The effect of oxygen and carbon dioxide partial pressure (p O 2 and p CO 2 , respectively) and temperature on respiratory patterns and quality of cut iceberg lettuce was examined in modified atmosphere (MA) packages. The changes in headspace p O 2 of packaged lettuce with time were related to void volume, storage temperature, mass, and decreasing respiration rate. Uptake of O2 was modeled using a Michaelis−Menten-type equation. At 5 and 10 °C, maximum O2 uptakes were 143 and 213 pmol·g-1·s-1 and the p O 2 at half-maximal (k 1/ 2) values were 0.26 and 0.19 kPa, respectively. On the basis of ethanol appearance in the headspace, the fermentation induction point was 0.3−0.4 kPa of O2 at 5 °C and 0.6−0.8 kPa of O2 at 10 °C. Acetaldehyde and ethyl acetate were detected at <0.4 kPa of O2 at 5, 10, and 20 °C (1 kPa ∼ 1% at STP). The extent of browning increased with headspace p O 2 but was not related to headspace p CO 2 . Keywords: Modified atmosphere packaging; cut iceberg lettuce; color; respiratory patterns; volatile production

To elucidate the roles of the head and tail portions of chicken breast muscle myosin in gelation, the thermal stability and aggregation behavior of myosin and seven subfragments in 0.6 M NaCl, pH 6.5, were investigated, namely, myosin heavy chain (MHC), light chains (LC), heavy meromyosin (HMM), light meromyosin (LMM), rod, subfragment 2 (S-2), and subfragment 1 (S-1). Myosin had four independent cooperative endothermic transitions (T m) at 47, 54, 57, and 63 °C and aggregated from 50 to 70 °C. The MHC endotherm had peaks at 46, 54, and 64 °C and aggregated between 45 and 63 °C. S-1 unfolded in a single transition, having a T m of 47.7 °C, and aggregated from 49 to 53 °C. The rod melted between 30 and 63.3 °C and continuously aggregated over this temperature range. Initial unfolding of the rod occurred in the LMM region. S-2 was primarily responsible for denaturation and aggregation above 55 °C. Transition temperatures of 48 and 57 °C were recorded for LC; however, no aggregation occurred. The rod had the biggest influence on gel formation. Light meromyosin and S-1 contributed to gel structure at temperatures less than about 55 °C, whereas S-2 was responsible for matrix formation above 60 °C. Keywords: Myosin; gelation; differential scanning calorimetry; denaturation

Chicken surimi was prepared from fresh mechanically separated chicken meat using a sodium bicarbonate washing process. The heat-induced gelation properties were assessed under different conditions of pH, temperature, heating rate, protein and sodium tripolyphosphate (TPP) concentrations. Surimi gel strength increased (p Ͻ 0.05) after: reducing pH from 6.4 to 6.0, increasing temperature from 40ЊC to 80ЊC, reducing heating rate from 5ЊC/min to 1ЊC/min, increasing protein concentration from 4% (w/w) to 8% (w/w) or addition of 0.3% (w/w) TPP. Freeze thaw stability studies revealed that the gel strength of surimi decreased (p Ͻ 0.05) when subjected to frozen storage at Ϫ18ЊC.

No abstract

The functions of thiol groups in the denaturation, aggregation and gelation of chicken breast muscle myosin during heating in 0.6M NaCl, 50mM sodium phosphate buffer, pH 6.5, was investigated by inhibiting disulfide (SS) bond formation using dithiothreitol (DTT). The endotherm of myosin heated in the presence or absence of DTT had similar thermal transition temperatures. Preventing SS bond formation increased the onset temperature for aggregation and gelation and decreased the elastic-like properties of the final gel matrix. Results indicated that SS bond formation was not a prerequisite for the gelation of chicken breast myosin. However, intermolecular SS bonds, especially from thiol groups on subfragment-1, contributed to gel network formation.