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Article

Effect of Drying Method on Selected Physical and Functional Properties of Powdered Black Soldier Fly Larvae

by
Radosław Bogusz
1,
Małgorzata Nowacka
1,*,
Ewa Gondek
1,
Murat Delman
2 and
Karolina Szulc
1
1
Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences—SGGW, 159c Nowoursynowska Street, 02-776 Warsaw, Poland
2
Biotechnology and Bioengineering Application and Research Center, Izmir Institute of Technology, 35430 Izmir, Turkey
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(8), 4097; https://doi.org/10.3390/app15084097
Submission received: 7 March 2025 / Revised: 1 April 2025 / Accepted: 3 April 2025 / Published: 8 April 2025
(This article belongs to the Special Issue Food Powders: Advanced Techniques, Properties and Industrial Applications)
Browse Figures
Versions Notes

Abstract

:
This research aimed to assay the impact of convective drying (CD) or infrared–convective (IR–CD) drying methods on the physical and techno-functional properties, FTIR spectra, and mathematical modeling of adsorption kinetics of black soldier fly larvae powders. By using convective drying, insect powder exhibited higher water content and water activity but lower hygroscopicity than powder dried with the infrared–convective method. After drying with the convective method, the powder exhibited a significantly lower loose and tapped bulk density and oil holding capacity (OHC). Furthermore, this powder was lighter and more yellow. The FTIR spectrum of the CD-dried powder showed lower absorption at key wavenumbers for the protein (1625 and 1350–1200 cm−1), indicating lower denaturation and less ability to bind water and water vapor. The mathematical modeling of the water vapor adsorption kinetics of insect powders via the second Fick’s law for transient diffusion showed that this equation is suitable for adjusting the experimental data based on the high coefficient of determination (0.997–0.999) and the low root mean square (2.50–3.34%). This study revealed that the drying method influences insect powder properties, and the IR–CD method seems better in terms of obtaining better techno-functional properties.

1. Introduction

The pressure to find sustainable and alternative protein sources becomes more urgent as the world’s population grows. People are increasingly looking at ways to diversify their diets to meet this rising demand [1]. A growing trend in the food industry is the search for proteins that are not only good for our health but also better for the environment. In this search, edible insects have emerged as a promising alternative [1,2]. Farming insects requires fewer natural resources, like water and land, and results in lower greenhouse gas emissions compared to traditional meat production [2,3]. However, compared to regions like Asia or Africa, insect consumption is a new strategy in human nutrition and is still in its infancy in Western countries. It is due to consumers’ opinion that insects are associated with filthy, contamination, and spoilage of food and limited promotion of insects as a sustainable source of essential nutrients [3,4,5]. The concerns about possible risks are eliminated by appropriate processing of the insects before consumption.
The insects are dried before use, extending their shelf life, increasing safety, and providing new processing possibilities. The drying process results in a reduction in water activity, so the product is preserved [6]. This makes it possible to limit the availability of the environment for microorganisms to grow and leads to the inhibition of both chemical and enzymatic reactions in the product [6,7]. Convective drying is a common method used in food processing to remove water from diverse raw materials. The process involves the convective heat delivery to the dried material placed in a drying chamber. The drying medium is hot air flowing around the product, which absorbs water evaporating from the dried material [8,9]. The main disadvantages are long drying times and high temperatures, making the product harder and darker and losing many valuable ingredients [8,10,11]. Convective drying combined with infrared radiation can improve the process. When infrared radiation is applied to the surface of the dried material, its energy is absorbed mainly by the surface layers of the material and converted into heat. Consistently, heat penetrating the material causes the vibration of internal water molecules, thus causing the mass transfer and drying process [12,13]. Using infrared radiation during convective drying provides a higher heat transfer rate, uniform (volumetric) heating, lower drying time and energy consumption, decreased requirement for airflow around the product, and improved final quality [11,12,14]. However, drying with infrared radiation may cause degradation of the color [11] and crust formation on the material’s surface, limiting water diffusion [14]. Nonetheless, correctly chosen air flow reduces the temperature of the surface of the dried material and reduces the risk of burning and crusting it [15].
After drying, the material can be powdered and used in different ways. The powdered form of food is known for its many benefits, including extended shelf life, convenience, ease of further processing, addition as an ingredient to other products, and its transport, storage, and packaging [16,17]. However, the properties of powders need to be characterized before use. This will make it easier to develop the formula and how it is applied during the production of various products. Still, it will also allow one to predict changes during transport, storage, and/or packaging.
The properties of powders, such as bulk density, flowability, and solubility, are crucial parameters for further application [17,18] as an ingredient for fortifying food with valuable nutrients, e.g., lysine-poor products such as pasta, noodles, bread, and bakery products [19,20,21,22,23,24] or as replacement of wheat flour in pâté recipe [25]. For example, flowability is associated with the size and shape of particles and the cohesive forces between powder particles. Additionally, the presence of fat in powders, especially surface fat, may influence its properties [17]. Fat globules on the particles’ surface lead to the formation of fatty liquid bridges and the sticking and caking of powder [26]. Also, the techno-functional properties of powders, such as water and oil holding, are the essential parameters considered for applicability as an ingredient during food formulation [27]. It is also worth noting that the color of the powder can affect the consumer’s perception of the final product. So far, research on the properties of whole insect powders has been limited. Only a few studies have focused on the techno-functional properties of powders, especially those from black soldier fly larvae [28,29,30].
Therefore, this study aimed to determine the selected physical and techno-functional properties, FTIR spectra, and mathematical modeling of adsorption kinetics of black soldier fly larvae powders obtained via different drying methods.

2. Materials and Methods

2.1. Material

The vacuum-packed black soldier fly (Hermetia illucens L.) larvae (already euthanized) were purchased from a local German producer (Ahaus, Germany) and kept at 4 ± 1 °C. The material originated from the same batch, guaranteeing identical feed sources (vegetables, cereal products) and consistent environmental factors. Before use, the larvae were washed with tap water to remove residual feces and gently dried with filter paper.

2.2. Technological Treatment

2.2.1. Convective Drying

The insect larvae were placed on the perforated tray (a sieve load of 2.71 kg/m2) and dried in duplicate using the prototype laboratory dryer with air heated to 90 °C being blown into the drying chamber and flowed parallel to the insect layer at the speed of 2 m/s. The drying was continued until a constant mass was achieved.

2.2.2. Infrared–Convective Drying

The insect larvae were placed on the perforated tray (a sieve load of 2.71 kg/m2) and subjected to drying using the prototype laboratory dryer. This dryer was equipped with nine lamps (emitting radiation of 7.9 kW/m2) positioned 0.25 m above the insect layer. Simultaneously, air heated to 40 °C was blown into the drying chamber and flowed parallel to the insect layer at a speed of 0.8 m/s. Due to technical limitations, the sample temperature was not measured due to the impossibility of inserting the thermocouple into the insect material. The drying was continued until a constant mass was achieved. The process was conducted in duplicate.

2.2.3. Grinding of Dried Material

The dried insect larvae were finely ground using an IKA Tube Mill analytical grinder (IKA-Werke GmbH & Co., Staufen, Germany) operating at 8500 rpm for 30 s. The resulting insect powder was then packaged in PET/AL/PE bags (Pakmar, Warsaw, Poland) designed to block air and light, ensuring proper storage.

2.3. Physical Properties of Insect Powders

2.3.1. Water Content and Water Activity

The water content was determined from the dry matter content by dehydrating approximately 1 g of insect powder in a laboratory dryer (Wamed, Warsaw, Poland) at 105 ± 1 °C for 17 h. The values were reported as grams of water per gram of dry matter (g H2O/g d.m.). Additionally, the water activity of the insect powders was assessed at 24 ± 1 °C using a HygroLab C1 hygrometer (Rotronic, Bassersdorf, Switzerland). Both measurements were conducted in three repetitions for each powder batch.

2.3.2. Hygroscopicity

The hygroscopicity (water vapor adsorption) was measured by placing insect powders (about 0.3 g) in an aluminum vessel into the desiccator filled with distilled water (water activity of 1.0, temperature of 22 ± 1 °C) for 1, 3, 6, 9, 12, 24, 48, and 72 h [31]. The results of hygroscopicity were expressed in grams of water adsorbed by 100 g of powder (g H2O/100 g d.m.). Measurements were conducted in triplicate for each powder batch.

2.3.3. Particle Size

The CILAS 1190 laser particle size analyzer (CILAS, Orleans, France) was used to assess the particle size of black soldier fly larvae powders. Measurements were performed in a recirculation chamber filled with isopropanol as the dispersing agent. The results were shown as mean particle size, expressed as the volume diameter D50. Measurements were conducted in triplicate for each powder batch.

2.3.4. Flowability

The flowability of insect powders was expressed as the Hausner ratio (HR), calculated as the tapped bulk density to the loose bulk density [31]. The loose bulk density was determined by measuring the volume occupied by 2.5 g of insect powder in a graduated cylinder. In contrast, the tapped bulk density was recorded after subjecting the powder to 100 taps using an STAV 2003 automatic volumeter (Engelsmann AG, Ludwigshafen, Germany). Measurements were conducted in triplicate for each powder batch.

2.3.5. Color Properties

The color characteristics (CIE L*, a*, b*) of the insect powders were analyzed using a CR-5 chromameter (Konica Minolta, Osaka, Japan) in reflectance mode. Measurements were conducted under a D65 standard illuminant, with a CIE 2° Standard Observer, an 8° viewing angle, and a 30 mm measurement diameter. The color was measured 20 times for each powder batch. The photos of the insect powders were captured with a Nikon D7000 digital camera (Nikon, Tokyo, Japan).

2.4. Measurement of Techno-Functional Properties of Insect Powders

The insect powders’ water holding capacity (WHC) and oil holding capacity (OHC) were determined by placing them (about 0.5 g) into a pre-weighed centrifuge tube and mixed with 2.5 mL of distilled water (for WHC) or refined rapeseed oil (for OHC), adding to tested powder at a temperature of 22 ± 1 °C. The mixtures were vortexed for 60 s (WHC) or 120 s (OHC) and then centrifuged at 3000× g for 20 min. After removing the supernatant, the tubes were weighed [31]. The WHC and OHC were calculated as the difference between the mass of the sample after supernatant removal and the initial mass of the powder in relation to the initial mass of the powder. Measurements were conducted in triplicate for each powder batch.

2.5. FTIR Measurement

The Agilent Cary 630 FTIR spectrometer (Agilent Technologies Inc., Santa Clara, CA, USA), fitted with an attenuated total reflectance (ATR) accessory, was utilized for analysis. A small quantity of insect powder was positioned on the ATR crystal and secured using a pressure clamp. Spectral scanning was conducted over the range of 650–4000 cm−1, with a resolution of 4 cm−1 and 32 scans per spectrum. This range was sufficient for the major peaks corresponding to the structures of amide A, amide B, alpha–chitin structure, amide I, amide II, and amide III. Data acquisition and management were performed by MicroLab PC 5.7 software (Agilent Technologies Inc., Santa Clara, CA, USA). Measurements were conducted in triplicate for each powder batch.

2.6. Mathematical Modeling

The second Fick’s law for transient diffusion was used to describe the water vapor adsorption kinetics of insect powders, using the Table Curve 2D v5.01 software (SYSTAT Software, Inc., Chicago, IL, USA) and the below Equations [32]:
A e x p ( − K τ ) = u τ − u e u 0 − u e ,
K = D e f f L 2 ,
where uτ is the water content during each moment of the adsorption process (g H2O/100 g d.m.), ue is the equilibrium water content (g H2O/100 g d.m.), u0 is the initial water content (g H2O/100 g d.m.), A is the shape factor, K is the coefficient linked to water diffusion (1/min), Deff is the effective moisture diffusivity (m2/min), L is the thickness of the insect powder layer (m), and τ is the sorption time (s).
Fitting the second Fick’s law for the transient diffusion kinetic model to the water vapor adsorption data was performed using the Table Curve 2D v5.01 software (SYSTAT Software, Inc., Chicago, IL, USA). The coefficient of determination (R2) and the root mean square (RMS) were calculated to evaluate the goodness of fit between experimental and predicted data:
R 2 = 1 − ∑ i = 1 N u p − u e x p 2 ∑ i = 1 N u e x p − u p ¯ 2 ,
R M S = ∑ i = 1 N u e x p − u p 2 u e x p N ,
where u e x p is the experimental water content during each moment of the adsorption process (g H2O/100 g d.m.), u p is the predicted water content during each moment of the adsorption process (g H2O/100 g d.m.), u p ¯ is the mean predicted water content during each moment of the adsorption process (g H2O/100 g d.m.), and N is the number of observations.

2.7. Statistical Analysis

The t-test assessed significant differences between the mean values of the tested properties. Statistical analysis was performed using STATISTICA 13.3 (TIBCO Software, Palo Alto, CA, USA) and a significance level of α = 0.05.

3. Results and Discussion

3.1. Water Content, Water Activity, and Hygroscopicity of Insect Powders

Understanding the water content in dry materials is crucial for determining their durability, storage conditions, and quality and influencing how they will be used in further production. A significantly lower water content was found for insect powder obtained by the convective method (Table 1). In general, infrared drying improves water removal from the material [33]. However, in this case, the formation of a hard crust on the surface of the insect’s tissue was observed due to faster surface water evaporation than the internal water migration, which, in effect, limited water evaporation [34]. What’s more, present fat was able to migrate more efficiently to the surface due to channels formed after denaturation and reorganization of the myofibrillar protein [35], which was observed for infrared dry-roasted almonds [36]. On the surface, fat creates a layer that impedes the evaporation of water. Additionally, it is suggested that the result is attributable to the interaction between components, as residual water present in the subsequent dehydration stage was bound [37], thereby providing a higher water content. Due to the material’s well-absorbed infrared radiation and fast internal temperature increase, proteins undergo denaturation, leading to higher exposure to hydrophilic sites and, thus, a greater ability to absorb water molecules [38]. Subsequently, denatured or damaged proteins formed larger structures—aggregates [39]—and it was more difficult to remove water molecules from them during drying. Furthermore, the smaller particles of the IR–CD-dried insect powder (see Table 3) provided a larger surface area that favored their interactions. The fat on the surface of the particles [26] and free water transformed from immobilized water due to infrared radiation [40] causes the formation of liquid bridges and sticking. It thus impedes the evaporation of water during the water content measurement. As a result, this may have influenced the higher water content of the test sample.
Water activity informs about the available water (free and partially bound) in the material and its susceptibility to microbial growth and exposure to chemical reactions [31]. The minimum water activity required for the growth of most bacteria is 0.91, and for yeasts and filamentous fungi, it is 0.88–0.80. However, there are organisms better adapted to water deficit, such as halophilic bacteria, osmotolerant yeasts, and xerophilic fungi. These organisms can develop in an environment with an aw of 0.75–0.60. It is assumed that microbial growth does not occur at an activity lower than 0.60 [41]. Despite a significantly lower water content for insect powder obtained by the convective method, the water activity values for both powders are close to 0.2 (Table 1). It indicates microbial stability (water activity below 0.6), and the slowest lipid oxidation due to water activity of 0.2–0.4 corresponds to the monolayer moisture content [42,43]. A higher water activity of IR–CD-dried powder was related, same as for water content, to interactions between protein and water molecules, as well as higher free water content released from the myofibrillar network of the powder particles [40].
The hygroscopicity of black soldier fly larvae powders is presented in Table 1. The powder received by convective drying (CD) exhibited a significantly lower hygroscopicity after 72 h of water vapor adsorption of water activity of 1.0. The powder properties, such as particle size distribution and surface area, influence hygroscopicity [44]. Applying the IR–CD method allows for obtaining smaller powder particles (Table 3) and an increased number of adsorption sites. Hence, insect powder could bind more water during the water vapor adsorption. Apart from that, the hygroscopicity of tested powders was influenced by the chemical compositions (CD-dried powder: 32.02 and 38.94 g/100 g d.m. of protein and fat, IR–CD-dried powder: 29.85 and 43.89 g/100 g d.m. of protein and fat), determined in our previous study [45]. A smaller amount of assayed protein for the IR–CD-dried powder indicates a greater amount of denatured protein, and this promotes water adsorption. Nevertheless, practically, this is a beneficial phenomenon, as the lower hygroscopicity ensures better stability of the powder during storage. Among the powders tested in our study, the one obtained by the IR–CD method will likely maintain better stability during storage, provided that the relevant environmental temperature and humidity conditions will be applied.
Both the water activity and water content of the obtained powders immediately after the drying process were low (Table 1), which indicates their microbiological safety and the stability of chemical and physical properties (described in Section 3.1). However, it should be considered that the powders may come into contact with the ambient air during their storage, packaging, and trade. In such situations, sorption properties become crucial from the safety point of view. Sorption properties characterize the product’s ability to adsorb or desorption water from the surrounding environment. The sorption properties of food products are mainly determined by the chemical composition and their physical properties and can also be shaped by technological processes [46,47,48]. Sorption properties can be studied using static, equilibrium methods, which lead to obtaining the dependence of water activity on water content called the sorption isotherm. A detailed analysis of the isotherm course allows, among other things, the determination of the capacity of the monolayer.
Tańska et al. [47] investigated the sorption isotherms of lesser mealworm (Alphitobius diaperinus) and house cricket (Acheta domesticus) powders, observing that both exhibited a sigmoidal curve characteristic of type II according to the Brunauer et al. [49] classification. Using the BET (Brunauer–Emmett–Teller) equation, they determined the monolayer capacity of 3.59 g water/100 g d.m. for lesser mealworm and 3.25 g water/100 g d.m. for house cricket powders. Their analysis of isotherm components suggested that variations in hygroscopic properties were primarily influenced by the chemical composition of the powders [47]. Kamau et al. [50] reported similar findings while examining the sorption behavior of dried and ground house cricket (Acheta domesticus) and black soldier fly larvae (Hermetia illucens) using the static method. Likewise, Sun et al. [51] assessed the sorption isotherms of processed lesser mealworm larvae (Alphitobius diaperinus) in different forms, including whole powder, protein concentrate, and textured protein. Their results were interpreted using the GAB (Guggenheim–Anderson–de Boer) model, classifying the obtained isotherms as type III according to the classification of Brunauer et al. [49].
An alternative approach to studying sorption properties is the dynamic method, which enables the determination of the water diffusion coefficient and equilibrium moisture content—the final moisture level a material reaches after prolonged storage in a given environment [32]. The results of the modeling of the adsorption kinetics of black soldier fly powders showed that Fick’s unsteady diffusion equation is suitable and satisfying for adjusting the experimental values due to the high correlation coefficient (R2) values ranging from 0.997 to 0.999 and the low root mean square (RMS) values ranging from 2.50–3.34% (Figure 1, Table 2). The effective water diffusion coefficient and equilibrium water content determined for the tested materials based on Fick’s unsteady diffusion equation are presented in Table 2. The powder obtained by the IR–CD drying method was characterized by a higher equilibrium water content (it is also worth noting that its initial water content was significantly higher). In turn, the water diffusion coefficient, which characterizes the dynamics of the sorption process, was significantly higher in the case of convective drying (CD). It should be assumed that the reason for this was the higher driving force of the sorption process, i.e., the difference between the water activity of the material and the ambient relative humidity. The observed results may be related to the particle size of insect powders. The smaller particle size of the IR–CD insect powder provided greater surface area and greater availability of hydrophilic sites, like polar amino acids, as observed for superfine ground white-spotted flower chafer (Protaetia brevitarsis) larvae [52]. Furthermore, changes in hydrophilic compounds (e.g., proteins) affected the water vapor adsorption. The overheating of the material via infrared radiation is highly probable, especially in its surface layers [53]. It leads to the denaturation of proteins, which exhibit a greater ability for water and water vapor adsorption [54]. That was confirmed via the FTIR spectrum (see Figure 4), as the IR–CD-dried insect powder exhibited a better absorption level for peaks related to amide I and amide II. Thermally treated proteins show higher intensity values of infrared bands, as observed for soy glycinin [54].

3.2. Bulk Density and Flowability of Insect Powders

Table 3 presents the loose and tapped bulk densities and the Hausner ratio of black soldier fly larvae powders. The IR–CD method resulted in significantly higher loose and tapped bulk densities than the CD method. Similar findings were reported by Ando et al. [55] and Chanadang et al. [56], who also observed differences in the bulk densities of edible insect powders obtained by different drying methods. For example, using a hot air oven and microwave drying, Pornsuwan et al. [30] obtained bulk densities of 381.54 and 494.58 g/dm3 of black soldier fly larvae powders. In this case, the increased bulk density in IR–CD powders results from the lower particle size (Table 3). Smaller particles can fill the voids between larger particles, resulting in a denser packing structure. The IR–CD may have contributed to obtaining reduced particle sizes compared to CD due to the combined effects of radiation and convective heat transfer. Intense heating from IR can cause rapid water evaporation [57], leading to micro-crack formation and weakening of the dried material structure. This increased breakability facilitates the breakdown of particles during subsequent grinding, resulting in finer powders. Additionally, surface fats may influence interparticle interactions, affecting bulk density. The adhesion between particles can lead to a more connected and stiffer network, affecting the powder’s bulk density—higher adhesion results in a denser and more rigid structure [58]. The presence of surface fat can act as a lubricant, reducing friction between particles and thus improving flowability [59]. On the other hand, excess interparticle force between particulate solids can lead to particle agglomeration due to increased cohesion, which can negatively affect flow properties [60]. However, in this study, interparticle forces were small, with a relatively coarse particle size distribution.
Bulk density is an important factor influencing the flowability of powders. Higher bulk density can reduce void spaces between particles, potentially enhancing flowability by minimizing interparticle friction. However, this relationship is complex, as increased bulk density might also result in greater particle cohesion, adversely affecting flow properties. More significant differences between tapped and loose bulk densities indicate a higher Hausner ratio, which indicates less fluid powders. Based on the Hausner ratio (Table 3), CD powder exhibited good (for HR values between 1.12–1.18), and IR–CD revealed fair (for HR values between 1.19–1.24) flow characteristics [61].

3.3. Color Properties of Insect Powders

The color of dried materials is not merely a visual characteristic; it often reflects essential changes in their composition and structure and influences consumers’ choices. A significantly lighter appearance (higher values of the L* color parameter) was noted for the CD-dried insect powder than for the IR–CD-dried insect powder (Table 4, Figure 2). This powder also exhibited a significantly lower proportion of the a* color parameter and a higher proportion of the b* color parameter than the IR–CD-dried insect powder. Based on the total color difference (ΔE = 6.23 ± 0.90), observers can notice two different colors between the CD-dried and the IR–CD-dried insect powders.
The main pigments of black soldier fly larvae are melanins and ommochromes, which can be yellow, brown, and black [62,63] and become darker due to drying at elevated temperatures for longer times [62]. However, the darker color of the IR–CD-dried insect powder is related to a longer drying time (228 ± 11 min for the CD method and 715 ± 14 min for the IR–CD method). The prolonged exposure to infrared radiation and heating of the material promotes the thermal destruction of pigments available and browning reactions [64]. Furthermore, a lower L* color parameter and higher a* color parameter of the IR–CD-dried insect powder indicate that more brown macromolecules (melanoidins) are available. These macromolecules form after polymerization of intermediary products forming between protein molecules and products of fat oxidation [64,65]. The elevated temperature for a longer time and higher water content of IR–CD-dried powder (Table 1) could accelerate the thermal hydrolysis of triacylglycerols, forming free fatty acids and their oxidation [66].

3.4. Techno-Functional Properties of Insect Powders

Water and oil holding capacities are important techno-functional properties related to a powder’s ability to retain water and oil molecules [56]. These properties are crucial in determining the powder’s potential use in food applications. It could be expected that the increased surface area from the finer particles produced by IR–CD would lead to a higher WHC. However, no significant differences in WHC were observed among the black soldier fly powders, as shown in Figure 3. It can be assumed that thermal and mechanical stresses associated with the IR–CD drying could have induced protein denaturation. Often, denatured or partially denatured conformations are prone to aggregate formation because they expose the protein’s hydrophobic core to solvent [67], which can limit water absorption despite an increased surface area. Moreover, the OHC for CD powder was significantly lower than the IR−CD sample. Differences in OHC between powders processed by CD and IR–CD method may be influenced by surface properties. The greater fragmentation of the IR−CD sample may affect the OHC by increasing the number of oil-holding sites.
Various values of WHC and OHC for edible insect powders have been reported [4,68,69]. For example, studies on the yellow mealworm (Tenebrio molitor) and house cricket (Acheta domesticus) powders showed WHC values of 1.62 g/g and 1.76 g/g, respectively, while the OHC values were 1.58 g/g and 1.42 g/g [70]. Comparing these values with the results obtained for black soldier fly larvae powders, it can be observed that both WHC and OHC were slightly lower. Although WHC remained unchanged, the OHC was impacted, which suggests that the drying methods may have selectively altered the functional properties of the powder. A high WHC improves texture and moisture retention in food products, enhancing their sensory properties and consumer acceptability. Insect powders with elevated WHC are particularly suitable for applications in soups, sauces, and bakery formulations, where moisture retention is crucial for product stability and quality [4]. Similarly, a high oil-holding capacity OHC plays a key role in flavor retention and mouthfeel by facilitating the binding of oils, which are carriers for lipophilic flavor compounds. Insect powders exhibiting high OHC are well-suited for incorporation into meat analogs, baked goods, and emulsified products [27]. Differences in WHC and OHC between insect powders may result from protein, fat, and chitin content. Insect powders are recognized for their high protein content, which is important in determining their WHC and OHC. For example, house cricket and yellow mealworm powders contain approximately 66% protein [71]. The solubility of proteins and their amino acid profiles also influence these properties, with house cricket protein being limited in tryptophan and yellow mealworm protein in lysine. Additionally, the lipid composition of insect powders varies, affecting their ability to retain oil. House cricket powder has a higher lipid content (16.1%) than yellow mealworm powder (13.7%) [71], which generally enhances OHC by increasing the capacity to bind and retain oil. Furthermore, chitin, a key structural component in insects, impacts WHC and OHC. Fractions rich in chitin tend to have lower emulsification capacity than protein fractions, suggesting that chitin may reduce the powder’s ability to retain water and oil [72]. However, specific structural properties of chitin, such as its degree of deacetylation, can also influence these functional characteristics [71].

3.5. FTIR of Insect Powders

FTIR allows us to predict molecular structure and identify functional groups in the tested materials [73]. FTIR spectra have shown similar patterns for tested insect powders but with diverse absorbance levels (Figure 4).
The spectral region between 3300 and 3200 cm−1 exhibits a weak, broad stretching vibration that corresponds to hydroxyl (–OH) groups in water molecules and amino acids, together with N-H bonds in the amide A group [74,75]. Two distinct C–H stretching peaks appear in the spectrum: a strong absorption at 2920 cm−1 corresponding to asymmetric stretching of methyl (–CH3) groups, generally observed in alkanes and alkene aromatics, alongside a medium-intensity peak at 2850 cm−1, representing symmetric stretching of methyl (–CH3) groups, typically found in alkanes and aldehydes [74]. These peaks are related to lipids rich in alkanes, alkenes [39], and chitin [74]. The peak at 2920 cm−1 also reflects the stretching vibration of the C–H bond in the amide B group [75]. The stretching vibration of the C≡N bond in nitrile compounds reflects a weak peak at 2360 cm−1 [76].
A medium peak at 1744 cm−1 for CD insect powder and 1736 cm−1 for IR–CD insect powder is connected to the stretching vibration of the C=O bonds in lipids [73,74]. A medium peak at 1625 cm−1 corresponds to the stretching vibration of the C=O bonds in the amide I group [75]. The powder produced by convective drying (CD) exhibited reduced absorption levels, generally linked to disruptions in protein secondary structures. This occurs because the C=O bond, critical for maintaining these structures, is particularly sensitive to CD processing conditions [29]. The spectral profile of three major peaks between 1744 and 1500 cm−1 is in parallel with literature indicating an α-chitin structure [75]. A medium peak at 1524 cm−1 and 1235 cm−1 corresponds to the bending vibrations of the N–H bond and the stretching vibrations of the C–N bond in the amid group. These peaks indicate, respectively, amide II and amide III [73,75]. Considering the amide III region (1350–1200 cm−1), the highest absorption was observed at 1235 cm−1. This indicates that the secondary structure of the protein molecules is dominated by β-sheets, related to the exoskeleton of the insect, and gives information on how chitin interacts with the protein molecules [77]. A moderate-intensity peak observed near 1457 cm−1 corresponds to C–H bond bending vibrations arising from lipids, proteins [73], and polysaccharides that contain –CH2– and –CH3 groups [74]. A medium-intensity absorption band centered at approximately 1400 cm−1 arises from C-N stretching vibrations [73].
In the fingerprint region, spanning from 1200 to 900 cm−1, the stretching vibrations of C–C, C–O–C, and C–O bonds, along with the bending vibrations of the C–O–H bond, are observed in various carbohydrate groups. The peak observed at 1040 cm−1 indicates the presence of galacturonic acid and glucuronic acid [75,76]. The region below 900 cm−1 in the FTIR spectrum is mainly associated with conformational changes caused by specific molecular vibrations in carbohydrates [73,74].

4. Conclusions

The impact of drying methods (convective and infrared–convective) on the physical and techno-functional properties, FTIR spectra, and mathematical modeling of adsorption kinetics of black soldier fly larvae powders were investigated in this study. Although the powder obtained by the infrared-convective method revealed a higher water content (0.137 g H2O/g d.m.) than the convective-dried powder (0.048 g H2O/g d.m.), it absorbed about 2.6% less water vapor after 72 h of hygroscopicity measurements. It can be characterized as more stable during storage under suitable environmental conditions. Furthermore, infrared–convective-dried powder exhibited a higher water-holding capacity (WHC) and oil-holding capacity (OHC), indicating greater application potential as an additive to other powder mixtures. This is also confirmed by the FTIR spectrum, indicating a higher absorbance for the peaks responsible for the proteins, which may be useful for application purposes and better properties if the protein is isolated. However, the results presented were obtained on a laboratory scale, so the drying process of insects should be performed on an industrial scale to compare the effect. Based on the obtained results, future studies should focus on examining the changes that occur in the powders during their storage, such as the techno-functional properties, the stability of the fat, and the profile of volatile compounds.

Author Contributions

Conceptualization, R.B. and K.S.; methodology, R.B. and K.S.; software, E.G.; formal analysis, R.B. and K.S.; investigation, R.B., E.G., M.D. and K.S.; resources, M.N.; data curation, R.B., E.G. and M.D.; writing—original draft preparation, R.B., E.G., M.D. and K.S.; writing—review and editing, M.N., E.G. and K.S.; visualization, R.B. and M.N.; supervision, M.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The research for this publication was carried out with the use of research equipment purchased as part of the “Food and Nutrition Centre—modernisation of the WULS campus to create a Food and Nutrition Research and Development Centre (CŻiŻ)” co-financed by the European Union from the European Regional Development Fund under the Regional Operational Programme of the Mazowieckie Voivodeship for 2014–2020 (project no. RPMA.01.01.00-14-8276/17). The authors would like to thank Yekta Günay Atlı of the Biotechnology and Bioengineering Research and Application Center (CFB, IZTECH) for her help.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
CDConvective drying
IR–CDInfrared–convective drying
HRHausner ratio
WHCWater-holding capacity
OHCOil-holding capacity
FTIRFourier transform infrared spectroscopy
ATRAttenuated total reflectance accessory
BETBrunauer–Emmett–Teller sorption model
GABGuggenheim–Anderson–de Boer sorption model

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Applsci 15 04097 g001
Figure 1. The water vapor adsorption kinetics of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods. Dotted lines represent values obtained from mathematical modeling.
Figure 1. The water vapor adsorption kinetics of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods. Dotted lines represent values obtained from mathematical modeling.
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Figure 2. The photos of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
Figure 2. The photos of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
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Figure 3. The water-holding capacity (WHC) and oil-holding capacity (OHC) of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods. The same letters above columns (small letters for WHC, capital letters for OHC) indicate no differences between the mean values (t-test, p < 0.05).
Figure 3. The water-holding capacity (WHC) and oil-holding capacity (OHC) of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods. The same letters above columns (small letters for WHC, capital letters for OHC) indicate no differences between the mean values (t-test, p < 0.05).
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Figure 4. The FTIR spectra of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
Figure 4. The FTIR spectra of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
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Table 1. The water content, water activity, and hygroscopicity of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
Table 1. The water content, water activity, and hygroscopicity of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
TreatmentWater Content
(g H2O/g d.m.)		Water Activity
(−)		Hygroscopicity After 72 h
(g H2O/100 g d.m.)
CD0.048 a 1 ± 0.0050.177 a ± 0.00941.13 a ± 1.76
IR–CD0.137 b ± 0.0140.246 b ± 0.00950.95 b ± 0.79
1 The same letters in columns indicate no differences between the mean values (t-test, p < 0.05).
Table 2. The parameters of water vapor adsorption kinetics modeling of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
Table 2. The parameters of water vapor adsorption kinetics modeling of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
TreatmentEquilibrium Water Content
(g H2O/100 g d.m.)		Effective Moisture Diffusivity
(×10−11 m2/min)		R2
(−)		RMS
(%)
CD45.48 a 1 ± 2.281.40 b ± 0.030.9992.50
IR–CD58.04 b ± 2.671.17 a ± 0.110.9973.34
1 The same letters in columns indicate no differences between the mean values (t-test, p < 0.05).
Table 3. The bulk density and flowability of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
Table 3. The bulk density and flowability of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
TreatmentParticle Size
(µm)		Loose Bulk Density
(kg/m3)		Tapped Bulk Density
(kg/m3)		Hausner Ratio
(−)
CD631.91 b 1 ± 45.34339.11 a ± 2.04391.28 a ± 2.351.15 a ± 0.01
IR–CD241.86 a ± 26.10352.73 b ± 2.02421.67 b ± 4.411.20 a ± 0.09
1 The same letters in columns indicate no differences between the mean values (t-test, p < 0.05).
Table 4. The color properties of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
Table 4. The color properties of black soldier fly powders processed by convective (CD) and infrared convective (IR–CD) drying methods.
TreatmentL* (−)a* (−)b* (−)
CD29.72 b 1 ± 1.135.82 a ± 0.1910.94 b ± 0.38
IR–CD23.91 a ± 1.056.22 b ± 0.318.89 a ± 0.57
1 The same letters in columns indicate no differences between the mean values (t-test, p < 0.05).
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MDPI and ACS Style

Bogusz, R.; Nowacka, M.; Gondek, E.; Delman, M.; Szulc, K. Effect of Drying Method on Selected Physical and Functional Properties of Powdered Black Soldier Fly Larvae. Appl. Sci. 2025, 15, 4097. https://doi.org/10.3390/app15084097

AMA Style

Bogusz R, Nowacka M, Gondek E, Delman M, Szulc K. Effect of Drying Method on Selected Physical and Functional Properties of Powdered Black Soldier Fly Larvae. Applied Sciences. 2025; 15(8):4097. https://doi.org/10.3390/app15084097

Chicago/Turabian Style

Bogusz, Radosław, Małgorzata Nowacka, Ewa Gondek, Murat Delman, and Karolina Szulc. 2025. "Effect of Drying Method on Selected Physical and Functional Properties of Powdered Black Soldier Fly Larvae" Applied Sciences 15, no. 8: 4097. https://doi.org/10.3390/app15084097

APA Style

Bogusz, R., Nowacka, M., Gondek, E., Delman, M., & Szulc, K. (2025). Effect of Drying Method on Selected Physical and Functional Properties of Powdered Black Soldier Fly Larvae. Applied Sciences, 15(8), 4097. https://doi.org/10.3390/app15084097

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