Tween 80 is required by some LAB for growth. They use this surfactant as fatty acid source. Some LAB can't grow in MRS without tween 80. I don't known if it is posible to replace tween 80 by tween 20.
CAN WE REPLACE TWEEN 80WITH TWEEN 20 OR VIS VERSA IN MOLECULAR EXPERIMENT !! FOR EXAMPLE CAN I USE TWEEN 20 AS A (DILUTION) OF TWEEN 80 AS DETERGENT !!!
I'm not sure about the differences, but depending on your experiment you could give it a try. For example, in order to prepare a lysis buffer that contains Tween20, I used Tween80 since I don't have T20. For me it worked perfect, since the main purpose in my case was avoiding the DNA to stick to magnetic beads and tube walls and I really noticed the difference.
I don't think it is a huge practical difference and my intuition is that Tween20 has been used for many years in some applications like immunoassays and that is the reason why is still being suggested as blocking agent while Tween80 seems to be used just in bacterial culture.