Influence of weak organic acids and salts on the denaturation characteristics of intramuscular connective tissue. A differential scanning calorimetry study

Intramuscular connective tissue obtained from Longissimus dorsi muscle of a 4-year-old beef carcass was treated with NaCl solutions of 2, 4, and 6% (w/v), and CaCl₂ solutions of 50, 100, and 150 mM, and citric and lactic acid solutions of 0.5, 1.0, and 1.5% for three different marinating periods (24, 46, and 72 h). Changes in denaturation characteristics were investigated using differential scanning calorimetry and it was found that the denaturation onset temperature (T_o) and the denaturation peak temperature (T_p) increased as the NaCl concentration increased but decreased as the CaCl₂ concentration increased, irrespective of marinating time. Lactic and citric acid decreased T_o to about 39°C, from over 60°C breaking the structure of fibrils.     

Extraction of Lipids from Aqueous Protein‐Rich Streams using Near‐Critical Dimethylether

An extraction process for obtaining lipids from aqueous protein/lipid mixtures has been developed using near‐critical dimethylether (DME) as the solvent. The process has been demonstrated on fresh and reconstituted egg yolks, and on selected dairy by‐product streams. The lipid yield is dependent on the processing temperature, solids content and feed ratio of solvent to liquid. The extent of protein denaturation is also dependent on these parameters. The phase equilibria of DME‐water‐phospholipid mixtures are presented with modeling of the DME‐water system using the Peng‐Robinson equation of state.     

Factors affecting the fate of active proteins introduced in wastewater sludges: investigation with green fluorescent protein

Green fluorescent protein (GFP) was used as a reporter protein to investigate the interactions and fate of the active conformation of proteins in wastewater sludge. GFP was chosen because its fluorescence is dependent on the integrity of its native conformation. We identified factors that cause the loss of GFP fluorescence when this protein is introduced in aerobic or anaerobic sludge. In both systems, soluble polymers present in the liquid fraction caused an initial loss of fluorescence, but stabilized the remaining fluorescent GFP molecules. In aerobic sludge, interaction of GFP with the sludge solids initially caused an additional loss of fluorescence but the remaining fluorescence kept fairly constant over the following hours. In anaerobic sludge, on the contrary, interaction of GFP with the sludge solids caused a temperature dependent loss of fluorescence, probably related to the presence of precipitated ferrous sulfide. No direct relationship was found between sludge protease activity and loss of GFP fluorescence, suggesting that proteases are not the primary factor controlling the fate of the active form of proteins in wastewater sludges.     

Effect of denaturation during extraction on the conformational and functional properties of peanut protein isolate

Peanut protein isolate (PPI) was extracted by alkali dissolution and acid precipitation from defatted peanut flour. The effects of extraction conditions on the denaturation and functional properties of PPI were investigated. In comparison with native peanut protein (NPP) which was extracted by ammonium sulfate, the PPI extracted by alkali dissolution and acid precipitation had a higher extent of denaturation. Arachin was affected more easily by the extraction process than conarachin and led to a noticeable decrease of thermal stability of PPI. PPI contained much lower sulfhydryl and disulfide bond contents than NPP. The analyses of intrinsic fluorescence spectra indicated a more compacted tertiary conformation of NPP than PPI. Extraction process influenced the functional properties of PPI, such as protein solubility, emulsifying activity index and foaming capacity. The relatively poor functional properties of PPI might be associated with protein denaturation/unfolding and subsequent protein aggregation.

Industrial relevance

Peanut is an important oilseed crop and a well-accepted food. After oil production through thermal treatment, the defatted peanut flour is the main byproduct, which possesses a large amount of proteins. However, due to the low extraction yield and poor functional properties of these proteins, they are not well utilised in industry till now. In this work, peanut proteins were extracted by two techniques. The results indicated that extraction technique could significantly modify the functional properties of peanut proteins. Therefore, this work is helpful for industrial utilisation of peanut proteins.     

Physical characterization of thermally induced networks of lupin protein isolates prepared by isoelectric precipitation and dialysis

Summary Protein isolates of Lupinus albus were obtained from full fat and defatted lupin flour using isoelectric precipitation or dialysis. Calorimetric tests demonstrated that the main protein fractions of the isolates denature well below 100 °C. Mechanical spectra of isolate dispersions obtained at 80 °C indicated the formation of a 'pseudogel' whose cohesion increased during cooling to 10 °C. Subsequent heating to 90 °C encouraged extensive formation of disulphide bonds as it produced gels that were insoluble in sodium dodecyl sulphate and urea solutions. Dialysis produced isolates of lower gelling concentrations, which also formed networks of a stronger relative elastic character. The presence of NaCl at concentrations up to 0.5 m had a reinforcing effect on networks. Protein over-aggregation caused the opposite effect at higher salt levels. Finally, a comparison with results in the literature on soybean protein gelation suggested similar denaturation temperatures and a common pattern of structure formation for the two legume proteins.     

Method for monitoring the fate of green fluorescent protein added to aerobic and anaerobic wastewater sludge

The fate of active proteins in environmental matrices such as wastewater sludge, soil, and organic amendments is not well understood . In the present paper, we report the use of green fluorescent protein (GFP) as a probe protein to investigate the behaviour of proteins in wastewater sludge. We developed a procedure to quantitatively detect the active form of this protein in such a matrix. The procedure is based on the fluorimetric analysis of GFP in the separated liquid and solid fractions of sludge. We then tested the suitability of the approach by monitoring GFP added to aerobic and anaerobic sludge. Under aerobic conditions at 20 °C, most GFP immediately associated with the sludge solid fraction. About 20% of the fluorescence due to solid fraction associated GFP was still present after 72 h, which suggests a relative persistence of proteins in this system. Under anaerobic conditions at 35 °C, fluorescence signal due to GFP was reduced by 90% after only 6 h.     

控制鱼糜制品中蔗糖含量的新策略

鱼糜制品因其健康和方便食用的特性而广受消费者喜爱。蔗糖常常作为冷冻保护剂和甜味剂添加到鱼糜及其制品中,以改善其低温抗冻特性和风味。然而,传统鱼糜制品的糖含量普遍偏高,这与当前追求健康的消费理念不符。如何在降低糖含量同时保证鱼糜制品的贮藏和感官特性是目前鱼糜工业生产面临的一个重大挑战。本文探讨了蔗糖在鱼糜加工贮藏中发挥的作用,分析了鱼糜制品减糖加工工艺存在的问题以及鱼糜蛋白低温下发生冷冻变性的机理。在此基础上,本文从三个方面综述了国内外降低鱼糜制品糖含量的最新研究进展：新型抗冻剂的应用;新型甜味剂的应用;物理加工技术的应用。并对减糖策略的发展方向进行了相关预测,以期为生产健康和低糖鱼糜制品加工提供理论依据。     

The effect of the pH at cooking on the properties of processed cheese spreads containing whey proteins

Processed cheese spreads were made with and without whey proteins under varying cooking pH conditions. The processed cheeses were cooked at one pH value and at the end of the cooking process the pH was adjusted to the final product pH of 5.7. The rheological properties and whey protein denaturation levels of the processed cheese spreads were measured. The rheological properties and texture of the processed cheeses containing whey proteins could be markedly modified by varying the cooking pH during processing, whereas those without whey proteins were unaffected. These textural modifications could not be explained solely by the changes in whey protein denaturation during cooking. It is proposed that the interactions of the whey proteins during cooking affect the processed cheese texture, and that these interactions are affected by the pH of the processed cheese during processing.     

Glycosylation,denaturation, and aggregation of soy proteins in defatted soy flakes flour: Influence of thermal and homogenization treatments

This article provides a systematic study of the impact of different thermal treatments (62 ± 2°C, without and with relative humidity control, 79%) on soy protein in defatted soy flour and their aqueous dispersions. The effect of dispersing treatments (magnetic stirring, high-speed, and high-pressure homogenization) on dispersions also was assessed. Changes in protein solubility (water and 0.2 g/100 g potassium hydroxide solution), apparent-reactive lysine content, urease and trypsin inhibitor activities, protein denaturation, and Fourier transform infrared spectra were studied. Glycosylation, aggregation, and denaturation of storage and biologically active soy proteins were observed in different degrees, being mainly promoted by the control of relative humidity and the dispersibility of the sample.     

Effect of Detoxification on Conformational and Functional Properties of Jatropha curcas Proteins

The effects of detoxification process on conformational and functional properties of Jatropha curcas proteins were investigated. The molecular fractions and structure of proteins were affected more easily by the detoxification process. Compared with the proteins in Jatropha curcas meal, the detoxification process decreased the thermal stability and led to an increase in the surface hydrophobicity with a decrease in the contents of sulfhydryl and disulfide bond of proteins in detoxified Jatropha curcas meal. These conformational sand compositional changes in proteins influenced by the detoxification process, contributed to the relatively good changes in functional properties of detoxified Jatropha curcas meal, such as solubility, water and fat holding capacities, emulsifying properties, and foaming properties. Therefore, the detoxification treatment was not only a promising way to detoxify, but also an effective means to improve the functional properties of detoxified Jatropha curcas meal.