title: Aspartic protease from Aspergillus (Eurotium) repens strain MK82 is involved in the hydrolysis and decolourisation of dried bonito (Katsuobushi).
abstract: BACKGROUND
  Katsuobushi is a dried, smoked and fermented bonito used in Japanese cuisine. During the fermentation process with several Aspergillus species, the colour of Katsuobushi gradually changes from a dark reddish-brown derived from haem proteins to pale pink. The change in colour gives Katsuobushi a higher ranking and price. This study aimed to elucidate the mechanism of decolourisation of Katsuobushi.
  
  
  RESULTS
  A decolourising factor from the culture supernatant of Aspergillus (Eurotium) repens strain MK82 was purified to homogeneity. The purification was monitored by measuring the decolourising activity using equine myoglobin and bovine haemoglobin as substrates. It was found that the decolourising factor had protease activity towards myoglobin and haemoglobin. Complete inhibition of the enzyme by the inhibitor pepstatin A and the internal amino acid sequence classified the protein as an aspartic protease. The enzyme limitedly hydrolysed myoglobin between 1-Met and 2-Gly, 43-Lys and 44-Phe, and 70-Leu and 71-Thr. The purified enzyme decolourised blood of Katsuwonus pelamis (bonito) and a slice of dried bonito.
  
  
  CONCLUSIONS
  It is proposed that aspartic protease plays a role in the decolourisation of Katsuobushi by the hydrolysis of haem proteins that allows the released haem to aggregate in the dried bonito.
authors.affiliation: Division of Nutritional Science, Graduate School of Nutritional Science, Sagami Women's University, 2-1-1 Bunkyo, Sagamihara, Japan. aoki_kenji@isc.sagami-wu.ac.jp
authors.forename: Kenji
authors.initials: K
authors.lastname: Aoki
authors.forename: Sayaka
authors.initials: S
authors.lastname: Matsubara
authors.forename: Mayo
authors.initials: M
authors.lastname: Umeda
authors.forename: Shusaku
authors.initials: S
authors.lastname: Tachibanac
authors.forename: Mikiharu
authors.initials: M
authors.lastname: Doi
authors.forename: Shinji
authors.initials: S
authors.lastname: Takenaka
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D057055:Aspartic Acid Proteases / Q000302:isolation & purification / Q000378:metabolism*; D001230:Aspergillus / Q000201:enzymology*; D002417:Cattle; D003116:Color; D003890:Desiccation; D004032:Diet; D005285:Fermentation; D005399:Fishes; D005516:Food Microbiology; D006454:Hemoglobins / Q000378:metabolism*; D006736:Horses; D006801:Humans; D006868:Hydrolysis; D009211:Myoglobin / Q000378:metabolism*; D010436:Pepstatins / Q000494:pharmacology; D010858:Pigmentation; D017747:Seafood / Q000032:analysis / Q000382:microbiology*
chemical_list: D000596:Amino Acids; D006454:Hemoglobins; D009211:Myoglobin; D010436:Pepstatins; D057055:Aspartic Acid Proteases; C031375:pepstatin