Correct choice is (c) Starch to glucose
To explain I would say: Starch to glucose using bacterial a-amylase and glucoamylase is an example for an extractive bioconversion. Starch partitions in lower, more hydrophilic, dextran-rich phase of a system comprising 3% polyethylene glycol (PEG 20,000) and 5% crude unfractionated dextran. The enzymes also partition in the bottom phase but the glucose produced distributes itself more evenly between the two phases. Glucoamylase enters the upper phase and converts any oligosaccharide entering that phase to glucose.