Effect of Cereal α-Amylase/Trypsin Inhibitors on Developmental Characteristics and Abundance of Digestive Enzymes of Mealworm Larvae (Tenebrio molitor L.)

SIMPLE SUMMARY: The main nutritionally relevant proteins of Tenebrio molitor L. larvae are cereal proteins. Cereals contain α-amylase/trypsin inhibitors (ATIs) that interact with digestive enzymes and which may impair the growth of the larvae. Despite the existing work on the subject, there is still a lack of information regarding the effects of ATIs on the relative abundance of various enzymes in larvae. Our aim was therefore to undertake an assessment of the potential effects of ATIs on the growth parameters and digestive enzyme contents of T. molitor. The larvae were fed with cereal meals containing different levels of ATIs. The developmental characteristics were evaluated and finally an analytical method based on liquid chromatography with tandem mass spectrometry (LC-MS/MS) was developed to quantify the relative abundance of enzymes in the larvae. The results indicated an increase in pupation and significantly higher protein concentrations in larvae fed with wheat meals compared to those fed with sorghum meals. Patterns of specific α-amylase activity (in mM maltose/min/mg protein) were similar to those of amylase activity (in mM maltose/min) and the larvae fed on high-ATI-content meals exhibited an increased death rate, although the results were not always significantly consistent. The results of the LC-MS/MS analysis showed a decrease of about half of the relative content of α-amylase among the three proteases monitored, as well as an increase in dipeptidylpeptidase I and chymotrypsin, whereas trypsin remained constant. Therefore, these results indicate that meal composition has an effect on the expression of T. molitor digestive enzymes. ABSTRACT: The objective of this work was to investigate the potential effect of cereal α-amylase/trypsin inhibitors (ATIs) on growth parameters and selective digestive enzymes of Tenebrio molitor L. larvae. The approach consisted of feeding the larvae with wheat, sorghum and rice meals containing different levels and composition of α-amylase/trypsin inhibitors. The developmental and biochemical characteristics of the larvae were assessed over feeding periods of 5 h, 5 days and 10 days, and the relative abundance of α-amylase and selected proteases in larvae were determined using liquid chromatography tandem mass spectrometry. Overall, weight gains ranged from 21% to 42% after five days of feeding. The larval death rate significantly increased in all groups after 10 days of feeding (p < 0.05), whereas the pupation rate was about 25% among larvae fed with rice (Oryza sativa L.) and Siyazan/Esperya wheat meals, and only 8% and 14% among those fed with Damougari and S35 sorghum meals. As determined using the Lowry method, the protein contents of the sodium phosphate extracts ranged from 7.80 ± 0.09 to 9.42 ± 0.19 mg/mL and those of the ammonium bicarbonate/urea reached 19.78 ± 0.16 to 37.47 ± 1.38 mg/mL. The total protein contents of the larvae according to the Kjeldahl method ranged from 44.0 and 49.9 g/100 g. The relative abundance of α-amylase, CLIP domain-containing serine protease, modular serine protease zymogen and C1 family cathepsin significantly decreased in the larvae, whereas dipeptidylpeptidase I and chymotrypsin increased within the first hours after feeding (p < 0.05). Trypsin content was found to be constant independently of time or feed material. Finally, based on the results we obtained, it was difficult to substantively draw conclusions on the likely effects of meal ATI composition on larval developmental characteristics, but their effects on the digestive enzyme expression remain relevant.