Bifidobacteria and lactobacilli due to their health promoting activity are commonly used as probiotic in dairy products for human consumption. Their suggested effective concentration is up to 106CFU/g of product. The correct identification and the monitoring of viable probiotics in the final product is an indispensable prerequisite for applications in industrial processes and in safety and quality control applications. The aim of this study was the optimization of routine laboratory methods for the enumeration and identification of probiotic species commercialized in dairy products. Nine fermented milk products of different marketed brands, purchased in Italian supermarkets, were tested. In these products, with or without starter cultures, Bifidobacterium animalis subsp.lactis and/or L. acidophilus, L. casei, L. johnsonii, L. paracasei, L. rhamnosus have been declared in the product label. The shelflife for all the products was about 20 days. Bifidobacteria were counted in TPY-mupirocin medium while lactobacilli were all counted using MRS-bile both in aerobiosis and anaerobiosis; in anaerobiosis MRS-pH 5.4 for L. acidophilus, L. johnsonii and L. paracasei, and MRS-vancomycin for L. casei and L. rhamnosus were also used. The obtained isolates have been catalogued basing on cell morphology and identified by species-specific PCR and ERIC-PCR. TPY-mupirocin has been confirmed as an optimal selective media for bifidobacteria; for L. rhamnosus and L. paracasei all the media tested were suitable while for L. acidophilus and L. johnsonii MRS-pH5.4 gave better results. All the probiotic dairy products contained the recommended levels of 106–107 CFU/g probiotic bacteria except one brand with 105 CFU/g. Morphology cannot help in distinguishing between the species L. casei, L. paracasei and L. johnsonii while L. acidophilus and L. rhamnosus show peculiar morphology; B. animalis subsp.lactis show the typical "bone" morphology. The present work confirm that ERIC-PCR is a valuable method to rapidly discriminate between lactobacilli closely related species while species-specific PCR does not discriminate between L. casei and L. paracasei. All the products declaring the presence of L. casei in the label actually contain L. paracasei.
Selective media and identification methods for probiotics in commercial dairy products / Lazzaroni S.; Pavon Y.; Rozicki S.; Modesto M.; Biavati B.; Di Gioia D.; Mattarelli P.. - STAMPA. - (2012), pp. 687-687. (Intervento presentato al convegno 23rd International Symposium FoodMicro 2012 - tenutosi a Istanbul nel 3-7 September 2012).
Selective media and identification methods for probiotics in commercial dairy products
MODESTO, MONICA MARIANNA;BIAVATI, BRUNO;DI GIOIA, DIANA;MATTARELLI, PAOLA
2012
Abstract
Bifidobacteria and lactobacilli due to their health promoting activity are commonly used as probiotic in dairy products for human consumption. Their suggested effective concentration is up to 106CFU/g of product. The correct identification and the monitoring of viable probiotics in the final product is an indispensable prerequisite for applications in industrial processes and in safety and quality control applications. The aim of this study was the optimization of routine laboratory methods for the enumeration and identification of probiotic species commercialized in dairy products. Nine fermented milk products of different marketed brands, purchased in Italian supermarkets, were tested. In these products, with or without starter cultures, Bifidobacterium animalis subsp.lactis and/or L. acidophilus, L. casei, L. johnsonii, L. paracasei, L. rhamnosus have been declared in the product label. The shelflife for all the products was about 20 days. Bifidobacteria were counted in TPY-mupirocin medium while lactobacilli were all counted using MRS-bile both in aerobiosis and anaerobiosis; in anaerobiosis MRS-pH 5.4 for L. acidophilus, L. johnsonii and L. paracasei, and MRS-vancomycin for L. casei and L. rhamnosus were also used. The obtained isolates have been catalogued basing on cell morphology and identified by species-specific PCR and ERIC-PCR. TPY-mupirocin has been confirmed as an optimal selective media for bifidobacteria; for L. rhamnosus and L. paracasei all the media tested were suitable while for L. acidophilus and L. johnsonii MRS-pH5.4 gave better results. All the probiotic dairy products contained the recommended levels of 106–107 CFU/g probiotic bacteria except one brand with 105 CFU/g. Morphology cannot help in distinguishing between the species L. casei, L. paracasei and L. johnsonii while L. acidophilus and L. rhamnosus show peculiar morphology; B. animalis subsp.lactis show the typical "bone" morphology. The present work confirm that ERIC-PCR is a valuable method to rapidly discriminate between lactobacilli closely related species while species-specific PCR does not discriminate between L. casei and L. paracasei. All the products declaring the presence of L. casei in the label actually contain L. paracasei.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
