Interaction of Starch with Soy and other ingredients in Fine Emulsion Meat Pastes.
Eben van Tonder’s personal notes.
5 December 2020

Introduction

We examine the interaction of soy protein and starch in a fine emulsion meat paste made from Chicken MDM, soy protein and starch. I am interested in the formulation of Russians, Hungarians and Polony (Origins of the South African Sausage, Called a Russian). These are fine emulsion products are all cooked during processing and Hungarians and Russians are normally consumed warm and polony is normally consumed cold.

Following Dr RA LaBudde’s definition, this class of meat products “is viewed as a water-plasticized, filled cell mixed-composite thermosetting plastic bio-polymer.” (LaBudde)

“Technically the uncooked meat mixture is a “paste”, not an “emulsion” or “sol”, since solids content is 40% or more. Upon cooking to a high enough temperature, the “paste” sets to hardened “plastic” material. Cooked sausage products are a mix of water, fat, protein, salts and carbohydrates gelled and set into a solid mass by the application of heat.” (LaBudde)

“The principal functionality in forming the gelled and set mass comes from the long-chain proteins present and to a lesser extent from the long-chain carbohydrates (starches and gums). . . When the meat paste is heated above the set-point temperature, the long-chain molecules, supported in solution or at least hydrated by water, are forced to partially uncoil and form irreversible cross-linkages. The result is a three-dimensional crosslinked matrix which incorporates the water, fats, salts and fillers within its structure. . .The water hydrates the protein molecules and allows mobility for unfolding and crosslinking.” Water in the final mix of products therefore plays an important function, as does salt which, “in the water phase, help ionically stabilize the unfolded protein molecules so that its structure can be more easily exposed.” (LaBudde)

The role of fats in stabalizing hydrophobic protein exposure must not be ignored. “They also serve, with other water-insoluble components, simply to fill space and stiffen the protein matrix formed.” (LaBudde)

“Starches and gums will hydrogen-bond and crosslink similar to proteins, and bind appreciable amounts of water. Generally, the gelling temperature for such compounds is 90 C or higher, which is seldom obtained in meat processing. Non-gelling or insoluble carbohydrates principally act as mild water binders and matrix fillers. The strength of water-binding is moderate and due to capillary action and hydrogen-bonding, as opposed to irreversible crosslinking. The crystalline nature of a cooled starch gel results in a brittle texture which has little strength after fracture.” (LaBudde)

The presence of soy proteins has however been put on the agenda with this statement. “Non-meat proteins which are soy- or milk-based (soy flour, soy protein concentrate, soy protein isolate, whey protein concentrate, whey protein isolate, casein) have gel-points of 90 C or more, and function similar to starches in hydrogen-bonding with water to form weak gels at low temperatures.” (LaBudde) This means that there is a difference in the role of soy protein at lower temperatures from that of meat proteins, for example at 69 or 72 deg C which is the customary cooking temperature of Russians and Hungarians. The question then comes up, why use soy at all, especially in light of the large cost difference in soy isolates and starch.

General Overview of Starches, their modification and Defining Solubility and Swelling

Kaur, et al. (2011) offers a general overview of starches, describes their modification and in the process, offers workable definitions for the concepts of swelling and solubility which we will encounter in the following sections. They state that “starch is the major reserve polysaccharide in plants and is in the form of granules that exist naturally within the plant cells. Starch can be used as thickener, an adhesive, binder, encapsulating agent, film former, gelling agent, water binder, texturizer and fat-sparing agent and with numerous other applications both in the food and non-food areas (Mauro 1996). Starch granules are composed of a mixture of two polymers, an essentially linear polysaccharide called amylose and a highly branched polysaccharide called amylopectin (Bemiller and Whistler 1996). Starch can be modified by acid hydrolysis, oxidation, etherification, esterification and cross-linking. Various methods such as acid, phosphate and H₂O₂ treatments can be employed to modify starch (Akubor 2007). The objective of starch modification is to alter the physico-chemical characteristics of native starch to improve functional characteristics. Modification is important for the continued and increased use of starch to provide thickening, gelling, binding, adhesiveness and film forming characteristics.

“Swelling power indicates the water holding capacity of starch, which has generally been used to demonstrate differences between various types of starches (Crosbie 1991). Swelling volume is the ratio of the sedimented gel to the dry weight of starch. Solubility is the percent amount of starch leached out into the supernatant in the swelling volume determination (Singh et al. 2005). The water-binding capacity in commercial starches is important to the quality and texture of some food products because it stabilize them against effects such as syneresis, which sometimes occurs during retorting of freezing (Baker et al. 1994). Scanning electron microscopy has been used to relate granules morphology to starch genotype (Fannon et al. 1992). Rapid visco-analyser (RVA) has been extensively used for measuring starch paste viscosity. Pasting properties helps in comparison between cooking behaviour of different starches with the aid of RVA thermal viscous graph. The present study was undertaken to investigate the effect of acid modification on physicochemical, morphological and pasting properties of starches extracted from different plant sources.”

Soy Protein and Solubility and Swelling

Since we intend investigating the interaction of heated starch and soy proteins in water, lets look at the behavior of soy on its own in terms of swelling and solubility.

As it approaches 90 deg C, predictably, the solubility increases as swelling decreases. At the tempretaures presented in the graph above, our main interest will not be in its swelling power but in its ability to form cross-linkages and interact with meat proteins and starch to the formation three-dimensional crosslinked matrix which incorporates the water, fats, salts and fillers within its structure.

Interaction between Soy Proteins and Starch

“Protein-polysaccharide interactions have been intensively reviewed by many researchers including Schmitt, Sanchez, Desobry-Banon, & Hardy, 1998; Tolstoguzov, 1997; Dickson & McClements, 1995; Tolstoguzov, 1991. Attraction and repulsion are the two major inter-biopolymer interactions (Tolstoguzov, 1997). Interactions between proteins and polysaccharides could result in co-solubility, incompatibility, or complexing. In mixed solutions, proteins and polysaccharides are in either stable or phase-separated states in single-phase systems and two-phase systems (Tolstoguzov, 1991).” (Song and Jane, 2000)

“Properties of protein and starch complex are significantly different from starch alone. Different proteins (zein, gliadin, glutelin, and glutenin) were used to study the effect of protein on rheological properties of starches with various amylose contents (Chedid & Kokini, 1992; Madeka & Kokini, 1992). Interaction between starch and protein increase viscosity once a threshold temperature is exceeded. The amylose-amylopectin ratio, the type of protein and moisture content affect the level of increase in viscosity.” (Song and Jane, 2000)

My first introduction to the interaction between soy proteins and starch comes from the work of Takahashi et al. (1983) who studied the effect of the addition of isolated soybean protein on gelatinization and retrogradation properties of various starches during heating and storage.

They made the following 4 observations in relation to the enzymic susceptibility, swelling power, solubility and X-ray diffraction.

1. Swelling power and solubility of potato and sago starch decreased remarkably by adding isolated soybean protein.
2. During heat gelatinization of starch, the addition of isolated soybean protein caused a delay of gelatinization of all the starches examined. By the prolonged heating at 92.5°C, the degree of gelatinization reached the same level as the starch paste without isolated soybean protein.
3. During the cold storage of starch paste, the retrogradation of potato starch remarkably was accelerated by the addition of isolated soybean protein. Potato starch retrograded at the highest rate by the existence of isolated soybean protein among the examined starches. The rest of the starches were less affected by the addition of isolated soybean protein.
4. X-ray diffractogram obtained by the cold-stored starch paste with isolated soybean protein showed a much sharper pattern than the normal retrograded starch paste.

It has important considerations for use in the production of Russian and Hungarian sausages in Southern and Central Africa. One would tend to conclude from this data that there seems to be no compelling reason to include soy isolate with potato starch or corn starch due to the negative impact on swelling in potato starch and the increase of solubility on carn starch while swelling in corn starch remains more-or-less unaffected.

Influence of Soy Protein on the Pasting Power of Starch

Let us define a few more terms before proceed.

• Peak viscosity indicates the water-holding capacity of the starch or mixture. It is often correlated with final product quality, and also provides an indication of the viscous load likely to be encountered by a mixing cooker.
• Final viscosity is the most commonly used parameter to define a particular sample’s quality, as it indicates the ability of the material to form a viscous paste or gel after cooking and cooling.
• The re-association between starch molecules during cooling is commonly referred to as the setback. It involves retrogradation, or re-ordering, of the starch molecules, and has been correlated with texture of various products.
• Pasting temperature, which provides an indication of the minimum temperature required to cook a given sample, can have implications for the stability of other components in a formula, and also indicate energy costs.

(Definitions from Rapid Visco Analyser (RVA) by Perten)

Kumar, R., & Khatkar, B. S. (2017) describes the pasting power of starch as follows. “Pasting involves heat mediated granular swelling, the transformation of starch granules in excess water from ordered to disordered state, exudation of the molecular components and eventually the total rapture of the starch granules. During the initial stage of RVA test, the starch granules imbibe water rapidly. However, as the mixture is heated granule begin to swell significantly and the imbibed water aids the melting of the crystalline regions of starch granules which allows for rapid movement of water into and within the granules (Hung and Morita 2005). Starch granules absorb and bind more water while swelling which reduces the available water resulting in physical interactions between them. These interactions referred to as the pasting and results in sudden increase in the viscosity of starch and water mixture.” On the other hand, gel firmness is related to gel strength. The more amylopectin there is in starch, the greater the swelling will be and therefore the starch pasting; the more amylose there is, the greater the gel strength.

Factors affecting gel strength and/ or swelling are:

1. The kind of starch – the amount of amylose or amylopectin will impact on the pasting or strength of the starch;
2. Stirring amount and type – granules can break apart due to stirring;
3. Heating rate – In general, the faster one heats a starch-water dispersion the thicker it will be at the identical endpoint temperature. This one of the reasons why casings break if you do not step the heating/cooking stage of the sausages. It related to both gel strength and gel viscosity.
4. End-point temperature – it is VERY important to know the endpoint temperature of the starch you are adding to the sausage mix. Optimum starch past viscosity and gel strength are reached at the endpoint temperature. After that point, viscosity and strength both decrease because the swollen granule easily fragmented with stirring or actually imploded due to the extensive loss of amylose from the granule.
5. Cooling and Storage Conditions – cooling conditions will impact the strength of the gel. Generally, if cooled too fast, the amylose will not have time to form the vital micelles necessary for the three-dimensional structure. If cooled too slowly, the amylose fractions will have a chance to align too much and become too close together and the liquid portion will not be trapped in the micelles. In both instances, there will be weeping and syneresis.
6. If dry heat is applied, dextrinization occurs. This is the breakdown of starch into dextrin (disaccharides) and can be identified by the non-enzymatic browning.  The heat hydrolyzes the starch polymers and the short chains mean that the granule will not remain intact. When this happens, the starch paste will be runnier with the dextrinization (sugar and acids can also cause dextrinization to take place). This has an important application in various heating systems used in the meat industry. Most smokehouse can be set to “dry heat” which in the case of Russians and Hungarian sausages will be undesirable.

From Bean (1978) and Johnston (1990)

Song and Jane (2000) studied the Effect of Soy Protein on Pasting Properties of Different Starchesas part of work, Characterization of biopolymers: starch and soy protein. They used soy protein isolate and soy protein fractions of P-conglycinin (7s) and glycinin (lis) to study its effects on the pasting properties of normal maize, waxy maize, and potato starches by using a Rapid Visco Analyser. They reported that the “effects on the viscosity profiles varied with starch variety, type of protein, and concentration of protein in the mixture. Pasting temperature decreased when soy protein was added to a normal maize starch dispersion; however, pasting temperatures increased when soy protein was added to a mixture of waxy maize or potato starch. When the protein concentration increased from 2 to 8% in the mixtures of starch and protein, peak viscosity and final viscosity increased. Salt residues in soy protein reduced the viscosity of the mixtures containing potato starch, which was attributed to the suppression of charge interactions. Setback viscosities of the mixtures of soy proteins and starches were increased.” (Song and Jane, 2000)

The Investigations by Song and Jane

“Rheological properties of heated corn starch and soy proteins were investigated by using a rheometer (Chen, Liao, Okichukwu, Damodaran, & Rao, 1996; Liao,Okichukwu, Damodaran, & Rao, 1996). It has been reported that corn starch and B-conglycinin fraction (7s) of soy protein dispersions are classified as weak gels, whereas the viscoelastic behavior of corn starch and glycinin fraction (lis) of soy protein dispersions was as the behaviour of true gels. Soy protein isolate dispersion showed gel-like behavior.” (Song and Jane, 2000)

In the Song and Jan (2000) study, “soy protein isolate and soy protein fractions (B-conglycinin and glycinin) were used to study effects of soy protein on pasting properties of starch. Different types of starches, normal maize, waxy maize, and potato starch, were used to investigate effects of starch structures on the interaction with soy protein.” (Song and Jane, 2000)

The onset of gelatinization is represented by T_o, the temperature at peak by T_p, the temperature at the end of gelatinization, T_c and enthalpy of gelatinization, ΔH_gel. Song and Jane found that the soy protein isolate dispersion (8%) had two thermal transition peaks at 75.9°C and 94.2°C (Table 1). The first peak (75.9°C) was attributed to the denaturation of (3-conglycinin and the second peak was that of glycinin (Hermansson, 1978). (Song and Jane, 2000)

From the table above, the problem with the combined use of starch and soy isolate is immediately clear if there was not an interaction between the two. T_c for potato starch is 71 deg C which is fractionally below T_o for soy isolate.

-> Potato Starch

“The viscosity profile of potato starch was significantly changed when soy proteins were added to the system (Fig. 2). The pasting temperature of the starch and protein mixture was higher than that of potato starch alone, and the peak viscosities of potato starch (8%) and soy protein (2% and 4%) mixtures were substantially lower than that of potato starch (8%) alone. Setback viscosity, which is the retrogradation tendency after gelatinization and cooling, of potato starch and soy proteins increased when protein concentration increased.” (Song and Jane, 2000)

I evaluate the date as follows. PS at 8% yields a maximum viscosity at around 80 deg C after < 5 minutes. PS (8%) + SPI (2%) as well as SP (8%) + SPI( 8%) were both lower than PS alone. The observation that a combination of SPI with PS leads to an increase in the retrogradation tendency after gelatinization and cooling further mitigates against the combination to be used with PS.

“It has been reported that salt has a significant effect on peak viscosity of potato starch. At a low concentration of 0.04%, NaCl significantly reduced the peak viscosity of potato starch but not normal maize and waxy maize starches (Paterson, Mathtashim, Hill, Mitchell, and Blanshard, 1994; Muhrbeck and Eliasson, 1987). Viscosity decreased with the presence of salts in potato dispersion. There was no significant effect of salt on pasting temperatures of starch dispersions. The salt contents of |3-conglycinin, glycinin, and soy isolate were 8.2, 7.1, and 4.2%, respectively. Sodium ions formed cation-ion layer on phosphate derivatives of potato starch and retarded the charge repelling between phosphate groups, which decreased viscosity. Peak viscosity of potato starch varied according to the salt concentration (Fig. 3). In order to study protein effect on pasting profile of potato starch, protein samples were dialyzed to remove salt. After dialysis, the salt content of soy isolate sample reduced to 1.7%. Pasting profiles of mixtures of potato starch with soy protein isolate with and without desalting are shown in Figure 4. Desalted soy protein produced higher peak viscosity and lower peak temperature compared with its counterparts without desalted soy protein isolate samples. The peak viscosities of potato starch mixtures containing desalted protein at 2% and 4% were lower than that of potato starch (8%) alone. This might be attributed to that potato starch contains 16.9% amylose (Jane et al., 1999). Formation of helical complexes between amylose and protein might have retarded the swelling of potato starch in the mixtures and caused the decrease in peak viscosity and the increase in pasting emperature of the mixtures.” (Song and Jane, 2000)

Since salt content is legislated and since it is added to the product before cooking and since there are a number of other benefits to the inclusion of some salt, we will keep salt levels at the maximum allowed inclusion levels under the legislation. Having said that, there is still no obvious benefit for the inclusion of SPI to PS.

-> Maize Starch

We now turn our attention to maize starch. Waxy maize starch contains only the highly branched component amylopectin. Normal maize starch consists of 22.5% amylose.

“Normal maize starch and soy protein mixtures displayed different pasting profiles (Fig. 6A, 6B, and 6C) from the mixtures of soy protein and the other two starches. Onset pasting temperatures of the mixtures of soy protein and normal maize starch were all lower than that of normal maize starch alone. 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. The peak viscosities of the mixtures of protein (2%) and starch (8%) were 111.4, 120.7, and 120.0 RVU for mixtures containing 3-conglycinin, glycinin, and soy isolate, respectively, which were lower than that of normal maize starch alone (8%, 151.3 RVU). No shear thinning was observed for mixtures of normal maize starch (8%) with B-conglycinin and with glycinin (4%). The peak viscosity of normal maize starch (8%) and soy isolate (4%) mixture (279.5 RVU) was higher than that of the mixture with B-conglycinin (165.0 RVU), and with glycinin mixture (204.2 RVU). Viscosities of the mixtures of protein (8%) and normal maize starch (8%) were significantly higher; 650.8 RVU, 485.8 RVU, and 605.5 RVU, for the mixture with B-conglycinin, glycinin, and soy isolate, respectively. Viscosities of starch and 3-conglycinin mixtures were higher than that of starch and glycinin mixture counterpart (Fig. 6A and 6B).” (Song and Jane, 2000)

The results above clearly show normal maize starch at 8% and SPI at 8% to be the optimal inclusion rate for the production of Russians and Hungarians. Even the protein (2%) and starch (8%) ratio are to be preferred over maize starch alone. Even though the peak viscosities, onset and peak pasting temperatures were all lower, it showed less shear thinning, and higher final viscosity than normal maize starch alone.

“The interaction between soya proteins and starch is explained as follows. With the addition of proteins, protein-lipid interaction facilitated starch swelling. As temperature reaches to starch gelatinization temperature, starch crystallites melt, granules swell dramatically, amylose leaches out of granule and viscosity of starch dispersion increases (French, 1984). As temperature reached protein denaturation temperature, protein molecules started unfold and more buried amino acid side chains could interact with water and facilitated protein solubility. The dispersed starch molecules then formed three dimensional network matrix with denatured protein molecules, therefore the peak viscosity and fmal viscosity were significantly increased. It is suggested by results of amino acid composition (Nielsen, 1985) that B-conglycinin has larger proportions of amino acids with polar side chains than glycinin. After gelation, B-conglycinin displayed a lower hydrophobicity and higher solubility than did glycinin (Song and Jane, 1998a, and b). It resulted in a better compatibility between B-conglycinin and normal maize starch than between glycinin and normal maize starch. Therefore, viscosity of the mixture of B-conglycinin and normal maize starch was higher than that of the mixture of glycinin and normal maize starch counterpart (Fig. 6A and 6B).” (Song and Jane, 2000)

Song and Jane summarise their results as follows. “Viscosity profiles of soy protein and starch mixtures differed from that of starch alone. Peak viscosity of mixtures of starch (8%) with soy protein (8%) significantly increased except the mixture of waxy maize starch and glycinin. High swelling temperature of soy protein, especially glycinin, caused the separated viscosity peaks in the pasting profiles of mixtures of waxy maize starch and glycinin, and of mixtures of potato starch and soy protein. Salt residue in soy protein decreased the viscosity of potato starch and soy protein mixtures. Interaction between amylose and soy protein retarded starch granule swelling and caused the decreased peak viscosity at low protein concentration in the mixtures containing normal maize starch or potato starch, and increased the pasting temperature of potato starch and protein mixtures. Protein-lipid interaction could facilitate starch granule swelling. Pasting temperature decreased when soy proteins were present in normal maize starch dispersion. Mixtures of starch and soy protein displayed higher setback viscosity than starch alone. Viscosity of mixtures of starch and soy proteins significantly increased compared with soy protein dispersion alone.”

The study above focused on the relationship between Soy Protein Isolate(see Soy: Its Utilisation and Processing) and starch. We have in mind, not only using the soy protein but the carbohydrate components as well as vitamins components obtained from the rest of the soy plant.

The Role Of Fillers on Gel Strength

Some of the parts of the soy plant we intent including in our soy mix will act as fillers only. I would like to briefly review the work of LaBudde in this regard. We wrote that “since meat’s texture is due to its property of heat-induced long-chain gelling or setting, cooked meat is classifiable as a water-plasticized, filled-cell mixed-composite thermosetting plastic biopolymer. The word “polymer” denotes long-chain macromolecules which are crosslinked, such as proteins or starches. The word “plasticizer” indicates that water is the filling solvent that hydrates the polymer and supports its “plastic” behavior. The word “mixed” denotes possible crosslinking between different polymers, such as different proteins or proteins and cross-linked gums or starches. The “fillers” present in meat products are fat or insolubles: in rubber tires, it is the carbon that makes the rubber black. Fillers normally will “stiffen” a plastic or rubber, making it harder and less stretchable. Sometimes fillers are active (such as the carbon in rubber tires) and actually bind to the setting polymers present. In this case, the filler may increase strength dramatically (ten times or more), and out of proportion to its relative presence on a formula basis.” (LaBudde)

The more water one adds, the softer the bulk texture will be and it will make the polymer matrix more stretchable. Removing water will result in a harder and more “brittle” (i.e., less stretchable) bulk texture. (LaBudde)

Smaller is Better for Gel Strength

In terms of processing, we intend using specialized equipment that has the ability to reduce particle small than can be achieved with any regular emulsifier. Again we look at LaBude’s comments in this regards. Time of chopping or mastication will affect final gel strength, due to the development of active ends of severed protein molecules. In addition chopping reduces fat particle size, breaks the containing fat cell layers, and melts fat droplets allowing surface smearing to take place. (LaBudde)

Fat and the Relation to Gel Strength

Since we plan to retain a significant amount of fat in our final soy, starch mix, we have a look at LaBudde’s comments on the relationship between fat and gel strength.

“Fat generally expands by 10% or more upon melting, and therefore stresses and strains the product before complete setting has taken place. It is essential that the fat droplets be coated with a closed-cell protein structure or embedded in a strainable gel to protect the structure against fracture by fat expansion with concomitant leakage of liquid fat along these fractures to relieve the stress imposed.” (LaBudde)

“Filled composites generally exhibit increased strength in compression and decreased strength in tension. Consequently, it would generally be expected that adding inert or insoluble materials (and displacing moisture) will stiffen the structure to compression and lower the strain needed for failure. However, both stress and strain would be lowered in tension.” (LaBudde)

“As a consequence, adding such fillers not bound to the stronger protein structure would be expected to lower skin strength, where the test condition is perpendicular to the skin, resulting in failure by shear or tension. Such fillers include non-gelling proteins, fats and carbohydrates.” (LaBudde)

Effect of Collagen on Gel Strength

A further feature of our approach is to include additional collagen into the final mix which we intend harvesting through the application of techniques that do not dehydrate the collagen, to be re-hydrated by the processor upon inclusion. “Collagen protein contracts by 10% or more upon reaching its gel-point of 60 C, and therefore has the effect of straining the entire thermoset product.” (LaBudde)

Protein and Lower Level Protein Content and Gel Strength

“The protein content of cooked meat products is usually between 10 and 20% of the composition, or a minor constituent compared to moisture and fat. Consequently, the stress and strain observed for a product will increase at least linearly with protein, and quadratically for low levels of protein.” (LaBudde)

Effect of Salt and Phosphates on Gel Strength

The particular observations of Song and Jane related to salt levels must be balenced out by observations by LaBudde. He claims that “the effects of salt level are to shift the pH sensitivity of the proteins and stabilize functional groups to the surrounding water. Higher salt levels generally will increase strength due to greater protein mechanical extraction, greater unfolding (resulting in increased cross-linkages) and lower the gel point temperature (resulting in more complete gelling in the cook cycle).

The effects of phosphate or lactate include:

1) increase in ionic strength (salt effect),

2) increase in pH and

3) special interactions to stabilize unfolded proteins.” (LaBudde)

Fillers with High WHC

We are considering using fillers in the final mix with from soy with high water holding capacity. We have to factor in, comments by LaBudde that “fillers with high water-holding capacity will effectively de-plasticize the system, resulting in lower strains to failure and higher stresses.” (LaBudde)

Conclusion

-> Soy Protein Isolate

In relation to soy protein isolates, SPI dispersion showed gel-like behaviour with two thermal transition peaks at 75.9°C and 94.2°C at SPI dispersion of 8%.

-> Potato and Corn Starch

From the work of Takahashi et al. (1983), we conclude that there appears to be insufficient motivation to include soy isolate with potato starch or corn starch due to its lowering effect on swelling in potato starch and the increase of solubility on corn starch while swelling in corn starch remains more-or-less unaffected.

From the Song and Jane study, we concluded that the peak viscosities of potato starch (8%) and soy protein (2% and 4%) mixtures were substantially lower than that of potato starch (8%) alone. Setback viscosity, which is the retrogradation tendency after gelatinization and cooling, of potato starch and soy proteins increased when protein concentration increased. Compare this with the fact that PS on its own, at 8% yields a maximum viscosity at around 80 deg C after < 5 minutes. PS (8%) + SPI (2%) as well as SP (8%) + SPI( 8%) yielded maximum viscosities which were both lower than PS alone. The final observation which negates it’s inclusion with SPI is the retrogradation tendency of the SPI/ PS mix after gelatinization and cooling.

-> Effect of Salt on Potato Starch

Salt has been shown to have a significant effect on peak viscosity of potato starch. At a low concentration of 0.04%, NaCl significantly reduced the peak viscosity of potato starch but not normal maize and waxy maize starches. We concluded that since salt content is legislated and since it is added to the product before cooking and since there are a number of other benefits to the inclusion of some salt, we will keep salt levels at the maximum allowed inclusion levels under the legislation. Having said that, there is no obvious benefit for the inclusion of SPI to PS.

-> Maize Starch

Pasting temperature decreased when soy protein was added to a normal maize starch dispersion. When the protein concentration increased from 2 to 8% in the mixtures of starch and protein, peak viscosity and final viscosity increased. Salt residues in soy protein reduced the viscosity of the mixtures containing potato starch, which was attributed to the suppression of charge interactions. Setback viscosities of the mixtures of soy proteins and starches were increased.

Peak pasting temperature of maize starch is (95°C) and (90°C) of normal maize starch (8%) and soy protein isolate (8%). 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. Results tend to show normal maize starch at 8% and SPI at 8% to be the optimal inclusion rate for the production of Russians and Hungarians. Even the protein (2%) and starch (8%) ratio are to be preferred to maize starch alone. Even though the peak viscosities, onset and peak pasting temperatures were all lower, it showed less shear thinning, and higher final viscosity than normal maize starch alone.

Song and Jane offers the following instructive explanation for the observed phenomena. With the addition of proteins, protein-lipid interaction facilitated starch swelling. As temperature reaches to starch gelatinization temperature, starch crystallites melt, granules swell dramatically, amylose leaches out of granule and viscosity of starch dispersion increases (French, 1984). As temperature reached protein denaturation temperature, protein molecules started unfold and more buried amino acid side chains could interact with water and facilitated protein solubility. The dispersed starch molecules then formed three dimensional network matrix with denatured protein molecules, therefore the peak viscosity and fmal viscosity were significantly increased. It is suggested by results of amino acid composition (Nielsen, 1985) that B-conglycinin has larger proportions of amino acids with polar side chains than glycinin. After gelation, B-conglycinin displayed a lower hydrophobicity and higher solubility than did glycinin (Song and Jane, 1998a, and b). It resulted in a better compatibility between B-conglycinin and normal maize starch than between glycinin and normal maize starch. Therefore, viscosity of the mixture of B-conglycinin and normal maize starch was higher than that of the mixture of glycinin and normal maize starch counterpart.

Viscosity profiles of soy protein and starch mixtures differed from that of starch alone. Peak viscosity of mixtures of starch (8%) with soy protein (8%) significantly increased except the mixture of waxy maize starch and glycinin. High swelling temperature of soy protein, especially glycinin, caused the separated viscosity peaks in the pasting profiles of mixtures of waxy maize starch and glycinin, and of mixtures of potato starch and soy protein. Salt residue in soy protein decreased the viscosity of potato starch and soy protein mixtures. Interaction between amylose and soy protein retarded starch granule swelling and caused the decreased peak viscosity at low protein concentration in the mixtures containing normal maize starch or potato starch, and increased the pasting temperature of potato starch and protein mixtures. Protein-lipid interaction could facilitate starch granule swelling. Pasting temperature decreased when soy proteins were present in normal maize starch dispersion. Mixtures of starch and soy protein displayed higher setback viscosity than starch alone. Viscosity of mixtures of starch and soy proteins significantly increased compared with soy protein dispersion alone.

In terms of the further inclusions into a starch or starch and soy mix, we largely followed the logic of LaBudde.

General processing principles have been identifies namely:

• The faster one heats a starch-water dispersion the thicker it will be at the identical endpoint temperature;
• It is VERY important to know the endpoint temperature of the starch you are adding to the sausage mix. Optimum starch past viscosity and gel strength are reached at the endpoint temperature. After that point, viscosity and strength both decrease because the swollen granule easily fragmented with stirring or actually imploded due to the extensive loss of amylose from the granule.
• Generally, if cooled too fast, the amylose will not have time to form the vital micelles necessary for the three-dimensional structure. If cooled too slowly, the amylose fractions will have a chance to align too much and become too close together and the liquid portion will not be trapped in the micelles. In both instances, there will be weeping and syneresis.
• If dry heat is applied, dextrinization occurs. This is the breakdown of starch into dextrin (disaccharides) and can be identified by the non-enzymatic browning.  The heat hydrolyzes the starch polymers and the short chains mean that the granule will not remain intact. When this happens, the starch paste will be runnier with the dextrinization (sugar and acids can also cause dextrinization to take place). This has an important application in various heating systems used in the meat industry. Most smokehouse can be set to “dry heat” which in the case of Russians and Hungarian sausages will be undesirable.
• The optimal cooking temperature must be determined experimentally being either 69, 72 80 or 90 deg C.

References

Bean, M.M. and W.T. Yamazaki. 1978. Wheat starch gelatinization in sugar soutions. I. Scurose: Microscopy and viscosity effects. Cereal Chemistry 55(6): 936-944.

Johnson, J.M., E.A. Davis, and J. Gordon. 1990. Interactions of starch and sugar water measured by electron spin resonance and differential scanning calorimetry. Cereal Chemistry 67(3): 286-291

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Perten’s Rapid Visco Analyser (RVA)

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Song, Y. 2000. Characterization of biopolymers: starch and soy protein. Iowa State University