Question: how can you tell by using this test that a substance contains protein
[{'answer': 'biuret test', 'provenance': [{'wikipedia_id': '4706278', 'title': 'Biuret test', 'start_paragraph_id': 1, 'start_character': 4, 'end_paragraph_id': 1, 'end_character': 15, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '4706278', 'title': 'Biuret test', 'start_paragraph_id': 13, 'start_character': 0, 'end_paragraph_id': 13, 'end_character': 535, 'bleu_score': 0.950027409461844, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16710445920857438877}, 'section': 'Section::::High sensitivity variants of the biuret test.\n'}]}]