There is an increasing consumer demand for dairy products which are safe and free from additives. Microbial starter strains, in combination with other factors, were studied for their contribution to the control of unwanted microbes, and maintaining the quality of soft cheese. The technological and functional characteristics of the starter culture strains Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris, and probiotic bacterial strains Bifidobacterium animalis subsp. lactis BB12, Lactobacillus acidophilus LA-5 and Lactobacillus casei Shirota were investigated. The tests included the milk fermentation, resistance to salt and heat, bile and acid resistance, and growth at a range of temperatures. The probiotic strains differed in their resistance to salt, bile salts and acid. Inhibitory interactions between probiotic bacterial strains with each other and with starter culture strains were not detected. The probiotic bacteria and starter culture strains used have an ability to grow together on homofermentative and heterofermentative differential agar and fermentation of fructose in different levels. Non-starter cheese (NSC), cheese with starter strains (SCS), and cheese with starter and probiotic strains (PSC) were manufactured. The levels of mesophilic aerobic and lactic acid bacteria, moulds and yeasts, and Enterobacteriaceae were evaluated in all cheeses. Their contents of fat, total solids, salt and pH value were tested during 21 days of storage at 2-5°C. Starter culture strains contributed to maintaining the quality of all cheeses, through decreasing the viable count of some undesirable microbes. Cheeses differed in the intensity of the crumbliness attribute, and in preference and intensity of colour attribute. The colour of starter soft cheese, which was tested using a colorimeter, was closer to the colour of probiotic soft cheese than those cheeses which were manufactured without starter culture. The microbial status, storage conditions, rancidity, and the sensory characteristics of unripened soft cheese, which was manufactured with starter culture strains only, were determined during the storage for 50 days at 2-5°C, as well as during their shelf life for the product. Modified Atmosphere Packaging (MAP) contributed to slowing the growth of unwanted microbes, and decreased the values of TBA, TVB-N and TMA in soft cheese. Consequently, delaying the undesirable changes and maintaining the quality of the product and extending its shelf life, when compared with vacuum, brine, and air packaging methods, under the same storage conditions. Potential effects of inulin on the cheese quality and sensory characteristics of probiotic soft cheese were investigated. The cheeses differed in their loads of lactic acid bacteria, in addition to the total solids and water activity. The levels of probiotic bacterial strains were higher in probiotic soft cheese that manufactured with inulin than in cheese without inulin, with a potential in the formation synbiotic between the probiotic strains LA-5 and BB12 and inulin. Both cheeses were recorded to have high acceptance in the cheese attributes, in terms of appearance, aroma, colour texture and the overall acceptance. The presence of inulin increased the hardness of cheese under vacuum packaging, after storage for 14 days at 2-5°C.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:686099 |
| Date | January 2016 |
| Creators | Jawad, Emad |
| Publisher | University of Plymouth |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10026.1/4377 |
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