טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentJoubran Yousef
SubjectImpact of the Maillard Reaction on the Antioxidant Capacity
of Bioactive Milk Proteins
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Professor Uri Lesmes
Full Thesis textFull thesis text - English Version


Abstract

Rational food processing offers various possibilities to tailor products for optimized ramifications to human health and well-being. Thermal processing is one of the most widely used unit operations employed to transform food and release its nutritional value. Such operations may result in chemical changes via a complex series of reactions termed the Maillard reaction in which protein and carbohydrates may cross-react and alter protein functionality. These reactions are greatly accelerated by heat and don’t require extraneous chemicals; hence, the Maillard reaction is probably the most promising approach to enhance protein alimentary value for food purposes. Nevertheless, gaps exist in understanding of the underlying principles, which can be applied to harness the Maillard reaction to improve protein functionality and digestibility. This study demonstrates a link between thermal processing conditions, protein structure and functionality of Maillard reaction products (MRPs) produced from lactoferrin and alpha-lactalbumin with the monosaccharaides: glucose, fructose and galactose.

MRPs were produced by either controlled heating of powders (79 %RH, ‘dry’ reaction) or solutions ('wet' reaction) for different heating durations and using 1:1 and 1:3 monosaccharide: protein mole ratios. Mean colloidal size at (3<pH<10) showed decreased colloidal stability of MRPs following conjugation, particularly around the protein’s pI. Protein structure determined by Fourier transform infrared spectroscopy and circular dichroism, indicated a slight change due to glycation. Surface hydrophobicity was evaluated by drop shape analysis and fluorescent probe and revealed that protein surface hydrophobicity significantly increased following glycation up to H0 value of 1.1*107 and depended on carbohydrate reactivity (glucose > fructose (‘dry’), fructose > glucose (‘wet’)). The antioxidant capacity (AOC) measurements demonstrated an overall glycation increase in AOC up to tenfold in LF and 27 times in α-la with aldehydes exhibiting on average 4 times larger AOC than fructose conjugates. Next, digestion and AOC of peptides were studied throughout in-vitro gastro-duodenal of adult and infant digestion and monitored using Sodium dodecyl sulfate polyacrylamide gel electrophoresis and antioxidant evaluation. Experiments demonstrated ‘dry’ fructose conjugates resisted 4 hours of digestion while aldehyde conjugates degraded before entering the duodenum. However, fructose ‘wet’ conjugates rendered MRPs more liable to enzymatic than glucose conjugates. Throughout digestion, the AOC of glycated digesta quadrupled following glycation. Further in depth proteomic analysis revealed the extensive breakdown during duodenal digestion were the quantity of liberate peptides doubled compared to the end of the gastric phase with galactose based conjugates releasing the highest amount of peptides at both phases. Ultimately, these differences could stem from multiple governing factors such as carbonyl electrophilicity, mutarotation speed and carbohydrate selectivity, which may affect reactivity and glycation sites; thus, alter protein’s conformation and digestion.

In conclusion, this study establishes a link between process parameters and functionality of MRPs with a unique look into their behavior during digestion. Results obtained demonstrated that varying processing parameters and physical state of reactants alters the hydrophobicity, conformation and enhances the AOC of MRPs. Overall, these results demonstrate the Maillard reaction may be harnessed to modulate protein functionality and delineate beneficial health outcomes through controlling the digestibility of bioactive proteins.