Tenebrio molitor larvae, commonly known as mealworms, as they are a rich source of nutrients and can be reared with relatively low resource input.
1. Introduction
The exploration of alternative food sources for human consumption has garnered significant attention due to several compelling factors, with most of them revolving around overpopulation and the high nutritional value of these novel food sources. This ongoing issue of overpopulation, which has been a topic of concern in the research community since 1997
[1], naturally correlates with an increasing demand for conventional protein sources, namely, meat and fish
[2][3][4][5]. The expansion of livestock farming, driven by this escalating demand, poses the risk of encroaching on previously uncultivated land, exacerbating the issue of land use, considering that 75% of arable land is currently dedicated to livestock activities
[6][7]. Moreover, the livestock sector is a major contributor, accounting for 14.5% of total anthropogenic greenhouse gas emissions
[8], raising concerns about the environmental impact of this sector, which is likely to escalate with an increase in livestock units
[9]. In the context of fish as a key source of protein, numerous fish species are endangered worldwide as a consequence of overfishing, pollution, coastal development, climate change and other anthropogenic actions
[10]. An example is
Chondrichthyes. The
Chondrichthyes species is in danger, since 32.6% (391 out of 1199 species) are threatened with complete extinction due to overfishing
[11]. This overexploitation of marine resources has resulted in the degradation of several marine habitats
[11][12][13]. Given these ecological and sustainability concerns surrounding conventional protein sources, the scientific community has shifted its focus toward identifying alternative, sustainable sources of protein. Among these, insects have emerged as one of the most promising options
[14][15][16][17][18].
Insects exhibit distinct advantages from economic and ecological standpoints. They require considerably less space, minimal water (relying primarily on moisture), and reduced feed to complete their biological life cycle compared to traditional protein sources
[19][20][21][22]. However, it is noteworthy that the concept of insects as a food source is not entirely novel. Recent archaeological evidence from Tanzania suggests that insects played a crucial role in the nutrition of early humans, dating back 1.8 million years
[23]. Additionally, historical depictions, such as those found in the Artamila caves in northern Spain (3000–9000 BC), portray the collection of bee nests and larvae, further highlighting the historical significance of insect consumption
[24]. Despite this historical practice, insect consumption has declined significantly over time and is now primarily narrowed to traditional practices in certain regions like Southeast Asia and Australia
[25][26]. In Europe, insect consumption remains relatively rare, largely due to “neophobia” surrounding insect consumption in any form
[27][28][29][30]. Nevertheless, as of 2021, three insect species have received approval for safe human consumption by the European Parliament and Council
[31]. In particular, on 12 November 2021 they authorized the placing on the market of frozen, dried, and powdered forms of
Locusta migratoria Linnaeus (Orthoptera: Acrididae)
[32], on 1 June 2021 the placing on the market of dried
Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae) larvae as a novel food
[33] and, most recently, on 5 January 2023, the frozen, paste, dried and powder forms of
Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae) larvae (lesser mealworm)
[34].
One of the approved species,
Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae), is particularly noteworthy for its potential to be more readily accepted by consumers, especially in Europe
[35][36][37][38]. For instance, Europeans tend to find the larvae of
T. molitor more appealing than alternatives like cockroaches or ants
[39]. Moreover, the rearing of
T. molitor shows great promise in the rapidly expanding, global, edible insect market, where it is already being widely produced as feed for fish and poultry
[40][41][42][43].
A comparative analysis of the rearing of
T. molitor and
Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae) reveals several advantages of the former.
T. molitor larvae complete their development and growth in a shorter time frame, boasting a higher survival rate and greater weight compared to
A. diaperinus [44]. Specifically, the survival rate of
T. molitor larvae is as high as 98.8%, while that of
A. diaperinus ranges from 88 to 95%. Additionally, the weight of
T. molitor larvae is substantially greater, compared to the weight of
A. diaperinus larvae
[45][46][47]. This disparity is expected, given that
T. molitor is larger than
A. diaperinus at all stages of development
[48][49]. When comparing the rearing of
T. molitor to that of
Locusta migratoria Linnaeus (Orthoptera: Acrididae), it becomes evident that
T. molitor rearing is both faster and more straightforward. The development of
T. molitor larvae is completed in just 2–3 months, whereas
L. migratoria larvae require 2–4 months for their development
[50][51][52]. This efficiency in rearing further highlights the potential of
T. molitor as a viable and sustainable protein source for human consumption, particularly in regions where insect consumption is gaining recognition as an environmentally responsible dietary choice.
2. Nutritional Value of T. molitor
As is frequently mentioned, their high nutritional value is the reason that led researchers to extensively study the larvae of
T. molitor. This species is, to this day, the main subject of research since it is characterized by its content of essential nutrients, including crude protein, essential amino acids (EAAs), fat, and essential fatty acids
[24][53][54][55][56][57]. The quantification of the crude protein of
T. molitor and its flour (dried and finely ground larvae) has received special attention. Due to this, several analytical methods have been used, such as the combustion (Dumas) method
[56], Randall method
[35], Kjeldahl method
[58], elemental analysis method
[59], Bradford method
[60], and precipitation
[61], yielding a variety of results, ranging from 36.8–75.1%. This variation can be attributed to the different rearing conditions of each
T. molitor larvae. At this point, it is worth emphasizing that conventional animal, protein-rich foods, such as beef, chicken, and tuna, contain 21.4, 19.4
[62], and 22.7% crude protein
[63], respectively, values that can easily be considered low compared to the protein content of
T. molitor larvae. In
Table 1 the crude protein values contained in
T. molitor larvae according to various surveys are presented.
Table 1. Nutritional value of T. molitor larvae according to the crude protein quantification method.
Histidine (His), isoleucine (Iso), leucine (Leu), lysine (Lys), methionine (Met), phenylalanine (Phe), threonine (Thr), tryptophan (Trp), and valine (Val) are nine amino acids that cannot be synthesized by mammals and they must be obtained through food consumption. Therefore, they are called dietarily essential, indispensable nutrients or essential amino acids (EAAs)
[64].
T. molitor larvae contain large amounts of Leu, Val, and Lys but low amounts of His, Met, and Trp EAAs, with Trp rarely occurring in these insects
[55]. Similarly, to crude protein, EAA concentrations are influenced by the rearing conditions of the
T. molitor larvae, temperature, humidity, feed substrate and rearing region
[65][66]. For instance, Lys quantities in
T. molitor larvae can range from 1.6 to 5.8%, Thr quantities can range from 1.3 to 4.3%, Met quantities can range from 0.6 to 2.2% and Trp quantities can range from 0.02 to 1.9%
[35][42][43][44][45]. More details for the quantities of the EAAs are presented in
Table 2.
Table 2. Amino acid composition (mg/g of dry weight) of T. molitor larvae.
The second most plentiful nutrient in the composition of
T. molitor larvae is crude fat
[70], which exhibits variability in values depending on the content of other nutrients and the processing method
[55]. Predominantly, these larvae contain about 27% fat, whereas the percentage was found to range from 19.1 to 32.2%
[56][57][58][59][60]. In
Table 1, a detailed presentation of the crude fat values, with the corresponding crude protein content, is shown. In addition to EAAs, in
T. molitor larvae, essential fatty acids (EFAs), such as linoleic acid (ω-6 group) and alpha-linolenic acid (ω-3 group)
[71], are also detected
[72]. Humans cannot produce these EFAs and thus must be obtained through the diet they are based on. The fatty acid composition of
T. molitor larvae is presented in
Table 3. As far as linolenic acid (C18:2 ω-6) is concerned, it is present in high amounts in
T. molitor larvae, ranging from 11.5 to 48.1%. In contrast, as far as the content of alpha-linolenic acid (C18:3 ω-3) in larvae is concerned, it covers a range of values, from 0.2 to 2.3%. Furthermore, considerable quantities of fatty acids such as myristic acid (C14:0), palmitic acid (C16:0), palmitoleic acid (C16:1), and ω-9 oleic acid (C18:1) are also detected
[38][42][45][46][47].
Table 3. Fatty acid composition (%) of T. molitor larvae.
Crude ash constitutes one more important aspect of
T. molitor larvae, which is tested in all studies investigating the nutritional value of
T. molitor larvae. Crude ash refers to the total of all mineral elements such as phosphorus (P), calcium (Ca), sodium (Na), and magnesium (Mg)
[73]. The crude ash as presented in
Table 1 ranges from about 1.0 to 4.2%
[56][57][58][59][60] and is also affected by the composition of the other nutrients, crude protein, and crude fat. Regarding, the minerals contained in
T. molitor larvae were identified and quantified in a number of studies. In particular, the P content of larvae has recorded values up to about 1.0%
[74], Ca content up to 0.5%
[58], Na content up to 0.4%
[57], Mg content up to 1.6%
[58] and potassium (K) content up to about 1.0%
[57]. In addition,
T. molitor larvae contain up to 100.02 mg/kg of iron (Fe), up to 117.4 mg/kg, of zinc (Zn), and 20.0 mg/kg of copper (Cu)
[74].
This entry is adapted from the peer-reviewed paper 10.3390/foods12234223