Soy: Notes on Reducing Sugars and the Millard Reaction in Relation to Human Health and heat damage to soy

Notes on Reducing Sugars

**Article still being written**


Temperature in is a key method used in the production of soy for human and animal consumption to deactivate components that may have a detrimental effect on human life and an animals ability to convert protein to meat. The extent to which these concerns are valid is debatable as it relates to raw soy as we noted in Soya: Review of Health Concerns and Applications in the Meat Industry. However, excessive heat processing of soy can have a serious impact on human health and the functionality of soy in meat products. This is mainly due to the Maillard reaction. It is the reaction that produces flavours and aroma during cooking. ;

We can refer to it as nonenzymatic browning reaction since the reaction does not involve enzymes. It is the reaction between reducing sugars and amino acids during high temperature cooking and is responsible for the formation of Maillard Reaction Products (MRPs). It is possible that both beneficial and toxic MRP’s are produced during cooking. In our discussion about the processing of soy, it is therefore crytically important for us to understand the different types of MRPs and their positive or negative health effects. Tamanna & Mahmood did a thorough review of these in 2015 in their Food Processing and Maillard Reaction Products: Effect on Human Health. We will review their findings here.

In this review we have summarized how food processing effects MRP formation in some of the very common foods. We will restrict our discussion to soy, meat and other constituents that are customarily used in meat formulations.

We will look more closely at the impact of different processing parameters on animal health and protein conversion rates. Before we do any of these, lets review the Millard reaction and before we do that, we briefly look at reducing sugars again.

Reducing Sugars

In order to understand the Millard reaction, we must first make some notes on reducing sugars. “A sugar that serves as a reducing agent due to a free aldehyde (H -C=O) or ketone  (C=O) functional groups in its molecular stucture, capable of reducing metal ions such as Cu+ and Ag+. Reducing sugars such as glucose and fructose will reduce solutions in Benedict’s test and FEHLING’S test.

An easy way to remember them is that all monosaccharides are reducing sugars. Some disaccharides, oligosaccharides and polysaccharides are reducing sugars. Examples of monosaccharide reducing sugars are the dietary monosaccharides galactose, glucose and fructose.

Galactose: Galactose (galacto- + -ose, “milk sugar”) sometimes abbreviated Gal, is a monossccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. (Spillane, 2006). A galactose molecule linked with a glucose molecule forms a lactose molecule. Galactose exists in both open-chain and cyclic form. The open-chain form has a carbonyl at the end of the chain. The name, galactose was coined by Charles Weissman (Weissman, C) in the mid 19th century and is derived from Greek galaktos (milk) and the generic chemical suffix for sugars -ose. (Bhat, 2008) The etymology is comparable to that of the word lactose in that both contain roots meaning “milk sugar”. Lactose is a disaccharide of galactose plus glucose. Lactose is also a reducing sugar.

Fructose: Fructose, or fruit sugar, is a simple ketonic monosaccharide found in many plants, where it is often bonded to glucose to form the disaccharide sucrose which itself is a non reducing sugar. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into blood during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847. (Dubrunfaut, 1847) (Fruton, 1972) The name “fructose” was coined in 1857 by the English chemist William Allen Miller. (William, 1857) Pure, dry fructose is a sweet, white, odorless, crystalline solid, and is the most water-soluble of all the sugars. (Hyvonen & Koivistoinen, 1982) Fructose is found in honey, tree and vine fruits, flowers, berries, and most root vegetables.

Commercially, fructose is derived from sugar cane, sugar beets, and maize. High-fructose corn syrup is a mixture of glucose and fructose as monosaccharides. Sucrose is a compound with one molecule of glucose covalently linked to one molecule of fructose. All forms of fructose, including fruits and juices, are commonly added to foods and drinks for palatability and taste enhancement, and for browning of some foods, such as baked goods. (Wolfgang, 2004)

Glucose: Glucose is a simple sugar with the molecular formula C6H12O6. Glucose is the most abundant monosaccharide (Domb, 1998), a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy from sunlight, where it is used to make cellulose in cell walls, which is the most abundant carbohydrate. (Kenji, 2005) In energy metabolism, glucose is the most important source of energy in all organisms. Glucose for metabolism is stored as a polymer, in plants mainly as starch and amylopectin (being one of the two constitutes of starch, the other being amylose), and in animals as glycogen. The polysaccharide structure of glycogen represents the main storage form of glucose in the body. Glucose circulates in the blood of animals as blood sugar. The name glucose derives through the French from the Greek γλυκός (‘glukos’), which means “sweet”, in reference to must, the sweet, first press of grapes in the making of wine. (Thénard, Gay-Lussac, Biot, and Dumas, 1838) (Online Etymology Dictionary) The suffix “-ose” is a chemical classifier, denoting a sugar.

To understand the use of dextrose, we have to look at the naming of glucose. Glucose was first isolated from raisins in 1747 by the German chemist Andreas Marggraf. (Encyclopedia of Food and Health, 2015) Glucose was discovered in grapes by Johann Tobias Lowitz in 1792 and recognized as different from cane sugar (sucrose). Glucose is the term coined by Jean Baptiste Dumas in 1838, which has prevailed in the chemical literature. Friedrich August Kekulé proposed the term dextrose (from Latin dexter = right), because in aqueous solution of glucose, the plane of linearly polarized light is turned to the right. In contrast, d-fructose (a ketohexose) and l-glucose turn linearly polarized light to the left. The earlier notation according to the rotation of the plane of linearly polarized light (d and l-nomenclature) was later abandoned in favor of the d- and l-notation, which refers to the absolute configuration of the asymmetric center farthest from the carbonyl group, and in concordance with the configuration of d- or l-glyceraldehyde. (Robyt, 2012) (Rosanoff, 1906)

With six carbon atoms, it is classed as a hexose, a subcategory of the monosaccharides. d-Glucose is one of the sixteen aldohexose stereoisomers. The d-isomer, d-glucose, also known as dextrose, occurs widely in nature, but the l-isomer, l-glucose, does not. Glucose can be obtained by hydrolysis of carbohydrates such as milk sugar (lactose), cane sugar (sucrose), maltose, cellulose, glycogen, etc. Dextrose is commonly commercially manufactured from cornstarch in the US and Japan, from potato and wheat starch in Europe, and from tapioca starch in tropical areas. (Yebra-Biurrun, 2005), The manufacturing process uses hydrolysis via pressurized steaming at controlled pH in a jet followed by further enzymatic depolymerization. (The Columbia Encyclopedia, 2015)

Dextrose: Dextrose is one of the most readily oxidized of the carbohydrates. (Benedict, 1907) ” It is often used in baking products as a sweetener and can be commonly found in items such as processed foods and corn syrup.

“Dextrose also has medical purposes. It is dissolved in solutions that are given intravenously, which can be combined with other drugs, or used to increase a person’s blood sugar. Because dextrose is a “simple” sugar, the body can quickly use it for energy.” (

“Many the reducing sugars are powerful reducing agents in alkaline solutions, while they exert, at most, slight action in neutral or acid solutions, is very commonly recognized. The substances formed when dissolved in an alkali solution appear to be oxidation products, possibly preceded by dehydration and decomposition. The destructive action of alkalies upon glucose is a common matter of reference throughout the literature upon the estimation of sugars.” (Benedict, 1907)

Sucrose is not a reducing sugar.

With this shortest of introductions to reducing sugars, we can now turn our attention to the Millard Reaction.

Looking closer at reducing sugars

A reducing sugar is a carbohydrate that is oxidized by a weak oxidizing agent (an oxidizing agent capable of oxidizing aldehydes but not alcohols, such as the Tollen’s reagent) in basic aqueous solution. The characteristic property of reducing sugars is that, in aqueous medium, they generate one or more compounds containing an aldehyde group.

eg. 1: α-D-glucose, which contains a hemiacetal group and, therefore, reacts with water to give an open-chain form containing an aldehyde group.

eg. 2: β-D-glucose, which contains a hemiacetal group and, therefore, reacts with water to give an open-chain form containing an aldehyde group.

eg. 3: α-D-fructose, which contains a hemiketal group and, therefore, reacts with water to generate an open-chain form, which, in basic medium, is converted to compounds containing an aldehyde group.

eg. 4: maltose, which contains a hemiacetal group and, therefore, reacts with water to generate an open-chain form containing an aldehyde group.

(by Gamini Gunawardena from the OChemPal site (Utah Valley University)

The Millard Reaction, considered from the perspective of human health

Our discussion on reducing sugars is, of course, only an overview to remind ourselves of the basic concepts so that we can have a closer look at the 2015 publication by Tamanna & Mahmood, Food Processing and Maillard Reaction Products: Effect on Human Health. I quote large sections of the article which I deem most applicable to our direct interest of soya and its application in the meat industry.



The Maillard reaction has been named after the French physicist and chemist Louis Camille Maillard (1878–1936) who initially described it. It is often defined as non-enzymatic browning reaction. While foods are processed or cooked at high temperature, a chemical reaction occurs between amino acids and reducing sugars which generate different flavours and brown colour (figure below). So it is often used in food industry for giving food different taste, colour, and aroma.

Schematic representation of “Maillard reaction” and flavour formation in food.

Based on literature, Hodge (1953) first described the steps involved in Maillard reaction products (MRPs), also known as advanced glycation end-products (AGEs), formation. The whole process of MRPs formation can be divided into three major stages depending on colour formation. At the first stage, sugars and amino acid condense, and following condensation, Amadori rearrangement and 1-amino-1deoxy-2 ketose form. In the second stage, dehydration and fragmentation occur in the sugar molecules. Amino acids are also degraded in this stage. Hydroxymethylfurfural (HMF) fission products such as pyruvaldehyde and diacetyl are formed in this intermediate stage. This stage can be slight yellow or colourless. In the final stage, aldol condensation occurs and finally the heterocyclic nitrogenous compounds form, melanoidins, which is highly coloured. Maillard reaction can also take place in living organisms. It has been reported that some MRPs particularly melanoidins have beneficial effects on health such as antioxidative and antibiotic effects. However some reports have also suggested that MRPs such as high carboxymethyl lysine (CML) promote diabetes and cardiovascular diseases while acrylamide acts as a carcinogen.

There is an ever-increasing preference for instant meal rather than traditional cooking, especially among the new generation of people. It has been reported that people consuming high amount of processed meat, pizza, or snacks develop insulin resistance and metabolic syndrome compared to people having high intake of vegetables and low processed food. MRPs that change during food processing might be one of the important factors for either disease progression or combating diseases. In this review, we have summarized the changes of MRPs which occur during processing of foods.

So far, a verbatim quote from Tamanna & Mahmood (2015). I now select the sections most applicable to our study on soya and its application in the meat industry which also includes vegetables and fruits. I again quote their work verbatim.

Soybean Processing and MRPs Formation

Soybean is widely used as flours, grits, flakes, isolates, concentrates, and textured soya proteins and also as cooking oil. Soybeans play important role in cardiovascular diseases, osteoporosis, and cancer. So processing of soybean is an important factor for maintaining its nutritional quality. Cooking at high temperature may generate MRPs which can be good or bad for health. However, soybean must be processed before consumption. Žilić et al. (2014) assessed the level of furosine, hydroxymethylfurfural (HMF), and acrylamide in soybean during extrusion, microwave, and infrared heating processes. They found that microwave heating for short time (1-2 min) generates high levels of acrylamide, whereas long time heating (3–5 min) generates lower levels of acrylamide. During extrusion and infrared heating, acrylamide formation greatly increased with time and temperature. HMF level increased in all three processes with increased time and temperature and it was significantly higher in microwave treatment. From the beginning of heat treatment, furosine level was higher in the extrusion and infrared treatment whereas in the microwave heating it was increased to maximum value after 3 min but at 4 min this value was similar with 2 min. Their results showed that microwave heating improved the antioxidant properties of soybean by 50% compared to raw soybean. Even though this study has reported that total flavonoids increase at 100°C with the exception of microwave heating which occurs at 45°C, another study showed that when soybean is soaked in water and heated afterwards at 98°C, almost half (44%) of the raw flavonoids were lost in the final product. This might be due to the presence of moisture content since decreasing moisture was shown to be associated with elevated levels of MRPs in the extrusion and infrared heat treatment.

Meat Processing and MRPs

MRPs like heterocyclic amine (HCA) level increases with elevated cooking temperature; and this phenomenon is more pronounced in meat than fish . Meat is cooked at high temperature either by frying, roasting, and boiling or in oven. While positive correlations have been found between the intakes of HCAs from foods and increased risk of various types of human cancer, some other studies have not found any correlation between HCAs and cancer risk. Several studies have demonstrated that processes like frying and broiling can cause the formation of high amounts of HCAs. On contrary, these HCAs produce different flavour and tastes in foods. Heterocyclic compounds such as pyrazine, oxazole, and thiazoles are primarily responsible for forming flavour in roasted compound. During high heat treatment and grilling process, pyrazines level significantly increased. It is suggested that the alkylpyrizne is formed via the condensation of two alpha amino ketone molecules derived from the Strecker degradation, which is an intermediate of Maillard reaction pathway.

In processed food, more than 25 types of heterocyclic amines (HCA) have been identified. A study has shown that when duck meat was cooked by charcoal grilling, deep-frying, roasting, microwave cooking, pan frying, or boiling, MRPs were higher in the pan frying process compared to the other four methods of cooking. Liao et al. (2012) reported that boiling and microwave cooking were the most appropriate methods to process duck meat in terms of MRPs formation. However in another study, it has been found that both charcoal grilled duck and chicken breast had high level of HCAs compared to pan fried meat. They found that roasting decreases HCAs significantly.

In another study, beef steak and hamburger patties were processed by pan-frying, oven-broiled, and grilled or barbecued to four levels of doneness (rare, medium, well cooked, or very well cooked). Beef roasts were processed on oven by rare, medium, and well cooking. They measured five different HCAs. The level of 2-amino-3,4-dimethylimidazo[4,5-f] quinoline was higher in well-cooked steak and hamburger patties. Like duck and chicken roast, roasting beef did not contain any of the 5 HCAs, but the gravy made from the drippings from well-done roasts had two types of HCAs. From the three different studies, it can be suggested that roasting of meat (chicken, duck, and beef) generates less amount of HCAs compared to other methods.

In recent days, people consume more ready-to-eat food due to lack of time. Puangsombat et al. (2011) assessed HCAs level in some ready-to-eat products. They found that HCAs were higher in rotisserie chicken skin. In the other assessed food, HCA level was found in the order as follows: rotisserie chicken meat, deli meat products, and pepperoni. However, it has been reported that commercially cooked meats and restaurant meats contain low amounts of HCAs.

Plant Derived Food Processing and MRPs

Consumption of diets rich in fruits and vegetables renders many health benefits to us. However, processing method plays an important role in dictating the magnitude of the beneficial health effects obtained from fruits and vegetables. Depending on treatment temperature, furoylmethyl derivatives (FM) have been found in processed vegetables and fruits like orange juices and processed tomato products and also in dehydrated carrots. It has been shown that dehydrated carrot contains significantly high amount of FM compared to carrot juices, baby carrot, or tinned carrot. It is suggested that processing time during the heat treatment plays an important role for FM formation. Dueik and Bouchon (2011) have reported that, by vacuum frying of carrot chips, potato and apple slices can help to retain their total carotenoids and ascorbic acid levels significantly.

When vegetables are treated at low temperature, prooxidants are generated, whereas treating at high temperature decreases the prooxidants and increases antioxidant properties due to the production of MRPs. Such antioxidant activity of the MRPs comes from the high molecular weight brown compounds that are formed in the advanced stages of the reaction. However, it should be mentioned here that MRPs can also exhibit prooxidant properties.

MRPs can prevent the enzymatic browning reaction caused by polyphenol oxidase (PPO). Plant derived products, such as fruits and vegetables, produce many endogenous phenolic compounds during postharvest handling and processing. These compounds are oxidized by oxidoreductase enzymes like polyphenoloxidases (PPOs) and tyrosinases. This reaction, in turn, generates highly reactive quinonic compounds that are condensed and polymerized to produce brown pigments and thereby decreases the quality of the food product. MRPs can prevent this enzymatic process at the initial step of this reaction and thereby help to maintain the product quality. Besides antibrowning, MRPs has also been shown to render antiallergenic property for cherry derived allergens.

Some Other Impacts of MRP-Derived Food

Angiotensin-I converting enzyme (ACE) is the regulatory enzyme for upregulation of blood pressure. ACE inhibitory peptide lowers blood pressure by inhibiting ACE enzyme. Rufián-Henares and Morales (2007) have demonstrated that the melanoidins isolated from seven amino acid-glucose model systems were all shown to cause inhibition of ACE in vitro. Recently, Hong and colleagues (2014) have shown that, under the appropriate conditions, Maillard reaction can effectively improve the ACE inhibitory activity of casein hydrolysate.

It has been claimed that administration of a Maillard browning reaction product obtained from an extract of Panax species plant comprising ginsenoside Re or ginsenoside-derived saccharide treated with amino acid at temperatures between 100 and 130°C can either prevent, improve, or treat a renal disease.

Food derived versatile MRPs can act as bactericidal for a wide number of pathogens. For example, aminoreductone can act as a more effective bactericidal for four Pseudomonas aeruginosa isolates, one multidrug-resistant Pseudomonas aeruginosa (MDRP), one Escherichia coli, one methicillin-susceptible Staphylococcus aureus, and one methicillin-resistant Staphylococcus aureus (MRSA) compared to mikacin, ciprofloxacin, imipenem, and levofloxacin. MRPs have also been shown to be effective against yeast.

Conclusion and Perspectives

Maillard reaction products have both positive and negative impacts on health. Diverse MRPs act as antioxidants, bactericidal, antiallergenic, antibrowning, prooxidants, and carcinogens. Most of these properties depend on processing of food. High temperature heating makes some food nutritious, whereas some of the foods lose their nutritional value. Many strategies are employed in the food industries to reduce the production of MRPs. For example, acrylamide has been classified as a probable carcinogen to humans by the International Agency for Research on Cancer. During food preparation at high temperature, acrylamides are formed in many types of foods via Maillard reaction. To reduce the amount of acrylamide, asparaginase has been successfully used in laboratory for potatoes and cereals. It has also been reported that injection of CO2 during extrusion process helps to reduce the level of acrylamide.

This review was aimed at summarizing our current knowledge regarding the changes in food mediated by Maillard reaction during the food processing steps. This may provide useful insights for those related to food processing facilities.

Heat Damage of Soyabean Meal

The matter of product quality is immediately before us when we realize that it can be over-processed.


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