(2020) 14:55
Flores et al. BMC Chemistry
https://doi.org/10.1186/s13065-020-00707-0

BMC Chemistry
Open Access

RESEARCH ARTICLE

Comparative study of composition,
antioxidant and antimicrobial activity of two
adult edible insects from Tenebrionidae family
Daniel R. Flores1, Luz E. Casados2, Sandra F. Velasco1, Ana C. Ramírez1 and Gilberto Velázquez1*

Abstract
In the case of Tenebrionidae family insects, studies focus on larval stage, leaving a lack of information regarding otherstages. Therefore, this study was performed in order to understand the differences between the nutritional composition and the bioactivity of two species of this family in their adult stage, fed with a specific diet. Adult beetles of both
species were defatted, lyophilized and protein extracted with buffer. Proximal and phytochemical analysis of theextracts of each insect were performed, along with protein extract and hydrolysis analysis by Tris-Tricine and Tris Glycine SDS PAGE. This analysis showed that T. molitor contained more protein and fat than U. dermestoides but contained
less crude fiber. The protein extraction was made with PBS, where 130 and 45 kDa bands showed predominant for
U. dermestoides, and less protein was present for T. molitor. Antioxidant and antimicrobial activities of the enzymatic
protein hydrolysates and protein crude extracts were determined. Presence of protein associated with the antioxidant
activity were found in both insects. Nonetheless U. dermestoides had a higher antioxidant activity with the protein
extract in contrast with the higher antioxidant activity shown by U. dermestoides once the extracts were digested.
After proteolysis, protein extracts showed an increasing antioxidant activity, plus, the ability to inhibit microbial
growth of Proteus, Shigella and Bacillus. Insect protein hydrolysates with protease open the possibility for the use of
these beetles as new sources of encrypted peptides for microbiological control once characterized.
Keywords: T. molitor, U. dermestoides, Antioxidant activity, Antimicrobial activity, Protein hydrolysates
Introduction
Entomophagy, the consumption of insects, has been promoted as an alternative sustainable protein source forhumans and animals [1]. Insect consumption by humans
is an old, historically and geographically, widespread phenomenon. The use of edible insects varies greatly by local
preference, sociocultural significance, and region [2].
Recently, European countries have an increased interestin studying insects as potential food sources, but it is stilla challenge to gain acceptance in society [3, 4]. However,*Correspondence: gilberto.velazquez@academicos.udg.mx
1
Chemistry Department, University of Guadalajara, 1421 Marcelino García
Barragán Blvd, 44430 Guadalajara, Jalisco, Mexico
Full list of author information is available at the end of the article

in Latin American cultures, especially in Mexico, theconsumption of insects is a tradition rooted in the local
cuisine; clear examples of this is the consumption of thegrasshoppers, ants, and worms. Despite the early acceptance of entomophagy in Mexico, there are not enoughstudies which promote the use of different edible insects
whose cultivation is simple, practical and under controlled conditions which ensure safe consumption [5].
Tenebrio molitor (T. molitor) and Ulomoides dermestoides(U. dermestoides) beetles, whether in larval or adultstage, are harmless, non-toxic and do not bite. These animals invade barns and are considered a plague by many
farmers, but when kept in captivity they can be fed with agreat variety of foods such as: wheat flour, maize or oats;barley and wheat bran, remnants of meat, dead insects© The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing,
adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) andthe source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material
in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material
is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds thepermitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat​iveco​
mmons​.org/licen​ses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creat​iveco​mmons​.org/publi​cdoma​in/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Flores et al. BMC Chemistry(2020) 14:55

and decaying trees. Though in terms of hydration, fruitor vegetables are enough to feed them. T. molitor andU. dermestoides belong to family Tenebrionidae, andare distributed all over the planet, especially in regionswith temperate climates. Their sizes varies between 1
and 30 mm. Although insects are known for their diverse
nutritional properties, specially associated with theirhigh percentage of protein and/or high content of fatty
acids (mono and polyunsaturated), they are also rich inminerals such as: copper, iron, magnesium, manganese,
phosphorus, selenium, zinc, vitamins such as: riboflavin, pantothenic acid, biotin and folic acid. Authors like
Nowak et al. [32] point out that existing information on
the contribution of insects to nutrient intake is still too
scarce. While, in some extent family Tenebrionidae has
been characterized in terms of nutritional value [6, 7],protein production [8], cytotoxic and genotoxic activity [9, 10], and some nutraceutical properties [11–13].
Aforementioned studies are focused only in the larvae’s
stage of the insect. This leaves a deficiency regarding thenutritional information and properties associated withthe adult stage of the family Tenebionidae. Even more,
there is practically no information comparing insects ofthe same family when they are fed a specific diet. The present study was conducted to understand the differences
between the nutritional composition, and bioactivities of
two adult edible insects: T. molitor and U. dermestoides.

Materials and methods

Page 2 of 9

CUCBA, SNIB CONABIO database, Project EC017 y
CE022. México, D. F.
Specimens from the Tenebrionidae family: Adult beetle T. molitor (Linnaeus, Coleoptera: Tenebrionidae) andadult beetle U. dermestoides were kindly donated fromthe identified taxonomic reservoir by Dr. J. Luis Navarrete Hereida and the offspring was deposited in a plastic container where the temperature was maintained
between 25 and 30 °C, once at the adult stage, insects
were separated into different deposits. Food consisted ofa mixture of oats and thin slices of apple (approximately
3.2–4.8 mm thick) every third day as source of hydration[11]. Insects were fasted for approximately 48 h to clear
their gastrointestinal tract of any residual food before
they were collected. Then they were defatted with hexane
for 2 h and set to solvent evaporation. Finally, the samples
were frozen with liquid nitrogen and stored at − 70 °C for
further experimentation.
Reagents

2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)(ABTS) and 2,2-diphenyl-1-picrylhydrazyl, (DPPH);
Aspergillus oryzae protease was purchased from SigmaAldrich. All of the other chemicals used were of analyticalgrade. Dialysis membranes with 1 kDa and 10 k cut-off
were purchased from Spectrum Lab. Culture medium forbacterial growth was Tryptic Soy Broth (TSB) and Tryptic Soy Agar (TSA) from Becton–Dickinson.

Methods of edible insect preparation

Ulomoides dermestoides Chevrolat [13] (= Palembus(Ulomoides) dermestoides, = Martianus dermestoides)
it’s an arthropod of the order Coleoptera, family Tenebrionidae, tribe diaperinae, genus Ulomoides, species U.
dermestoides, originary from the southeast of Asia. The
taxonomical identity of U. dermestoides was obtained following the keys published by Kim & Jung [14]; Tenebrio
molitor [15] it’s an arthropod of the order Coleoptera,family Teneobrinidae, species Tenebrio molitor, originallyfrom Europe.
The taxonomical identity of Tenebrio molitor was
obtained following the keys published by the National
Science Foundation Grants DRL 0089283, DRL 0628151,
DUE 0633095, DRL 0918590, and DUE 1122742. Additional support was granted by the Marisla Foundation,
UM College of Literature, Science, and the Arts, Museumof Zoology, and from Information and Technology Services at University of Michigan. Both identifications werelater validated by Dr. J. Luis Navarrete Hereida responsible of the scarabaeidae and entomology collection at
the reservoir from the Botany and Zoology departmentof the University of Guadalajara’s Center of Biologicaland Agricultural Sciences (CUCBA); CZUG collection.

Proximate analysis

All samples were lyophilized and preserved in a freezer
at − 80 C (model SC-10 N, brand Scientz). The proximal
analysis was performed at the Laboratory of Quantitative Chemical Analysis of the Chemistry Department in
the University of Guadalajara´s Center of Exact Sciencesand Engineering (U de G). Following the methods by the
Association of Official Analytical Chemist [16], such as
AOAC-934.01 for moisture, AOAC-928.08 for Nitrogencontent and Protein content estimation, AOAC-920.39
for Fat/Crude fat, AOAC-962.09 for crude fiber and
AOAC-923.03 for Ash content.
Qualitative phytochemical analysis

Extracts of each insect (0.1 g/ml) were subjected to preliminary phytochemical screening (acidic, alkaline andneutral aqueous systems were used when necessary) bystandard methods [17] for detection of the following constituents: tannins [18], alkaloids, triterpenoids, carbohydrates, steroids [19], saponins, glucosides [20], flavonoids[21], and anthraquinones [22].

Flores et al. BMC Chemistry(2020) 14:55

Protein extract preparation

Proteins were extracted as follows: 1.0 g of insects (previously treated as above mentioned) were weighted andextracted with buffer Phosphate-Buffered Saline (PBS)(for most cases unless specified) in 1:9 ratio (insect:buffer), then each sample was sonicated for 5 min (during a 30 s interval on, and, 15 s off ). The sonicated extract
was centrifuged at room temperature for 10 min at
8000g, and supernatant was collected; when necessary,acetone (4:1 acetone: supernatant) or ammonium sulfate (30% saturation) was used for the concentration ofprotein extract, followed by resuspension in PBS. All thesupernatants (either concentrated or not) were subjected
to overnight dialysis (using a 10 kDa cut-off membrane).
Supernatants were stored at 4 °C to further analysis.
Tris glycine and Tris tricine SDS‑PAGE protein
electrophoresis

Analysis of the extracts were performed on 12% of SDSPAGE electrophoresis gel according to the protocol
established by Laemmli (Tris Glycine system). A MiniProtean BioRad (BioRad, Hercules, CA, USA) electrophoresis system with 20 mA was used. Samples weremixed with Laemmli buffer (1:1, v/v) and heated at 90 C
for 5 min prior to the electrophoresis. Gels were stainedwith Coomassie Blue R-250 using the thermo molecularmarker (page ruler unstained broad range protein ladder and page ruler unstained low range protein ladder).
When necessary (peptide visualization) a Tris Tricine
system on 16% of SDS-PAGE was performed according
to the protocol of Schägger H [23]. Protein quantification
was done using Bradford method [24].
Protease digestion

Samples were treated with Aspergillus oryzae (A. Oryzae) protease from sigma (1:200) (protease: sample) in a
500 μL reaction volume. Untreated samples, buffer alone,or enzyme solutions were used as controls. Treated samples and controls were incubated at 37 °C for 24 h. They
were then dialyzed on a 1 kDa cut-off membrane (toavoid loss of peptides) against PBS for 2 h at 4 °C, before
its use on antioxidant and antimicrobial activity assays.
ABTS radical scavenging activity

ABTS Assay (­ABTS+) was determined according to Re
et al. [25] with some modifications. The radical A­ BTS+was chemically generated using ammonium persulfate,
diluted in deionized water until a final concentration of
7 mM. The solution was diluted to reach an absorbancearound 0.7 at 750 nm. In a 96-well microplate, 20 µL of
sample and 280 µL of ­ABTS+ solution was mixed. The

Page 3 of 9absorbance change (750 nm) was measured after 15 minof incubation at room temperature. The percentage scavenging activity was calculated according to Eq. 1:Acontrol − Asample
× 100
Scavengingactivity(%) =Acontrolwhere: ­Asample is the absorbance of the A­ BTS+ solution
with the sample; and A­ control is the absorbance of the­ABTS+ solution without the sample.
Antimicrobial activity

Samples were assayed by the well diffusion method
according to de la Fuente Salcido et al. [26, 27] with somemodifications. Briefly: twenty-five mililiters of freshly
prepared sterile Tryptic Soy Agar (cooled to 40–50 °C)
was poured into sterile Petri dishes containing 115 µL(1 × 109 cells/mL) of the following bacteria: Micrococcus
luteus, Bacillus aerius, Samonella spp., Bacillus wiedmannii, Streptococcus canis, Enterococcus casseliflavus,
Bacillus cereus strain JCM 2152, Bacillus cereus strain
183, Listeria monocytogenes and Listeria innocua andVibrio parahaemolyticus. These bacteria are maintainedin a stock collection of microorganisms in our laboratory. Once the mixture solidified, wells of 6 mm in bothdiameter and depth were made on the plates using sterile cork borers. 90 µL of the prepared sample was thendispensed into the wells, allowed to equilibrate at room
temperature for 30 min, and then incubated overnight at
37 °C. Zones of growth inhibition (in mm), were measured as the diameter of the clear zones around each well,and, then compared with the antimicrobial standards. All
the experiments were done in triplicates and the data ispresented as mean values.
Statistical analysis

The experiments shown are the mean value ± standard
error (SE) of the data from at least three experiments.
Statistical analyses were performed using Graph Pad
Prism 8 statistical software. Differences with p values ofless than 0.05 were considered significant.

Results and discussion
Proximate analysis

Insects are well known to be rich in nutrients: proteins,
lipids, carbohydrates, vitamins and minerals [28, 29].
There are several reports suggesting that insects could be
an excellent source of protein, since their availability innature is very abundant and their breeding economicallyfeasible [30]. Composition of adult beetles of T. molitor
and U. dermestoides are shown in Table 1. The highest
content of protein and fat was found in T. molitor, whilein terms of crude fiber U. dermestoides had the highest

Flores et al. BMC Chemistry(2020) 14:55

Page 4 of 9

Table 1 Physicochemical composition of Tenebroideae
beetles T. molitor and U.dermestoides

AshProtein (N × 6.25)
Fat

Crude fiber
NFE

U. dermestoides

T. molitor

2.12 ± 0.71

3.24 ± 1.48

40.36 ± 0.79 *8.33 ± 0.69 *49.17 ± 0.32 *0.02 ± 1.38

54.86 ± 1.70 **12.50 ± 1.46 **26.63 ± 0.69 **2.77 ± 0.94

Values are expressed as mean ± standard deviation (n = 3). All data areexpressed as g/100 g dry mass, N: Nitrogen

Table 2 Qualitative
phytochemical
resultsof Tenebroideae beetles T.molitor and U. dermestoides
Phytochemical
constituents

Test performed

U. dermestoides T. molitor

Tannins
Saponins

Superficial foam

Glucosides

Keller-Kiliani
Borntrager’s

Carbohydrates

Molisch’s
Benedict’s*At the exponential, in the same row, show there are significant differences(p-value < 0.05)

Fehling’s
Flavonoids

Lead acetate
Salkowski’s:value. There is no statistical difference between adultbeetles in term of ash contents. It is important to noticethat all results were expressed in dry mass in order tohave a comparative value for other studies.
The protein content found in this work for T. molitor
was 54.86 ± 1.70% which fits within the range reported
in previous studies [31–33]; while the protein found forU. dermestoides in this work is slightly lower than the
48.31% reported by Zhou and Chen [34]. In contrast withthe protein content found in other insects’ orders, it fits
within the range of grasshoppers/locust 40–74.28%, Lepidoptera (wax moth and butterflies) 14 –68%, Hemiptera
42–74%, Orthoptera (crickets) 55.65–75% and Diptera(common housefly) 55–70% [35–38]. Our data allows us
to support what is suggested in previous studies such as
the ones published by Payne CLR et al. and Halloran et al.
[29, 30]. Which expose the viability for the use of insects
to transform low value organic by-products into highvalue foods with very low greenhouse gas emissions.
In terms of fiber content, U. dermestoides presented avery high value (49.17 ± 0.32%) compared with the 22.1%
reported by Jasso-Villagomez et al. [39]. When comparedwith other insect orders like Orthoptera, the differencein fiber content for U. dermestoides is more significant,for example, the grasshopper C. rosea has 12.38% of fiber
content, while bush criket B. orientalis has only 8.75%[33, 38].
Qualitative phytochemical analysis

In the qualitative phytochemical analysis (Table 2), thepresence of some secondary metabolites commonly
associated with the antioxidant activity (tannins or flavonoids) were not found, neither in T. molitor nor U. dermestoides, this analysis was performed after the defatting of
the insects in order to confirm that the antioxidant activity evaluated was only due to the protein fraction. Carbohydrates and reducing sugars were detected in both
insects. Glucosides, flavonoids, alkaloids and steroids

ShinodaProteins

Bradford

Alkaloids

Dragendorff’s:
Mayer’s
Wagner’s
Hager’s:

Steroids
Anthraquinones

Insect aqueous extract

−

++
−

−

+

−

−

−

+

+

+

+

+

+

−

−

−

−

+

−

−

−

−

−

++
−

−

−

−

−

−

−

Liebermann Burchard’s −−Values are expressed as positive (+), very clear result (++), negative (−); notapplicable (NA). Acidic extraction and alkaline extraction were used for alkaloids
and steroids (nevertheless, no positive results were detected)

were absent using the procedures indicated for each test.
Proteins were detected using Bradford reagent with both
beetles; there was a major color intensity on the qualitative test of T. molitor in comparison with the test of U.
dermestoides, in agreement with the nitrogen content
estimated by the proximal analysis. The stable foam formation suggested the presence of saponins. No qualitative tests were considered as positive in this work foralkaloids, steroid or anthraquinones [40].
Protein extract preparation

Three buffering systems were used to evaluate the best
extraction conditions for U. dermestoides and T. molitor
insect proteins. Despite the differences in pH of theextraction systems (Citrate buffer pH 5, carbonate buffer
pH 9 and PBS buffer pH 7), polyacrylamide gel denaturing electrophoresis (SDS PAGE), showed no significant
differences in band patterns for the extracts (Fig. 1). We
then decided to use PBS as a buffer for protein extraction. Spite the several replicates obtained by the sonication method (regardless of the buffer) on the extractionof T. molitor, the electrophoretic profile always showed
few bands.The protein profile revealed by electrophoresisof both insects’ crude extracts showed very different patterns and molecular weight bands. For U. dermestoides
most of the bands center around 45 kDa; but there isFlores et al. BMC Chemistry(2020) 14:55

Page 5 of 9

obtained in this work, except no bands above 95 KDa
were detected as aforementioned studies report. [41].
Protease digestion of PBS extract

Fig. 1 SDS-PAGE of protein extracts from T. molitor and U.
dermestoides adult insects. A 15% of Tris Tricine SDS-PAGE gel ispresented. There was no significant difference among the buffers
tested in terms of protein band detection. Elecrophoresis shows
better resolution of the bands for U. dermestoides extract incomparison with T. molitor’s. Protein extracts show that the numberof peptides present in the direct extraction is practically absent. MW:
Protein Molecular Weight Marker in KDa

a presence of low molecular bands between 25 and
15 kDa, and a very strong band around 130 kDa. By theother hand, very few bands were distinguishable in the
T. molitor protein crude extracts, two strong bands: onenear to 95 kDa and the other around 37 kDa. This canbe explained by the conditions used for the extraction inthis work, where the selected buffers did not count withthe presence of caothrophic agents such as urea or detergents as SDS or Triton, which contributed to the low protein extraction of T. Molitor.
These parameters where employed in urge to minimize
further effects on the protein quantifications assays suchas the digestion of crude extracts. It’s worth mentioningthat previous works reporting any electrophoretic profile where focused on the larvae stage of the insect [37]rather the adult stage, and, applying rougher extraction
conditions (prolongated agitation [42], or extended sonication time [43]), conditions that we avoided in orderto restrict the protein degradation in this work. Studies
such as Zielińska et al. [11], state that the electrophoretic
protein profile for a specified extraction may vary greatly
due to changes on the conditions employed.
Although the methodology for protein extraction was
not the same as in the protein profile previously reported
for T. molitor, we were able to detect some of the bands
present on those studies [12, 34, 35]; for example, thebands in the range of 32–95 KDa in T. molitor were also

In order to explore the diversity of encrypted peptides we
decided to achieve proteolysis of the PBS extracts fromthe U. dermestoides and T. molitor insects. Using an A.
oryzae protease containing both endoprotease’s andexopeptidase’s activity, the PBS extracts were digested,
and the peptide profile was analyzed with an optimizedgel (Tris-Tricine SDS-Gel) for peptides [20]. Figure 2
shows in lane 1 the autoproteolysis control and in lane
2 the digested extract of U. dermestoides. It is possible
to observe that the digested extract presents two major
bands of peptides between 15 and 35 kDa with differential bands compared to the autoproteolysis control, there
is also a digested fraction under 15 kDa present in the gel.
Meanwhile T. molitor digested extract showed a range of
1.5–25 kDa peptide profile. No bands above 40 KDa weredetected for any of the digested extracts, and the protein
profile is completely different respect to the total protein
extracts.
Due to the use of a protease with both endo- and exopeptidase activities, as it is A. Oryzae, it is likely thatthe liberated fragments are attributable to an exhaustive
proteolysis of the hemolymph proteins of the insects.
It is reported for T. Molitor a defensin (small cationic
cysteine rich peptide) [42], with a molecular weight
below 10 kDa, known as tenecin-1 [43]. More experimental data is required for a detailed characterization of
the peptides liberated throughout the process applied byfungal proteases as A. Oryzae, however, the approach of
the encrypted peptides obtention process by this kind ofproteases looks promising [42, 44].
Total antioxidant capacity of protein insect extracts

The antioxidant activities of the extracts were expressed as
micromoles of Trolox/g insect (Fig. 3a). Protein concentrations were adjusted to obtain similar amounts of protein for the antioxidant activity test. If we compare PBS
extract from U. dermestoides and T. molitor there was no
statistically significant difference at 95% confidence interval by a student’s t test. Although, the antioxidant activity found for Tenebrio protein extract (41.4 ± 2.3 µmol
Trolox/g) and U. dermestoides protein extract(54.8 ± 3.1 µmol Trolox/g) was less than the reported for
fruits such as strawberry (358 µmol Trolox/g), blueberries (348.25 µmol Trolox/g) and pomegranate peel andpulp (4.6–6.3 mM Trolox/g); higher than the water-soluble extracts of grasshoppers (2.55 + 0.05 µmol Trolox/g),
silkworm(2.48 + 0.19µmol
Trolox/g),
crickets(2.37 + 0.03
µmol
Trolox/g)
andfreshorange juice (0.40 ± 0.01); and similar to theFlores et al. BMC Chemistry(2020) 14:55

Page 6 of 9

Fig. 2 Tris Tricine SDS-Gel with the hydrolysate U. dermestoides and T. molitor extract with A. oryzae protease. MW1. Protein marker (numbers
indicate KDa). Lane 1. Control of autoproteolysis with A. oryzae protease under the same conditions of digested extracts. Lane 2. Digested extract of
U. dermestodies with A. oryzae protease. Lane 3. Non-digested extract of U. dermestoides in PBS. Lane 4. Digested extract of T. molitor with A. oryzae
protease. Lane 5. Non-digested extract of T. molitor with PBS. MW2. Peptide protein marker (numbers indicate KDa)

Fig. 3 Total antioxidant activity of the protein extract from U. dermestoides and T. molitor. a Comparison of the antioxidant activity of protein
extracts before and after digestion with protease. The asterisks show that there is a statistical difference between the protein digested extract at
95% of confidence. b Inhibition of ABTS radical assay with the non-digested and digested protein extract

activity found in freeze-dried peel of purple star apple(3310.95 μM Trolox/100 g DW) and yellow cashew(3322.31 μM Trolox/100 g DW) [43–45]. Nevertheless, the activity we obtained with the extract is referred

exclusively to protein fraction per insect gram. Moreover,when a digestion with A. oryzae protease was performedon the protein crude extract, there was a significant
increase on the total antioxidant capacity for the sample,

Flores et al. BMC Chemistry(2020) 14:55

Page 7 of 9

Table 3 Antimicrobial activity of the enzymatic hydrolysates of protein extract from U. dermestoides and T. molitor
against selected microorganisms
Protein digested extract

Diameter of growth inhibition zone (mm)P. vulgaris

S. flexnerii

Bacillus t.
subsp. Tenebrionis

Bacillus t.
subsp. kenyae

Enzymatic control

U. dermestoides

9 (+++)

11 (++++)

13.5 (++++)

7.7 (+++)< 1 (−)

T. molitor

7.5 (+++)

12 (++++)

8.5 (+++)

5.5 (++)< 1 (−)

Each value is expressed as mean (n = 3) and standard deviations were less than 5%. No antimicrobial activity (−), inhibition zone < 1 mm. Slight antimicrobial activity(+), inhibition zone 2–3 mm. Moderate antimicrobial activity (++), inhibition zone 4–5 mm. High antimicrobial activity (+++), inhibition zone 6–9 mm. Strong
antimicrobial activity (++++), inhibition zone > 9 mm. Standard deviation ± 0.4 mm. The protein crude extracts showed no inhibition zone

reaching 206 ± 8.5 µmol Trolox/g for T. molitor extract
and 104 ± 6.2 µmol Trolox/g for U. dermestoides extract
respectively.
We evaluated the ABTS radical inhibition percentage (Fig. 3) using the insect protein extracts (PBS andprotease digested). The results showed that a 100% of
the ABTS radical inhibition was reached at approximately 0.4 mg/mL of protein for the digested extractof T. molitor and it takes 0.8 mg/mL of protein for thedigested extract of U. dermestoides. When the PBS protein extracts were used no complete radical inhibition for
either insect was achieved, under the kinetic conditions
used. Even though both insects belong to the same family
and were fed under the same diet, the kinetic profiles of
the antioxidant activity were very different. In the case of
the U. dermestoides digested extract, it took almost twice
the amount of protein in order to achieve a 100% of the
ABTS radical inhibition.
Protease digestion of PBS extract for antimicrobial activity
evaluation

41.4 and 54.8 µmol Troxol/g respectively, however oncethe extracts were digested with A. oryzae protease, theantioxidant activities increased to 206 for T. molitor
and 104 for U. dermestoides. The digested extracts presented different kinetic patterns on the inhibition of
ABTS radicals, where U. dermestoides needed twice asdigested protein extract compared to T. molitor. Thesealso showed antimicrobial activity against P. vulgaris, S.
flexnerii and Bacillus spp. All this data suggests that T.
molitor and U. dermestoides are an excellent possibility as sources of fiber and protein moreover their antioxidant properties make them suitable as nutraceuticalfood.
Acknowledgements
To CONACyT (Consejo Nacional de Ciencia y Tecnología de México) for the
Master scholarship 714080 of D.R.F, scholar number/590744.
Authors’ contributions
DRF and LEC carried out the experimental part. ACR performed antioxidant
activity analysis. SFRV performed some of the experimental and language
editing. GVJ wrote and edited the manuscript. All authors shared equally therevision of the manuscript. All authors read and approved the final manuscript.

We decided to test if the hydrolysates obtained with theA. oryzae protease were able to inhibit the growth ofsome of the bacteria on a well diffusion method test. Only
three microorganisms among the tested in our assay, presented inhibition by the digested extracts. Two gram negative microorganisms (P. vulgaris and Shigella flexnerii)
and one gram positive (Bacillus spp) presented inhibitionby the digested protein extracts of both insects. Results
are summarized in Table 3. Extracts digested with protease open the possibility for the use of these beetles asa new source of encrypted peptides for microbiologicalcontrol once characterized.

Funding
The authors have no funding to report.

Conclusion
High fiber and protein content values were obtainedwith the diet supplied to insects during this work.
Antioxidant activity for the protein crude extracts of
T. molitor and U. dermestoides showed values around

Author details
1
Chemistry Department, University of Guadalajara, 1421 Marcelino García
Barragán Blvd, 44430 Guadalajara, Jalisco, Mexico. 2 Life and Science Division,
Food Department, University of Guanajuato, Campus Irapuato-Salamanca, Km
9 carretera Irapuato‑Silao ap 311, 36500 Irapuato, Guanajuato, Mexico.

Ethics approval and consent to participate
Corresponding to the Mexican law on the protection of animals used forscientific purposes (NORMA Oficial Mexicana NOM-062-ZOO-1999), this article
does not contain studies with animal subjects as experiments with insects orinvertebrates are not classified as animal experiments.
Competing interests
The authors declare that they have no competing interests. All authors of themanuscript have read and agreed to its content and are accountable for all
aspects of the accuracy and integrity of the manuscript. This article is original,
has not already been published in a journal, and is not currently under consideration by another journal. Authors agree to the terms of the BioMed Central
Copyright and License Agreement.

Received: 24 January 2020 Accepted: 2 September 2020

Flores et al. BMC Chemistry(2020) 14:55

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