Inhibitory Activity of Lactic Acid Bacteria against Spoilage Yeast Rhodotorula Mucilaginosa
Rhodotorula spp. are implicated for spoilage of cut vegetables producing slimy surfaces and off odours. This study evaluated the antiyeast activity of lactic acid bacteria (LAB) isolated from different sources against two local strains of R. mucilaginosa CBR and R. mucilaginosa CRT isolated from...
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| Summary: | Rhodotorula spp. are implicated for spoilage of cut vegetables producing slimy
surfaces and off odours. This study evaluated the antiyeast activity of lactic acid
bacteria (LAB) isolated from different sources against two local strains of R.
mucilaginosa CBR and R. mucilaginosa CRT isolated from carrot and cucumber,
respectively. A total of 38 LAB isolates were screened for antiyeast activity using dual
agar overlay method against the target yeast. Three isolates identified by API 50CH
kit and 16s rDNA as Lactobacillus casei DF22, L, casei YG 1 and L. plantarum C 16
showed highest inhibition activity (>13rnm) after 48 h incubation at 30°C. Cell free
supernatant (CFS) of all LAB reduced growth of target yeast by 96 to 99% and
resulted in 6 loglo reduction within 2411 incubation at 30°C. Adjusting pH of CFS to 3,
5,6 and 7 resulted in variable antiyeast activity ranging from 23.4% to 54.8%. CFS of
L. casei DF22 showed highest activity at pH 3, 5, 6, and 7 compared to other LAB.
Heating the CFS LAB at 90°C for 30 rnin and 120°C for 30 min significantly (P<0.05)
reduced the antiyeast activity of different LAB. Heating of CFS (pH 3.8 to 3.9) at
90°C for 30 min reduced the antiyeast activity of L. casei YG1 by 59.2%, while the
activity L. plantarum C16 was maintained 50.2% at 121°C for 30 min. Treatment of
CFS with pepsin, papain and proteinase K significantly (K0.05) reduced the antiyeast
activity by 26.8% to 52.5% indicating the presence of protein. Treatment with papain
significantly reduced (P<0.05) the inhibitory activity of CFS L. casei YG1. L. casei
YG1, L. casei DF22 and L. plantarum C16 have the ability to inhibit each other by
dual agar ovelay method indicating the presence of bacteriocin. CFS of LAB showed
anti-adhesion activity against biofilm produces by R. mucilaginosa CBR by precoating
and co-incubation method. Adjusting pH of CFS resulted in significantly
reduced activity ranging from 50.4% to 69.7%. Heating the CFS LAB at 90°C for 30
min and 120°C for 30 min significantly (P<0.05) reduced the anti-adhesion activity of
different LAB ranging from 40.5% to 66.4%. CFS of L. plantarum C16 was
maintained by 66.4% at 90°C. Treatment of CFS with pepsin, papain and proteinase K
significantly (P<0.05) reduced the anti-adhesiont activity by 26.2% to 60.6%. CFS
were significantly (P<0.05) affected by enzyme papain with L. casei YG1 resulted in
significantly (W0.05) lost of activity by 26.2%. This study demonstrated that the
selected LAB-CFS produced con~pounds in the supernatant that have the ability as
antiyeast and anti-adhesion against R. mucilaginosa and have potential to be used as
biopreservative in food industry. |
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