Protein contents

There is no direct evidence for the alternative mode of conjugation of the protein through a peptide linkage although oxidation of tyrosine containing peptides by tyrosinase was reported, first by Bu Lock and Harley-Mason (30) and later by Yasunobu et al. (284) and Rosel et al. (225a) using model peptides. 

Benathan and Wyler (S) found that native sepiomelanin loses on treatment with hot 6 M HCl, most of the proteic component during the first 15 min, the remaining part being removed in about an hour. Analysis of the solubilized fraction revealed a mixture of amino acids (11%) along with a small amount of glucosamine. The result indicates that a major portion of protein is loosely bound to the pigment granules. 

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Hard red winter (HRW) is an important bread wheat that accounts for more than 40% of the United States wheat crop and wheat exports. This fall-seeded wheat is produced in the Great Plains, which extend from the Mississippi River west to the Rocky Mountains, and from the Dakotas and Montana south to Texas. Significant quantities are also produced in California. HRW has moderately high protein content, usually averaging 11—12%, and good milling and baking characteristics. 

The protein fraction is filtered and dried to become high (60%) protein content com gluten meal. The starch slurry can be dewatered and dried to produce regular com starch. Dry starch can be sold as is or heat treated in the presence of acid catalysts to produce dextrins. Or, it is chemically modified before dewatering and drying to produce modified starches used in food and industrial appHcations. Lasdy, it can be hydroly2ed to produce corn sweeteners. 

Crude protein = %nitrogen X 6.25. Does not accurately reflect true protein content. Algal cells may contain nonprotein nitrogen substances, eg, 4—6% nucleic acids, dry wt basis. 

The 1993 market for LPC-type products in the United States was for dried alfalfa meal for animal feed. This product is sold for both protein and carotenoid content. The USDA Pro-Xan product attempts to obtain improved xanthophyU contents for use in egg-laying rations in addition to protein contents. The limitations to commercial development of LPC products for human food use are high capital costs as compared with the low yields of protein, seasonal availabihty of raw materials, and the need in the United States for FDA approval of the products. 

The sacroplasmic proteins myoglobin and hemoglobin are responsible for much of the color in meat. Species vary tremendously in the amount of sacroplasmic proteins within skeletal muscle with catde, sheep, pigs, and poultry Hsted in declining order of sarcoplasmic protein content. Fat is also an important component of meat products. The amount of fat in a portion of meat varies depending on the species, anatomy, and state of nutrition of the animal. The properties of processed meat products are greatiy dependent on the properties of the fat included. Certain species, such as sheep, have a relatively higher proportion of saturated fat, whereas other species, such as poultry, have a relatively lower proportion of saturated fat. It is well known that the characteristic davors of meat from different species are in part determined by their fat composition. 

Protein Content. The protein content of milk can be determined using a variety of methods including gasometric, Kjeldahl, titration, colorimetric, and optical procedures (see Proteins). Because most of the techniques are too cumbersome for routine use in a dairy plant, payment for milk has seldom been made on the basis of its protein content. Dye-binding tests have been appHed to milk for determination of its protein content these are relatively simple to perform and can be carried out in dairy plant laboratories. More emphasis will be given to assessing the nutritional value of milk, and the dependence on fat content as a basis for payment will most likely change. 

In dye-binding tests, milk is mixed with excess acidic dye solution where the protein binds the dye in a constant ratio and forms a precipitate. After the dye—protein interaction takes place, the mixture is centrifuged and the optical density of the supernatant is determined. Utilization of the dye is thus measured and from it the protein content determined. Several methods for appHcation of dye-binding techniques to milk are given (24,25). 

Most nuts for commercial use are characteri2ed by high oil and protein contents (see Proteins) as well as a low percentage of carbohydrates (qv). However, some varieties, mostly inedible tree nuts such as acorn, horse chestnut, and chufa, contain at least as much sugar and/or starch as protein. The edible water chestnut is also in this category, as is the cashew nut, which contains starch in addition to a rich store of oil. The proximate composition of a number of nuts and of some nut products are given in Table 2 (3). 

Oilseed proteins are used as food ingredients at concentrations of 1—2% to nearly 100%. At low concentrations, the proteins are added primarily for their functional properties, eg, emulsification, fat absorption, water absorption, texture, dough formation, adhesion, cohesion, elasticity, film formation, and aeration (86) (see Food processing). Because of high protein contents, textured flours and concentrates are used as the principal ingredients of some meat substitutes. 

Compressed yeast is also sold in supermarkets in 18-g and 56-g packages. Since this product contains approximately 10% added starch to increase its shelf life, it has a lower protein content and fermentative activity than the compressed yeast sold to bakeries. 

Bakers inactive dry yeast is also widely used in the food industry. This yeast may be grown specifically as a food supplement and consequently there is a choice in its composition by varying growth conditions and feedstock makeup. It can possibly produce high levels of nicotinic acid and thiamin, the cmde protein content can be raised to 50—55% and it can be used as a vehicle for the incorporation of micronutrients such as selenium or chromium into the diet. 

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. 

High-speed hammer or pin mills result in some selective grinding. Such mills combined with air classification can produce fractions with controlled protein content. An example of such a combination is a Bauer hurricane hammer mill combined with the Alpine Mikroplex superfine classifier. Flour with different protein content is needed for... 

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