The Yogurt ( Chemical and Microbiological Aspects )

The yoghurt Chemical and microbiological aspects costs and eco sustainability Comenius: One step closer to a better future
Our Class 2AOCB I.P.S.I.A San Benedetto del Tronto
Starting from fresh non pasteurized milk we prepared homemade yoghurt using commercial yoghurt as a starter (sample B) and lyophilized enzymes (sample C).
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
What happens when Streptococcus thermophilus and Lactobacillus bulgaricus are put into the milk? They transforme lactose into lactic acid The yoghurt: chemical aspects
To 50 ml of milk or yoghurt we add 3-4 drops of phenolphthalein, titrated by NaOH 0,25 N. The acidity degree, expressed in Soxlet Hankel degree, derives from the mls of NaOH needed to titrate 100 ml of milk. Let’s compare the acidity of milk and yoghurt Fresh Milk Yogurt (sample B and C) ml NaOH 4 S.H degree = 8 ml NaOH 46 SH degree = 92
acidity determination
The taste of a yoghurt depends not only on organoleptic aspects but also on the number of lactic enzymes contained. We compared the quantity of these enzymes in sample A (commercial yoghurt), Sample B (yoghurt prepared with commercial yoghurt), Sample C (yoghurt prepared with lyophilized lactic enzymes) The different samples have been inoculated with on Rogosa Agar and incubated for 48h at 37°C and observed soon after prepared, after 5 days, and after 10 days . The yoghurt: microbiologycal aspects
yoghurt taking
Sowing the petri dish
Colony counting
the results
Sample C at different dilutions after 10 days.
Sample C at different dilutions
Sample A: no growth!!! Note the difference between A and C After 10 days Sample c
* 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
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
With 1 l of milk we can make 7 yoghurt pots, using both commercial yoghurt and lyophilized enzymes. Savings and Eco sustanibility of homemade yoghurt B C Milk price 1 € 1 € Starter price from 0,65 to 1 € 1 € Price of a single pot of yoghurt (about 125 grams) from 0,235 € to 0,285 € 0,285 €
ecosostenibility If we don’t buy plastic bottled milk but we use milk directly bought from the vending machines, using only glass bottles (that we can use thousands times), then we put our yoghurt in glass jars (that we can use again and again) we avoid to carry aluminium and plastic to the rubbish tip. If, for example we use 1 yoghurt pot per person, per day, we could easily know the quantities of plastic and aluminium saved in a year time.
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
thank you for your attention

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