Thanks Buddolla Viswanath so much,

But the coffee must be sterilized in a high temperature (>100C) and sodium (hydro)bicarbonate will be decomposed into Na2CO3 + H2O + CO2. I wonder whether the pH level of coffee decrease?

And the infomation that I found is in the black coffee. That mean we no need to adjust the pH level(in my opinion). Or they just want to adjust the sour taste?

I agree with Buddolla. Natural coffee contains various organic acids (nonvolatile acids such as caffeic, chlorogenic, citric, malic, oxalic, quinic and tartaric) to make the beverage quite acidic. There is a great possibility of milk getting coagulated and thus spoiling taste of the beverage even when you add hot milk in a freshly prepared coffee brue ( if the decoction is excessively hot) and thereby spoiling the taste, body and flavor of coffee beverage. Situation is not different in canned coffee ad well.

However as Huy has doubted the coversion of bi carbonate to carbonate is not possible or could be at the minimal (if excess bi carbonate has been added than what is really required). IBecause you have been adding bi carbonate before it is canned and thermally processed. The moment you add the bi carbonate the excess acidity is neutralised and thermal treatment of sterilisation takes place after most of the coffee brue acids have been already neutralised. The buffered conditions provided after neutralising excess acidity would prevent any possibility of milk coagulation.

Regards,

Sodium bicarbonate is used as anticaking agent or it also helps in color retention because when coffee absorb moisture it color changes from brown to dark brown or vlack

Thanks Mr. Arun Padhye, that helps me a lot. And we no need to adjust pH level of black coffee (no added milk)?

Thanks Hauwa Dauda, could you please give me some papers that prove "sodium bicarbonate help in color retention"? I want to know what mechanism it is.