The document summarizes an experiment comparing the production of homemade yogurt using commercial yogurt or lyophilized enzymes as starters. Samples of yogurt were tested for acidity, microbial content over time, and cost-effectiveness compared to purchasing yogurt commercially. Using lyophilized enzymes as a starter resulted in yogurt with higher acidity and microbial levels over 10 days compared to yogurt made with commercial yogurt or no starter. Producing homemade yogurt can be more cost effective and reduces plastic and aluminum waste compared to purchasing yogurt in stores.

1. the yoghurt Chemical and microbiological aspects costs and eco sustainability Comenius: One step closer to a better future

2. Our Class 2AOCB I.P.S.I.A San Benedetto del Tronto

3. Starting from fresh non pasteurized milk we prepared homemade yoghurt using commercial yoghurt as a starter (sample B) and lyophilized enzymes (sample C).

4. Fresh milk Heating 60°C Cooling at 45°C Aliquot 1 Aliquot 2 White whole commercial yoghurt Lyophilized milk enzymes Sample B Sample C Sample A Flow chart Incubation at 37°C 24 h Incubation at 37°C 24 h

7. acidity determination

9. yoghurt taking

10. Sowing the petri dish

11. Colony counting

12. the results

13. Sample C at different dilutions after 10 days.

14. Sample C at different dilutions

15. Sample A: no growth!!! Note the difference between A and C After 10 days Sample c

17. * N.B. used 10 days before the expiring date . Commercial Yoghurt Just open 48.000.000 ufc/ml After 5 days 26000 ufc/ml After 10 days 0 ufc/ml

18. Homemade Yoghurt B With commercial yoghurt C prepared With lyophilized enzymes Just prepared 17.100.000 ufc/ml 114.000.000 ufc/ml After 5 days 215.000 ufc/ml 1.208.000. ufc/ml After 10 days 120.000 ufc/ml 812.000 ufc/ml

21. Aluminium per year per person Plastic per year per person 17,15 grams 3,6 kg Grams of aluminium Grams of pot Grams bottle 0,49 5,98 27,5

22. thank you for your attention