Effecting factors of microorganism growth osmotic pressure Objective

Effecting factors of microorganism growth –osmotic pressure • Objective – Compare bacterial growth in different osmotic pressure reacted with sugar or salt • Principle – Bacterial growth needs an environment with a high water activity. Therefore, when sugar or salt is added into food, the water activity of the food will be decreased but osmotic pressure will be increased. – It is an oldest method to inhibit the bacterial growth in food. Chapter 24

Materials and methods • Bacteria: – Escherichia coli, – Staphylococcus aureus • Media – tryptic soy agar (TSA) – Regular salt and sugar

• Salt and sucrose – 0, 3, 6, 9% – Each concentration has two plates – 16 plates per group • Methods – Separate the plates to four sections – Streak each bacterial species onto each section – Incubate plate at 37℃ – Observe growth one the next day – Compare different species and plates

Water activity of agar Aw 1 平均 Aw 2 0%TSA 0. 987 0. 986 0. 987 3% salt +TSA 0. 972 6% salt +TSA 0. 959 0. 953 0. 956 9% salt +TSA 0. 937 3%sugar +TSA 0. 984 0. 982 6%sugar +TSA 0. 975 0. 98 0. 978 9%sugar +TSA 0. 977 0. 976 0. 977

1 0. 99 0. 98 0. 97 0. 96 0. 95 0. 94 salt sugar 0. 93 0. 92 0. 91 0 3 6 9

• Compare results between different bacterial species • Compare results between sugar and salt. Which one is more effective?

Effecting factors of microorganism growth –p. H • Objective – Compare bacterial growth in different p. H • bacteria: – Escherichia coli – Lactobacillus acidophilus • Medium – TSB at p. H 4. 0, 5. 0, 7. 0, 9. 0, 10. 0 Chapter 23

Difco™ Lactobacilli MRS Agar • • • Approximate Formula Per Liter Proteose Peptone No. 3. . . 10. 0 g Beef Extract. . . . 10. 0 g Yeast Extract. . . . 5. 0 g Dextrose. . . . . 20. 0 g Polysorbate 80. . . . 1. 0 g Ammonium Citrate. . . . 2. 0 g Sodium Acetate. . . . 5. 0 g Magnesium Sulfate. . . . 0. 1 g Manganese Sulfate. . . . 0. 05 g Dipotassium Phosphate. . . 2. 0 g

procedures – Each p. H has two tubes – 10 MRS tubes per group – Inoculate E. coli and L. acidophilus into MRS tubes in the same range of p. H 4. 0 -10. 0

• Incubate at 37°C • Observe growth in on the next day – Compare different species and plates