Proteins thermal treatment

Muscle-Based Food Proteins Thermal treatment... 

It is interesting to compare the thermal-treatment effect on the secondary structure of two proteins, namely, bacteriorhodopsin (BR) and photosynthetic reaction centers from Rhodopseudomonas viridis (RC). The investigation was done for three types of samples for each object-solution, LB film, and self-assembled film. Both proteins are membrane ones and are objects of numerous studies, for they play a key role in photosynthesis, providing a light-induced charge transfer through membranes—electrons in the case of RC and protons in the case of BR. 

Of the visible spectroscopic techniques, CD spectroscopy has seen the most rapid and dramatic growth. The far-UV circular dichroism spectrum of a protein is a direct reflection of its secondary structure [71]. An asymmetrical molecule, such as a protein macromolecule, exhibits circular dichroism because it absorbs circularly polarized light of one rotation differently from circularly polarized light of the other rotation. Therefore, the technique is useful in determining changes in secondary structure as a function of stability, thermal treatment, or freeze-thaw. 

The results obtained with this procedure are similar to those previously reported in the literature by Hangartner, Hagenguth et al and Zeman et al (4, 2, 5, 6). The major exception, being the complete lack of alkylated pyrazines and alkylated thiophenes. These odour-intensive compounds arise from the thermal decomposition of proteins and sulphur containing amino acids. They also develop in the thermally induced reaction of proteins with carbohydrates (Maillard reaction). The authors indicated above have demonstrated that these compounds are invariably produced during the thermal treatment of sludge, a process which is not used in this Authority. 

A physical approach was also applied to reduce the allergenicity of psyllium and psyllium-containing food products (Wullschleger, 1993). Psyllium was subjected to a thermal treatment imder certain pressure and moisture content for a predetermined time period to destroy the allergenic proteins. The preferred treatment conditions included a temperature of 245-265 °F, pressure range of 14—20 psi, and a time period between 55 and 75 min. This procedure may eliminate up to 100% of the allergenicity of psyllium. 

HPLC analysis of food proteins and peptides can be performed for different purposes to characterize food, to detect frauds, to assess the severity of thermal treatments, etc. To detect and/or quantify protein and peptide components in foods, a number of different analytical techniques (chromatography, electrophoresis, mass spectrometry, immunology) have been used, either alone or in combination. The main advantages of HPLC analysis lie in its high resolution power and versatility. In a single chromatographic run, it is possible to obtain both the composition and the amount of the protein fraction and analysis can be automated. 

Thermal treatment of proteins present in processed foods may have implications beyond food safety to the functionality of these proteins. For this purpose, specific antibodies raised against native and denatured proteins which could distinguish the two forms would enable one by immunoassay to determine the extent of protein denaturation in the product and its associated implication in safety and functionality of the finished food. Paraf (87) discusses this aspect in his review on monoclonal antibodies in the analysis of food proteins. The ability of IA s to distinguish native versus heat-denatured ovalbumin dependent on the assay protocol used. One can foresee this... 

Heating experiments on Nautilus shell material (see page 10) indicates a retardation in the rates of thermal decomposition of mineral and organic phase. This has been attributed to the development of a topochemical boundary at the contact protein-mineral. X-ray diffraction analysis gives no evidence for structural alteration of the original aragonite during the thermal treatment up to 200 °C. 

Some organisms, such as algae and yeast, release proteases from vacuoles that rapidly reduce protein yields and produce undesirable cleavage products unless strong inhibitory agents are used to block proteolytic activity. One solution to mitigate this issue involves a rapid electroseparation of proteins (36). Alternatively, precipitation of proteins by the addition of trichloroacetic acid or by a brief thermal treatment also can stabilize proteins in protease-rich samples (37). 

The third path to aromas are non-enzymat1c processes resulting from thermal treatment such as cooking and roasting. These reactions typically Include thermal decomposition of I1p1d, carbohydrates and proteins, and are responsible for the aroma of foods such as coffee, meat, nuts, cereals, and also contribute to the aromas of heat processed foods and vegetables. 

Although less frequently discussed, heat processes often influence the textures and chemistries of the intermediate and end products, and thermal treatments are not without consequences on milk proteins that are denatured. Denaturation of proteins occurs under precise conditions of pH, temperature and ionic strength leading to their unfolding. Denaturation is significantly slower when proteins are near their isoelectric point. Only (3-lactoglobulin is irreversibly denatured at pH 7 and 70°C a-lactalbumin is denatured at pH 6.7 and 65°C. Aggregation of these proteins, besides hydrophobic... 

Thermal treatment of meat products ensures microbial destruction of microorganisms but also the denaturation of structural proteins, forming a gelled structure, and the inactivation of many endogenous enzymes (see Figure 21.3 above). In precooked products, characteristic color and flavor of the product are also developed during heating. Thermal treatment can be performed in forced convection ovens, both in... 

Furosine, a marker of the Maillard reaction product, is a valuable indicator of food protein quality. It is a marker for thermal treatment in foodstuffs and is directly related to the loss of lysine availability. IPC was employed to determine furosine content in beverages based on soy milk and cow milk supplemented with soy isoflavones [39]. Furosine was also analyzed in 60 commercial breakfast cereals to assess their protein nutritional values. The higher the protein content in the formulation, the higher the furosine levels [40]. A simple IPC technique that uses 1-octanesulfonic acid as the IPR allowed the selective determination of histamine levels in fermented food [41]. 

The remedy to this situation is to perform a thermal treatment of the frozen solution. This treatment consists of a controlled rewarming of the solution until devitrification and recrystallization of the excipient occurs, followed by a last freezing step below the solidification temperature. A typical excipient justifiable of such a treatment on thermodynamic grounds is mannitol. In the absence of proteins that maintain the structural integrity of the pellet, mannitol solutions often yield cakes of poor appearance. The induction of mannitol crystallization by rewarming around -25°C evades this problem and allows one to obtain elegant pellets that are easy to lyophilize and do not shrink. 

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