Thermal Inactivation of Listeria monocytogenes in Crab Meat

Listeria monocytogenes is an important bacterial pathogen in seafood products, but limited information is currently available on the thermal resistance of relevant isolates in seafood. Thermal inactivation studies were undertaken (i) to provide much needed thermal inactivation data for L. monocytogenes in crab meat and (ii) to investigate whether tryptone soya broth (TSB) is representative of crab meat in thermal inactivation studies involving L. monocytogenes. D-values were obtained for a cocktail of two crab isolates (serotypes 1/2a and 4b) at 50, 55, and 60°C. In crab meat, D-values were 174.4, 28.2, and 1.6 min, respectively. Similar D-values of 176.4, 28.8, and 1.4 min were obtained in TSB. The corresponding z-values were 4.9°C (crab meat) and 4.8°C (TSB), respectively. The conclusions were that (i) current pasteurization conditions (e.g., 70°C for 2 min) would achieve complete destruction of any L. monocytogenes present in crab meat and (ii) TSB could be used as a model matrix for assessing the thermal inactivation of L. monocytogenes in crab meat.

An assessment of the application of ultrasound in the processing of ready-to-eat whole brown crab (Cancer pagurus)

This study assesses the potential of incorporating ultrasound as a processing aid in the production of whole cooked brown crab (Cancer pagurus). The FDA recommended heat treatment to reduce Listeria monocytogenes by 6 log₁₀ cycles in this product is a F₇₀^7.5 of 2min. An equivalent F value was applied at 75°C in presence and absence of ultrasound in water alone or in water with 5% w/v NaCl added. Heat penetration, turbidity and conductivity of the cook water and also salt and moisture content of the crab meat (white and brown) were determined. Ultrasound assisted cooking allowed a reduction of the cooking time by up to 15% while still maintaining an F₇₀^7.5 of 2min. Ultrasound also enhanced the rate and total amount of compounds released from the crab, which suggests that crabs cooked in the presence of ultrasound would be expected to be cleaner. Ultrasound also proved to be effective in reducing the salt content but hardly affected the final moisture content of the crab meat.

Dielectric and thermophysical properties of meat batters over a temperature range of 5-85 °C

Dielectric (dielectric constant (ε(')) and loss factor (ε″)) and thermal (heat capacity (c), thermal conductivity (k) and thermal diffusivity (α))) properties of two meat batters (pork luncheon roll (PLR) and white pudding (WP)) were measured between 5 and 85 °C. Radio frequency (RF) and microwave (MW) ε″ values varied across 5-85 °C (P<0.05). MW ε(') and ε″ values for WP tended to peak at 45 °C and decrease thereafter, whereas for PLR, ε(') and ε″ peaked at 65 °C which appeared to match potato starch gelatinisation within this product. WP and PLR had significantly higher c values at 25 °C, which corresponded to the MP of pork fat. For PLR, an additional c peak was noted at 65 °C, which appeared to correspond to potato starch gelatinisation. At 85 °C, k values were higher (P<0.05) than at 5, 25 and 45 °C but were not higher than values at 65 °C. α values increased with temperature (P<0.05).

Effect of ultrasound and blanching pretreatments on polyacetylene and carotenoid content of hot air and freeze dried carrot discs

The effect of ultrasound and blanching pretreatments on polyacetylene (falcarinol, falcarindiol and falcarindiol-3-acetate) and carotenoid compounds of hot air and freeze dried carrot discs was investigated. Ultrasound pretreatment followed by hot air drying (UPHD) at the highest amplitude and treatment time investigated resulted in higher retention of polyacetylenes and carotenoids in dried carrot discs than blanching followed by hot air drying. Freeze dried samples had a higher retention of polyacetylene and carotenoid compounds compared to hot air dried samples. Color parameters were strongly correlated with carotenoids (p<0.05). This study shows that ultrasound pretreatment is a potential alternative to conventional blanching treatment in the drying of carrots.

Quality and Antioxidant Properties of Fresh-cut Apple Wedges from 10 Cultivars During Modified Atmosphere Packaging Storage

Antioxidant activity and quality parameters of skin-on apple wedges from 10 cultivars were examined during chill storage and over two growing seasons. Storage of fresh-cut apple wedges had a significant impact on quality parameter indices such as browning index (p < 0.001) and texture firmness (p < 0.001). Headspace gas analysis indicated that the degree of browning negatively correlated to oxygen (-0.69) and positively (0.70) correlated to carbon dioxide levels. Antioxidant capacity as assessed by three in vitro methods (DPPH, FRAP and ORAC) decreased significantly for 9 of the 10 cultivars after 5 days of storage at 3 ± 1 °C (p < 0.001). These indices increased in case of Shampion apples over the same storage period for all three assays. With regard to antioxidant capacity and quality parameters, the cultivars Gloster, Alwa, Idared and Jonica were the best performing overall and could therefore be recommended as a core ingredient in fresh-cut fruit products.

Effect of ultrasound processing on anthocyanins and color of red grape juice

Grape juice samples were sonicated with processing variables of amplitude level (24.4-61.0microm) and treatment time (0-10min) at a constant frequency of 20kHz and pulse durations of 5s on and 5s off. A full factorial experimental design with regression modeling was employed to investigate the main effects of amplitude level and treatment time on anthocyanins and color parameters. Significant effects of sonication on major anthocyanins cyanidin-3-O-glucosides (CA), malvanidin-3-O-glucosides (MA) and delphinidin-3-O-glucosides (DA), color values (L*, a*, b*) and color index (CI) were observed. Prediction models were found to be significant (p<0.05) with low standard errors and high coefficients of determination (R(2)). Model predictions for critical quality parameters of anthocyanins (CA; MA; DA), color values (L*, a*, b*), TCD and CI inactivation were closely correlated to the experimental results obtained. Significant retention of anthocyanin content in grape juice was observed for CA (97.5 %); MA (48.2 %) and DA (80.9%) during sonication. CI and other color combinations (L*a*b*, L*a*/b* and L*b*/a*) were found to be strongly correlated with anthocyanin content. This study shows that sonication could be employed for as a preservation technique for fruit juice processing where anthocyanin retention is desired.

Anthocyanins and color degradation in ozonated grape juice

Grape juice samples were ozonated with processing variables of ozone concentration (1.6-7.8% w/w) and treatment time (0-10 min). Effects of processing variables on grape juice color values (L, a and b) and anthocyanins were determined. The changes in lightness (L) values and total color difference (TCD) values were fitted well to zero-order kinetics whereas, a and b followed first-order kinetics. Three major anthocyanins were observed in the grape juice namely cyanidin-3-O-glucoside (Cy3Gl, 133.9 mg/L), delphinidin-3-O-glucoside (Dy3Gl, 21.4) and malvidin-3-O-glucoside (My3Gl, 3.2mg/L). Significant reductions in anthocyanin content were observed during ozonation. During ozonation Cy3Gl was found to be stable compared to Dy3Gl and My3Gl. Changes in Cy3Gl were fitted well to the fraction conversion model. The results presented in this study indicate that both color and anthocyanin content are significantly affected during ozone processing. Thus, the effects of ozonation on the grape juice should be considered by processors prior to its adoption as a preservation technique.