Microbial_Analysis_of_Cheese

Microbial Analysis of White Cheese This paper evaluated the study on microbial analysis of white cheese by L. Jovanovic at Belgrade on August, 2005. Application of Generalizations to New Situations Collection of Data The researcher introduced that fresh soft cheeses are usually manufactured by using conventional methods namely fermentation, renneting curd formation and pre-market preparations. Cheeses resulting from these methods are consumed in fresh form. These cheeses have white, compact masses and are typically milky in flavour. They are made directly from raw milk in the absence of species initiators. Thus, the ripening process is carried out only by the milk’s natural flora. Depending only on these factors, in the presence of uncontrolled temperature and relative humidity throughout the process of ripening, the final product becomes variable. Because of this variability, recognition and distribution of the products are limited in markets. Consuming the products has no records of health problems. Yet, they may possibly be unsafe and might cause future troubles if production conditions are not improved. Pasteurization of the milk to be used, a specific starter and controlled conditions will permit the production of uniform fresh white cheeses of constant quality. These factors would all allow a safer production to get rid of health risks to the consumer. In this study, the researcher aimed to investigate the microbial features of this fresh cheese and to isolate and identify the milk’s natural flora throughout the ripening process. To gather data, an experiment was conducted by the researcher. Skim raw milk was coagulated through addition of rennet at 28-32ºC. Two hours after the addition of rennet, the curd was cut into equal parts, 5 cm each and was placed in wood molds containing holes for the whey to drain at room temperature. After 20 minutes, the whey was allowed to drain again for 40-60 minutes along with the pressure of 4 kg. Dry salt was then added to the surface. The ripening process was done in aerated rooms at 18ºC for 8-10 hours and relative humidity. Samples of milk, curd and cheese were taken from different locations (Sopot, Divčibare, Mali Mokri Lug, , Ivanjica, Zaječar, Obrenovac, Ub, Niš) and are transferred and analyzed immediately under refrigeration (below 5ºC). From each location, 10 samples were taken. The cheese samples were removed aseptically, 20 g of these samples were homogenized in 180 ml of 2% Sodium citrate solution. Then, a series of 10-fold dilutions were prepared from this homogenized solution using 0.1% peptone water. After incubation at 30ºC for 48 hours, Aerobic mesophilic bacteria were listed in standard plate count agar while aerobic psychrotropic bacteria were enumerated in standard plate count agar after incubation at 7ºC for 10 days, lactic acid bacteria in the Man Rogosa Sharpe (MRS) M 17 (Merck) agar and Rogosa agar, after incubation at 30ºC for 3 days, Micrococacceae in manitol salt agar (MSA) (Oxoid) incubated for 48 h at 30°C, enterococci in kanamycin aeskulin azide agar incubated for 1 day at 37°C, Enterobacteriaceae in violet red bile agar (VRBG) (4-5 cm) incubated for 18 to 24 hours at 37°C and molds and yeasts in Sabourousd agar (Torlak) incubated for 5 days at 22ºC. Then, 1 ml of each dilution was inoculated in standard plate count agar, MRS agar, KAA agar, VRBG agar and Sabouroud agar. They were mixed before solidification occurred. Before incubation, MRS and VRBG agar plates were covered with the same medium’s layer. 0.1 ml volumes of each dilution were surface plated in duplicates in mannitol salt agar. Those plates containing 30 to 300 colonies were counted. Analysis of Data Results were obtained and analyzed by the researcher through showing the development of the different microbial group counts throughout the production of the cheese. High microbial counts were obtained from the milk used in cheese making (log total viable counts 7.22/g on the average). Microbial group counts were two log units higher in curd than those counts recorded in milk. This increased count in curd was in part due to the physical retention of the microbes in the coagulum and in part due to multiplication of microorganisms during coagulation and whey drainage. The lowest count increase was observed in the molds and yeasts (1 log unit). This group seemed to be the only one that did not undergo multiplication during coagulation and whey drainage. According to the researcher, this circumstance can be attributed to the high coagulation temperature. Nevertheless, the highest counts were obtained for almost all the microbial groups in the curd. According to the researcher, lactic acid bacteria are the most important group in the production and ripening process of the cheese since this group showed all sampling points counts equal to or even higher compared to those of the aerobic mesophilic flora. This lactic acid bacteria predominance was collaborated by the high correlation coefficient (r=0.96) between their counts and that of the total flora during process of ripening. On the other hand, the researcher reported that the aerobic psychrotrophic flora counts were repeatedly a log unit lower than those of the aerobic mesophilic flora counts. The researcher noted that counts of Micrococcacceae dropped after the initial increase in the curd to values on the order of 103 colony forming units (CFU)/g. The counts remained at these levels throughout the ripening period. According to the researcher, these results suggested a low participation of Micrococcacceae in the ripening process. Conversely, enterococci did not undergo any remarkable reduction from the curd counts (levels of about 105 CFU/g). The researcher obtained mold and yeast counts that undergone a log unit increase during coagulation and whey drainage. This group continued increasing to reach a maximum. According to the researcher, the high count of lactic acid bacteria suggested that this certain flora has a significant role in the process of cheese ripening. The researcher showed the evolution of species isolated during the whole process. Results obtained showed that Lactococcus lactis subsp. lactis was the most predominant species in milk (62.5%) rising to 82.5% in curd. However, only 5% of the curd was isolated Lactococcus lactis subsp. diacetitylactis. Three were only three species of lactobacilli isolated namely, L.casei subsp. casei, L.casei subsp. alactosus and L.brevis. The most recurrent lactobacillus species isolated was L.casei subsp. casei. Thus, according to the researcher, L.casei subsp. casei plays an essential role in the development of the organoleptic quality of fresh white cheese. Proceeding to observing the occurrence of heterofermentative lactobacilli, the researcher reported a very low presence of this group in the cheeses. In addition, only six of the isolates were identified as L. brevis. According to the researcher, it was observed that the isolation of L. brevis is not very distinctive in this cheese in contrast to other cheeses where this species were primarily isolated during the first ripening stage. Leuconostoc lactis was reported to be the most abundant species of the genus in the milk. This species was known to be the most acidic among all the lauconostoc species. The researcher noted that leuconostoc levels fell after the first month of ripening, which agreed with earlier observations done by other researchers. Because of the considerable levels of leuconostocs found in the white cheese, the researcher suggested that they have an extra role in the organoleptic characteristic development of this cheese. The researcher indicated that there were twenty strains of streptococci; however they cannot be precisely identified at a species level by the use of biochemical and cultural tests alone. From all the results obtained, the researcher assessed that the main functions that a starter species should develop are acid production, lipolysis, production of aroma, proteolysis, and inhibition of unwanted microbes. Synthesis of data From the results obtained in this work, the researcher concluded that a sufficient starter species, chosen from numerous microbes seemed to be the main cause of the lipolytic and proteolytic phenomena, and of the development of the flavour characteristics. In addition, the researcher also concluded that leuconostoc species are capable of improving the organoleptic characteristic of the cheese. Evaluation of Data