The estimation of the available lysine in animal-protein foods

Impact of gamma radiation, potassium sorbate and low temperature on shrimp (Penaeus monodon) preservation

The objective this study was to assess the effect of gamma radiation and 2% potassium sorbate with low temperature (4 °C) for shrimp (Penaeus monodon) preservation. Fresh samples were prepared for treatment with gamma radiation at 1.0 and 1.5 kGy doses and potassium sorbate (2%) soaked for 30 s (PS 30 s) and 60 s (PS 60 s). Organoleptic score (OS), biochemical composition and microbiological analysis were performed to evaluate the shelf-life extension and quality changes during the storage periods. Data showed that combination treatment of gamma irradiation at 1.5 kGy with low temperature was the most effective in extending shelf-life of shrimp. The isolated bacteria associated with shrimp samples were identified through PCR technique. Antibiotic sensitivity test was examined using ten commonly used antibiotics against these pathogenic isolates. Gentamicin and Imipenem showed up to 50% resistance on Gram-positive (Bacillus cereus and Staphylococcus aureus). This study indicates that gamma irradiation treatment with low temperature was most effective way for shelf-life extension of shrimp which might reduce the wastage of this important nutritional source.

Boosted Cross-Linking and Characterization of High-Performing Self-Assembling Peptides

Tissue engineering (TE) strategies require the design and characterization of novel biomaterials capable of mimicking the physiological microenvironments of the tissues to be regenerated. As such, implantable materials should be biomimetic, nanostructured and with mechanical properties approximating those of the target organ/tissue. Self-assembling peptides (SAPs) are biomimetic nanomaterials that can be readily synthesized and customized to match the requirements of some TE applications, but the weak interactions involved in the self-assembling phenomenon make them soft hydrogels unsuited for the regeneration of medium-to-hard tissues. In this work, we moved significant steps forward in the field of chemical cross-linked SAPs towards the goal of stiff peptidic materials suited for the regeneration of several tissues. Novel SAPs were designed and characterized to boost the 4-(N-Maleimidomethyl) cyclohexane-1-carboxylic acid 3-sulpho-N-hydroxysuccinimide ester (Sulfo-SMCC) mediated cross-linking reaction, where they reached G′ values of ~500 kPa. An additional orthogonal cross-linking was also effective and allowed to top remarkable G′ values of 840 kPa. We demonstrated that cross-linking fastened the pre-existing self-aggregated nanostructures, and at the same time, a strong presence of ß-structures is necessary for an effective cross-linking of (LKLK)₃-based SAPs. Combining strong SAP design and orthogonal cross-linking reactions, we brought SAP stiffness closer to the MPa threshold, and as such, we opened the door of the regeneration of skin, muscle and lung to biomimetic SAP technology.

Over-processed meat and bone meal and phytase effects on broilers challenged with subclinical necrotic enteritis: Part 1. Performance, intestinal lesions and pH, bacterial counts and apparent ileal digestibility

This feeding study investigated the hypothesis that over-processing of meat and bone meal (MBM) would impair the performance, gut health and ileal digestibility of nutrients in birds challenged with necrotic enteritis (NE). The effect of phytase (500 vs. 5,000 FTU/kg) was also examined using manufacturers recommended matrix values for 500 FTU for both levels. Ross 308 male broilers (n = 768) were assigned to 8 diets, with 6 replicate pens per diet and 16 birds per replicate pen using a randomized design with a factorial arrangement of treatments. Factors were NE challenge (no or yes), MBM (as received or over-processed), and phytase level (500 or 5,000 FTU/kg). Half of the birds were challenged with 5,000 oocysts of field strains of Eimeria acervulina and Eimeria brunetti, and 2,500 oocysts of Eimeria maxima on d 9 and 108 CFU/mL of Clostridium perfringens strain EHE-NE18 on d 14 and 15 post-hatch. Challenge × MBM interactions were detected for weight gain (WG), feed conversion ratio (FCR) and feed intake (FI) at d 14, 21 and 28, showing that challenged birds fed over-processed MBM had decreased WG (P < 0.05) and FI (P < 0.05) at d 14, increased FCR (P < 0.05) at d 21 and decreased WG (P < 0.05) and FI (P > 0.05) at d 28. Birds fed low phytase had increased livability (P < 0.05) at d 42. The challenge increased the prevalence and severity of NE induced lesions in the jejunum (P < 0.05) and ileum (P < 0.05). The birds fed over-processed MBM had decreased pH in the jejunum (P < 0.05) and ileum (P < 0.05) at d 16. High phytase increased apparent ileal digestibility (AID) of Ca (P < 0.05) and P (P < 0.05), and over-processed MBM increased AID of carbon (C; P < 0.05) and Ca (P < 0.05) at d 29. The challenge increased the caecal counts of Lactobacillus spp. (P < 0.05) and C. perfringens (P < 0.05) at d 16. The results indicated that supplementation of diets with high phytase reduces the negative impact on performance from over-processed MBM during NE as a result of increased nutrient digestibility.

Preparation of horsegram protein concentrate with improved protein quality, in vitro digestibility and available lysine

Horsegram (Macrotyloma uniflorum or Dolichos biflorus), an inexpensive pulse crop with high lysine and iron contents, is underutilized due to the presence of antinutrients like lectin and trypsin inhibitors, which limit protein digestibility and availability. Horsegram protein concentrate (HGPC) was prepared, which had 80.4 ± 3.5% protein and 94.2 ± 1.4% in vitro protein digestibility compared to dehulled horsegram flour (22.8 ± 0.8% and 82.3 ± 1.2%, respectively). Available lysine content in concentrate was increased by 64% compared to dehulled horsegram flour. The trypsin inhibitory activity in the protein concentrate decreased by 51% from 36.6 ± 3.5 TIU/mg in horsegram flour to 17.6 ± 2.5 TIU/mg in HGPC. Nutritional indices, including PDCAAS values for different age groups, were calculated and found to be slightly lower due to the loss of methionine and tryptophan in the concentrate. However, branched amino acids and lysine contents were higher. Thus, a vegetarian source with high protein digestibility and available lysine content could be prepared as a protein ingredient for the food industry.

Quantification of Maillard reaction products in animal feed

Individual Maillard reaction products (MRPs), namely furosine, which is formed from Amadori product of lysine during acid hydrolysis, as well as N-ε-(carboxymethyl)lysine (CML), pyrraline and the arginine derivative MG-H1 (methylglyoxal-derived hydroimidazolone 1) were quantified in 78 samples of animal feed, belonging to 17 different feed types. The concentrations of the MRPs were dependent on the heat treatment during processing. Within similar feed types, significant differences in concentrations could be observed. MRPs can be suitable indicators to evaluate the impact of technological processing on the nutritional quality of animal feed.

Available energy and amino acid digestibility of defatted rice bran fed to growing pigs

This study was conducted to determine and compare available energy and apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of CP and AA in 9 samples of defatted rice bran (DFRB) fed to growing pigs and to generate prediction equations for DE and ME based on chemical analysis. In Exp. 1, 60 crossbred growing pigs (Duroc × Landrace × Yorkshire; 40.7 ± 3.5 kg BW) were fed 1 of 10 diets in a completely randomized design to determine the available energy of DFRB. The diets included a corn-soybean meal-basal diet and 9 experimental diets formulated by replacing the corn and soybean meal with 29.16% DFRB. In Exp. 2, 6 growing pigs (initial BW = 28.5 ± 2.8 kg) were surgically equipped with a T-cannula in the distal ileum and arranged in a 6 × 6 Latin square design with 6 diets and 6 periods. The diets included an N-free diet based on cornstarch and sucrose and 5 experimental diets containing 60% DFRB as the sole source of AA. Chromic oxide (0.3%) was used as an indigestible marker. Among the 9 samples, the concentrations of ether extract (EE), crude fiber (CF), NDF, ADF, starch, Ca, and P averaged 1.33 (0.50% to 4.14%), 14.54 (9.78% to 23.85%), 28.62 (20.19% to 38.85%), 14.22 (9.32% to 23.99%), 38.80% (30.62% to 47.55%), 0.16% (0.09% to 0.24%), and 1.96% (1.11% to 2.28%), respectively. The average DE and ME were 2,643 and 2,476 kcal/kg DM, respectively, and ranged from 2,039 to 3,157 kcal/kg DM and 1,931 to 2,978 kcal/kg DM, respectively. In Exp. 2, there were significant differences in the AID and SID of CP and most AA except for His, Tyr, and Met (P < 0.05). The AID and SID of CP averaged 67.75% and 76.37%, respectively. The digestibility of Met was the greatest, averaging 86.15% and 90.08% for AID and SID, respectively. The AID and SID of Lys ranged from 51.88% to 71.43% (mean = 63.27%) and from 61.93% to 79.98% (mean = 72.97%), respectively. These results indicated that there is significant variability in chemical composition, energy content, and the SID and AID of CP and most AA among the selected DFRB. The DE and ME of DFRB are primarily related to their NDF and starch concentrations.

Invited review: Further progress is needed in procedures for the biological evaluation of dietary protein quality in pig and poultry feeds

Abstract. Recently, biological procedures for feed protein evaluation in pig and poultry diets have been based on the amino acid composition of feed ingredients considering the animal's losses during processes of digestion or total protein utilization in a different manner. Such a development towards individual amino acids (AAs) was inevitable according to the disadvantage of traditional protein quality measures, like biological value (BV) or net protein utilization (NPU), to be non-additive in complex animal diets. In consequence, such measures are generally not suitable for predicting the final protein quality of protein mixtures from the individual protein value of feed ingredients. Otherwise, recent measures of AA disappearance from the small intestine up to the end of the ileum (ileal AA digestibility) also do not provide a true reflection of the biological availability of individual feed AAs independent of the extent of taking into account endogenous AA losses during digestion processes. Sophisticated procedures for protein evaluation are needed considering the AA losses, both during absorption and utilization after absorption. Advantages and limitations of important developments in procedures are discussed. Accordingly, the development of an exponential modelling approach is described (the Göttingen approach), which overcomes some of the traditional disadvantages by measuring the individual AA efficiency. Connecting feed protein evaluation, the modelling of quantitative AA requirements, and improved ideal protein concepts offers different fields of application. In addition, as demonstrated by example, the modelling of nitrogen losses per unit protein deposition and the minimizing of this parameter yields a further interesting tool for lowering the nitrogen burden from protein utilization processes. Finally, it is pointed out that traditional laboratory procedures also need to be updated, adapted to current knowledge, and validated according to the increasing hurdles for animal studies from the viewpoint of animal welfare. Modelling is a procedure with the potential to reduce the number of experimental animals significantly. This development needs more attention, higher acceptance, and wider application in the future of protein evaluation.

Optimization of mold wheat bread fortified with soy flour, pea flour and whey protein concentrate

The objective of this work was to study the effect of replacing a selected wheat flour for defatted soy flour, pea flour and whey protein concentrate on both dough rheological characteristics and the performance and nutritional quality of bread. A mixture design was used to analyze the combination of the ingredients. The optimization process suggested that a mixture containing 88.8% of wheat flour, 8.2% of defatted soy flour, 0.0% of pea flour and 3.0% of whey protein concentrate could be a good combination to achieve the best fortified-bread nutritional quality. The fortified bread resulted in high protein concentration, with an increase in dietary fiber content and higher calcium levels compared with those of control (wheat flour 100%). Regarding protein quality, available lysine content was significantly higher, thus contributing with the essential amino acid requirement.

Revision: Indicadores del deterioro de la calidad proteica y del valor nutritivo de la leche / Review: Indicators of damage of protein quality and nutritional value of milk

The nutritional value of milk can be negatively affected by thermal treatments. The quality of the proteins can be modified as a consequence of a set of reactions, the most important of which are the interactions between protein and carbohydrates, also known as Maillard reactions. These reactions can also occur when the storage conditions of moisture and temperature are unfavorable. The differ ent thermal treatments involved in processing milk (pasteurization, sterilization, drying, etc.) lead to different steps of the Maillard reaction and therefore to the formation of different compounds that can be useful as chemical markers of milk alteration, or more exactly of protein alteration. Estimating these markers is useful in monitoring the changes, especially those related to proteins, that happen during processing and storage. A review of the literature on the markers used to evaluate the modi fications that milk undergoes during thermal treatment and subsequent storage was carried out, focusing mainly on proteins. Special attention was paid to the analytical aspects. The chemical mark ers taken into account can be classified into two groups according to their relation with the Maillard reaction:

1. Specific markers of Maillard reaction: undesirable compounds (furosine, lisinoalanine, histidinalanine, furfurals, melanoidins); loss of nutrients (available lysine).

2. Non-markers of Maillard reaction: galactose; lactulose; protein-reducing substances; denaturation of protein; in vitro digestibility of proteins; others—pH, viscosity, free fatty acids.

Development of baked and extruded functional foods from metabolic syndrome specific ingredient mix

The study was aimed to develop baked and extruded functional foods from Metabolic Syndrome (MS) specific designed ingredient mixes with optimum amino acid makeup using key food ingredients with functional properties such as whole cereals, legumes, skimmed milk powder, along with flaxseeds and fenugreek seeds. Two cereals viz. barley and oats and four pulses viz. mung bean, cowpea, bengal gram and soybean were blended in different proportions in order to balance the limiting amino acid lysine in the wheat flour. Three products namely bread, extruded snack and noodles prepared from twenty five ingredient mixes. Six ingredient mixes of breads and four ingredient mixes each of extruded snack and noodles specifically designed for MS patients were organoleptically at par with control wheat flour products. The acceptable products had significantly (p ≤ 0.05) higher lysine, crude protein, ash and fibre and low carbohydrates in compare control whole wheat flour products, hence appropriate for MS patients.

Baking, ageing, diabetes: a short history of the Maillard reaction

The reaction of reducing carbohydrates with amino compounds described in 1912 by Louis-Camille Maillard is responsible for the aroma, taste, and appearance of thermally processed food. The discovery that non-enzymatic conversions also occur in organisms led to intensive investigation of the pathophysiological significance of the Maillard reaction in diabetes and ageing processes. Dietary Maillard products are discussed as "glycotoxins" and thus as a nutritional risk, but also increasingly with regard to positive effects in the human body. In this Review we give an overview of the most important discoveries in Maillard research since it was first described and show that the complex reaction, even after over one hundred years, has lost none of its interdisciplinary actuality.

Functional and nutritional evaluation of supplementary food formulations

Two type of ready to eat supplementary food formulations were developed by roller drying based on wheat, soy protein concentrate, whey protein concentrate, and green gram flour and were fortified with vitamins and minerals to meet the one third of the Recommended daily allowance (RDA). The supplementary food formulations contained 20-21% protein, 370-390 kcal of energy and 2,300 μg of β-carotene per 100 g serving. The physico-chemical, functional and nutritional characteristics were evaluated. The chemical score indicated that sulphur containing amino acids were the first limiting in both the formulations. The calculated nutritional indices, essential amino acid index, biological value, nutritional index and C-PER were higher for formula II. Rat bioassay showed higher PER (2.3) for formula II compared to formula I (2.1). The bioaccessibility of iron was 23%. Sensory studies indicated that the products were acceptable with a shelf life of 1 year under normal storage condition. However, the formulations were nutritionally better than only cereal based supplementary food formulations available commercially. The product could be served in the form of porridge with water/milk or in the form of small laddu.

The Maillard reaction and pet food processing: effects on nutritive value and pet health

The Maillard reaction, which can occur during heat processing of pet foods or ingredients, is known to reduce the bioavailability of essential amino acids such as lysine due to the formation of early and advanced Maillard reaction products (MRP) that are unavailable for utilisation by the body. Determination of the difference between total and reactive lysine by chemical methods provides an indication of the amount of early MRP present in foods, feeds and ingredients. Previous research reported that the difference between total and reactive lysine in pet foods can be up to 61.8%, and foods for growing dogs may be at risk of supplying less lysine than the animal may require. The endogenous analogues of advanced MRP, advanced glycation endproducts, have been associated with age-related diseases in humans, such as diabetes and impaired renal function. It is unknown to what extent advanced MRP are present in pet foods, and if dietary MRP can be associated with the development of diseases such as diabetes and impaired renal function in pet animals. Avoidance of ingredients with high levels of MRP and processing conditions known to favour the Maillard reaction may be useful strategies to prevent the formation of MRP in manufactured pet food. Future work should further focus on understanding the effects of ingredient choice and processing conditions on the formation of early and advanced MRP, and possible effects on animal health.

Determination of protein and amino acid digestibility in foods including implications of gut microbial amino acid synthesis

To meet the protein and amino acid requirements of individuals and of populations requires information not only about their requirements but also about the capacity of available foods to meet those requirements. Most of our current knowledge of the digestibility of food proteins and the methods to estimate it has been derived from work with animals. Because the microbiota of the large intestine alter the amino acid composition of the digesta, and because only trivial quantities of amino acids are absorbed intact from the large intestine, the current method of choice for assessing amino acid digestibility is ileal digestibility corrected for basal endogenous losses, that is, standardized ileal digestibility. For protein as a whole, however, because nitrogen absorbed in forms other than as amino acids can contribute to the nitrogen economy, the absorption of nitrogen over the whole digestive tract is the more appropriate measure. Most of the methods developed for estimating ileal amino acid outflow in animals are not directly applicable to man: the exception is the use of volunteers with an ileostomy. The flow and composition of ileal digesta in human subjects can also be measured by the infusion of a marker and withdrawal of samples through a naso-intestinal tube. However, this method is too demanding for routine use and is likely to be restricted to validating the application to humans of digestibility data obtained either from animals, of which the pig seems most suitable, orin vitromethods. Microbial activity in the gastrointestinal (GI) tract is not confined to the large intestine: the numbers and metabolic activity of the upper GI microbiota lead to substantial amounts of microbial protein leaving the ileum. It appears however that a large proportion of the amino acids used by the upper GI microbiota are preformed - from the diet or from endogenous materials - rather than fromde novosynthesis. Although there are still uncertainties about the impact of microbial activity in the upper GI tract, the amino acid composition of ileal digesta provides the best available basis for estimating the proportion of dietary amino acids available for metabolism.

Available versus digestible dietary amino acids

Available amino acids are those absorbed from the gastrointestinal tract in a form suitable for body protein synthesis. True ileal digestible amino acids are determined based on the difference between dietary amino acid intake and unabsorbed dietary amino acids at the terminal ileum. The accuracy of ileal digestible amino acid estimates for predicting available amino acid content depends on several factors, including the accuracy of the amino acid analysis procedure. In heat processed foods, lysine can react with compounds to form nutritionally unavailable derivatives that are unstable during the hydrochloric acid hydrolysis step of amino acid analysis and can revert back to lysine causing an overestimate of available lysine. Recently, the true ileal digestible reactive (available) lysine assay based on guanidination has provided a means of accurately determining available lysine in processed foods. Methionine can be oxidised during processing to form methionine sulphoxide and methionine sulphone and cysteine oxidised to cysteic acid. Methionine sulphoxide, but not methionine sulphone or cysteic acid, is partially nutritionally available in some species of animal. Currently, methionine and cysteine are determined as methionine sulphone and cysteic acid respectively after quantitative oxidation prior to acid hydrolysis. Consequently, methionine and cysteine are overestimated if methionine sulphone or cysteic acid are present in the original material. Overall, given the problems associated with the analysis of some amino acids in processed foodstuffs, the available amino acid content may not always be accurately predicted by true ileal amino acid digestibility estimates. For such amino acids specific analytical strategies may be required.

In Vitro assessment of the nutritive value of expanded soybean meal for dairy cattle

Little information is available about the nutritive value of expanded soybean meal, which is produced by expansion of soybeans prior to solvent extraction of the oil. During processing, expanded soybean meal is subjected to additional heat, which might increase the concentration of ruminally undegraded protein. Processing of soybeans with heat during oil extraction could affect lysine availability by increasing ruminally undegraded protein or by impairing intestinal digestion. Our objective was to compare solvent and expanded soybeans with regard to chemical composition and nutritive value for dairy cattle. Samples of expanded soybean meal (n = 14) and solvent-extracted soybean meal (n = 5) were obtained from People's Republic of China to study effects of the expansion process on nutritive value for dairy cattle. Solvent-extracted soybean meal (n = 2) and mechanically extracted (heated) soybean meal (n = 2) from the United States served as references for comparison. Samples were analyzed for crude fat, long-chain fatty acids, crude protein, amino acids, chemically available lysine, in situ ruminal protein degradation, and in vitro intestinal digestibility. No differences were found between solvent-extracted soybean meals from China and expanded soybean meals from China for crude fat, crude protein, amino acids, or chemically available lysine. In situ disappearance of nitrogen, ruminally undegraded protein content, and in vitro intestinal digestion of the ruminally undegraded protein were generally similar between solvent-extracted soybean meals made in China and expanded soybean meals made in China; variation among soybean meals was small. Results indicate that the additional heat from the expansion process was not great enough to affect the nutritive value of soybean meal protein for ruminants. Although expansion may improve the oil extraction process, the impact on the resulting soybean meal is minimal and does not require consideration when formulating ruminant diets.

The nutritive value of separated milk for pigs. I. A comparison of two diets containing separated milk with a standard all-meal diet

One hundred and forty-four Large White weaner pigs were used in each of two experiments to investigate the nutritive value of liquid separated milk. Two experimental diets, one based on separated milk and barley meal, the other on separated milk, soya bean meal and barley meal were compared with control meals of the type used in the Pig Industry Development Authority's progeny testing stations. The amounts of milk in the experimental diets were adjusted so that the lysine concentrations in the dietary dry matter were similar to those of the control meals. All diets were given according to a restricted scale relating daily dry matter allowance to live weight, to a scale relating digestible energy allowance to live weight and to ‘appetite’. In the first experiment, pigs were slaughtered at 200 lb live weight, in the second at 260 lb live weight.

Pigs given the separated milk and barley meal diet performed similarly to those given the control meals; those given the separated milk, soya bean meal and barley meal diet had better feed conversion efficiencies than control pigs, particularly over the range 200 to 260 lb live weight. Pigs given diets containing milk had higher killing-out percentages and shorter carcasses than those given the control meals. Diet had no statistically significant effect on the percentages of fat and lean in the sides.

The effects of plane of nutrition were demonstrated by the faster rate of gain and poorer carcass quality of pigs fed to ‘appetite’.

It was concluded that the nutritive value of separated milk is explained by its high energy and lysine content. There was no evidence of any unknown beneficial factor in it.

Performance and nutrient utilization of growing pigs given an expanded and pelleted diet

A grower diet containing barley, wheat and soya-bean meal was expanded at 110°C and subsequently pelleted at 80°C. This processing was evaluated in laboratory tests as well as in digestibility experiments involving 12 barrows with an average initial live weight of 40 kg. The unprocessed control diet was offered as a meal. Each diet was offered ad libitum to six pigs during a 5-week period. The 1st week was an adaptation period and measurements were not carried out. Each pig was used in two 5-day digestibility trials which were performed in weeks 2 and 4. Neither food intake, weight gain nor food: gain ratio during the whole 4-week experimental period, nor apparent faecal digestibility and apparent retention of protein were significantly affected (P > 0·05) by expanding and pelleting the diet. Processing caused an increase in the in vitro protein solubility (P < 0·05) and reduced the dietary contents of free lysine and methionine (P < 0·05) while the contents of available lysine and free threonine and tryptophan were not significantly changed (P > 0·05). Apparent faecal digestibility of crude fibre increased substantially (P < 0·05) when the diet was processed, resulting in significantly lower production of faecal mass (P < 0·05) as well as lowerfaecal moisture content (P < 0·05). These phenomena were parallelled by a smaller water consumption (P < 0·05). Apparent digestibility and retention of phosphorus and calcium were diminished (P < 0·05) when the diet was expanded and pelleted.

The value of feather meal as a protein supplement for growing pigs

The results of a nitrogen balance experiment with growing pigs have shown that 5 % feather meal was inferior to 7 % white-fish meal, when both supplements supplied the same amount of total crude protein in a barleyweatings- minerals-vitamins ration.

A comparative feeding trial in which white-fish meal was partially replaced by feather meal in the diets given to growing pigs gave inconclusive results.

Changes in chemical and sensory properties of migaki-nishin (dried herring fillet) during drying

Migaki-nishin is a Japanese term that refers to dried herring fillets. It is widely consumed in Japan due to its characteristic flavor enhancing properties. This study was conducted to investigate the changes in chemical and sensory properties of migaki-nishin during drying. Chemical analyses showed that extractive nitrogen and amount of peptides increased significantly (P < 0.05) up to the 8th day of drying and then slightly decreased by the 10th day. Glutamic acid, alanine, glycine, and histidine were the most abundant free amino acids and the largest increase was found in samples dried for 10 d. A decrease in Hunter's L* value (lightness) and increase in b* value (yellowness) as well as browning intensity suggested that nonenzymatic browning occurred in migaki-nishin during drying. Fluorescence spectrophotometric determination also revealed that Maillard reactions progressed throughout the drying period. In addition, available lysine content and free amino groups decreased significantly (P < 0.05) as drying progressed. Sensory evaluation showed that addition of water-soluble extracts to Japanese noodle soup (mentsuyu) linearly enhanced the flavor characteristics such as thickness, mouthfulness, and continuity with the increased length of drying time. These results suggest that during the drying period, proteolysis as well as Maillard reaction products increased markedly, which might contribute to the characteristic taste and flavor of migaki-nishin.

A quantitative study of changes in dried skim-milk and lactose-casein in the ‘dry’ state during storage

Changes in dried skim-milk and in lactose-casein in the ‘dry’ state during storage at 45 °C and 75% r.h. have been studied by the determination of free amino-N, ε-amino groups of lysine, galactose, lactulose, tagatose and 1-amino-1-deoxy-2-ketoses, and by the measurement of changes in colour, solubility and ferricyanide reducing power.

In both systems there is initially a close relationship between the formation of 1-amino-1-deoxy-2-ketoses and the decrease in free amino-N. This conforms with an Amadori rearrangement of an initially formed lactose-protein complex. Change in colour is rapid only after there has been a rapid formation of 1-amino-1-deoxy-2-ketoses and a corresponding decrease in free amino-N. This conforms with browning being due to a breakdown of the Amadori rearranged complex.

It is postulated that galactose and tagatose may be formed by both the basecatalysed degradation of lactose and also by breakdown of the Amadori rearranged lactose-protein complex. Lactulose is postulated to be formed only by base-catalysed degradation of lactose.