Effect of Chemico-Physical Parameters on the Histidine Decarboxylase (HdcA) Enzymatic Activity in Streptococcus thermophilus PRI60

Authors

  • Giulia Tabanelli,

    1. Authors Tabanelli and Gardini are with Dipto. di Scienze degli Alimenti, Univ. degli Studi di Bologna, Piazza Goidanich 60, 47023 Cesena, Italy. Authors Torriani, Rossi, and Rizzotti are with Dipto. di Biotecnologie, Univ. degli Studi di Verona, Strada Le Grazie 8, 37134 Verona, Italy. Direct inquiries to author Gardini (E-mail: fausto.gardini@unibo.it).
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  • Sandra Torriani,

    1. Authors Tabanelli and Gardini are with Dipto. di Scienze degli Alimenti, Univ. degli Studi di Bologna, Piazza Goidanich 60, 47023 Cesena, Italy. Authors Torriani, Rossi, and Rizzotti are with Dipto. di Biotecnologie, Univ. degli Studi di Verona, Strada Le Grazie 8, 37134 Verona, Italy. Direct inquiries to author Gardini (E-mail: fausto.gardini@unibo.it).
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  • Franca Rossi,

    1. Authors Tabanelli and Gardini are with Dipto. di Scienze degli Alimenti, Univ. degli Studi di Bologna, Piazza Goidanich 60, 47023 Cesena, Italy. Authors Torriani, Rossi, and Rizzotti are with Dipto. di Biotecnologie, Univ. degli Studi di Verona, Strada Le Grazie 8, 37134 Verona, Italy. Direct inquiries to author Gardini (E-mail: fausto.gardini@unibo.it).
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  • Lucia Rizzotti,

    1. Authors Tabanelli and Gardini are with Dipto. di Scienze degli Alimenti, Univ. degli Studi di Bologna, Piazza Goidanich 60, 47023 Cesena, Italy. Authors Torriani, Rossi, and Rizzotti are with Dipto. di Biotecnologie, Univ. degli Studi di Verona, Strada Le Grazie 8, 37134 Verona, Italy. Direct inquiries to author Gardini (E-mail: fausto.gardini@unibo.it).
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  • Fausto Gardini

    1. Authors Tabanelli and Gardini are with Dipto. di Scienze degli Alimenti, Univ. degli Studi di Bologna, Piazza Goidanich 60, 47023 Cesena, Italy. Authors Torriani, Rossi, and Rizzotti are with Dipto. di Biotecnologie, Univ. degli Studi di Verona, Strada Le Grazie 8, 37134 Verona, Italy. Direct inquiries to author Gardini (E-mail: fausto.gardini@unibo.it).
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Abstract

Abstract:  In this study the activity of the histidine decarboxylase (HdcA) of Streptococcus thermophilus PRI60 was determined during growth and in crude enzyme preparations to evaluate its hazardousness in dairy products. The effect of different pH values, lactose availability, NaCl concentration, and growth temperature on histamine production was evaluated in M17 medium during 168 h incubation. In each case, the production of histamine increased concomitantly with the cell number with a relatively small further rise during the stationary phase. In all cultures the maximum histamine levels were reached at the end of active growth. Histamine was detectable (10 to 55 mg/L) even when growth was strongly inhibited. The HdcA enzyme in crude cell-free extracts was mostly active at acidic pH values common in dairy products. NaCl concentrations lower than 5% did not affect its activity. The enzyme was quite resistant to heat treatments resembling low pasteurization, but was inactivated at 75 °C for 2 min. Given the features of the enzyme studied, efforts must be dedicated to a thorough risk analysis and development of strategies to contrast the presence of histaminogenic S. thermophilus strains in products from raw or mildly heat-treated milk.

Practical Application:  During its growth Streptococcus thermophilus can produce histamine over a wide range of conditions encountered in cheesemaking and cheese ripening. The histidine-decarboxylase is even more active in cell-free extract and histamine can be accumulated independently of cell viability.

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