title: Colour evaluation of a phycobiliprotein-rich extract obtained from Nostoc PCC9205 in acidic solutions and yogurt.
abstract: BACKGROUND
  Phycobiliproteins are coloured proteins produced by cyanobacteria, which have several applications because of their colour properties. However, there is no available information about the colour stability of phycobiliproteins from Nostoc sp. in food systems. The aim of this work was to study the colour stability of a purple-coloured phycobiliprotein-rich extract from the cyanobacterium Nostoc PCC9205 in acidic solutions and yogurt.
  
  
  RESULTS
  Variations of pH for Nostoc PCC9205 extract have shown stability for the L* (lightness) and a* (redness) indexes in the range 1.0-7.0. The b* index (blueness), however, increased at pH values below 4.0, indicating loss of the blue colour. The Nostoc PCC9205 extract was used as colorant in yogurt (pH 4.17) stored for 60 days. Instrumental colour analysis showed no changes for the L* and a* indexes during storage, whereas the b* index changed after 20 days of storage. A multiple comparison test showed colour instability after 20 days of storage. A hedonic scale test performed on the 60th day of storage showed acceptability of the product.
  
  
  CONCLUSIONS
  The red component of the phycobiliprotein-rich extract from Nostoc PCC9205 presented an improved stability in acidic media and yogurt compared with the blue component of this extract.
authors.affiliation: Departamento de Bromatologia, Faculdade de Farmácia, Universidade Federal Fluminense, Rio de Janeiro, Brazil.
authors.forename: Isabela
authors.initials: I
authors.lastname: de O Moreira
authors.forename: Thaís S
authors.initials: TS
authors.lastname: Passos
authors.forename: Claudete
authors.initials: C
authors.lastname: Chiapinni
authors.forename: Gabrielle K
authors.initials: GK
authors.lastname: Silveira
authors.forename: Joana C M
authors.initials: JC
authors.lastname: Souza
authors.forename: Luis Guillermo
authors.initials: LG
authors.lastname: Coca-Vellarde
authors.forename: Rosires
authors.initials: R
authors.lastname: Deliza
authors.forename: Kátia G
authors.initials: KG
authors.lastname: de Lima Araújo
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis* / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D001938:Brazil; D003116:Color; D045424:Complex Mixtures / Q000737:chemistry* / Q000302:isolation & purification; D005505:Food Coloring Agents / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D005518:Food Preferences; D063427:Food Quality; D061353:Food Storage; D006801:Humans; D006863:Hydrogen-Ion Concentration; D046937:Nostoc / Q000737:chemistry* / Q000378:metabolism; D052979:Phycobiliproteins / Q000032:analysis* / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D010860:Pigments, Biological / Q000032:analysis* / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D055550:Protein Stability; D012677:Sensation; D012995:Solubility; D013053:Spectrophotometry; D015014:Yogurt / Q000032:analysis*
chemical_list: D001426:Bacterial Proteins; D045424:Complex Mixtures; D005505:Food Coloring Agents; D052979:Phycobiliproteins; D010860:Pigments, Biological