Aims: To screen various Streptomyces cultures producing l‐leucine aminopeptidase (LAP).
Methods and Results: Twenty‐one Streptomyces strains were screened for LAP production. The best three producers were found to be Streptomyces mobaraensis NRRL B‐3729, Streptomyces gedanensis IFO 13427, and Streptomyces platensis NRRL 2364. pH optima of the three enzymes were in the range of 8·0–8·5 and the temperature optima varied between 50 and 65°C. LAP of S. mobaraensis was stable at 60°C and pH 8·5 for 60 min. Metal ion salts, CoCl2.6H2O and ZnSO4.7H2O in 0·7 mmol l−1 concentration enhanced the relative enzyme activity in all three enzymes. Molecular mass of LAP of S. mobaraensis was found to be approx. 37 kDa.
Conclusions: Streptomyces mobaraensis NRRL B‐3729, S. gedanensis IFO 13427, and S. platensis NRRL 2364 were found to be good producers of extracellular LAP. The approx. 37 kDa enzyme of S. mobaraensis is considerably thermostable.
Significance and Impact of the Study: A good number of Streptomyces were screened and the ability of the aminopeptidases to release a particular N‐terminal amino acid along with its good thermal stability makes them interesting for controlling the degree of hydrolysis and flavour development for a wide range of substrate.
: The aim of the present study was to evaluate the efficiency of amino peptidase (AP) from Streptomyces gedanensis to produce protein hydrolysates (PHs) with better antioxidant, nutritional, and functional properties and to compare it with the PHs produced by commercial protease. Three proteins, soy, casein, and wheat protein were employed to produce their hydrolysates by applying 2% (w/w) AP at optimal conditions of pH 8.5 and temperature 55 °C. The results disclosed that the degree of hydrolysis ranges from 15.93 to 20.68% after 6 h showed better antioxidant activity and functional properties such as solubility, foaming properties, and water holding capacity than the commercial protease treated hydrolysates. AP treated PHs were enriched in Glu followed by Leu, Tyr, Lys, Phe, Asp, Met, His, Ile, Ala, and Val. Therefore, S. gedanensis AP would be an attractive microbial AP with high potential for the preparation of PHs which could offer industrial applications especially in the realm of producing food formulations as food additives in medicine and sport.
Practical Application: AP from S. gedanensis was found to be the most effective enzyme to produce PHs with good antioxidant, nutritional, and functional properties. The antioxidant and essential amino acids of AP treated PHs unveiled that this amino peptidase could give credence to eliminate the bitter taste by hydrolysis of peptides and could offer interesting possibilities for industrial applications, including debittering of protein hydrolysates. The findings could be useful in the food industry especially in the realm of producing food formulations requiring high protein supplements.
A bioprocess was developed for the production of L-leucine aminopeptidase under solid-state fermentation (SSF) by cultivating Streptomyces gedanensis in an inert support impregnated with a minimal medium. Response surface methodology of Box Behnken design was used to derive the optimum level of significant factors (3 ml inoculum (1.2 × 10(9) CFU/ml); 0.275% w/v (NH(4))(2)SO(4); 0.275% w/v MgSO(4)·7H(2)O and 0.55% w/v Tryptone) for maximum LAP production (489 IU/g PUF) as compared to the initial level of 176.3 ± 0.02 IU/g PUF. The high level of extracellular aminopeptidase yield achieved in this work showed the technical feasibility of LAP production under SSF using inert support and is the first report of this kind. The ability of Streptomyces amino peptidase to release particular N-terminal amino acids made them interesting for controlling the degree of hydrolysis and flavor development for a wide range of substrates in food like industries.
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