The Impact of NaCl Substitution with KCl on Proteinase Activities Cell-Free Extract and Cell-Free Supernatant at Different pH Levels and Salt Concentrations: Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus

Authors

  • M. M. Ayyash,

    1. Authors Ayyash and Shah are with the School of Biomedical and Health Sciences, Victoria Univ., Werribee Campus, P.O. Box 14428, Melbourne, Victoria 8001, Australia. Author Sherkat is with the School of Applied Sciences, RMIT Univ., P.O. Box 2476, Melbourne, Victoria 3001, Australia. Author: Shah is with the School of Biological Sciences, The Univ. of Hong Kong, Pokfulam Road, Hong Kong. Direct inquiries to author Shah (E-mail: npshah@hku.hk).
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  • F. Sherkat,

    1. Authors Ayyash and Shah are with the School of Biomedical and Health Sciences, Victoria Univ., Werribee Campus, P.O. Box 14428, Melbourne, Victoria 8001, Australia. Author Sherkat is with the School of Applied Sciences, RMIT Univ., P.O. Box 2476, Melbourne, Victoria 3001, Australia. Author: Shah is with the School of Biological Sciences, The Univ. of Hong Kong, Pokfulam Road, Hong Kong. Direct inquiries to author Shah (E-mail: npshah@hku.hk).
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  • N. P. Shah

    1. Authors Ayyash and Shah are with the School of Biomedical and Health Sciences, Victoria Univ., Werribee Campus, P.O. Box 14428, Melbourne, Victoria 8001, Australia. Author Sherkat is with the School of Applied Sciences, RMIT Univ., P.O. Box 2476, Melbourne, Victoria 3001, Australia. Author: Shah is with the School of Biological Sciences, The Univ. of Hong Kong, Pokfulam Road, Hong Kong. Direct inquiries to author Shah (E-mail: npshah@hku.hk).
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Abstract

Abstract:  The effect of NaCl substitution with KCl at different pH levels (6.0, 5.5, and 5.0) and salt concentrations on proteinase activities of cell-free and supernatant of Lactobacillus delbrueckii ssp. bulgaricus 11824 (L. bulgaricus) and Streptococcus thermophilus MS (ST) was investigated. MRS broths were separately mixed with 4 salt treatments (NaCl only, 1NaCl:1KCl, 1NaCl:3KCl, and KCl only) at 2 different concentrations (5% and 10%) and incubated at 37 °C for 22 h. The cell pellets were used to prepare proteinase of cell-free extract and the cell-free supernatants were used as source of extracellular proteinases. The proteolytic activities and protein contents of both fractions were determined. The supernatants after incubation of both fractions with 3 milk caseins (α-, β-, κ-casein) were subjected to angiotensin-converting-enzyme inhibitory (ACE-inhibitory) activity and proteolytic activity by ortho-phthalaldehyde (OPA) method. Significant differences were observed in ACE-inhibitory activities and proteolytic (OPA) between salt treatments of cell-free extract and cell-free supernatant of L. bulgaricus and S. thermophilus at same salt concentration and same pH level. There was a significant effect of pH level and salt treatments interaction on ACE-inhibitory activity, OPA activity and azocasein activity.

Practical Application:  To reduce sodium concentration in cheese by substituting of NaCl with KCl, it was important to study the effect on starter culture proteinases which play a vital role in ripening and texture profile of cheese.

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