Nonenzymatic deamidation of food proteins

Many cereal proteins, such as wheat, com, and oat proteins, have high levels of the amide‐containing amino acids, glutamine and asparagine. These side chains are susceptible to hydrolysis of the amide bond, which leads to release of ammonia and transformation to acidic groups. The released ammonia has been implicated in the formation of aroma compounds and pigments because of its participation in the Maillard browning reaction. The conversion of the amide groups to acid groups may partially unfold the protein, resulting in an amphiphilic molecule that can be used as a surface active agent or emulsifier by food processors. This review provides general information on the factors that affect deamidation of proteins as well as the implications of deamidation for food processing.     

Extrusion of food proteins.

Protein extrusion has frustrated earlier predictions regarding its impact in the development of food products. The main reason for this disappointing performance has been its failure to yield fabricated food products with textural quality close enough to that of natural products at competitive prices. Texturized soya protein by extrusion is presently the only commercial success in this area, being incorporated into several convenience products, increasing their protein content and quality and conferring them some desirable sensory properties. Technological and scientific gaps in the extrusion texturization are still to be bridged if this technique is to be applied for upgrading unconventional protein. The precise mechanisms responsible for protein texturization through extrusion are still unclear. Proteins show a very wide range of extrusion behavior that is probably related to large differences in their association properties. New peptide bonds, formed by free amino and carboxylic groups of the protein, were postulated as being responsible for the cross-linking that takes place in protein extrusion. However, disulfide bonds and electrostatic and hydrophobic interactions are regarded presently as the texturization mechanism in this process. The recently suggested suspension (or filled "melt") model for biopolymer extrusion offered a new framework for testing extrusion of novel proteins. According to this view, the large differences between the association properties of proteins produce different types of aggregates. Some of them can be insoluble under extrusion conditions and act as a dispersed phase within the melt phase. The extrusion performance of a protein will thus depend on the amount of insoluble aggregate produced inside the extruder and on protein-protein interactions that occur after the superheated molten mass leaves it.     

食品生物技术在大豆蛋白食品中的应用

<正> 食品生物技术是现代生物技术及其研究方法应用于食品生产和加工过程中的一门新兴学科,用于解决食品质量、营养、卫生安全以及储藏过程中存在的问题。大豆蛋白是人类十分重要的食用植物蛋白,早期人们利用微生物发酵等食品生     

Evauation of lysinoalanine determinations in food proteins

Summary A comparison is made between lysinoalanine (LAL) determinations both with an automatic amino acid analyzer (AAA) and with thin layer chromatography-densitometry (TLC) in different types of food and food ingredients, taken from the Dutch market.Generally there is a reasonable agreement between the LAL content obtained by both methods. However, some results indicate that a single technique is not always conclusive about the real identity of the ninhydrin-positive compound at the same position as LAL on the chromatogram. By TLC for instance, in yeast a content of about 800 mg of LAL/kg in protein is found, but according to the AAA method no LAL is present. In heated milk and milk products the LAL content determined by the TLC method is also higher than that found by the AAA method.This is caused by a preceding unknown ninhydrinpositive compound in TLC, occurring in all heated milk products and practically coinciding with LAL. In the AAA technique similar interferences of unknown ninhydrin-positive compounds could be avoided by choosing a suitable elution temperature; however, application of this temperature modification to foaming agents gave no satisfactory results.

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Auswertung von Lysinoalaninbestimmungen in Lebensmittelproteinen

Zusammenfassung Um zwei Bestimmungsmethoden von Lysinoalanin (LAL) miteinander zu vergleichen, wurden Analysen sowohl mit einem automatischen. Aminosäureanalysator als auch mit Dünnschichtchromatographie-Densitometrie, mit verschiedenen in den Niederlanden käuflichen Lebensmitteltypen und Ingredienten durchgeführt.Daraus ergibt sich eine ziemlich gute Übereinstimmung im LAL-Gehalt nach beiden Methoden. Einige Resultate deuten jedoch darauf hin, daß eine einzelne Methode nicht immer eindeutig ist, was die Identität der auf Ninhydrin positiv reagierenden Verbindung, bei gleicher Position im Chromatogramm als LAL angesprochen, betrifft.In Hefe z. B. fand man mit Dünnschichtchromatographie einen Gehalt von etwa 800 mg LAL/kg Protein, mit dem Aminosäurenanalysator jedoch kein LAL. Auch in erhitzter Milch und Milchprodukten ist der LAL-Gehalt, bestimmt mit Dünnschichtchromatographie, höher als der mit dem Aminosäurenanalysator gefundene Wert. Die Ursache ist, daß bei der Dünnschichtchromatographie von erhitzten Milchprodukten eine unbekannte auf Ninhydrin positiv reagierende Verbindung dem LAL-Fleck vorangeht, der praktisch mit dem LAL zusammenfällt. Um Störung durch unbekannte Verbindungen dieser Art beim Aminosäurenanalysator zu vermeiden, kann man eine geeignete Elutionstemperatur wählen. Bei einigen Schaummitteln jedoch erhält man durch Temperaturveränderung keine gute Trennung.

     

A rapid in vitro enzymic and chromatographic predictive model for the in vivo rat-based protein efficiency ratio of mixed food proteins

A nutritional quality index in the nature of an enzymatic protein efficiency ratio (E-PER) was computed from the amino acid data of 18 different food products by means of multiple regression equations. The regression was performed by setting amino acid values derived from enzymic hydrolysis of the food proteins as the independent variables with the rat-based PER values as the dependent variables. The multiple regression gave the following equation. The multiple correlation coefficient for this regression was 0.942 and the coefficient of variation was 88.7%. The prediction equation was tested on amino acid-PER data of 22 different foodstuffs and it successfully predicted (± 0.22) the PER of 17 and an effectiveness of 77.3%.     

Change in food proteins during technological processing

Changes in protein fractions of casein during production of milk-protein concentrates (casecite and casein hydrolysate) were studied by double disk-electrophoresis in poly-acrylamide gel. Significant changes were observed during casein treatment with pancreatin at pH-6.6-7.0. beta-casein was subjected to the highest proteolytic decomposition, it was separated into two fractions attended by isolation of a great number of positively charged fractions of gamma-casein. The amount of beta-casein, as compared to freshly-precipitated casein, diminished by 3.5 and 11.7%, depending on the decomposition degree. Increment of the portion of positively charged fractions correlated with increased bitter flavor. The method of double disk-electrophoresis in polyacrylamide gel can be recommended for the regulation of the hydrolysis process during food production.     

Chemistry of milk proteins in food processing.

This paper analyzes the current knowledge of mild protein chemistry to explain the reactions and their control for the major processes utilized by the modern milk processing industry. The compositon and chemical properties of casein micelles and whey proteins are summarized. The effect of processing upon denaturation, aggregration, and destabilization of milk proteins is updated. The role of milk proteins in the gelation of sterile milk concentrates, destabilization of frozen milk, rennet-clotting of milk, and stabilization of the fat emulsion in milk is also described.     

食品蛋白来源生物活性肽

生物活性肽是蛋白质功能片段经酶解产生具有特殊生理调节功能肽段。该文主要介绍降血压肽、高F值寡肽、酪蛋白磷酸肽、免疫活性肽、清除自由基活性肽等几种国内外广泛关注生物活性肽,并在此基础上对生物活性肽开发进行展望。     

Clinical role of lipid transfer proteins in food allergy

Lipid transfer proteins are widespread plant food allergens, highly resistant to food processing and to the gastrointestinal environment, which have recently been described as true food allergens in the Mediterranean area, where they have been associated with severe allergic reactions to foods in patients without pollen allergy. In this review we analyze their molecular structure, biological function, and clinical relevance in food allergy.     

食品蛋白质的琥珀酰化修饰研究进展

琥珀酰化修饰是一种常用的蛋白质结构修饰手段,其通过增加蛋白质分子净负电荷含量而改变蛋白质结构,从而使蛋白质性质显著改善。本文综述了蛋白质的琥珀酰化修饰条件以及修饰后蛋白质主要功能性质的变化程度,为蛋白质改性研究提供参考依据。     

食品加工中蛋白酶对乳清蛋白作用敏感性研究

研究了几种食品加工中常用的蛋白酶对乳清蛋白作用的影响,并通过聚丙烯酰氨凝胶电泳进行定量分析得出结论,通过酶类可以改变乳清蛋白的某些特性以满足食品加工中的特殊需求。     

Raman spectroscopic study of amidated food proteins

Various amounts of tryptophan were attached to three food protein products: soy protein isolates, spray-dried egg white and gluten, using a water-soluble carbodiimide method. The extent of amidation was determined by a spectrophotometric method. Raman spectra (600–2000 cm⁻¹) of the modified proteins were obtained and analyzed. The phenyl stretching vibration at 1552 cm⁻¹, directly attributed to the attached tryptophan, was used as a marker band, and increases in band intensity were observed in the modified protein samples. Calibration curves were constructed by plotting the intensity ratio of the 1552 cm⁻¹ band to the 1003 cm⁻¹ phenylalanine stretching band (used as an internal standard) against the amount of tryptophan attached. High correlation coefficients, (r) ? 0.99, were obtained from these calibration curves. The Raman spectral data showed a transition from ordered conformation to random coil structures in the amidated food protein products.     

Deamidation of food proteins to improve functionality

Many proteins, particularly those in plants, require structural modifications to improve their functional properties for expanded use. Several chemical and enzymatic methods are described for food protein deamidation to improve solubility, emulsification, foaming, and other functional properties of the proteins. The use of enzymes in protein modification is more desirable than chemical treatments because of their speed, mild reaction conditions, and their high specificity. Transglutaminase, protease, and peptidoglutaminase (PGase) are the only enzymes reported in the literature for protein deamidation. Of these, PGase appears to be the most feasible for practical application. PGase production, purification, and use in deamidation are discussed.     

用蛋白质羰基含量评价抗氧化保健食品的研究

为建立以蛋白质羰基含量为检测指标评价抗氧化保健食品的方法 ,用 2 ,4 二硝基苯肼比色法测定幼龄和老龄小鼠不同组织蛋白质羰基含量 ,用 3种具有抗氧化功能的保健食品饲喂小鼠 ,观察其对脑蛋白羰基含量的影响。发现随着年龄的增加 ,小鼠各组织中蛋白质羰基增量为脑 >肝 >心 >血清。因此脑组织是实验的灵敏材料。利用本实验方法能够将抗氧化保健食品对蛋白质的保护功能反映出来。检测结果得出的结论与用卫生部《保健食品功能学评价程序和检测方法》所判定的结论相吻合。采用本方法可为评价抗氧化保健食品的功能提供有力的证据     

Analysis of proteins in food with electrophoretic and chromatographic methods

The efficiency of electrophoretic methods (gel electrophoresis, isoelectric focusing, twodimensional techniques) and of chromatographic methods (size exclusion and ion exchange chromatography, reversed phase HPLC) to analyze proteins in foods is reviewed. Several selected applications are discussed in detail. The large diversity of proteins in a particular food results in a unique electrophoretic or chromatographic pattern, that can be used for identification purposes, by means of the so called indicator proteins. The adaptability and resolving power of the methods assure their extended application to many protein containing foods. The uniqueness of the patterns obtained warranties differentiations of even closely related animal or plant foods as well as mixtures of them. The methods also allow quantitative determinations of mixtures of foods. Their ease of handling and good reproducibility and reliability favours their use in routine analyses. Numerous investigations on fish, meat and derived products, non-meat proteins in meat products, milk, cheese, cereals and products made of cereals, oilseed proteins, legumes, fruits and vegetables described in the literature are here presented.     

Recent advances in phosphorylation of food proteins: A review

Phosphorylation is a useful method for improving the functional properties of food proteins. In this article, various methods of phosphorylation are reviewed. Dry-heating phosphorylation, a method developed recently, is also introduced. Some characteristics of phosphate groups are involved, and the effects of phosphorylation on the structural changes, the functional properties, and the physiological functions in vitro of food proteins, are discussed. The types of phosphate linkages and the phosphopeptides from phosphorylated proteins are identified. The molten (partially unfolded) conformations of food proteins formed by phosphorylation are discussed. The phosphorylation of food proteins improved a number of functional properties, including heat stability, emulsifying properties, foaming properties, gelling properties, water absorption capacity, oil absorption capacity, and calcium phosphate-solubilizing ability. In vitro physiological function studies of protein (α-lactoalbumin) indicated that the digestibility (ovalbumin) was improved and the inflammatory response (α-lactoalbumin) was suppressed by phosphorylation. Experiments with animals are necessary to evaluate the toxicity and physiological functions of phosphorylated proteins.