Vegetables, amino acid content

Oily fishmeal is allowed in organic rations and it has an even higher essential amino acid content than full-fat soya. However, its use in poultry rations is limited partly by cost, restrictions on the source of the fishmeal imposed by organic standards, the fact that some customers demand birds that are fed on a vegetable-based diet and concerns about fishy taints to the product (Walker and Gordon, 2001). 

The nutritional value of proteins (see p. 360) is decisively dependent on their essential amino acid content. Vegetable proteins—e.g., those from cereals—are low in lysine and methionine, while animal proteins contain all the amino acids in balanced proportions. As mentioned earlier, however, there are also plants that provide high-value protein. These include the soy bean, one of the plants that is supplied with NH3 by symbiotic N2 fixers (A). 

Anon (1999c) Fruit and vegetable juices. Determination of free amino acids content liquid chromatographic method. BS EN 12742 1999. Available from the British Standards Institute (BSI) or one of the other EU standards bodies. 

Proteins are not alike. They vary according to their origin (animal, vegetable), amino acid composition (particularly their relative content of essential amino acids), digestibility, texture, etc. Good quality proteins are those that are readily digestible and contain the essential amino acids in quantities that correspond to human requirements. 

The three available industrial methods for the production of HVPs are (i) enzymatic a slow process that may result in the formation of bitter peptides and typically lacks the desired aroma/taste profile [20,21,39] (ii) alkaline hydrolysis which typically results in unacceptable flavor profile and an unbalanced amino acid content, and (iii) acid hydrolysis the most preferred method that is cost effective and yields a range of good flavors (see Chapter 11, section 11.4.1.2 Hydrolyzed Vegetable Proteins). 

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. 

The use of nitrogen fertilization results in higher content of N-containing compounds, including free amino acids, and also increases in terpene content in wood plants, whilst starch, total carbohydrates, phenylpropanoids and total carbon-based phytochemicals decreased (Koricheva et al., 1998). Higher levels of nitrogen favoured its uptake and increased the nitrate content of the crop, which is critical for salad vegetables and baby foods. 

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. 

Other early food applications included the analysis of pesticide residues in fruits and vegetables, organic acids, lipids, amino acids, toxins (e.g., aflatox-ins in peanuts, ergot in rye), and contaminants. As with pharmaceutical analysis, HPLC provides the ability to analyze for vitamin content in food... 

Proteins occur in animal as well as vegetable products in important quantities. In the developed countries, people obtain much of their protein from animal products. In other parts of the world, the major portion of dietary protein is derived from plant products. Many plant proteins are deficient in one or more of the essential amino acids. The protein content of some selected foods is listed in Table 3-1. 

Flavor enhancers are substances that carry the property of umami (see Chapter 7) and comprise glutamates and nucleotides. Glutamic acid is a component amino acid of proteins but also occurs in many protein-containing foods as free glutamic acid. In spite of their low protein content, many vegetables... 

Table 7. Contents of Free Amino Acids in Vegetables...

Many different types of fruit and vegetable crops and other processed foods are analysed for a variety of trace organics both for impurities (such as pesticides) and for content (e.g. amino acids, lipids, etc.). As with soil, it is important to take a representative sample for analysis. 

The average conversion factor for estimation of true protein, based on the ratios of total amino acid residues to amino acid N, determined for 23 various food products is 5.68 and for different classes of foods, 5.14-6.61 (Table 1.2). The N P factor of 4.39, based on analysis of 20 different vegetables, has been proposed by Fujihara etal. (2001) for estimating the true protein content in vegetables. A common N P factor of 5.70 for blended foods or diets has been recommended by Sosulski and Imahdon (1990). 

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