Protein quality of insects as potential ingredients for dog and cat foods

Abstract

Insects have been proposed as a high-quality, efficient and sustainable dietary protein source. The present study evaluated the protein quality of a selection of insect species. Insect substrates were housefly pupae, adult house cricket, yellow mealworm larvae, lesser mealworm larvae, Morio worm larvae, black soldier fly larvae and pupae, six spot roach, death's head cockroach and Argentinean cockroach. Reference substrates were poultry meat meal, fish meal and soyabean meal. Substrates were analysed for DM, N, crude fat, ash and amino acid (AA) contents and for in vitro digestibility of organic matter (OM) and N. The nutrient composition, AA scores as well as in vitro OM and N digestibility varied considerably between insect substrates. For the AA score, the first limiting AA for most substrates was the combined requirement for Met and Cys. The pupae of the housefly and black soldier fly were high in protein and had high AA scores but were less digestible than other insect substrates. The protein content and AA score of house crickets were high and similar to that of fish meal; however, in vitro N digestibility was higher. The cockroaches were relatively high in protein but the indispensable AA contents, AA scores and the in vitro digestibility values were relatively low. In addition to the indices of protein quality, other aspects such as efficiency of conversion of organic side streams, feasibility of mass-production, product safety and pet owner perception are important for future dog and cat food application of insects as alternative protein source.

Full text

WALTHAM SUPPLEMENT
Protein quality of insects as potential ingredients for dog and cat foods*
Guido Bosch
1†
, Sheng Zhang
1
, Dennis G. A. B. Oonincx
2
and Wouter H. Hendriks
1
1
Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH Wageningen, The Netherlands
2
Laboratory of Entomology, Wageningen University, PO Box 8031, 6700 EH Wageningen, The Netherlands
(Received 7 November 2013 –Final revision received 26 January 2014 –Accepted 20 February 2014)
Journal of Nutritional Science (2014), vol. 3, e29, page 1 of 4 doi:10.1017/jns.2014.23
Abstract
Insects have been proposed as a high-quality, efficient and sustainable dietary protein source. The present study evaluated the protein quality of a selection
of insect species. Insect substrates were housefly pupae, adult house cricket, yellow mealworm larvae, lesser mealworm larvae, Morio worm larvae, black
soldier fly larvae and pupae, six spot roach, death’s head cockroach and Argentinean cockroach. Reference substrates were poultry meat meal, fish meal and
soyabean meal. Substrates were analysed for DM, N, crude fat, ash and amino acid (AA) contents and for in vitro digestibility of organic matter (OM) and
N. The nutrient composition, AA scores as well as in vitro OM and N digestibility varied considerably between insect substrates. For the AA score, the first
limiting AA for most substrates was the combined requirement for Met and Cys. The pupae of the housefly and black soldier fly were high in protein and
had high AA scores but were less digestible than other insect substrates. The protein content and AA score of house crickets were high and similar to that
of fish meal; however, in vitro N digestibility was higher. The cockroaches were relatively high in protein but the indispensable AA contents, AA scores and
the in vitro digestibility values were relatively low. In addition to the indices of protein quality, other aspects such as efficiency of conversion of organic side
streams, feasibility of mass-production, product safety and pet owner perception are important for future dog and cat food application of insects as alter-
native protein source.
Key words: Dog: Cats: Nutritional value: Amino acid composition: In vitro digestibility
Trends towards 2050 predict an increased demand for animal-
derived protein sources for human foods due to the combined
effects of human population increase and increasing standards
of living in developing countries
(1)
. This demand will increase
the global competition for proteins in human food, pet food
and livestock feed and stimulate the development of alterna-
tive and sustainable protein sources for assuring food security.
The Food and Agricultural Organization of the United
Nations has highlighted the potential of insects as food
and feed sources
(2)
. Insects are in general proteinaceous
(3)
and some species can be efficiently grown on organic side
streams making these potentially sustainable alternatives for
current proteinaceous feed ingredients
(3–5)
. In addition, insects
are commonly consumed by feral cats around the world
contributing up to 6 % of their diet
(6)
. The information on
the protein quality is, however, currently limited for most
insect species. The aim of the present study was, therefore,
to evaluate the protein quality of a selection of insect species
as potential ingredients for dog and cat foods.
Experimental methods
Substrates
Insect substrates were housefly pupae (Musca domestica)
(donated by Jagran B. V. Hillegom), adult house cricket
(Acheta domesticus), yellow mealworm larvae (Tenebrio molitor),
lesser mealworm larvae (Alphitobius diaperinus), Morio worm
larvae (Zophobas morio) (all purchased from Kreca), black
* This article was published as part of the WALTHAM International Nutritional Sciences Symposium Proceedings 2013.
Abbreviations: AA, amino acid; CP, crude protein; OM, organic matter.
†Corresponding author: G. Bosch, email guido.bosch@wur.nl
© The Author(s) 2014. The online version of this article is published within an Open Access environment subject to the conditions of the Creative
Commons Attribution license <http://creativecommons.org/licenses/by/3.0/>.
JNS
JOURNAL OF NUTRITIONAL SCIENCE
1

soldier fly(Hermetia illucens) larvae and pupae (donated by
Laboratory of Entomology, Wageningen University) and adult
six spot roach (Eublaberus distanti), adult death’s head cockroach
(Blaberus craniifer) and adult female Argentinean cockroach
(Blaptica dubia) (donated by D. G. A. B. Oonincx). The black sol-
dier fly larvae were fed a broiler starter diet (Agruniek Rijnvallei
Voer BV) and the roaches were fed household food waste. The
other insect species were sourced from companies that keep the
diet compositions confidential. Reference substrates were poult-
ry meat meal (Sonac), fish meal (Research Diet Services) and
soyabean meal (Research Diet Services). Housefly pupae,
black soldier fly larvae, and pupae and cockroaches were
freeze-dried to a constant weight. House crickets, yellow meal-
worms, lesser mealworms and Morio worms were already
freeze-dried. Remaining poultry manure attached to the house-
fly pupae and dirt attached to black soldier fly pupae were
removed by hand. Before milling, housefly pupae, Morio
worms, black soldier fly larvae and pupae, and cockroaches
were broken using an ultracentrifugal mill without a sieve
(Retsch ZM 100, F. Kurt Retsch GmbH& Co. KG). Then
these insects were ground using a laboratory analytical mill
(A10, Janke & Kunkel GmbH u. Co KG), except for house
crickets that were ground in centrifugal mill with a 1 mm
sieve (Retsch ZM 100). Reference substrates were already in
a dried and ground form.
In vitro digestion
Substrates were in vitro digested according to an up-scaled
Boisen two-step method
(7)
with modifications
(8,9)
simulating
the canine gastric and small intestinal digestive processes.
Chloramphenicol was added during incubation for its antibiotic
effect. The number of replicate incubations required was cal-
culated on the anticipated amount of residue per replicate
and the total amount of residue required for chemical analyses.
Substrates (10 g) were incubated in beakers with a phosphate
buffer solution (250 ml, 0·1M,pH6·0) and an HCl solution
(100 ml, 0·2M). The pH was adjusted to 2·0 with 1 MHCl
or 10 MNaOH. Fresh pepsin solution (10 ml, 25 g/l, porcine
pepsin 2000 FIP U/g, Merck 7190) and 10 ml chlorampheni-
col solution (0·005 g/mol ethanol) were added and each bea-
ker was covered with a glaze and placed in a heating chamber
at 39°C for 2 h under constant magnetic stirring. Then, 90 ml
phosphate buffer (0·2M,pH6·8) and 50 ml of a 0·6MNaOH
were added into the solution. The pH was adjusted to 6·8 with
1MHCl or 10 MNaOH. Fresh pancreatin solution (10 ml,
100 g/l pancreatin, Porcine pancreas grade VI, SigmaP-1750)
was added and incubation was continued for 4 h under the
same conditions. After incubation, the residues were collected
by filtration of the slurries on a nylon gauze (37 µm) folded in
a Büchner porcelain funnel. The sample was washed twice
with acetone (99·5 %) followed by ethanol (96 %). Then the
cloth with the residue was temporarily placed on a clean
paper to evaporate the remaining ethanol/acetone overnight.
The residue was collected from the nylon cloth and dried at
70°C overnight in a preweighed jar. Then the oven-dried
jars were reweighed to determine the amount of dry residue
for each replicate, which allowed the calculation of DM
digestibility for each replicate. For each type of substrate, the
selected oven-dried residues were pooled and ground in
laboratory analytical mill (A10, Ika-Werk). The ground resi-
dues were transferred into a new jar, pending further chemical
analyses for calculating the in vitro DM, organic matter (OM)
and N digestibility for each substrate.
Chemical analyses
DM and ash were determined by drying to a constant weight at
103°C and combusting at 550°C, respectively. Nitrogen was
determined using the Kjeldahl method
(10)
, and crude fat
was analysed according to the Berntrop method
(11)
. Amino
acids (AA) were analysed by ion exchange chromatography
and ninhydrin derivatisation
(12)
.
Calculations
OM content was calculated at the 100 –ash content (percent-
age of DM). Crude protein (CP) was calculated as 6·25 × N
and AA content was expressed as percentage of CP.
Digestibility of substrate OM and N was calculated as the
amount of residue collected (in g DM) × content in residue
(in percentage of DM basis)/amount of substrate incubated
(in g DM) × content in substrate (in percentage of DM
basis). The AA scores were calculated as described in Kerr
et al.
(13)
using minimal requirements for growth of kittens
and puppies
(14)
as reference values.
Results and discussion
Protein and fat contents varied considerably between insect
substrates (Table 1). The CP content of insect substrates
was in general higher than that in soyabean meal and close
to that in poultry meat meal and fish meal. House crickets con-
tained the most CP followed by lesser mealworms and the roa-
ches. Fat content ranged from 12·8to39·6 % of DM for black
soldier fly larvae and Morio worms, respectively. Crude ash
content of insect substrates was between 3·0 and 5·6% of
DM, except for the black soldier fly larvae and pupae contain-
ing about 13 %. Ash contents of black soldier fly larvae ranged
in literature from 9·0to14·6% of DM
(15,16)
and 15·5% of
DM in prepupae
(17)
. Phe and Met contents of CP varied the
most between insect substrates, with highest contents found
for the housefly pupae. Housefly pupae were also high in
Lys as were the lesser mealworms. House crickets were rela-
tively high in Arg but low in His. As it has been suggested
that CP approximates the true protein for most species of
insects
(18)
, the AA were expressed on a CP basis to gain insight
in the protein quality. Chitin contributes to non-protein N and
contributes 1–7 % of the whole-body N
(18)
. Differences in chi-
tin content of insect substrates may confound the estimation
of protein quality. AA contents for insect species vary consid-
erably among studies. For example, for house crickets, Arg
content in the present study (5·7 % of CP) was within the
range of other studies
(3)
(4·9–6·0 % of CP) but His was higher
(3·4v. 2·1–2·6 % of CP). Depending on the diet fed, Met con-
tent of yellow mealworms ranged from 0·48 to 1·80 % of
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CP
(19)
. For application of insects as a protein source in pet
food or feed, it would be of importance to monitor and con-
trol the variation in AA composition. Met and Cys in poultry
meat meal was lower in the present study than reported in the
literature, i.e. 1·05 v. 1·07 % in Clapper et al.
(20)
to 2·11 % in
Johnson et al.
(21)
and 0·69 % (data not shown) v. 1·34 % in
Clapper et al.
(20)
to 2·66 % in Murray et al.
(22)
, respectively.
For the AA score, the first limiting AA for most substrates
was the combined requirement for Met and Cys. Highest
AA scores were found for housefly pupae, followed by black
soldier fly pupae and Morio worm and lowest scores for the
cockroaches.
In vitro OM digestibility was highest for yellow mealworms,
Morio worms and lesser mealworms (Table 2). Black soldier
fly pupae had lowest in vitro OM digestibility and was
16·2 % lower than for the larvae. This difference in digestibil-
ity is likely caused by a higher cuticular protein-sclerotisation in
the pupae. In vitro N digestibility was relatively high for the
house crickets, yellow mealworms, lesser mealworms and
Morio worms and low for black soldier fly pupae, six spot
roach and death’s head cockroach. Information on the digest-
ibility of evaluated insect species is limited in the literature.
Apparent faecal N digestibility of a diet containing 33 %
black soldier fly larvae meal as the main protein source was
76·0 % in 8·2–14·7 kg barrows
(16)
and a diet containing 50
% housefly pupae meal had an apparent faecal N digestibility
of 79·0 % in broilers
(23)
.
Selected insect substrates differed considerably in nutrient
composition as well as in vitro OM and N digestibility. Of
the insect substrates studied, the pupae of the housefly and
black soldier fly were high in CP and had high AA scores
but were less digestible than the other insect substrates. The
CP content and AA score of house crickets were high and
similar to that of fish meal but with slightly higher in vitro
N digestibility. The cockroaches were relatively high in CP but
the indispensable AA contents, the AA scores and in vitro digest-
ibility values were relatively low. Next to these indices of protein
quality, other aspects such as efficiency of conversion of organic
side streams
(2,24)
, feasibility of mass-production
(24)
, product
safety
(24,25)
and pet owner perception will determine if insect
species are used in future pet food formulations. These and
other aspects require further study.
Acknowledgements
This research was funded by Wageningen University. All authors
contributed fundamentally to the present manuscript. G. B. con-
tributed to all facets including research questions and design,
Table 1. Proximate composition ( percentage of DM), indispensable amino acid composition ( percentage of CP) and amino acid (AA) score of insect and
reference substrates
Insect substrates Reference substrates
Parameter HFp BSFl BSFp HC YMW LMW MW SSR DHCR ACR* PMM FM SBM
CP 62·556·152·170·652·064·847·066·365·064·469·171·051·6
Fat 19·212·819·717·733·922·239·625·122·024·512·89·22·5
Ash 5·612·613·95·33·94·13·03·63·94·415·419·96·8
AA
Arg 4·23·74·25·74·64·84·63·63·93·55·84·56·3
His 4·84·44·73·45·14·94·84·34·64·53·73·43·1
Ile 4·04·04·24·04·64·65·03·43·73·23·84·85·0
Leu 6·16·16·56·67·36·77·25·45·95·36·47·17·8
Lys 6·25·45·45
·85·56·55·34·34·74·05·67·46·2
Met 2·61·41·71·61·41·31·61·31·21·31·01·92·0
Phe 5·23·13·33·23·43·93·72·62·72·73·33·55·2
Thr 3·83·63·63·64·04·04·13·13·33·13·64·03·9
Val 5·05·55·75·76·35·96·55·66·15·44·65·05·0
tIAA 41·837·139·339·642·342·742·733·536·233·137·841·544·4
AA scores†
Dog 94·063·474·469·368·460·473·853·055·559·744·673·189·1
Cat 106·179·293·086·685·575·592·266·269·474·655·891·6 107·5
CP, crude protein; HFp, housefly pupae; BSFl and BSFp, black soldier fly larvae and pupae; HC, house cricket; YMW, yellow mealworm; LMW, lesser mealworm; MW, Morio
worm; SSR, six spot roach; DHC, death’s head cockroach; ACR, Argentinean cockroach; PMM, poultry meat meal; FM, fish meal; SBM, soyabean meal; tIAA, total indispensable
amino acids.
*Females.
†Calculated as described in Kerr et al.
(13)
using minimal requirements for growth of kittens and puppies
(14)
as reference values.
Table 2. In vitro digestibility (%) of insect and reference substrates
Digestibility
Substrate OM N
Insect
Housefly pupae 83·284·3
BSF larvae 84·389·7
BSF pupae 68·177·7
House cricket 88·091·7
Yellow mealworm 91·591·3
Lesser mealworm 90·291·5
Morio worm 91·192·0
Six spot roach 77·876·4
Death’s head CR 79·478·4
Argentinean CR* 84·083·8
Reference
Poultry meat meal 85·887·9
Fish meal 82·185·7
Soyabean meal 80·694·7
OM, organic matter; BSF, black soldier fly; CR, cockroach.
*Females.
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execution of the study, analysing the data and writing the initial
manuscript. S. Z. contributed to execution of the study, analysing
the data and writing the manuscript. D. G. A. B. O. contributed
to research design, data interpretation and manuscript
preparation. W. H. H. contributed to securing funding, data inter-
pretation and manuscript preparation. There are no conflicts of
interest to declare.
This paper was published as part of the WALTHAM
International Nutritional Sciences Symposium Proceedings
2013, publication of which was supported by an unrestricted
educational grant from Mars Incorporated. The papers
included in these proceedings were invited by the Guest
Editor and have undergone the standard journal formal review
process. They may be cited.
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