Growth of spoilage organisms and Yersinia enterocolitica in osmotically dehydrated carrot slices under modified atmospheres held at 4ℓ̊and 10C̊

Author

Jianjin Hou

Date of Award

5-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

Frances A. Draughon

Committee Members

John R. Mount, David A. Golden

Abstract

The effects of the combination of osmotic dehydration and modified atmosphere on growth of spoilage organisms and pathogenic Yersinia enterocolitica on carrot slices stored at 4° and 10°C were determined in this study. Microbiological analyses showed that during 21 days storage at 4°C, the initial aerobic plate count (APC) and psychrotrophic counts on carrots ranged from 3.5-4.4 log CFU/g and significantly increased to maximum levels of 7.4-8.5 log CFU/g, respectively; a range of 2.7-3.8 log CFU/g initial number of coliforms increased to 6.7-7.7 log CFU/g; lactic acid bacterial counts of 2.1-2.9 log CFU/g increased to 4.6-8.6 log CFU/g, mesophilic spore forming counts of 1.7 log CFU/g increased to 3.7 log CFU/g; pectinolytic bacteria increased approximately 3.7 log CFU/g; initial numbers of yeasts were 2.0-3.0 log CFU/g increased approximately 3 log CFU/g; and molds did not grow well in packages with either treatment. A statistical con^arison of growth between dehydrated and non-dehydrated carrot san:q)les showed that osmotic dehydration significantly slowed growth of aerobes, psychrotrophic, coliforms, pectinolitics, and yeast before 9 days storage, but reached a higher maximum population than that of non-dehydrated carrots after 21 days at 4°C; mesophilic anaerobic spore forming bacteria did not significantly increase at 4°C. Salt treatment significantly stimulated growth of lactic acid bacteria which reached significantly higher maximum numbers in osmotically treated carrots than that in non-treated samples. A storage temperature of 10°C caused a faster increase and higher maximum populations of organisms on carrots within 15 days compared to that at 4°C. The APC and psychrotrophic counts for carrots with salt treatment increased from approximately 4.0 and 3.4 log CFU/g to 9.2 and 9.1 log CFU/g. The counts for non-dehydrated carrots were increased from initially 4.4 and 4.1 log CFU/g to 7.5 and 7.4 log CFU/g, respectively; the maximum coliform counts reached 8.6-9.0 log CFU/g for dehydrated carrots; significantly better growth and higher maximum counts of lactic acid bacteria occurred in osmotically treated carrots (7.8 CFU/g for dehydrated and 3.6-4.9 log CFU/g for non-dehydrated samples); the storage time, temperature of 10°C, and osmotic dehydration significantly increased the levels of mesophilic anaerobic spore forming bacteria; pectinolytic bacteria increased approximately 3.7 log CFU/g, but were not significantly affected by salt treatment; the number of yeasts was increased approximately 2.4 log CFU/g at 10°C after 15 days, and osmotic dehydration significantly increased their growth on carrots; carrots packaged in air or vacuum did not support the growth of molds at 10°C. Packaging atmosphere did not significantly affect growth of most bacteria, but significantly greater growth of lactic acid bacteria at 4°C and mesophilic anaerobic spore forming bacteria at 10°C occurred under vacuum condition.

The numbers of Yersinia enterocolitica rapidly grew up from the range of 3.9-4.6 to 6.6-8.2 log CFU/g for the carrots at 4°C after 21 days, and from 3.2-3.8 to 6.8-8.9 log CFU/g at 10°C after 15 days storage. Osmotic dehydration did not significantly affect the growth of Y. enterocolitica at 4°C, but significantly increased its growth on carrots at 10°C. The increased storage temperature greatly reduced the lag phase and increased maximum counts, especially, for the osmotically dehydrated carrots. Atmosphere conditions had less effect on the growth of Y. enterocolitica. Congo red assay and salicin fermentation test found Y. enterocolitica retained their virulent plasmid. Minimally processed vegetables are ready-to-eat foods and the cut surfaces and high moisture level could provide Y. enterocolitica with good conditions for growth. High CO₂ levels in packages and inadequate temperature control during refrigeration storage may favor the growth of Y. enterocolitica. From these data, modified atmosphere combined with osmotic dehydration does not seem to be an effective way to reduce growth of Y. enterocolitica in minimally processed carrots. An additional barrier (s) is necessary to prevent growth of Y. enterocolitica during storage of the products.

The increased temperature and osmotically dehydration caused an increased respiration rate of plant tissue and microbial metabolism resulting in high CO₂ concentrations in packaging and reduced shelf life of products due to the physiological damage of plant tissue and rapid growth of lactic acid bacteria and yeasts. Although osmotic dehydration increased the spoilage of carrots, it provided a way to prevent moisture loss and discoloration of carrot surfaces dming storage. This might be a new way for improving appearance of carrots during cold storage.

Recommended Citation

Hou, Jianjin, "Growth of spoilage organisms and Yersinia enterocolitica in osmotically dehydrated carrot slices under modified atmospheres held at 4ℓ̊and 10C̊. " Master's Thesis, University of Tennessee, 1996.
https://trace.tennessee.edu/utk_gradthes/6819