Mozzarella is one of the most known Italian traditional fresh cheeses, usually stored into a cold governing liquid in order to maintain its typical organoleptic characteristics. These storage conditions favour the growth of psychrotrophic bacteria among which some are responsible for cheese spoilage. In this work, bovine lactoferrin (BLF) and its pepsin-digested hydrolysate (LFH) were tested in vitro to evaluate their efficacy as potential control agents of Mozzarella cheese spoilage bacteria growing during refrigeration period. At first, five bacterial strains (Pseudomonas fragi 23A, P. gessardi 2A, Serratia proteamaculans 19A, Aeromonas salmonicida 22DB and Rahnella aquatilis 19B), previously isolated from different cold-stored Mozzarella cheese samples, were tested for their ability to grow at 4 °C in the governing liquid-based medium, in which Mozzarella releases debris, sugars and salts, and to promote proteolytic activities against casein fractions. In order to check the efficacy of BLF or LFH to control spoilage bacteria, target strains were inoculated in the governing liquid-based medium at two levels of initial inoculum (3 and 6 log cfu/mL), and incubated at 4 °C or 30 °C for two weeks. At the initial inoculum of 3 log cfu/mL all strains grew well in the governing liquid at 4 °C, reaching 7.1 log cfu/mL, on average, after four days of cold storage. The most proteolytic strains were P. gessardi 2A and P fragi 23A that were able to digest completely all casein fractions, flowed into the governing liquid, after five and eight days, respectively. The remaining strains caused the disappearance of some casein bands on SDS-PAGE patterns, after twelve days of incubation. Viable cells of P. gessardi 2A and R. aquatilis 19B were undetectable when 3 log cfu/ml of each microorganism were inoculated in the governing liquid supplemented with 10 mg/mL of LFH. S. proteomaculans 19A, A. salmonicida 22DB and P. fragi 23A resulted partially inhibited as their bacterial loads resulted 2.3 log cfu/mL, on average, lower than those of the un-supplemented control up to day 5 of cold storage. After additional two days at 4 °C, this difference decreased by 1 log cfu/mL. The inhibitory activity of LFH resulted higher than BLF against all strains grown in the governing liquid-based medium. No antimicrobial activity was observed when the governing liquid, amended with BLF or LFH, was inoculated with target strains at 6 log cfu/mL. Also the increase in temperature of incubation advantaged microbial cells, reducing the inhibitory efficacy of BLF and LFH: after one day of incubation at 30 °C, a decrease of bacterial growth was registered only for P. fragi 23A and R. aquatilis 19B and only at 3 log cfu/ml of initial inoculum level. As expected, casein band intensities in SDS-PAGE patterns were comparable with those of the uninoculated control sample only in experiments showing the lowest microbial viable cell concentration. In conclusion, we demonstrate the efficacy of LFH to control some psychrotrophic proteolytic bacteria during the early days of cold storage and at a low initial microbial concentration. In any way, the addition of LFH in the governing liquid makes it feasible to extend the shelf-life of traditional Mozzarella cheese when other factors, as microbial milk quality, hygienic procedures and maintenance of refrigeration temperature, are met.
Control of Mozzarella spoilage bacteria by using bovine lactoferrin pepsin-digested hydrolysate
Quintieri L;Caputo L;Morea M;Baruzzi F
2012
Abstract
Mozzarella is one of the most known Italian traditional fresh cheeses, usually stored into a cold governing liquid in order to maintain its typical organoleptic characteristics. These storage conditions favour the growth of psychrotrophic bacteria among which some are responsible for cheese spoilage. In this work, bovine lactoferrin (BLF) and its pepsin-digested hydrolysate (LFH) were tested in vitro to evaluate their efficacy as potential control agents of Mozzarella cheese spoilage bacteria growing during refrigeration period. At first, five bacterial strains (Pseudomonas fragi 23A, P. gessardi 2A, Serratia proteamaculans 19A, Aeromonas salmonicida 22DB and Rahnella aquatilis 19B), previously isolated from different cold-stored Mozzarella cheese samples, were tested for their ability to grow at 4 °C in the governing liquid-based medium, in which Mozzarella releases debris, sugars and salts, and to promote proteolytic activities against casein fractions. In order to check the efficacy of BLF or LFH to control spoilage bacteria, target strains were inoculated in the governing liquid-based medium at two levels of initial inoculum (3 and 6 log cfu/mL), and incubated at 4 °C or 30 °C for two weeks. At the initial inoculum of 3 log cfu/mL all strains grew well in the governing liquid at 4 °C, reaching 7.1 log cfu/mL, on average, after four days of cold storage. The most proteolytic strains were P. gessardi 2A and P fragi 23A that were able to digest completely all casein fractions, flowed into the governing liquid, after five and eight days, respectively. The remaining strains caused the disappearance of some casein bands on SDS-PAGE patterns, after twelve days of incubation. Viable cells of P. gessardi 2A and R. aquatilis 19B were undetectable when 3 log cfu/ml of each microorganism were inoculated in the governing liquid supplemented with 10 mg/mL of LFH. S. proteomaculans 19A, A. salmonicida 22DB and P. fragi 23A resulted partially inhibited as their bacterial loads resulted 2.3 log cfu/mL, on average, lower than those of the un-supplemented control up to day 5 of cold storage. After additional two days at 4 °C, this difference decreased by 1 log cfu/mL. The inhibitory activity of LFH resulted higher than BLF against all strains grown in the governing liquid-based medium. No antimicrobial activity was observed when the governing liquid, amended with BLF or LFH, was inoculated with target strains at 6 log cfu/mL. Also the increase in temperature of incubation advantaged microbial cells, reducing the inhibitory efficacy of BLF and LFH: after one day of incubation at 30 °C, a decrease of bacterial growth was registered only for P. fragi 23A and R. aquatilis 19B and only at 3 log cfu/ml of initial inoculum level. As expected, casein band intensities in SDS-PAGE patterns were comparable with those of the uninoculated control sample only in experiments showing the lowest microbial viable cell concentration. In conclusion, we demonstrate the efficacy of LFH to control some psychrotrophic proteolytic bacteria during the early days of cold storage and at a low initial microbial concentration. In any way, the addition of LFH in the governing liquid makes it feasible to extend the shelf-life of traditional Mozzarella cheese when other factors, as microbial milk quality, hygienic procedures and maintenance of refrigeration temperature, are met.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
