1. Introduction
Throughout Indonesia, 20 million people suffer from undernourishment, which is approximately 8% of the Indonesian population [
1]. In Indonesia, one in every five children suffers from malnutrition and one in every three children suffers from from stunting [
2]. In the tropical Indonesian island of Sumatra, the diet consists mainly of rice, fruit and vegetables; meat, dairy products and bread are minor components [
3].
Edible insects are one of the traditional, readily available and nutritious foods [
4,
5] in Indonesia, and can be a source of animal protein and fat. However, insects are consumed randomly, and not systematically implemented in the menu. Knowledge of the nutritional values of edible insect in this area is not sufficient. This creates a blank field in the evaluation of the menu of the indigenous inhabitants. Therefore, the subsequent influence of edible insect consumption on the health of the local people is not yet known [
6].
Thanks to its nutritional composition, edible insects can be a good food source for the local population, and can, to a certain extent, alleviate the problem of malnutrition [
7].
The aim of this work is to analyze the nutritional values of selected edible insect species, reared on the island of Sumatra, as a traditional and readily available food source for the indigenous inhabitants. This aim was chosen due to the missing complex data about nutritional values of edible insects reared in this area. Results are compared with nutritional analyses of edible insects from different regions of the world.
For easy breeding (successfully mastered at an industrial level in the following three species),
Tenebrio molitor, Gryllus assimilis and
Zophobas morio are chosen and used for our analyses. They are, to varying degrees, able to dispose of waste grain and vegetable and fruit scraps from markets [
8,
9]. Apart from the feed, the nutritional value of edible insects is influenced mainly by other factors—such as species, developmental stage, sex, diet and the environment [
10,
11,
12]. As stated by Reference [
13], the species itself is not as important as the composition of the insect feed.
4. Discussion
As early as 1975, Reference [
7] pointed out that the one way to help solve the problem of undernourishment in the world would be the use of edible insects, which are readily available and nutritious [
4,
5]. Edible insects have high protein content, which has exceptional importance in a healthy diet and cannot be replaced by other nutrients. Also, the content of all essential amino acids, which have to be received through food, is high [
22]. Proteins are of high quality [
24] and, besides being eaten, they can be used in other food-related branches [
25]. Another protein quality indicator is its digestibility, the usability by the human body. According to Reference [
19], insect protein digestibility is as high as 86–89%.
Crude protein content in insects is generally within the range of 40 to 75 g/100 g in dry matter, which is comparable to the crude protein content in common commodities of animal origin [
26]. Reference [
27] declared a greater range of 15% to 81%. The crude protein content in CML (
Tenebrio molitor) was in accordance with the literature. Reference [
18] stated the content in this species to be 50.9%; Reference [
28] reported 49.1%; and Reference [
29] stated the value of 45.1–48.6%, depending on the feed. Similarly, in the giant mealworm beetle (
Zophobas morio), our result corresponds with Reference [
20]—46.8%. Reference [
18] stated the content to be 54.3% in the same species, and Reference [
29] stated the content to be between 34.2–42.5%, depending on the feed. In the field cricket (
Gryllus assimilis), the crude protein content from our research is similar to Reference [
18], who detected the value of 59.2%. Reference [
28] stated a content of 46.8% in a similar species—home cricket (
Acheta domesticus). Analyses confirm Reference [
29], that differences up to 11% can be caused by a different feed composition.
Edible insects display great variability considerng not only proteins, but also fats. Fat is an energy source, and its content may be from 7 to 77 g/100 g of edible insect dry matter [
30]. These variabilities depend on the season, development stage, sex, environment and feed. Fat content was detected within the range of 31% to 35%. In CML, the value was 31%. This value is in accordance with the references, that state, e.g., 32.0% [
31], 36.1% [
18], 35.0% [
28], 27.1% (recalculated from the content in fresh weight 9.9% [
24]) or 18.9–38.3% depending on the feed composition [
29]. This value is the same as stated by Reference [
32], who found a fat content of 34.54% in
Tenebrio molitor larvae. Fat content in larvae did not differ significantly from that of pupae (32%). The highest content of fat among the analyzed samples was the giant mealworm (larva) with 35%, which could be a suitable source of nutritional energy. Reference [
29] stated the content to be between 32.8% and 43.5% in the same species, depending on the feed, while Reference [
28] reported 42.0% and Reference [
18] declared the value of 40.3%. Similarly, the measured value of 32% for field crickets is in accordance with the literature. Reference [
18] stated that the value is 34.3%. Reference [
28] declared in a similar species, the house cricket, to be only 14.4%, similar to Reference [
24], who declared the value of 12.3% (recalculated from the content in fresh weight 3.6%) or Reference [
31], which reported 15.3%. The majority of the most common species of edible insects is thus comparable with some traditional foods such as eel meat (30% dry matter), pork (32% dry matter) or young goose meat (36% dry matter) [
33,
34].
Analyses of the fatty acid profile were aimed at the essential fatty acid profile, especially the content of linoleic acid, which is important for physiological processes and the creation of linolenic acid. Another polyunsaturated fatty acid (PUFA) benefit is the prevention of cardiovascular diseases [
22]. Polyenic fatty acids in edible insect fatty acid profiles may comprise up to 70% of the total fats [
35]. According to the analyses of Reference [
36], the minimal total content of polyenic fatty acids in termites was 5.9% to 12.2% of the total fat. Reference [
36] found that the most abundant fatty acids were C18, among them the oleic acid C18:1, the content of which was from 41.7% to 50.2% of the total fat in termites. In the case of the larvae of
Zophobas morio and
Tenebrio molitor, the content presented is the same or lower [
19,
20,
21]. Also, linoleic acid C18:2, linolenic acid C18:3 and saturated stearic acid C18:0 belong to C18 fatty acids [
36]. The ratio of n-6 and n-3 fatty acids is mostly 5.8:10 to 57.7:10 [
37]. From a nutritional point of view, they are important for the proper development of the brain and nervous system in children and newborns. In developing countries, insect fat could cover the deficit of n-3 and n-6 fatty acids [
38]. Also, saturated fatty acids (palmitic acid, stearic acid) have a significant content in the fatty acid profile.
A comparison of the fatty acid profile of giant mealworm larvae (
Zophobas morio) showed that the sequence of the first four fatty acids (C18:1 (cis-9), C18:2 (cis-9,12), C16:0, C18:0) is identical to reports by other authors, as well as in CML (
Tenebrio molitor). Only Reference [
21] documented myristic acid in the fourth place, unlike other authors, who report stearic acid as the fourth. In the field cricket (
Gryllus assimilis) and related species house cricket (
Acheta domesticus), many studies showed linoleic acid as the most abundant, as was the case in our analyzed samples. Reference [
39] detected alpha-linolenic acid as the most abundant in the samples of
Chorthippus parallelus, representing up to 40.4% of the total fatty acid content. On the contrary, Reference [
21] declared oleic acid as the most plentiful in the samples of (
Acheta domesticus), while other papers placed it second or third (e.g., [
19,
20]), as was the case in our analysed samples. Oleic and palmoitic acids are equally abundant. Stearic acid is in the fourth place in our analyses and also in the literature.
According to Reference [
40], the content of fatty acids is determined by several factors such as species, life-cycle phase, environmental factors and nutrition. A comparison of the fatty acid profile with species bred in Czech Republic with controlled feed, analyzed by Reference [
41], proved differences dependening on the breeding location. The comparison also revealed differences in essential fatty acid proportions (linoleic and linolenic acid), as the samples from Sumatra had higher content of these fatty acids.
Chitin is considered as an indigestible fibre with protective effects on human health [
42,
43], even though the enzyme chitinase is found in human gastric juices [
44]. However, it was found that this enzyme may be inactive. In this case, only in saliva and in the stomach is it partially hydrolyzed by lysozyme and hydrochloric acid. Active chitinase response in the body prevails among people from tropical countries where the consumption of insects has a long-term tradition [
38]. Chitin is present in the cuticles of arthropods, which can be hardened (e.g., by crabs, crayfish, insects) and transformed into exoskeleton [
45]. The removal of chitin improves the digestibility of insect protein [
46].
The composition and amount of chitin in insects varies according to the species and development stage. For the common mealworm, Reference [
47] gave an average chitin content of 5%; Reference [
48] reported 1.2%, and Reference [
49] declared the average chitin content of insects to be 10%. In
Cirina forda larvae, the chitin content is 9.4% [
50]. In field cricket (
Gryllus testaceus walker), Reference [
43] declared 8.7% of chitin in dry matter. This is in accordance with our value of 7%. Our result of chitin content in the larval stage of the same species was 12%. Chitin content is influenced by amino acids [
51]. Chitin content in giant mealworm larvae in our research was 6% in dry matter. The available literature does not mention the chitin content in this species.