Investigation Of The Reactivities Of Monomeric And Polymeric Components In Some Foods In Digestion Conditions In Vitro

Abstract

After foods have entered the digestive tract, they are exposed to various changes as a result of varying pH and enzymatic conditions. The changes in food components during digestion are of importance. Thermal process contaminants are the monomeric compounds that exert various harmful effects on health and are formed during thermal treatment in foods. These toxic compounds are found in most of thermally processed foods and enters the body within consumption of these foods. However, after being ingested, it is expected that these compounds will undergo chemical changes under digestion conditions as in the case of other food components. Due to their health concern, to determine the changes they are exposed to is an important issue. Besides, carbohydrates are the main energy sources in human nutrition. One of the complex carbohydrates having polymeric structure is starch and constitutes to several grain-based foods. Since consumption of these foods is related with many chronic diseases, to investigate the fate of this polymeric food component during digestion and factors affecting their digestion behaviour is another important point. The aim of this PhD thesis is the investigation of the fate of these food components and their possible reactions during digestion. To achieve the aim, simulated in vitro digestion procedure was used; both model and actual food systems were submitted to digestive process.In the first part, bakery and fried potato products were tested to understand the fate of acrylamide during in vitro multi-step enzymatic digestion system. At the end of digestion, acrylamide decreased in biscuits and it was confirmed in model systems that this was due to Michael addition of amino acids to acrylamide during digestion. In contrast to bakery products, acrylamide levels increased during gastric digestion of fried potatoes. The results exhibited that intermediates like Schiff base accumulated in potatoes during frying are potential precursors of acrylamide under gastric conditions. Similarly, interactions of reactive α-dicarbonyl compounds, particularly methylglyoxal (MGO) and 3-deoxyglucosone (3-DG), and HMF during in vitro digestion process were investigated in commercial biscuits. MGO and 3-DG concentrations decreased under intestinal digestion conditions. Results of the model systems composed of MGO and lysine, cysteine or ovalbumin and model biscuits containing lysine, cysteine or ovalbumin revealed that disappearance in dicarbonyl contents was due to interactions of reactive dicarbonyl compounds with the accumulating amino acids during digestive process. On the other hand, HMF contents of biscuits increased during gastric phase. It was confirmed that sugar degradation products such as 3-DG and 3,4- dideoxyglucosone (3,4-DG) accumulated in biscuits during baking were converted to HMF under gastric conditions. However, reactions of HMF with amino acids proceeded with the progress of digestion leading to a significant decrease in the concentrations of HMF during intestinal phases. High-resolution mass spectrometry (HRMS) analysis in both HMF-amino acid model systems and in biscuits confirmed that HMF reacted with amino and sulfhydryl groups through Michael type addition and Schiff base formation. Following the reactions of HMF with amino and sulfhydryl compounds during digestion, reactions of HMF with selected amino acids (arginine, cysteine and lysine) were investigated in HMF- amino acid (high moisture) and Coffee-amino acid (low moisture) model systems at 5, 25 and 50oC. The results presented that HMF reacted efficiently and effectively with amino acids in both high and low moisture model systems. From the kinetic evaluation of these reactions, cysteine was determined as the most reactive amino acid towards HMF owing to its thiol group. As the tendency of cysteine for the reactions with acrylamide and HMF was considered, cysteine was found as effective in reacting with carbonyl compounds. Thus, different sulphur sources were additionally examined for their scavenging abilities of an α-dicarbonyl compound, glyoxal (GO) in various model systems under simulated physiological conditions (37oC & 7.4 pH, 2 hours). The results presented that some of these sulphur sources could scavenge GO under these conditions. Potassium metabisulphite and cysteine was found to be effective in GO scavenging, however, methionine could not scavenge GO. The results of the extracts of digested raw, steamed and boiled broccoli sprouts and wine indicated that GO was scavenged by these foods. In the second part, effect of cooking treatment, different shapes and sizes on digestibility of polymeric component, starch was determined. Baking and frying was compared as cooking treatments and potatoes were cut into thick strip, thin strip, cube, and disk shapes prior to cooking. Cooked potatoes were subjected to in vitro digestion to determine their nutritionally important starch contents (rapidly, slowly digestible and available starch). Frying and baking differed on available starch formation in potatoes for all shapes and sizes. The amounts of different digestible starch fractions were correlated with surface-to-volume ratio. The results suggested that the surface-to-volume ratio could be a potential factor on controlling different digestible starch contents of cooked potatoes. Additionally, the effect of consumption of other foods together with potato on digestibility of potato starch was examined in different binary and ternary systems of baked potato with olive oil, wine, wheat bran or meat. The results of binary systems showed that consumption of potato together with olive oil, wine, wheat bran or meat caused to significant decrease in amylolytic hydrolysis. Wine could amount to the highest inhibition in digestibility of potato and it was followed by olive oil, wheat bran and meat. Lastly, more inhibition was observed in ternary combinations of these foods.