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Full Research Article

Effects of Curing on the Protein Quality and Amino Acids Profiles of Hercules Beetle (Dynastes hercules) Larvae Flours

N
N.E. Njoku1
A
A.F. Ofoedum1,*
https://orcid.org/0000-0001-9935-5853
C
C.C. Ezegbe2
N
N.V. Amadi3
P
P.O. Ohaegbulam3
M
M.U. Nwuka3
G
G.K. Elemuo1
C
C.A. Alozie4
O
O.M. Ukadike1
1School of Engineering and Engineering Technology, Federal University of Technology, Owerri, PMB 1526, Imo State, Nigeria.
2Nnamdi Azikiwe University, Awka, Anambra State, Nigeria.
3Federal Polytechnic Nekede, Owerri, Imo State, Nigeria.
4Sheda Science and Technology, Complex (SHESTCO), Abuja.

ABSTRACT

Background: This study focused on the toasting of the larva, protein digestibility and amino acid composition assays of Hercules beetle larva flour.

Methods: Four samples of the Hercules beetle larva were produced; sample BOH (40°C oven dried Hercules beetle larva without condiments flour), sample COH (40°C oven dried Hercules beetle larva with condiments flour) and Sample AOH (toasted Hercules beetle larva without condiments flour) and sample GOH (Toasted Hercules beetle larva with condiments flour).

Result: From the result of proximate analysis, the protein content varied from 59.09% to 50.07%, fat content varied from 21.98% to 12.59%, ash content varied from 7.43% to 6.19% fibre content varied from 17.62% to 15.32%, moisture content varied from 9.10% to 5.13% and carbohydrate varied from 11.42% to 3.58%. From the result the invitro protein digestibility content varied from 23.53% to 16.59%. The result of the amino acid profile showed it contained 18 amino acids, 9 of which are essential amino acids. For the essential amino acids, leucine showed a range of 7.52 mg/100 g to 6.64 mg/100 g, lysine varied from 3.04 mg/100 g to 2.39 mg/100 g, isoleucine varied from 4.07 mg/100 g to 2.94 mg/100 g, phenylalanine varied from 5.01 mg/100 g to 4.11 mg/100 g, valine varied from 4.28 mg/100 g to 3.74 mg/100 g, methionine varied from 1.36 mg/100 g to 1.17 mg/100 g, threonine varied from 3.83 mg/100 g to 3.03 mg/100 g, histidine showed a range of 2.51 mg/100 g to 1.68 mg/100 g and tryptophan varied from 1.15 mg/100 g to 0.81 mg/100 g.

INTRODUCTION

Insects are part of the traditional diets of approximately 2 billion people worldwide (van Huis  et al., 2013). Insects can contribute to food security and be a part of the solution to gases, Insects emit fewer greenhouse gases compared to traditional livestock. They have a smaller environmental footprint, contributing less to climate change, low requirements for land and water and the high efficiency at which they can convert feed into food (Elemo et al., 2011).
       
As stated by the Food and Agriculture Organization, trends toward 2050 predict a steady world population increase to 9 billion (van Huis  et al., 2013). In addition, the results of studies reported in the scientific literature on consumer acceptance of this type of food are quite fragmented and, in some cases, even present contradictory results (van Huis  et al., 2013). Mexico is the country with the highest number of insect species used for human consumption, with more than 300 species (549 actually reported), followed by the countries of Southeast Asia (200-300 species), Australia, South America and some African countries (50-200 species) and Middle Eastern and European countries (10-50 species) (Kröger  et al., 2022).
       
From a nutritional aspects, insects stand out for their high protein content. Although this nutritional value can be influenced by diet, developmental stage, sex, species, growth condition and analytical methods (de Castro  et al., 2018). On the average, the protein content of edible insects ranges between 10% and 70% of dry weight or between 10% and 25% of fresh weight, values higher than some plant products known for their high content of this macronutrient, such as cereals, soybeans and lentils (Schlüter  et al., 2017); edible insects also provide more proteins than chicken meat and eggs (Kim et al., 2019). However, one aspect to consider is the variability of the digestibility of insect proteins due to the presence of a hard exoskeleton.
       
The aim of the study is to produce cured Hercules beetle larvae flour, investigate the amino acid profile of the cured Hercules beetle larvae flour and study the protein quality of the cured Hercules beetle larvae flour.

MATERIALS AND METHODS

Raw material procurement
 
About 2 kg of the Hercules beetle larvae was bought from a commercial dealer in Bayelsa state and transported in a bucket filled with saw dust. The sample of the hercule beetle larvae is shown in Plate 1.

Plate 1: Hercules beetle larvae.


 
Place and duration of study
 
This work was carried out in the Department of Food Science and Technology, FUTO, for a period of 18 months, from April 2024 to October, 2025.
 
Preparation of 50°C oven dried Hercules beetle larva flour
 
Approximately 500 g of live Hercules beetle larvae were washed properly and the water drained, proceeded to oven drying with oven Model (DHG-9101-05A) at 50°C for 24 hours. The dried larvae were milled with the attrition mill (Model 368 corona) to obtain the coarse Hercules beetle larvae flour. N-hexane was used during defatting (ratio 1:10 w/v) for about 3 hours to obtain 50°C oven dried Hercules beetle larvae.
 
Preparation of toasted hercules beetle larvae flour with condiments
 
Approximately 350 g of live Hercules beetle larvae was properly washed and water was drained using a sieve. Half a tablespoon of table salt and half a tablespoon of ground pepper was added to the larvae. The larvae was placed on a heated frying pan and toasted continuously for about 10 minutes until it was evenly fried taking proper consideration in temperature not exceeding 80°C with the aid of a thermometer. The toasted larvae were cooled and milled using attrition mill (Model 368 Corona) to obtain the oily coarse Hercules beetle pulp. It was defatted using N-hexane (1:10 w/v) for 3 hours to obtain defatted flour. The flour was packaged using airtight container and stored for further analysis.
 
Preparation of toasted Hercules beetle larvae flour without condiments
 
Approximately 350 g of live Hercules beetle larvae was washed properly and water was drained using a sieve. The Hercules beetle larvae was placed on a heated frying pan and toasted without condiments continuously for about 10 minutes taking proper consideration in temperature not exceeding 80 with the aid of a thermometer. The toasted larvae without condiments was cooled, milled using attrition mill (Model 368 Corona) obtain the oily coarse Hercules beetle larvae pulp. It was defatted using N-hexane (1:10w/v) for 3 hours to obtain Hercules beetle larvae flour which was packaged in an air tight container and stored for further analysis as shown in Fig 1.

Fig 1: Production of hercules beetle larvae flour.



Chemical analysis of the samples
 
Proximate analysis of the sample
 
The standard method of AOAC (2010) was used to determine the proximate compositions of the samples which includes the moisture contents, Ash, crude fibre, Protein, Crude fats and Carbohydrates.
 
Determination of amino acid profiles of the samples: Loading of the hydrolyzate TSM analyzer and calculation of amino acid values
 
The Amino acids profile of the samples were determined using standard analytical procedures described by Olawuni et al., (2019).
 
In vitro protein digestibility
 
Protein digestibility was measured using the method developed by Mertz et al. (1984) with modifications as reported by Gulati et al. (2017).
 
Amino acid score
 
This was expressed as the ratio of the essential amino acid content (mg/g insect crude protein) to the same essential amino acid (mg/g protein) in the scoring pattern for children and adults (WHO/FAO/UNU, 2007).
 
 
 
 
Essential amino acid index
 
The essential amino acid index was computed as the geometric mean of the amino acid scores using the amino acid scoring pattern for children and adults (WHO/FAO/UNU, 2007) as reference protein, assuming that the maximum amino acid score is 1 and the minimum is 0.01 (Oser, 1959).
 
  
 
Where,
n= Number of essential amino acids.
AAS= Amino acid score.
 
Statistical analysis
 
Data obtained from the analysis were subjected to statistical analysis of variance (ANOVA) using SPSS version 2023 to separate the mean, standard deviation of triplicate runs at 95% confidence level.

RESULTS AND DISCUSSION

Proximate composition
 
The result obtained from the proximate analysis of the flour samples of the Hercules beetle larva are presented in Table 1. Protein an essential macronutrient which makes up the biochemical component of the studied larvae with the values for each sample; for sample BOH (59.09%), COH (55.37%), AOH (54.31%), GOH (50.07%). These protein contents are higher than those reported for other edible insects which includes Brachytrypes spp 6% (Banjo  et al., 2006), Oryctes boas 26% (Banjo  et al., 2006), Anaphe recticulata 23% (Banjo  et al., 2006). The result showed that sample BOH produced the highest protein content compared to the other samples. An increase in crude protein signals enzymes and antibody activation (Njoku et al., 2025). The high protein content of the larva in this study indicates that they may invariably contribute to the daily protein requirements of humans (Ifie and Emeruwa, 2011). Larvae are potential sources of protein which solves global protein deficiencies (Van Huis  et al., 2013; Ofoedum et al., 2025).

Table 1: Proximate Composition of Hercules beetle larva flour (%).


       
The fat content of the sample GOH (21.98%) was higher than that of sample BOH (15.40%), COH (19.25%), AOH (12.59%). This may be as a result of the concentration of the dry matter with decrease of moisture because of the oven drying. The lower levels of fat in samples BOH, COH and AOH may be due to loss of oil during toasting, since the larva was fried without additional oil.
       
The ash content of the larva flour was observed and the result showed (6.37%) for sample BOH, (6.80%) sample COH, (7.43%), sample AOH, (6.19%) sample GOH. The ash content for sample COH (7.43 was higher than the value of the other samples but lower than the value for O. rhinoceros (12.70%) as documented by Uzoukwu et al., (2025). This may be attributed to the drying ash temperature and duration and also the moisture content of the larva. The ash content obtained indicates the presence of mineral compounds (Alinnor and Akalezi, 2010), this is a pointer that D. hercules are rich in minerals.
         
The results obtained for crude fibre content of the samples; for sample BOH (7.80%), COH (4.35%), AOH (7.44%), GOH (7.84%). These crude fibre contents are lower compared to the crude fibre compositions of O. rhinoceros (8.70±0.70%), Z. variegatus (22.07±0.38%) and the value reported for Polyrhachis vicina (13.2%) (Shen et al., 2006). Fibre in diets aid in fat reduction and proper digestion of food so as prevent diverticulitis (Oduor et al., 2008), which is the inflammation of irregular bulging pouches in the wall of the large intestine.
       
The sample COH had the lowest moisture content (5.13) followed by sample AOH (6.83), sample BOH (7.41 and lastly GOH (9.10). The moisture content of 5.13% obtained in this study for sample COH compares unfavorably with 16.73% reported for Oryctes rhinocerous larvae flour by Okaraonye and Ikewuchi (2009). The high moisture content of food indicates a short shelf life, as it determines the quality and susceptibility of food to microbial spoilage (Frazier and West off, 2003). 
       
The result obtained for the carbonhydrate content showed, 3.58% (sample BOH), 9.12% (sample COH), 11.84% (sample AOH), 4.84% (sample GOH). The carbonhydrate content varied as sample BOH was lower compared to the other sample and this may be attributed to the oven treatment done on it.
 
In vitro protein digestibility
 
Table 2 presented the invitro digestibility of the samples BOH (18.69%), COH (20.31%), AOH (23.53%), GOH (16.59%). Large differences are observed, which can be attributed to the method of digestion, the method used to assess digestibility and the species or the developmental stage of the insect (Njoku  et al., 2025). Exposure to denaturation temperatures may increase digestibility of native proteins by unfolding the polypeptide chain and rendering the protein more susceptible to digestive enzymes (Opstvedt et al., 2003). On the other hand, when proteins are exposed to some heat treatments, digestibility may be reduced due to formation of disulphide bonds in the protein (Njoku et al., 2025).

Table 2: In vitro digestibility of the samples.


       
The protein digestibility of most species are between 80% and 90% and even the larva of the lepidopteran Laniifera cyclades is reported to have 98.9% protein digestibility (Ramos-Elorduy  et al., 1981). Few studies have compared insects with other reference feeds, but those analysed have shown that insects show a similar digestibility to fish meal 84.9% (Arango et al., 2004); 85,7% (Bosch et al., 2016) and slightly lower digestibility than soybean meal 95% (Bosch et al., 2016).
 
Amino acid profile of the hercules beetle larva flour
 
The amino acid composition of the Hercules beetle larva flour is presented on Table 3. The total essential amino acid is 30.1 g/100 g and it represents 41.47% of total amino acid.

Table 3: Amino acid profile of the Hercules beetle larva flour samples (mg/100 g).


       
For sample COH the total amino acid is 78.22 g/100 g protein. The total essential amino acid is 32.89 g/100 g and represents 42.04% of total amino acid.
       
For sample AOH the total amino acid is 84.76 g/100 g protein. The total amino essential amino acid is 35.71 g/100 g and it represents 42.13% of total amino acid.
       
For sample GOH the total amino acid is 72.88 g/100 g protein. The total essential amino acid is 30.61g/100g and it represents 42% of total amino acids.
       
Glutamic acid was the pre amino acid present in the larva containing 12.85 g/100 g in sample BOH, 13.79 g/100 g in sample COH, 14.41 g/100 g in sample AOH and 13.52 g/100 g in sample GOH. Also, there was no significant difference in the glutamic acid composition of sample COH and GOH. The glutamic acid composition of the Hercules beetle larva flour is in agreement with Ogbuagu and Emodi (2014) on R. ferrugineus who also stated that glutamic acid was the predominant amino acid (12.68 g/100 g).  
       
The leucine content of the sample were 6.80 g/100 g for sample BOH, 7.24 g/100 g for sample COH, 7.52 g/100 g for sample AOH and lastly for sample GOH 6.64 g/100 g. These values are in agreement with the result obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (7.52 g/100 g). It also compares favorably to FAO/WHO (1973) reference value (6.6 g/100 g). Leucine is a branched-chain amino acid that is essential for the synthesis of protein and repairing of muscle. Additionally, it facilitates blood sugar control, promotes wound healing and generates growth hormones (Campbell, 2022).
       
The lysine content of the Hercules beetle larva flour varied from 2.54 g/100 g (sample BOH) to 2.85 g/100 g (sample COH) 3.04 g/100 g (sample AOH) and 2.39g/100 g (sample GOH). The values are lower compared to the 4.2 g/100 g observed by Elemo et al., (2011) for R. phoenicis and 4.51 g/100 g reported by Ogbuagu and Emodi (2014) for R. ferrugineus. The main functions of lysine are in calcium absorption, hormone and enzyme production and protein synthesis. Additionally important for immunological function, collagen and elastin production (Campbell, 2022).
       
Isoleucine present in the sample were 2.94 g/100 g for sample BOH, 3.38 g/100 g (sample COH), 4.07 g/100g (sample AOH), 3.09/100 g (sample GOH). These values compare well to the results obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (4.08 g/100 g). They are also higher than the value reported by Adepoju and Ayenitaju (2021) on R. phoenicis (0.92 g/100 g). Isoleucine is heavily concentrated in muscle tissue and has a role in muscle metabolism. It is essential for the production of hemoglobin, the regulation of electricity and immunological function (Ofoedum et al., 2024).
       
The phenylalanine content in the samples varied from 4.30 g/100 g (sample BOH), 4.61g/100g in sample COH, 4.11 g/100 g in sample GOH to 5.01 g/100 g in sample AOH. The phenylalanine + tyrosine values were 7.58 g/100 g for sample BOH, 8.17 g/100 g for sample COH, 8.85 g/100 g for sample AOH, 7.24 g/100 g for sample GOH. These values suggest that the samples can sufficiently meet their respective reference standard (6.0 g/100 g) by FAO/WHO (1973). Phenylalanine plays a crucial role in the production of various amino acids as well as the shape and characteristic of proteins and enzymes (Campbell, 2022). 
       
The valine content of the samples were 3.87 g/100 g in sample BOH, 3.93 g/100 g in sample COH, 4.28 g/100 g in sample AOH and 3.74 g/100 g in sample GOH. These values compare favorably with the 3.49 g/100g reported by Elemo  et al. (2011) and the 4.1 g/100 g observed for R. ferrugineus by Ogbuagu and Emodi (2014). The proline content of the Hercules beetle larva flour varied from 4.06 g/100g in sample AOH to 3.47 g/100 g in sample BOH. Although these values compare favourably with the report (3.29 g/100 g) of Ogbuagu and Emodi (2014), they are lower than the result (10.2 g/100 g) reported by Elemo et al., (2011) on R. phoenicis.
       
The methionine content ranges from 1.36 g/100 g in sample AOH to 1.17 in sample GOH. The cystine content also ranges from 1.78 g/100 g in sample AOH to 1.11 g/100 g in sample GOH. The methionine + cystine value was 2.53 g/100 g in sample BOH, 2.75 g/100 g in sample COH, 3.14 g/100 g in sample AOH, lastly, 2.28 g/100 g in sample GOH; these values are however lower than their respective reference standard (3.15 g/100 g) by FAO/WHO (1973). The methionine content of the samples are lower than the value of 2.1 g/100g reported for R. phoenicis (Elemo et al., 2011). The low methionine may be attributed to diverse locality or nutrient intake of the larva. In metabolism and detoxification, methionine plays a crucial role. Additionally, it’s necessary for mineral absorption (zinc and selenium) and tissue growth, both of which are crucial for your health (Ofoedum et al., 2024).
       
Histidine present in the samples ranged from 2.51 g/100 g in sample AOH to 2.05 g/100 g in sample BOH to 2.23 g/100 g in sample COH and finally, 1.68 g.100 g in sample GOH. The values of histidine present are greater than that reported by Elemo et al., (2011) on R. phoenicis (1.1 g/100 g) and lower than the result gotten by Ogbuagu and Emodi (2014) on R. ferrugineus (3.51 g/100 g).
       
The values presented for the alanine content of the samples were 3.93 g/100 g in sample BOH, 4.47 g/100 g in sample COH, 5.08 g/100 g in sample AOH, 4.55 g/100 g in sample GOH. The values compare favorably to the results obtained by Njoku et al., (2025) on R. ferrugineus (4.21 g/100 g).
       
The Glycine present in the samples were 3.75 g/100 g for sample BOH, 3.91 g/100 g for sample COH, 4.32 g/100 g for sample AOH, 3.46 g/100 g for sample GOH. The values of glycine content are similar to the result obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (3.65 g/100 g). They are however lower than the result obtained by Elemo et al., (2011) on R. phoenicis (4.8 g/100 g).
       
The arginine content of the sample; 4.68 g/100 g for sample BOH, 4.91 g/100 g for sample COH, 5.22 g/100 g for sample AOH, 4.92 g/100 g for sample GOH. There was no significant difference (P>0.05) in the arginine composition of sample COH and GOH. The arginine content of the 4 samples compares favourably to the results obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (6.47 g/100 g).
       
The serine present in the sample was found to be 3.74 g/100 g in sample BOH, 4.10 g/100 g in sample COH, 4.41 g/100 g in sample AOH, 4.02 g/100 g in sample GOH. The values compare favorably to the results obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (3.64 g/100 g).
       
Aspartic acid was found to be 8.02 g/100 g in sample BOH, 8.43 g/100 g in sample COH, 8.87 g/100 g in sample AOH and 7.55 g/100 g in sample GOH. There were major differences in the aspartic acid composition of the three samples.
       
Threonine present in the Hercules beetle larva flour ranges from 3.83 g/100 g in sample AOH to 3.03 g/100 g in sample BOH, 3.36 g/100 g in sample COH and 3.25 g/100 g in sample GOH. There was no significant difference (P>0.05) in the threonine content of the samples. The values of threonine present are similar to the result obtained by Njoku et al., (2025) on R. ferrugineus (3.51 g/100 g) and slightly higher than that reported by Elemo et al., (2011) on R. phoenicis (2.9 g/100 g). The amino acid threonine is a crucial component of structural proteins like collagen and elastin, which are essential components of connective tissue and the skin. It also contributes to immunological function and the metabolism of fat (Campbell, 2022).
       
Tryptophan was the amino acid present in the least amount in the Hercules beetle larva flour, ranging from 1.15 g/100 g in sample AOH to 0.81 g/100 g in sample BOH. This is lower than the reported content of 6.0 g/100 g for R. phoenicis (Odimegwu et al., 2025). In addition to aiding in nitrogen stability, tryptophan is a precursor to serotonin, a neurotransmitter that controls your mood, appetite and sleep (Njoku  et al., 2025).
 
Effects of curing on the protein quality indices of hercules beetle larva
 
The protein quality of the Hercules beetle larva expressed in terms of various parameters are presented in Table 4. From the amino acid score, the first limiting amino acid for sample BOH is leucine (0.10), Histidine (0.37) for sample COH and Histidine (0.42) for sample AOH and histidine (0.28) for sample GOH. The second limiting amino acid in the Hercules beetle larva was Histidine (0.34) for sample BOH, Lysine (0.52) for sample COH, lysine (0.55) for sample AOH and lysine (0.43) for sample GOH. Some of the amino acid score were greater (>) than 1 which implies that in 1g of the palm weevil larva, the amino acid were present in quantities higher than in 1g of the reference scoring pattern for children and adult (WHO/FAO/UNU, 2007). Therefore, the Hercules beetle larva contains excess of some essential amino acid and as such can be incorporated in foods deficient in these essential amino acids. The ratios E/N and E/(E + N) of the hercules beetle larva ranged from 0.68 to 0.69 and from 0.39 to 0.41. The above ratios are comparable to the standard (0.6 and 0.4 respectively) recommended by the EFSA (2012) and FAO/WHO/UNU (1985) Joint Expert Consultation Report on energy and protein requirements in humans.  

Table 4: Effects of curing on the amino acid contents of hercules beetle larva flour samples (mg/100 g).

CONCLUSION AND RECOMMENDATION

The study shows that the oven dried Hercules beetle larva flour with condiments has high protein and fat content. The toasted Hercules beetle larva flour with condiments had the highest moisture content indicating a short shelf life and also had the highest fat content.
       
The in vitro protein digestibility of the Hercules beetle larva was relatively low compared to other edible insects. This is as a result of the heat processing method carried out during the production process of Hercules beetle larva flour.
       
The hercules beetle larva flour toasted and oven dried either with condiments or not was found to contain 18 amino acids, 9 of which are essential amino acids indicating it is a complete protein. Some of the essential amino acid values for the toasted and oven dried larva with and without condiments including; tryptophan, leucine, phenylalanine, isoleucine, met and/or surpassed the FAO/WHO reference values.
       
Incorporation of Hercules beetle larva flour into different food products such as protein bars, snacks and dietary supplements to promote its acceptance and utilization should also be considered.

ACKNOWLEDGEMENT

The co-operations of all the staff of the Department of Food Sci. and Tech., Federal University of Technology, Owerri are hereby acknowledged.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Informed consent
 
All animal procedures for this experiment were approved by the committee of Experimental Animal Care and Handling techniques were approved by the University authority.
 
Source of funding
 
None.
 

CONFLICT OF INTEREST

All the authors have declared that there are no conflicts of interest.

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    Full Research Article

    Effects of Curing on the Protein Quality and Amino Acids Profiles of Hercules Beetle (Dynastes hercules) Larvae Flours

    N
    N.E. Njoku1
    A
    A.F. Ofoedum1,*
    https://orcid.org/0000-0001-9935-5853
    C
    C.C. Ezegbe2
    N
    N.V. Amadi3
    P
    P.O. Ohaegbulam3
    M
    M.U. Nwuka3
    G
    G.K. Elemuo1
    C
    C.A. Alozie4
    O
    O.M. Ukadike1
    1School of Engineering and Engineering Technology, Federal University of Technology, Owerri, PMB 1526, Imo State, Nigeria.
    2Nnamdi Azikiwe University, Awka, Anambra State, Nigeria.
    3Federal Polytechnic Nekede, Owerri, Imo State, Nigeria.
    4Sheda Science and Technology, Complex (SHESTCO), Abuja.

    ABSTRACT

    Background: This study focused on the toasting of the larva, protein digestibility and amino acid composition assays of Hercules beetle larva flour.

    Methods: Four samples of the Hercules beetle larva were produced; sample BOH (40°C oven dried Hercules beetle larva without condiments flour), sample COH (40°C oven dried Hercules beetle larva with condiments flour) and Sample AOH (toasted Hercules beetle larva without condiments flour) and sample GOH (Toasted Hercules beetle larva with condiments flour).

    Result: From the result of proximate analysis, the protein content varied from 59.09% to 50.07%, fat content varied from 21.98% to 12.59%, ash content varied from 7.43% to 6.19% fibre content varied from 17.62% to 15.32%, moisture content varied from 9.10% to 5.13% and carbohydrate varied from 11.42% to 3.58%. From the result the invitro protein digestibility content varied from 23.53% to 16.59%. The result of the amino acid profile showed it contained 18 amino acids, 9 of which are essential amino acids. For the essential amino acids, leucine showed a range of 7.52 mg/100 g to 6.64 mg/100 g, lysine varied from 3.04 mg/100 g to 2.39 mg/100 g, isoleucine varied from 4.07 mg/100 g to 2.94 mg/100 g, phenylalanine varied from 5.01 mg/100 g to 4.11 mg/100 g, valine varied from 4.28 mg/100 g to 3.74 mg/100 g, methionine varied from 1.36 mg/100 g to 1.17 mg/100 g, threonine varied from 3.83 mg/100 g to 3.03 mg/100 g, histidine showed a range of 2.51 mg/100 g to 1.68 mg/100 g and tryptophan varied from 1.15 mg/100 g to 0.81 mg/100 g.

    INTRODUCTION

    Insects are part of the traditional diets of approximately 2 billion people worldwide (van Huis  et al., 2013). Insects can contribute to food security and be a part of the solution to gases, Insects emit fewer greenhouse gases compared to traditional livestock. They have a smaller environmental footprint, contributing less to climate change, low requirements for land and water and the high efficiency at which they can convert feed into food (Elemo et al., 2011).
           
    As stated by the Food and Agriculture Organization, trends toward 2050 predict a steady world population increase to 9 billion (van Huis  et al., 2013). In addition, the results of studies reported in the scientific literature on consumer acceptance of this type of food are quite fragmented and, in some cases, even present contradictory results (van Huis  et al., 2013). Mexico is the country with the highest number of insect species used for human consumption, with more than 300 species (549 actually reported), followed by the countries of Southeast Asia (200-300 species), Australia, South America and some African countries (50-200 species) and Middle Eastern and European countries (10-50 species) (Kröger  et al., 2022).
           
    From a nutritional aspects, insects stand out for their high protein content. Although this nutritional value can be influenced by diet, developmental stage, sex, species, growth condition and analytical methods (de Castro  et al., 2018). On the average, the protein content of edible insects ranges between 10% and 70% of dry weight or between 10% and 25% of fresh weight, values higher than some plant products known for their high content of this macronutrient, such as cereals, soybeans and lentils (Schlüter  et al., 2017); edible insects also provide more proteins than chicken meat and eggs (Kim et al., 2019). However, one aspect to consider is the variability of the digestibility of insect proteins due to the presence of a hard exoskeleton.
           
    The aim of the study is to produce cured Hercules beetle larvae flour, investigate the amino acid profile of the cured Hercules beetle larvae flour and study the protein quality of the cured Hercules beetle larvae flour.

    MATERIALS AND METHODS

    Raw material procurement
     
    About 2 kg of the Hercules beetle larvae was bought from a commercial dealer in Bayelsa state and transported in a bucket filled with saw dust. The sample of the hercule beetle larvae is shown in Plate 1.

    Plate 1: Hercules beetle larvae.


     
    Place and duration of study
     
    This work was carried out in the Department of Food Science and Technology, FUTO, for a period of 18 months, from April 2024 to October, 2025.
     
    Preparation of 50°C oven dried Hercules beetle larva flour
     
    Approximately 500 g of live Hercules beetle larvae were washed properly and the water drained, proceeded to oven drying with oven Model (DHG-9101-05A) at 50°C for 24 hours. The dried larvae were milled with the attrition mill (Model 368 corona) to obtain the coarse Hercules beetle larvae flour. N-hexane was used during defatting (ratio 1:10 w/v) for about 3 hours to obtain 50°C oven dried Hercules beetle larvae.
     
    Preparation of toasted hercules beetle larvae flour with condiments
     
    Approximately 350 g of live Hercules beetle larvae was properly washed and water was drained using a sieve. Half a tablespoon of table salt and half a tablespoon of ground pepper was added to the larvae. The larvae was placed on a heated frying pan and toasted continuously for about 10 minutes until it was evenly fried taking proper consideration in temperature not exceeding 80°C with the aid of a thermometer. The toasted larvae were cooled and milled using attrition mill (Model 368 Corona) to obtain the oily coarse Hercules beetle pulp. It was defatted using N-hexane (1:10 w/v) for 3 hours to obtain defatted flour. The flour was packaged using airtight container and stored for further analysis.
     
    Preparation of toasted Hercules beetle larvae flour without condiments
     
    Approximately 350 g of live Hercules beetle larvae was washed properly and water was drained using a sieve. The Hercules beetle larvae was placed on a heated frying pan and toasted without condiments continuously for about 10 minutes taking proper consideration in temperature not exceeding 80 with the aid of a thermometer. The toasted larvae without condiments was cooled, milled using attrition mill (Model 368 Corona) obtain the oily coarse Hercules beetle larvae pulp. It was defatted using N-hexane (1:10w/v) for 3 hours to obtain Hercules beetle larvae flour which was packaged in an air tight container and stored for further analysis as shown in Fig 1.

    Fig 1: Production of hercules beetle larvae flour.



    Chemical analysis of the samples
     
    Proximate analysis of the sample
     
    The standard method of AOAC (2010) was used to determine the proximate compositions of the samples which includes the moisture contents, Ash, crude fibre, Protein, Crude fats and Carbohydrates.
     
    Determination of amino acid profiles of the samples: Loading of the hydrolyzate TSM analyzer and calculation of amino acid values
     
    The Amino acids profile of the samples were determined using standard analytical procedures described by Olawuni et al., (2019).
     
    In vitro protein digestibility
     
    Protein digestibility was measured using the method developed by Mertz et al. (1984) with modifications as reported by Gulati et al. (2017).
     
    Amino acid score
     
    This was expressed as the ratio of the essential amino acid content (mg/g insect crude protein) to the same essential amino acid (mg/g protein) in the scoring pattern for children and adults (WHO/FAO/UNU, 2007).
     
     
     
     
    Essential amino acid index
     
    The essential amino acid index was computed as the geometric mean of the amino acid scores using the amino acid scoring pattern for children and adults (WHO/FAO/UNU, 2007) as reference protein, assuming that the maximum amino acid score is 1 and the minimum is 0.01 (Oser, 1959).
     
      
     
    Where,
    n= Number of essential amino acids.
    AAS= Amino acid score.
     
    Statistical analysis
     
    Data obtained from the analysis were subjected to statistical analysis of variance (ANOVA) using SPSS version 2023 to separate the mean, standard deviation of triplicate runs at 95% confidence level.

    RESULTS AND DISCUSSION

    Proximate composition
     
    The result obtained from the proximate analysis of the flour samples of the Hercules beetle larva are presented in Table 1. Protein an essential macronutrient which makes up the biochemical component of the studied larvae with the values for each sample; for sample BOH (59.09%), COH (55.37%), AOH (54.31%), GOH (50.07%). These protein contents are higher than those reported for other edible insects which includes Brachytrypes spp 6% (Banjo  et al., 2006), Oryctes boas 26% (Banjo  et al., 2006), Anaphe recticulata 23% (Banjo  et al., 2006). The result showed that sample BOH produced the highest protein content compared to the other samples. An increase in crude protein signals enzymes and antibody activation (Njoku et al., 2025). The high protein content of the larva in this study indicates that they may invariably contribute to the daily protein requirements of humans (Ifie and Emeruwa, 2011). Larvae are potential sources of protein which solves global protein deficiencies (Van Huis  et al., 2013; Ofoedum et al., 2025).

    Table 1: Proximate Composition of Hercules beetle larva flour (%).


           
    The fat content of the sample GOH (21.98%) was higher than that of sample BOH (15.40%), COH (19.25%), AOH (12.59%). This may be as a result of the concentration of the dry matter with decrease of moisture because of the oven drying. The lower levels of fat in samples BOH, COH and AOH may be due to loss of oil during toasting, since the larva was fried without additional oil.
           
    The ash content of the larva flour was observed and the result showed (6.37%) for sample BOH, (6.80%) sample COH, (7.43%), sample AOH, (6.19%) sample GOH. The ash content for sample COH (7.43 was higher than the value of the other samples but lower than the value for O. rhinoceros (12.70%) as documented by Uzoukwu et al., (2025). This may be attributed to the drying ash temperature and duration and also the moisture content of the larva. The ash content obtained indicates the presence of mineral compounds (Alinnor and Akalezi, 2010), this is a pointer that D. hercules are rich in minerals.
             
    The results obtained for crude fibre content of the samples; for sample BOH (7.80%), COH (4.35%), AOH (7.44%), GOH (7.84%). These crude fibre contents are lower compared to the crude fibre compositions of O. rhinoceros (8.70±0.70%), Z. variegatus (22.07±0.38%) and the value reported for Polyrhachis vicina (13.2%) (Shen et al., 2006). Fibre in diets aid in fat reduction and proper digestion of food so as prevent diverticulitis (Oduor et al., 2008), which is the inflammation of irregular bulging pouches in the wall of the large intestine.
           
    The sample COH had the lowest moisture content (5.13) followed by sample AOH (6.83), sample BOH (7.41 and lastly GOH (9.10). The moisture content of 5.13% obtained in this study for sample COH compares unfavorably with 16.73% reported for Oryctes rhinocerous larvae flour by Okaraonye and Ikewuchi (2009). The high moisture content of food indicates a short shelf life, as it determines the quality and susceptibility of food to microbial spoilage (Frazier and West off, 2003). 
           
    The result obtained for the carbonhydrate content showed, 3.58% (sample BOH), 9.12% (sample COH), 11.84% (sample AOH), 4.84% (sample GOH). The carbonhydrate content varied as sample BOH was lower compared to the other sample and this may be attributed to the oven treatment done on it.
     
    In vitro protein digestibility
     
    Table 2 presented the invitro digestibility of the samples BOH (18.69%), COH (20.31%), AOH (23.53%), GOH (16.59%). Large differences are observed, which can be attributed to the method of digestion, the method used to assess digestibility and the species or the developmental stage of the insect (Njoku  et al., 2025). Exposure to denaturation temperatures may increase digestibility of native proteins by unfolding the polypeptide chain and rendering the protein more susceptible to digestive enzymes (Opstvedt et al., 2003). On the other hand, when proteins are exposed to some heat treatments, digestibility may be reduced due to formation of disulphide bonds in the protein (Njoku et al., 2025).

    Table 2: In vitro digestibility of the samples.


           
    The protein digestibility of most species are between 80% and 90% and even the larva of the lepidopteran Laniifera cyclades is reported to have 98.9% protein digestibility (Ramos-Elorduy  et al., 1981). Few studies have compared insects with other reference feeds, but those analysed have shown that insects show a similar digestibility to fish meal 84.9% (Arango et al., 2004); 85,7% (Bosch et al., 2016) and slightly lower digestibility than soybean meal 95% (Bosch et al., 2016).
     
    Amino acid profile of the hercules beetle larva flour
     
    The amino acid composition of the Hercules beetle larva flour is presented on Table 3. The total essential amino acid is 30.1 g/100 g and it represents 41.47% of total amino acid.

    Table 3: Amino acid profile of the Hercules beetle larva flour samples (mg/100 g).


           
    For sample COH the total amino acid is 78.22 g/100 g protein. The total essential amino acid is 32.89 g/100 g and represents 42.04% of total amino acid.
           
    For sample AOH the total amino acid is 84.76 g/100 g protein. The total amino essential amino acid is 35.71 g/100 g and it represents 42.13% of total amino acid.
           
    For sample GOH the total amino acid is 72.88 g/100 g protein. The total essential amino acid is 30.61g/100g and it represents 42% of total amino acids.
           
    Glutamic acid was the pre amino acid present in the larva containing 12.85 g/100 g in sample BOH, 13.79 g/100 g in sample COH, 14.41 g/100 g in sample AOH and 13.52 g/100 g in sample GOH. Also, there was no significant difference in the glutamic acid composition of sample COH and GOH. The glutamic acid composition of the Hercules beetle larva flour is in agreement with Ogbuagu and Emodi (2014) on R. ferrugineus who also stated that glutamic acid was the predominant amino acid (12.68 g/100 g).  
           
    The leucine content of the sample were 6.80 g/100 g for sample BOH, 7.24 g/100 g for sample COH, 7.52 g/100 g for sample AOH and lastly for sample GOH 6.64 g/100 g. These values are in agreement with the result obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (7.52 g/100 g). It also compares favorably to FAO/WHO (1973) reference value (6.6 g/100 g). Leucine is a branched-chain amino acid that is essential for the synthesis of protein and repairing of muscle. Additionally, it facilitates blood sugar control, promotes wound healing and generates growth hormones (Campbell, 2022).
           
    The lysine content of the Hercules beetle larva flour varied from 2.54 g/100 g (sample BOH) to 2.85 g/100 g (sample COH) 3.04 g/100 g (sample AOH) and 2.39g/100 g (sample GOH). The values are lower compared to the 4.2 g/100 g observed by Elemo et al., (2011) for R. phoenicis and 4.51 g/100 g reported by Ogbuagu and Emodi (2014) for R. ferrugineus. The main functions of lysine are in calcium absorption, hormone and enzyme production and protein synthesis. Additionally important for immunological function, collagen and elastin production (Campbell, 2022).
           
    Isoleucine present in the sample were 2.94 g/100 g for sample BOH, 3.38 g/100 g (sample COH), 4.07 g/100g (sample AOH), 3.09/100 g (sample GOH). These values compare well to the results obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (4.08 g/100 g). They are also higher than the value reported by Adepoju and Ayenitaju (2021) on R. phoenicis (0.92 g/100 g). Isoleucine is heavily concentrated in muscle tissue and has a role in muscle metabolism. It is essential for the production of hemoglobin, the regulation of electricity and immunological function (Ofoedum et al., 2024).
           
    The phenylalanine content in the samples varied from 4.30 g/100 g (sample BOH), 4.61g/100g in sample COH, 4.11 g/100 g in sample GOH to 5.01 g/100 g in sample AOH. The phenylalanine + tyrosine values were 7.58 g/100 g for sample BOH, 8.17 g/100 g for sample COH, 8.85 g/100 g for sample AOH, 7.24 g/100 g for sample GOH. These values suggest that the samples can sufficiently meet their respective reference standard (6.0 g/100 g) by FAO/WHO (1973). Phenylalanine plays a crucial role in the production of various amino acids as well as the shape and characteristic of proteins and enzymes (Campbell, 2022). 
           
    The valine content of the samples were 3.87 g/100 g in sample BOH, 3.93 g/100 g in sample COH, 4.28 g/100 g in sample AOH and 3.74 g/100 g in sample GOH. These values compare favorably with the 3.49 g/100g reported by Elemo  et al. (2011) and the 4.1 g/100 g observed for R. ferrugineus by Ogbuagu and Emodi (2014). The proline content of the Hercules beetle larva flour varied from 4.06 g/100g in sample AOH to 3.47 g/100 g in sample BOH. Although these values compare favourably with the report (3.29 g/100 g) of Ogbuagu and Emodi (2014), they are lower than the result (10.2 g/100 g) reported by Elemo et al., (2011) on R. phoenicis.
           
    The methionine content ranges from 1.36 g/100 g in sample AOH to 1.17 in sample GOH. The cystine content also ranges from 1.78 g/100 g in sample AOH to 1.11 g/100 g in sample GOH. The methionine + cystine value was 2.53 g/100 g in sample BOH, 2.75 g/100 g in sample COH, 3.14 g/100 g in sample AOH, lastly, 2.28 g/100 g in sample GOH; these values are however lower than their respective reference standard (3.15 g/100 g) by FAO/WHO (1973). The methionine content of the samples are lower than the value of 2.1 g/100g reported for R. phoenicis (Elemo et al., 2011). The low methionine may be attributed to diverse locality or nutrient intake of the larva. In metabolism and detoxification, methionine plays a crucial role. Additionally, it’s necessary for mineral absorption (zinc and selenium) and tissue growth, both of which are crucial for your health (Ofoedum et al., 2024).
           
    Histidine present in the samples ranged from 2.51 g/100 g in sample AOH to 2.05 g/100 g in sample BOH to 2.23 g/100 g in sample COH and finally, 1.68 g.100 g in sample GOH. The values of histidine present are greater than that reported by Elemo et al., (2011) on R. phoenicis (1.1 g/100 g) and lower than the result gotten by Ogbuagu and Emodi (2014) on R. ferrugineus (3.51 g/100 g).
           
    The values presented for the alanine content of the samples were 3.93 g/100 g in sample BOH, 4.47 g/100 g in sample COH, 5.08 g/100 g in sample AOH, 4.55 g/100 g in sample GOH. The values compare favorably to the results obtained by Njoku et al., (2025) on R. ferrugineus (4.21 g/100 g).
           
    The Glycine present in the samples were 3.75 g/100 g for sample BOH, 3.91 g/100 g for sample COH, 4.32 g/100 g for sample AOH, 3.46 g/100 g for sample GOH. The values of glycine content are similar to the result obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (3.65 g/100 g). They are however lower than the result obtained by Elemo et al., (2011) on R. phoenicis (4.8 g/100 g).
           
    The arginine content of the sample; 4.68 g/100 g for sample BOH, 4.91 g/100 g for sample COH, 5.22 g/100 g for sample AOH, 4.92 g/100 g for sample GOH. There was no significant difference (P>0.05) in the arginine composition of sample COH and GOH. The arginine content of the 4 samples compares favourably to the results obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (6.47 g/100 g).
           
    The serine present in the sample was found to be 3.74 g/100 g in sample BOH, 4.10 g/100 g in sample COH, 4.41 g/100 g in sample AOH, 4.02 g/100 g in sample GOH. The values compare favorably to the results obtained by Ogbuagu and Emodi (2014) on R. ferrugineus (3.64 g/100 g).
           
    Aspartic acid was found to be 8.02 g/100 g in sample BOH, 8.43 g/100 g in sample COH, 8.87 g/100 g in sample AOH and 7.55 g/100 g in sample GOH. There were major differences in the aspartic acid composition of the three samples.
           
    Threonine present in the Hercules beetle larva flour ranges from 3.83 g/100 g in sample AOH to 3.03 g/100 g in sample BOH, 3.36 g/100 g in sample COH and 3.25 g/100 g in sample GOH. There was no significant difference (P>0.05) in the threonine content of the samples. The values of threonine present are similar to the result obtained by Njoku et al., (2025) on R. ferrugineus (3.51 g/100 g) and slightly higher than that reported by Elemo et al., (2011) on R. phoenicis (2.9 g/100 g). The amino acid threonine is a crucial component of structural proteins like collagen and elastin, which are essential components of connective tissue and the skin. It also contributes to immunological function and the metabolism of fat (Campbell, 2022).
           
    Tryptophan was the amino acid present in the least amount in the Hercules beetle larva flour, ranging from 1.15 g/100 g in sample AOH to 0.81 g/100 g in sample BOH. This is lower than the reported content of 6.0 g/100 g for R. phoenicis (Odimegwu et al., 2025). In addition to aiding in nitrogen stability, tryptophan is a precursor to serotonin, a neurotransmitter that controls your mood, appetite and sleep (Njoku  et al., 2025).
     
    Effects of curing on the protein quality indices of hercules beetle larva
     
    The protein quality of the Hercules beetle larva expressed in terms of various parameters are presented in Table 4. From the amino acid score, the first limiting amino acid for sample BOH is leucine (0.10), Histidine (0.37) for sample COH and Histidine (0.42) for sample AOH and histidine (0.28) for sample GOH. The second limiting amino acid in the Hercules beetle larva was Histidine (0.34) for sample BOH, Lysine (0.52) for sample COH, lysine (0.55) for sample AOH and lysine (0.43) for sample GOH. Some of the amino acid score were greater (>) than 1 which implies that in 1g of the palm weevil larva, the amino acid were present in quantities higher than in 1g of the reference scoring pattern for children and adult (WHO/FAO/UNU, 2007). Therefore, the Hercules beetle larva contains excess of some essential amino acid and as such can be incorporated in foods deficient in these essential amino acids. The ratios E/N and E/(E + N) of the hercules beetle larva ranged from 0.68 to 0.69 and from 0.39 to 0.41. The above ratios are comparable to the standard (0.6 and 0.4 respectively) recommended by the EFSA (2012) and FAO/WHO/UNU (1985) Joint Expert Consultation Report on energy and protein requirements in humans.  

    Table 4: Effects of curing on the amino acid contents of hercules beetle larva flour samples (mg/100 g).

    CONCLUSION AND RECOMMENDATION

    The study shows that the oven dried Hercules beetle larva flour with condiments has high protein and fat content. The toasted Hercules beetle larva flour with condiments had the highest moisture content indicating a short shelf life and also had the highest fat content.
           
    The in vitro protein digestibility of the Hercules beetle larva was relatively low compared to other edible insects. This is as a result of the heat processing method carried out during the production process of Hercules beetle larva flour.
           
    The hercules beetle larva flour toasted and oven dried either with condiments or not was found to contain 18 amino acids, 9 of which are essential amino acids indicating it is a complete protein. Some of the essential amino acid values for the toasted and oven dried larva with and without condiments including; tryptophan, leucine, phenylalanine, isoleucine, met and/or surpassed the FAO/WHO reference values.
           
    Incorporation of Hercules beetle larva flour into different food products such as protein bars, snacks and dietary supplements to promote its acceptance and utilization should also be considered.

    ACKNOWLEDGEMENT

    The co-operations of all the staff of the Department of Food Sci. and Tech., Federal University of Technology, Owerri are hereby acknowledged.
     
    Disclaimers
     
    The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
     
    Informed consent
     
    All animal procedures for this experiment were approved by the committee of Experimental Animal Care and Handling techniques were approved by the University authority.
     
    Source of funding
     
    None.
     

    CONFLICT OF INTEREST

    All the authors have declared that there are no conflicts of interest.

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