Effect of Brazilian green propolis on microorganism contaminants of surface of Gorgonzola-type cheese.

Blue cheeses are susceptible to yeast and bacterial growth on their surface, which causes spoilage during ripening process and the formation of slime. The dairy industry frequently control the proliferation of undesirable microorganisms with natamycin and high salt concentration. The green propolis is a complex of substances that presents antimicrobial properties with great potential as preservative in the food industry. The aims of the present study were to identify the mesophilic aerobic microorganisms present on the surface of Gorgonzola-type cheese, evaluate the antifungal and antibacterial effects of the ethanol extract of green propolis (EEP) on the development of those microorganisms and verify the effects of EEP on the sensory quality of cheese. Ten yeast species belonging to genera Yarrowia, Candida, Debaryomyces and Saccharomyces were identified, as well as seven species of bacteria belonging to genera Staphylococcus, Bacillus, Enterococcus, Corynebacterium and Proteus. The EEP showed minimum biocide concentration (MBC), between 0.3% (weight/weight) and 5% for Bacillus cereus and Proteus vulgaris, respectively. Saccharomyces cerevisiae was the most sensitive species (MBC of 0.63%) and Candida parapsilosis the most resistant one (MBC of 5%). In the sensory analysis, the cheeses involved with EEP at 5% concentration did not differ from the control, while at 10%, there was a slight decrease in acceptance. The EEP has potential and feasibility to be used in Gorgonzola-type cheese, inhibiting the main bacteria and yeasts without affecting largely the sensory characteristics of the product.

Survival of Kluyveromyces lactis and Torulaspora delbrueckii to simulated gastrointestinal conditions and their use as single and mixed inoculum for cheese production.

The demand for new probiotic products has shown recent increases alongside a growing interest in studying starter cultures of cheeses. This study thus aims to evaluate the ability to survive under simulated gastrointestinal conditions and impact of Torulaspora delbrueckii B14 and Kluyveromyces lactis B10 as single and mixed inocula for cheese production. These two yeast strains were subjected to simulated gastrointestinal tracts and tested for self-aggregation, hydrophobicity, pathogen inhibition, antibiotic resistance, and ß-galactosidase production. The yeast strains were also assessed for their ability to survive in different NaCl concentrations (2.5%, 5%, and 10% w/v), multiple temperatures (4 °C and 40 °C), and used as single and mixed starter cultures for cheese production. Yeasts population levels were monitored by YPD plating and MALDI-TOF and metabolites were analyzed by HPLC and GC-MS over the course of the 21 days cheese maturation process. T. delbrueckii B14 and K. lactis B10 both showed >80% viability after the passage through the simulated gastrointestinal tract, had self-aggregation rates >90%, and displayed ß-galactosidase activities of 0.35 U/g and 0.53 U/g, respectively. Both yeasts survived at 2.5%, 5%, and 10% NaCl for 21 days and showed growth at 4 °C. In cheese, the single inoculum of K. lactis B10 and mixed inoculum showed the highest levels of lactose consumption. HS-SPME GC-MS analysis of cheese samples allowed the identification of 38 volatile compounds. The highest concentrations of most of these compounds were observed after 21 days of maturation for the cheese produced with mixed inoculum. The most abundant acids detected were hexanoic and decanoic acid; the most abundant alcohols were 2,3-butanediol, 2-phenylethanol and isoamyl alcohol, and the most prevalent ester compounds were isoamyl acetate and phenethyl acetate. Our results therefore show that T. delbrueckii B14 and K. lactis B10 are interesting yeasts for further studies in the context of probiotics and positively impact the composition of desirable volatile compounds in cheeses, particularly when used as mixed inoculum.

Extraction and identification of antimicrobial peptides from the Canastra artisanal minas cheese.

Canastra artisanal Minas cheese samples were collected in Minas Gerais - Brazil. The samples were evaluated in order to observe the presence of antimicrobial peptides during 30 days of ripening. Soluble peptides extracted from the cheeses were fractionated by reverse phase liquid chromatography and their fractions evaluated for inhibitory action of E. coli. Fractions containing antimicrobial activity were analyzed by MALDI-TOF/TOF and then peptides were sequenced and identified using MASCOT Daemon coupled with UniProt database. The identified peptides were then validated by SCAFFOLD application. The peptides present in fractions with antimicrobial activity were RPKHPIKHQ, RPKHPIKHQG, RPKHPIKHQGLPQ and RPKHPIKHQGLPQE, HQPHQPLPPT and MHQPHQPLPPT. Peptide sequences PKHPIKHQ, RPKHPIKHQG, RPKHPIKHQGLPQ and RPKHPIKHQGLPQE were originated from αs1-casein and are their fragments belonging to Isracidine, which in turn is a well known antimicrobial peptide. The HQPHQPLPPT and MHQPHQPLPPT peptides were related to ß-casein and were isolated in other studies, but their biological activities are still unknown.