*3.3. Protein Solubility*

Figure 3 shows the protein solubility of TMI, TMD, NDSP, and HDSP fractions at pH 5, 7, and 9. Both the type of fraction and the pH had a significant impact on protein solubility (*p* < 0.0001). Similar solubilities were obtained for HDSP and NDSP at pH 7 and 9, whereas the solubility of HDSP was calculated to be lower than NDSP at pH 5. As expected, and whatever the pH value, protein fractions recovered from HDSP and NDSP (soluble fraction) were more soluble than TMI and TMD. A similar increase in solubility was observed for TMI and TMD when the pH increased, except at pH 9 where the solubility of TMI was higher than TMD. Globally, results showed that fractions had minimum and maximum solubilities at pH 5 and 9, respectively.

**<sup>1</sup>**Actin-87E-like protein

**<sup>2</sup>**Cockroach allergen-like protein

**4** 12 kDa hemolymph protein b

inducing protein (*Tenebrio molitor*)

Hexamerin 2

**<sup>7</sup>**Arginine kinase (Fragment)

**<sup>10</sup>** Melanin-inhibiting protein

**<sup>8</sup>**α-amylase

**<sup>11</sup>** Chitinase

**6** 

Molecules 2021, 26, x FOR PEER REVIEW 7 of 14

*Molecules* **2021**, *26*, x FOR PEER REVIEW 8 of 14

Figure 2. Two-dimensional electrophoresis of T. molitor proteins for (A) TMI, (B) TMD, (C) NDSP, and (D) HDSP. Proteins composing each numbered spot were characterized by proteomics (Table 2). **Figure 2.** Two-dimensional electrophoresis of *T. molitor* proteins for (**A**) TMI, (**B**) TMD, (**C**) NDSP, and (**D**) HDSP. Proteins composing each numbered spot were characterized by proteomics (Table 2). bility of TMI was higher than TMD. Globally, results showed that fractions had minimum and maximum solubilities at pH 5 and 9, respectively.

**Figure 3.** Protein solubility at pH 5, 7 and 9 of TMI, TMD, NDSP, and HDSP fractions. Different letters indicate significant differences (*p* < 0.05). **Figure 3.** Protein solubility at pH 5, 7 and 9 of TMI, TMD, NDSP, and HDSP fractions. Different letters indicate significant differences (*p* < 0.05).


**Table 2.** Proteins identified by proteomics in *T. molitor* 2D gels.
