PET Food Processing - March 2021 - 38

FORMULATION

Beyond the recommendations

AAFCO in the United States and FEDIAF in Europe
make recommendations for dietary AAs which are
similar to those established by the NRC. However,
they have been scaled up to account for ingredient-toingredient differences in AA digestibility (the amount
of an AA that is transported out of the gut and into the
body) and bioavailability (the amount of an AA that
can be used for protein synthesis in the body).
Determining AA digestibility and bioavailability
of different ingredients is important when formulating diets. This is, in part, because many AA minimum
requirements presented by the NRC are also based
upon data from studies utilizing purified diets with
highly digestible ingredients, such as crystalline AAs.
Crystalline AAs are assumed to be 100% bioavailable
while commercial diets are typically formulated with
natural intact-based protein sources that are generally
assumed to have a protein digestibility of approximately 80% (NRC 2006). However, AA digestibility does
not necessary correlate to nitrogen digestibility. The
most accurate method for determining AA digestibility is measurement of ileal AA digestibility by collecting digesta from the end of the small intestine (NRC
2006). This method determines what proportion of the
AAs supplied in the diet are absorbed by the animal,
since protein is digested, and AAs are absorbed before
the end of the small intestine. However, this method
is invasive, requiring surgical insertion of a cannula at
the end of the small intestine, and for this reason, is no
longer done in dogs. Alternate methods for determining digestibility of AAs in dogs have been used with
the most common in the pet food industry being the
assessment of total-tract AA digestibility (NRC 2006).
While certainly less invasive, as this method only requires collection of feces, it overestimates AA digestibility from the diet as the feces will also include AAs
produced by the bacteria in the large intestine and endogenous losses (e.g. enzymes, sloughed cells, bacteria,
and mucus) (NRC 2006). As digestibility is often considered an indication of bioavailability, this demonstrates that bioavailability may also be overestimated
when extrapolated from total tract digestibility.
Processing and storage of ingredients can also affect
the bioavailability of an AA even if it is digestible. For
example, lysine can react with reducing sugars in carbohydrates in the presence of heat (referred to as Maillard
reaction products) and during alkali treatments (formation of cross-linked AAs) (Fernandez and Parsons 1996)

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PET FOOD PROCESSING | March 2021 | www.petfoodprocessing.net

(González-Vega, et al. 2011). These products can be
absorbed, but bound lysine cannot be used by protein
synthesis. Therefore, digestibility values of an AA may
remain the same, but bioavailability may be reduced.
Digestibility of indispensable AAs in intact protein ingredients can be further affected by other dietary components such as fermentable carbohydrates.
Fermentable carbohydrates reduce ileal digestibilities, nitrogen retention, and average daily gain in pigs
(Myrie, et al. 2008). The addition of dietary pectin has
been reported to reduce total tract crude protein digestibility in dogs (Silvio, et al. 2000). In addition to
reducing ileal digestibility of the AA, fermentable fibers such as oligosaccharides result in greater colonic
weight of rats (Campbell, et al. 1997), which may affect
the utilization of AAs, specifically those that are used
in considerable amounts by the gut (e.g. methionine)
(Shoveller, et al. 2003) (Riedijk, et al. 2007). Therefore,

" Determining amino
acid digestibility and
bioavailability of
different ingredients
is important when
formulating diets. "
Crosbie, et al, University of Guelph

it is important to know not only what indispensable
AAs are provided by specific protein ingredients but
also the digestibility of these indispensable AAs on
their own and in the presence of other ingredients
to ensure the requirements for these indispensable
AAs can be met accurately. This also provides a further case for additional supplementation of crystalline
AAs when meeting indispensable AA requirements
through only intact ingredients.
Regardless of what method is used to determine AA
digestibility and bioavailability in intact ingredients,
processing (especially heat treatment) can impact digestibility/bioavailability of AAs, as many ingredients
require processing treatments before consumption to
improve digestibility and eliminate bacteria. A trend in
commercial dog diets, especially grain-free diets, is the
use of legumes (such as peas, chickpeas, and lentils) to
supply carbohydrates and protein. Legumes cannot be
consumed in their native form and must be processed
before consumption. Leguminous ingredients in their
raw forms contain anti-nutritional factors (ANF). Of
the ANFs found in legumes, trypsin and chymotrypsin

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(Moughan 1999). Therefore, alternative and more sensitive techniques for determining AA requirements in
adult dogs should be considered in the future.


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PET Food Processing - March 2021

Table of Contents for the Digital Edition of PET Food Processing - March 2021

PET Food Processing - March 2021 - Intro
PET Food Processing - March 2021 - 1
PET Food Processing - March 2021 - 2
PET Food Processing - March 2021 - 3
PET Food Processing - March 2021 - 4
PET Food Processing - March 2021 - 5
PET Food Processing - March 2021 - 6
PET Food Processing - March 2021 - 7
PET Food Processing - March 2021 - 8
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http://digital.petfoodprocessing.net/sosland/pfp/pet-food-processing-march-2021
http://digital.petfoodprocessing.net/sosland/pfp/2020_12_01
http://digital.petfoodprocessing.net/sosland/pfp/2020_10_01
http://digital.petfoodprocessing.net/sosland/pfp/2020_09_01
http://digital.petfoodprocessing.net/sosland/pfp/2020_06_01
http://digital.petfoodprocessing.net/sosland/pfp/2020_03_01
http://digital.petfoodprocessing.net/sosland/pfp/2019_12_01
http://digital.petfoodprocessing.net/sosland/pfp/2019_10_01
http://digital.petfoodprocessing.net/sosland/pfp/2019_09_01
http://digital.petfoodprocessing.net/sosland/pfp/2019_06_01
http://digital.petfoodprocessing.net/sosland/pfp/2019_03_01
http://digital.petfoodprocessing.net/sosland/pfp/2018_12_01
http://digital.petfoodprocessing.net/sosland/pfp/2018_09_01
http://digital.petfoodprocessing.net/sosland/pfp/2018_06_01
http://digital.petfoodprocessing.net/sosland/pfp/2018_03_01
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