## 4 Discussion
### Impacts of Killing Methods on Chemical Composition and Physicochemical Properties
#### 4.2.2 Physicochemical Properties  
The color of BSFs is an absolutely important factor in terms of farmer acceptance because insect meal in light brown shades of beige, tan and khaki is preferred by farmers or users, whereas dark brown or black is not accepted. The browning reaction and melanization are the chemical reactions which influence color alterations after killing and processing [8; 9]. The enzymatic browning reaction or polyphenol oxidation in an aerobic condition promoted the darkish effects on BSFs [29; 30]. Moreover, the complex between amino acids and reducing sugars was present after the drying process, leading to a darker color, which is called the Maillard reaction or non-enzymatic browning reaction [31; 32]. Melanin was produced as the end product of melanization, which was the innate immune response of insects to harmful environments and promoted a darker color of BSF [9]. The low level of browning reaction in BSFs with heat treatment was caused by enzyme destruction by heat [8; 9]. Heat treatment can only terminate the enzymatic browning reaction [31; 32]; however, the decline of the non-enzymatic browning reaction was observed in this study, which may have resulted from a short time available for metabolism, as the killing process was rapid by heating [8]. The slow killing methods without an enzyme destruction protocol, such as freezing and asphyxiation, promoted the activation of several metabolic processes, mainly lipolysis, melaninization and browning, which led to a darker color [9]. The darker color developed immediately after blending the prepupae of BSFs because the enzymatic browning reaction between substrates and enzymes released from cell destruction was increased in the homogenized samples. Therefore, the darkest color was found in the blending procedure [8]. For these reasons, the BSF color is greatly influenced by the killing procedures. The lightest BSFs were observed in the hot treatment group, which agreed with other research studies [8; 9]. Therefore, limitation on the initiation of the browning reaction and melanisation was a major factor to prevent color alteration of BSFs. Blanching was considered the best killing method to preserve the integrity and quality of BSFs, which agreed with the report of [PERSON] et al. [8]. In contrast, [PERSON] et al. [10] reported blending or grinding of live black soldier fly prepupae as the best killing method due to homogenization of BSF prepupae in a specific solvent mixture that was water free and composed of chloroform-methanol 2:1 (_v/v_), from which water was subtracted by methanol slowing down enzymatic activity (hydrolytic), especially lipase for generated reaction of fat acidity and lipid oxidation. The mechanisms by which different killing procedures affect BSF quality were described in detail. Fat acidity was used to represent the amount of free fatty acids in samples which correlated with lipase activity respectively [10], the fat acidity in the asphyxiation and freezing groups was higher than that in the heat treatment group by approximately three and ten times respectively, which agreed with this study [7; 8]. In this study, the extremely high value of fat acidity was observed in the blending group, which represented the high lipase activity in this sample. The freezing technique only decreased lipase activity, which remains in a low temperature environment (5 \({}^{\circ}\)C), even at -30 \({}^{\circ}\)C [33]. On the other hand, heat treatment can destroy lipase, which minimizes fat acidity and prevents the pH reduction after killing compared with other methods. Another parameter representing the integrity of BSFs is lipid oxidation; the high activity of this chemical reaction promotes several adverse outcomes for consumers such as nutrient loss, lower digestibility of products, rancidity, carcinogen substances and toxicity [34].