Detailed study and molecular identification of bacteria spp. causing bitter flavour in pasteurized cream

Subject Areas : Food Microbial Contamination

Hoda Dezhkhi ¹ , Sajjad Yazdansetad ² , Nazila Arbabsoleymani ³ , Reza Najafpour ⁴ , Seyed Mohammad Gheibi hayat ⁵ , الیکا فرج تبریزی ⁶

1 - Department of Microbiology, Faculty of Basic Sciences, Karaj Branch, Islamic Azad University, Alborz, Iran.
2 - Young Researchers and Elite Club, Damghan Branch, Islamic Azad University, Damghan, Iran.
3 - Department of Microbiology, Faculty of Basic Sciences, Damghan Branch, Islamic Azad University, Damghan, Iran.
4 - Department of Microbiology, Faculty of Basic Sciences, Qom Branch, Islamic Azad University, Qom, Iran.
5 - Student Research Committeee, Department of Medical Biotechnology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
6 - دانشگاه آزاد اسلامی، واحد قم، دانشکده علوم پایه، گروه میکروب شناسی، قم، ایران.

Received: 2016-09-04 Accepted : 2017-04-15 Published : 2017-04-21

Keywords: Bacillus, cream, Protease, bitter,

Abstract :

Cream enabled the growth of most microorganisms due to the adequate moisture, pH close to neutral, and nutrient rich. The major cause of bitter flavour in cream is degradation of proteins to the hydrophobic peptides by protease enzyme derived from the thermostable bacteria resistant to the pasteurization temperature. The present study was aimed to investigate and molecular identify of bacteria spp. causing bitter flavour in pasteurized cream. The pasteurized cream samples were collected, then microbiological tests such as total count of microorganisms, psychrotrophic bacteria count, coliform bacteria count, thermostable bacteria count, sporogen bacteria count and also chemical tests such as acidity and pH measurement were carried out. The tests were fulfilled with three repetitions at 4ºC and 15ºC in first, third, fifth, seventh, ninth, and eleventh days after the cream production. The isolates causing bitter flavour in creams were identified by physiological, biochemical, phylogenetical, and molecular methods. The bacterial isolates were inoculated into the pasteurized creams and assayed for changing in flavour. The two species of bacteria causing bitter flavor were isolated from the pasteurized creams. The sequencing of 16S rRNA gene of isolates indicated that they were Bacillus cereus and Bacillus subtilis. The temperature of preservation is one of the most important agents of microorganisms’ activity and dairy product durability. Keeping raw milk for a long time before the pasteurization leads to increasing proteolytic bacteria resistant to the pasteurization temperature, producing protease by the organisms and finally, changing the product flavour.