Evaluating the palatability of fermented foods

ABSTRACT

The present review deal with the novel studies which present possibility of generating a novel sensory evaluation instrument for describing comprehensive food palatability. These studies suggest the palatability can be dissected into its componential subdomains and the subdomains in turn reconstitute comprehensive palatability with evaluation of the quantitative contribution of each subdomain. The studies suggest the novel instrument is useful for comprehensive evaluation of palatability of multifarious fermented foods.     

Effect of cheese consumption on emergence of antimicrobial resistance in the intestinal microflora induced by a short course of amoxicillin-clavulanic acid

AIM: To study in a sequential prospective trial, the effect of cheese consumption on the emergence of Escherichia coli and enterococci resistance to amoxicillin after amoxicillin-clavulanic acid (amoxiclav) treatment. METHODS AND RESULTS: The study comprised two phases separated by 1 year. Each phase lasted 75 days for each volunteer (from day -13 to day 61). During the first phase, 18 healthy volunteers were given a 1-g dose of amoxiclav orally twice a day for 5 days (from day 0 to day 4). The design of phase 2 was identical to that of phase 1, except that the volunteers consumed 100 g of hard-cooked cheese from day -6 to day 19. Faecal samples were collected 20 times throughout the trial and were quantitatively assayed for total and amoxicillin-resistant (Amox(R)) E. coli and enterococci. The consumption of experimental cheese was associated with a decrease of Amox(R) enterococci during the post-antibiotic period, with the maximum level of Amox(R) enterococci falling from 6.2% to 0.03%. This effect was not observed for E. coli, and the type of cheese (raw milk vs pasteurized milk) did not influence the results. CONCLUSIONS: Consumption of cheese during amoxiclav treatment reduces the emergence of Amox(R) enterococci in faeces. SIGNIFICANCE AND CLINICAL IMPACT OF THE STUDY: Our clinical pilot trial suggests that there are likely to be benefits from consuming probiotic-containing cheese during antibiotic treatment.     

Whey-cheese production using freeze-dried kefir culture as a starter

AIMS: The aim of the present study was to evaluate the use of a freeze-dried kefir culture in the production of a novel type of whey-cheese similar to traditional Greek Myzithra-cheese, to achieve improvement of the quality characteristics of the final product and the extension of shelf-life. METHODS AND RESULTS: The use of kefir culture as a starter led to increased lactic acid concentrations and decreased pH values in the final product compared with whey-cheese without starter culture. The effect of the starter culture on production of aroma-related compounds responsible for cheese flavour was also studied using the solid phase microextraction gas chromatography/mass spectrometry technique. Spoilage in unsalted kefir-whey-cheese was observed on the thirteenth and the twentieth day of preservation at 10 and 5 degrees C, respectively, while the corresponding times for unsalted whey-cheese preservation were 11 and 14 days. CONCLUSIONS: The cheeses produced were characterized as high-quality products during the preliminary sensory evaluation. An indication of increased preservation time was attributed to the freeze-dried kefir culture, which also seemed to suppress growth of pathogens. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggested the use of kefir culture as a means to extend the shelf-life of dairy products with reduced or no salt content.     

Acid adaptation and survival of Listeria monocytogenes in Italian-style soft cheeses

AIMS: The ability of Listeria monocytogenes to survive and grow at high salt concentrations and low pH makes it a potential hazard after the consumption of milk and dairy products, often implicated in severe outbreaks of listeriosis. This study was designed to evaluate the behaviour of L. monocytogenes in traditional acid and salted Italian-style soft cheeses and to investigate whether Listeria occurrence and growth in these environments may represent a potential increase of hazard. METHODS AND RESULTS: A first approach was addressed to in vitro evaluate survival, acid tolerance response, ability to produce biofilm, and capability to invade intestinal-like cells of a L. monocytogenes strain grown under experimental conditions mimicking environmental features that this pathogen encounters in soft cheeses (such as acid pH and high NaCl content). A second set of experiments was performed to monitor, during the storage at 4 degrees C, the survival of acid-adapted and nonadapted Listeriae in artificially contaminated soft cheeses. Both acid tolerance response and invasion efficiency of acid-adapted bacteria resulted in an increase, even when bacteria were simultaneously pre-exposed to increasing salt stress. The contamination of cheeses with acid-adapted and nonadapted bacteria evidenced in all products a good survival. A significant increased survival, the recovery of bacterial cells highly resistant to lethal pH exposure, and the prevalence of filamentous structures were observed in crescenza cheese during the storage. CONCLUSIONS: The Listeria survival and acid pH tolerance observed during refrigerated storage are probably related to the intrinsic acid and saline features of soft cheeses analysed. SIGNIFICANCE AND IMPACT OF THE STUDY: Italian soft cheeses tested may represent a potential hazard for the recovery of acid-adapted L. monocytogenes cells with enhanced ability to adhere to inert surfaces and/or to penetrate host cells.     

Survival of surface ripening cultures during storage and monitoring their development on cheese

AIMS: To study the survival of bacteria isolated from the surface of smear cheese and monitor their development during cheese ripening. METHODS AND RESULTS: The storage of five potential bacterial surface-ripening cheese cultures, Brevibacterium aurantiacum, Corynebacterium casei, Corynebacterium variable, Microbacterium gubbeenense and Staphylococcus saprophyticus, in maximum recovery diluent (MRD), containing 0.85% w/v or 5% w/v NaCl, at 21 or 4 degrees C for 40 days, was investigated. All five strains studied survived well with a maximum decrease of c. 2.5 log(10) CFU ml(-1) after storage for 40 days at 4 degrees C in 0.85% or 5% w/v NaCl. Survival, especially of C. variable, was less at 21 degrees C. The development of defined ripening cultures containing C. casei and Debaryomyces hansenii on two farmhouse cheeses was also evaluated. Using pulsed-field gel electrophoresis (PFGE) for the bacteria and mitochondrial DNA restriction fragment length polymorphism (mtDNA-RFLP) for the yeast, it was shown that the ripening cultures could be re-isolated in high numbers, 10(8) CFU cm(-2) for C. casei and 10(6) CFU cm(-2) for D. hansenii, from the cheese surface after 2.5 weeks of ripening. CONCLUSIONS: Ripening strains of surface ripening cultures can be stored in MRD containing 5% w/v salt at 4 degrees C for at least 40 days. Such cultures are recovered in high numbers from the cheese during ripening. SIGNIFICANCE AND IMPACT OF STUDY: This study has provided a low-cost and efficient way to store bacteria that could be used as ripening cultures for smear cheese. Such cultures can be recovered in high numbers from the cheese surface during ripening.     

The effect of low pressure-homogenized lactic cultures on the development of proteolysis in cheese slurry

Summary The aim of this study was to determine the effect of low pressure-homogenization of lactic acid bacteria (LAB) on the development of proteolysis in the slurry medium. For the slurry, the milk was pasteurized at 65 °C for 30 min, cooled to 32 °C and coagulated. The curd obtained was blended; the dry matter was adjusted to 30% by adding distilled water, placed into the flasks and autoclaved. The LAB Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris, Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, and Lactobacillus helveticus were used in cheese slurry. Homogenization was performed at 30 MPa and 40 °C. The cheese slurries were incubated with and without homogenized cultures at 9 and 30 °C for up to 72 h. During incubation, the changes in trichloroacetic acid-soluble nitrogen (TCA-SN) and phosphotungstic acid-soluble nitrogen (PTA-SN) as well as pH were monitored. The results showed that pH development was slower in the slurries to which homogenized culture was added. Higher TCA-SN and PTA-SN values were obtained from the slurries incubated at 30 °C. Moreover, higher TCA-SN and PTA-SN values were found in the slurries incubated with homogenized mesophilic culture and Lb. helveticus (P<0.05). The results suggested that homogenization of the cultures was a promising method for the acceleration of cheese ripening.     

Microbiological characterization of Civil cheese, a traditional Turkish cheese: microbiological quality, isolation and identification of its indigenous Lactobacilli

Summary The aim of this study was to investigate the microbiological quality and the indigenous lactic acid bacteria (Lactobacillus) of Civil cheese. In this study, for identification of lactic acid bacteria isolated from cheese samples, the Microbiology Identification System (MIS) was used. In the samples, average of total aerobic mesophilic bacteria, yeast and moulds, lactic acid bacteria and Staphylococcus aureus (Staph. aureus) were determined to be 3.0×10⁸, 2.0×10⁶, 1.4×10⁷, 4.10×10⁴ c.f.u./g, respectively. Coliform bacteria were lower than <10 c.f.u./g in 26.67 % of the samples. On the other hand, the coliform-positive samples showed an average of 4.2×10⁴ c.f.u./g. Staph. aureus was not detected in 33.33% of Civil cheese samples. Seventy-two strains of Lactobacillus isolated from Civil cheese were identified. Growth at 5, 10 and 37 °C, 2.5% and 6.5% NaCl and gas (CO₂) production from glucose of the isolated strains were also determined. Of the 72 isolates, 20 were identified as Lb. malefermentans, 18 as Lb. fermentum, 17 as Lb. parabuchneri, 10 as Lb. vaccinostercus, 2 as Lb. oris, 1 as Lb. bifermentans, 1 as Lb. delbruecki subsp. bulgaricus, 1 as Lb. cellobiosus, 1 as Lb. hilgardii, 1 as Lb. paracasei subsp. tolerans.     

Maturing dynamics of surface microflora in Fontina PDO cheese studied by culture-dependent and -independent methods

Aims:  To study the evolution of rind microbial communities in Fontina PDO cheese.
Methods and Results:  Four batches were examined for their surface microflora during ripening, carried out in two different maturing caves, at Ollomont and Pré-Saint-Didier, Aosta Valley region, Northwest of Italy. Culture-dependent methodologies were combined with culture-independent analysis (PCR-DGGE). Yeasts were found to increase from 10³ to 10⁶ CFU cm⁻² in 28 days, with consequent rise of surface pH, which allowed the growth of salt-tolerant bacteria, in particular coryneforms which reached 10⁹ CFU cm⁻² at the end of 3 months. Coagulase-negative cocci and lactic acid bacteria reached 10⁷ CFU cm⁻² in the same period. Debaryomyces hansenii and Candida sake were the species more constantly present throughout the whole maturing process. As early as after 1 day since manufacture, Lactococcus lactis subsp. lactis and Streptococcus thermophilus were detected on cheese rinds. Arthrobacter nicotianae , Brevibacterium casei and Corynebacterium glutamicum were found after 7–28 days .
Conclusions:  According to cluster analysis of DGGE profiles, the maturing environment seemed to influence the dynamics of microbial groups on Fontina surfaces.
Significance and Impact of the Study:  These results represent a first picture of micro-organisms colonizing Fontina PDO rinds. Further studies are in progress to better understand the origin of this surface microflora and to formulate surface starters.     

The effect of carbon and nitrogen sources on bovicin HC5 production by Streptococcus bovis HC5

Aims:  To investigate the effect of media composition and agroindustrial residues on bovicin HC5 production by Streptococcus bovis HC5.
Methods and Results:  Batch cultures of S. bovis HC5 were grown in basal medium containing different carbon and nitrogen sources. The activity of cell-free and cell-associated bovicin HC5 was determined in culture supernatants and acidic extracts obtained from cell pellets, respectively. Streptococcus bovis HC5 produced bovicin using a variety of carbon and nitrogen sources. The highest specific activity was obtained in media containing 16 g l⁻¹ of glucose, after 16 h of incubation. The peak in cell-free and cell-associated bovicin HC5 activity was detected when S. bovis HC5 cultures reached stationary phase. The bovicin HC5 specific activity and bacterial cell mass increased approximately 3-fold when yeast extract and trypticase (0·5 and 1·0 g l⁻¹, respectively) were added together to the basal medium. Streptococcus bovis HC5 cultures produced bovicin HC5 in cheese whey and sugar cane juice and maximal volumetric productivity was obtained after 12 h of incubation.
Conclusions:  Streptococcus bovis HC5 is a versatile lactic acid bacterium that can utilize several carbon and nitrogen sources for bovicin HC5 production. This bacterium could be a useful model to study bacteriocin production in the rumen ecosystem.
Significance and Impact of the Study:  The use of agroindustrial residues as carbon sources could have an economical impact on bovicin HC5 production. To our knowledge, this is the first report to show the use of sugar cane juice for bacteriocin production by lactic acid bacteria.