Introduction

Meat processing is a study in protein, its functionality and characteristics. Soy protein is a very popular meat extender and alternative protein for meat. I am considering its use in a econo bacon formulation and we already use soy protein extensively in sausage formulations. Pea protein emerged as a good alternative.

There are drawbacks using legume protein generally. Both soy and peas are part of the legume family. Allergens and taste are the main ones. Legume proteins have a distinct “beany” and “hay-like” flavor that is hard to mask (Rackis et al., 1979, as cited in Aspelund and Wilson, 1983, p. 539). These off-flavors may contribute to a reduced consumer acceptance for food products and thus also the success for these kinds of food products on the market (Owusu-Ansah and McCurdy, 1991). (Söderberg, J., 2013)

Another “drawback with using legume proteins in foods is the facts that they have limiting amino acids (Leterme et al.,1990) and that they contain anti-nutritional factors that affect the digestibility and thus, the bioavailability of proteins in a negative way (FAO, 2011).

One benefit of using pea protein instead of soy is allergens. Pea allergy is rare (San Ireneo et al., 2000) and studies show that the functionality and protein quality of pea may be as good as those of soy protein (O’Kane et al., 2004), making pea protein a viable alternative. (Söderberg, J., 2013)

The use of soy in meat formulations are however so wide spread that, depending on the particular market you formulate for, it may be unavoidable due to cost considerations. The question then comes up if alternatives to soy TVP exists. Besides, we found that soy based extended meat products have a massive appeal in certain market segments in South Africa.

Summary

I use the masters thesis submitted by Johanna Söderberg to the faculty of natural resources and agricultural sciences, Department of Food Science at the Swedish University of Agricultural Sciences, as basis for comparing soy and pea proteins on their own. How do they fare if we compare the two products head to head. I quote relevant parts of her thesis with a few short comments.

The entire thesis is available for upload under the reference section.

We then move to understand what TVP is. In our emulsified sausage formulation we use soy isolates. Soy concentrates are available but we mostly use it in its texturized form as TVP in fresh sausage formulations. What exactly is Textured Vegetable Protein?

We conclude the article by asking if there are alternatives to soy TVP. What about blends? How do they compare with soy, by far, the best plant protein to be used in meat formulations for certain market segments.

Functional properties of food proteins

“The functional properties of a protein are:

“Those physical and chemical properties, which affect the behavior of proteins in food systems during storage, processing, preparation and consumption. It is these characteristics, which influence the ‘quality’ and organoleptic attributes in food.” (Kinsella, 1982, p. 51).” (Söderberg, J., 2013))

“The functional properties of a protein are affected by both intrinsic and extrinsic factors. The intrinsic factors are: shape, size, amino acid composition and sequence, the distribution of net charges, the ration between hydrophobicity/hydrophilicity, secondary, tertiary and quaternary structures of the protein as well as the protein’s capacity to interact with other components in the food system (Damodaran, 1997). The extrinsic factors that affect the functionality of proteins are: pH, temperature, moisture, chemical additives, mechanical processing, enzymes and ionic strength (Kinsella, 1982). There are proteins that are associated with specific functional properties, such as egg proteins with coagulation, or soy proteins for their use in forming food gels (Vaclavik and Christian, 2003). Some example of functional properties can be seen in Table 1 (Kinsella, 1982).” (Söderberg, J., 2013)

Table 1. Functional properties of proteins in food applications

In order to evaluate if a protein is applicable and suitable in certain food systems and food products, it is important to characterize the functionalities of the protein (Kinsella 1982; Vaclavik & Christian 2003). For the proteins to be used in foods they must possess or contribute characteristics that are appropriate in interaction with other food components (e.g. water and lipids) or be suitable for processing. The functional properties that are required from a protein vary with different food applications and food systems. The three most important functional properties of food proteins in general are solubility, emulsification and foaming (Kinsella, 1982).” (Söderberg, J., 2013)

“The type of functional requirements that are needed of a protein in different food systems is shown in Table 2. It is important to remember that no single protein exhibits all the functional properties (Vaclavik and Christian, 2003).” (Söderberg, J., 2013)

Table 2. Functional properties performed by functional proteins in food systems.

“Proteins must show good and multiple functionalities in order to perform well in food systems. This requires a deeper understanding of the structure-function relationship, which sometimes can be hard to determine. One reason why proteins possess such different functional properties is the fact that all proteins are built up by different amino acids (Nakai, 1983). The amino acid composition affects the functional properties of a protein according to how they are disposed in the polypeptide chain, as well as what type and how many of those amino acids that are present (Kinsella, 1981).” (Söderberg, J., 2013)

“Something worth mentioning, but that will not be discussed further in this study, is that to improve the functionality and nutritional quality of the protein, modification of the proteins can be applied (Barac et al., 2010). Enzymatic hydrolysis is the most common and simplest method. During this process the protein is treated with an enzyme, acid or alkali that degrades the protein to its amino acid constituents (Lasztity, n.d.).” (Söderberg, J., 2013)

Solubility

The solubility of a protein is the most important functional property since the protein needs to be soluble in order to be applicable in food systems. Other functional properties like emulsification, foaming, and gelation are dependent on the solubility of proteins (Vaclavik and Christian, 2003). Solubility can be described as when equilibrium exists between hydrophilic and hydrophobic interactions. The solubility of a protein is related to the pH, where it is minimal at the isoelectric point, making the environmental pH the most important factor when it comes to the degree of protein solubility. The solubility is also influenced by temperature and ionic strength, (Bolontrade et al., 2013). Freezing, heating, drying and shearing are also factors that have an influence of protein solubility in food systems (Vaclavik and Christian, 2003). Insoluble proteins are not good for food applications and thus it is important that denaturation caused by e.g. heat is controlled so that the protein solubility will not be affected in a negative way (Raikos et al., 2007).” (Söderberg, J., 2013)

Emulsions

Emulsions consist of two liquids that are immiscible, where one of the liquids is dispersed in the other in form of small droplets. Emulsions can be classified according to the distribution of the oil and the aqueous phase. A system where the oil droplets are dispersed in the aqueous phase is called oil-in-water emulsion (O/W). Food systems like this are mayonnaise, milk, cream, soups and sauces. The opposite of an O/W emulsion is water-in-oil (W/O) but there are also water free emulsions and multiple emulsions (O/W/O or W/O/W). The droplets in an emulsion are called the dispersed (or internal) phase, whereas the surrounding liquid is referred to the continuous (or external) phase (Dickison and McClements, 1995, as cited in McClements, 2005, p.3).” (Söderberg, J., 2013)

“When water and oil are homogenized they rapidly separate into two layers, one layer of oil, which has high density, and one layer with water that has low density. This is called phase separation and has to do with the fact that the droplets fuses together with adjacent droplets that are similar to themselves. To get a stable emulsion (both in a short and long term perspective) it is of great importance to add an emulsifier. An emulsifier is a surface-active molecule that allows the two phases to homogenize. Surface-active molecules are mostly amphiphilic i.e. they have both hydrophobic and hydrophilic parts, which allow the two liquids to blend together.” (Söderberg, J., 2013)

Foaming

Foams consist of a gas phase, a liquid phase and a surfactant (e.g. proteins) and whipping or shaking form foams. Foods made up by foams are e.g. whipped toppings, meringues, ice creams, chiffon desserts and angel cakes (Kinsella, 1981; Yang and Baldwin, 1995). Angel cakes and other baked goods are solid foams. Foams are formed through unfolding and absorption of the protein, at the air-water interface, as well as film formation around the air bubbles. Different proteins have different abilities to form and stabilize foams, and just as in the case of proteins and their different emulsifying properties, this is related to different physical properties of the proteins. For a protein to have superior foaming properties, it must possess high solubility in the liquid phase as well as the ability of quickly forming a film around the air bubbles in the food system (Kinsella, 1981).” (Söderberg, J., 2013)

“The extrinsic factors that affect the foaming properties are e.g. pH, temperature and ionic strength. Foam stability and the proteins ability to form foams are also of big importance. In order for a protein to form stable foams the interfacial film should be rigid and not let the entrapped air escape (i.e. it should be almost impermeable). The protein should also have the ability to form strong bonds like hydrogen bonding and hydrophobic interactions. The protein should also possess limited denaturation at the surface to keep viscosity and rigidity (Kinsella, 1981).” (Söderberg, J., 2013)

Gelling / coagulation

The globular proteins’ gelling properties are of big importance in foods (Van Kleef, 1986; Beveridge et al., 1984). According to Ikeda and Nishinari (2001) is protein gelation one of the most important functional properties when it comes to modify the structure and texture of foods. One example is the importance of the gelation properties of egg in foods like cakes, omelets and confectionary. The texture of foods and thus, the gelation properties of a protein, affect consumer acceptability (Kiosseoglou and Paraskevopoulou, 2005).” (Söderberg, J., 2013)

“Globular proteins, such as egg white and soybean protein, are able to form gels upon heating (Doi, 1993). For a gel to form it is important that the functional groups (e.g. hydrophobic groups) within the protein are exposed. This makes it easier for the groups to interact and form a three dimensional network. Gel formation is complicated, and affected by the concentration of protein, amount of water, ionic strength, time and temperature as well as pH and interaction with other components in the food system (Raikos et al., 2007). The process for gelation in short, is:

The heat will make the native protein to denaturate, and during the denaturation disulfide bonds will be formed and hydrophobic amino acid residues are exposed (Shimada and Matsushita, 1980). After denaturation and further heating, the proteins will aggregate and interact with other proteins and form either a gel or a coagulum. Which type that is formed depends on conditions like molecular weight, heating time and protein concentration (Raikos et al., 2007; Shimada and Matsushita, 1980). The gel structure is a more structured network compared to the coagulum that is a disorganized aggregation (Raikos et al., 2007).” (Söderberg, J., 2013)

Legume proteins

Legumes are cheap and a high quality alternative to food based on animal products. They contain high amounts of proteins, dietary fibers, minerals and vitamins that are essential for good human health (Abd El-Hady and Habiba, 2003).The protein content in legumes varies between 17-30% depending on origin and the proteins are present as globulins (60-90%) and albumins (10-20%) (Sathe et al., 1984).

Today, soybean proteins are the most used and researched pulse proteins on the market, but the interest in functional properties and nutritional quality of unconventional legume proteins as an ingredient in new food products has increased (Chavan et al., 2001). The alternative legume proteins that are being researched are the ones that are believed to possess the same, or similar, functional properties and nutritional qualities as soy protein. The proteins should also have a price competitive to that of soybean (Marcone et al., 1998; Vose, 1980). One alternative pulse protein that is said to have big potential for food applications are pea protein (Pisum sativum L.) (O’Kane et al., 2004). Except the potential good functional properties of pea proteins, they are also said to be lesser in anti-nutritional substances than soy protein (Gwiazda et al., 1979), and are not classified as an allergen (like soy and egg proteins). This has to do with the fact that the allergic reaction to peas has been infrequent in humans (San Ireneo et al., 2000).” (Söderberg, J., 2013)

Soybean protein (Glycine max L.)

“Soy proteins are used in foods because of their excellent emulsifying and gelling properties, which mimic the functional properties of egg proteins (Ratnayake et al., 2012). Soybeans as well as soybean products are classified as a health food due to their content of e.g. omega-3 fatty acids, isoflavones, dietary fiber, essential amino acids and high protein content (Variyar et al., 2004) One drawback concerning soybeans is their very distinct flavor that is hard to mask, and thus, their application are limited to just some food products (Endres, 2001).” (Söderberg, J., 2013)

“Soybean proteins are used as a food ingredient in infant formulas, flours, protein isolates and concentrates as well as in textured form. Examples of soy foods are: imitation cheese, miso, tempeh, tofu and meat substitutes, and new soy foods are frequently developed (Liu, 2000; Singh et al., 2000, as cited in Friedman and Brandon, 2001, p. 1070).” (Söderberg, J., 2013)

“The functional properties that can be ascribed to the soybean proteins are solubility, water absorption and binding, viscosity, gelation, cohesion-adhesion, elasticity, emulsification, fat absorption, flavor binding and color control. Among the plant proteins, soybean proteins are the most studied (and thus the best understood plant protein) and are often used in comparison with other plant proteins in order to evaluate their functional properties (Mcwatters and Cherry, 1977).” (Söderberg, J., 2013)

Mainly soy protein isolates (SPI) and soy protein concentrates (SPC) are used in the food industry (Varzakas et al., n.d.). SPI has the highest protein content (90%) and are thus the most expensive (Riaz, n.d.). SPI are made from defatted soybean flakes, where the sugars and dietary fiber have been removed. It is used in a variety of foods. Some examples are dairy type products, fruit drinks, power bars, soups and sauces, meat analogs, bread and baked goods, breakfast cereals and protein powders (Soyfoods, 2013). SPI do not affect color and flavor of the end product to any great extent (Riaz, n.d.). SPC are made by removal of the carbohydrates from soy flakes or soy flours. It has a protein content of 65-70% and is used in foods like baked goods, breakfast cereals and meat products to increase nutritional value and functional properties (Soya, n.d.).” (Söderberg, J., 2013)

“Native soybeans have a protein content of 40% and they comprise the storage proteins albumin and globulin, where globulins are the dominant ones. The globulins are salt- extractable while the albumins are water soluble (Derbyshire et al., 1976). The globulins can be grouped into 7S globulins and 11S globulins according to their sedimentation coefficients (Shigeru Utsumi et al., 1997). The 7S globulins can be further divided into β-conglycinin, γ-conglycinin and basic 7S globulin (Bg) and all of them differ in their functional properties. As an example does Bg have a higher isoelectric point (pH 9.05-9.26) than the other globulins. The function of Bg is yet unknown (Shigeru Utsumi et al., 1997). β-conglycinin is a trimer and consists of four subunits: major α’, α and β and minor: γ (Shigeru Utsumi et al., 1997). The 11S globulins are also known by the name glycinin, which consists of disulfide-linked acidic and basic amino acids. There are two groups consisting of five subunits in the soybean glycinin that have been identified: A1aB2, A1bB1b, A2B1a (group I) and A3B4, A5A4B3 (group II) (Adachi et al., 2003; Mujoo et al., 2003). In soybeans it is the glycine and β-conglycinin that gives soy proteins their functional properties (Lee, 2011).” (Söderberg, J., 2013)

Pea protein (Pisum sativum L.)

Peas have a high content of proteins, minerals vitamins, starches and fibers. They are used in human foods like: soups, puddings, snacks, and stews or as sprouted. Peas are also used in animal feed, where they are mixed with cereals or canola oil in order to improve the protein quality (Betker, 1990; Hoang, 2012). Studies show that pea proteins may be a good substitute for soybean proteins as a functional additive in food products intended for human consumption (Barac et al., 2010; Maninder et al., 2007; Aluko et al., 2009), but in order to increase the utilization of pea proteins, their functional properties must be further evaluated (Aluko et al., 2009).

Pea protein concentrate (PPC) and pea protein isolate (PPI) have the biggest potential as food ingredients (Choi and Han, 2001). PPC is made from pea flour, where the protein has been removed from the starch granules by air-classification (Owusu- Ansah and McCurdy, 1991), resulting in a protein content of 47% (Sosulski and McCurdy, 1987). PPI is also made from pea flour but by aqueous extraction and isoelectric precipitation of the protein (Owusu-Ansah and McCurdy, 1991). The protein content in pea isolate is approximately 80% (Sosulski and McCurdy, 1987).

Peas have a protein content around 25 %, but the content varies depending on pea variety (Aluko et al., 2009; Gueguen and Barbot, 1988). Pea protein consists of legumin (11S), vicillin (7S) and albumins (2S), where 11S and 7S are the most abundant ones (O’Kane et al., 2005). The legumin and vicilin have similar amino acid composition and subunit structure as the glycinin and β-conglycinin of soy proteins (Derbyshire et al., 1976).” (Söderberg, J., 2013)

Functional properties of soy and pea protein

In order for the consumer to accept legume proteins in foods, and to optimize its utilization, the functional properties of the protein must be studied. It is the functional properties and nutritional value as well as the sensory characteristics of the legume proteins that are crucial for the quality and acceptance of the end product (Adebowale and Lawal, 2004). As mentioned in the beginning of this study, the functional properties of proteins are affected by environmental factors as pH, temperature and ionic strength. Due to limited published studies concerning some of these factors in relation to the functionality of soy and pea protein, they will only be discussed if applicable studies regarding this have been found.” (Söderberg, J., 2013)

Solubility

“Protein solubility is affected by extrinsic factors like pH, temperature and ionic strength (Bolontrande et al., 2013). The effect of pH on soy protein solubility (i.e. solubility profile) gives a u-shaped curve, where the highest solubility is shown to be on both sides of the isoelectric point, (pI) 4.5, with a high solubility above the pI and a low solubility below the pI (Lee, 2011). Lee et al. (2003) showed that commercial SPI and SPC had similar solubility profiles, but that the amount of soluble proteins in the two samples differed at same pH values. Since legume proteins have to go through thermal heating in order to remove the anti-nutritional factors, the effect of heating on protein solubility is extremely important (Lee, 2011). There are, however, few studies on how heat treatment affects soy protein solubility. Ionic strength also affects protein solubility. Renkema et al. (2001) studied the effect of NaCl on soy protein solubility as a function of pH. The results showed that high NaCl concentrations increased the solubility of the protein near its isoelectric point.” (Söderberg, J., 2013)

“Pea proteins also shows a u-shaped curve as a function of pH, with a high solubility above the pI, and a moderate solubility below the pI (Adebiyi and Aluko, 2011; Tömössközi et al., 2001). Tömössközi et al. (2001) showed that PPI had the same solubility profile as other legume proteins. Tian (1998) found that PPI had higher solubility than SPI, and the same was stated in a study performed by Naczk et al. (1986). Heat treatment studies regarding pea proteins are few. One study found showed, though, that heat treatment reduced the solubility of pea proteins (Habiba, 2002).” (Söderberg, J., 2013)”

Emulsifying properties

It has been reported that SPI shows great emulsifying properties. This is related to its high solubility and high protein content (Gwiazda et al., 1979).

Jideani (2011) write that SPI, as well as SPC, are good emulsifiers but that SPC shows lower emulsifying capacity than SPI. Environmental factors, such as pH, affect the emulsifying properties of soy protein and this was studied by McWatters and Cherry (1977). They saw that soybean flour was able to create a mayonnaise-like emulsion that was extremely thick (at pH 6.5 and pH 8.2). At lower pH values, a salad-like dressing emulsion was created. Emulsifying properties can be evaluated by the protein’s emulsion stability (ES) and emulsion activity (EA). The ES is a measure of the stability of the emulsion over a certain time span and EA is a measurement of how much oil a protein can emulsify per unit protein (Boye et al., 2010). Gwiazda et al. (1979) presented the result that SPI and SPC had different emulsifying properties. SPI showed an EA of 96%, and an ES of 92%. SPC had an EA of 55.6% and an ES of 56.8%. In the same study, pea protein concentrate showed an EA of 60.6 and an ES of 65.3%.” (Söderberg, J., 2013)

It has been reported that PPI have similar or better emulsifying properties than SPI (Vose, 1980). Aluko et al. (2009) showed that PPI actually had better emulsifying capacity than SPI. There is another study that shows a different result; Tömössközi et al. (2001) found that PPI had quite good emulsifying capacity but low emulsion stability in comparison to SPI. In a study done by McWatters and Cherry (1977) it is shown that the emulsifying properties of pea protein are minor compared to soy protein but it is still able to produce both semi-thick and thick mayonnaise-like emulsions at different pH values.” (Söderberg, J., 2013)

“The effect of temperature on the emulsifying properties of pea protein is that, when the temperature increase the emulsifying properties decrease. It has also been reported that addition of NaCl increase the emulsion capacity of both pea and soy proteins but that the emulsion stability decreases with increased NaCl concentrations (Tian, 1998).” (Söderberg, J., 2013)

Both pea and soy isolates are therefore effective ingredients in an emulsion type sausage. I would not use protein concentrates in emulsified products. In choosing between soy, pea or a blend of soy and pea isolates, I would do extensive tests to verify under factory conditions with specific list of ingredients to determine which one is better due to the Tömössközi et al. (2001) results. As always, I would keep the temperature down in the emulsifier or bowl cutter.

Foaming properties

“To evaluate the foaming properties of a protein, foam stability (FS), foam capacity (FC) and foam expansion (FE) can be measured. FE and FC are measured in volume (%) when whipped, while the volume of the foam over time (normally 0-30 min) gives the protein’s FS (Boye et al., 2010). In a study done by Boye et al. (2010) SPI showed a FE of 41.8% and a FS of 93 %.” (Söderberg, J., 2013)

“Fuhrmeister and Meuser (2003) showed that the foam forming properties of pea protein isolate were best at pH 5 and 7. The stability of the foam showed to be much lower than that of egg white. In a study done by Fernández-Quintela et al. (1997) the FE of pea protein showed to be around 15 % and the FS around 94 %. The FC was greater in acid and alkaline regions. The FS increased with pea protein concentration and ionic strength (Akintayo, et al., 1999). Another study showed, however, that the FS of pea protein was around 76-79%. The foam volume also decreased relatively fast compared to other legume proteins. It was also shown that PPI had a significantly higher FC than SPI. The foam stability of PPI was better than SPI at pH 5.0 but minor in other pH values (Toews and Wang, 2013). Tian (1998) showed that the addition of NaCl improved the foaming properties of pea protein, but only up to an addition of 0.5% (w/v). Increased temperature also improved the foaming properties.” (Söderberg, J., 2013)

Gelling properties

“Studies have shown that the concentration of soy proteins affects the hardness of the gel and that the gelation properties of soybean proteins depend on temperature, pH, and ionic strength. In SPI the ratio between β-conglycinin and glycinin can influence gelation (Renkema et al., 2001) Varzakas et al. (n.d.) studied the gelling properties of SPI and SPC. The results showed that both SPI and SPC showed different gelling strength at different protein concentrations and temperatures. The conclusion drawn was that strong gels were formed at low temperature and high protein concentrations.” (Söderberg, J., 2013)

For this reason SPC is an effective ingredient in non emulation, fresh sausage production. Im considering its inclusion in a catering bacon formulation where the temperature will not be raised above 48 deg C.

“O’Kane et al. (2004) write that pea protein forms more unstructured gels than soy protein and thus their gelling properties are not that good as those of soy. Akintayo et al. (1999) reported that pea protein concentrate (72 % protein) had low gelling properties. Another study showed that pea protein isolate forms a paste instead of a rigid gel (Adebiyi and Aluko 2011). Nunes et al. (2006) studied pea protein as a replacer of dairy and egg proteins in a gelled vegetable dessert. The results showed that pea proteins produced good gels that were highly applicable as a food product.” (Söderberg, J., 2013)

In choosing between soy, pea or a blend of the two, I would conduct extensive factory trails to choose between the two before I include it in bacon production.

Protein quality

“Food proteins are divided into high quality (complete) protein and low quality (incomplete) protein. A complete protein contains all the essential amino acids, while incomplete proteins have limiting amino acids. Limiting amino acids are the ones that are present in such low amounts that they are not able to take part in the synthesis of other proteins. Animal proteins are complete proteins, while plant proteins are incomplete proteins. If the intake of protein mainly consists of incomplete protein sources the body is not able to make certain amino acids. In order to get a more complete protein, protein from different sources, like legumes and cereals can be combined. This is called mutual supplementation (Gropper et al., 2012).” (Söderberg, J., 2013)

“Legume proteins are generally high in lysine, but the content of sulfur containing amino acids, like methionine and cysteine, is limited. Both soy protein and pea protein has a high content of lysine and low content of methionine, cysteine and tryptophan (Leterme et al., 1990). The tables below show the amino acid composition of soybean and pea.” (Söderberg, J., 2013)

“There are several ways to determine the quality of proteins. One of the most admitted and approved method is the protein digestibility-corrected amino acid score (PDCAAS) (Hughes et al., 2011). According to McMann (2000, p.7) is PDCAAS “based on several factors; a food proteins profile of essential amino acids; the digestibility of the protein and the protein’s ability to supply essential amino acids in the amounts needed to meet the requirements of growing human beings.” The PDCAAS is calculated by using the formulas prescribed by FAO/WHO (1991, as cited in Hughes et al. 2011, p.12708):

1) Amino acid score = Amino acid content of test protein / Reference amino acid pattern

2) PDCAAS = Amino acid score (of the most limiting amino acid) x true digestibility (%)

At first, calculation of the amino acid score is performed. This is done by dividing the content of the most limiting amino acid in the test protein by the content in one of the reference proteins. Thereafter, the result is multiplied with the true digestibility of the test protein. As an example: If a protein has a chemical score of 0.70 and a true digestibility of 80 %, the PDCAAS is calculated to 0.56 (Insel et al., 2004).” (Söderberg, J., 2013)

“The highest PDCAAS a food protein can get is 1.0 or 100% (Hughes et al., 2011; McMann, 2000) but it is also possible that the protein get a score over 1.00. This is usually truncated to 1.00 because the amino acid in excess are often not required and thus catabolized (Tome, 2012). A score of 1.00 means that the protein provides proper amounts of all the essential amino acids, assumed that the intake is in appropriate amounts (Hughes et al., 2011).” (Söderberg, J., 2013)

“The PDCAAS of soy protein show varying numbers in various studies, where SPI showed to have a PDCAAS ranging from 0.92 to 1.00 and SPC 0.99-1.00 (FAO/WHO, 1991; Sarwar, 1997, as cited in Hughes et al., 2011, p. 12707). There are also studies done that just show the PDCAAS value from soy protein, without defining the protein type further i.e. if its SPI or SPC. These studies showed the PDCAAS values of 0.94 and 0.99 (Gropper et al., 2012; Tome 2012). The reason why there is a variation in the PDCAAS values, was investigated by Hughes et al. (2011). In the study the SPI and SPC had to be truncated to 1.00 in the first testing, but the second testing showed values ranging from 0.95-1.00. The authors write that the variations may depend on errors in the analytical methods. Egg white protein has a PDCAAS of 1.00 and pea protein concentrate 0.73 (Hughes et al., 2011). No studies concerning PPI were found. For a summary of the PDCAAS for the various protein sources see table below.” (Söderberg, J., 2013)

“In the United States, using PDCAAS is required before labeling foods (Hughes et al., 2011). Gropper et al. (2012) write that before labeling foods with information about the amount of protein (g) as well as the Daily Value (%) for proteins, PDCAAS is used to determine the protein quality. If the food protein has a PDCAAS equal or higher in quality than milk protein, 50 g of protein is sufficient. However, if the PDCAAS is lower in quality than that of milk protein, an intake of 65 g protein is required to meet the Daily Value.” (Söderberg, J., 2013)

“Some studies found have criticized PDCAAS (Schaafsma, 2005; Hughes et al., 2011) and FAO (2011) write that this method may not be appropriate for novel protein with known anti-nutritional substances (factors that can disrupt the protein digestion and metabolism, see section 7.1), and that PDCAAS may overestimate the protein quality in these foods. Therefore, some other methods for measuring the protein quality will now be presented.” (Söderberg, J., 2013)

“There are several other ways to determine the quality of a food protein. One simple way is to compare the amino acid pattern of the test protein with the amino acid pattern of a reference protein (usually egg or milk protein). This is called amino acid score (AAS) or chemical score (CS) (Gropper et al., 2009).” (Söderberg, J., 2013)

“Chemical Score (CS) = mg of essential amino acid / mg essential amino acid in 1 g reference protein x 100

The essential amino acid that has the lowest chemical score is the limiting amino acid. The CS is not a good measure alone since it does not account for protein digestibility or amino acid bioavailability (FAO, 1992).” (Söderberg, J., 2013)

“The protein efficiency ratio (PER) is another way of determining protein quality. This method accounts for to what extent the body can use the protein in terms of digestibility and availability, and also reflects the amino acids composition (Insel et al., 2004).

Protein efficiency ratio (PER) = weight gain in g / protein intake in g

The PER method is based on how well the protein contributes to the growth in young rats and in recent years some questions have been raised towards this method. It is now known that PER overestimates values of certain animal protein, and underestimates values of certain plant proteins needed for human growth. Rats grow much faster, and thus, needs more essential amino acids than humans (Boutrif, 1991).” (Söderberg, J., 2013)

“Net protein utilization (NPU) is a measure of protein utilization within the body. The more nitrogen the body keeps, the higher NPU value and protein quality the protein has (Insel et al., 2004). This method is also performed by doing tests on young rats and it has the same drawbacks as the PER method (FAO, 1985).” (Söderberg, J., 2013)

“Net protein utilization (NPU) = nitrogen retained / nitrogen intake x 100

The biological value (BV) of a protein is a measure of how much protein the body absorbs and keeps for other processes in the body This method is also performed on laboratory animals (Insel et al., 2004).

Biological value (BV) = nitrogen retained / nitrogen absorbed x 100

In the table below, the values for the chemical score (CS), protein efficiency ratio (PER), nitrogen protein utilization (NPU) and biological value (BV) of whole egg, soy and pea are given.” (Söderberg, J., 2013)

Anti-nutritional factors

“Anti-nutritional factors (ANF) are naturally present or can be formed during processing of legume proteins (FAO, 2011; Sarwar Gilani et al, 2005). The seeds of legumes contain ANF like protease inhibitors, lecitins, tannins, saponins and phytates (Liener, 1994). These factors can affect the protein digestibility, and thus, amino acid bioavailability in a negative way (FAO, 2011). Different ways to remove or inactivate some of the ANF have been established through physical (e.g. dehulling) and chemical methods (e.g. soaking, heating, irradiation) (Melcion and Van der Poel 1993, as cited in Fernández-Quintela et al., 1997 p. 332). Factors as genetic selection, fermentation and germination are also used for the same purpose (Frias et al., 1995; Kozlowska et al., 1996; Kothekar et al., 1996). The content of ANF in soybean and pea varies depending on variety (Adsule and Kadam, 1989; Hedley, 2001, as cited in Vidal-Valverde et al., 2003, p. 298; Becker-Ritt et al., 2004).” (Söderberg, J., 2013)

“In a study by Khattab et al. (2009) different pulse proteins were investigated for ANF reduction; different heating methods showed to be the best. The authors strongly suggested that those methods were carried out before human consumption. Fernández-Quintela et al. (1997) showed that the tannin and phytase activity decreased after protein isolate preparation of soy and pea protein. The trypsin inhibitor activity was also reduced in SPI by 27 % and in PPI with 47 %. The tannins were reduced by 67% in SPI and the phytates by 30%. The phytase reduction in PPI was 46%.” (Söderberg, J., 2013)

“In order for legume proteins to be used as a substitute for animal proteins, it is of big importance that the quality as well as the traditional characteristics of the food is maintained. It is also important to remember that the organoleptic and kinesthetic properties e.g. color, flavor, taste, texture and appearance of foods, are related to the proteins in the food (Endres 2001).” (Söderberg, J., 2013)

“In order for pulse proteins, such as soy and pea protein, to be successful and gain consumer acceptance, it is important that the flavor (aroma and odor) of the product appeal to the customers (Heng, 2005). One of the constraints with using soy and pea protein in food products is the distinct off-flavors that are hard to mask. It is the volatile, saponins, and non-volatile, ketone and aldehyde compounds that are responsible for this (Murray et al., 1979). These off-flavors are often described in terms like “beany” and “green” and are formed during autooxidation or lipoxygenase activity (Rackis et al., 1979, as cited in Aspelund and Wilson, 1983, p. 539). The flavor compounds interact with the proteins in soybean and peas and therefore they are also present in isolates and concentrates, which limit the uses and lower the consumer acceptance for these products (Meyer, 1970; Kalbrener et al., 1971; Eldridge, 1978; Smith and Circle, 1978; Wolf and Cowan, 1975 as cited in Aspelund and Wilson, 1983 p. 539). Some studies show that it is possible to remove the off- flavor compounds (Even though many researchers have studied the functional properties of soy proteins, and to some extent those of pea proteins, there are limited. Organoleptic aspects, kinesthetic aspects and consumer acceptance of soy and pea protein foods, see Maheshwari, Ooi and Nikolov, 1995; Samoto et al., 1998).” (Söderberg, J., 2013)

“One way to do this is to remove the lipids. If the lipids are removed the proteins will not be able to bind to them (Wu et al., 2001). It is also of big importance to choose the right extraction method. Wu et al. (2011) reported that the extraction method may be efficient in the terms of removal of off-flavor compounds, but may have a negative effect on the functional properties of the protein, like denaturation of the protein or decreased protein solubility.” (Söderberg, J., 2013)

Schyver and Smith (2005) investigated what factors that affect soy food consumption. The results showed that those who consumed soy foods were the ones that wanted to exclude or minimize animal products in their diet, wanted to adapt a healthier lifestyle or had environmental concerns. The main reason why consumers continued to eat soy was the fact that they thought it tasted good. The non-consumers in this study thought the sensory attributes of soy products were unfavorable, but the main reason behind not consuming soy foods was the fact that they were unfamiliar with the products. Both consumers and non-consumers agreed upon the fact that in order to increase the soy consumption by non-consumers it was not necessarily to improve the taste but to improve the perception in soy foods. A study that points out the issues with perceived taste, was done by Wansink (2003). In this study a snack bar with soy as a phantom ingredient was tested. The result showed that the taste and attitudes towards the snack bar were negative. The conclusion drawn from this was the fact that consumers may exclude products labeled with soy ingredients and that perceived taste plays a substantial role in this.” (Söderberg, J., 2013)

Garcia et al. (2009) studied the acceptability of mayonnaise-type emulsions based on different concentrations of SPC and rice bran oil (RBO). It was shown that a higher content of SPC lowered the acceptability of the color in the final product. This was probably related to the fact that SPC are known to darken the products to which they are added. A high content of SPC also lowered the odor acceptability. Taste acceptability did not differ significantly among the samples (60.4-60.7 on a scale of 100). The mouth-feel score also showed that an addition of SPC over 8% was not accepted. The spreadability showed greater acceptance with higher content of SPC. The study also showed that few consumers were willing to buy this type of mayonnaise, mainly due to the bland taste. When an ultimate content of SPC had been established, the authors performed a test with this mayonnaise. The mayonnaise was presented in three different flavors and one plain. The results showed that the flavored ones were highly acceptable, and that the plain was not accepted at all (49%). Other results shown in the same study was that people who were health conscious selected this type of mayonnaise, and that the three most important attributes for purchasing this type of product were taste, mouth-feel and overall acceptability. The purchase increased (with 70%) when the health benefits of this type of products was exposed to the test panel.” (Söderberg, J., 2013)

“Tian (1998) carried out a study on the overall acceptability and beany flavor in sponge cakes and a mayonnaise-type product with pea protein as an egg replacer. The findings concerning the sponge cake showed that the panelist thought that a 25 % replacement of egg by pea protein did not give the product a beany flavor, and that a 75% replacement by pea protein was acceptable concerning the cake quality. The negative notations were that pea protein gave the sponge cake a crumbly and coarse mouth-feel at higher protein concentrations. Some of the panelist noted, though, that they liked the pea flavor in the sponge cake. This probably had to do with the different backgrounds of the participants. The acceptability of the mayonnaise-type product was high up to 25% replacement of egg, while 50% was not acceptable and the panelist described the mayonnaise as having watery texture and that the mouth- feel were coarse and oily.” (Söderberg, J., 2013)

“Northern Pulse Growers Association (2009) performed a baking test on how well pea protein isolate and concentrate could replace whole egg in cakes and cookies. The study compared cakes made with pea protein with those made with commercial cake and cookie mixes. The result was that the pea protein cakes were more moist and that pea protein isolate created higher cakes than pea protein concentrate and that the cakes was comparable in height to the reference cake. The protein isolate also created more moisture cookies than eggs. This study did not evaluate the sensory characteristics concerning consumer acceptance.” (Söderberg, J., 2013)

TVP

The cheapest form of soy is Textured Vegetable Protein. It is the form that we use in one of our fresh sausage formulations and the one that I want to use in an economic bacon formulation.

What is TVP?

TVP is described as “fabricated palatable food ingredients” made from edible protein sources including soy grits, soy protein isolates, and soy protein concentrates with or without ingredients added for nutritional or technological reasons. The end products is sold in several forms as fibers, shreds, chunks, bits, granules, slices, or other forms. It is prepared by dehydration, cooking, retorting, or other production methods, the integrity of the structure is retained and its characteristic chewy texture. TVP is a registered trademark of the Arthur Daniel Midland (ADM) company, in Decatur, Illinois, USA. TSP is a registered trademark of PMS Foods, now Legacy Foods in Hutchinson, Kansas, USA. It typically means defatted soy flour or concentrates mechanically processed by extruders to achieve meat like chewiness when rehydrates and cooked. TVP therefore refers to a broad category of products with distinct production processes and apart from broad similarities, have varied specific characteristics. Soy is most often used to produce TVP, but others cereals and legume products are used to produce it in a texturized for flour, isolates or concentrates. When buying TVP, it is important to understand the specific characteristics of the product you are buying. (Phillips and Williams, (Ed.), 2011)

What is it made off?

* Oilseed proteins: oilseed clops, soybeans, rapeseed/ canola, cottonseed, peanut/ groundnut, and sunflower seed. Sesame, safflower, and flaxseed are minor oilseeds proteins. (Phillips and Williams, (Ed.), 2011)

* Cereal proteins: Wheat, corn, rice, barley, oats, sorghum, grain amaranth.

* Legume and pulse protein: Beans, gram, guar, lentils, lupines, peas.

* Leaf proteins: Alfalfa, lucern, tobacco, mulberry bush, grass, sugar cane, cloves.

What raw material is used is heavily dependent upon availability and there are times when there is for example no leafy proteins available for TVP processing. Cost, functional and physiological characteristics, nutritional value and customs/ taste are other driving forces dictating the particular raw material used. (Phillips and Williams, (Ed.), 2011)

Soybeans as the main source for TVP production.

From oilseeds, soybeans is the main source of TVP production. Availability and cost are the main reasons for this. The basic process of production is cleaning the soybeans, drying, conditioning, cracking and then it is converted into flakes. Oil is extracted and the defatted soy product is then ground into soy flour. The same product is the starter product for producing soy concentrate and isolate. (Phillips and Williams, (Ed.), 2011)

Most TVP is made from flour, but sometimes, also from grits. The difference between the two is the particle size. The grits are course (10 – 20 mesh), medium (20 – 40 mesh), or fine (40 – 80 mesh). High-end TVP’s like soy fibre or high moisture meat analogs are made from soy concentrate and isolates. (Phillips and Williams, (Ed.), 2011)

Process for making TVP.

Both peas and soy are available in their their texturized form. The main method of production is through the use of extrusion technology. The product is re-hydrated to 60% or 65% moisture and blended into meat products. (Phillips and Williams, (Ed.), 2011)

Smith (1975) describes the process as a “process in which a moistened, expansile starchy and/ or proteinaceous material are plasticized in a tube by a combination of moisture, pressure, heat and mechanical shear. This result in a elevated product temperature within the tube, gelatinization of starchy components, denaturation of proteins, the stretching or restructuring of tactile components, and the exothermic expansion of the extrudate.” (Phillips and Williams, (Ed.), 2011)

Extrusion is used to restructure many protein based products to a texturized form. Mechanical and thermal energy are applied to the protein containing material. The macro molecules loose their organised state and form “a continuous, viscoelastic mass.” (Phillips and Williams, (Ed.), 2011)

It is typically bought in granular form of between 2mm and 12mm. It may be coloured to mimmic a particular type of meat and it may be flavoured. (Phillips and Williams, (Ed.), 2011)

Alternatives to Soy TVP

In response to rapid population growth, a study was done in co-operation with the Swiss Federal Institute of Technology in Zurich, Bühler AG into alternatives to soy TVP in terms of the sustainability, availability, texturizing capacity, nutritional value and taste of possible alternatives. “Promising raw materials were texturized either individually or as part of a mixture in a twin shaft heat extrusion process, and the properties of the end product were compared to those of soybean textrudates.” (Brugger, et al, 2017)

The results is interesting. “Promising alternatives were found which could partially or completely replace soybeans (Table below).

The mixture of pea isolate and gluten scored highest and exceeded the soybean reference in terms of protein content, amino acid profile and taste. In the future, feeling in the mouth and texture could be further improved upon by optimizing the process parameters.

The second best result was achieved by the mixture of pea isolate and soybean concentrate. This mixture achieved better results than the soybean reference except in the case of texture which was given particular weighting in this assessment. However, further improvements can be expected by optimizing the extruder parameters. Having said that, this end product served only as a partial replacement for soybeans.

Pea concentrate with gluten also achieved a good result. Here, the fact that the product color and protein content are better than the soybean reference is especially noteworthy. In addition, soybeans can be completely eliminated with this mixture. The amino acid profile could be further optimized by a third component. The combination of broad beans with gluten stands out as the only alternative through a better feeling in the mouth than the reference. Here too, the amino acid profile could be improved upon by adding other sources of protein.” (Brugger, et al, 2017)

Again, I made the entire article available below as a download. Mixtures of for example pea isolate and soybean concentrate are probably already commercially available and can already be incorporated into meat formulations if it makes sense from a price and functional properties standpoint.

Conclusion

The onus is more than ever on the NPD managers to keep abreast of rapid developments in the field of functional ingredients and extenders. I am excited to get to work on alternative formulations for products like catering bacon and braai grillers.

The key lesson I learned from the studies quoted above is that thorough studies should be done. If pea isolates, concentrates or TVP makes any economic sense, I have to test it against its soy counterparts and have to include the best blend available in the market as a 3rd alternative. The products must be tested and compared on every level before a final decision is made on product formulation. Practical factory and market conditions along with the variations of one particular formulation vary so much that none of these tests can be taken as fait accompli. At best it moves the alternatives onto the table of valid alternatives to be considered.

References

Brugger, C., Dellemann, J-P, Petry, C., Laporte, M., Müller, N., Windhab, E. J., Bühler AG, Swiss Federal Institute of Technology (ETH). 2017. Next Generation Texturized Vegetable Proteins. Food Marketing and Technology Download article: food_2_2017_proc.pdf

Phillips, G. O., Williams, P. S. (Ed.). 2011. Handbook of Food Proteins. Woodhead Publishing

Söderberg, J.. 2013. Functional properties of legume proteins compared to egg proteins and their potential as egg replacers in vegan food. Swedish University of Agricultural Sciences. Upload her thesis: soderberg_j_131101.pdf

Image Credit: http://www.nutritioningredients.co.uk/product/pea-protein-isloate/