RESUMEN
A total of 143 presumptive yeast isolates were obtained from the predominant microflora of 21 short-ripened starter-free raw cow's milk cheeses made in Galicia (NW Spain), and the following 68 isolates were identified by both genotyping and sequencing methods: Yarrowia lipolytica (21 isolates), Kluyveromyces lactis (18), Debaryomyces hansenii (11), Pichia guilliermondii (11), Pichia fermentans (4) and Saccharomyces cerevisiae (3). Of these, Y. lipolytica and K. lactis displayed the strongest extracellular proteolytic activity on skim milk agar, and none of the D. hansenii isolates showed any activity on this medium. Y. lipolytica also displayed the highest lipolytic activity on Tween 80 and on tributyrin. This species, which was characterized by production of butanoic acid, free fatty acid esters and sulfur compounds in pasteurized whole milk, was responsible for rancid and cheesy flavors. K. lactis mainly produced acetaldehyde, ethanol, branched chain aldehydes and alcohols, and acetic acid esters, which were responsible for alcoholic, fruity and acetic notes. The volatile profiles of D. hansenii were rather limited and characterized by high levels of methyl ketones. Most of the yeast isolates were described as tryptamine producers, although low concentrations of histamine were produced by five Y. lipolytica and two P. fermentans isolates. We conclude that selected Y. lipolytica strains could be used as adjunct cultures in the manufacture of Arzúa-Ulloa and Tetilla cheeses, and selected K. lactis strains could be used as co-starters in the manufacture of acid curd Cebreiro cheese, thus contributing to the sensory quality and typicality of the cheeses.
Asunto(s)
Queso/microbiología , Levaduras/aislamiento & purificación , Animales , Biodiversidad , Bovinos , Microbiología de Alimentos , Genotipo , Filogenia , España , Levaduras/clasificación , Levaduras/genéticaRESUMEN
Antibiotic susceptibility against 19 antimicrobial agents was evaluated in isolates of the genera Lactococcus (46 isolates), Leuconostoc (22), Lactobacillus (19), Staphylococcus (8), Enterococcus (7), and Microccoccus/Kocuria (5) obtained from the predominant microflora of nonrecent and recent types of artisanal raw cow's milk cheeses. Beta-lactams showed broad activity against all genera, although leuconostocs and lactobacilli were highly resistant to oxacillin (80% to 95.5%). Resistance to aminoglycosides was frequent for lactococci and enterococci (particularly for streptomycin), whereas lower rates of resistance were detected for lactobacilli and leuconostocs. Technologically interesting traits for the food industry were distributed among isolates that showed different degrees of resistance to common antibiotics. However, isolates showing resistance to less than 2 antibiotics were mainly those with properties of greatest technological interest (acidifying activity, proteolytic/lipolytic activities, or diacetyl production).
Asunto(s)
Antibacterianos/farmacología , Queso/microbiología , Farmacorresistencia Bacteriana , Manipulación de Alimentos/métodos , Microbiología de Alimentos , Micrococcaceae/efectos de los fármacos , Staphylococcaceae/efectos de los fármacos , Contaminación de Alimentos/prevención & control , Industria de Alimentos , Cocos Grampositivos/efectos de los fármacos , Cocos Grampositivos/genética , Cocos Grampositivos/aislamiento & purificación , Cocos Grampositivos/metabolismo , Bacilos Grampositivos/efectos de los fármacos , Bacilos Grampositivos/genética , Bacilos Grampositivos/aislamiento & purificación , Bacilos Grampositivos/metabolismo , Pruebas de Sensibilidad Microbiana , Micrococcaceae/aislamiento & purificación , Micrococcaceae/metabolismo , Micrococcaceae/patogenicidad , España , Staphylococcaceae/aislamiento & purificación , Staphylococcaceae/metabolismo , Staphylococcaceae/patogenicidad , Factores de TiempoRESUMEN
In this work, four cDNA clones (Pd-ACS1,AJ890088; Pd-ETR1 and Pd-ERS1, AJ890092, AJ890091; and Pd-CTR1, AJ890089) encoding an ACC-synthase, two putative ethylene (ET) receptors, and a putative MAPKKK, respectively, were isolated and phylogenetically characterized in Prunus domestica L. subsp. insititia. Their expression was studied by real-time PCR during flower (closed, open and senescent) and fruit (early green, late green, maturation and ripening) development of damson plum, which is climateric. While two peaks of ET production were quantified at early green and ripening stages in whole fruits, the seed was not able to produce it during maturation and ripening stages. All studied genes were differentially expressed during flower and fruit development. In general, the level of transcripts of Pd-ACS1 was higher in fruits than in flowers. However, it was noteworthy that: (1) Pd-ACS1 expression was hardly detected in closed flowers and at low levels during early green stage; and fruit development provoked a notable differential expression in seeds, and pericarp; (2) the results of Pd-ACS1 expression during fruit development suggest a preponderant role of this gene from late green stage onward. The stamen was the only floral organ in which expression of both Pd-ETR1 and Pd-ERS1 receptor genes was not significantly altered during development; however, their expression decreased concomitantly with development of pistil (only floral organ to register a net ET production when fertilized) and during first days of ovary development (the highest ET production during all fruit development). Contrary to Pd-ERS1, the level of Pd-ETR1 mRNA was temporally quite similar in the seed. With regard Pd-ETR1, even its expression was very scarce during maturation of mesocarp, was stimulated during ripening. In the epicarp, Pd-ERS1 and Pd-ETR1 were low expressed during pit hardening increasing onward and decreasing during ripening. Pd-CTR1 expression was in the seed>mesocarp>>epicarp. Spatial and temporal levels of Pd-ACS1, Pd-ETR1, Pd-ERS1 and Pd-CTR1 mRNAs described in this work demonstrate that the expression of these genes is not always constitutive and that control of its transcription may play an important role in regulating the development of reproductive organs of damson plum.