total dietary fibre????

Dietary Fibre :

Dietary fibre is usually determined by fractionation procedures and the one proposed by Southgate is now widely used. The estimate of amount of dietary fibre in a food will depend upon the analytical method used for the estimation and the values so obtained need not necessarily be considered always precise. Dietary fibre estimation is still considered to be only semi-quantitative.

True Protein and total Protein :

The Kjeldahl Test

Historically, the Kjeldahl method has

been the primary procedure used to test

milk protein reference samples. These

protein reference samples are used by

milk plants, cooperatives and DHIAs,

among others, to calibrate automatic

milk protein testing equipment.

Milk protein content is not measured

directly by the Kjeldahl. The test instead

measures the nitrogen content of milk.

Milk protein contains 15.65% nitrogen.

To convert the Kjeldahl nitrogen

reading to milk protein, the nitrogen

measurement is multiplied by a factor

of 6.38 (100 ÷ 15.65). For example, if a

milk sample is determined to contain

.55% nitrogen by Kjeldahl analysis,

then its protein content is .55 x 6.38, or

3.5%.

Use of the Kjeldahl method presumes

that all of the nitrogen found in milk is

contained in protein. However, this is

not the case. A portion of the nitrogen

in milk comes from non-protein sources,

such as urea and uric acid. These other

protein sources are called non-protein

nitrogen (NPN). The Kjeldahl method

therefore actually measures what is

termed total protein. Total protein is the

nitrogen in milk multiplied by 6.38.

True Protein

The true protein in milk is the total

nitrogen minus the NPN, then multiplied

by 6.38. The textbook average

level of NPN in milk is about 5%. Dr.

David Barbano of Cornell University

conducted a yearlong national milk

composition study in 1985. His findings

showed an average total protein

value of 3.27%, a true protein value of

3.11%, and average NPN of 4.78%.

Assuming an average NPN value of

5%, then the true protein content of a

milk testing 3.2% total protein would

be calculated as follows:

0.5% x 3.2% = 16% NPN

3.20% Total Protein

– .16% NPN

3.05% True Protein

The 5% NPN is an average. The percent

NPN varies among breeds, seasons

and regions. Table 1 was obtained from

a study showing differences in NPN levels

by breeds. This table shows that Jersey

milk contains less non-protein nitrogen

(3.6%) than other dairy breeds.

A University of Vermont study examined

seasonal variations in NPN among

Vermont cheese plants. The graph in

Figure 1 demonstrates these results. Dr.

Barbano’s work mentioned earlier

showed seasonal and regional variations

in NPN as well. His research revealed

that NPN as a percentage of total nitrogen

varied seasonally from 4.33% to

5.22%. Perfect NPN is the highest in the

summer and lowest in the winter. The

study also found the lowest monthly

regional NPN was 3.9% and the highest

5.6%.

Another Barbano project found significant

variation among farms. In a limited

study on 24 western New York farms,

results were obtained showing NPN

variation from a low of 2.9% to a high

of 6.1%.

What Is The Point?

Why make an issue of whether true

protein or total protein is used? Fifteen

years ago, Vernal Packard, food scientist

at the University of Minnesota, addressed

this question and gave the following

reasons for why true protein

should be used instead of total protein.

1. NPN does not have biological

value as protein. For the most part,

it cannot be used by the body to

perform functions characteristic of

protein.

Table 1. Nitrogen distribution in milk (milk total N equals 100%).

NPN Protein N Casein N

(%) (%) (%)

Jersey 3.6 96.4 80.2

Guernsey 3.9 96.1 77.7

Holstein 4.9 95.1 78.2

Ayrshire 4.9 95.1 78.7

Brown Swiss 5.4 94.6 77.4

Milking Shorthorn 7.5 92.5 74.8

Average 4.9 95.1 77.9

Source: J. Dairy Sci. 58: 417

Figure 1. Variation of mean percentage nonprotein

nitrogen (NPN) of total nitrogen (TN)

in milks from seven Vermont cheese plants

by months (1980-1981).

True vs. Total Protein

(continued from page XX)

2. NPN does not add cheese yield. It

has no place in a purchase plan for

milk in which cheese yield is the

major consideration.

3. If all dairy plants are not on the

same program—either true or total

protein—the difference becomes a

source of confusion.

4. Level of NPN is highly variable in

milk. Because the Kjeldahl method

is used as the official method for

calibration and daily control of infrared

and dye binding testing devices,

NPN becomes a source of

variability in these other methods,

even though they do not measure

NPN as such.

5. Seasonal variations in NPN–and

these are significant–must either be

ignored or adjustments in equipment

made on a seasonal basis.

6. Breeding programs for protein can

be more tightly monitored on true

than total protein. Because increases

in percentage of protein

come very slowly and in very small

increments, NPN may mask these

changes. In other words, true protein

is by far the better basis for

evaluating progress of breeding

programs.

Packard noted, “Of the several factors

that have some influence on NPN level

in milk, feeding practices on the farm

may be the most important. Whenever

the ratio of protein to energy in the feed

goes up, NPN level increases. Feed more

protein and less grain, and not protein

but NPN level (%) increases in milk. This

kind of change in protein/energy ratio

is characteristic, in some parts of the

country, of the change from winter to

summer (pasture) feeding. As a rule, NPN

% increases in summer and drops in the

winter.

“Considering the preceding factors,”

Packard concluded, “compelling reasons

appear to exist for basing protein

purchase on the true rather than total

protein, as is done in most European

nations. In doing so, a regional policy

and, preferably, a national policy to that

effect becomes essential, so that neighboring

plants and states are all testing

on the same basis.”

Testing For True Protein

The Kjeldahl method can still be used

to prepare true protein calibration

samples. The difference in testing for

true protein rather than total protein involves

sample preparation and additional

procedures. As with total protein,

the Kjeldahl procedure for true protein

produces accurate and reliable true protein

calibration samples.

Adjustments In MCP Plans Using

True Protein

In 1988, the New York State Department

of Agriculture and Markets required

all protein payment programs to

use true protein instead of total protein.

Protein pricing programs in New York

state were adjusted accordingly. For example,

Eastern Cooperative previously

paid a protein premium of 10 cents for

each 0.1% of protein above 3.3%. Using

true protein, the cooperative lowered

its base to 3.1%.

On the average, most dairy farmers

did not see any change in their total

protein premium dollars. Their true protein

tests were approximately 5% lower

than their total protein tests. However,

the difference was compensated for by

lowering the protein base.

For those plants using End Product

Pricing (EPP), an adjustment was made

in the percentage of protein that is

casein. The original cheese yield formula

estimates casein to be 78% of total

protein. If true protein is used, casein

is 82% of true protein.

Implications For Jersey Milk

The Federal Order Reform decision

requiring the use of true protein instead

of total protein is a positive one for Jersey

producers, because of the lower percent

of non-protein nitrogen in Jersey

milk compared to average milk. Payment

on the basis of true protein will

make milk pricing more equitable.

Consider the example of a plant paying

a protein premium of 10¢ per 0.1%

above 3.2% based upon total protein.

Jersey milk testing 4.0% total protein

would receive a premium of 80¢ per

hundredweight (8 points x 10¢).

On a true protein basis, using an average

NPN of 5%, the base would be adjusted

to 3.04% to reflect true protein.

Non-protein nitrogen in Jersey milk is

3.6%, leaving a true protein content of

3.86%. At 10¢ for each point of protein,

the premium for Jersey milk increases

from 80¢ to 82¢ per hundredweight.

In addition, cheese yield is more accurately

predicted using true protein

measures. The value of Jersey milk sold

under End Product Pricing therefore increases

when true protein is the basis

for calculating payment.

For example, assume that a plant is

using a cheese yield value of $1.20 per

pound. Jersey milk testing 4.8% butterfat

and 4.0% protein and producing

12.90 lbs. cheese would be valued at

$15.49 under EPP. Jersey milk testing

4.8% butterfat and 3.86% true protein

would yield 12.98 lbs. cheese, which is

worth $15.58 at $1.20 per pound.

Crude Protein and Total protein :

Yes crude protein is sometimes called as total protein content

Try solubility tests.