Abstract
This study was dedicated to increasing the efficiency of producing plant-based protein hydrolysate using traditional and non-traditional treatments. Low- and high frequency ultrasound (US) at different intensities were applied to corn steep liquor (CSL) at 50 °C for 30 min, and enzymatic hydrolysis was performed using industrially produced alkaline protease. The efficiency of US and enzymatic treatments was characterized by protein solubility (soluble protein (SP) content, hydrolyzed protein (HP) concentration, and free amino acid (FAA) profile) and kinetic parameters: Michaelis–Menten constant (KM) and apparent breakdown rate constant (kA). A significant effect of 37 kHz US pre-treatment for CSL enzymatic hydrolysis was found and resulted in the highest HP concentration (17.5 g/L) using the lowest enzyme concentration (2.1 g/L) and the shortest hydrolysis time (60 min). By using US pre-treatment, on average, a 2.2 times higher FAA content could be achieved compared to traditional hydrolysis. Additionally, results for the kinetic parameters kM and kA confirmed the potential of applying US treatment before hydrolysis. The effect of CSL protein hydrolysate on plant growth was tested in vivo on wheat grain seed germination and resulted in the significant increase in germination parameters compared to the control treatment. These findings indicate that by-products of starch industry could be a promising source for the production of low-cost sustainable biostimulants.
Highlights
This paper focused on the alkali-soluble proteins in corn steep liquor (CSL) and their hydrolysis into free amino acids (FAA) for biostimulant production
CSL is produced during corn starch production, and 44.4% of the protein
Our study on the application of low and high frequency US treatment before enzymatic hydrolysis to produce biostimulants enriched with FAA shows that CSL sonication could be an effective way to accelerate the hydrolysis process and enhance protein solubility
Summary
One major group of plant biostimulants is protein hydrolysates, defined as a mixture of peptides and amino acids [2]. One traditional option for processing protein hydrolysates is the use of biocatalysts to transform these residual feedstocks into high-value target protein hydrolysates. Microbial proteases such as Alcalase, Protamex, and Flavourzyme were used to hydrolyze corn gluten meal [3]. Amino acids are important for the central metabolism of seeds. They are used for the synthesis of seed-storage proteins; they are used as precursors for the production of secondary metabolites and as an energy source [4]. A number of studies confirmed that biostimulants based on amino acid have a significant impact on plant growth in winter wheat [6], lettuce [7], and soybean [8]
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