Protein source humans

In general, nonconventional protein foods must be competitive with conventional plant and animal protein sources on the bases of cost delivered to the consumer, nutritional value to humans or animals, functional value in foods, sensory quality, and social and cultural acceptability. Also, requirements of regulatory agencies in different countries for freedom from toxins or toxic residues in single-cell protein products, toxic glycosides in leaf protein products, pathogenic microorganisms, heavy metals and toxins in fish protein concentrates, or inhibitory or toxic peptide components in synthetic peptides must be met before new nonconventional food or feed protein products can be marketed. 

Bacteria, yeast and algae are produced in massive quantities of protein sources as food for animals and humans.1 SCP is considered a major source of feed for animals. The production of valuable biological products from industrial and agricultural wastes is considered through the bioconversion of solid wastes to added-value fermented product, which is easily marketable as animal feedstock. The waste streams that otherwise would cause pollution and threaten the environment can be considered raw material for CSP production using suitable strains of microorganisms. 

Based on the above principles, it might be assumed that a therapeutic protein obtained by direct extraction from human sources (e.g. some antibody preparations) or produced via recombinant expression of a human gene/cDNA sequence (e.g. recombinant human hormones or cytokines) would be non-immunogenic in humans whereas foreign therapeutic proteins (e.g. non-engineered monoclonal antibodies) would stimulate a human immune response. This general principle holds in many cases, but not all. So why do therapeutic proteins of human amino acid sequences have the potential to trigger an immune response Potential reasons can include ... 

Since most snack foods are based on cereals (wheat, corn, rice), a great deal of attention has focused on fortification/supplementation of traditional cereal-based foods. Worldwide, cereals represent the major source of calories and proteins for humans i.e. 52% and 47% of the world s average per capita... 

Legume seeds, such as soy and other pulses, are widely used as protein sources in the human diet. Recent advances in technology suggest that protein concentrates and isolates made by relatively simple methods can be incorporated into food products. 

Effects of Protein Sources on the Utilization of Trace Minerals in Humans... 

The effects of various potentially deleterious components of plant protein sources, as indicated by the results of studies conducted with humans, are briefly discussed. Examples of contradictory results are given. 

From a global view, plant protein sources (cereals, legumes, oilseeds, vegetables, fruits) have always been the primary source of dietary energy and protein for the majority of the world s population. In addition, in recent years, the use of vegetable protein products as sources of dietary protein, as supplements, and as extenders of more traditional animal protein sources has been increasing markedly in the developed countries. These factors are responsible for our interest in determining the effects of plant protein sources on the utilization of minerals in the human diet. 

The effects of plant protein sources on iron and zinc utilization have been of particular concern and the subject of the most studies with humans. Accordingly, the following discussion is focused on studies concerned with these two minerals. 

A serious problem with some vegetables and particularly with fruit as a source of protein is the dilution of protein with carbohydrates so that an inordinate amount of calories must be consumed to obtain the needed amount of protein and amino acids for human growth. A survey of calories and protein content/100 g fresh weight of several different leaves, pods, seeds and tubers is shown in Table VIII. This indicates the desirability of certain leaves, pods and seeds over tubers, for example, as a protein source. 

Figure 7.1. Effect of GM-CSF on neutrophil protein biosynthesis. Human neutrophils were incubated in RPMI1640 medium supplemented with 2.5% foetal calf serum and 60 jtCi/ml [35S]-methionine, in the presence and absence of 50 U/ml GM-CSF. After 4 h incubation at 37 °C, the cells were pelleted by low-speed centrifugation. The proteins in the cell pellets were precipitated by 10% trichloracetic acid and then analysed by two-dimensional polyacrylamide gel electrophoresis, using iso-electrofocussing in the first dimension. Electrophoresis in the second dimension was performed in the presence of SDS and used a 12% acrylamide gel. Source Experiment of Becky Stringer.

Figure A2.10 Protein structure human deoxyhemoglobin. Source Protein Data Bank,PDB ID lA3N.Tame J, Vallone B. http //www.rcsb.org/pdb/cgi/explore.cgi job= graphics pdbId=lA3N page=0 opt=show size=250 [accessed April 16, 2003]. Used with permission.)...

Natural feedstocks must serve many human purposes. Carbohydrates are valuable raw materials due to their actual or potential value. For example, protein plants are already utilizing rapidly reproducing reengineered bacteria that metabolize cellulose wastes converting it to more protein-rich bacteria that are harvested and then used as a protein source feed-meal for animals. Further, natural materials can be used in applications now largely reserved only for synthetic polymers. Sufficient natural materials are available for the supply of both food and polymer needs. 

Nevertheless, it is an important source of protein for humans. Processing of wheat is necessary before use, and thermal processing is often employed in some manner. Much information is available regarding the effects of milling on nutrients in wheat, but little work has been done regarding the effects of heat treatment on amino acid availability. 

Protein hydrolysates are usually produced by limited enzymatic hydrolysis of protein molecules in foodstuff, yielding polypeptides that are smaller in molecular mass. Protein hydrolysis has several aims. The most common is to make the protein moiety of afoodstuff soluble by reducing the size of the peptides. Solubilization simplifies isolation of the protein moiety by physical means. Protein hydrolysis has also been applied to improve the functional, organoleptic, and nutritional value of a foodstuff. Advances in the technology of protein hydrolysate production has allowed the use of unconventional protein sources for animal and human food. 

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