David O’Beirne

Evaluation of the impact of short-term temperature abuse on the microbiology and shelf life of a model ready-to-use vegetable combination product

The growth dynamics of indigenous aerobic mesophilic populations (AMP), lactic acid bacteria (LAB) and inoculated (Listeria spp.) microbial populations on cooked and fresh vegetable products, packaged as separate entities and in combination, subjected to temperature fluctuation, were assessed. Microbial proliferation was temperature and product dependent, being most pronounced at 12 degrees C in all products with maximum growth rates of 0.140, 0.175 and 0.126 log10 CFU/g per h being identified for Listeria, aerobic mesophilic and LAB populations, respectively. Listeria spp. and AMP generally demonstrated higher rates of growth within products containing cooked vegetables. Prolonged storage at 3 degrees C resulted in a reduced ability by AMP and Listeria spp. to proliferate upon exposure to growth temperatures; this was not the case with LAB populations. Comparison of Listeria population estimates made using selective (Oxford) and non-selective (nutrient agar) identified reduced recovery on the former. The magnitude of the deviation increased with the duration of exposure of Listeria populations to 3 degrees C with recoveries on selective systems being reduced by 6.3% immediately after inoculation and 82.3% after 168 h at 3 degrees C, respectively. Growth of populations associated with exposure to abuse temperatures was not accompanied by significant changes in product colour (P < 0.05).

Effects of sodium caseinate concentration and storage conditions on the oxidative stability of oil-in-water emulsions.

The oxidative stability of various oils (sunflower, camelina and fish) and 20% oil-in-water (O/W) emulsions, were examined. The mean particle size decreased from 1179 to 325 nm as sodium caseinate (emulsifier) concentration was increased from 0.25% to 3% in O/W emulsions (P<0.05). Increasing the microfluidisation pressure from 21 to 138 MPa, resulted in a particle size decrease from 289 to 194 nm (P<0.05). Emulsified oils had lower detectable lipid hydroperoxide and p-Anisidine values than their corresponding bulk oils (P<0.05). The lipid hydroperoxide and p-Anisidine values of emulsions generally decreased as sodium caseinate concentration increased, and similarly decreased as microfluidisation pressure increased (P<0.05). Increasing storage temperature of the emulsions from 5 to 60°C, resulted in lower detectable lipid oxidation products during storage (P<0.05).

Effects of Argon Enriched Low-Oxygen Atmospheres and of High-Oxygen Atmospheres on the Kinetics of Polyphenoloxidase (PPO)

The reported benefits of enrichment of air atmospheres with argon or oxygen for control of enzymatic browning were investigated by determining the effects of these atmospheres on PPO kinetics. Kinetics of purified apple PPO and a commercially available mushroom PPO were studied in an in vitro model system. Enrichment with argon produced greater inhibitory effects than the current industry practice of enrichment with nitrogen. Km(app) values (mM) for apple PPO in 3%O(2)/97%Ar, 3%O(2)/97%N(2), and air, were 133, 87, and 48, respectively. The data indicate that inhibition by both gases is competitive, and also support the hypothesis that the greater inhibitory effect of argon was proportional to the size of the Van der Waals radius of argon against nitrogen (1.91 Å against 1.54 Å). Much smaller inhibitory effects were observed in the presence of 80% O(2) (Km(app) 57 mM), and the nature of this inhibition was less clear. The results suggest that the benefits of argon enrichment may be relatively small, and may require critical enzyme, substrate, and gas levels to be successful. However, these benefits may be exploitable commercially in some fresh-cut products, and may allow less anoxic atmospheres to be used. Practical Application: Control of enzymatic browning without sulfites continues to be a challenge in some fresh-cut products. While sporadic benefits of these atmospheres in control of enzymatic browning have been reported, results have been inconsistent in commercial practice. The results suggest that the benefits of argon enrichment may be relatively small, and may require critical enzyme, substrate, and gas levels to be successful. However, these benefits may be exploitable commercially in some fresh-cut products, and allow less anoxic atmospheres to be used.