# Brewer's Spent Grains: Possibilities of Vaporization, a Review
## 3 Possible Uses of BSG
### Proteins, Protein Hydrolysates, Bioactive Peptides  
Because of the upward trend of vegetarianism and veganism, it is necessary to find sources of protein and natural protein derivatives from plants. There are several possibilities of using proteins derived from plants due to the functional effects on the human body (related to physiological and nutritional properties) and technical positive properties (related to physicochemical properties: appearance, texture, stability) as well as for nutrients for fortified foods and dietary supplements, technical-functional ingredients in terms of emulsification and gelification properties, or as materials for the development of biopolymers [67]. The application of proteins from BSG include antioxidant and antimicrobial packaging materials production, edible films (obtained from proteins and polysaccharides/ chitosan), complexing proteins, fermented beverages, cookies, enzymes, and edible proteins. Proteins and protein hydrolyses derived from BSG, as resulted from the study of [PERSON] et al. (2017) [9], present immunomodulatory effects that can be useful to anti-inflammatory diseases control, hypertension, and diabetes treatment [8]. The most abundant protein in BSG is horbein, with a content of 43% of the total content of proteins, followed by glutelins with 21.5% [9]. Amino acids play an important role in human health, and BSG is a good source of these components. Essential amino acids from BSG are methionine, phenylalanine, tryptophan, histidine, and lysine, and the non-essential are serine, alanine, glycine, and proline [9]. A study conducted by [PERSON] et al. (2019) revealed the fact that BSG has a similar composition in amino acids as in germinated barley--rich in glutamine/glutamic acid, vanillin, and leucine but with a smaller content of cysteine and methionine [68]. According to the studies of [PERSON] et al. (2018), protein products can be classified in:  
* protein containing flour up to 65% protein;
* protein hydrolyses containing concentrates between 65-90% protein;
* protein isolates containing more than 90% protein [67]. For an increased extraction yield, pretreatment BSG is applied (with diluted alkaline, enzymatic, or hydrothermal acids, or combinations thereof). Pretreatment with diluted acids can extract 90% of the total protein; it is not a selective method, extracting carbohydrates and lignin along with proteins. Hydrothermal pretreatment offers this selectivity, although the extraction yield is 64-66%, but it is a more environmentally friendly method, thus it is carried out at low temperatures and does not require the addition of chemicals [69]. The extraction methods used are largely synthesized in the following categories:* dry extraction techniques: fractions with high impurity and agglomerated particles. This category includes two-step electrostatic separation, which involves loading particles and separating them in an electric field [67];
* wet extraction techniques: acidic extractions are less effective because they do not degrade the cell wall, resulting in less protein in the extraction environment. Alkaline extractions are more effective but at high alkaline concentrations after the Maillard reaction, which affects the nutritional properties of proteins. Extracts with organic solvents are also used [68]. Combinations of water with enzymes, water in subcritical conditions, or protein extraction through reverse smalls attract more and more of the attention of researchers [67]. Alkalis are used as extraction solvents at high temperatures, followed by precipitation with alcohol or isoelectric precipitation, treatment with NaOH/KOH (0.1 M, 0.5 M, 4 M) for 24 h at room temperature, acidification with citric acid up to pH = 3, then precipitation with ethanol, an enzymatic hydrolysis-effective technique for extractions [9];
* other extraction methods are microwave-assisted extraction (MAE), ultrasonic-assisted extraction (EAU), electrically pulsed energy extraction, or extraction using high hydrostatic pressure [67].