Purification and characterization of ß-galactosidase from probiotic Pediococcus acidilactici and its use in milk lactose hydrolysis and galactooligosaccharide synthesis.

ß-galactosidase is a commercially important enzyme that was purified from probiotic Pediococcus acidilactici. The enzyme was extracted from cells using sonication and subsequently purified using ammonium sulphate fractionation and successive chromatographies on Sephadex G-100 and Q-Sepharose. The enzyme was purified 3.06-fold up to electrophoretic homogeneity with specific activity of 0.883 U/mg and yield of 28.26%. Molecular mass of ß-galactosidase as estimated by SDS-PAGE and MALDI-TOF was 39.07 kDa. The enzyme is a heterodimer with subunit mass of 15.55 and 19.58 kDa. The purified enzyme was optimally active at pH 6.0 and stable in a pH range of 5.8-7.0 with more than 97% activity. Purified ß-galactosidase was optimally active at 50 °C. Kinetic parameters Km and Vmax for purified enzyme were 400 µM and 1.22 × 10-1 U respectively. Its inactivation by PMSF confirmed the presence of serine at the active site. The metal ions had different effects on enzyme. Ca2+, Mg2+ and Mn2+ slightly activated the enzyme whereas NH4+, Co2+ and Fe3+ slightly decreased the enzyme activity. Thermodynamic parameters were calculated that suggested that ß-galactosidase is less stable at higher temperature (60 °C). Purified enzyme effectively hydrolysed milk lactose with lactose hydrolysing rate of 0.047 min-1 and t1/2 of 14.74 min. This is better than other studied ß-galactosidases. Both sonicated Pediococcus acidilactici cells and purified ß-galactosidase synthesized galactooligosaccharides (GOSs) as studied by TLC at 30% and 50% of lactose concentration at 47.5 °C. These findings indicate the use of ß-galactosidase from probiotic bacteria for producing delactosed milk for lactose intolerant population and prebiotic synthesis. pH and temperature optima and its activation by Ca2+ shows that it is suitable for milk processing.

Extraction, purification and characterization of low molecular weight Proline iminopeptidase from probiotic L. plantarum for meat tenderization.

Membrane bound proline iminopeptidase (PIP) from lactic acid bacteria (LAB) L. plantarum was extracted and purified using CM-sephadex, Sephadex G-100 and Q-sepharose column chromatography. PIP was purified with purification fold 7.13 and 33.5% yield. SDS-PAGE and MALDI-TOF revealed it as homodimer with molecular weight of 37.9 kDa and subunit of mass 18.9 kDa. Purified enzyme exhibited maximum activity at 45 °C and pH 7.0. Km and Vmax of purified PIP were 65 µM and 25.9 nm/min/ml respectively. Inhibition by PMSF confirmed it a serine protease. Metal ions and EDTA showed no effect on enzyme activity. The enzyme mainly hydrolysed Pro-4mßNA. The effectiveness of enzyme in purified form, membrane bound form and in combination with other enzymes to degrade collagen resulting in pharmaceutically significant collagen hydrolysates and in meat tenderization marks its industrial importance. There are very few PIPs are characterized from LAB, and therefore this study is industrially significant and brings some new knowledge into this area.

Dipeptidyl peptidase-II from probiotic Pediococcus acidilactici: Purification and functional characterization.

Dipeptidylpeptidase-II (DPP-II, E.C. 3.4.14.2), an exopeptidase was purified 15.4 fold with specific activity and yield of 15.4U/mg/mL and 14.68% respectively by a simple two step procedure from a probiotic Pediococcus acidilactici. DPP-II is 38.7KDa homodimeric serine peptidase with involvement of His and subunit mass of 18.9KDa. The enzyme exhibited optimal activity at pH 7.0 and 37°C with activation energy of 24.97kJ/mol. The enzyme retained more than 90% activity upto 50°C thus adding industrial importance. DPP-II hydrolysed Lys-Ala-4mßNA with KM of 50µM and Vmax of 30.8nmol/mL/min. In-silico characterization studies of DPP-II on the basis of peptide fragments obtained by MALDI-TOF revealed an evolutionary relationship between DPP-II of prokaryotes and phosphate binding proteins. Secondary and three-dimensional structure of enzyme was also deduced by in-silico approach. Functional studies of DPP-II by TLC and HPLC-analysis of collagen degraded products revealed that enzyme action released free amino acids and other metabolites. Microscopic and SDS-PAGE analysis of enzyme treated analysis of chicken's chest muscle (meat) hydrolysis revealed change and hydrolysis of myofibrils. This may affect the flavor and texture of meat thereby suggesting its role in meat tenderization. Being a protein of LAB (Lactic acid bacteria), it is also expected to be safe.