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B16-P: EFFECTS OF PROCESSING CONDITIONS ON AVAILABLE LYSINE CONTENT
AND THE FORMATION OF HEAT-INDUCED CONTAMINANTS IN SOYBEAN PRODUCTS

S. Žilić, I. Božović

Maize Researach Institute “Zemun Polje”, Slobodana Bajića 1, Belgrade-Zemun, Serbia

 

One of the most important objectives of the food industry is to develop safe and healthy products for the customers. Heat-induced food contaminants have attracted attention of both the scientific community and the public in recent years. The presence of substances considered possibly or probably carcinogenic to humans has triggered an extensive debate on the healthiness of even staple foods. In that respect, acrylamide, furan and chloropropanols are the main substances of concern. The occurrence of chloropropanols and furan in food has been known since the late 1970s, whereas acrylamide was detected in food only a few years ago [1, 2]. Since its discovery in food, acrylamide has nearly become a synonym for heat-induced food contaminants. The International Agency for Research on Cancer (IARC) classified acrylamide as probably carcinogenic to humans (group 2A) [3]. There is no doubt that most laboratories working in the field of acrylamide analysis in food apply one of the following three, briefly outlined methods. These are based on liquid chromatography–tandem mass spectroscopy (LCMS/MS) or gas chromatography–mass spectroscopy (GCMS) either with or without derivatization of acrylamide. A different approach for the determination of acrylamide in food was chosen by Gökmen et al., [4] and Paleologos and Kontominas, [5]. Acrylamide in foods largely results from the Maillard reaction between amino acids (primarily asparagine) and a reactive carbonyl (e.g., glucose and fructose), proceeding through intermediates that include a Schiff’s base [6]. Other amino acids producing low amounts of acrylamide include alanine, arginine, aspartic acid, cysteine, glutamine, methionine, threonine, and valine [7]. In this study we used the changes of available lysine content as an indicator of food quality changes due to Maillard reaction influenced by heat processing treatments of soybean kernel. Namely, lysine has highly reactive ε-amino group which reacts mainly with reducing sugars through the Maillard reaction, also known as nonenzymatic glycosylation or nonenzymatic browning. Low molecular compounds developed by the reaction of glucose with lysine have an exceptionally important role in the formation of flavour, aroma, colour and texture, which furthermore even more reduce a nutritional value of food. The obtained results point that the changes in available lysine content could be used as indicator of the degree of chemical changes due to thermal treatment, with possible correlation with the content of toxic and carcinogenic compounds produced in the Maillard reaction. Several factors, such as the initial concentration of reactants and their ratio, temperature and time of processing, and pH and water activity, have been shown to influence the content of available lysine, as well as, the levels of food contaminants in heat-processed foods. Higher temperatures during processes of micronization and microwave roasting caused a very pronounced reduction of lysine availability and dark, almost black color of soy products. the drop of the available lysine content after soybean kernel micronization at 150oC ranged from 21.5% to 44.7% and from 35% to 40% after five-minute kernel microwave roasting. As the Maillard reaction is a type of redox reactions, dry extrusion and autoclaving proceeding within the closed systems within which the higher relative humidity has a special effect by blocking the access of air oxygen, caused a significantly lesser changes in the content of available lysine.

References

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2. Swedish National Food Administration, http://www.slv.se, 2002.
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