Partial pretreatment of ingredient mixture effectively improved feed chemical composition, physicochemical properties and in vitro digestibility

Abstract

Physical pretreatment, using microwave, has been performed to qualitatively improve feed ingredients prior to inclusion in aquafeed. Both partial and full microwaving pretreatments of solid ingredient mixture were investigated. Three feeds containing either pretreated protein (PP; fish meal, meat and bone meal, and soybean meal), pretreated carbohydrate (PC; broken rice and rice bran) or pretreated completely of both protein and carbohydrate (PPPC) were formulated and compared with a control feed containing non-pretreated ingredient mixture (NP). Significantly improved proximate chemical compositions were observed in both partial and full pretreatments of the ingredient mixture (P < 0.05). Qualitative changes in nutritive profiles assessed through Fourier transform infrared spectroscopy were also observed. Decreased pH and water absorption capacity, increased turbidity, with more irregular, aggregation and fusion in microstructure, and modified secondary protein structure (height and area of amides I and II, and quantities of ß-turns and random coils) indicated desirable characteristics for the pretreated feeds over the NP feed. In vitro digestibility based on crude digestive enzyme extracts from economically important fishes, Nile tilapia (Oreochromis niloticus) and striped catfish (Pangasianodon hypophthalmus), exhibited significantly improved availability of both protein and carbohydrate digestibility in all pretreated feeds (P < 0.05), and indicated that striped catfish could utilize the four feeds better than Nile tilapia did (P < 0.05). Surprisingly, the partial microwaving of only carbohydrate in the ingredient mixture (PC feed) improved aquafeed with the significantly highest bioavailability of both protein and carbohydrate (P < 0.05). This production process can be directly applied in aquafeed production.