Comparison of Selected Sensory and Physicochemical Indicators of Insect Powders and Flours During Storage

Abstract

The observed growth of the global population and concern for the natural environment require the supply of inexpensive food with a low-carbon footprint. These requirements can be met, among others, by insect-derived raw materials, such as insect powders commonly referred to as flours. The aim of this study was to compare and assess the effects of four-month storage of insect powders (cricket, mealworm) and cereal flours (millet, oat, rice) under conditions similar to household storage (room temperature, partially emptied packages) on selected quality characteristics. It was assumed that, due to their different protein–fat composition and high degree of comminution, insect powders may exhibit a different dynamic of changes compared to flours in which starch is the dominant matrix. The scope of the research included the assessment of moisture content, acidity, ash content and total protein content, analysis of the amino acid profile, color parameters in the CIE L*a*b* space, changes in volatile compounds, and determination of heavy metal content (Cd, Pb, Hg, As). The obtained results enabled a comprehensive characterization of the quality stability and nutritional value of the tested raw materials after the storage period. The analyses revealed clear differences between cereal flours and insect powders, resulting from differences in chemical composition and production technology. Insect powders were characterized by a higher protein content and a more favorable amino acid profile compared to cereal flours. In addition, they exhibited lower moisture content, different color, and a distinct aroma profile, which can be attributed both to their production technology and to a higher proportion of hydrophobic components. It was shown that during storage the amino acid composition of the tested flours remained relatively stable, as did color; however, mealworm powder exhibited the lowest color stability. It was also demonstrated that cereal flours are characterized by a greater capacity for water sorption, which is related to their starch matrix, whereas insect powders undergo processes related to lipid degradation, leading to increased acidity and changes in the profile of volatile compounds. Certain safety concerns may arise from the exceeded permissible cadmium content observed in mealworm powder.

1. Introduction

Population forecasts indicate that by 2050 the global population will reach nearly 10 billion people. This poses a major challenge for farmers, breeders, and food producers. Increasing cultivation areas through deforestation or the use of genetically modified crops is harmful to the environment and lacks widespread public acceptance. At the same time, agriculture at its current level of development would need to increase productivity by more than 100% [1]. According to literature reports, the demand for protein-rich food is expected to increase to approximately 60% [2,3]. Scientists predict that by 2030, demand for edible insects will reach 3 million tons, and the edible insect powders market alone will generate approximately USD 20 million in revenue [4]. Therefore, the search for innovative food sources on an industrial scale appears to be the only viable solution. Many researchers are currently focusing on the use of insects as a source of protein, fat, and minerals. Their studies concentrate on breeding methods, processing technologies, the use of insects as functional food ingredients, consumer acceptance assessment, and the analysis of the chemical composition of finished products.

Consumption patterns in many countries perceive the consumption of insects as repulsive and unacceptable [5,6]. They are often associated with dirt and a lack of hygiene rather than with food. In addition, a significant proportion of the world’s population exhibits neophobia toward edible insects, which greatly hinders their overall acceptance [7,8]. However, in recent years an upward trend in interest in insects as a protein source has been observed, driven by legal regulations and increased consumer acceptance [9,10]. For example, in the literature on the subject there are studies available related to eliminating unfavorable sensory changes in products enriched with insects, e.g., the addition of cocoa [11]. The main factors currently encouraging consumers to purchase insect-based products are curiosity about this type of food, as well as the belief that such products are nutritionally superior to conventional meat sources. Food law regulations allow the sale of insects in three forms: whole dried insects, powders, or pastes. In particular, the processed form of insects as powders has gained considerable popularity among consumers and, consequently, higher acceptance. Insect powders differ from cereal flours in their dominant protein-fat fraction, while cereal flours are primarily starch-based. This makes the storage stability of insect powders particularly critical: a higher lipid content (including the unsaturated fraction) increases susceptibility to oxidation, while a high degree of fineness (high specific surface area) favors contact with oxygen and accelerates reactions leading to changes in acidity, volatile compound profile, and color. These changes have direct qualitative and consumer implications, as flavor deterioration and product darkening are among the factors limiting the acceptance of insect raw materials.

From a nutritional perspective, insect powders constitute a rich source of nutrients, characterized by a high content of valuable and highly digestible protein, essential amino acids, polyunsaturated fatty acids ω-3 (α-linolenic acid) and ω-6 (linoleic acid), dietary fiber (chitin components of the exoskeleton and chitosan), vitamins (A, B, C, and D groups), minerals (zinc, phosphorus, copper, magnesium, manganese, selenium, calcium, and iron), and polysaccharides [12,13,14,15,16,17,18]. In addition, insect powders are gluten-free products and are safe for individuals with digestive system disorders, including those suffering from celiac disease. They are characterized by a low carbohydrate content while containing a high amount of dietary fiber, the main source of which is chitin, which supports skin tissue regeneration and helps prevent blood clot formation. Moreover, insect powders, on a dry matter basis, exhibit a higher protein content (ranging from 50% in Tenebrio molitor larvae to as much as 62% in Alphitobius diaperinus larvae), with a favorable and comparable amino acid profile relative to animal- and plant-derived products [19,20]. At the same time, the amino acid composition of insect protein meets the nutritional recommendations of the World Health Organization [21,22,23,24,25].

The literature analysis indicates that factors contributing to differences in protein content and amino acid profiles in insect powders of the same species include variations in diet (type of feed), rearing conditions, physiological maturity of the insects, and processing methods [26]. However, the effect of storage time on insect powders remains poorly recognized. Due to their specific chemical composition—particularly the high protein and fat content compared with cereal flours—these products may be susceptible to unfavorable physicochemical and sensory changes during storage. Such changes may result from lipid oxidation, Maillard reactions, or alterations in color and aroma, significantly affecting the final product quality as well as its sensory acceptability and consumer perception. The storage stability of cereal flours depends both on the degree of grain milling and on storage conditions. Excessive moisture, high temperature, oxygen availability, and prolonged storage time may initiate unfavorable reactions in lipids, starch degradation, and non-enzymatic oxidation [27,28]. The intensity of these changes additionally depends on fat and protein content. Therefore, the aim of this study was to compare changes in selected physicochemical and nutritional properties of insect powders (cricket and mealworm) and selected cereal flours (millet, oat, and rice) occurring during four months of storage at room temperature. Considering the protein–fat composition and fine particle size, it was hypothesized that insect powders would undergo faster changes during storage than cereal flours. The effect of storage time on the fat quality of cereal and insect powders has been described in detail in a previous publication [29].

2. Materials and Methods

2.1. Materials

The experiment was conducted on insect powders (yellow mealworm (Tenebrio molitor) and house cricket (Acheta domesticus)) and cereal flours (millet flour (Panicum miliaceum), rice flour (Oryza), and oat flour (Avena sativa)). The production dates of the analyzed flours were similar. According to the information provided on the labels, the flours were produced between September and October 2024. The insect powders were produced in Belgium and purchased online, whereas the cereal flours were produced in Poland and purchased from a retail chain in the city of Koszalin. Baseline analyses (time zero samples) were performed immediately after purchase. For this purpose, samples were taken directly from the original packages. The remaining “partially used” portion of the flours, corresponding to approximately 50% of the package volume, was stored for a period of four months. The adopted experimental design reflects typical household conditions, in which only part of the flour is used for meal preparation while the remainder continues to be stored. The four-month storage period corresponds to the average duration of flour use under domestic conditions [29]. Flour quality was assessed based on changes in moisture content, acidity, ash content, and total protein content. The amino acid profile, as well as changes in color and volatile compounds, were also evaluated. In addition, safety aspects related to the presence of heavy metals (cadmium, lead, mercury, and arsenic) were taken into account.

2.2. Preparation of Samples for Analyses and Storage

All flour analyses were performed on the same day. The flour samples were divided into two portions of approximately 500 g each. One portion of the material was used on the first day of analysis (reference sample, zero days of storage—D0), while the second portion was transferred to PA/PE bags, with a thickness of approximately 0.12 mm, sealed, and stored for four months (D120) at room temperature (20 °C ± 2 °C) and 40% humidity, without access to light. During storage, the packages were periodically opened every two weeks to briefly mix the contents. This was associated with a controlled influx of oxygen and a short-term exchange of air in the headspace above the sample. This solution represents a compromise between the realism of household conditions and the requirements for comparability and repeatability of the experiment. After the storage period, each sample was homogenized by thorough mixing and then subjected to analyses.

2.3. Analytical Techniques

2.3.1. Physicochemical Properties of Flours and Insect Powder

The proximal analysis of flour and insect powder was carried out by the Association of Official Analytical Chemists (AOAC): protein (AOAC 992.15) [30], acidity (AOAC 939.05) [31] and ash (AOAC 923.03) [32] contents. Protein content was performed by the Kjeldahl method. The nitrogen-to-protein conversion factor used was 6.25 for cereal flours and 5.33 for insect powders. Moisture content was performed by TGA method (ang. Thermogravimetric Analysis, TGA) with using radiation infrared (IR) in a hot air oven at 105 °C. Total acidity was performed by titrating the sample with a standardized base solution (0.1 M NaOH). This process neutralizes the acidic components. And ash content was conducted after mineralization in a muffle furnace at 900 °C.

2.3.2. Determination of Amino Acid Content in Insect Powders and Cereal Flours

The amino acid content of the analyzed samples was determined using HPLC (High-Performance Liquid Chromatography; Biochrom 30, Biochrom Ltd.) with an automatic amino acid analyzer. Amino acid analysis was performed in a manner analogous to that described by McCusker et al. [33]. In the first stage of the analysis, acid hydrolysis of the samples (5 mg of protein) was carried out using 10 mL of 6 N HCl. Hydrolysis was performed in Schott-type glass vessels (Schott AG, Mainz, Germany) at 110 °C for 24 h under vacuum conditions. After acid hydrolysis, the samples were cooled and then neutralized with 1 N NaOH to obtain pH 2.2. Norleucine in citrate buffer (Merck, Darmstadt, Germany) was used as an internal standard. The resulting solution was filtered through a PTFE syringe filter (pore size: 0.45 μm; Merck, Darmstadt, Germany). The prepared samples were then separated using an automatic amino acid analyzer (Biochrom 20 Plus, Biochrom Ltd., Cambridge, UK). Amino acid separation was performed using a high-performance protein hydrolysate column (200 × 4.6 mm). Sodium citrate buffer (Merck, Darmstadt, Germany) was used as the mobile phase at a flow rate of 20 mL/h. To determine tryptophan in the analyzed samples, alkaline hydrolysis with barium hydroxide (Merck, Darmstadt, Germany) was performed instead of acid hydrolysis (20 h, 110 °C). For aspartic acid, the reported value represents the sum of asparagine and aspartic acid; for glutamic acid, the value represents the sum of glutamine and glutamic acid; and for cysteine, the value represents the sum of cystine and cysteine. Amino acid content was expressed as g/100 g. Aspartic acid—the result is the sum of asparagine, aspartic acid and its salts. Glutamic acid—the result is the sum of glutamine, glutamic acid and its salts. Cysteine—the result is the sum of cystine and cysteine.

2.3.3. Color Measurement

The color was measured using a colorimeter (RT100, Lovibond Tintometer, Dortmund, Germany) and reported in the CIE L*a*b* system, where color is represented by an achromatic component L* and two chromatic components a* and b*, (−a* greenness; +a* redness; −b* blueness; +b* yellowness). Prior to each measurement series, the device was calibrated using certified black and white reference tiles. Overall color change during storage was quantified as the total color difference (ΔE), calculated according to Equation (1). Based on ΔE values, color changes were interpreted as imperceptible (0–0.5), barely perceptible (0.5–1.5), perceptible (1.5–3), clearly visible (3–6), or large (>6), following the classification described in Mierzejewska et al. (2025) [34]. Each sample was analyzed in five replicates.

$$\mathbf{∆}\mathit{E}=\sqrt{\mathbf{(}{\mathit{L}}^{\mathit{*}}\mathbf{-}{{\mathit{L}}_{\mathbf{0}}}^{\mathit{*}}{\mathbf{)}}^{\mathbf{2}}\mathbf{+}{\mathbf{(}{\mathit{a}}^{\mathit{*}}\mathbf{-}{{\mathit{a}}_{\mathbf{0}}}^{\mathit{*}}\mathbf{)}}^{\mathbf{2}}\mathbf{+}\mathbf{(}{\mathit{b}}^{\mathit{*}}\mathbf{-}{{\mathit{b}}_{\mathbf{0}}}^{\mathit{*}}{\mathbf{)}}^{\mathbf{2}}}$$

(1)

where

• L₀*, a₀*, b₀*—Color parameters of cereal flours and insect powders before storage (D0)
• L*, a*, b*—Color parameters of cereal flours and insect powders after storage (D120)

The color results were also expressed in the cylindrical color space L*∆C*∆H*. For this purpose, the measured results were converted to saturation (∆C*) and hue angle (H*). The ∆C* value is the radial distance from the neutral axis and describes the color saturation (so-called color purity). Higher ΔC* values indicate a more intense and “purer” color, while values close to 0 correspond to weakly saturated (nearly gray) tones. The further from the center of the arrangement (from the value 0), the deeper and purer the color is. The hue angle ∆H* describes the visual impression and can be interpreted by its angular range: 0–90° corresponds to yellow–red tones, 90–180° to yellow–green, 180–270° to green–blue, and 270–360° to blue–red, as reported in Mierzejewska et al. (2025) [34]. To compare the degree of color browning of cereal flours and insect powders, the Browning Index (BI) was applied. This index integrates the effects of the L*, a*, and b* color components into a single parameter reflecting the advancement of non-enzymatic browning processes and lipid oxidation, which are common to both types of matrices (Equations (2) and (3)). Although the White Index (WI) is typically used as a color indicator for cereal flours, the application of BI enabled direct comparison between very light, starch-rich cereal flours and darker, protein–fat-rich insect powders using a single quantitative index. Moreover, BI better corresponds to the perception of product “darkness” than individual L*, a*, or b* parameters.

$$\mathit{B}\mathit{I}\mathbf{=}\mathbf{100}{\displaystyle \frac{\mathbf{(}\mathit{x}\mathbf{-}\mathbf{0.31}\mathbf{)}}{\mathbf{0.172}}}$$

(2)

$$\mathbf{x}\mathbf{=}{\displaystyle \frac{\mathbf{(}{\mathbf{a}}^{\mathbf{*}}\mathbf{+}\mathbf{1.75}\mathbf{\cdot }{\mathbf{L}}^{\mathbf{*}}\mathbf{)}}{\mathbf{(}\mathbf{5.645}\mathbf{\cdot }{\mathbf{L}}^{\mathbf{*}}\mathbf{+}{\mathbf{a}}^{\mathbf{*}}\mathbf{-}\mathbf{3.012}\mathbf{\cdot }{\mathbf{b}}^{\mathbf{*}}\mathbf{)}}}$$

(3)

2.3.4. Instrumental Measurement of Volatile Compounds—E-Nose Analysis

Volatile profiles of the five flour types were examined using an electronic nose system (Heracles II, Alpha M.O.S., Toulouse, France). This technique allows rapid comparison of aroma fingerprints based on retention index data and odour reference libraries, although it does not permit the resolution of chiral isomers. The analytical procedure was adapted from previously published methodologies [35,36].

The electronic nose operates on the principle of ultra-fast gas chromatography combined with headspace sampling. The instrument is fitted with two capillary metallic columns differing in polarity: a non-polar MXT-5 column and a slightly polar MXT-1701 column (both 10 m in length and 180 µm internal diameter), each connected to a flame ionisation detector (FID). Kovats retention indices were determined using a homologous series of n-alkanes (from n-butane to n-hexadecane; Restek) analysed under identical chromatographic conditions. Volatile compounds were tentatively assigned using the AroChemBase database (Alpha MOS Co., Toulouse, France), which contains approximately 44,000 reference compounds along with associated sensory descriptors.

For headspace generation, 2 g of each flour sample were combined with 2 g of distilled water, placed in 20 mL headspace vials, and sealed with Teflon-lined silicone septa. Samples were incubated at 45 °C for 900 s under continuous agitation (8.33 Hz). Hydrogen served as the carrier gas at a constant flow rate of 1 mL min⁻¹. The injector temperature was set at 200 °C, with an injection volume of 2500 µL and an injection speed of 125 mL s⁻¹. Volatile compounds were initially trapped at 15 °C, subsequently split, and simultaneously transferred to both chromatographic columns. The carrier gas pressure was maintained at 80 kPa, and the split flow at the column inlets was set to 10 mL min⁻¹. The oven temperature programme consisted of an initial hold at 60 °C for 2 s, followed by a ramp of 3 °C s⁻¹ to 270 °C and a final hold of 20 s. Both FIDs were operated at 280 °C.

All measurements were performed in quadruplicate at day 0 and after 120 days of storage (D0 and D120). The resulting volatile profile data, expressed as normalised relative peak areas, were analysed using Principal Component Analysis (PCA) to reduce data dimensionality and to visualise similarities and differences among the flour samples. PCA was conducted using AlphaSoft software (version 8.0).

2.3.5. Determination of the Content of Lead, Arsenic, Cadmium, and Mercury in Insect Powders and Cereal Flours

Sample Preparation and Extraction

Samples for the determination of heavy metals were prepared in accordance with European Standard EN 13804 (2013). Samples of insect powders and cereal flours were homogenized using a titanium homogenizer (Knief Mill, GM 200; Retsch, Haan, Germany). Subsequently, a 50 g portion of each sample was weighed into laboratory vessels and 5 mL of nitric acid (65.0% v/v) was added. Sample mineralization was carried out in a microwave digestion system with controlled pressure and temperature (Milestone ultraCLAVE system). During mineralization, the temperature was increased from 60 to 200 °C (30 min cycle, pressure 120 bar). After digestion, each sample was diluted to a final volume of 50 mL with high-purity deionized water. Then, 6 mL of each sample was transferred into ICP-MS vessels. The prepared samples were used for the determination of heavy metals. Results for individual heavy metals were expressed in mg/kg.

Determination Conditions

The determination of heavy metal content in the samples was carried out using the ICP–MS technique (Inductively Coupled Plasma–Mass Spectrometry). All samples were analyzed in accordance with European Standard EN 15763 (2010). An inductively coupled plasma mass spectrometer equipped with a quadrupole mass analyzer and collision cell technology (7700 ICP-MS, Agilent) was used. The operating parameters were as follows: ICP radiofrequency power, 1500 W; plasma gas flow rate, 15.0 L/min; auxiliary gas flow rate, 1.0 L/min. The helium flow rate in the collision cell was 4.50 mL/min. All measurements were performed in helium mode.

2.4. Statistical Analysis

The results of the chemical analyses are reported as means based on 3–4 replicate measurements. Statistical analysis was carried out using two-factor analysis of variance (ANOVA), with storage time and flour type treated as the two independent factors. When significant effects were found, post hoc comparisons were performed using Tukey’s HSD test, and differences were considered significant at p < 0.05. All computations were conducted in STATISTICA software (StatSoft Inc., Tulsa, OK, USA; version 13.3, 2005; currently distributed by TIBCO Software Inc., Palo Alto, CA, USA).

3. Results and Discussion

3.1. Physicochemical Properties of Flours and Insect Powder

The moisture content and acidity of cereal flours and insect powders immediately after purchase and after four months of storage are presented in

Table 1. Changes in moisture content, acidity, and ash content during storage of cereal flours and insect powders.

	Millet	Oat	Rice	Cricket (Acheta domesticus)	Mealworm (Tenebrio molitor)
Before storage (D0)
Moisture [%]	10.27 ± 0.04 e′	9.00 ± 0.08 c′	9.94 ± 0.12 d′	4.47 ± 0.06 a′	6.04 ± 0.02 b′
Acidity [°]	4.84 ± 0.05 d′	4.39 ± 0.09 c′	2.21 ± 0.01 a′	6.32 ± 0.08 e′	3.38 ± 0.06 b′
Ash [%]	1.077 ± 0.072 b′	1.475 ± 0.078 b′	0.372 ± 0.020 a′	4.290 ± 0.587 c′	4.448 ± 0.075 c′
After storage (D120)
Moisture [%]	11.21 ± 0.08 D′′	10.31 ± 0.04 C′′	11.37 ± 0.09 D′′	4.81 ± 0.03 A′′	5.56 ± 0.03 B′′
Acidity [°]	5.56 ± 0.15 D′′	4.68 ± 0.07 C′	2.22 ± 0.02B A′	6.70 ± 0.16 E′′	3.82 ± 0.11 B′′
Ash [%]	1.070 ± 0.029 B′	1.467 ± 0.083 C′	0.467 ± 0.003 A′	4.430 ± 0.164 D′	4.510 ± 0.026 D′

D0—day 0 (start of storage); D120—after 120 days (4 months) storage at room temperature. Different lowercase letters (a–e) indicate significant differences (Tukey’s test p ≤ 0.05; n = 5) among the samples before storage (D0). Different uppercase letters (A–E) indicate significant differences (Tukey’s test p ≤ 0.05; n = 5) among the samples after storage (D120). Primes (′ and ′′) indicate significant differences (Tukey’s test p ≤ 0.05; n = 5) between the same type of flour or powder before (D0) and after storage (D120).

. These parameters are widely recognized as key indicators of product freshness and storage stability during storage, as they reflect ongoing physicochemical and microbiological processes. In addition, Table 1 summarizes the ash content, which indicates the mineral composition of the analyzed flours and relates to their technological quality.

As indicated by the data, insect powders were characterized by a statistically significantly lower initial moisture content (D0) compared to cereal flours. This may be attributed both to the processing technologies used and to their chemical composition. Typical processing methods applied to ensure microbiological safety and extend the shelf life of insect powders include blanching, high-temperature drying, or freeze-drying, which lead to the effective removal of water from the product [37,38,39,40,41]. Another factor limiting water binding is the chemical composition of insect powders. They contain high levels of protein, fat, and chitin, which reduce product hydrophilicity compared with cereal flours rich in starch. Starch, in turn, exhibits a high capacity for water sorption. Therefore, cereal flours more readily retain moisture both during production and storage and are thus characterized by a higher initial moisture content. The obtained values fell within the typical ranges reported in the literature for individual cereal and insect species [42,43,44,45,46,47,48]. After four months of storage, an increase in moisture content was observed in the tested products compared to the initial samples, ranging from 7% (cricket powder) to approximately 15% (rice and oat flours). Differences in water sorption from the environment are likely due to the hygroscopicity of the analyzed flours and their chemical composition (hydrophilic starch vs. hydrophobic proteins and fats). No increase in moisture content was observed in mealworm powder. Prolonged storage under the applied conditions may result in a further gradual increase in water content, which would promote microbial growth, activation of hydrolytic enzymes, intensification of lipid and protein degradation, and product caking. Consequently, this would lead to reduced shelf life and product safety.

The chemical composition of the analyzed flours is also reflected in their acidity values. In particular, the presence of fats, proteins, and nitrogen-containing compounds (mainly in insect powders) affects the value of this quality indicator. These compounds exhibit, among other properties, buffering capacity and participate in chemical reactions such as lipid degradation processes, including hydrolysis and oxidative rancidity, which lead to the formation of free fatty acids. This relationship is clearly illustrated by rice flour, which is characterized by a low fat content and is rich in chemically inert starch (70–80% dry matter). As a result, rice flour shows the lowest acidity, at a level of 2.21%. Mineral composition is also an important factor influencing acidity. The higher ash content in insect powders (4.29–4.45%) compared to cereal flours (0.37–1.48%) indicates a greater proportion of mineral ions, which affect the acid–base balance [49]. Therefore, despite the high proportion of proteins and fats in insect powders, their acidity is not relatively high compared to cereal flours due to the neutralizing effect of mineral ions. The high ash content in insect powders results from the high mineral content of the insects’ chitinous exoskeleton, whereas the low ash content in, for example, rice flour is due to the absence of a seed coat in this grain [24,45,50]. According to the literature, the mineral content of insect powders also depends on the developmental stage (adult insect or larva) and ranges from 2.95 to 5.22% [37,38,42,51,52,53,54,55]. Literature data indicate that ash is composed mainly of calcium, iron, magnesium, phosphorus, potassium, and sodium [56,57].

After four months of storage, a slight but statistically significant increase in acidity was observed in insect powders and millet flour. This may indicate ongoing lipid hydrolysis and oxidation processes, particularly in insect powders [29], as well as enzymatic activity and starch aging in the case of millet flour. Minor changes in acidity indicate a lack of significant intensification of hydrolytic processes during the study period, but do not allow for clear conclusions about oxidative rancidity or microbial growth. Assessment of oxidative rancidity requires determining fat oxidation indices. In the publication Domiszewski et al. (2026) [29], based on the same samples and storage conditions, an increase in PV (meq O₂/kg lipids), AsV, and TOTOX was noted after 120 days, confirming the progression of oxidative processes in the lipid fraction. Verification of microflora development requires microbiological testing and water activity determination, which were not included in this project. At the same time, given the low moisture content of the tested powders, the risk of microbial growth should be considered limited. No statistically significant changes in ash content were observed. The recorded variations in this parameter result from changes in the moisture content of the flours.

3.2. Amino Acid Content in Insect Powders and Cereal Flours

The analysis of total protein content and the amino acid profile of the examined flours and insect powders demonstrated significant qualitative differentiation of these products both before storage (D0) (

Table 2. Protein content (Kp = 6.25 for cereal flours; Kp = 5.33 for insect powders) and amino acid profile of cereal flours (rice, millet, oat) and edible insect powders (cricket, mealworm) before storage (D0).

Before Storage (D0)
Protein [g/100 g] Amino Acid [g/100 g]	Rice	Millet	Oat	Cricket (Acheta domesticus)		Mealworm (Tenebrio molitor)
	Kp = 6.25	Kp = 6.25	Kp = 6.25	Kp = 6.25	Kp = 5.33	Kp = 6.25	Kp = 5.33
Protein	7.45 ± 0.93 a′	11.19 ± 1.33 ab′	16.60 ± 1.87 b′	76.77 ± 3.23 d′	65.47 ± 2.76 d′	59.31 ± 2.55 ′	50.58 ± 2.17 ′
Aspartic acid	0.40 ± 0.08 a′	0.26 ± 0.00 a′	0.68 ± 0.01 a′	4.51 ± 0.04 b′		4.41 ± 0.46 b′
Glutamic acid	1.14 ± 0.09 a′	2.08 ± 0.01 b′	2.16 ± 0.02 b′	7.71 ± 3.31 d′		6.56 ± 0.20 c′
Serine	0.31 ± 0.03 a′	0.60 ± 0.01 b′	0.46 ± 0.00 ab′	2.94 ± 0.12 c′		2.76 ± 0.07 c′
Histidine	0.15 ± 0.02 a′	0.21 ± 0.00 a′	0.22 ± 0.00 a′	1.73 ± 0.07 b′		1.95 ± 0.04 c′
Glycine	0.30 ± 0.05 a′	0.24 ± 0.00 a′	0.49 ± 0.00 a′	3.90 ± 0.16 c′		3.14 ± 0.08 b′
Arginine	0.51 ± 0.07 a′	0.31 ± 0.00 a′	0.65 ± 0.00 a′	4.62 ± 0.19 c′		3.24 ± 0.09 b′
Threonine	0.22 ± 0.03 a′	0.29 ± 0.00 a′	0.27 ± 0.00 a′	2.54 ± 0.11 c′		2.29 ± 0.05 b′
Alanine	0.40 ± 0.07 a′	1.21 ± 0.00 b′	0.48 ± 0.00 a′	7.88 ± 0.36 d′		4.41 ± 0.11 c′
Proline	0.31 ± 0.05 a′	0.80 ± 0.00 b′	0.55 ± 0.00 ab′	4.51 ± 0.20 d′		3.95 ± 0.11 c′
Tyrosine	0.24 ± 0.05 a′	0.34 ± 0.00 a′	0.28 ± 0.00 a′	4.24 ± 0.19 b′		4.20 ± 0.12 b′
Valine	0.42 ± 0.07 a′	0.55 ± 0.00 a′	0.53 ± 0.01 a′	4.70 ± 0.23 c′		3.61 ± 0.11 b′
Methionine	0.16 ± 0.03 a′	0.33 ± 0.00 b′	0.17 ± 0.00 a′	1.01 ± 0.05 d′		0.78 ± 0.05 c′
Cysteine	0.08 ± 0.00 a′	0.08 ± 0.01 a′	0.21 ± 0.02 bc′	0.18 ± 0.01 b′		0.25 ± 0.00 c′
Isoleucine	0.28 ± 0.05 a′	0.44 ± 0.00 a′	0.38 ± 0.00 a′	2.82 ± 0.14 c′		2.37 ± 0.07 b′
Leucine	0.55 ± 0.09 a′	1.40 ± 0.00 b′	0.76 ± 0.01 a′	5.10 ± 0.24 d′		4.27 ± 0.12 c′
Phenylalanine	0.37 ± 0.06 a′	0.64 ± 0.00 b′	0.54 ± 0.00 ab′	2.17 ± 0.11 c′		2.15 ± 0.06 c′
Lysine	0.25 ± 0.03 a′	0.14 ± 0.00 a′	0.39 ± 0.00 a′	3.73 ± 0.17 b′		3.38 ± 0.11 b′
Tryptophan	0.11 ± 0.00 a′	0.19 ± 0.00 a′	0.16 ± 0.01 a′	0.63 ± 0.02 b′		0.61 ± 0.06 b′

D0—day 0 (start of storage); D120—after 120 days (4 months) storage at room temperature. Different lowercase letters (a–d) indicate significant differences (Tukey’s test p ≤ 0.05; n = 3) among the samples before storage (D0). Different uppercase letters (A–D) indicate significant differences (Tukey’s test p ≤ 0.05; n = 3) among the samples after storage (D120). Primes (′ and ′′) indicate significant differences (Tukey’s test p ≤ 0.05; n = 3) between the same type of flour or powder before (D0) and after storage (D120).

) and after 120 days of storage (D120) (

Table 3. Protein content (Kp = 6.25 for cereal flours; Kp = 5.33 for insect powders) and amino acid profile of cereal flours (rice, millet, oat) and edible insect powders (cricket, mealworm) after storage (D120).

After Storage (D120)
Protein [g/100 g] Amino Acid [g/100 g]	Rice	Millet	Oat	Cricket (Acheta domesticus)		Mealworm (Tenebrio molitor)
	Kp = 6.25	Kp = 6.25	Kp = 6.25	Kp = 6.25	Kp = 5.33	Kp = 6.25	Kp = 5.33
Protein	7.22 ± 0.23 A′	11.79 ± 0.51 B′	13.56 ± 0.93 B′	67.84 ± 1.39 D′	57.85± 1.19 D′	51.27 ± 0.94 C′	43.72 ± 0.80 C′
Aspartic acid	0.58 ± 0.02 A′	0.56 ± 0.03 A′′	0.88 ± 0.02 A′′	4.99 ± 0.22 C′		4.38 ± 0.19 B′
Glutamic acid	1.20 ± 0.02 A′	2.36 ± 0.03 B′′	2.33 ± 0.03 B′′	7.28 ± 0.29 D′		6.33 ± 0.06 C′
Serine	0.34 ± 0.00 A′	0.69 ± 0.01 B′′	0.57 ± 0.01 AB′′	2.91 ± 0.11 C′		2.80 ± 0.06 C′
Histidine	0.16 ± 0.00 A′	0.22 ± 0.00 A′′	0.25 ± 0.00 A′′	1.78 ± 0.06 B′		1.94 ± 0.04 C′
Glycine	0.33 ± 0.00 A′	0.26 ± 0.00 A′′	0.62 ± 0.00 A′′	4.15 ± 0.21 C′		3.13 ± 0.05 B′
Arginine	0.56 ± 0.01 AB′	0.35 ± 0.01 A′′	0.80 ± 0.00 B′′	4.53 ± 0.20 D′		3.14 ± 0.08 C′
Threonine	0.23 ± 0.01 A′	0.31 ± 0.00 A′′	0.36 ± 0.00 A′′	2.50 ± 0.09 C′		2.27 ± 0.05 B′
Alanine	0.40 ± 0.00 A′	1.17 ± 0.01 B′	0.55 ± 0.01 A′′	7.55 ± 0.34 D′		4.25 ± 0.03 C′
Proline	0.35 ± 0.00 A′′	0.86 ± 0.01 B′′	0.68 ± 0.00 AB′′	4.81 ± 0.23 D′		3.99 ± 0.10 C′
Tyrosine	0.27 ± 0.00 A′	0.36 ± 0.00 A′′	0.35 ± 0.01 A′′	4.35 ± 0.21 B′		4.35 ± 0.03 B′
Valine	0.39 ± 0.01 A′	0.51 ± 0.01 A′′	0.55 ± 0.01 A′	4.20 ± 0.20 C′		3.54 ± 0.01 B′
Methionine	0.18 ± 0.01 A′	0.35 ± 0.01 B′	0.21 ± 0.00 A′′	0.98 ± 0.03 D′		0.81 ± 0.01 C′
Cysteine	0.12 ± 0.00 A′′	0.14 ± 0.02 A′′	0.19 ± 0.00 B′	0.26 ± 0.00 C′′		0.33 ± 0.00 D′′
Isoleucine	0.27 ± 0.01 A′	0.41 ± 0.00 A′′	0.41 ± 0.00 A′′	2.51 ± 0.10 C′		2.30 ± 0.03 B′
Leucine	0.57 ± 0.01 A′	1.41 ± 0.02 B′	0.88 ± 0.01 A′′	4.90 ± 0.20 D′		4.12 ± 0.03 C′
Phenylalanine	0.37 ± 0.01 A′	0.62 ± 0.01 B′	0.60 ± 0.00 B′′	2.06 ± 0.07 C′		2.13 ± 0.03 C′
Lysine	0.25 ± 0.01 AB′	0.15 ± 0.00 A′	0.45 ± 0.01 B′′	3.44 ± 0.13 D′		3.15 ± 0.03 C′
Tryptophan	0.09 ± 0.01 A′′	0.15 ± 0.00 B′′	0.15 ± 0.00 B′	0.47 ± 0.01 C′′		0.54 ± 0.01 D′

D0—day 0 (start of storage); D120—after 120 days (4 months) storage at room temperature. Different lowercase letters (a–d) indicate significant differences (Tukey’s test p ≤ 0.05; n = 3) among the samples before storage (D0). Different uppercase letters (A–D) indicate significant differences (Tukey’s test p ≤ 0.05; n = 3) among the samples after storage (D120). Primes (′ and ′′) indicate significant differences (Tukey’s test p ≤ 0.05; n = 3) between the same type of flour or powder before (D0) and after storage (D120).

). Cereal flours (rice, millet, and oat) were characterized by a low total protein content (7–16 g/100 g) and small amounts of amino acids, forming predominantly homogeneous statistical groups. This confirms their similar amino acid profile, which is typical of cereal-based products. The literature indicates that cereals contain moderate amounts of protein (approximately 6–15%); however, this protein is of limited biological value due to deficiencies in lysine, threonine, and tryptophan [58,59,60]. In contrast to cereal flours, insect powders were characterized by a significantly higher total protein content and a markedly richer amino acid profile. This is consistent with literature data indicating the higher quality of insect protein [24,61,62,63,64,65].

The highest protein content was observed in cricket powder (77 g/100 g), whereas a slightly lower value was found in mealworm powder (59 g/100 g). After storage, the protein content remained significantly higher than that of cereal flours (68 and 51 g/100 g, respectively). These results are consistent with literature reports indicating that edible insects typically contain 35–77% protein on a dry matter basis, and that in the case of crickets and locusts, these values may reach 60–80% [24,66,67]. In interpreting the obtained results regarding protein content, it is necessary to consider the limitations of analytical methods based on the determination of total nitrogen content. The commonly used conversion factor of 6.25, which assumes a constant proportion of nitrogen in protein, does not fully reflect the specificity of insect-derived raw materials. In insects, a substantial proportion of nitrogen occurs in non-protein forms, primarily as a component of chitin forming the exoskeleton, but also in nucleic acids and inorganic compounds. Consequently, the calculated protein content may be overestimated relative to the actual amount of proteins composed of amino acids [68,69,70]. This phenomenon may be of greater significance in the case of crickets, which, as an adult form, possess a more highly developed chitinous exoskeleton, whereas mealworms analyzed at the larval stage contain relatively more soft tissue [71,72]. Studies based on amino acid composition analysis have demonstrated that the actual nitrogen-to-protein conversion factors for insects are lower than the value of 6.25 and depend on both the species, the developmental stage, and the degree of purification of the protein fraction [69,73,74]. In studies involving Tenebrio molitor, Acheta domesticus, and Locusta migratoria, the mean nitrogen-to-protein conversion factor (Kp) was shown to be approximately 5.33 [75]. In light of these reports, the protein content determined in the present study (Kp = 6.25) should be regarded as crude protein; however, even after accounting for possible overestimation (Kp = 5.33), insect powders remain a raw material with a distinctly higher protein content and a more favorable amino acid profile than the cereal flours analyzed.

The amino acid profile revealed significant differences among the products analyzed. Cricket powder contained higher amounts of glutamic acid, glycine, arginine, threonine, alanine, proline, valine, methionine, isoleucine, and leucine compared with both mealworm powder and cereal flours. In turn, mealworm powder was characterized by a relatively higher content of histidine and cysteine, which is consistent with previous studies [76]. Cereal flours contained significantly lower amounts of all analyzed amino acids, including essential amino acids, which confirms their lower biological value. The high proportions of essential amino acids in insect powders such as histidine, arginine, threonine, valine, methionine, isoleucine, leucine, phenylalanine, lysine, and tryptophan, resulting from the presence of hemolymph and muscle tissue proteins in insects, indicate their potential applicability in human nutrition, particularly in the context of body protein synthesis, maintenance of muscle mass, and supplementation of limiting amino acids in diets based on cereal products [63,76,77]. The obtained results are consistent with literature reports indicating that the protein of edible insects is characterized by high nutritional quality and an amino acid profile comparable to that of traditional animal protein sources [65]. The comparison of results obtained before and after storage revealed statistically significant differences in the content of selected amino acids. However, the magnitude of these changes was small and resulted mainly from very low standard deviations. From a biological and nutritional perspective, these changes should be considered negligible, indicating high chemical stability of proteins and amino acids in the analyzed products during storage. This is consistent with reports describing the high stability of proteins and amino acids in products with low water activity [59,78]. Particular attention was paid to the observed increase in the determined cysteine content after 120 days of storage in most samples. It should be emphasized, however, that this result represents the sum of cysteine and cystine, and its increase most likely reflects transformations of sulfur containing protein forms that may occur under conditions of low humidity, moderate temperature, and limited oxygen availability [78,79,80]. In dry matrices, proteins may undergo subtle structural changes during storage, and one of the most common processes is the reduction in disulfide bonds, which are among the most sensitive elements of protein structure [81]. This means that S–S bonds are cleaved, releasing sulfhydryl groups (–SH), which are subsequently detected by analytical methods based on reduction and determination of free cysteine amino acids [80,82]. The observed changes related to cysteine are not of significant importance from the perspective of the biological value of the protein. Cysteine is an endogenous amino acid that can be synthesized in the human body from methionine provided that there is an adequate dietary intake of sulfur containing amino acids [83,84,85]. Therefore, slight variations in its content do not affect the ability of the protein to meet the requirements for exogenous amino acids.

3.3. Color Measurement

Among the analyzed flours and insect powders, rice flour was characterized by the lightest color (mean L_t0 = 96.55), followed by oat and millet flours (approximately L_t0 = 91.9) what was presented in

Table 4. Color components of cereal flours (rice, millet, oat) and edible insect powders (cricket, mealworm) expressed in the CIE L*a*b* color space and the cylindrical C*H* coordinates at day 0 and after 120 days of storage at room temperature.

	Millet	Oat	Rice	Cricket (Acheta domesticus)	Mealworm (Tenebrio molitor)
Before storage (D0)
CIE L*	91.90 ± 0.36 c′	91.88 ± 0.62 d′	96.55 ± 0.19 c′	58.28 ± 0.37 b′	32.68 ± 1.27 a′
CIE a*	1.17 ± 0.10 b′	1.21 ± 0.07 b′	0.10 ± 0.09 a′	5.32 ± 0.14 c′	8.18 ± 0.83 d′
CIE b*	24.80 ± 0.46 d′	11.14 ± 0.33 b′	7.43 ± 0.13 a′	15.97 ± 0.93 c′	16.18 ± 2.13 c′
Chroma ∆C*	24.83 ± 0.46 d′	11.20 ± 0.33 b′	7.43 ± 0.12 a′	16.84 ± 0.85 c′	18.17 ± 1.87 c′
Hue ∆H* [°]	87.29 ± 0.24 cd′	83.82 ± 0.30 c′	89.19 ± 0.73 d′	71.52 ± 1.36 b′	62.92 ± 4.09 a′
BI	31.30 ± 0.58 b′	13.44 ± 0.49 a′	7.80 ± 0.10 a′	37.78 ± 2.13 b′	84.55 ± 13.38 c′
After storage (D120)
CIE L*	92.32 ± 0.47 C′	93.31 ± 0.45 D′′	98.68 ± 0.61 E′′	57.80 ± 0.58 B′	32.79 ± 0.46 A′
CIE a*	1.18 ± 1.12 B′	1.08 ± 0.21 B′	0.21 ± 0.09 A′	5.26 ± 0.24 C′	7.15 ± 0.76 D′′
CIE b*	23.36 ± 0.33 E′	11.16 ± 0.27 B′	7.05 ± 0.25 A′	17.97 ± 0.56 D′′	12.54 ± 1.08 C′′
Chroma ∆C*	23.39 ± 0.33 E′	11.22 ± 0.26 B′	7.06 ± 0.25 A′	18.73 ± 0.54 D′′	14.47 ± 0.68 C′′
Hue ∆H* [°]	87.10 ± 0.28 CD′	84.46 ± 1.16 C′	88.29 ± 0.68 D′	73.67 ± 0.84 B′	60.18 ± 4.54 A′
BI	29.12 ± 0.41 C′	13.14 ± 0.28 B′	7.30 ± 0.18 A′	42.80 ± 1.58 D′	82.77 ± 4.54 E′

D0—day 0 (start of storage); D120—after 120 days (4 months) storage at room temperature. Different lowercase letters (a–e) indicate significant differences (Tukey’s test p ≤ 0.05; n = 5) among the samples before storage (D0). Different uppercase letters (A–E) indicate significant differences (Tukey’s test p ≤ 0.05; n = 5) among the samples after storage (D120). Primes (′and ′′) indicate significant differences (Tukey’s test p ≤ 0.05; n = 5) between the same type of flour or powder before (D0) and after storage (D120).

. Insect powders exhibited a much darker color, with mealworm powder being the darkest (L*_t0 = 32.68). As reported by other authors, the initial color of cereal flours is significantly influenced by the presence of pigment fractions (e.g., the degree of removal of the seed coat and germ), as well as by the method of preliminary grain processing related to drying prior to milling [86]. Since cereal flours with a higher proportion of grain outer layers (i.e., oat and millet) contain more pigments (carotenoids, phenolic compounds), they are noticeably darker than rice flour. This explains the differences in lightness between rice flour (L* ≈ 96.55) and oat or millet flours (L* ≈ 91.9), as well as differences in the CIE color coordinates a* and b*, which are responsible for redness and yellowness, respectively. In the case of insect powders, the applied thermal treatments and processing methods are of key importance. These include the type of blanching (immersion or steam) [39], freezing of larvae [37,38,39,53,54,87] and drying prior to milling (air, contact, microwave drying, or freeze-drying) [40,41,54,88,89]. These processes may largely determine the degree of initial browning of the raw material (cricket powder: BI = 37.78; mealworm powder: BI = 84.55), as they may intensify non-enzymatic browning reactions, mainly Maillard reactions occurring between amino acids (especially ε-NH₂ groups of lysine residues) and reducing sugars. As a result, this will lead to the formation of melanoidins responsible for the brown color as well as modification of taste and aroma [41,54,90]. Thermal processes may also accelerate lipid oxidation, which will also affect the darker color of insect powders and their sensory attributes. Unfortunately, the manufacturer of the insect powders used in this study did not provide information on either larval rearing conditions or powder production technology, which hinders a clear interpretation of the obtained results regarding the initial color of insect powders. At the same time, it is generally accepted that the aforementioned thermal and drying processes may significantly affect not only color but also the content of other nutrients and bioactive compounds present in insect powders [34,51] as discussed in other sections of this article.

Analysis of the color components (a* and b*) of cereal flours in the chromatic space showed that they were characterized by low saturation of the yellow color component (a* values in the range of 0.10–1.21) and varying saturation of the red component (b* values ranging from 7.43 for rice flour to 24.80 for millet flour). Additional analysis of hue (∆H*) and chroma (∆C*) for these flours indicated that they exhibited a light color with low to moderate saturation (∆C*: 7.43–24.83), with a hue close to pure yellow with a red admixture (∆H*: 83.82–89.19°). Rice flour showed the lowest chroma value (∆C* = 7.43), close to white or slightly creamy, which is consistent with its very high lightness (L*). The obtained color results for cereal flours are consistent with reports by other authors [91,92]. In the case of insect powders, the color components a* and b* differed significantly from those obtained for cereal flours. Both insect powders exhibited a similar intensity of the yellow component (b*; no significant differences) and a pronounced red component (a*: 5.32–8.18), significantly higher than in cereal flours. Moreover, the a* value of 8.18 for mealworm powder indicates a strong red–brown hue. This shift toward red is consistent with reports by other authors and suggests that T. molitor powders after thermal processing associated with drying are browner than powders obtained from A. domesticus. It is assumed that this phenomenon may be related to the high protein and fat content of this powder. The proportion of these components may promote the intensification of the Maillard reactions as well as chemical and enzymatic oxidation of unsaturated fatty acids during thermal processing. This will promote the formation of red–brown pigments (including melanoidins, carotenoid degradation products, and reactive oxidation products) and will translate into an increase in the value of color components [34,41,93,94,95]. Furthermore, analysis of the ∆H* and ∆C* parameters confirmed that the investigated insect powders were characterized by a red–brown hue (H: 62.92–71.52) with low color saturation (C: 16.84–18.17). The obtained color results for insect powders are in agreement with those reported by other authors [96]. The browning index (BI), calculated based on the color components, indicated that T. molitor powder exhibited the highest initial degree of browning (BI_t0 = 84.55), which is typical of matrices with advanced Maillard reactions and lipid oxidation. The lowest BI values were observed for rice and oat flours (7.80 and 13.44, respectively). No significant differences in BI were detected between millet flour and Acheta domesticus powder, both of which exhibited a moderate degree of browning.

It was observed that in cereal flours, after 120 days of storage under dry and dark conditions, a slight increase in color lightness (L*) occurred compared to the initial samples (D0). At the same time, these changes were accompanied by alterations in the a* and b* color components, with practically unchanged chroma (∆C*) and hue (∆H*). In most of the analyzed cases, these changes were not statistically significant (α = 0.05). The whitening of cereal flours may primarily result from enzymatic lipoxygenase reactions associated with the oxidation and degradation of carotenoid compounds and vitamin E [91,97,98,99]. These phenomena were particularly evident in oat and rice flours, for which significant differences between D0 and D120 were observed for the L* component.

Analysis of the L* component after 120 days of storage of insect powders indicated that cricket powder slightly darkened (L₀: 58.28 → L₁₂₀: 57.80), whereas mealworm powder became slightly lighter (L₀: 32.68 → L₁₂₀: 32.79); however, these changes were not statistically significant (α = 0.05). In contrast, statistically significant changes were observed in the a* and b* components. In the case of A. domesticus powder, an increase in the component responsible for yellowness was noted (b₀: 15.97 → b₁₂₀: 17.97), accompanied by an increase in color saturation (∆C₀: 16.84 → ∆C₁₂₀: 18.73), which may suggest ongoing lipid oxidation processes [95,100]. Conversely, for T. molitor powder, an opposite trend was observed. The color components responsible for red (a*) and yellow (b*) decreased significantly, along with a reduction in color saturation (∆C*). Additionally, the hue angle (∆H*) shifted toward yellowness. Combined with the increase in the L* component, these changes indicate that the color of T. molitor powder became more muted, with a gray–brown appearance. This may be attributed to the degradation of colored pigments formed, among others, during Maillard reactions and advanced lipid oxidation [21,99,101]. At the same time, it was demonstrated that with prolonged storage time of the flours (except for A. domesticus powder), the BI value decreased, although not statistically significantly compared to the samples evaluated at D0.

The values of the total color difference (ΔE) after 120 days of storage presented in Figure 1 indicate that the smallest color changes (ΔE: 1.47–2.19) were observed in plant-based flours (millet, oat, and rice). This corresponds to minor differences that are often barely perceptible visually. Acheta domesticus (cricket) powder exhibited a similar level of color change (ΔE ≈ 2.12), with no statistically significant difference compared to cereal flours. The greatest color change was observed in Tenebrio molitor (mealworm) powder, where ΔE = 3.88, which was significantly higher than in the other samples. This suggests that mealworm powder is the most susceptible to processes leading to color modification during storage (e.g., lipid oxidation and pigment degradation), whereas the other analyzed products are more color-stable during storage. This interpretation is confirmed by the results of our previous publication Domiszewski et al. (2026) [29] regarding changes in the lipid fraction in the same samples and storage conditions. The greatest changes in fat quality and oxidation markers were observed compared in the mealworm powder compared to the other materials, which is consistent with the lowest color stability in this study.

3.4. Instrumental Measurement of Volatile Compounds—E-Nose Analysis

The PCA score plot (Figure 2) illustrates the distribution of five different flour types based on volatile compound profiles determined using an electronic nose. The first two principal components explain 94.61% of the total variance, with PC1 accounting for 82.47% and PC2 for 12.14% of the variability. The high discrimination index (94) confirms the strong ability of the method to differentiate samples based on their volatile profiles.

The greatest differences among samples are observed along PC1, which clearly separates insect flours from plant-based flours. Cricket powder and mealworm flour are located on the negative side of PC1, forming two distinct and well-defined clusters. Such separation is consistent with previous research showing that edible insect matrices often exhibit a volatile composition strongly shaped by their high protein and lipid content as well as processing conditions, resulting in a characteristic contribution of Maillard reaction products and secondary lipid oxidation products that can differ markedly from plant-derived raw materials [94].

Plant-based flours are clearly separated on the positive side of PC1. Millet powder forms a compact cluster at the highest PC1 values, while rice flour is located in the mid-range of positive PC1 values. Oat flour is positioned close to the PC1 axis and shows pronounced differentiation along PC2.

The effect of storage time (D0 vs. D120) is reflected by shifts in sample clusters along PC2, particularly evident for oat flour and mealworm powder, where D120 samples are positioned higher than D0 samples. Notably, millet powder stored for 120 days partially overlaps with rice flour samples, indicating convergence of their volatile profiles during storage. This pattern may reflect storage-induced changes in volatiles, including the formation or intensification of compounds related to lipid oxidation (commonly yielding aldehydes and alcohols) and/or to Maillard-type pathways and their interactions with lipid-derived intermediates, which are known to contribute substantially to aroma formation in foods [102].

The analysis of volatile organic compounds (VOCs) presented in

Table 5. Presence of Volatile Organic Compounds in cereal flours and insect powders at day 0 (D0) and day 120 (D120).

IR * DB-5	IR * DB-1701	Compound	Sensory Descriptors	Millet		Oat		Rice		Cricket (Acheta domesticus)		Mealworm (Tenebrio molitor)
				D0	D120	D0	D120	D0	D120	D0	D120	D0	D120
ALCOHOLS
629	725	1-propanol, 2-methyl	bitter	+	+		+		+			+	+
655	778	n-butanol	alcoholic				+		+		+	+
860	966	(Z)-3-hexen-1-ol	fresh						+		+
895	1031	3-heptanol	green		+		+						+
ALDEHYDES
515	616	2-methylpropanal	fresh		+				+	+	+	+	+
564	661	Butanal	green		+		+		+	+	+	+	+
665	744	3-methylbutanal	almond	+	+	+	+	+			+		+
790	822	Hexanal	grassy	+	+	+	+	+	+
833	965	Furfural	bread				+	+	+	+	+	+	+
904	983	Heptanal	fresh									+
942	1079	Benzaldehyde	fruity				+		+	+	+
1002	1153	2,4-Heptadienal, (E, E)-	hay						+				+
1036	1183	Benzeneacetaldehyde	grassy	+	+	+		+	+		+
1048	1140	(Z)-2-octenal	fruity	+	+	+
1207	1291	decanal	waxy		+				+
1227	1343	(E, E)-2,4-nonadienal	cereal	+	+	+	+		+		+
1235	1494	4-octanolide	fatty	+				+
DIOL
745	956	Propylenglycol	caramelized								+		+
ESTERES
628	705	Izopropyl acetate	etheral				+		+	+	+
726	822	Ethyl isobutyrate	alcoholic		+		+	+	+	+		+	+
733	767	Ethyl propanoate	fruity	+	+				+	+	+	+
755	836	Methyl 2-methylbutanoate	green	+	+	+	+	+	+	+	+
789	863	Ethyl butyrate	caramelized								+		+
807	854	Propyl propanoate	fruity						+			+	+
823	870	Butyl acetate	sweet		+					+	+
844	1031	Ethyl 2-methylbutyrate	sweet		+	+		+	+	+	+
903	918	Izoamyl acetate	fruity			+					+
1004	1081	Z-3-Hexen-1-ol, acetate	green		+		+
1083	1162	Pentyl butanoate	fruity		+						+
1115	1215	Ethyl3-(methyl,thio)propanoate	fruity					+
1123	1153	Ethyl heptanoate	fruity		+		+		+		+
1171	1291	Benzyl acetate	floral		+
1191	1235	Ethyl octanoate	fruity	+
1212	1235	ethyl octanoate	waxy	+				+
KETONES
563	688	Butane-2,3-dione	butter	+		+	+	+
678	790	Pentan-2-one	etheral							+	+	+	+
703	809	2,3-pentanedione	almond	+	+					+	+		+
LACTONE
1133	1346	5-propyldihydro-2(3H)-furanone	fatty					+
ORGANIC ACIDS
636	779	Acetic acid	acetic	+		+		+		+
727	897	Propanoic acid	acidic			+			+		+
812	965	Butanoic acid	butter					+		+	+
836	1031	3-methylbutanoic acid	cheese	+	+
902	1084	Pentanoic acid	acidic					+			+
1005	1183	Hexanoic acid	fatty	+						+		+
PYRAZINES
926	984	2,6-Dimethylpyrazine	nutty				+				+
937	1020	2,3-dimethylpyrazine	cereal	+		+	+		+
987	1104	Trimethylpyrazine	green		+				+		+
1029	1140	Acetylpyrazine	bread	+						+
1110	1180	Tetramethylpyrazine	hay		+				+		+		+
SULFUR COMPOUNDS
516	550	Dimethyl sulfide	sulfurous	+		+	+		+	+
970	1020	Dimethyl trisulfide	sulfurous	+	+			+			+	+	+
TERPENES
912	918	Alpha-pinene	aromatic	+	+	+	+	+	+	+	+	+	+
971	991	Beta-Pinene	hay		+	+					+
986	1031	Myrcen	sweet				+						+
1028	1083	p-Cymene	fruity				+
1034	1079	1,8-cineole	sweet				+			+		+	+
1047	1082	Limonene	fruity						+
			TOTAL	21	26	14	22	17	26	19	30	14	18

* retention indexes for DB-5 and DB-17 columns.

revealed clear qualitative differences between cereal flour samples (millet, oat, and rice) and insect-derived samples (cricket Acheta domesticus and mealworm Tenebrio molitor), as well as the significant effect of storage time (D0 and D120) on the composition of the aroma profile.

Across all analyzed samples, aldehydes, esters, alcohols, and organic acids were the predominant chemical classes. Cereal flour samples were primarily characterized by compounds associated with green, grassy, fresh, cereal-like, and bread-like notes, such as hexanal, benzaldehyde, furfural, and selected pyrazines. These compounds are well-recognized markers of cereal aroma and are typically formed as a result of mild lipid oxidation processes and low-intensity Maillard reactions [103]. The relatively minor qualitative changes observed between D0 and D120 indicate a high aroma stability of the cereal flour matrix during storage.

In contrast to cereal flours, insect powder samples exhibited a markedly higher complexity of the volatile profile, particularly after 120 days of storage. In addition to aldehydes and esters, short-chain fatty acids, ketones, sulfur-containing compounds, and pyrazines were more frequently identified, contributing to fatty, buttery, sulfurous, nutty, and roasted sensory notes. The presence of compounds such as butanoic acid, hexanoic acid, dimethyl sulfide, dimethyl trisulfide, and acetylpyrazine indicates an intensification of lipid degradation and amino acid breakdown processes, which are characteristic of raw materials rich in fat and protein. The detection of furfural in insect flour samples, despite the absence of hexanal—a typical marker of lipid oxidation—suggests that the aroma profile of these samples is predominantly shaped by Maillard reactions and the thermal degradation of carbohydrates, promoted by the high protein content and the availability of free amino acids in the insect matrix [104].

Storage time had a significant impact on the volatile composition of insect powder samples. After 120 days, an increase in both the number and diversity of detected compounds was observed, particularly those associated with waxy, fatty, and sulfurous descriptors. This finding suggests progressive lipid oxidation and secondary chemical reactions occurring during storage, which may lead to the formation of sensory off-notes. In the case of cereal flours, these changes were considerably less pronounced, further confirming their greater aroma stability.

It should be emphasized that despite the high usefulness of the electronic nose as a rapid and reproducible tool for comparative analysis of volatile compound profiles, the identification of individual compounds is inherently tentative and based on pattern recognition of sensor responses rather than on unequivocal chemical identification. Consequently, the obtained results should be interpreted as relative comparative profiles.

3.5. Heavy Metal Content in Cereal Flours and Insect Powders

The results of heavy metal content (Pb, As, Cd, and Hg) determined in cereal flours and insect powders are presented in

Table 6. Heavy metal content in cereal flours and insect powders.

	Millet	Oat	Rice	Cricket (Acheta domesticus)	Mealworm (Tenebrio molitor)
Pb	<0.010	<0.010	<0.010	0.036 ± 0.009	<0.010
As	<0.010	<0.010	0.25 ± 0.05 c	0.011 ± 0.002 a	0.068 ± 0.013 b
Cd	0.012 ± 0.003 a	0.037 ± 0.009 b	0.014 ± 0.003 a	0.0046 ± 0.0011 b	0.110 ± 0.03 c
Hg	<0.0010	<0.0010	0.0018 ± 0.0003	<0.0010	<0.0010

Different lowercase letters (a–c) indicate significant differences (Tukey’s test p ≤ 0.05; n = 3) among the samples before storage (D0).

. When comparing the obtained results with the relevant EU Commission Implementing Regulations for cereal flours (2023/915) [105], powdered forms of house cricket [106], and powdered mealworm larvae (2021/882) [107], it can be concluded (with one exception) that the analyzed flours and powders complied with EU requirements. The metal that did not meet EU limits was cadmium in mealworm powder. The maximum permissible level of cadmium in powdered mealworm larvae according to EU regulations is 0.1 mg/kg, indicating a 10% exceedance of this limit. Taking into account legal requirements, food with elevated levels of heavy metals, including cadmium, may not be authorized for sale (EU 1993/315) [108]. Therefore, mealworm insect powder should be withdrawn from the market, as its consumption poses a risk to human safety and health. In order not to expose other consumers to risk, in accordance with Article 50 of Regulation (EU) 2002/178, mealworm powder should be entered into the Rapid Alert System for Food and Feed (RASFF) database [109].

The presence of chemical contaminants in agricultural by-products used as feed for insects may pose real risks to human health [110]. Even slightly elevated levels of heavy metals in food may increase, among others, the risk of cancer development or cause adverse changes in cellular DNA [111].

Prolonged exposure, even to low doses of cadmium, contributes to the accumulation of this metal in the kidneys, liver, and bones. In these organs, the concentration of this element increases with a person’s age. This phenomenon is attributed to the long biological half-life of cadmium, which averages approximately 20 years [112,113]. Long-term exposure of the human body to cadmium leads, among other effects, to chronic kidney disease [114], kidney damage [112], albuminuria [115] and proteinuria [116].

According to Diener et al. (2015) [117], heavy metals, including cadmium, may bioaccumulate in farmed insects. One of the main sources of chemical contamination is the substrate on which insects are reared. Similar conclusions were drawn by Van der Fels-Klerx et al. (2018) [118], who demonstrated a relationship between the concentration of heavy metals in the substrate and their levels in insects. The accumulation of chemical contaminants in insects depends primarily on the type of contaminant, the insect species, and its developmental stage [117,118]. The cadmium exceedance observed in our study in mealworm powder was most likely the result of elevated cadmium levels in the substrate used for insect rearing. Studies conducted by Muhammad et al. (2022) [119] on grasshoppers, locusts, and termites showed that heavy metal levels in these insects exceeded WHO recommendations. Similarly, Mlček et al. (2017) [120] reported high concentrations of, among others, cadmium and copper in insects, rendering them unsuitable for human consumption. Likewise, Papastavropoulou et al. (2024) [121] also reported low levels of heavy metals in insects. As indicated by the cited studies, low levels of heavy metals in insect feed or substrate ensure low concentrations of these contaminants in insect powders.

The relatively low levels of heavy metals observed in cereal flours result from several factors. In the European Union, maximum limits for chemical contaminants in various food groups, including cereal products (such as flours), have long been established. Consequently, farmers are required to comply with stringent regulations governing cereal cultivation. A frequent source of chemical contamination in plant production is the soil itself. The presence of heavy metals such as cadmium or arsenic in soil results from both natural and anthropogenic activities, including pollutant emissions [122]. Plants can absorb heavy metals from soil through their roots, in accordance with the “soil–plant barrier” theory [123]. For this reason, some countries, including Poland, have introduced national legal regulations specifying maximum permissible levels of heavy metals in different types of land, including agricultural soils [124]. These regulations have undoubtedly contributed to reducing contamination levels in cereal grains.

Other factors influencing the level of contaminants in cereals, and consequently in flours, include irrigation practices, the use of fertilizers, and plant protection products [125,126]. For this reason, cereal grains originating from organic farming generally contain lower levels of chemical contaminants than those from conventional farming systems [127]. To further limit heavy metal contamination in crop production, the EU has introduced a number of legal regulations specifying maximum permissible levels of contaminants in fertilizers and plant protection products [128,129,130]. Nevertheless, there are many regions worldwide where soil contamination with heavy metals is high [122], resulting in elevated levels of these metals in flours as well [131,132].

Based on the conducted research, we believe that monitoring and control of heavy metal levels in insect powders available on the market should be intensified.

4. Conclusions

The conducted research allowed for the comparison of the quality and storage stability of cereal flours (millet, oat, rice) and insect powders (Acheta domesticus, Tenebrio molitor) stored for 120 days in standardized conditions similar to home conditions. The examination of initial samples showed that insect powders clearly differed from cereal flours in terms of higher protein and ash content, lower moisture content, darker color, and a different profile of volatile compounds assessed by the e-nose method. It was shown that insect powders are characterized by a several times higher protein content than cereal flours and a more favorable amino acid profile. They provide significantly more key exogenous amino acids (including lysine, leucine, methionine, and tryptophan), which makes them have a higher nutritional value than cereal flours. In the safety assessment, most of the determined heavy metals were within the applicable limits, while in mealworm powder, cadmium content was found above the indicated regulatory threshold, which justifies the need to monitor the content of this element in mealworm powders available on the market.

Storage of cereal flours and insect powders at room temperature and 40% humidity resulted in a greater increase in moisture content in cereal flours than in insect powders, indicating higher water sorption under these conditions. Titratable acidity increased slightly in insect powders and millet flour, while ash content remained essentially unchanged (the observed differences resulted from concomitant changes in humidity). Amino acid profiles of all tested materials remained stable during storage. The small, statistically significant differences in selected amino acids are of little biological significance, indicating high stability of the protein fraction under the tested storage conditions. Color analysis revealed generally high stability of CIE L*a*b* parameters in cereal flours and cricket powder, while mealworm powder was characterized by the highest total color difference (ΔE) and the lowest color stability among the tested products. E-nose analysis with PCA clearly separated insect powders from cereal flours and indicated shifts in the volatile compound profile after storage in selected samples, particularly in oat flour and mealworm powder.

The research also enabled the identification of parameters important for quality control during storage. The tested parameters, in the context of assessing storage stability, require different interpretations depending on the type of product tested. This is due to differences in their nutritional composition and production technologies. For example, insect powders are characterized by significantly lower initial moisture content than cereal flours. This is related to their production technology (blanching, freezing, drying), the degree of grinding, and the greater share of hydrophobic components (protein, fat, chitin) in comparison to hydrophilic starch, which dominates in cereal flours. Therefore, the moisture content of insect powders does not change radically during storage, in contrast to cereal flours. It can therefore be assumed that while moisture control is of significant practical importance in the case of cereal flours, as it potentially increases the risk of caking and enzyme activation, this parameter may not be of such great practical importance in the quality control of insect powders. Research in this area should be ex-tended to longer storage periods. In relation to the conducted research, an important parameter in the quality control of insect powders is the measurement of acidity. Although insect powders did not exhibit high initial acidity compared to cereal flours (due to the buffering effect of mineral ions resulting from high ash content), the increase in acidity during storage indicates mild lipid hydrolysis and oxidation processes *. This is also reflected in the observed changes in color and volatile compound profile.

Overall, the studies confirmed the assumed comparative objective and showed that insect powders, despite relatively low moisture content and overall protein stability, are more sensitive to quality changes manifested in parameters related to moisture, color, and volatile compounds, which may be a consequence of lipid transformations *. Cereal flours, within the analyzed period, showed greater stability of these characteristics but exhibited stronger water sorption from the environment.

* Conclusions regarding the lipid fraction changes were based on the results of the complementary work by Domiszewski et al. (2026) [29], performed on the same samples and under the same storage conditions, in which an increase in PV, AsV and TOTOX was noted after 120 days, confirming the progress of lipid oxidation processes during storage under the same conditions.