Orange juice (OJ) is a food product available in various formswhich can be processed to a greater or lesser extent.
Minimally-processedOJ has a high consumer perception but presents a potential microbiological risk due to acidtolerant
bacteria. Clarification of OJ (such as removal of cloud) is a common processing step inmany OJ products.
However, many of the antimicrobial components of OJ such as essential oils are present in the cloud fraction.
Here, the effect of clarification by filtration on the viability and physiology of Escherichia coli K-12 was tested
using total viable count (TVC) and flowcytometric (FCM) analysis. The latter technique was also used tomonitor
intracellular pH during incubation in OJ. Removal of the OJ cloud fraction was shown to have dramatic effects on
bacterial viability and physiology during storage at a range of incubation temperatures. For instance, at 4 °C, a
significantly lower number of healthy cells and a significantly higher number of injured cells were observed in
0.22 μm-filtered OJ at 24 h post-inoculation, compared to filtered OJ samples containing particles between
0.22 μm and 11 μm in size. Similarly, there was a significant difference between the number of healthy bacteria
in the 0.7 μm-filtered OJ and both 0.22 μm-filtered and 1.2 μm-filtered OJ after 24 hour incubation at 22.5 °C. This
indicated that OJ cloud between 0.7 μmand 0.22 μmin sizemight have an adverse effect on the viability of E. coli
K-12. Furthermore, FCM allowed the rapid analysis of bacterial physiology without the requirement for growth
on agar plates, and revealed the extent of the viable but non-culturable (VBNC) population. For example,
at 4 °C, while the FCMviable count did not substantially decrease until 48 h, decreases in TVC were observed
between 0 and 48 hour incubation, due to a subset of injured bacteria entering the VBNC state, hence being
unable to grow on agar plates. This study highlights the application of FCM in monitoring bacterial physiology
in foods, and potential effects of OJ clarification on bacterial physiology.
Orange juice (OJ) is a food product available in various formswhich can be processed to a greater or lesser extent.Minimally-processedOJ has a high consumer perception but presents a potential microbiological risk due to acidtolerantbacteria. Clarification of OJ (such as removal of cloud) is a common processing step inmany OJ products.However, many of the antimicrobial components of OJ such as essential oils are present in the cloud fraction.Here, the effect of clarification by filtration on the viability and physiology of Escherichia coli K-12 was testedusing total viable count (TVC) and flowcytometric (FCM) analysis. The latter technique was also used tomonitorintracellular pH during incubation in OJ. Removal of the OJ cloud fraction was shown to have dramatic effects onbacterial viability and physiology during storage at a range of incubation temperatures. For instance, at 4 °C, asignificantly lower number of healthy cells and a significantly higher number of injured cells were observed in0.22 μm-filtered OJ at 24 h post-inoculation, compared to filtered OJ samples containing particles between0.22 μm and 11 μm in size. Similarly, there was a significant difference between the number of healthy bacteriain the 0.7 μm-filtered OJ and both 0.22 μm-filtered and 1.2 μm-filtered OJ after 24 hour incubation at 22.5 °C. Thisindicated that OJ cloud between 0.7 μmand 0.22 μmin sizemight have an adverse effect on the viability of E. coliK-12 นอกจากนี้ FCM อนุญาตวิเคราะห์สรีรวิทยาของแบคทีเรียโดยไม่มีข้อกำหนดสำหรับการเจริญเติบโตอย่างรวดเร็วบนแผ่น agar และเปิดเผยขอบเขตของประชากร (VBNC) ทำงานได้ แต่ culturable ไม่ ตัวอย่างที่ 4 ° C ขณะนับ FCMviable ได้ไม่มากลดลงจนถึง 48 h ลดใน TVC สุภัคระหว่าง 0 และบ่ม 48 ชั่วโมง เนื่องจากการย่อยของแบคทีเรียบาดป้อนสถานะ VBNC ดังนั้นการไม่สามารถเติบโตบนแผ่น agar การศึกษานี้เน้นของ FCM สอบสรีรวิทยาของแบคทีเรียอาหาร และผลกระทบอาจชี้แจง OJ สรีรวิทยาของแบคทีเรีย
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