Maillard reaction is an extensively studied, yet unresolved chemical reaction that occurs as a result of application of the heat and during the storage of foods. The formation of advanced glycation end products (AGEs) has been the focus of several investigations recently. These molecules which are formed at the advanced stage of the Maillard reaction, are suspected to be involved in autoimmune diseases in humans. Therefore, understanding to which extent this reaction occurs in foods, is of vital significance. Because of their composition, milk products are ideal media for this reaction, especially when application of heat and prolonged storage are considered. Thus, in this work several chemical approaches to monitor this reaction in an early stage are reviewed. This is mostly done regarding available lysine blockage which takes place in the very beginning of the reaction. The most popular methods and their applications to various products are reviewed. The methods including their modifications are described in detail and their findings are discussed. The present paper provides an insight into the history of the most frequently-used methods and provides an overview on the indicators of the Maillard reaction in the early stage with its focus on milk products and especially milk powders.
The impact of different drying techniques and storage conditions on the formation of carboxymethyl lysine (CML) as an advanced glycation end product (AGE) was investigated in various pilot-scale produced skim milk powders (SMP). CML, an indicator of advanced stages of the Maillard reaction, was analyzed by isotope dilution ESI-LC-MS/MS after drying and at intervals during storage for 200 days. The aim of this study is to increase the awareness that the development of AGEs can be hindered by controlled storage, which is mostly neglected at the domestic level by the consumers. Pilot-scale freeze-dryer, spray-dryer, and drumdryer were utilized for manufacturing SMPs. The storage was designed in such a way that it simulated how an average consumer keeps the dried products at home, specifically after opening the packages and how the products may be exposed to unfavorable conditions. To do so, four storage conditions including two temperatures (20°C, 30°C) and two relative humidities RH (33%, 52%) were studied and CML formation was monitored using LC-MS/MS. Our results show that the spray-dried samples developed two times higher CML after 200 days, compared to the freeze-dried samples, and this value was 1.6 times for the drum-dried samples. Storage at 52% RH developed 9.8-10 times more CML in the samples, in comparison with 33% RH, at the same storage temperature (P < 0.05). Our findings demonstrate that AGEs, molecules suspected to be involved in risks factors for auto-immune diseases, may be formed during storage of SMPs after opening the packages by the consumers.
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