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Insect farming, a potential way to meet the growing global demand for protein, is also a new activity in the Western world, raising many questions about the quality and safety of the products. Insects can play an important role in the circular economy by converting biowaste into valuable biomass. About half of the mealworm diet is wet feed. This can be produced from biowaste, which will improve the sustainability of insect farming. This article reports on the nutrient composition of mealworms (Tenebrio molitor) fed with organic supplements from by-products. These included unsold vegetables, potato slices, fermented chicory roots and garden leaves. The assessment was carried out by analyzing the proximate composition, fatty acid profile, minerals and heavy metal content. Mealworms fed potato cubes had a doubled fat content, as well as an increase in both saturated and monounsaturated fatty acids. Fermented chicory root consumption increased mineral content and accumulated heavy metals. Furthermore, mealworms were selective in consuming minerals, as only calcium, iron and manganese concentrations increased. Addition of vegetable mixes or garden leaves to the diet did not significantly change the nutrient content. In conclusion, the side stream was successfully converted into protein-rich biomass, the nutritional value and bioavailability of which influenced the mealworm composition.
The world’s population is expected to reach 9.7 billion by 20501,2 putting pressure on our food production to cope with the high demand for food. It is estimated that food demand will increase by 70–80% between 2012 and 20503,4,5. The natural resources we currently use to produce food are being depleted, putting our ecosystems and food supply at risk. In addition, large amounts of biomass associated with food production and consumption are lost. It is estimated that by 2050, global waste will reach 27 billion tonnes per year, most of which will be biowaste6,7,8. In light of these challenges, innovative solutions, alternative foods and sustainable development of agriculture and food systems have been proposed9,10,11. One approach is to use organic waste to produce feedstocks, such as using edible insects as a sustainable source of food and feed12,13. Insect farming produces lower greenhouse gas and ammonia emissions, requires less water than traditional protein sources, and can be carried out in vertical farming systems, requiring less space14,15,16,17,18,19. Studies have shown that insects are able to convert low-value biowaste into valuable protein-rich biomass with dry matter contents of up to 70%20,21,22. Moreover, low-value biomass is currently used for energy production, landfill or recycling and therefore does not compete with existing food and feed sectors23,24,25,26. The yellow mealworm (T. molitor)27 is considered one of the most promising species for large-scale food and feed production. Both larvae and adults feed on a variety of materials such as cereal products, as well as animal waste, vegetables, fruits, etc. 28,29. In Western societies, T. molitor is reared in captivity on a small scale, mainly as food for domestic animals such as birds or reptiles. Currently, increasing attention is being paid to their potential use as food and feed30,31,32. For example, T. molitor has been granted a new food dossier, including for use in frozen, dried and powdered form (Regulation (EU) No 258/97 and Regulation (EU) 2015/2283)33. However, large-scale production of insects for food and feed is still a relatively new concept in Western countries. The industry faces a number of challenges, such as knowledge gaps regarding optimal diets and production, nutritional value of the final products, and safety issues such as toxic build-up and microbial hazards. Unlike traditional livestock farming, insect farming does not have the same historical track record17,24,25,34.
Although many studies have been conducted on the nutritional value of mealworms, the factors affecting their nutritional value are still not fully understood. Previous studies have suggested that the insects’ diet may have some effect on their composition, but no clear patterns have yet been identified. Furthermore, these studies have focused on the protein and fat composition of mealworms but have had limited effects on the mineral composition21,22,32,35,36,37,38,39,40. Further studies are needed to understand the mineral uptake capacity. A recent study concluded that mealworm larvae fed radish had slightly elevated levels of some minerals. However, these results are limited to the matrix tested and further field trials are needed41. It has been reported that the accumulation of heavy metals (Cd, Pb, Ni, As, and Hg) in Tenebrio molitor was significantly correlated with the metal content of the substrate. Although the metal concentrations found in the diet were below acceptable levels for animal feed42, bioaccumulative accumulation of arsenic, but not cadmium and lead, was detected in mealworm larvae43. Understanding the effects of diet on the nutritional composition of mealworms is important for their safe use in food and feed.
The study presented in this paper focused on the effect of using agricultural by-products as a source of wet feed on the nutrient composition of Tenebrio molitor. In addition to dry feed, wet feed should be provided to the larvae. Wet feed provides essential moisture and also serves as a nutritional supplement for mealworms, improving growth rate and maximum body weight44,45. According to our data on standard mealworm rearing practices in the Interreg-Valusect project, the total mealworm diet contains 57% wet feed. Fresh vegetables (e.g. carrots) are commonly used as a source of wet feed35,36,42,44,46. Using low-value by-products as a source of wet feed will bring greater sustainability and economic benefits to insect farming17. The objectives of this study were to (1) investigate the effects of using biowaste as wet feed on the nutritional composition of mealworms, (2) determine the macro- and micronutrient contents of mealworm larvae reared on mineral-fortified biowaste to test the feasibility of mineral fortification, and (3) evaluate the safety of these by-products in insect culture by analyzing the presence and accumulation of heavy metals Pb, Cd, and Cr. This study will provide further insight into the effects of supplementing mealworm larvae with biowaste on their nutritional value and safety.
The lateral flow dry matter content was higher compared to the control wet feed agar. The vegetable mixture and garden leaves had a DM content of less than 10%, while potato slices and fermented chicory roots had a higher DM content (13.4 and 29.9 g/100 g fresh matter, FM).
The vegetable mixture had higher crude ash, fat and protein contents and lower non-fibrous carbohydrate contents than the control diet (agar), while the amylase-treated neutral detergent fibre content was similar. The carbohydrate content of the potato cubes was the highest of all the by-products and comparable to that of the agar. Overall, its crude composition was closest to the control diet, but with the addition of a small amount of protein (4.9%) and crude ash (2.9%)47,48. The pH of potatoes is between 5 and 6, and it should be noted that this potato by-product is more acidic (4.7). Fermented chicory root contains a lot of ash and is the most acidic of all the by-products. Since the roots were not washed, most of the ash was expected to consist of sand (silicon dioxide). The only alkaline product compared to the control and other side streams was the horticultural leaves. It contained a high amount of ash and protein, and significantly less carbohydrates than the control. The crude composition was closest to fermented chicory root, but with a higher crude protein concentration (15.0%), which is comparable to the protein content of the vegetable mixture. Statistical analysis of the above data showed that the side streams differed significantly in crude composition and pH.
Addition of vegetable mixture or garden leaves to the mealworm diet had no effect on the biomass composition of mealworm larvae compared to the control group (Table 1). Addition of potato shavings resulted in the most significant differences in biomass composition compared to mealworm larvae fed the control group and other wet food sources. Regarding the protein content of mealworms, different approximate side stream compositions, with the exception of potato shavings, did not affect the protein content of larvae. Feeding potato shavings as a moisture source resulted in a doubling of the fat content of larvae, while the content of protein, chitin, and non-fibrous carbohydrates decreased. Fermented chicory roots increased the ash content of mealworm larvae by one and a half times.
Mineral profiles were expressed as macromineral (Table 2) and micromineral (Table 3) content of wet feeds and mealworm larval biomass.
In general, the agricultural waste was richer in macrominerals compared to the control, except for potato waste, which had lower Mg, Na and Ca contents. Potassium concentration was higher in all sidestreams compared to the control. Agar contained 3 mg/100 g DM potassium, while the potassium concentration in the sidestream ranged from 1070 to 9909 mg/100 g DM. The macromineral content of the vegetable mixture was significantly higher than that of the control, but the Na content was significantly lower (88 vs. 111 mg/100 g DM). The macromineral concentration of potato shavings was the lowest among all sidestreams. The macronutrient content of potato shavings was significantly lower than that of the other sidestreams and the control. With the exception of magnesium content, the results were comparable to those of the control. Although fermented chicory root did not have the highest concentration of macrominerals, this by-stream had the highest ash of all the by-streams. This is probably due to the fact that they are not purified and may contain high concentrations of silica (sand). The Na and Ca contents were comparable to those of the vegetable mixture. Fermented chicory root contained the highest concentration of Na of all the by-products. With the exception of Na, the horticultural leaves had the highest concentration of macrominerals of all the wet forages. The potassium concentration (9909 mg/100 g DM) was three thousand times higher than the control (3 mg/100 g DM) and 2.5 times higher than the vegetable mixture (4057 mg/100 g DM). The Ca content was the highest among all side streams (7276 mg/100 g DM), 20 times higher than the control (336 mg/100 g DM) and 14 times higher than the Ca concentration in the fermented chicory root or vegetable mixture (530 and 496 mg/100 g DM).
Although significant differences were observed in the macromolecular mineral composition of the diets (Table 2), no significant differences were observed in the macromolecular mineral composition of mealworms raised on the vegetable mixture or control diet.
Potato grit fed larvae had significantly lower concentrations of all macrominerals compared to the control group, with the exception of Na, which remained comparable. Additionally, potato grit feeding resulted in the greatest reduction in macromineral content in larvae compared to the other sidestreams. This is consistent with the lower ash content observed in the mealworm coarse diet. However, although phosphorus and potassium levels were significantly higher in this wet diet than in the other sidestreams and the control, larval composition did not reflect this. The low concentrations of Ca and Mg found in mealworm biomass may be related to the low concentrations of Ca and Mg present in the wet diet itself.
Feeding fermented chicory roots and garden crop leaves resulted in significantly higher calcium levels than the control. Garden crop leaves contained the highest levels of P, Mg, K and Ca of all wet diets, but this was not reflected in mealworm biomass. Na content was lowest in these larvae, while Na concentration was higher in garden crop leaves than in potato cuttings. Ca content increased in larvae (66 mg/100 g DM), but the Ca concentration was not as high as in mealworm biomass in the fermented chicory root experiment (79 mg/100 g DM), although the Ca concentration in garden crop leaves was 14 times higher than in fermented chicory roots.
Looking at the trace element content of the wet feed (Table 3), the mineral composition of the plant mixture was similar to the control, except that the Mn concentration was significantly lower. Concentrations of all analyzed trace elements were lower in the potato slices compared to the control and other by-products. Fermented chicory root contained almost 100 times more iron, 4 times more copper and 2 times more zinc than the control sample, while manganese levels were comparable. The zinc and manganese content of the leaves of horticultural crops was significantly higher than in the control group.
No significant differences were found between the trace element content of the larvae fed the wet diet of the control group, the vegetable mixture, and the potato scraps. However, the Fe and Mn content of the larvae fed the fermented chicory roots was significantly different from that of the mealworms fed the control group. The increase in the iron content may be due to the hundred-fold higher concentration of trace elements in the wet diet itself. However, although no significant difference was observed in the Mn concentration between the fermented chicory roots and the control group, the Mn content increased in the larvae fed the fermented chicory roots. It should also be noted that the Mn concentration was higher (3-fold) in the diet consisting of garden leaves compared to the control, but no significant differences were observed in the biomass composition of the mealworms. The only difference between the control and garden leaves was the Cu content, which was lower in the leaves.
Table 4 shows the concentrations of heavy metals found in substrates. The maximum European levels of Pb, Cd and Cr in complete animal feeds have been converted to mg/100 g DM and added to Table 4 to allow comparison with concentrations found in by-products47.
No lead was detected in the control wet feed, vegetable mix or potato slices, whereas the garden crop leaves contained 0.002 mg Pb/100 g DM and the fermented chicory roots had the highest concentration at 0.041 mg Pb/100 g DM. Cr concentrations in the control diet and garden crop leaves were comparable (0.023 and 0.021 mg/100 g DM), whereas Cr concentrations in the vegetable mix and potato slices were lower (0.004 and 0.007 mg/100 g DM). The Cr concentration in the fermented chicory roots was significantly higher (0.135 mg/100 g DM) compared to the other substrates and six times higher than in the control diet. No Cd was detected in either the control stream or any of the side streams used.
Significantly higher levels of Pb and Cr were found in larvae fed fermented chicory roots. However, Cd was not detected in any of the Tenebrio molitor larvae.
A qualitative analysis of the fatty acids in the crude fat was carried out to investigate whether the fatty acid profile of mealworm larvae could be influenced by the different composition of by-products fed to them. The distribution of these fatty acids is shown in Table 5. The fatty acids are listed by their common name and molecular structure (expressed as “Cx:y”, where x is the number of carbon atoms and y is the number of unsaturated bonds).
The fatty acid profile of mealworms fed potato shavings was significantly altered. They contained significantly higher levels of myristic acid (C14:0), palmitic acid (C16:0), palmitoleic acid (C16:1), and oleic acid (C18:1). Concentrations of pentadecanoic acid (C15:0), linoleic acid (C18:2), and linolenic acid (C18:3) were significantly lower compared to other mealworms. The ratio of C18:1 to C18:2 in potato shavings was inversely related to other fatty acid profiles. Mealworms fed horticultural leaves contained higher amounts of pentadecanoic acid (C15:0) compared to mealworms fed other wet diets.
Fatty acids are divided into saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA). Table 5 shows the concentrations of these fatty acid groups. Overall, the fatty acid profiles of mealworms fed potato waste were significantly different from those of the control group and other by-product sources. For each fatty acid group, mealworms fed potato waste were significantly different from all other groups. They contained more SFA and MUFA, but less PUFA.
There were no significant differences in survival and total harvest weight between larvae reared on different substrates. The overall average survival was 90%, and the total average harvest weight was 974 g. Mealworms successfully utilize by-products as a source of wet feed. The wet diet of mealworms accounted for more than half of the total diet weight (dry + wet). Using agricultural waste instead of fresh vegetables as a regular wet feed has economic and environmental benefits for mealworm farming.
Table 1 shows that the biomass composition of mealworm larvae reared on the control diet was approximately 72% moisture, 5% ash, 19% lipid, 51% protein, 8% chitin and 18% non-fibrous carbohydrates on a dry matter basis, which is comparable to values reported in the literature48,49. However, other components can be found in the literature, often depending on the analytical method used. For example, we use the Kjeldahl method to determine crude protein content with an N:P ratio of 5.33, whereas other researchers use the more widely used ratio of 6.25 for meat and feed samples50,51.
Supplementation of the diet with potato scraps, a wet food rich in carbohydrates, resulted in the fat content of mealworms doubling. The carbohydrates in potato are expected to be composed mainly of starch, whereas agar contains sugars (polysaccharides)47,48. This finding is in contrast to another study that found that fat content decreased when mealworms were fed a diet supplemented with steam-peeled potatoes, which are low in protein (10.7%) and high in starch (49.8%)36. When olive pomace was added to the diet, the protein and carbohydrate contents of mealworms matched those of the wet food, whereas the fat content remained unchanged35. In contrast, other studies have shown that the protein content of larvae reared in side streams undergoes dramatic changes, as does the fat content22,37.
Fermented chicory roots significantly increased the ash content of Tenebrio molitor larvae (Table 1). There are few studies on the effects of by-products on the ash and mineral content of mealworm larvae. Most studies on by-products have focused on the fat and protein content of larvae without analyzing the ash content21,35,36,38,39. However, when the ash content of larvae fed by-products was analyzed, an increase in ash content was found. For example, feeding mealworms garden waste increased their ash content from 3.01% to 5.30%37, while adding watermelon waste to the diet increased the ash content from 1.87% to 4.40%.52
Although all wet food sources varied significantly in their approximate composition (Table 1), the biomass composition of mealworm larvae fed the respective wet food sources did not differ significantly. Significant changes were observed only in mealworm larvae fed potato chips or fermented chicory roots. A possible explanation for this result is that in addition to chicory roots, potato chips were also partially fermented (pH 4.7, Table 1), making the starch/carbohydrates more digestible/utilizable by mealworm larvae. How mealworm larvae synthesize lipids from nutrients such as carbohydrates is of great interest and future studies should fully understand this. A previous study on the effect of wet diet pH on the growth of Tenebrio molitor larvae concluded that there were no significant differences when using wet diet agar blocks at pH values ranging from 3 to 9, suggesting that fermented wet diet could be used for the rearing of mealworms. 53 Similar to Coudron et al. 53 , the control experiment used agar blocks in the wet diet because they lacked minerals and nutrients. Their study did not examine the effect of a wet diet source with a more diverse nutritional composition (e.g., vegetables or potatoes) on improving digestibility or bioavailability. Further studies on the effects of wet diet fermentation on mealworm larvae are needed to further explore this theory.
The mineral distribution in the control mealworm biomass found in this study (Tables 2 and 3) is comparable to the range of major and micronutrients found in the literature48,54,55. Providing mealworms with fermented chicory root as a wet diet can maximize their mineral content. Although the vegetable mix and orchard leaves were richer in most macro- and micronutrients (Tables 2 and 3), they did not have the same effect on the mineral content of mealworm biomass as fermented chicory root. One possible explanation is that the nutrients in the alkaline orchard leaves are less bioavailable than those in the other more acidic wet diets (Table 1). Previous studies feeding fermented rice straw to mealworm larvae showed that they thrived in this sidestream and suggested that pre-treatment of the substrate by fermentation stimulated nutrient uptake.56 The addition of fermented chicory roots increased the Ca, Fe, and Mn contents of mealworm biomass. Although this sidestream also contained higher concentrations of other minerals (P, Mg, K, Na, Zn, and Cu), the levels of these minerals in mealworm biomass were not significantly increased compared to the control, indicating that mineral uptake was selective. Increasing the content of these minerals in mealworm biomass has nutritional value for use as food and feed. Calcium is an essential mineral that plays a critical role in neuromuscular function and many enzyme-mediated processes such as blood clotting, bone formation, and teeth.57,58 Iron deficiency is a common problem in developing countries, where children, women, and the elderly often do not get enough iron from their diets.54 Although manganese is an essential element in the human diet and plays a central role in many enzymes, excessive intake can be toxic. Higher manganese levels in mealworms fed fermented chicory root were not a concern and were comparable to those in chickens.59
The heavy metal concentrations found in the waste were below the European standards for complete animal feed. Analysis of heavy metal content in mealworm larvae showed that Pb and Cr levels were significantly higher in mealworms fed fermented chicory roots than in the control group and those fed other substrates (Table 4). Chicory roots grow in soil, which is known to absorb heavy metals60, while other sidestreams arise from controlled human food production. Mealworms fed fermented chicory roots also had higher Pb and Cr levels (Table 4). The calculated bioaccumulation factors (BAF) were 2.66 for Pb and 1.14 for Cr, i.e. greater than 1, indicating that mealworms have the ability to accumulate heavy metals. With regard to lead, the EU sets a maximum lead content for human consumption of 0.10 mg per kg fresh meat61. In our experimental data, the maximum Pb concentration detected in mealworms fermenting chicory roots was 0.11 mg/100 g DM. Recalculation of this value using the dry matter content of these mealworms (30.8%) yielded a Pb content of 0.034 mg/kg wet matter, below the maximum level of 0.10 mg/kg. There is no maximum level for chromium in European food regulations. Cr is widely distributed in the environment, foodstuffs and food additives and is known to be an essential nutrient for humans at low levels62,63,64. The analytical results (Table 4) indicate that heavy metals can accumulate in T. molitor larvae when present in the diet. However, the levels of heavy metals detected in mealworm biomass in this study are considered safe for human consumption. Regular close monitoring is recommended when using side streams that may contain heavy metals as a wet food source for T. molitor.
The most abundant fatty acids in the biomass of all T. molitor larvae were palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2) (Table 5), which is consistent with previous studies on the fatty acid profile of T. molitor36,46,50,65. The fatty acid profile of T. molitor generally consists of five major components: oleic acid (C18:1), palmitic acid (C16:0), linoleic acid (C18:2), myristic acid (C14:0), and stearic acid (C18:0). Oleic acid is reported to be the most abundant fatty acid (30–60%) in mealybugs, followed by palmitic acid and linoleic acid22,35,38,39. Previous studies have shown that the fatty acid profile of mealworm larvae is influenced by diet, but the differences do not follow the same trend as diet38. The C18:1–C18:2 ratio in potato mash was inversely related to other fatty acid profiles. Similar results were found when examining changes in the fatty acid profile of mealworms fed steamed potato peelings36. These results suggest that although the fatty acid profile of mealworm oil may be altered, it is still a rich source of unsaturated fatty acids.
The aim of this study was to evaluate the effects of feeding four different types of agro-industrial by-products as wet feed on the composition of mealworms. The impact was assessed based on the determination of the nutrient composition of the larvae. The results showed that the by-products were successfully converted into protein-rich biomass (protein content 40.7–52.3%), which can be used as a source of food and feed. In addition, the study showed that feeding the by-products as wet feed affected the nutrient composition of mealworm biomass. In particular, feeding the larvae with a high concentration of carbohydrates (e.g., potato slices) increased their fat content and changed the fatty acid composition: polyunsaturated fatty acids decreased, and saturated and monounsaturated fatty acids increased, but the concentration of unsaturated fatty acids (monounsaturated fatty acids + polyunsaturated fatty acids) remained predominant. The study also showed that mealworms selectively accumulate calcium, iron and manganese from side streams rich in acidic minerals. The bioavailability of the minerals appears to play an important role and further studies are needed to fully understand this. Heavy metals present in the side stream may accumulate in mealworms. However, the final concentrations of Pb, Cd and Cr in larval biomass were below acceptable levels, so these side streams can safely be used as a source of wet feed.
Mealworm larvae were reared by Radius (Geel, Belgium) and Inagro (Rumbeke-Beetham, Belgium) at the Thomas More University of Applied Sciences at 27 °C and 60% relative humidity. The density of mealworms reared in a 60 cm × 40 cm feeder was 4.17 mealworms/cm2 (10,000 mealworms). Larvae were initially fed 2.1 kg of wheat bran as dry feed per feeder and this was supplemented as needed. Agar blocks were used as wet control feed. Starting from week 4, feed the side stream (also a water source) ad libitum with wet feed instead of agar. The percentage of dry matter in each side stream was determined in advance and taken into account to ensure the same amount of moisture for all insects across treatments. The feed is distributed evenly throughout the pen. Larvae are collected when the first pupae emerge in the exposed groups. The larvae are collected using a mechanical shaker with a mesh size of 2 mm. The potato cutting experiment was an exception. Larger portions of dried potatoes are also separated by passing the larvae through this sieve and collecting them in a metal tray. The total harvest weight was determined by weighing the total harvest weight. Survival was calculated by dividing the total weight of the individuals captured by the weight of the larvae. Larval weight was determined by selecting at least 100 larvae and dividing their total weight by the number. Before analysis, the collected larvae were starved for 24 hours to empty their intestines. Finally, the larvae were sieved again to separate them from the remains. They were frozen, euthanized, and stored at -18 °C until analysis.
Wheat bran (Molens Joye, Belgium) was used as dry feed. Wheat bran was pre-sifted to a particle size of less than 2 mm. In addition to dry feed, mealworm larvae should be given wet feed to maintain moisture and replenish minerals needed by mealworms. Wet feed constituted more than half of the total feed volume (dry feed + wet feed). In our experiments, agar (Brouwland, Belgium, 25 g/l) was used as a control wet feed45. As shown in Figure 1, four agricultural by-products with different nutrient contents were tested as wet feeds for mealworm larvae. These by-products include (a) leaves from cucumber cultivation (Inagro, Belgium), (b) potato trimmings (Duynie, Belgium), (c) fermented chicory roots (Inagro, Belgium) and (d) unsold food from fruit and vegetable auctions (Belorta, Belgium). Chop/grind the side stream into pieces to make it suitable for use as wet mealworm feed.
Agricultural by-product watercourses as wet food for mealworms: (a) garden crop leaves from cucumbers, (b) potato cuttings, (c) force-grown chicory roots, (d) unsold vegetables from auctions and (e) agar blocks as controls.
The composition of the diet and mealworm larvae was determined three times (n = 3). Proximate analysis, mineral composition, heavy metal content and fatty acid composition were assessed. A homogenized sample of 250 g, obtained from the collected and starved larvae, was dried at 60 °C to constant weight, ground (IKA, Tube mill 100) and sieved through a sieve with a mesh size of 1 mm. The dried samples were sealed in dark containers.
The dry matter content (DM) was determined by drying the samples in an oven at 105 °C for 24 hours (Memmert, UF110). The percentage of dry matter was calculated based on the weight loss of the samples.
The crude ash (CA) content was determined by weight loss after combustion in a muffle furnace (Nabertherm, L9/11/SKM) at 550°C for 4 hours.
The determination of crude fat content or ether extraction (EE) was carried out with petroleum ether (b.p. 40–60 °C) using a Soxhlet apparatus. About 10 g of sample was placed in an extraction thimble and covered with ceramic wool to prevent sample loss. The samples were extracted with 150 ml petroleum ether overnight. The extract was cooled, the organic solvent was removed and recovered by rotary evaporation (Büchi, R-300) at 300 mbar and 50 °C. The crude lipid or ether extract was cooled and weighed on an analytical balance.
The crude protein (CP) content was determined by analysing the nitrogen present in the sample using the Kjeldahl method BN EN ISO 5983-1 (2005). To calculate the protein content, use the appropriate N and P factors. For standard dry feed (wheat bran), a general factor of 6.25 was used. For side stream, a factor of 4.2366 was applied and for vegetable mixture, a factor of 4.3967. The crude protein content of larvae was calculated using an N to P ratio of 5.3351.
The fibre content included neutral detergent fibre (NDF) determined based on the Gerhardt extraction protocol (manual fibre bag analysis, Gerhardt, Germany) and the van Soest method68. For NDF determination, 1 g of sample was weighed into a special fibre bag (Gerhardt, ADF/NDF bag) with a glass liner. The fibre bags filled with samples were first defatted in petroleum ether (TP 40-60 °C) and then dried at room temperature. The defatted samples were extracted in a neutral detergent fibre solution containing heat-stable α-amylase at boiling temperature for 1.5 h. The samples were then washed three times with boiling deionised water and dried at 105 °C overnight. The weight of the dried fibre bags (containing fibre residues) was determined using an analytical balance (Sartorius, P224-1S) and then burned in a muffle furnace (Nabertherm, L9/11/SKM) at 550 °C for 4 hours. The weight of the ash was determined again and the fibre content was calculated based on the weight loss between the samples during drying and burning.
To determine the chitin content of larvae, we used a modified protocol based on the crude fiber analysis by van Soest68. A 1 g sample was weighed into a special fiber bag (Gerhardt bag, CF) and a glass liner. The samples were packed into the fiber bags, defatted in petroleum ether (TP 40-60 °C) and air-dried. The defatted samples were first extracted in 0.13 M sulfuric acid at boiling temperature for 30 min. The extraction fiber bag containing the sample was washed three times with boiling deionized water and then extracted in 0.23 M potassium hydroxide solution for 2 h. The extraction fiber bag containing the sample was again washed three times with boiling deionized water and dried at 105 °C overnight. The dry bag containing the fibre residue was weighed on an analytical balance and burned in a muffle furnace at 550°C for 4 hours. The ash was weighed and the fibre content was calculated based on the weight loss of the burned samples.
Total carbohydrate content is calculated based on . Non-fibrous carbohydrate (NFC) concentrations in feed were calculated using NDF analysis and insect concentrations were calculated using chitin analysis.
The pH of the matrix was determined after extraction in deionized water (1:5 v/v) according to NBN EN 15933.
Samples were prepared as described by Brox et al.69. Mineral profiles were determined using ICP-OES (Optima 4300™ DV ICP-OES, Perkin Elmer, MA, USA).
The heavy metals Cd, Cr and Pb were analyzed by graphite furnace atomic absorption spectrometry (AAS) (Thermo Scientific, ICE 3000 series, equipped with a GFS furnace autosampler). About 200 mg of sample was hydrolyzed in acidic HNO3/HCl (1:3 v/v) using a microwave oven (CEM, MARS 5). Microwave treatment was carried out at 190 °C for 25 minutes and 600 W power. Dilute the extract with ultrapure water.
Fatty acids were determined by GC-MS (Agilent Technologies, 7820A GC system with 5977 E MSD detector). Fatty acid methyl esters (FAMEs) were obtained from the ether extracts by esterification with 20% BF3/MeOH in methanolic KOH according to the method of Joseph and Akman70. Fatty acids can be identified by comparing their retention times with 37 FAME mixture standards (Chem-lab) or by comparing their MS spectra with online libraries such as the NIST database. Qualitative analysis was performed by calculating the percentage of peak area from the total peak area of the chromatogram.
Data were analyzed using JMP Pro 15.1.1 software from SAS (Buckinghamshire, UK). Evaluation was performed using one-way analysis of variance with a significance level of 0.05 and Tukey’s HSD test as a post hoc test.
Bioaccumulation factors (BAFs) were calculated by dividing the concentration of heavy metals in mealworm larval biomass (BM) by the concentration in wet food (WF)43. A BAF value greater than 1 indicates that heavy metals bioaccumulate from wet food in larvae.
The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.
United Nations Department of Economic and Social Affairs, Population Division. World Population Prospects 2019: Highlights (ST/ESA/SER.A/423) (2019).
Cole, MB, Augustine, MA, Robertson, MJ and Manners, JM. Food safety science. NPJ Sci. Food 2018, 2. https://doi.org/10.1038/s41538-018-0021-9 (2018).
Post time: Feb-11-2025