Sources of proteins

Rice is grown in more than 100 countries and on every continent except Antarctica. In the world economy rice is an extremely important food, second only to wheat in total world production, and its yield per hectare exceeds that of wheat (57). Rice is the main staple food for more than half of the world s population and it accounts for one-third to one-half of the daily caloric intake in many Asian countries. It is also the major source of protein for the masses of Asian people. In many African and South American countries rice is rapidly becoming the staple food for much of the population. 

The Protein Advisory Group, ad hoc, is the working group of the WHO United Nations system involving WHO, EAO, and the United Nations International Childten s Emergency Eund (UNICEE). It has developed guidelines for the evaluation of novel sources of protein, eg, single-cell protein ... 

Whole blood is seldom used ia modem blood transfusion. Blood is separated into its components. Transfusion therapy optimizes the use of the blood components, using each for a specific need. Red cell concentrates are used for patients needing oxygen transport, platelets are used for hemostasis, and plasma is used as a volume expander or a source of proteins needed for clotting of the blood. 

Soybean Protein Isolates. Soybean protein isolates, having a protein content of >90 wt%, are the only vegetable proteins that are widely used in imitation dairy products (1). Most isolates are derived from isoelectric precipitation, so that the soybean protein isolates have properties that are similar to those of casein. They are insoluble at thek isoelectric point, have a relatively high proportion of hydrophobic amino acid residues, and are calcium-sensitive. They differ from casein in that they are heat-denaturable and thus heat-labile. The proteins have relatively good nutritional properties and have been increasingly used as a principal source of protein. A main deterrent to use has been the beany flavor associated with the product. Use is expected to increase in part because of lower cost as compared to caseinates. There has been much research to develop improved soybean protein isolates. 

For us to remain perfectly healthy, the protein in our diet must supply suffident quantities of amino acids. We prefer to eat our protein in particular forms, that is in foods having particular textures, tastes and smells (these are called organoleptic properties). Conventional sources of protein are plants, mainly as cereals and pulses, and animals, mainly as meat, eggs and milk. The proportions of such proteins eaten in various parts of the world differ widely (Figure 4.1). 

Let us consider some of the disadvantages of micro-organisms compared to conventional sources of protein. 

With increased CO2 concentrations, by the injection of CO2 gas into ponds, outputs of 3 x 104 kg dry protein per hectare per year are possible. This compares very favourable with conventional sources of protein (Table 4.3), note the low yields of meat and milk. 

In terms of amino acids bacterial protein is similar to fish protein. The yeast s protein is almost identical to soya protein fungal protein is lower than yeast protein. In addition, SCP is deficient in amino acids with a sulphur bridge, such as cystine, cysteine and methionine. SCP as a food may require supplements of cysteine and methionine whereas they have high levels of lysine vitamins and other amino acids. The vitamins of microorganisms are primarily of the B type. Vitamin B12 occurs mostly hi bacteria, whereas algae are usually rich in vitamin A. The most common vitamins in SCP are thiamine, riboflavin, niacin, pyridoxine, pantothenic acid, choline, folic acid, inositol, biotin, B12 and P-aminobenzoic acid. Table 14.4 shows the essential amino acid analysis of SCP compared with several sources of protein. 

Nutrient analysis of stabilized rice bran and its derivatives indicates that it is a good source of protein, dietary fiber and carbohydrates, in addition to several valuable phytonutrients, antioxidants, vitamins and minerals (Table 17.1). SRB and its water-soluble and water-insoluble derivatives contain all the nutrients at different levels. They are gluten and lactose free and do not give rise to any food allergy. 

Bernard, J. K. (1997). Milk production and composition responses to the source of protein supplements in diets containing wheat middlings. /. Dairy Sci. 80, 5938-5942. 

For decades microorganisms have served as a source of proteins for structural and mechanistic protein biochemistry. Throughout the last decade, as new proteomics strategies were developed, these have usually been demonstrated... 

In order to conduct basic research and address the need for reagents and standards, several cell lines have been modified to express individual transporters. These can serve as a source of active protein to validate a chemical as a substrate or inhibitor, or as a source of protein to validate the specificity of an antibody. In order for this approach to be sufficiently robust to establish specificity (and to minimize false-negative findings), all of the key proteins need to be available and active in the system. However, as specific probes are being increasingly identified and developed, valuable mechanistic studies can be performed with the transporters and substrates/inhibitors that are currently available. 

The protein content of milk is primarily influenced by the breed of cow, the stage of lactation, type of diet being fed and the health status of the cow, and is important in processing because the protein (and specifically casein) content of milk determines its cheese yield. Milk provides a highly digestible source of protein for a large proportion of the world s population, either as raw milk or processed into dairy products. In addition to this basic nutrition, milk... 

Figure 1. The effect of different ration levels of phosphorus (Pi = 0.3% and P2 = 1.2%) and source of protein (E = egg white and S = soy) on bone breaking strength. There was no interaction main effect was significant. Phosphorus P < 0.018 protein P < 0.027.

Table V shows the composition of the liquid meals for this study. As in the previous study, two levels each of cottage cheese and beef were fed to the subjects. In addition, 45 g of protein from soy isolate was also fed. The phytic acid content of this meal was 126 mg. A basal diet containing all nutrients except protein was also included in this study. It was necessary to reduce the fat content of the basal diet for palatability the total energy for this meal only was 250 kcal. In this study, the calcium and phosphorus levels of each meal were equalized across all levels and sources of protein. Levels of other meal components were maintained as constant as possible and are shown at the bottom of Table V.

Since the source of protein appeared to affect the maximum kidney Ca level reached (Table XII) we decided to determine the effect of feeding, for 6 weeks, soy assay protein or spray-dried egg white on kidney calcification in rats. The results are summarized in Table XIV. To our surprise kidneys of male and female rats fed egg white powder showed a normal Ca content. It is likely that the increased urinary sulphate excretion by rats fed egg white (28) prevented the precipitation of calcium phosphate in the... 

Table XIV. Kidney calcium in rats fed different sources of protein for 6 weeks (mg/g dry weight)3...

---