Mary Smiddy

Use of oxygen sensors to non-destructively measure the oxygen content in modified atmosphere and vacuum packed beef: impact of oxygen content on lipid oxidation

The ability of optical oxygen sensors to monitor the levels of oxygen in raw and cooked beef was investigated. Raw and cooked beef slices were vacuum packaged and cooked beef slices were modified atmosphere packaged MAP, (60% N(2): 40% CO(2)) and held under refrigerated display (4 °C) for 15 or 35 days for MAP and vacuum packed samples, respectively. Oxygen sensors attached to the inside of the lidding material in modified atmosphere packages, or inserted into vacuum packages, were capable of monitoring changes in oxygen levels in all packaged samples. Lipid oxidation of samples was measured at regular intervals. Oxygen contents detected, ranged from 1.15 to 1.26% and 0.07-0.55% in MAP and vacuum packed samples, respectively. Samples containing greatest levels of oxygen were most oxidised and cooked samples were significantly (P<0.05) more oxidised than raw samples.

Role for compatible solutes glycine betaine and L-carnitine in listerial barotolerance

ABSTRACT Increased listerial barotolerance at elevated osmolarity is attributed, in part, to the presence of accumulated betaine and l-carnitine. The percentage of listerial survival following exposure to 400 MPa for 5 min increased from 0.008 to 0.02% with added l-carnitine (5 mM) and to 0.05% with added betaine (5 mM). Furthermore, listerial cells incapable of transporting compatible solutes fail to adapt to high pressure at elevated osmolarity.

Evaluation of oxygen content in commercial modified atmosphere packs (MAP) of processed cooked meats

Abstract Twenty-five packs of each of 13 processed cooked meats products, produced by three manufacturers, were analysed. Analysis was performed 1, 7, 14 and 21 days after obtaining samples at the point of manufacture. Although all products were packaged in modified atmospheres of 70% N2 and 30% CO2, oxygen was present in 88% of packs 24 h after packaging. Overall percentages of packs containing 0.0, 0.01–0.5, 0.51–1.2 and >1.2% oxygen were 11.7, 38.4, 29.4 and 20.4%, respectively on day 1 and 0.0, 15.5, 5.3 and 79.3%, respectively, on day 21. Three comparable pork products produced by three different manufacturers contained different levels of oxygen on day 1. The high proportion of packages containing rejectably high levels of oxygen may pose a potential risk of product quality deterioration and reduced shelf-life of muscle-based foods. Results emphasize the necessity to monitor oxygen levels within packs of oxygen-sensitive foods, including processed, cooked muscle foods.

Reformation of casein particles from alkaline-disrupted casein micelles

In this study, the properties of casein particles reformed from alkaline disrupted casein micelles were studied. For this purpose, micelles were disrupted completely by increasing milk pH to 10.0, and subsequently reformed by decreasing milk pH to 6.6. Reformed casein particles were smaller than native micelles and had a slightly lower zeta-potential. Levels of ionic and serum calcium, as well as rennet coagulation time did not differ between milk containing native micelles or reformed casein particles. Ethanol stability and heat stability, >pH 7.0, were lower for reformed casein particles than native micelles. Differences in heat stability, ethanol stability and zeta-potential can be explained in terms of the influence of increased concentrations of sodium and chloride ions in milk containing reformed casein particles. Hence, these results indicate that, if performed in a controlled manner, casein particles with properties closely similar to those of native micelles can be reformed from alkaline disrupted casein micelles.