The objective was to determine the effects of drying and blanching methods on the nutrient utilization of black soldier fly larva (BSFL; Hermetia illucens) meal by pigs using in vitro assays. Two-step and three-step in vitro assays were employed to simulate the gastrointestinal tract of pigs. Four BSFL meals were prepared using the following pretreatment methods: (1) microwave drying at 80 °C for 32 min, (2) hot-air drying at 60 °C for 17 h, (3) blanching for 5 min in boiling water and hot-air drying at 60 °C for 17 h, and (4) 2% citric acid solution blanching for 5 min in boiling solution and hot-air drying at 60 °C for 17 h. After the drying process, each BSFL was defatted and ground to obtain BSFL meals. The nitrogen (N) concentration in the test ingredients ranged from 8.5 to 9.4%, and the ether extract ranged from 6.9 to 11.5% on an as-is basis. The amino acid (AA) concentration in the BSFL meals ranged from 2.80 to 3.24% for Lys and 0.71 to 0.89% for Met on an as-is basis. Hot-air-dried BSFL meal had a greater in vitro ileal disappearance (IVID) of N compared with microwave-dried BSFL meal (p < 0.05). However, blanched BSFL meals in water or 2% citric acid solution before hot-air drying had a lower (p < 0.05) IVID of N compared with microwave-dried or hot-air-dried BSFL meal. Blanched BSFL meals in water or 2% citric acid solution before hot-air drying showed a lower (p < 0.05) in vitro total tract disappearance of dry matter and organic matter compared with microwave-dried or hot-air-dried BSFL meal. Microwave-dried BSFL meal had a lower (p < 0.05) IVID of indispensable AA, except for His, Lys, Met, and Phe, compared with hot-air-dried BSFL meals. However, blanched BSFL meals in water or 2% citric acid solution before hot-air drying showed a lower (p < 0.05) IVID of indispensable AA compared with microwave-dried or hot-air-dried BSFL meal. In conclusion, hot-air-dried BSFL meal presented greater nutrient utilization compared with microwave-dried BSFL meal for pigs. However, blanching in water or citric acid solution negatively affected the nutrient digestibility of BSFL meal based on in vitro assays.
Keywords: black soldier fly larva meal; blanching method; drying method; in vitro assays; pigs.