Monday, December 19, 2011


Food industry in almost all countries are being forced to include nutritional information on the label so that consumers can have an idea as to the foods they are buying. Prominent nutrients to be declared include Protein, Sugar, Fat and dietary fiber besides the energy value per serving. While quantitative figures do give the extent of the nutrient present, there is no provision to indicate their quality. In the case of fat at least there is a direction to declare the extent of trans fats and sat fats. With wide variations in the quality of proteins from different sources and also the pace of  release of glucose from carbohydrates, a time has come probably to indicate the efficacy of these components in the food vis-a-vis nutrition. Probably the time has come to at least insist on stating the quality of the protein in the food on the label of the package and this assumes all the more significance when it comes to high protein foods being marketed by the well being industry.  

Even a child in to day's modern world knows how critical is protein in the food they consume for ensuring growth and high protein food products lead the portfolio of well being foods in the market. However what is not known so very well is the importance of quality of protein consumed that can make a difference in their effectiveness. In almost all food science courses it is dinned into the ears of the students that animal proteins are superior in quality to that contained in plant foods. Probably this assumption is based on the fact that the nutritional quality of a protein is closely related to the proportion of essential amino acids present in them and it may be true that some plant proteins do lack some of theses amino acids and different proteins may have different "limiting" amino acids bringing down their overall value as a complete protein source.

The concept of mutual supplementation evolved when limiting amino acid issue came to the fore and in order to overcome deficiency of any amino acid two or three sources of proteins are blended to neutralize such a draw back. For example it is presumed that groundnut protein is deficient in Lysine while cereal proteins do not contain adequate Methionine. Soybean is rich in Lysine A blend of groundnut protein and soy protein, therefore can be expected to be a more or less complete protein product, nearly equivalent to egg protein. In spite of the rapid advances made in the field of Biochemistry, there are widely differing perceptions regarding quality of protein and the vested interests in boosting one protein over others from different sources have clouded the understanding of real value of proteins in general. No matter what sophisticated instruments or techniques are employed for protein analysis ultimately what influences the real effectiveness is the extent of proteins that get into the body across the digestive tract which is influenced by many variable factors. This is a problem ignored when high protein foods are designed, produced and marketed by most of the players in this field.

Classically protein was always deduced by estimating the nitrogen present in the sample using the age old Kjeldahl Method and multiplying it with a factor varying from 5.46 to 6.38 which reflects the extent of Nitrogen present in relation to carbon, oxygen and hydrogen moieties in the protein under consideration. Nitrogen content is influenced by the extent of different amino acids present in the protein. Thus the factor used for Milk products is 6.38, for meat and egg 6.25, for grains 5.8 and for nuts 5.46. Unfortunately presence of nitrogenous compounds other than proteins vitiate the results so obtained, often giving a higher value for the protein content. Direct methods are also available based on specific chemical reactions but they are also influenced by chemical substances in the complex food system that can interfere with the results. As for quality of the protein both Protein Efficiency Ratio (PER) and Biological Value (BV) are the preferred tools in the hands of Biochemists and Nutritionists but they need experimental animals and require a few days to get the results. Net Protein Utilization ( NPU) is another indicator of protein quality and used by many to compare quality of different proteins in relative terms.

In a recent new study the present scenario vis-a-vis protein quality assessment has been critically evaluated and it has been found that most traditional assay methods do not present the real picture regarding the protein quality in foods. It was pointed out that the current methods  for determining protein quality shows most plant proteins as of lower quality compared to animal-based proteins. The Food and Agriculture Organization (FAO) and the World Health Organization (WHO) recommend the protein digestibility-corrected amino acid score (PDCAAS) as a simple and scientific procedure for assessing protein quality. This methodology focuses on three different parameters which include the amount of each essential amino acid present in the protein, how easily it is digested and by taking both of those parameters into account, whether the protein meets the FAO/WHO's amino acid requirements set for children aged 2 to 5 years, as they have higher needs to support growth and development than adults.

According to the above method, a protein having a score of 1 in the PDCAAS scale is supposed to be the highest in quality whereas a zero scale makes it the lowest quality. Measured on this scale Casein, Egg White, Soy protein isolate and Whey proteins have PDCAAS scores of 1, Beef protein scores 0.92 while all proteins from plant sources have scores between 0.42 (whole wheat) and 0.9 (soybean). What is interesting is that when PDCAAS score is determined for plant sources except soybean, proteins were not isolated but assessment was made with the food materials themselves which could have vitiated the results very significantly. Also to be noted is that no human diet is made of a single protein source and when different food sources are combined in evolving a diet there is the distinct possibility that a mixed diet may have PDCAAS scores even beyond 1 if properly assessed.

It must be realized that precise methods for determining protein quality are critical for planning any healthy diet. Currently there is lot of interest in including plant-based proteins in the diet and accurate information on protein quality is needed to demonstrate that a diet can include quality plant-based proteins to achieve same results as with animal based proteins. Variations do occur in results from laboratory to laboratory in the amino acid analysis but if the PDCAAS determinations take nitrogen recovery into account necessary corrections can be made to counter act the analytical method error. Isolated soy proteins and soy concentrates are reported to have a PDCAAS of 1.00 indicating that plant proteins can also be as good as that in meat, egg and dairy products. Same may be true with many other plant proteins if they are isolated and quality assessed by the PDCAAS Method. Already Quinoa and Amaranth Seed have established themselves as sources containing high quality proteins similar to animal proteins. All said and done, consumers need not be too much concerned about protein quality if normal mixed diets are consumed regularly. However industry which designs high protein products must consider PDCAAS score of ingredients used in formulating their products and declare the same for justifying the claim that the high protein foods marketed by it is really efficient.


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