A new approach to microwave food research: Analyzing the electromagnetic response of basic amino acids

Measurement of the electromagnetic properties of food is important for its electromagnetic protection, microwave heating and sterilization. Much research had focused on describing the non-thermal mechanism of electromagnetism and locating its site of action. Amino acids are the basic units of proteins, and therefore their electromagnetic characteristics are central to understanding the transmission and loss of microwave energy in food and the non-thermal mechanism of electromagnetic effects. Herein, the dielectric properties and conductivity characteristics of solutions of basic amino acids, at an electromagnetic frequency of 2.45 GHz and at temperatures between 10 °C and 70 °C, have been measured. The results show that the dielectric constant and dielectric loss decrease with increasing temperature, for example, increase the temperature form 10 °C to 70 °C, the dielectric constant of lysine at 2% decreased from 77.259 to 68.601, and the dielectric loss decreased from 13.412 to 10.302, due to the decrease of the solution viscosity and the relaxation time, causing an increase of the dipole moment. Increasing the concentration of the basic amino acids leads to an increase of the dielectric loss, fix the temperature at 20 °C, the concentration of lysine increased from 0.5% to 10%, the dielectric loss increased from 10.191 to 23.232, which is related to the change of the conductivity. The conductivity has positive correlation with the concentration and temperature of the amino acid solution, fix the temperature at 20 °C, the concentration of lysine increased from 0.5% to 10%, the conductivity increased from 234 to 2840 μS/cm, and when the temperature was increased form 10 °C to 70 °C, the conductivity of lysine at 2% increased from 694 to 1347 μS/cm. The absorption properties of the solutions are characterized by the loss of reflection, and the absorption characteristics of the basic amino acids are related to the electromagnetic frequency, the concentration and the thickness of the absorbing layer, the variation of which affects the impedance matching. In this paper, through the study of the electromagnetic characteristics of basic amino acids in solution, a theoretical basis for the application of basic amino acids in microwave sterilization, as well as a mechanism for the microwave effect, are proposed.     

CHANGES IN NITROGEN FRACTIONS AND FREE AMINO ACIDS DURING RIPENING OF SPANISH DRIED BEEF "CECINA"

The changes in nitrogen fractions (total nonprotein nitrogen -NPN-, amino acid nitrogen, peptide nitrogen and volatile basic nitrogen) and free amino acids during the ripening of "cecina" (a Spanish dried beef product) were tracked. The amount of total NPN, amino acid nitrogen and volatile basic nitrogen increased during processing, while peptide nitrogen decreased in the last stage. An increase was observed in all amino acids except taurine. In the final product, the most abundant free amino acids were leucine-isoleucine mixture, lysine and proline-methionine mixture. Taking into account the concentrations of the most abundant amino acids detected in cecina and the taste thresholds described for L-amino acids in water, it appears that several amino acids i.e. lysine, alanine, valine and glutamic acid, could contribute to the flavor of this meat product.     

RELATION BETWEEN THE FREE AMINO ACIDS, ANSERINE AND THE TOTAL VOLATILE BASIC NITROGEN PRODUCED IN MUSCLE OF HAKE (MERLUCCIUS MERLUCCIUS, L.) DURING ICED STORAGE

This work studied the development of free amino acids (FAAs) and dipeptide anserine as quality indices for gutted hake stored in ice for 25 days. The correlation of these compounds was determined with total volatile basic nitrogen (TVBN) which has been used as a quality index, for fish stored in ice. The most abundant free amino acids in hake muscle were found to be threonine, glycine, alanine, glutamic acid, β-alanine methylhistidine. lysine and the dipeptide, anserine. The only hydrophobic free ammo adds which exhibit significant differences (P<0.05) throughout storage was tryptophan. moreover, this amino acid exhibited a very high correlation (r=0.951) with TVBN. A significant decrease in anserine (P<0.05) correlated with the increases in 1-methylhistidine and β-alanine throughout storage. These changes also exhibited a very high correlation with TVBN. Therefore, 1-methylhistidine, β-alanine anserine and tryptophan could be used as quality parameters for hake stored in ice.     

Nonenzyme browning and its effect on protein nutrition

The nonenzyme browning involves the thermal decomposition of sugars, the caramelization, the decomposition of oxi‐acids, the so called “Maillard reaction” between amino acids and carbohydrates, the reaction between oxidized fats and proteins, and those alterations which take place by the alkaline treatment of proteins. The Maillard reaction is of secondary importance in the case of foodstuffs and fodders with low carbohydrate contents (meats, meat meal, fish meal). By the heat treatment, the sulphur‐containing amino acids of proteins (cystine, methionine) are damaged primarily because of oxidation, but the decrease in the amount of threonine, serine, tryptophan, and lysine is observable too. According to the formation of enzyme resistant cross‐links, the in vitro and in vivo digestibility of protein decreases after the heat treatment and the communication with oxidized fats. Besides the amino acids mentioned, the possibility of enzymatic break‐off of leucine and isoleucine is reduced too. In the course of the heating of proteins the occurance of racemization has to be considered too (formation of alloisoleucine). The basic mechanism of the reaction between sugars and simple amino acids is already essentially explained: amino‐acids break off after the formation glycosilamines and Amadori products but they are linked irreversibly to some, partly unsaturated decomposition products of sugars, types of 6 and 3 carbon atoms. The decrease in the biological usability of amino acids starts already with the Amadori products. The reactivity of the single amino acids depends on the number of carbon atoms, on the basicity, and on the polarity of the amino acid molecule. The especially highly reactive amino acids of proteins are (1) the essential lysine (because of its 6‐NH₂ group), (2) other types of basic amino acids, and (3) tryptophan (because of the lability of the indole ring), methionine, cystine and threonine. In the Maillard reaction of tryptophan the —NH— group of the indole ring is involved too. The Maillard reaction is highly influenced by the pH of foodstuffs or other agents. The reduction of pH which may be performed by the increase of fermentation in the baking industry, lessens the decomposition of lysine and tryptophan in proteins. The raise of pH in basic domain enhances the Maillard reaction up to a maximal value but a decrease may be observed when the pH is raised further on. In foodstuffs and in other solid protein‐carbohydrate systems the increase of the moisture content generally enhances the Maillard reaction, the sensibility of the single amino acids to the changes in the moisture content is different. In the case of the alkaline treatment of proteins, we must reckon not only with the decomposition of single amino acids, first of all that of cystine by beta‐elimination, but with the formation of some amino acid derivatives as lysinoalanine, lanthionine, and in ornithinoalanine too. Presently lysinoalanine is of toxicological importance as proved by experiences on rats. The isomerization of essential amino acids may appear too during the alkaline treatment of proteins and this bears a reducing effect on the nutritive’ value.     

氨基酸对葡萄糖-天冬酰胺模拟体系中丙烯酰胺形成的抑制作用研究

研究4种氨基酸对已建立的葡萄糖-天冬酰胺模拟体系中丙烯酰胺生成的影响。方法 以葡萄糖-天冬酰胺组为对照组, 在此基础上分别加入半胱氨酸、甘氨酸、赖氨酸和谷氨酸4种氨基酸为实验组, 于140 ℃反应5~30 min, 测定反应后模拟体系的褐变程度、色差值、生成丙烯酰胺含量和剩余葡萄糖含量。 结果 4种氨基酸中, 半胱氨酸和谷氨酸对模拟体系中的褐变度和色差值的抑制作用较好; 半胱氨酸和赖氨酸对底物葡萄糖的消耗作用较快; 半胱氨酸对丙烯酰胺的抑制效果最好, 抑制率为(76.00±0.73)%, 其他氨基酸的抑制率分别为甘氨酸(38.39±0.44)%、赖氨酸(51.03±3.09)%和谷氨酸(28.76±2.43)%; 进一步研究发现, 当添加4.2 mmol半胱氨酸时, 丙烯酰胺抑制率达(95.32±0.47)%。结论 4种氨基酸相比, 半胱氨酸对丙烯酰胺形成的抑制效果最好, 且对于降低葡萄糖-天冬酰胺模拟体系的褐变度、色差值、葡萄糖含量有较好的效果。     

Effect of Amino Acids on Microwave Dielectric Properties of Minced Antarctic Krill (<Emphasis Type="Italic">Euphausia superba</Emphasis>)

The dielectric properties of ten solid amino acids, namely, glycine, proline, cysteine, glutamine, lysine, methionine, histidine, arginine, tyrosine, and tryptophan, and the effects of amino acid concentrations (0, 1, 3, and 5%) on the dielectric properties of minced Antarctic krill (Euphausia superba) were studied within a frequency range of 300–3000 MHz at 20.0 ± 0.5 °C. The dielectric constants and dielectric loss factor of amino acids were 2.0 ± 0.4 and 0.2 ± 0.3, respectively (moisture contents, 0.05–0.33%), except those of lysine (5.5 ± 0.5 and 1.5 ± 1.0, respectively) (moisture content, 4.5%). The dielectric properties of non-polar, neutral-polar, alkaline amino acids added to Antarctic krill were affected by the frequency and moisture contents, molecular weight, and isoelectric points (pI) of amino acids. As the molecular weight and pI values increased, the critical frequencies of aliphatic amino acid added to minced Antarctic krill decreased, whereas heterocyclic amino acid added to minced Antarctic krill increased. Quantitative relationships between parameters that define both the real and the imaginary parts of the Debye relations and the weight fraction of amino acid contents in Antarctic krill were determined. Moreover, glycine (at 5%) or lysine (at 5%) significantly influenced the dielectric constants and dielectric loss factor of minced Antarctic krill (p < 0.05) but did not have significant effects on temperature history and distribution (p < 0.05) during microwave heating at 2450 MHz.     

Browning and Amino Acid Loss in Model Total Parenteral Nutrition Solutions

The kinetics of browning and amino acid loss due to the Maillard reaction was studied in model total parenteral nutrition (TPN) systems containing glucose and either lysine, tryptophan, and cysteine alone or in combination. Cysteine systems showed the highest molar rate of browning while lysine showed the slowest rate. The molar rate of browning with all amino acids combined was significantly less than that of the sum of the individual rates, indicating interactions or inhibition. TPN electrolytes had no significant effect on the browning rate. The amino acids showed an initial rapid pseudo-first-order decrease in concentration followed by an apparent recovery and stabilization at an equilibrium concentration of about 60-80% of the original level.     

NUTRITIVE AND ORGANOLEPTIC CHARACTERISTICS OF NONDAIRY IMITATION MILKS

SUMMARY –13 nondairy imitation milk powders, concentrates and bottled beverages were analyzed for general composition, nutrients and organoleptic properties. These products were obtained from 11 domestic sources, which decreased to eight by the end of the study. Nondairy imitation milks were characterized by wide fluctuations in riboflavin (1.9–418.0 μ per 100 ml) and thiamine (0.2–54.7 μ per 100 ml), protein (0.76–3.67%) and amino acids like lysine (4.7–13.6 μmole per ml). Calcium and magnesium in all imitation milks were well below levels of the same elements in cow's milk reconstituted from whole milk powder, whereas sodium generally was much higher, almost threefold in several instances. The appearance of most nondairy imitation milks closely resembled fresh, pasteurized cow's milk, but the flavor, ascertained by three milk judges, was not similar nor as acceptable to them. Several imitation milks scored in flavor as well as or slightly better than cow's milk reconstituted from whole milk powder, but in all these instances, including the cow's milk, the flavor quality was only fair. Most imitation milks contained less protein than reconstituted cow's milk, but two contained concentrations of 3.26 and 3.67%, comparable to cow's milk. A number of nondairy imitation milks showed very low levels of calcium, riboflavin, thiamine and essential amino acids, lysine and methionine, in relation to cow's milk.     

The effect of long‐term storage on amino acid content of ready‐to‐eat entrées

The effect of 24‐month storage at three different temperatures (6 ± 2 °C, 26 ± 2 °C, 37 ± 2 °C) on quality of three types of ready‐to‐eat entrées (MRE) was evaluated by means of amino acid, ammonia, moisture and crude protein contents. Spicy risotto, Pork meat with carrots and potatoes and Pork goulash with pasta, that are included into the Czech combat rations, were selected for the experiment. During storage, all the explored samples did not significantly differ in moisture and crude protein content. Higher losses of amino acids (e.g. sulphuric amino acids, lysine, leucine) were detected with the increasing storage time and temperature. Growing losses of amino acids resulted in rising ammonia content as a product of amino acid degradation process. The biological value expressed by essential amino acid index declined with higher temperature and longer time of storage. The dependence of amino acid losses on moisture content was observed, too.     

Effects of Acidified Processing and Storage on Proteins and Lipids in Mung Bean Sprouts

Fresh mung bean sprouts contained 5.3g protein/100g fresh weight which decreased slightly on blanching and on bottling and canning. Storage of bottled seedlings for 6 months at 35°C caused the largest loss in total protein. The protein contained the essential amino acids tryptophan, valine, leucine, phenylalanine, arginine, lysine and histidine. Total lipids of fresh mung bean sprouts were 350 mg/100g fresh weight and were not greatly affected by blanching nor by canning or bottling. When the bottled seedlings were stored at 10°C and at RT, the canned seedlings at RT, there was some effect on total lipids in that only bottled seedlings at 35°C showed a significant decrease in lipids. After storage at the three temperatures there were increases in glycolipids and decreases in phospholipids, due mainly to increases in monogalactosyldiglyceride and decreases in phosphatidic acid respectively.     

Limiting amino acid for protein synthesis with mammary cells in tissue culture.

To identify the limiting amino acid in the minimal essential medium as published by Eagle (Science 130:432, 1959) for milk protein synthesis in rat mammary cells in tissue culture, two different experimental approaches were used. The first study involved the reduction of amino acids singly from the total amino acid complement of the medium for milk protein synthesis. The second study was to investigate the effect on milk protein synthesis of single amino acid addition to the basic complement of amino acids. Order of limiting amino acids was lysine (first) and possible methionine, valine, or arginine (second).     

Heat-Induced Changes in Free Amino Acids on Manufacturing Heated Pulps, Purées and Pastes from Tomatoes

The effect of heating on the free amino acid composition of processed tomato products, heated pulps, purées and pastes was examined. The major components of the fresh pulp were glutamic acid, γ-aminobutyric acid, aspartic acid, glutamine and asparagine. The heating process caused about a 40% loss of the total amino acids, which was attributable mostly to decreases in glutamic acid, glutamine and aspartic acid. Neither aromatic amino acids nor basic amino acids decreased in this process. Additional low temperature heating applied to the heated pulp to manufacture purées and pastes caused less effects than the high temperature heating used to prepare the pulp.     

Tissue degradation,amino acid liberation and bacterial decomposition of bulk stored capelin

Bulk stored capelin with high contents of feed in the gut is easily solubilised because of high proteolytic activity. The amino acids most quickly liberated are arginine, serine, histidine, leucine, lysine and tyrosine; glycine, aspartic acid and glutamic acid are liberated at a slower rate. Bacterial activity results in a rapid and considerable decrease in total amounts of tyrosine, lysine, serine, arginine and histidine. The main products formed by bacterial decomposition of lysine, histidine and arginine are cadaverine, histamine and putrescine, respectively. Storage of capelin in the presence of antibiotics increased the amounts of free amino acids and total amino acids. After 10 days' storage at 6°C, about 30% of the total amino acid content in fish treated with antibiotics were fee amino acids.     

Application of Plackett–Burman experimental design for investigating the effect of wort amino acids on flavour‐active compounds production during lager yeast fermentation

Aroma‐active higher alcohols and esters are produced intracellularly in the cytosol by fermenting lager yeast cells, which are of major industrial interest because they determine aroma and taste characteristics of the fermented beer. Wort amino acid composition and their utilization by yeast during brewer's wort fermentation influence both the yeast fermentation performance and the flavour profile of the finished product. To better understand the relationship between the yeast cell and wort amino acid composition, Plackett–Burman screening design was applied to measure the changes in nitrogen composition associated with yeast amino acids uptake and flavour formation during fermentation. Here, using an industrial lager brewing strain of Saccharomyces pastorianus , we investigated the effect of amino acid composition on the accumulation of higher alcohols and volatile esters. The objective of this study was to identify the significant amino acids involved in the flavour production during beer fermentation. Our results showed that even though different flavour substances were produced with different amino acid composition in the fermentation experiments, the discrepancies were not related to the total amount of amino acids in the synthetic medium. The most significant effect on higher alcohol production was exercised by the content of glutamic acid, aromatic amino acids and branch chain amino acids. Leucine, valine, glutamic acid, phenylalanine, serine and lysine were identified as important determinants for the formation of esters. The future applications of this information could drastically improve the current regime of selecting malt and adjunct or their formula with desired amino acids in wort. Copyright © 2017 The Institute of Brewing & Distilling     

和田红葡萄汁熬煮过程中游离氨基酸检测与分析

目的研究和田红葡萄汁在熬煮过程中,游离氨基酸含量随糖度升高的变化趋势。方法利用AccQ-Tag-高效液相色谱法对和田红葡萄熬煮汁中游离氨基酸进行定量检测。结果脯氨酸和精氨酸在慕萨莱思中含量最多,其次是赖氨酸、丝氨酸、谷氨酸、丙氨酸、苯丙氨酸,甲硫氨酸含量最少,半胱氨酸未检出。熬煮过程中多数氨基酸含量平稳上升,天冬氨酸和甘氨酸含量略有下降;当糖度达到26°Brix之后,丝氨酸、谷氨酸和甲硫氨酸含量有所下降。结论氨基酸的变化明显受到美拉德反应的影响,总氨基酸的浓缩为慕萨莱思自然发酵及其香味积累提供了前提条件。     

Effect of cooking on tryptophan,basic amino acids,protein solubility and retention of some vitamins in two varieties of chick pea

Egyptian and Italian varieties of chick pea were analysed chemically to study their total constituents. The two varieties were cooked for 1 and 2 h and autoclaved for 1 h at 121°C. Their constituent basic amino acids, tryptophan, thiamin, pyridoxin and niacin, were determined.There were differences in the chemical constituents between the two varieties. Cooking decreased lysine, histidine and arginine, the effect being highly significant. Tryptophan decreased, the effect being significant. In addition, protein solubility decreased with increased cooking time.The vitamin content also decreased with increased cooking time. It is preferable to cook chick pea in an autoclave at 121°C for not more than 1 h to minimise losses in vitamins and amino acids.     

Digestive utilisation of protein and amino acids from raw and heated lentils by growing rats

The effect of autoclave treatment on the digestive utilisation of protein and amino acids from lentils was studied in growing rats. Twenty 3‐week‐old Wistar rats (mean live weight 59 ± 4.8 g) were fed two experimental diets (n = 10 rats per diet) consisting of raw lentils (Lens culinaris M, var vulgaris, cv magda‐20) (diet RL) or lentils autoclaved at 120 °C and 1 atm for 30 min (diet AL). An additional group of 10 animals was fed a low‐protein (4%) diet and used to estimate metabolic nitrogen and amino acid excretion. Autoclaving caused a 76% reduction in the levels of trypsin inhibitor activity, but failed to improve the faecal digestive utilisation of protein or total amino acids. Lowest essential amino acid true digestibility in diets RL and AL was found for cysteine (60.2 vs 60.1%) and methionine (68.9 vs 66.6%). The protein digestibility‐corrected amino acid score was 71.2 and 66.4% and the availability of sulphur amino acid‐corrected amino acid score was 57.1 and 52.1% for diets RL and AL respectively. Sulphur amino acids were the first limiting ones. Overall, autoclave treatment did not improve protein or total amino acid digestibility from lentils, but caused a significant improvement in leucine and lysine digestibility and a significant decrease in the digestive utilisation of tyrosine and methionine. © 2002 Society of Chemical Industry     

5—THE CONSTITUTION OF THE EPICUTICLE OF WOOL

Epicuticle, isolated from wool via the Allwörden reaction, was examined by electron microscopy and analysed chemically. It is proteinaceous; lipids and carbohydrates could not be detected. The component amino acids are: cystine, glycine, glutamic acid, serine, valine, alanine, lysine, α-amino-adipic acid, and threonine. A tentative model for the epicuticle is proposed.     

The effect of storage conditions on the composition and functional properties of blended bulk tank milk

The objective of this study was to investigate the effects of storage temperature and duration on the composition and functional properties of bulk tank milk when fresh milk was added to the bulk tank twice daily. The bulk tank milk temperature was set at each of 3 temperatures (2, 4, and 6°C) in each of 3 tanks on 2 occasions during two 6-wk periods. Period 1 was undertaken in August and September when all cows were in mid lactation, and period 2 was undertaken in October and November when all cows were in late lactation. Bulk tank milk stored at the 3 temperatures was sampled at 24-h intervals during storage periods of 0 to 96 h. Compositional parameters were measured for all bulk tank milk samples, including gross composition and quantification of nitrogen compounds, casein fractions, free amino acids, and Ca and P contents. The somatic cell count, heat stability, titratable acidity, and rennetability of bulk tank milk samples were also assessed. Almost all parameters differed between mid and late lactation; however, the interaction between lactation, storage temperature, and storage duration was significant for only 3 parameters: protein content and concentrations of free cysteic acid and free glutamic acid. The interaction between storage temperature and storage time was not significant for any parameter measured, and temperature had no effect on any parameter except lysine: lysine content was higher at 6°C than at 2°C. During 96 h of storage, the concentrations of some free amino acids (glutamic acid, lysine, and arginine) increased, which may indicate proteolytic activity during storage. Between 0 and 96 h, minimal deterioration was observed in functional properties (rennet coagulation time, curd firmness, and heat stability), which was most likely due to the dissociation of β-casein from the casein micelle, which can be reversed upon pasteurization. Thus, this study suggests that blended milk can be stored for up to 96 h at temperatures between 2°C and 6°C with little effect on its composition or functional properties.     

Effect of variety and crude protein content on nutrients and certain antinutrients in field peas (Pisum sativum)

Protein content was used as an indicator of environmental conditions for a study on varietal and environmental variation in proximate composition, minerals, amino acids and certain antinutrients of field peas. Four field pea varieties, each with three levels of protein content, were selected. Crude protein content overall ranged from 20.2 to 26.7%. Analysis of variance showed that both variety and environmental conditions had a significant effect on starch, acid detergent fibre (ADF), neutral detergent fibre (NDF) and fat content, but ash content was only affected by variety. Significant varietal and environmental differences in potassium (K), manganese (Mn) and phosphorus (P) were noted. Calcium (Ca) and copper (Cu) showed significant varietal differences, while iron (Fe), magnesium (Mg) and zinc (Zn) had significant environmental differences. Environmental conditions showed significant effects on alanine, glycine, isoleucine, lysine and threonine content. Variety had a significant effect on sucrose, raffinose and phytic acid content, whereas environmental conditions had an influence on trypsin inhibitor activity (TIA). The major pea components protein and starch were inversely correlated. ADF, NDF, Fe, Mg, Zn and the amino acid arginine were positively correlated with protein content. The amino acids glycine, histidine, isoleucine, lysine and threonine were negatively correlated with protein content. It was found that tryptophan was the most deficient amino acid and the sulphur‐containing amino acids were the second limiting amino acids in peas. Raffinose was positively correlated with sucrose but negatively correlated with verbascose. There were significant correlations between mineral contents and some of the proximate components. Copyright © 2004 Society of Chemical Industry