses, there is a decrease in the ability to hold moisture during centrifugation (Foegeding and Ramsey, 1987). These investigations suggest that textural and water-holding properties develop independently, although not exclusively.” (Foegeding, 1988)
Meat Batters as Filled, Mixed and Complex Gels
“Components other than muscle proteins, such as nonmeat proteins, carbohydrates and lipid, can contribute to the texture and water-holding properties of meat batters. Their functional roles can be described under the definition of filled, mixed and complex gels. In all of the investigations covered in the following discussion, there is a lack of information required to fully classify the type of gel; however, support for certain categories is discussed.” (Foegeding, 1988)
“Lipid can function as a filler or, if protein-lipid interactions affect the gel matrix, the system would be a mixed gel. Increasing the fat content from 10% to 25.5% caused an increase in hardness and shear stress to failure, with no significant change in strain to failure (Foegeding and Ramsey, 1987). Fat was acting as a filler in that system. The filler effect of fat will vary in accordance with the texture of added fat. An increase in fat firmness causes an increase in force to fracture (Lee and Abdollahi, 1981)” (Foegeding, 1988)
“Nonmeat proteins can combine with muscle proteins to form filled, complex or mixed gels. Parks and Carpenter (1987) investigated the effects of substituting meat with nonmeat proteins (nonmeat proteins referring to commercially available powders which also can contain fat, carbohydrate and minerals). The data presented did not allow for determination of gel type; however, it did show that soy flour and autolyzed yeast could decrease texture (rupture force) without a significant decrease in cook yields. Whey protein concentrate was shown to increase hardness without a significant change in cooked yield (Ensor et al., 1987). This once again demonstrates that water holding and texture are regulated by different factors.” (Foegeding, 1988)
“Polysaccharides can be used as functional ingredients in muscle protein gels. Starch and kappa-carrageenan act as fillers, increasing shear stress to failure without changing shear strain at failure (Foegeding and Ramsey. 1987; Wu et al., 1985). The result is quite different with pregelatinized starch. The stress and strain at failure are decreased and the heated mixture is more paste-like than gelled (Wu et al., 1985). Xanthan gum, a non-gelling, viscous polysaccharide, has the same effect as pregelatinized starch (Foegeding and Ramsey, 1987). The data suggest that muscle protein gelation will be disrupted if there is competition for the available
water. When iota-carrageenan is added to meat batters at 1% (w/w/), the water-holding ability, shear stress and shear strain at failure are increased (Foegeding and Ramsey, 1987). This suggests that the gel matrix is altered and a mixed or complex gel is formed.” (Foegeding, 1988)
Starch as a Constituent of the Complex Gel
What follows is a placeholder for my notes that pertain to starch as a constituent of a complex gel. Here I will file such notes that deals with starch in relation to other ingredients customarily found in meat batters.
– Starch and Collagen
Perreira (2011) has shown that collagen fiber additions of between 0.4% and 1.0% were able to minimize the negative effects of higher amounts of Mechanically Debones Poultry Meat, particularly color and cooking loss. One of the constituents currently under investigation, is the use of collagen on a wider scale in cooked sausage production.
“Collagen is the most abundant protein in vertebrates and constitutes about 25% of vertebrate total proteins. To date, some 27 different types of collagen have been identified. Type I collagen occurs widely, primary in connective tissue such as skin, bone and tendons. Type II collagen occurs practically exclusively in cartilage tissue. Type III collagen is strongly dependent on age. For example, very young skin can contain up to 50%, but in the course of time is reduced 5-10%. The other collagen types are present in very low amounts only and are mostly organ-specific. From that different kinds of collagen, type I collagen is the most widely occurring collagen in connective tissue. The collagen molecule is formed by three chains building a triple helix. The triple helical collagen molecule consists of about 1,000 glycine, 360 prolines and 300 hydroxyprolines. Because of its spatial structure and high molecular weights, native collagen naturally insoluble in water. In order to be separated from the other constituents of animal tissues, it is made soluble through an extraction process which includes partial and controlled hydrolysis of the protein chain and then a warm water extraction. This yields hydrolysed collagen.” (Mohammad, 2014) The processes we employ to create Type A gelatin is by acid processing of collagenous raw material and type B is produced by alkaline or lime processing. “Because it is obtained from collagen by a controlled partial hydrolysis and does not exist in nature, gelatin is classified as a derived protein.” (Keenan, 2000) The value in making extensive use of collagen is in the fact that it is characterized by a hydrophilic behaviour due to its hydrophilic groups (carboxyl, amino, hydroxyl, and amide groups)”. (Tzoumani, et al, 2019)
Our sources for collagen are:
– 42.4% from pig skin,
– 29.3% bovine hides,
– 27.6% bones
– 0.7% from other sources (GEA, 2010).
Collagen hydrolysate is a polypeptide composite made by further hydrolysis of denatured collagen (Zhang et al., 2005) or gelatine. “It is also called collagen peptide, hydrolysedgelatine or gelatinehydrolysate. The molecular weights of hydrolysed collagen are within the range of approximately 500-25 000 Da. The hydrolysed collagen will dissolved in cold water and have no bitter taste due to the high glycine content of gelatine. During the manufacturer of hydrolysed collagen, very little bitter peptide is produced compared to the amount formed with other hydrolyzed proteins, so that it is more neutral in taste.” (Mohammad, 2014). For a briefly describe the process design, application and market demand, existing process technology, research and development work and potential future research development for the production of hydrolysed collagen, see Process for Production of Hydrolysed Collagen from Agriculture Resources: Potential for Further Development by Mohammad, et al, 2014.
Part of our work focuses on the conversion of collagen to gelatin during the cooking step of the sausages. It is important to be aware of the characteristics of these gelatins. “While most proteins, when cooked, become more solid (think of the white of an egg or raw chicken flesh), some proteins are soluble under certain conditions. Specifically, the collagen that forms connective tissue in bones, skin, and ligaments—if cooked long and at a simmering temperature—will release gelatin into an aqueous solution. Individual molecules of protein drift as tiny strands throughout the liquid. As water is removed through evaporation, some of the strands connect to one another, forming a three-dimensional network that stabilizes the liquid, preventing it from flowing freely. The liquid becomes more viscous. If the resulting gelatin solution is further reduced (bringing the strands into even closer contact), a gel forms that is solid at room temperature (such as glace de viande, aspic, or Jell-O).” The challenge in using it in sausage production is the fact that such gels melt when reheated. “The increased movement of the liquid’s molecules (that’s all heat is) pushes the strands apart, and the glace melts. Chunks of solidified glace, when added to other liquids, melt, giving them increased viscosity and a rich mouth-feel.” (Allan, 2019)
During the extraction phase of the collagen, a partial hydrolysis takes place and gelatin is produced, whereas a stronger hydrolysis results in low molecular weight peptides called collagen hydrolysates. Uses of gelatin are based on its combination of properties; reversible gel‐to‐sol transition of aqueous solution; viscosity of warm aqueous solutions; ability to act as a protective colloid; water permeability; and insolubility in cold water, but complete solubility in hot water. It is also nutritious.” (Keenan, 2000)
For food or nutritional purpose, collagen is broken down into gelatin which can be broken down further into hydrolysed collagen. Hydrolysed collagen is a polypeptide composite made by further hydrolysis of denatured collagen or gelatin and the molecular weights are within the range approximately 500 to 25000 Da. In hydrolysate, the molecular mass and the size of the molecules have been deliberately decreased by hydrolysis part of peptide bonds of the gelatin molecules. This will make the hydrolysed collagen dissolved in cold water and does not gel anymore but still has surface active properties. The processes involved in processing hydrolysed collagen are demineralization, extraction of collagen to gelatin, enzymatic hydrolysis to obtain hydrolysed collagen, ion exchange, filtration, evaporation, sterilization and finally drying. (Mohammad, 2014)
Acosta (2015) investigated the incorporation of gelatin of bovine origin and lipids to glycerol-plasticized cassava starch films. They noted that in terms of the combination, gelatin incorporation gives rise to harder films with greater resistance to break and extensibility, while the lipids decrease film harness and resistance but enhance the stretchibility. (Acosta, et al, 2015) The application is beyond our scope, but the interaction between starch and gelatin is clear.
– Starch and Soya
See a separate article dedicated to this, Interaction of Starch with Soy and other ingredients in Fine Emulsion Meat Pastes
Properties of Different Starches
Despite the fact that we work with complex gels and that we have seen that retrogradation for our purposes more important is that gelation, it is still important to have a firm handle on the functional qualities of different starches. I will use what follows as a place-holder where I will list the different important characteristics that I come across in my reading schedule.
– Corn Starch/ Maize Starch
For Russian/ Hungarian, polony and lunch loave production, the usefulness of corn starch is that it thickens as it heats but also sets as it cools. Also, as cornstarch becomes clear when thick, while flour remains somewhat opaque.” It makes a statement that is of supreme importance to the food formulation specialist namely that “the colour of fruit sauces is deeper and more appealing when those sauces are thickened with cornstarch.” (The Accidental Scientist)
“Cornstarch also sometimes appears to thin as it stands. This is due to a process called syneresis (commonly referred to as weeping). What you’ll see is a fluid seeping from the gel. This problem is more evident if the gel also contains eggs or has a high sugar concentration.” (The Accidental Scientist)
Some recipes included flour and useful comments are made about it. “Both are cereal starches, but cornstarch is pure starch while flour contains gluten. The gluten reduces the thickening power of flour. One tablespoon of cornstarch thickens one cup (250 mL) of liquid to a medium consistency. It takes two tablespoons of flour— twice as much—to thicken the same amount of liquid.” (The Accidental Scientist)
There are some who reports that cornstarch is not very freeze-thaw stable. Freezing damages the molecules in the starch and when thawed, the liquid will revert to its runny state. A product made with corn starch tends to become spongy if it has been frozen and thawed out. (Allan, 2019)
D F Coral et al (2009) investigated the influence of the moisture and the grain size on the gelatinization temperature (Tp1) of starch from four industrial maize flours as well as an unprocessed maize sample is presented. According to them, “the use of physical modification techniques such as heat-moisture treatment without destroy its granular structure has been widely applied. The mean thermal transition of the starch is gelatinization, it is used to describe the molecular behavior of starch related with heat and moisture content. In this process the starch changes its semi-crystalline phase to an amorphous phase. In excess of water, the hydrogen bridges are broken allowing water be associated with the free hydroxyl groups. This change, in turn, facilitates its molecular mobility in the amorphous regions and allowing the swelling of the grains. The most important parameter in the gelatinization study is the temperature. In the gelatinization process, To is defined as the initial temperature, Tp1 is the begin of gelatinization or crystal melting and Te is the final temperature. The gelatinization temperature range ∆T = Te-To and the energy necessary to complete the process or gelatinization enthalpy ∆Hp are also important. The starch is composed by amylose and amylopectin, both with a semicristaline phase. If there is an excess of water and the temperature increases, crystals of starch are molten cooperatively at Tp1. When the water content is limited, only a few part of crystals are melted by this mechanism, and the rest produce a second transition at high temperature (Tp2) which is in agree with the Flory theory . Results of Differential Scanning Calorimetry (DSC) are presented to determinate gelatinization parameters. The gelatinization process is presented in the DSC as and endothermic peak. The results are used to determinate the width of the endothermic peak (∆T) and the peak high index (PHI), these parameters are used to determinate the homogeneity and uniformity of the starch gelatinization. This study was made using four different maize flours, and one sample of natural maize with the aim of compare the degree of gelatinized starch in relation with the natural product.” (Coral et al, 2009)
“Figure 1 presents a typical DSC thermogram for the sample E, natural milled maize with 75% (w/w) of water and grain size 250µm. The endothermic peak shows the gelatinization transition of the starch. The area between the base line and the thermogram represent the gelatinization enthalpy (∆Hp), and it is related with the amount of starch in amorphous phase. The gelatinization temperature (Tp1) was 70.07◦C and the gelatinization enthalpy was 2.228J/g, the ∆T for this sample was 19.5◦C.” (Coral et al, 2009)
“Figure 2, presents two peaks behavior for the sample B with 60% (w/w) of moisture and grain size 420µm. A second peak is observed at 97,14◦C when the moisture is not enough to complete the transition. All samples were analyzed in the same way, using different moisture content.” (Coral et al, 2009)
“In figure 3 the relation between the moisture content and Tp1, for samples with 250µm is presented. It shows that Tp1 moves to lower temperatures when the moisture content is incremented. This can be explained because the water favors the beginning of the process. Results in figure 3 indicate that the higher moisture contributes to produce starch gelatinization; the gelatinzation values obtained for this samples are in agreed with other studies. Water molecules act as plasticizers agents of polymeric molecules, it means that for the lower values of moisture, the higher values of Tp1 were obtained. It was found that the gelatinization temperature is not an intrinsic property, it depends on the process parameters such as water content and particle size.” (Coral et al, 2009)
They concluded that “the Tp1 was found between 70 to 75◦C for all studied samples. Tp1 decreases for high values of moisture content and it increases when the grain size increases. The second peak (Tp2) is related to the amount of water present in the system and it appears only for samples with lower water content. Industrial samples show lower enthalpy in cooperation with the native sample, which indicates that the industrial process affects the starch molecule causing a pre-gelatinization. The knowledge of the Tp1 and Tp2 lead make a control in the industrial process of flours preparation.” (Coral et al, 2009)
For the Russian/ Hungarian sausage producer, there is a way to reduce the peak temperatures by adding soy. “Peak pasting temperature (95°C) of normal maize starch (8%) and glycinin (8%) mixture was higher than that (93°C) of normal maize starch (8%) and P-conglycinin (S%) mixture and that (90°C) of normal maize starch (8%) and soy protein isolate (8%). The viscosities of the protein samples (8%) were substantially lower than that of normal maize starch (8%, dsb). The viscosity profiles of the mixtures changed with the concentration of soy protein in the mixture. Mixtures of protein (2%) and starch (8%) displayed lower peak viscosities, lower onset and peak pasting temperatures, less shear thinning, and higher final viscosity than normal maize starch alone.” See the complete discussion on this in my notes, “Interaction of Soy and Starch in Fine Emulsion Meat Paste and Formulating the Optimal Blend to be added to Chicken MDM for Russian and Hungarian Production.”
– Wheat Starch (flour)
Its gel is not as strong as corn starch. A lot less transparent. The least expensive form of starch. It is not possible to remove all protein (gluten) from it and is therefore not suited for kosher or gluten-free formulations. (Allan, 2019)
– Potato Starch
In contrast to corn starch, potato starch can be heated to much higher temperatures. Many claims that potato starch thickens better than corn starch. It also remains clear despite long cooking times. It is kosher and gluten-free. (Allan, 2019)
– Tapioca Starch
70 – 85% amylopectin which form a transparent gel, but it does not stand up to intense re-heating. Due to this its not often used in canning, to the same extent as Potato Starch. (Allan, 2019) Tapioca Starch is very bland and clean in flavor and is not masking the flavors used. Tapioca starch has a good mouth feel, and is often used in the food industry for thickening.
Gelatinization temperature: 59 – 65 C. The pH of a slurry in water is neutral.
Starch is one of the most heavily researched food stuffs for both food and industrial application. Inventions and novel adaptations and applications see the light almost on a daily basis. Here I list the opportunities that come across my desk which I want to bookmark for future investigation.
– Effects of Citric Acid on Starch
Erick Olsson (2013) addresses the creation of a water barrier on a water sensitive material, potato starch. He writes about the problem that “sometimes it can be good to listen to the critics and use what they say in order to think around the problem. Why do you only have to use potatoes, can’t you add something which makes the material water insensitive? Cross-linking is a well-known method for reducing the water sensitivity of starch, however most cross-linking agents are toxic (read reactive and/or efficient) and that kind of chemicals are perhaps not a hit for products in direct contact with food. So, how do you find a non-toxic cross-linker that works efficiently? That is hard!” The points of application to us is clear in the fact that he is looking at citric acid as a crosslinking agent. Lets follow a bit of his logic below and get a feel for how and why this can work. I quote a few extracts from his work which is available in the reference section for download.
“He used citric acid was as a cross-linker of the starch “and it was found to reduce the moisture sorption, the molecular movement and swelling at high relative humidity. It was seen that cross-linking and hydrolysis due to the low pH both affected the barrier properties significantly, but in opposing directions. By controlling these two reactions it was seen that this could lead to reduced gas permeability. It was also seen that cross-linking of starch by citric acid occurs at low temperatures, 70 °C at pH as high as 6.5.
The degree of cross-linking is however small and it can be easily broken by subjecting the material to a strong base and performing basic esterhydrolysis.
Cross-linking increases the Tg since it binds different chains together, thus forcing parts of them to be more closely attached (Painter and Coleman, 1997). Cross-links have a particular stiffening effect on the polymer in the rubbery state (Stephens, 1999).
Cross-linking is a subgroup of the substitution reactions whereby the reagent is a poly-functional chemical that contains two or more functional groups able to react with the starch hydroxyl groups. Cross-linking the starch polymers with covalent bonds can take place either within the same polymer chain, intramolecularly
or between different polymer chains, inter-molecularly. Only intermolecular cross-linking reactions increase the average molecular weight of the starch (Rutenberg, Morton W., Solarek Daniel, 1984). Cross-linking reduces swelling in water and at high RH and reduces the solubility of the starch and increases the viscosity of starch pastes (Wurzburg, 1986b). Chemically cross-linked polymers have the disadvantage that they cannot be dissolved, molded or recycled (Stephens, 1999). Chemicals that have been successfully used for cross-linking of starch include epichlorohydrin (Lelievre, 1984), sodium trimetaphosphate, sodium tripolyphosphate (Deetae, et al., 2008), phosporous oxochloride (Wang and Wang, 2000), monochloroacetic
acid, dichloroacetic acid (He, et al., 2007) and glutaraldehyde (Yoon, et al., 2006). Another group of chemicals which can be used for cross-linking of starch are poly-carboxylic acids and these will be described in more detail in later.
The molecular weight of starch can be reduced by exposing starch to a low pH and elevated temperatures. This process is called hydrolysis or acidolysis of starch and is mainly used to lower the paste viscosity of starches.
The reduction in molecular weight is well known to increase the molecular movement in polymeric films which increases the diffusion and permeability. CA can react with starch and cause hydrolysis, thereby reducing the molecular weight. This seems to be the dominant reaction between starch and CA at high
moisture content (Shi, et al., 2007). Hydrolysis of starch with CA have been shown to occur during melt processing (Carvalho, et al., 2005) and during gelatinization (Hirashima, et al., 2004). The onset of acid hydrolysis on starch undergoing gelatinization is not dependent on the type of acid used but is rather an effect of pH (Hirashima, et al., 2005), the lower the pH the more pronounced the chain reduction (Shi, et al., 2007). With the addition of CA to a corn starch paste prior to gelatinization, it was seen that the viscosity increased significantly at low shear rates between pH 3.6 and 5.5. Below pH 3.6 a rapid decrease was observed. This was probably due to hydrolysis as a result of the low pH. At even lower pH, below 2.7 precipitation occurred, probably due to massive breakdown of amylose chains. However, if the acid was added after the gelatinization, no detectable hydrolysis occurred (Hirashima, et al., 2004). In Paper II (Menzel, et al., 2013), it is seen that hydrolysis even occurs in heating of pre-dried films. Paper III (Olsson, et al., 2013b), demonstrates how it is possible to eliminate the occurrence of hydrolysis by pH adjustment.
– Cross-linking with citric acid
Polysaccharides containing hydroxyl groups have the possibility to be crosslinked by poly-functional carboxylic acids. Examples of poly-carboxylic acids that have been used to cross-link polysaccharide materials are 1,2,3,4-butanetetracarboxylic acid (Andrews and Collier, 1992, Blanchard, et al., 1994, Yang, et al., 1996), poly(maleic acid) (Yang, et al., 1996) and CA (Andrews and Collier, 1992, Blanchard, et al., 1994, Ma, et al., 2008, Ma, et al., 2009, Xie and Liu, 2004). Some examples of polysaccharide materials which have been crosslinked with poly-carboxylic acids are starch granules (Ma, et al., 2009, Xie and Liu, 2004), starch nanoparticles (Ma, et al., 2008), starch films (Jiugao, et al., 2005, Reddy and Yang, 2010), starch gels (Seidel, et al., 2001), cotton fibers (Blanchard, et al., 1994), cellulose fibers (Andrews and Collier, 1992), paper (Yang, et al., 1996) and modified cellulose (Coma, et al., 2003). In all these studies, the reaction temperature is high, well above 100 °C and long reaction times (minutes) are used. This is because of the slow reaction kinetics of esterification of poly-carboxylic acids with hydroxyl groups on polymers due to the low amount of poly-carboxylic acid used in these studies compared to that in the papers presented in this thesis.
It has also been seen that in films containing starch, PVOH and glycerol, the CA reacted with all hydroxyl groups present, but less on PVOH than on starch (Shi, et al., 2008). In presence of excess glycerol, the reaction took place solely on glycerol, which was explained by the lower reactivity of the secondary hydroxyl groups present in the starch compared to the primary hydroxyls of glycerol (Holser, 2008). The same phenomenon was seen with addition of poly(ethylene glycol), PEG, to cotton fabric (Andrews and Collier, 1992).
CA has the possibility to react with two or more of the hydroxyl groups present in the starch. One good reason for using citric acid as a cross-linker is due to the fact that the unreacted CA is considered nutritionally harmless and may also act as a plasticizer for starch (Shi, et al., 2008).
Esterification cross-linking reaction between CA and starch can be performed at both acidic and basic conditions. Here only acidic conditions are considered. For acidic conditions, known as Fischer esterification, the esterification reaction is an equilibrium controlled reaction between a carboxylic acid group and a hydroxyl group. The reaction starts with protonation of the carboxylic acid group, which in turn can be attacked by the alcohol group forming an ester. In this reaction, water is produced as a by-product that limits
the equilibrium unless it is evaporated (Ellervik and Sterner, 2004). The reaction can be performed both with and without additional catalysts. Often the catalyst is a strong inorganic acid. The acid used as the catalyst needs to be stronger than the poly-carboxylic acid to be esterified otherwise excessive neutralization of the catalyst will retard the crosslinking reaction. The catalyst should be able to neutralize the carboxylic acid group, but not vice versa (Andrews, 1996). It has been indicated that it is not the addition of catalysts as such, but rather that the pH was the important factor for the esterification reaction to take place (Coma, et al., 2003).
Structural properties of the reaction chemicals affect both the reaction rate as well as the equilibrium. Primary alcohols are more readily esterified than secondary alcohols, which in turn are more easily esterified than tertiary alcohols due to steric reasons. The reaction rate in acidic conditions is proportional to both the reactants and the H+ ion concentration. The equilibrium constant of the esterification reaction is dependent on the temperature and the presence of salts. Usually, in order to achieve completion of the esterification equilibrium reaction either the water or the ester is removed from the reaction mixture. In laboratory scale, sulphuric and hydrochloric acid is often used as the classical catalyst for acid catalyzed esterification reactions. Phosphoric acid also works as catalysts but yield slower reaction kinetics. Another way is by the addition of acid anhydrides which has a higher rate of reaction than carboxylic acids and can be reacted with alcohols with the production of an ester and a carboxylic acid (Aslam, et al., 1996).
CA has two pathways for the esterification of hydroxyl groups, both the Fisher esterification and by an anhydride formation mechanism. When CA is heated, it dehydrates yielding a highly reactive cyclic anhydride which easily reacts with the hydroxyl groups in the starch. This reaction has been shown to start at temperatures around 140-160°C (Noordover, et al., 2007). The reaction kinetics of the esterification of CA by ethanol show that the reaction is much faster with the two first carboxylic acid groups than with the third group, which was demonstrated both with and without added catalyst (Kolah, et al., 2007).
– Citric acid as a dispersant
One of the limiting factors when using small fillers with high specific area is their tendency to form aggregates. One method to minimize this aggregate formation is to add dispersants. CA and salts of CA are well known dispersants and have been successfully used to disperse different inorganic particles such as
calcium phosphate (Leeuwenburgh, et al., 2010) and montmorillonite (Wang, et al., 2009) as well as organic starch nanoparticles (Ma, et al., 2008).
Dispersants can be used for controlling the rheological properties and the dispersion of sols. The dispersants stabilize the particles from aggregation by electrostatic, steric or electrosteric mechanisms. Dispersants are often more effective in dispersing particles whose charge is dependent on pH compared to mere changes in the pH (Vishista and Gnanam, 2004). CA dispersion works by adsorption to positively charged surfaces of negatively charged CA anions. Using the pKa values of CA of 3.14, 4.77 and 6.39 (Stadlober, et al., 2001) with
the method described in (Billo, 2001) it was possible to produce an equilibrium diagram showing CA and its mono, di and trivalent acid salts shown in the figure below.
This figure shows the fraction of CA and its deprotonated forms at different pH values and is important for an understanding the properties of CA at different pH. It shows that the net negative charge on the citric acid molecule increases with increasing pH due to deprotonation of the carboxylic acid groups.” Erick Olsson (2013)
I do not see the need for including soy in sausage formulations, but I recognize the immense value of starch. Especially in conjunction with other functional ingredients of animal origin such as collagen. Much work remains!
Further Reading and Reference Work
Acosta S, Alberto Jiménez, Amparo Chiralt, Chelo González-Martínez, Maite Cháfer. Physical properties and stability of starch-gelatin based films as affected by the addition of esters of fatty acids Food hydrocolloids.. 2015 Jul;49:135-143. DOI: 10.1016/j.foodhyd.2015.03.015.
Allan, G.. 2019. Sauces Reconsidered: Après Escoffier. Rowman and Littlefield.
Boussingault, J. B. (1852). Dela transformationdu pain tendreenpain rassis. Annales Chimie
Physique 36, 490.
Charles E. Carraher, Jr.. 2003. Seymour-Carraher’s Polymer Chemistry. Sixth Edition. Marcel Dekker Inc.
D.F. Coral, D.F., Pineda-Gomez, P., Rosales-Rivera, A. and Rodriguez-Garcia, M.E.. 2009. Determination of the gelatinization temperature of starch presented in maize flours. l 2009 J. Phys.: Conf. Ser. 167 012057
Foegeding, E. A.. 1988. Gelation In Meat Batters. Presented at the 41 st Annual Reciprocal Meat Conference
of the American Meat Science Association in cooperation with the National Live Stock and Meat Board University of Wyoming Laramie, Wyoming. June 12-15, 1988
GEA, 2010. Gelatin Processing Aids. Vol. 2010, GEA Group, Hudson.
Ibanez, A. M., Zhong, F. and Charles F Shoemaker, C.. 2007. Gelatinization and Pasting Properties of Waxy and Non‐waxy Rice Starches. Article in Starch – Starke · August 2007; DOI: 10.1002/star.200600570
Keenan, T. R. Gelatin. First published: 04 December 2000. Wiley Online Library. https://doi.org/10.1002/0471238961.0705120111050514.a01
Ya fei Liu, Kalaya Laohasongkram, Saiwarun Chaiwanichsir. 2016. Effects of heat-moisture treatment on molecular interactions and physicochemical properties of tapioca starch. MOJ Food Processing & Technology. Volume 3 Issue 3 – 2016
Abdul Wahab Mohammad, Norhazwani Mohd. Suhimi, Abdul Ghani Kumar Abdul Aziz and Jamaliah Md. Jahim, 2014. Process for Production of Hydrolysed Collagen from Agriculture Resources: Potential for Further Development. Journal of Applied Sciences, 14: 1319-1323. DOI:10.3923/jas.2014.1319.1323. URL: https://scialert.net/abstract/?doi=jas.2014.1319.1323. Received: April 06, 2013; Accepted: April 08, 2013; Published: April 11, 2014
Marie-Astrid Ottenhof & Imad A. Farhat (2004) Starch Retrogradation, Biotechnology and Genetic Engineering Reviews, 21:1, 215-228, DOI: 10.1080/02648725.2004.10648056
Tzoumani, I., Lainioti, G. Ch., Aletras, A. J., Zainescu, G., Stefan, S., Meghea, A., Kallitsis, J. K.. Modification of Collagen Derivatives with Water-Soluble Polymers for the Development of Cross-Linked Hydrogels for Controlled Release. Received: 24 September 2019; Accepted: 27 November 2019; Published: 6 December 2019. MDPI, Materials 2019, 12, 4067; doi:10.3390/ma12244067. http://www.mdpi.com/journal/materials