Loss Of Lysine Research Articles

The FAST method, a rapid approach of the nutritional quality of heat-treated foods.

The FAST method is based on the determination of maximal fluorescence emission when exciting at 330-350 nm, which corresponds to molecular structures formed between reducing sugars or oxidizing lipids and lysine residues of proteins. This fluorescence is dependent on heat treatment and related to protein nutritional loss. Applied to a soluble extract of the food and corrected for the protein concentration of the solution obtained, using Trp fluorescence, the method allows to calculate the FAST index (FI), an indicator of the nutritional damage during heat process. The method, firstly validated on milk samples, is demonstrated here to well correlate with lysine damage on various food products, such as heat-treated milk and breakfast cereals, essentially modified by the Maillard reaction, and roasted soybean or cooked salmon, where interactions between oxidizing lipids and proteins better take place. Independently on the food product or the type of heat process, the FAST index appears always well correlated (r2: 0.84-0.98) to the lysine loss, the latter being estimated by determination of acid-released lysine, fluorescamine-reactive lysine or infrared. Shortly, roasted corn flakes appeared to be more damaged than extrudated flour (FI 100 and lysine blockage 40% instead of 55 and 30%), condensed milk more than UHT milk (FI 150 and 85% of acid-released lysine instead of 80 and 94%), and steam-cooked salmon much less than pan-fried (FI 28 instead of 372). Roasted soy can reach FI of more than 300 corresponding to chemical lysine loss of 40% and poultry-digestive lysine loss of 100%. As a conclusion, the FAST method, once precisely calibrated with pertinent nutritional indicators, should be of great interest for controlling or adapting a process in order to ensure a better nutritional quality for the food product.

Influence of Dietary Protein Level and Origin on the Flow of Mucin Along the Small Intestine of the Preruminant Calf

The objective of this study was to investigate the effect of the dietary crude protein (CP) content and origin on the flow of mucin protein along the small intestine of the preruminant calf. Diets contained 1, 10, 20 and 28% of CP supplied by skim milk powder (SMP) in experiment 1. Diets differed by the nature of protein [soybean protein concentrate (SPC), partially hydrolyzed soybean protein isolate (HSPI) or potato protein concentrate (PPC)] in experiment 2. Duodenal, jejunal, and ileal digesta were collected from calves fitted with simple cannulae and continuously infused the milk replacers into the abomasum. In experiment 1, the basal flow of mucin protein was 1.1, 1.8, and 4.0 g/kg of dry matter intake at the duodenum, jejunum, and ileum, respectively. Mucin protein contributed to 19 and 40% of ileal loss of CP and lysine, respectively. When dietary CP rose from 1 to 28%, the flow of mucin protein increased at the duodenum (+300%). In experiment 2, the flow of mucin protein increased by 70% at the duodenum and at the jejunum when SMP was partially replaced by SPC and HSPI. With PPC, this flow increased at the duodenum (+24%) and ileum (+52%). These data demonstrate the importance of mucin as a source of endogenous nitrogen and the impact of dietary protein content and origin on this flow.

Contribution of Microbial Amino Acids to Amino Acid Homeostasis of the Host

Among the reasons suggested for the discrepancy between N balance and tracer-derived indispensable amino acid (IAA) requirement estimates is the possibility that the metabolic requirement is met not only by the diet but also by IAA synthesized de novo by the gastrointestinal microflora, which are then absorbed. It is therefore crucial to better understand and quantify the microbial biosynthesis of amino acids in the human gastrointestinal tract and its potential role in providing IAA to meet human amino acid requirement. Here, the available evidence on the contribution of microbial amino acids to the host's amino acid homeostasis, applying the (15)N labeling paradigm, is summarized. Between 1 and 20% of circulating plasma lysine, urinary lysine and body protein lysine of the host, respectively, is derived from intestinal microbial sources and corresponds to a gross microbial lysine contribution of 11-68 mg. kg(-1). d(-1) in adult humans with an adequate protein intake when fecal or ileal microbial lysine enrichment is used as precursor. Factors affecting estimates of net microbial IAA contribution are discussed. It appears that the small intestine is responsible for a large part of microbial lysine uptake, although some absorption from the large intestine cannot be excluded. Nonoxidative lysine losses from the human gastrointestinal tract, which were found to be between 3.9 to 8.5 mg. kg(-1). d(-1), are necessary to estimate the net contribution of microbial IAA. It is reasonable to assume that microbial amino acid synthesis in the human gastrointestinal tract utilizes a mixture of various nitrogen sources, i.e., endogenous amino acids, urea and ammonia. Microbes in the small intestine may rely more on endogenous amino acids. Deprivation of nutrients, the intake of certain dietary nonstarch oligosaccharides, lipids, as well as protein intake level and source and level of consumption of certain amino acids can affect the composition and metabolic activity of the intestinal microflora and thus its fermentation products potentially available to the host. In conclusion, with the use of the (15)N labeling paradigm, a significant contribution of microbial lysine to the host lysine homeostasis is found. However, to assess the net contribution of microbial IAA and its importance in defining the adult IAA requirement, this is not the ultimately successful experimental strategy because the interpretation of results is complicated by the nitrogen recycling in the gut, the uncertainty of the precursor pool of absorption and the limited data on nonoxidative IAA losses from the human gastrointestinal tract.

Modification of bovine serum albumin structure following reaction with 4,5(E)-epoxy-2(E)-heptenal.

Bovine serum albumin (BSA) was incubated for different periods of time and in the presence of several concentrations of 4, 5(E)-epoxy-2(E)-heptenal, at pH 7.4 and 37 degrees C, in an effort to analyze the changes produced in its structure as a consequence of its reaction with this product of lipid oxidation. The epoxyalkenal modified the primary structure of BSA as determined by lysine losses and formation of oxidative stress product epsilon-N-pyrrolylnorleucine (Pnl), which depended on the concentration of the aldehyde and the incubation time. These changes also modified secondary and tertiary structures of the protein, which were determined by studying protein denaturation and polymerization. In addition, all these modifications were parallel to the development of color and fluorescence, which were produced as a consequence of the formation and polymerization of pyrrole amino acid residues. The above results indicated that epoxyalkenals modify the protein structure and develop color and fluorescence. A failure in the degradation of these modified proteins might induce their accumulation and, thus, participation in lipofuscin or age pigments formation.

Effects of thermal processing and storage on available lysine and furfural compounds contents of infant formulas.

The Maillard reaction-related effects that thermal treatments during the manufacturing process and storage (at 20 and 37 degrees C) have on powdered adapted and follow-up milk-based infant formulas were estimated by measuring the available lysine and furfural compounds contents of raw cow milk used in manufacturing, intermediate products and formulas. A fluorimetric method was used to measure the available lysine contents, and free and total furfural compounds were determined by HPLC. Statistically significant losses in available lysine (about 20%) in the infant formulas with respect to raw milk were found. The storage period did not affect the available lysine contents of adapted formulas but reduced (16%) the contents of the follow-up ones (from 6.61 to 5.33 g/100 g of protein). No furfural compounds were detected in raw milk, and free and total furyl methyl ketone (FMC) and methylfurfural (MF) were not observed in the analyzed samples. After 6 months of storage, an increase in free hydroxymethylfurfural (HMF) (from 0.34 to 0.77 mg/100 g of protein) and furfural (F) (from nondetectable to 0.1 mg/100 g of protein) in adapted formulas and free HMF (from 1.84 to 2.62 mg/100 g of protein) in follow-up formulas was observed.

Human apo-lipoprotein B from normal plasma contains oxidised peptides

Oxidation of low density lipoprotein (LDL) may be atherogenic, but radical-initiated oxidation of its apoprotein B-100 (apoB) has been little studied. Transition metal ions iron and copper are candidates for mediating radical oxidation of LDL in vivo. Therefore, we studied the copper-ion-induced oxidation of apoB in human LDL. Using HPLC methods developed in our recent work, we studied the destruction of native and the generation of six oxidised amino acids; we also assessed the release of peptides from the LDL particle by FPLC. We observed time-dependent losses of apoB histidine, lysine and glycine. Long-lived reactive species, the reductant DOPA, and the oxidant hydroperoxides of valine and leucine (measured as hydroxides after reduction), were generated. Their relative abundance (mol/mol of parent amino acid) was DOPA> o- and m-tyrosine>dityrosine, valine-hydroxides, leucine hydroxides. Low molecular weight fragments were also released from the LDL in a time-dependent manner, contained hydroperoxides sensitive to GSH peroxidase, and generated radicals on reaction with iron–EDTA. The fragments contained peptides active in the quinone redox cycling procedure, comprising 0.25% of the supplied LDL amino acids. Characteristic peptides were present in each FPLC fraction containing the fragments, as judged by further HPLC fractionation. Some fragments were present in the unoxidised LDL preparations, and when these were largely removed by FPLC, copper oxidation could still generate fragments, suggesting that those present in the starting material might indicate prior oxidation. Concordantly, we found that fresh plasma LDL apoB contained ∼3% of total plasma protein-bound oxidised amino acids, and with the same relative abundance. We conclude that plasma proteins including apoB are subject to physiological oxidation, similar to that inflicted by copper ions; the latter may contribute to intimal LDL oxidation, which could be the source of oxidised plasma apoB.

Blockage of available lysine at different stages of infant cereal production

Determination of available lysine was used to assess the heat damage produced during the processing of cereals for infant foods. The infant cereals analysed were: wheat, 7 and 8 cereals, rice, rice–corn, rice–corn–soy and oat. Lysine losses during the toasting of flours ranged between 14 and 29%. Roller-drying treatment caused considerable heat damage, with a 53% decrease of available lysine in roller-dried rice–corn–soy. However, oat flour was less susceptible, with a 5% reduction in available lysine during roller-drying. © 1999 Society of Chemical Industry

Disruption of the KEX1 gene in Pichia pastoris allows expression of full-length murine and human endostatin.

Endostatin is a potent angiogenesis inhibitor. In order to isolate sufficient quantities of soluble protein for in vivo studies in mice, we expressed murine endostatin in Pichia pastoris. Analysis of the expressed protein by mass spectrometry indicated that the protein was truncated. N-terminal sequence analysis determined that the N-terminus was intact, suggesting that the C-terminal lysine was missing. In Saccharomyces cerevisiae, Kex1p can cleave lysine and arginine residues from the C-terminus of peptides and proteins. We hypothesized that the KEX1 homologue in P. pastoris is responsible for the loss of the C-terminal lysine of endostatin. To test this hypothesis, we cloned and disrupted the P. pastoris KEX1 gene. Although the overall amino acid identity between the P. pastoris and the S. cerevisae Kex1p is only 36%, the amino acid residues involved in the catalytic activity or close to the active residues are highly conserved. Disruption of the KEX1 reading frame allowed expression of murine and human endostatin with the C-terminal lysine. The KEX1 disruption strain may be a useful tool for the expression of other proteins with a C-terminal basic amino acid. Addition of a lysine to the C-terminus of recombinant proteins may protect the C-terminus from degradation by other carboxypeptidases.

Influence of feeding alkaline/heat processed proteins on growth and protein and mineral status of rats.

Effects of feeding alkaline (0.1 N NaOH) and heat treated (75 degrees C for 3 h) proteins (lactalbumin and soybean protein isolate, SPI) on growth, and protein and mineral status of rats have been determined. The untreated and alkaline/heat treated lactalbumin contained 0.10 and 4.42 g lysinoalanine (LAL)/100 g protein, respectively. Similarly, the untreated and treated SPI contained 0.03 and 1.94 g LAL/100 g protein, respectively. The formation of LAL in the treated proteins was accompanied with a loss of cystine (73-77%), threonine (35-45%), serine (18-30%) and lysine (19-20%). The alkaline/heat treatments caused significant (P < 0.05) reductions in protein digestibility of lactalbumin (99 vs. 73%) and SPI (96 vs. 68%). The processing treatments also caused a drastic negative effect on protein quality, as measured by rat growth methods such as relative protein efficiency ratio (RPER) and relative net protein ratio (RNPR). The RPER and RNPR values of untreated lactalbumin and SPI were 89-91 and 56-64%, respectively. But the RPER and RNPR values of the treated lactalbumin and SPI were 0%. The mineral status of rats was also compromised by feeding alkaline/heat treated proteins. Liver iron levels in male rats (165-180 micrograms/g dry weight) and female rats (306-321 micrograms/g dry weight) fed the treated proteins were about half the levels in male rats (229-257 micrograms/g dry weight) and female rats (578-697 micrograms/g dry weight) fed the untreated proteins. The kidney iron contents of rats fed the treated proteins were also lower than that of rats fed the untreated proteins. Liver copper levels of male and female rats fed the treated proteins were up to three fold higher than those found in rats fed the untreated proteins. The data suggested that LAL, an unnatural amino acid derivative formed during processing of foods, may produce adverse effects on growth, protein digestibility, protein quality and mineral bioavailability and utilization. The antinutritional effects of LAL may be more pronounced in sole-source foods such as infant formulas and formulated liquid diets which have been reported to contain significant amounts (up to 2400 ppm of LAL in the protein) of LAL.

Investigation of the suitability of Western and Southern Cape wheat flour for production of traditional South African steamed bread

Due to a lack of electrical ovens, it is often found that in the households of the lower-income communities, a home-made steamed bread is prepared in a saucepan on a gas cooker or an open fire. The requirements of flour used to produce high-quality steamed bread are poorly defined. The suitability of Western and Southern Cape wheat for steamed bread production was, therefore, investigated. A marked increase in the nutritive value of steamed bread was reported compared to that of conventionally baked bread, mainly due to the loss of available lysine during conventional baking. Samples of three spring wheat cultivars that were produced during the 1995 and 1996 seasons in the Western and Southern Cape were selected. Flour protein content of these samples varied between 8 and 16%. Flour protein content, Falling Number determinations, gluten content, Mixograph, Alveograph and Rheofermentometer measurements and the 10 g baking test were performed on each of the flours. Steamed and conventionally baked breads were prepared for each cultivar at the four selected flour protein levels, respectively. Total bread volume, weight, height and texture, crust and crumb colour and lysine availability were measured for each loaf of bread. None of the Rheofermentometer measurements correlated significantly with flour protein content or any of the analytical and rheological measurements performed on the flour. All the crust colour parameters of conventionally baked bread correlated significantly with flour protein content. Even though significant correlation was observed for three crust colour parameters of steamed bread, the correlation was lower compared to that of conventionally baked bread. At the four different protein levels, more variation was observed in the elasticity of conventionally baked bread compared to the steamed bread, the texture of the steamed bread was finer and firmer and the crumb was more sticky. The browning reaction occurring in conventionally baked bread results in less available lysine than would be the case for steamed bread. In this study, higher availability of lysine was only the case when steamed bread was produced from high protein flour. Western and Southern Cape spring wheat, irrespective of protein content are, therefore, suitable for the production of good quality steamed bread.

Oxidation of Adrenaline by Ferrylmyoglobin

The oxidation of adrenaline by ferrylmyoglobin, the product formed by the oxidation of myoglobin with H 2O 2, was examined by absorption, fluorescence, and EPR spectroscopy in terms of the formation of intermediate free radicals and stable molecular products and the binding of adrenaline oxidation products to the apoprotein. The reaction of adrenaline with ferrylmyoglobin resulted in reduction of the hemoprotein to metmyoglobin and consumption of adrenaline. Quantification of metmyoglobin formed per adrenaline yielded a ratio of 1.66. The reaction was found first order on adrenaline concentration and second order on ferrylmyoglobin concentration. This, together with the above ratio, suggested a mechanism by which two oxoferryl moieties (ferrylmyoglobin) were reduced by adrenaline yielding metmyoglobin and the o-semiquinone state of adrenaline. The decay of the o-semiquinone to adrenochrome was confirmed by an increase in absorbance at 485 nm. The product was nonfluorescent; alkalinization of the reaction mixture resulted in a strong fluorescence at 540 nm ascribed to 3,5,6-trihydroxyindol or adrenolutin. Hence, adrenochrome and its alkali-catalyzed product, adrenolutin, are the major molecular products formed during the oxidation of adrenaline by ferrylmyoglobin. Semiquinones formed during the adrenaline/ferrylmyoglobin interaction were detected by EPR, spin stabilizing these species with Mg 2+. The six-line EPR spectrum observed (a N = 4.5 G, a N(CH 3) = 5.1, and a 2H = 0.91; g = 2.0040) may be assigned to the semiquinone forms of adrenochrome and/or adrenolutin or a composite of these species. The intensity of the EPR signal increased with time and its subsequent decay followed a second-order kinetics as inferred by the proportionality of the square of the EPR line intensity with H 2O 2 concentration. Heme destruction and lysine loss, inherent in the reaction of metmyoglobin with H 2O 2, were prevented 80 and 34% by adrenaline, respectively. The low protection exerted by adrenaline against lysine loss was possibly due to the formation of Schiff bases between the ϵ-NH 2 group of lysine and the o-quinone oxidation product(s) of adrenaline. The yield of Schiff base formation was 20–25%. The autoxidation of adrenaline at physiological pH is extremely slow or nonexistent. These data provide a rationale for the primary oxidation of adrenaline by the pseudoperoxidatic activity of ferrylmyoglobin and suggest implications of the free radicals thereby formed for the oxidative damage in reperfusion injury.

Reducing sugars effect on available lysine loss of casein by moderate heat treatment

In order to investigate the effect of various reducing sugars on the available lysine loss by Maillard reaction, four model systems were prepared by mixing casein with glucose, fructose, lactose or maltose, followed by storage at 37 °C, 50 °C and 60 °C. The available lysine contents were monitored periodically. Highest and lowest reaction rates were observed in the model systems containing glucose and fructose, respectively, at the three temperatures. The two disaccharides behaved very similarly, with reaction rates between those of the monosaccharides studied. The activation energies of glucose, lactose and maltose systems were similar (116–132 kJ mol −1), while that of fructose was somewhat higher (166kJ mol −1). This difference was supposed to be in part due to the different mechanism of tautomerization of fructose, highly dependent on temperature. Therefore, though the potential nutritional damage at moderate temperatures is lower when fructose is used instead of other reducing sugars, its higher activation energy can reverse the effect at higher temperatures.

Influência da secagem à alta temperatura nas características das massas com ovos

Dois processos de alta temperatura foram empregados na secagem de macarrao com ovos e comparados com o processo convencional. Em um dos processos, a temperatura elevada foi aplicada na fase inicial da secagem e no outro, na fase final. Os resultados obtidos mostraram que os produtos secos a alta temperatura apresentaram cor mais clara, maior resistencia a mastigacao e menor gomosidade que o seco pelo processo convencional. Os processos de alta temperatura proporcionaram ainda menor perda de solidos soluveis durante o cozimento. O teor de lisina disponivel de cada massa foi avaliado antes e apos secagem. A alta temperatura, principalmente quando aplicada na fase inicial da secagem, propiciou perdas de lisina disponivel bem superiores as encontradas para o processo convencional. Quanto as analises microbiologicas, os tres processos estudados apresentaram resultados semelhantes.

Maillard Reaction in Milk-Based Foods: Nutritional Consequences

Chemical reactions occurring during industrial treatments or storage of foods can lead to the formation of ε-deoxyketosyl compounds, the Amadori products. Food protein value can be adversely affected by these reactions, and in particular lysine, an essential amino acid having on its side chain a free amino group, can be converted to nonbioavailable N-substituted lysine or blocked lysine. By acid hydrolysis of ε-deoxyketosyl compounds, furosine is formed. In this paper furosine prepared from milk-based commercial products has been evaluated by use of a recently developed HPLC method using a microbore column and phosphate buffer as the mobile phase at controlled temperature. Furosine levels have been used, together with protein, total amino acids, and lysine content, as an estimate of protein quality of a few different products such as cooked-cream dessert, yogurt mousse, white chocolate, milk chocolate, milk chocolate with a soft nougat and caramel center, milk chocolate with a whipped white center, chocolate spread, part-skim milk tablets, milk-based dietetic meals, and baby foods. The protein content of the analyzed products ranged from 34.3g · kg−1 (milk nougat) to 188.4g · kg−1 (milk tablets). The Maillard reaction caused a loss in available lysine that varied from 2.5% (cooked cream) to 36.2% (condensed milk). The contribution to the lysine average daily requirement is heavily affected by this reaction and varied from 13% (milk tablets and soft nougat) to 61% (dietetic meal). Variable results were also obtained for the other essential amino acids.

Free lysine ( l-lysine · HCl) is utilized for growth less efficiently than protein-bound lysine (soybean meal) in practical diets by young channel catfish ( Ictalurus punctatus)

Two 10-week feeding experiments were conducted with channel catfish fingerlings in aquaria to compare the efficiency of utilization for growth of free versus protein bound lysine in practical diets. In experiment 1, a basal, 26% protein diet, deficient only in lysine, was formulated with a combination of peanut meal and corn gluten meal as the primary protein source. The diet was then supplemented with graded levels of lysine by either adding l—lysine · HCl or substituting soybean meal for the peanut meal—corn gluten meal combination to produce two series of diets with increasing concentrations of either free lysine or protein-bound lysine. In experiment 2, the basal diet contained sesame meal as the primary protein source and was supplemented with free or protein-bound lysine as in experiment 1. Slope ratio analysis of response data showed that the efficiency of utilization of protein-bound lysine in soybean meal relative to free lysine from lysine-HCl was 196 and 163% for experiments 1 and 2, respectively, based on weight gain. A subsequent feeding experiment was conducted in which the peanut meal-corn gluten meal basal diet was supplemented with lysine alone or with lysine plus histidine, isoleucine, threonine, and tryptophan to match the essential amino acid composition of the diet in which soybean meal provided the protein. Supplementation of the basal diet with the additional amino acids did not improve fish weight gain relative to that from supplementation with lysine alone. Overfortification of the basal diet with free lysine improved weight gain of fish to equal that obtained with the diet containing soybean meal. Loss of lysine due to leaching of diets in water was 12.7 and 2.0% of the original lysine concentration for free lysine and protein-bound lysine, respectively. When leaching losses are subtracted from the lysine concentrations in the test diets, the efficiency of utilization of protein-bound lysine is still higher than that of free lysine, 175 and 146%, based on weight gain, for experiments 1 and 2, respectively. These results indicate that protein-bound lysine is more efficiently utilized than free lysine in practical type diets for young channel catfish.

Soybean Heat-treated using a Fluidized Bed

The fluidized bed technique was evaluated for treating soybeans with two purposes: drying and inactivation of heat-labile inhibitors. The effect of air temperature, soybean initial moisture and treatment time on moisture, urease activity, trypsin inhibitor activity and available lysine were determined. No inactivation was detected at 100 °C at any initial moisture content, while at 110 °C and any initial moisture level drying occurred before inactivation. At 120, 130 and 140 °C inactivation was produced before drying at 175 and 235 g/kg water content. At these temperatures, no significant losses of available lysine were detected. Consequently, soybean drying and inactivation can be performed in a single step, while maintaining nutritional value.

Application of the Clarifying Reagent Index as a Heat-Induced Parameter in Commercial Milk

The absorbance at 340nm of transparent modified milk solutions (designated as Clarifying Reagent index) from industrially processed samples as well as from milk-resembling systems was measured in order to test the validity of this index for determining the extent of previous heat treatment. A statistical study (n = 81) of the Clarifying Reagent index of different commercial milks was carried out. There was a significant difference (P < 0.001, Student's t test) between three groups of samples: (1) raw and pasteurized milk, (2) UHT-treated milk, and (3) in-bottle sterilized milk. The Clarifying Reagent index showed significant relationships (P < 0.001, Student's t test) with other heat-induced parameters such as hydroxymethylfurfural formation, loss of available lysine, and free fluorescent intermediary compounds formed by the Maillard reaction. Between 90 and 140°C, the Clarifying Reagent index of the clarified milk or milk-resembling systems followed zero-order kinetics as determined by nonlinear regression analysis.

α-Tocopherol does not inhibit hypochlorite-induced oxidation of apolipoprotein B-100 of low-density lipoprotein

The amount of α-tocopherol (α-TOH) can dramatically alter the extent of radical-induced oxidation of low density lipoprotein (LDL) lipids, a process generally thought to be important in atherogenesis. However, LDL with atherogenic features can also be formed in vitro by exposure to the strong non-radical oxidant hypochlorite (HOCl), which preferentially oxidises LDL apolipoprotein B-100. Here we show that varying LDL content of α-TOH by vitamin supplementation or depletion has no effect on the extent of HOCl-induced oxidation of apolipoprotein B-100 as measured by the loss of lysine and tryptophan residues, and the alteration in relative electrophoretic mobility of the lipoprotein particle.

Available Lysine Content during Cereal Flake Production

The available lysine contents during industrial production of wheat, rye, barley and oat flakes have been investigated. Obtained results show that hydrothermal treatment (120°C, 60 min, 1.99 x 10 5 Pa) of whole cereal grain as well as flaking process (70°C, gap 0.3 mm) did not significantly affect lysine availability. When summary effects in particular processing phases, including thermal treatment (100°C) of oat grains-before fragmentation and hydrothermic treatment-is calculated, the loss of available lysine was significant during production of rye flakes (4.90%) and oat flakes (8.22%). Protein nutritive quality, expressed as a chemical score based on the available lysine contents in relation to NAS/NRC reference pattern was on the average 47.9%, 46.5%, 41.0% and 38.6% for oat, rye, barley and wheat flakes, respectively.

Effect of iron and lactose supplementation of milk on the Maillard reaction and tryptophan content

New liquid UHT milks supplemented with iron (0.9–1.4 mg/100 ml), vitamin C (1–7 mg/100 ml), lactose (2.4 g/100 ml) and linoleic acid (200–400 mg/ 100 ml), named growth milks, have recently become available to satisfy the specific nutritional needs of children aged 1–3 years. But the iron‐vitamin C mixture could activate the lactose‐induced Maillard reaction and tryptophan (Trp) oxidation in proteins. We have therefore examined the Amadori product and Trp concentrations of these milks. Forty‐two commercial growth milks from five firms were analysed for the Maillard reaction and the soluble protein Trp content and compared with 64 UHT milks. The furosine concentration of total proteins was two to four times higher in growth’ milks than in standard UHT milks, indicating a proportional loss of available lysine. The Trp fluorescence of undenatured proteins soluble at pH 4.6 was almost three times lower in ‘growth’ than in standard milks and Trp concentration 36% lower suggesting destruction of this oxidation‐sensitive amino‐acid. The mechanism of Trp destruction remains to be elucidated, and the roles of iron and Amadori products determined.