Food Science and Technology Programme, Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore.
Int J Food Microbiol. 2013 Jan 1;160(3):239-44. doi: 10.1016/j.ijfoodmicro.2012.11.003. Epub 2012 Nov 12.
The aim of this study was to determine survival or growth of unadapted, acid-adapted and cold-stressed Salmonella spp., and natural microbiota on fresh-cut dragon fruits at different storage temperatures. Dragon fruits were sliced and spot inoculated with five-strain cocktail of Salmonella spp. at two inoculum levels (2.5 or 5.5 log CFU/g). Inoculated fruits were stored at 28°C for 48h and at 4°C and 12°C for 96 h. Salmonella population significantly increased by 2.4 to 3.0 log CFU/g at low inoculum level, whereas the numbers increased by 0.4 to 0.7 log CFU/g at the high inoculum level on fruits held at 28°C for 48h. Only unadapted and acid-adapted cells grew with 0.7 to 0.9log increase at the low inoculum level at 12°C for 96h. No significant growth was observed at both inoculum levels during storage at 4°C. Overall, acid, starved and cold adaptation of Salmonella spp. did not show significant difference in survival or growth on fresh-cut dragon fruits during storage compared to unadapted control cells. For natural microbiota on the fruit, mesophilic bacterial counts reached to 5-log CFU/g at 28 and 12°C by 9.9 and 52.9h. Similar with Salmonella spp. there was no growth of natural microbiota at 4°C. These results showed that Salmonella spp. could grow on fresh-cut dragon fruits under inappropriate storage conditions, indicating that fresh-cut dragon fruits could be a potential vehicle for salmonellosis. Thus, this study suggests that fresh-cut dragon fruits should be stored at 4°C to ensure the safety as well as to extend the shelf life of fresh-cut dragon fruits.
本研究旨在确定未经适应、酸适应和冷应激的沙门氏菌和天然菌群在不同储存温度下的鲜切火龙果上的存活或生长情况。将火龙果切片并以两种接种水平（2.5 或 5.5 log CFU/g）点接种由五种沙门氏菌组成的鸡尾酒混合菌。接种后的果实分别在 28°C 下储存 48h，在 4°C 和 12°C 下储存 96h。在 28°C 下储存 48h 时，低接种水平的沙门氏菌数量增加了 2.4 至 3.0 log CFU/g，而高接种水平的数量增加了 0.4 至 0.7 log CFU/g。只有未经适应和酸适应的细胞在低接种水平下于 12°C 下储存 96h 时可增长 0.7 至 0.9 log。在 4°C 下储存时，两个接种水平均未观察到显著生长。总体而言，与未适应对照细胞相比，沙门氏菌在鲜切火龙果上的酸、饥饿和冷适应在储存过程中的存活或生长没有明显差异。对于果实上的天然菌群，在 28°C 和 12°C 下，嗜温菌的计数在 9.9 和 52.9h 时分别达到 5-log CFU/g。与沙门氏菌类似，在 4°C 下，天然菌群没有生长。这些结果表明，沙门氏菌可以在不适宜的储存条件下在鲜切火龙果上生长，这表明鲜切火龙果可能是沙门氏菌病的潜在载体。因此，本研究表明，为确保鲜切火龙果的安全性和延长其货架期，应将鲜切火龙果储存在 4°C 下。
