You need to look for C. botulinum mainly when there are symptoms of botulism in food poisoning. Botulism clinical symptoms: omiting, abdominal pain, fatigue, muscle weakness, headache, dizziness, ocular disturbance, constipation, dry mouth and difficulty in swallowing and speaking, and ultimately paralysis and respiratory or heart failure. 

Particularly frequent among Alaskan populations. 

Mode of transmission and associated foods: Ingestion of toxin pre-formed in food. This may occur when raw or under-processed foods are stored in anaerobic conditions that allow growth of the organism. Most outbreaks are due to faulty preservation of food. 

Diagnosis using food: simplest is immunoassay for the detection of botulinum neurotoxins.

Continuous work in an anaerobic workstation is a necessity for successful culture.

Do you any laboratory that i can get information about analysing in food.

C. botulinum food poisoning/ botulism is rare. If your lab has stringent anaerobic culture system you can try it yourself. For immunoassay you need to follow a kit method of ELISA. 

Sorry I do not know labs particularly working on C. botulinum.

You can try to get in touch with labs working on Food Microbiology.

All the best.

You can find detailed protocols for C. botulinum in microbiology text books.  There are also standard official protocols used by major organizations such FAO, FDA (USA), etc.  Spain probably is govern by EU regulation, so you should be able to find all relevant information on the EU commission web site.  The most practical approach for you, I would suggest is to contact your local health authorities in Barcelona for guidelines.