Rikke Susanne Vingborg Hedegaard

Oxidative stability of buttermilk as influenced by the fatty acid composition of cows' milk manipulated by diet

Milk from cows fed a low-fat diet high in cereals designed to stimulate fat synthesis de novo was lower in unsaturated fatty acids (21.3%) than milk from cows fed a diet high in fat, mainly from roasted soy beans (41.3% unsaturated fatty acids). Buttermilk from the more unsaturated milk was less oxidatively stable during storage (at 4 degrees C, followed for 11 d) than buttermilk from the more saturated milk, as monitored both by primary lipid oxidation products (lipid hydroperoxides) and by the secondary lipid oxidation product, hexanal. Fat-soluble antioxidants, beta-carotene and alpha-tocopherol, analysed by HPLC, were not consumed during storage for either of the two types of buttermilk. In contrast, the antioxidative capacity of the serum phase decreased during storage as evaluated in a radical scavenging assay based on the semi-stable water-soluble radical nitrosodisulphonate (Fremys salt). The time course for the decrease in water-soluble antioxidants was very similar for the two types of buttermilk suggesting that oxidation is initiated in the serum phase independently of fatty acid composition.

Kinetics of formation of acrylamide and Schiff base intermediates from asparagine and glucose

From the concentration of glucose and asparagine as reactants and of acrylamide as product each determined by LC-MS during reaction in an acetonitrile/water (68:32) model system at pH 7.6 (0.04M phosphate buffer) and from the relative concentration of the Schiff base intermediate, the decarboxylated Schiff base intermediate, the Amadori product and aminopropionamide determined in the same reaction mixtures at 120°C, 140°C, 160°C and 180°C for up to 16min, the energy of activation for formation of the Schiff base intermediate was found to have the value 50±2kJmol(-1), while the apparent activation energy for formation of acrylamide was 64.4±0.6kJmol(-1), for formation of the decarboxylated Schiff base intermediate 92±2kJmol(-1), and for formation of the Amadori compound 59±4kJmol(-1), respectively. At high temperature conditions, formation of the Schiff base is accordingly rate determining, while at lower temperatures, decarboxylation becomes rate determining. Aminopropionamide was only detected at reaction times at which acrylamide formation already is significant in favor of, a reaction path including direct formation of acrylamide from the decarboxylated Schiff base, rather than including dissociation of ammonia from aminopropionamide.

Acrylamide–asparagine relationship in baked/toasted wheat and rye breads

Acrylamide in baked and toasted wheat and rye bread was studied in relation to levels of asparagine in flour, dough, bread and toasts. Asparagine was consumed during bread preparation resulting in reduced acrylamide content in the products. In wheat bread, 12% of the asparagine initially present in the flour (0.14 g kg−1) remained after yeast fermentation and baking; for rye bread, 82% of asparagine remained after sourdough fermentation and baking. Asparagine present in untoasted wheat bread had totally reacted after hard toasting. Toasted wheat and rye bread slices contained 11–161 and 27–205 µg kg−1 acrylamide, respectively, compared to untoasted wheat and rye bread with <5 and 7–23 µg kg−1 acrylamide, respectively. The dietary intake of acrylamide from bread (untoasted) of 2 µg day−1 is relatively low; however, acrylamide exposure from bread increases several fold for people eating toasted bread.

Short-term effects of dietary advanced glycation end products in rats

Dietary advanced glycation end products (AGE) formed during heating of food have gained interest as potential nutritional toxins with adverse effects on inflammation and glucose metabolism. In the present study, we investigated the short-term effects of high and low molecular weight (HMW and LMW) dietary AGE on insulin sensitivity, expression of the receptor for AGE (RAGE), the AGE receptor 1 (AGER1) and TNF-α, F2-isoprostaglandins, body composition and food intake. For 2 weeks, thirty-six Sprague-Dawley rats were fed a diet containing 20% milk powder with different proportions of this being given as heated milk powder (0, 40 or 100%), either native (HMW) or hydrolysed (LMW). Gene expression of RAGE and AGER1 in whole blood increased in the group receiving a high AGE LMW diet, which also had the highest urinary excretion of the AGE, methylglyoxal-derived hydroimidazolone 1 (MG-H1). Urinary excretion of N ε-carboxymethyl-lysine increased with increasing proportion of heat-treated milk powder in the HMW and LMW diets but was unrelated to gene expression. There was no difference in insulin sensitivity, F2-isoprostaglandins, food intake, water intake, body weight or body composition between the groups. In conclusion, RAGE and AGER1 expression can be influenced by a high AGE diet after only 2 weeks in proportion to MG-H1 excretion. No other short-term effects were observed.

Quantification of radicals formed during heating of β-lactoglobulin with glucose in aqueous ethanol

Heating β-lactoglobulin alone, or in the presence of glucose, at moderately elevated temperatures (50, 70 and 80°C) in 30% aqueous ethanol at pH 6.0, 7.0 and 8.0 led to an iron catalysed formation of highly reactive radicals at concentrations of up to 1.0 mmol/mol protein as trapped by α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN) and quantified by ESR spectroscopy. Oxidation of β-lactoglobulin was favoured by increasing temperature and high pH conditions, whereas presence of glucose decreased oxidation, indicating that oxidation of β-lactoglobulin involves either amine or thiol side chain group blocked as oxidation substrate by reaction with glucose as a reducing sugar. The oxidation of β-lactoglobulin was hampered by the phenolic antioxidant 4-methylcatechol and to an even larger extent by the oxidised quinone form 4-methyl-1,2-benzoquinone, suggesting that it is the quinone forms of phenolic antioxidants which compete with reducing sugars in protecting proteins against oxidation.

Formation of Advanced Glycation End Products (AGEs) are Influenced by Lipids in Milk Powders

Advanced glycation end products (AGEs) were determined by a polyclonal ELISA method in three milk powders of varying lipid content, during storage in sealed containers at 65°C for up to 20 days. AGEs content correlated with increased water activity (aw), decreased glass transition temperature (Tg), increased lactose crystallisation, and browning in the three milk powders. Formation of stable radicals as detected by electron spin resonance spectroscopy correlated with crystallisation of lactose and brown discoloration in the three powders indicating origin from Maillard reactions rather than lipid oxidation. AGEs content was greatest in whole milk powder with highest lipid content, while in butter milk powder formation of secondary lipid oxidation products increased faster as determined by thiobarbituric acid reactive substances.

Formation of radicals during heating lysine and glucose in solution with an intermediate water activity.

Abstract Heating glucose with lysine under alkaline conditions (pH 7.0–10.0) was found to take place with consumption of oxygen together with formation of brown-colored compounds. Highly reactive intermediary radicals were detected when lysine and glucose were heated at intermediate water activity at pH 7.0 and 8.0. The detection was based on initial trapping of highly reactive radicals by ethanol followed by spin trapping of 1-hydroxyethylradicals with α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN) and Electron Spin Resonance (ESR) spectroscopy. The generation of reactive intermediary radicals from the Maillard reactions was favored by enhancing alkaline conditions (pH 8.0) and stimulated by presence of the transition metal ion Fe2+. The stability of the nitrone spin traps, N-tert-butyl-α-phenylnitrone and POBN was examined in buffered aqueous solutions within the pH range 1–12, and found to be less temperature dependent at acidic pH compared to alkaline conditions. A low rate (kobs) of hydrolysis of POBN was found at the used experimental conditions of 70°C and pH 7.0 and 8.0, which made this spin trap method suitable for the detection of radicals in the Maillard reaction system.

Palatability and chemical safety of apple juice fortified with pomegranate peel extract

Pomegranate peel extract (PPE), a by-product of the pomegranate juice industry with potential health effects, was explored for use to fortify reconstituted apple juice in the concentration range 0.5 to 2.0% (w/w). Radical scavenging and antioxidative capacities of the fortified apple juices were evaluated using (i) electron spin resonance (ESR) to quantify their ability to scavenge the stable radical Fremys salt and (ii) the Trolox equivalent antioxidant capacity (TEAC) assay and compared to apple juice without fortification as control. The highest antioxidative capacity was found in the apple juice fortified with the highest percentage of pomegranate peel extract, while the optimal sensory quality was found by addition of 0.5 g PPE per 100 mL. The Artemia salina assay was used as a fast screening method for evaluating overall toxicity, and showed little toxicity with up to 1.0 g per 100 mL addition of PPE, but increasing toxicity at higher concentrations. Accordingly, it is important to balance addition of PPE, when used for enrichment of apple juice in order to obtain a healthier product, without compromising the sensorial quality or toxicological safety of the apple juice. Concentrations between 0.5 and 1.0 g PPE per 100 mL seem to be acceptable.

Effect of plant polyphenols on the formation of advanced glycation end products from β-lactoglobulin

Dietary exposure to advanced glycation end products (AGEs) formed from proteins and reducing sugars is of increasing concern to human health. AGEs may form in protein-based powders containing sugars for instant beverages during drying and storage of the product. Chlorogenic acid, a plant phenol characteristic of coffee, was found to protect against the formation of AGEs at a concentration of 50mM during heating of β-lactoglobulin in the presence of glucose as a reducing sugar in 30% aqueous ethanol at 70°C. Epicatechin, a plant phenol characteristic of green tea, had no similar effect for the equivalent concentration of phenol on the formation of AGEs. Immunochemical detection (ELISA) using polyclonal antibodies raised against AGEs showed a dose-dependent effect of protection by chlorogenic acid on AGE formation and is recommended for routine quality control of sugar containing milk-based powders for instant beverages.

Free Radical Processes in Non-enzymatic Browning of Glucose and Lysine: Influence of Temperature and Unsaturated Lipids

Formation of dialkylpyrazinium radical cations in aerated 70 % aqueous glycerol solutions of glucose and lysine during heating resulting in browning (90, 110, and 130°C, investigated) was more dependent on temperature than formation of brown colour. Activation energy (Ea) for radical formation was ~83 kJ mol–1, compared with ~70 kJ mol–1 for browning, and was unaffected by methyl linolenate. Low-temperature browning was influenced by non-radical degradation of Amadori products, whereas radical processes were prominent at higher temperatures and were unaffected by unsaturated lipids. In contrast, methyl linolenate reacts with lysine in the absence of glucose to form fluorescent products at a slow rate (Ea 25 kJ mol–1). Glucose increased the rate of formation of fluorescent products (Ea ~60 kJ mol–1), in agreement with Maillard reactions at low temperatures involving glucose as a rate-determining reagent. Lipid oxidation does not have a direct effect on lysine and glucose browning reactions at conditions relevant for food; effects of lipids on Maillard reactions are matrix-related.