Polygalacturonase, pectinesterase, and lipoxygenase activities in high-pressure-processed diced tomatoes

High-pressure processing (HPP) can inactivate pathogenic microorganisms and degradative enzymes without the use of heat, thereby minimizing the destruction of flavors, nutrients, and other quality attributes. Lipoxygenase plays a role in the off-flavor production of tomatoes, whereas pectinesterase and polygalacturonase impact tomato texture. The purpose of this study was to determine HPP's ability to inactivate lipoxygenase, pectinesterase, and polygalacturonase in diced tomatoes. Processing conditions used were 400, 600, and 800 MPa for 1, 3, and 5 min at 25 and 45 degrees C. The magnitude of applied pressure had a significant effect on inactivating lipoxygenase and polygalacturonase (p < 0.05), with complete loss of activity occurring at 800 MPa. Pectinesterase was very resistant to pressure treatment. Percent soluble solids, pH, titratable acidity, and color a/b values did not differ significantly among the high-pressure-processed samples as compared to the control, but color L values increased. This change in L values was not considered of practical importance. Apparent protein content decreased in the pressure-processed samples, due possibly to protein denaturation, loss of solubility, and/or a decrease in dye binding sites to assay protein content.     

Frequency-dependent selection by wild birds promotes polymorphism in model salamanders

Background  

Co-occurrence of distinct colour forms is a classic paradox in evolutionary ecology because both selection and drift tend to remove variation from populations. Apostatic selection, the primary hypothesis for maintenance of colour polymorphism in cryptic animals, proposes that visual predators focus on common forms of prey, resulting in higher survival of rare forms. Empirical tests of this frequency-dependent foraging hypothesis are rare, and the link between predator behaviour and maintenance of variation in prey has been difficult to confirm. Here, we show that predatory birds can act as agents of frequency-dependent selection on terrestrial salamanders. Polymorphism for presence/absence of a dorsal stripe is widespread in many salamander species and its maintenance is a long-standing mystery.     

An Approximate Bayesian Analysis of Somatic Cell Score Curves in Holsteins

Somatic cell score (SCS) decreases to a minimum at around 60 days postpartum and then increases until the end of lactation. This pattern was described with three non-linear mixed effects models. Parameters of the models were linear in fixed and random (cow) effects. Data were 1705 SCS test-day records (155 primiparous Holsteins) taken from 14 to 300 days in milk. Point estimates were the mode of the joint posterior distribution of fixed and random effects (given dispersion parameters) and approximate marginal maximum likelihood estimates of covariance components. Intramammary infection during lactation, season and period of calving affected SCS patterns. Estimates were similar with or without a relationship matrix. There was between-cow variation of trajectories, suggesting that SCS curve parameters can be modified by selection in some advantageous manner.     

Effect of Mycobacterium paratuberculosis infection on production, reproduction, and health traits in US Holsteins

Our objective was to estimate the effect of Mycobacterium paratuberculosis infection on milk, fat, and protein yield deviations, pregnancy rate, lactation somatic cell score, and projected total months in milk (productive life). A serum ELISA and fecal culture for M. paratuberculosis were performed on 4375 Holsteins in 232 DHIA herds throughout the US. Primarily first through third lactation cows (99% of total) were assayed for infection. Trait information (except productive life) was obtained for the lactation concurrent with disease tests. Productive life was total months in milk through a cow's life, which was projected if a cow was still milking. For most analyses, case definition for M. paratuberculosis infection was defined as either an ELISA S/P ratio>or=0.25 or a positive fecal culture for M. paratuberculosis or both. To determine if diagnostic test affected estimates, case definition was redefined to include only cows with ELISA S/P ratios>or=0.25 or only fecal culture-positive cows. Linear models were used to estimate effect of M. paratuberculosis infection on traits. M. paratuberculosis-infected cows (7.89% of cows) produced 303.9 kg less milk/lactation, 11.46 kg less fat/lactation, and 9.49 kg less protein/lactation (P相似文献