Apparent dry matter, energy, protein and amino acid digestibility of four soybean ingredients in white shrimp Litopenaeus vannamei juveniles

Dry matter, energy, protein and amino acid apparent digestibility coefficients (ADC) were determined in Pacific white shrimp juveniles (6 g average initial weight) for four soybean products: full fat soybean meal (FFSBM, 38% CP in dry matter), solvent extracted soybean meal (SBM, 52% CP), soybean protein concentrate (SPC, 71% CP) and soybean protein isolate (SPI, 89% CP), obtained from soybeans processed by different manufacturers in USA and México. The test diets included 30% of the test ingredients and 70% of a ground commercial diet supplemented with 1% chromic oxide and 1% sodium alginate. Amino acid contents in the ingredients, diets and feces were analyzed by HPLC at Evonik-Degussa laboratory. Amino acid profiles of the four soybean product samples were quite similar except for a lower content of methionine and cystine in SPI. In general, nutrient digestibility values were far higher in the soy products than in the fish meal-based reference diet. Dry matter and energy ADCs were significantly higher for SPI (92 and 98%, respectively) than for FFSBM, SBM and SPC (83 and 89%, respective averages). Crude protein ADC was not significantly different among FFSBM, SBM and SPI, but SPC had significantly a lower value (93 vs 96%). Total amino acid (92 vs 97%) and essential amino acid (91 vs 96%) digestibility profiles were almost identical for FFSBM, SBM and SPI, while the SPC profile was parallel but 3.5 to 7 percentage units lower. Cys and Thr were the least digestible amino acids in all samples, while Gly and Arg were generally the most digested. Compared to the ADC of crude protein, the ADCs for Thr and Cys were 3–4% lower, while arginine ADC was 2–3% higher. The ADCs for Lys and Met were similar to that of crude protein, although Lys and Met digestibility may be overestimated due to their high solubility in seawater.