Production of a soybean meal with high-protein and low anti-nutritional factors for fish feed.

摘要

Aquaculture is one of the fastest growing areas of the food production system. According to the FAO, its rise is expected to continue through the year 2030 in order to maintain per-capita consumption levels required for the increasing population. Fishmeal--obtained from wild-harvested fish--has been the source of protein for fish feed. However, data indicates that these fish harvests are in decline, which could restrain that growth. The possibility of a shortage of fishmeal prompted the industry to look into possible alternatives. Soybean meal appears as a promising substitute since it is an affordable high quality source of protein. However, the presence of anti-nutritional factors--trypsin inhibitors, lectins, glycinin, beta-conglycinin, saponins, phytates, and oligosaccharides--can negatively affect the growth and the general health of fish, limiting its inclusion as fish food. Several studies have been done in order to reduce these anti-nutritional factors. However, there is no method that eliminates all of them while preserving the protein content of the soybean meal. The aim of this work was to obtain a protein-rich soybean meal with low anti-nutritional factors and a greater protein digestibility to be used for fish food. To accomplish this, the deactivation kinetics (D and Z-values) of glycinin and beta-conglycinin at different temperatures were studied using Differential Scanning Calorimetry (DSC). The reduction in the content of phytate was evaluated by pre-treatment of soybean meal with phytase. And lastly, Central Composite Rotatable Design (CCRD) was employed to determine the best combination of factors (temperature, time, pH, and ethanol concentration) that maximizes the extraction of soluble sugars, saponins, and phytate while increasing protein content and digestibility. Results indicated that the inclusion of phytase under different conditions reduced the phytate content. The CCRD determined that a pH of 4.5 at 59oC, 35% ethanol concentration for 65 minutes are the optimal conditions for the highest extraction of soluble anti-nutritional factors, which increased the content of total protein and digestibility of the soybean meal. However, according to the kinetics studies, the deactivation of glycinin--the more resistant of the two proteins--at this temperature is not complete.