Which has better scope: biomedical engineering or food processing technology?
You are asking about two different fields, biomedical engineering and food processing. Biomedical engineering is the the newer field of the two. It involves using engineering geared toward health care applications including prosthetics design, diagnostic imaging (MRI for example), medical implants (like pacemakers), and pharmaceutical delivery devices.
Food processing technology involves the design and implementation of machinery and computer systems for the food processing industry. It is the older of the two fields but it has obviously changed greatly in the computer era. It can be thought of as closer to classical manufacturing engineering.
In terms of scope, both fields are pretty solid choices. Both health care and food processing are fields that have been around and will continue to be around for the foreseeable future. These are also industries that are harder to outsource to other countries due to the need for strict oversight for the preparation of food and medicine/medical devices. Also, both fields will need constant updating as technology changes and improves. I can tell you that biomedical engineering will require more coursework to obtain a degree. Both will require plenty of math and physics due to the engineering aspects, but biomedical engineering will also require biology, chemistry, and biochemistry as well. So take that factor into account as well. The bottom line, though, is that it is hard to go wrong with either career choice.