**2.1 Soybean (***Glycine max***)**

Soybean (*Glycine max*) is the leading oilseed crop in the world and occupies the first place as a global APS for FM due to its large amounts of protein ( 40%) and reasonable EAA profile as well as its most availability in the global market [8]. Moreover, owing to genetic engineering technologies and plant biotechnology available for the crop, the output traits of soybean also improved for aquaculture purposes [15]. The global production of soybean was estimated to be 336.7 MT in 2020 and projected to reach to 371.3 MT in 2030 with annual growth rate of 1.8% from 2020 to 2030. A huge amount of this crop used for oil extraction that yield a cake with high levels of protein that will be processed to a wide range of soy products including soy flour, soybean meal (SBM), full-fat SBM, soy protein concentrate (SPC), soy protein isolate (SPI), soy protein hydrolysate (SPH) and fermented SBM (FSBM).

## **2.2 Soybean meal**

Unprocessed SBM contains 30-50% protein, about 30% carbohydrates including oligosaccharides (*e.g.* stachyose and raffinose), starch and NSP (*e.g.* cellulose, hemicellulose, and pectins; **Table 1**) [16–18]. Except for cystine, the amounts of the EAA (mainly lysine, methionine and threonine; **Table 2**), taurine and tyrosine in SBM are generally lower than FM [8]. The protein level and EAA content can be enhanced by chemical processing of soy flakes to SPC and SPI or through hydrolysation and fermentation of SBM. In addition, high levels of ANF in SBM can be reduced by conventional processing (*e.g.* heat, autoclaving, and use of solvents).

#### **2.3 Soy protein concentrate**

Soy protein concentrate is commonly obtained by fractionation of SBM through aqueous alcohol that not only enhance protein content ( 70%) [19–21] by extracting carbohydrates but also remove ANF (*e.g.* saponin), soluble oligosaccharides and fiber [21–23] that eventually increase its palatability and protein digestibility [24]. Soy protein concentrate has been getting more attention in aquafeed industry because of its well-balanced AA profile compared to other APPS [23, 25].
