CONSIDERING TRUE

PROTEIN BIOAVAILABILITY:

IMPACT OF PROCESSING HEAT TO

PROTEINS

REDUCING NITROGEN EXCRETION

Joel F. Mangalindan DVM

Clinical Nutrition Practitioner

In the last 2 decades, significant advances

in technology and equipment have allowed

deeper insights into protein

bioavailabilities, well beyond the traditional

analysis which have been the standard basis

of identifying the immediate cause.

Processing protein sources for drying and preservation inevitably involves heat.

Although other non-heat methods are now available (i.e. ultrafiltration and ultracentrifugation), their high operating costs render them non-attractive and impractical for mainstream protein feed products.

BIOAVAILABILITY = TRUE PROTEIN VALUE

% OF PROTEIN INTAKE THAT IS USED AS PROTEIN

BY THE BODY

represents what actually happens to the material ingested, from the time it reacts with the different digestive processes, then absorbed and processed by the liver, to the time it is utilized by the cells, and the eventual production and excretion of by products and wastes

Amount absorbed = intake – excretion (fecal and urine)

Bioavailability tests on most ingredients show a wide disparity between what is analyzable and what is bioavailable

- revealed that most prepared foods reflect a predominantly overfeeding of proteins in terms of actual requirement but generally underdosing in terms of what are biologically available to the animal.

TYPICAL PROTEIN INTAKE, UTILIZATION AND

EXCRETION IN PIGS : PROTEIN BIOLOGIC VALUE

OF STANDARD CORN-SOY RATION

PROTEIN in Feed

55 gm N/ 100%

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Retention Feces Urine

17 gm N/ 30% 11 gm N/ 20% 27 gm N/ 50%

*From; Aarnink, et.al. 1997; Nitrogen Chain tests on growing-finishing pigs

EFFECT OF NUTRIENT CONTENT IN DIETS ON NUTRIENT BALANCE, TYPICAL NITROGEN

AND P CONSUMPTION, DEPOSITION AND EXCRETION PROFILE IN PIGS

kg/sow/yr__________________________________________________________________________________

Phosphorous Protein (N)

----------------------------------- -------------------------------------------

High Basal Low High Basal Low

----------------------------------- -------------------------------------------

Per Sow Integrated

(includes 22 pigs/sow/yr

to slaughter)

Consumed (kg) 39.1 27.9 24.3 177 161 145

Deposited (kg) 11.2 11.2 11.2 55 55 55

Excreted (kg) 27.9 16.7 13.1 122 106 90

% excreted 71 60 54 69 66 62

___________________________________________________________________________________From: Lawlor,P. Pig Int.,May 2001.vol 31,no. 5, p 15-16.

NITROGEN (PROTEIN) EXCRETION POULTRY

DIET CP NITROGEN

% OUTPUT/DAY % OF TOTAL % N IN MANURE

in gms. N INTAKE DM BASIS

BROILERS (3-6 WKS)

21 2.70 62.49 5.29

18 1.98 54.40 4.72

LAYERS

18 2.3 66.90 5.84

15 1.39 60.14 4.60

*adapted fr: CANADA-BC GREEN PLAN FOR AGRICULTURE

The high N/protein excretion in corn-soy is due to

the:

1. inherent LOW BIOLOGIC VALUE of

plant proteins.

2. up to 40% of plant proteins are trapped

within the plant fiber, making them

unavailable

Molecular view of Xylan-cellulose complex in wheat showing 3D physical,

geometric and surface characteristics, and trapping of proteins and other

nutrients inside fiber matrix

PLANT FIBERS ARE NORMALLY

INDIGESTIBLE TO MONOGASTRICS LIKE

PIGS, POULTRY AND HUMANS, AS THEY

DO NOT PRODUCE THE BETA ENZYMES

NEEDED TO DIGEST THE BETA - LINKED

FIBERS

CURRENT UNDERSTANDING

OF PROTEINS

Crude protein (CP), the traditional way of establishing protein value, is now recognized as a misleading measure, oftentimes overestimating the true protein value.

As the CP test is simply based on the amount of N in the material multiplied by a factor (N x 6.25), it obviously represents a chemical value, rather than a biological one.

Proteins exist in a helical form, and must stay that way in order to be biologically active.

The way the helical forms fold and unfold determine and affect functionality.

IMPACT OF PROCESSING

HEAT ON PROTEINS

The impact of processing heat application on nutrient bioavailability is now well understood.

MAIN EFFECT - disruption of the hydrogen bonds.

H Bonds

responsible for holding the chemical components together

determine both the physical form and functional activity of the nutrient.

hydrogen bonds bind amino acids into complex proteins, fatty acids into fats/lard and sugars into carbohydrates and fiber, and organic acids to minerals.

The degree of heat applied and length of exposure determines the degree of disruption of the bonds.

DISRUPTION OF H BONDS

CALLED

PROTEIN

DENATURATION

Protein denaturation and coagulation of proteins.

LEVEL OF DENATURATION CAUSED BY HEAT

DEPENDS ON

TYPE OF PROTEIN

TEMPERATURE AND LENGTH OF

EXPOSURE

THE HIGHER THE TEMPERATURE AND

THE LONGER THE EXPOSURE, THE

HIGHER IS THE LEVEL OF DENATURATION

Type of protein material

Naked proteins – non-cellular in nature, like plasma, secretory products like milk, egg white

- very sensitive, denatured at temperatures beyond 60degC

Cellular proteins – with cell walls like muscles, organs, rbc, yeast, bacteria

- less sensitive, denatured at temperatures beyond 80degC

Temperature and length of exposure

Rendering – >110degC for 30 minutes, >80% denaturation<20% bioavailability

Spray dry - >65-85degC for 2-5 seconds, <10% denaturation>90% bioavailability Used with liquid, naked proteins and enzymatically digested proteinsproteins like milk, milk products, blood and blood components, fish solubles and

porcine solubles

Flash dry and dry extrusion- 75-110degC for <10sec>10% denaturation >80% bioavailability

PROTEIN DIGESTIBILITY (%), PROTEIN DIGESTIBILITY CORRECTED AMINO ACID SCORE (PDCAAS, %), RELATIVE PROTEIN EFFICIENCY RATIO (RPER %) AND RELATIVE NET PROTEIN RATIO (RNPR %) OF UNTREATED AND HEAT TREATED PROTEINS*

Product TrueProt. Dig. PDCAAS (rat) PDCAAS(human RPER RNPR

Casein+met 100 100 100 100 100

Casein 99 85 100 80 84

Lactalbumin untreated 99 100 100 89 91

Lactalbumin treated 73 55 67 0 0

Soy protein isolate untreated 96 62 100 56 64

Soy protein isolate treated 68 44 49 0 0

_____________________________________________________________________________________

*Sarwar, 1997

Heat Treatment at 250oF for 30min

PDCAAS % = True protein Dig X amino acid score (lowest amino acid ratio)

Amino acid score - mg of essential amino acid in 1 g of test protein/mg of same amino acid in ref protein X 100

RPER = PER of test diet/PER of control diet X 100

RNPR = NPR or test diet/NPR of control diet

PER (protein efficiency ratio) = weight gain of test rat/protein consumed by rat

NPR (net protein ratio) = weight gain of test rat + weight loss of non-protein rat/protein consumed by test rat

RPER and RNPR are BIOLOGIC VALUE DETERMINATIONS - 0% RPER and RNPR indicate at least 50% of proteins were deaminated/not used as proteins.

In canned, wet foods, protein digestibility

has been shown to be severely impacted.

In simulated canned cat food studies, at

250degF, protein digestibility decreased

with increasing exposure time,

progressing from 38% decrease at 5

minutes exposure to over 80% decrease

at 25 minutes exposure (Hendricks, et.al.

1999).

Opposite effect on carbs and fats -heat application improves carbohydrate and fat bioavailability but on the other hand, reduces protein bioavailability

FATE OF DENATURED

PROTEINS

Denatured proteins, if absorbed, are recognized by the liver not as proteins, but as keto-carbohydrate energy like nutrient.

Denatured and precipitated proteins are insoluble and thus excreted with manure

The N is cleaved off (deamination) keto skeleton enters the Glycogenic/Krebs pathway and used as energy.

The free nitrogen is conjugated blood stream kidney into the urine.

Large amounts of denatured protein intake invariably leads to high levels of nitrogen concentration in the bladder/urine

The Mitochondria and the CITRIC ACID CYCLE

The freed nitrogen is then conjugated for transport, released into the blood stream and joins the excess nitrogen excretion in the kidney and into the urine.

As CP is evidently a poor indicator of true protein value, and Pepsin Digestibility as grossly outmoded and biologically unreliable, the need to come up with alternate indicators and procedures to establish true protein value is indicated.

1. FAO has recently recommended the RAT BALANCE METHOD as the most suitable, practical and reliable assay of true protein digestibility.

A = I – (F - Fk )where A = absorbed nitrogen

I = intake nitrogenF = fecal nitrogenFk = metabolic nitrogen (urine N)

2. Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF) – can be used as indicator of denaturation level in animal proteins

Example, in the NRC Ingredient Analysis Table,rendered meat and bone meal (50%CP) has 32.5% NDF and 5.6% ADF.

As animal protein has no fiber, these valuesmay logically represent denatured andprecipitated proteins , indicating that at least60% of the proteins therein are denatured and/or precipitated.

(Not yet accepted as a recommended test)

IMPACT ON MEAL SELECTION AND VALUE

1. Valuation of protein meals primarily depend on the production process, where the highest price tends to provide the highest biologic value.

COMPARATIVE PRICES OF PROTEINS DEPENDING ON PROCESS _________________________________________________________________

USD/MT FOB

Spray dry egg powder 1,380Flash dry egg powder 950Ring dry egg powder 875Rendered Meat & Bone meal, beef 250Flash dry meat and bone meal 480Spray dry meat solubles 1,490Spray dry blood meal 1,280Rendered dry blood meal 420Steam dry fish meal 900Spray dry fish soluble 2,100_____________________________________________________________________

COMPARATIVE VALUE ANALYSIS BASED ON BIOAVAILABLEPROTEIN

_____________________________________________________________

Blood Meal CP Cost USD %Bioavailable Cost/gram bioavailable

Spray dry 80 1280 92 1.73cRendered 80 420 22 2.39c

__________________________________________________________

Inspite of the spray dry form having more than 75% higher product cost, the rendered form is almost 1.4 times the cost in terms of bioavailable protein.

2. Selection of spray dry protein meals for young animals can now be strongly justified by the markedly high bioavailability of proteins, required by animals with underdeveloped digestive capability.

3. Solvent extracted vegetable protein meals (i.e soybean meal, copra meal, etc) will be preferable over mechanically extracted ones, as steam used in conditioning materials for mechanical extraction imparts a denaturing effect on the proteins (although it improves carbohydrate bioavailability).

*New mechanical extractors - extruder

expellers - greatly lower temperatures

and shorten exposure time to below 5

sec resulting to much lowered

denaturation effect (less than 10%

denaturation).

recognition of how much denatured/unfolded proteins will be used as energy will significantlyaffect formulations, as it is well recognized that high energy to protein ratio results not only to high backfat but also to decreased protein accretion/musculature.

Use of higher bioavailability proteins will also allow lower feed CP (i.e. 14%CP for grower rations instead of 18% CP) without affecting performance.

Invariably, in properly implemented regimens, such strategy gives rise to better performance indices - energy costs of digestion and reduction of heat increment effects are diverted to production.

Phenomenon is commonly observed in tropical production.

CONCLUSION

These new insights allow a more accurate

formulation of feeding regimens, one that

considers actual protein bioavailabilities rather

than analysis, and which satisfies nutrient

requirements in much lower dosages/intake,

without resulting to large amounts of nitrogenous

excretory products.