Modelling the formation of heat-induced contaminants during thermal processing of food

Many of our food products have undergone a heat-treatment before consumption, either at home or at the food industry. Heat treatments not only bring out desired characteristics of the food products such as flavour, texture, taste and safety aspects but also leads to the formation of undesired compounds that may have negative impacts for human health. Such undesired compounds that are generated from the Maillard reaction are neo-formed food contaminants (NFC). NFC are present in many common heat-processed foods, such as potatoes-based products, cereal-based products, baby foods, and dairy products. Therefore, effective mitigation measures are being developed to minimize the generation of such undesired compounds while maintaining the organoleptic attributes of the food products as consumer’s demands. This thesis aimed at understanding the mechanistic pathways for the formation of three neo-formed food contaminants: acrylamide, 5-hydroxymethylfurfural (HMF), and NƐ-(carboxymethyl)lysine (CML), using multireponse kinetic modelling. First, the topic of the Maillard reaction, occurrence and human exposure to the three NFC in heated foods, and multiresponse kinetic modelling is introduced. Then, scientific literature on analytical methods, formation pathways, occurrence in processed foods, and health impacts of CML was reviewed. Based on the literature, an experiment was set up to understand the formation pathway for CML in caseinate-lactose/glucose solutions, each heated at 120oC and 130oC. According to the best fitting mechanistic model, the formation of CML in the two model solutions originated from the reaction between lactose/glucose and lysine residues via the Amadori rearrangement product formation. Moreover, glucose and lactose were degraded via Lobry de Bruyn-Alberda van Ekenstein (LA) arrangement. CML seems to be not thermally stable, and may thus not be an optimal indicator for heat damage of foods. Another experiment was done for gaining insights into the formation of acrylamide and HMF in biscuits during baking at 200oC. Four biscuit recipes were prepared with three sugar types: (1) sucrose (35 g), (2) glucose (17.5 g) and fructose (17.5 g), (3) fructose (17.5 g), and (4) glucose. The molar ratio of total glucose and fructose to asparagine in each type of biscuit was higher than 1. The concentrations of acrylamide and HMF were lowest in the sucrose-prepared biscuits. Kinetic modelling results suggested that during baking of these four kinds of biscuits, acrylamide was formed via the specific amino acid route, i.e., a reducing sugar reacts with asparagine to form the Schiff base without the Amadori product formation (not via Strecker degradation), and that HMF was formed via caramelisation. Fructose played a key role in the formation of both acrylamide and HMF. In a similar experiment, the effects of different types of wheat flour on acrylamide and HMF formation in sucrose-prepared biscuits during baking at 200oC were investigated. Four types of wheat flour, which had the most different concentrations of asparagine, and total glucose and fructose (the reducing sugar), were selected for the preparation of four kinds of biscuits. Out of four wheat flour types, two had the molar ratio of reducing sugars to asparagine lower than 1, and the other two had a ratio higher than 1. Results showed that those different molar ratios in wheat flour did not have effects on the pathways leading to the formation of acrylamide and HMF in all four types of biscuits. Acrylamide was formed via the specific amino acid route, and HMF was formed via caramelisation. No clear correlation was found between the concentration of either acrylamide or HMF in biscuits and the concentration of asparagine or the reducing sugars in wheat flour. Asparagine was not a limiting factor for acrylamide generation in biscuits. The outcomes of this thesis give insights into the actual reaction pathways for the formation of acrylamide and HMF in biscuits during baking at 200oC and for the formation of CML in the model solutions. These modelling results may help to control the formation of these NFCs in a quantitative way.