**8. Hydrogen peroxide production**

The demonstration of hydrogen peroxide formation by meat-borne lactic acid bacteria is of considerable importance for the characterization of individual strains, the selection of suitable starter and protective cultures for various applications for meat and meat products as well as for the search of potential microbiological causes for undesired sensory deviations (discolourations/'greening', rancidity). Many LAB are able to form hydrogen peroxide as a by-product of O2-dependent metabolic pathways. Dependent on the environment, this trait may be desired or undesired [1,23,67,69,104].

In foods and feed it may contribute to the inhibition of an undesired accompanying microbiota [67]. The H2O2 formed by LAB acts bacteriostatic on GRAM-positive bacteria and bactericidal on Gram-negatives [12,68].

In a recent study a novel agar medium ('Prussian Blue' (PB) agar) was applied for the first time to lactic acid bacteria relevant to meat and meat products [69]. The PB agar detects H2O2 through the formation of Prussian Blue (Figure 5). It principally delivers similar results as the traditional manganese dioxide agar. However, it is more sensitive and, it is also more easily prepared and delivers results more quickly. A representative number of strains was used in the evaluation of the new medium (Table 2).

138 Lactic Acid Bacteria – R & D for Food, Health and Livestock Purposes

smoked salami

'probiotic poultry salami with three probiotic cultures (*Bifidus, Lb. casei, Lb. acidophilus*)'

Type soft, quickly ripened,

n. d., not determined; D, Germany; CH, Switzerland.

meat industry as a starter culture [66].

**8. Hydrogen peroxide production** 

may be desired or undesired [1,23,67,69,104].

bactericidal on Gram-negatives [12,68].

Characteristics pH 4.7;

Claims

advertised

detected potentially probiotic culture

Viable counts (cfu/g) of probiotic culture

Sausage no. 1 2 3 4

very hard, airdried salami

Origin D CH D D

culture detectable no not labeled yes not labeled

**Table 1.** Detection of probiotic cultures in probiotic raw fermented sausages from retail [57].

subsp. *paracasei*

bacteriocin-producing LAB with anti-listerial activity naturally occur on a wide range of ready-to-eat foods, including meats [63-65]. From a meat point of view the sakacins of *Lb. sakei* are the most interesting because of the high competitivity of this species in the meat environment [22,49]. The pediocin producer *Pc. acidilactici* is commonly used by the Spanish

The demonstration of hydrogen peroxide formation by meat-borne lactic acid bacteria is of considerable importance for the characterization of individual strains, the selection of suitable starter and protective cultures for various applications for meat and meat products as well as for the search of potential microbiological causes for undesired sensory deviations (discolourations/'greening', rancidity). Many LAB are able to form hydrogen peroxide as a by-product of O2-dependent metabolic pathways. Dependent on the environment, this trait

In foods and feed it may contribute to the inhibition of an undesired accompanying microbiota [67]. The H2O2 formed by LAB acts bacteriostatic on GRAM-positive bacteria and

In a recent study a novel agar medium ('Prussian Blue' (PB) agar) was applied for the first time to lactic acid bacteria relevant to meat and meat products [69]. The PB agar detects H2O2 through the formation of Prussian Blue (Figure 5). It principally delivers similar results

*Lb. rhamnosus Lb. paracasei* 

'probiotic', with beef and pork

aw 0.954 pH 5.6 pH 4.9 n. d.

1-6 x 107 4-9 x 107 3 x 107 1 x 107

quickly ripened, thincalibre, smoked sausage

'probiotic culture in high numbers (5x108 cfu/g)', with beef and pork

*Lb. paracasei* subsp. *paracasei* 

smoked, dryfermented salami with 30% weightloss

'Probiotic !!!, naturally ripened', with beef and vegetable fat (no lard)

*Lb. paracasei* subsp. *paracasei* 

As to the production of H2O2, the study revealed large differences within the *Lb. sakei/curvatus* group. The bacteriocin producers frequently seemed to be relatively weak peroxide producers, while many commercial starter cultures were recognized as more or less strong peroxide producers. More recent field isolates of *Lb. sakei/curvatus* from prepackaged sliced Bologna-type sausage gave an essentially similar picture. In this case, however, only one of ten isolates of *Lb. curvatus* gave rise to a positive reaction.


a) strains have been obtained from the German Collection of Microorganisms (DSM) and the strain collections of MRI Location Kulmbach (Lb) and INRA at Jouy-en-Josas (23K)

**Table 2.** Reaction of different LAB species on PB agar with BHI or MRS base, and on MnO2 agar. -, no production of H2O2 ; +/++/+++, moderate to strong production of H2O2 ; nd, not determined [69].

**Figure 5.** Reaction of different LAB species on MnO2 agar (A) and on PB agar with MRS (B) or BHI (C) base. Production of H2O2 is indicated by bright and blue halos, resp. [69].
