Abstract
Debaryomyces hansenii yeast was grown in Malt Extract Broth medium at 30 °C for 5 days until the total count reached 5.6 ×108 colony forming units/ milliliter, Monterey cheese was made from cow's milk and adding of starter bacteria Lactococcus lactis subsp. lactis and Lactococcus lactis subsp.cremoris with D.hansenii yeast as adjunct starter in 2% for each treatment included M1 (100% starter bacteria), M2 (50% starter bacteria + 50% live D.hansenii) and M3 (50% starter bacteria + 50% dead D.hansenii),the ripening of Monterey cheese was done at 15°C and (85% relative humidity) for 56 days. The highest count of starter bacteria was 9.7 ×108 cfu/g in M1 treatment after 3 days of ripening, the lowest number of starter bacteria was 6.9 ×108 cfu/g in M2 treatment. The highest count of D.hansenii yeast was 4.3 x108 cfu/g after 3 days of ripening in M2 treatment, while the lowest count was 2.6 ×108 cfu/g in the same treatment after 56 days of ripening, no yeast was found in the treatments that had dead yeast cells, all treatments under study were decreased in the total count of coliform bacteria, Staphylococcus aureus and psychrotrophic bacteria after 14 days as they were within the standard specifications of these groups of microorganisms, Then reached to zero in the late time of ripening. M2 showed the best results of sensory evaluation in taste, flavor, textures, color and bitterness after 56 days of ripening.
Highlights
Debaryomyces hansenii yeast is a mesophilic yeast, the best temperature for its growth is 30° C, It had a pH range 4-6 and water activity of 0.99
The D.hansenii had enzymatic degradation of lipids, the main factors of lipid degradation in cheese include the lipase enzyme produced from the starter bacteria and the adjunct starter (D.hansenii yeast) to improve the flavor of cheeses, the short-chain fatty acids contribute directly to the enhancement of flavor, but fatty acids can act as raw materials to produce a wide range of other flavor compounds such as esters and methyl ketones that give distinctive flavors to the cheeses
Monterey cheese was made from cow's milk after pasteurization at 65° C for 30 minutes and milk was cooled to 32°C, Lactococcus lactis subsp lactis and Lactococcus lactis subsp. cremoris were added, and D.hansenii yeast was added as adjunct starter in 2%, for each treatment, included M1 (100% starter bacteria), M2 (50% starter bacteria + 50% live yeast), and M3 (50% starter bacteria and 50% dead yeast), 0.1% of microbial rennet made from Mucor miehei was added,wait until coagulation, curd was cut and cooked at 32°C for 30 minutes, whey separated fill the cheese in molds and salt added in 2%, cheese molds pressed for 24 hour, paraffin wax was heated at 118°C for 5 seconds covered cheese [9]
Summary
Debaryomyces hansenii yeast is a mesophilic yeast, the best temperature for its growth is 30° C , It had a pH range 4-6 and water activity of 0.99. Decreasing in starter bacteria counts may be attributed to nutrient consumption, low water activity and high salt concentration in cheese and may decrease temperature 15° C at maturity, as the two types of Lactococcus lactic ssp lactic and Lactococcus lactic ssp cremoris 30° C, which reduces the growth of lactic acid bacteria [15].
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