Tesis doctoral de Diana Maricela Espinosa Pesqueira
The aim of this work was to evaluate the effect of the high hydrostatic pressure (hhp) on the formation of biogenic amines (ba) in raw milk cheeses. For this purpose, two spanish artisan cheese factories were selected to provide the cheeses to be used in the survey. These factories were previously visited to check the compliance with the hygienic standards required by european regulations. One variety of cheese was chosen from each factory, both made from raw milk. One of them was made from ovine milk and the other from caprine milk. A hhp treatment of 400 mpa during 10 min at 2 ºc was chosen as the most suitable. These conditions were applied at the begging of the ripening between 3rd and 7th day (hhp1) or on the 15th day (hhp15), in each case the effect of the treatments on the microbial, physicochemical, textural, and sensory parameters, as well as on the formation of different ba were assessed during the maturity period. the ba forming capacity of the microbiota present in the cheeses was also evaluated. To this purpose a qualitative screening method to detect the amino acid decarboxylase activity of baceria was validated and the frequency of the different species and strains with this capacity was determined in either the ovine and caprine raw milk cheeses studied. the hygienic quality system based on the haccp principles of the two visited artisan cheese factories was not strictly stablished. However, the prerequisites program was applied according to their necessities, although in most cases the procedures and results of the controls were not appropriately written or registered. The preventive maintenance of the facilities and equipments, cleaning and sanitation procedures, and the whey waste disposal were the main weaknesses found in both cheese factories. Besides, the water supply control was also unsuitable in one of them. biogenic amine content in both types of cheeses was greatly influenced by hhp. The treatments applied on the beginning and on the 15th day of ripening displayed 75 and 35% lower amounts of ba, respectively, than those obtained in the control untreated samples, being ty and pu the most affected amines in caprine milk cheeses, while ty and ca were so in ovine milk cheeses. The ba reduction in the caprine and ovine hhp1-samples can be explained as a result of a significant decrease of microbiological counts observed one day after the hhp-treatment (specially in the lactoccocci, lactobacilli, enteroccocci and enterobacteria groups) and the slower proteolysis detected in these samples, which showed 34 and 48% less free amino acids than the control caprine and ovine milk cheese samples at the 60th day of ripening, respectively. On the other hand, the hhp treatment applied on the 15th day also resulted in the decrease of microbiological counts, although in this case the liberation of amino acids was not different than the control samples. the amino acid decarboxylase microplate screening method using low nitrogen decaboxylase (lnd) and low glucose decaboxylase (lgd) broths had satisfying diagnostic parameters to detect the pu, ca and ty- forming bacteria, being their optimal cut off between 10-25 mg l-1, with an area under roc curve above 0.90 and a sensitivity and specificity values above 84 and 92%, respectively. Nevertheless, the test had less capacity to detect the hi-forming bacteria. According to the diagnosis parameters evaluated, this test was considered only as acceptable and poor, for lnd snd lgd media, respectively. among the isolates obtained from caprine and ovine milk cheeses with amino acid decarboxylase activity, the ty forming bacteria were the most frequent, showing a strong production (exceeding 100 mg l-1), followed by those with ca and pu-forming ability with strong and prolific production (100-1000 and over 1000 mg l-1, respectively). In the first case, strains belonging to the lactococcus, lactobacillus, enterococcus and leuconostoc groups were found as the main ty producers, whereas enterobactericeae and staphylococcus strains were the main pu and/or ca forming bacteria, although some enterococcus, lactococcus, leuconostoc, and pediococcus strains showed an ability to produce diamines at levels above 100 mg l-1. the decelerated rate of proteolysis in hhp1 samples, combined with the structural changes caused by the pressure, could contribute to reduce the fracturability of cheeses. However, this decrease could be only due to the formation of a more homogeneous microstructure in the ovine milk cheeses with the hhp15 treatment. The sensory panel noticed that the firmness in the hhp1 and hhp15 samples was significantly different than in control samples. The total color differences (¿e) in the hhp samples was higher during the first stages of the ripening (around 4.4 in hhp1 and hhp15 samples), decreasing as the sample aged. In addition, differences in color were also perceived by the sensory panel, being significant only in ovine milk cheeses with the hhp1-treatment.
Datos académicos de la tesis doctoral «Effect of high hydrostatic pressure procesing on biogenic amines formation in artisan caprine and ovine raw milk cheeses«
- Título de la tesis: Effect of high hydrostatic pressure procesing on biogenic amines formation in artisan caprine and ovine raw milk cheeses
- Autor: Diana Maricela Espinosa Pesqueira
- Universidad: Autónoma de barcelona
- Fecha de lectura de la tesis: 24/02/2011
Dirección y tribunal
- Director de la tesis
- Artur Xavier Roig Sagués
- Tribunal
- Presidente del tribunal: María carmen Vidal carou
- claudia Ruiz-capillas pérez (vocal)
- (vocal)
- (vocal)