Role of Whey Components in the Kinetics and Thermodynamics of β-Lactoglobulin Unfolding and Aggregation

The optimisation of dairy unit operations involving heat transfer requires the control of fouling and aggregation phenomena following the denaturation of thermosensitive proteins, in particular β-lactoglobulin (β-lg). This study intends to give a better view of the influence of whey components (whey proteins, lactose, and minerals such as calcium) on β-lg denaturation through a combined kinetic and thermodynamic approach. β-lg denaturation in model solutions of increasing complexity (pure β-lg solution, whey protein solution, and two model wheys differing in mineral content) was characterised at temperatures ranging from 64.5 to 98 °C by following the evolution of soluble β-lg concentration with HPLC. It was demonstrated that whatever the model solution composition, a two-step mechanism (unfolding followed by aggregation) of 1.5-order kinetics could be adopted to describe β-lg denaturation reaction, as the temperature dependence of the denaturation reaction rate was properly fitted by Arrhenius equation. The dependency of kinetic and thermodynamic parameters on solution composition indicated that the presence of whey proteins enhanced β-lg aggregation, whereas lactose showed a small protective effect against β-lg unfolding. Additionally, minerals, especially calcium, tended to stabilise β-lg native state while increasing β-lg aggregation rates. However, at high mineral content, calcium influence could be hindered or even reversed, presumably owing to a lower bioavailability due to complexation with anions such as inorganic phosphates.     

High trimethylamine concentration in milk from cows on standard diets is expressed as fishy off-flavour

To establish whether fishy off-flavour observed in cows' milk in Sweden is due to abnormal concentrations of trimethylamine (TMA) in milk, 15 milk samples from 13 cows of the Swedish Red and White breed (SRB) were analysed for this compound using dynamic headspace (DHS) gas chromatography (GC). A mass selective detector (MSD) was used for the qualitative and a flame ionization detector (FID) for the quantitative analyses. Further confirmation was obtained using a solid phase microextraction (SPME) followed by GC-olfactometry (GC-O) and GC-NPD (nitrogen and phosphorus detector). Samples were also evaluated by a two-person organoleptic panel for the presence of fishy off-flavour. Results showed that the seven milk samples with a fish-like taint contained > 1 mg TMA/kg milk, whereas, with a single exception, the seven samples that were judged to be normal did not contain this compound. Furthermore, there were indications of a dose-dependent relationship between TMA concentration and fishy off-flavour score.     

A comparison of the retention of vitamins B1, B2 and B6, and cooking yield in pork loin with conventional and enhanced meal-service systems

In this study different simulated meal-service systems were compared with respect to vitamin B₁, B₂ and B₆ retention, and cooking yield in pork roasts. Initially the roasts were cooked traditionally or sous vide. No significant differences were observed between cooking methods. Further processing included warm-holding, conventional cook-chill, modified atmosphere packaging (MAP) and sous vide. Compared to retention in the freshly cooked samples, vitamin B₂ retention remained unaffected, irrespective of the meal-service system used and storage period. As regards vitamin B₁ and vitamin B₆, retentions declined significantly, by 14% and 21% respectively during 3 h of warm-holding, and by 11% and 19% respectively after 1 day of storage and subsequent reheating (cook-chill, MAP and sous vide). Vitamin B₁ retention declined by an extra 4% during storage for 14 days (sous vide) (not significant) It is concluded that conventional and enhanced meal-service systems produce roasts with similar quality attributes. Adjustment factors of 15% and 20% for vitamin B₁ and B₆ respectively are suggested, in addition to the losses caused by the initial heat treatment.     

Recovery of volatile fruit juice aroma compounds by membrane technology: Sweeping gas versus vacuum membrane distillation

The influence of temperature (10–45 °C), feed flow rate (300–500 L/h) and sweeping gas flow rate (1.2–2 m³/h) on the recovery of berry fruit juice aroma compounds by sweeping gas membrane distillation (SGMD) was examined on an aroma model solution and on black currant juice in a lab scale membrane distillation set up. The data were compared to recovery of the aroma compounds by vacuum membrane distillation (VMD). The flux of SGMD increased with an increase in temperature, feed flow rate or sweeping gas flow rate. Increased temperature and feed flow rate also increased the concentration factors (C_permeate/C_feed) of the aroma compounds. At 45 °C the most volatile and hydrophobic aroma compounds obtained the highest concentration factors: 12.1–9.3 (black currant juice) and 17.2–12.8 (model solution). With black currant juice a volume reduction of 13.7% (vol.%) at 45 °C, 400 L/h, resulted in an aroma recovery of 73–84 vol.% for the most volatile compounds. Compared to VMD, the aroma recovery with SGMD was less influenced by the feed flow rate but more influenced by the temperature. Higher fluxes were achieved during concentration by VMD and this reduced the operation time, which in turn reduced the degradation of anthocyanins and polyphenolic compounds in the juice.

Industrial relevance

High temperature evaporation is the most widely used industrial technique for aroma recovery and concentration of juices, but membrane distillation (MD) may provide for gentler aroma stripping and lower energy consumption. This study gives important clues about the fate of berry juice aroma compounds and polyphenols during concentration by MD, and identifies the main factors influencing the aroma recovery efficiency with MD. Both SGMD and VMD are promising techniques for gentle stripping of berry juice aroma compounds and deserve further consideration as alternative techniques for gentle aroma stripping in industrial fruit juice processing.     

Prediction of the failure probability of the overhead power line exposed to large-scale jet fires induced by high-pressure gas leakage

A thermal failure model (TFM) is proposed to predict the failure probability of Aluminum Conductor Steel-Reinforced (ACSR) typed power line close to a large-scale jet fire of leaked high-pressure gases. It introduces a newly developed method for heat transfer from jet fires and a distribution model for conductor failure probability via IEEE Standard 738–2012. Comparisons covering van der Waals equation, jet flame length correlations (Chamberlain, Schefer, Molkov and Bradley) and thermal radiation models (point source, multi-point source and line source) were made to illustrate priority with respect to experimental measurement of large hydrogen and natural gas jet fires. Results show that a theoretical framework incorporating van der Waals equation, Molkov's correlation for jet flame length, radiative fraction model and point source model is adequately precise to predict high-pressure leakage process, total flame length and received radiant heat flux (far-field). Predicted total flame lengths of a large jet fire for nearby power lines within 50–200 m to the accident site correspond well to reported results and the conservative hazard ranges are predicted based on harm criteria of wood and Probit equations. In simulations, an acceptable safety distance for power line carrying 907 A and below is determined to be 150 m.     

Enriching breakfast sausages by feeding pigs with CLA supplemented diets

Approaches for improving the profile of functional unsaturated fatty acids in pork products include dietary supplementation of pigs with functional oils. Little information is available to indicate the benefit of this approach in a processed and cooked pork product such as breakfast sausages. Therefore, the aim of the present study is to examine the fatty acid profile and oxidation level in cooked pork sausages, produced following dietary supplementation with CLA compared to sunflower oil (SFO). Fat and moisture percentages, total fatty acid profiles and TBARS were analysed. Fatty acid profiles were altered in the sausages following all treatments. While a stronger effect was seen for CLA treatments, addition of SFO in the diet also resulted in linear increases of CLA in the sausages. CLA supplementation resulted in increased saturated fatty acid content; however, all treatments were within the recommended polyunsaturated/saturated fatty acid ratio of above 0.4. Improved oxidative stability was observed in sausages from CLA supplemented diets.     

Observation versus self-report: validation of a consumer food behavior questionnaire

A reliable and validated set of food safety behavior questions that could be used with confidence when evaluating food safety education programs was identified in this study. A list of 29 food-handling and consumption behaviors rank-ordered within five pathogen control factors by nationally recognized food safety experts was the basis for the development of the behavior questions. Questions were evaluated for reliability and several forms of validity. During a kitchen activity session, 70 graduates of a nutrition education program completed four food preparation tasks while being observed and videotaped. The individuals also participated in an in-depth interview to validate behaviors that could not be observed during the food preparation activity, e.g., refraining from preparing food for others when experiencing diarrhea. Criterion validity was established by comparing questionnaire responses to observed behavior and interview responses. Twenty-eight questions met the validity criterion (> or = 70% agreement between observed and interviewed responses and self-reported responses), with three or more questions from each of five pathogen control factor areas. Observation assessments revealed that hand washing was more likely to be performed prior to beginning food preparation than between working with raw meats and fresh produce. Errors in methods of washing hands, utensils, and preparation surfaces between food preparation tasks were common. Most participants did not use thermometers to evaluate doneness but still cooked to safe internal temperatures. The results provide a tool that educators can use to evaluate food safety programs and will help guide the development of more effective food safety education programs targeting needed improvements in behavioral skills.     

Modeling the kinetics of the competitive adsorption and desorption of glyphosate and phosphate on goethite and gibbsite and in soils

The herbicide glyphosate and inorganic phosphate compete for adsorption sites in soil and on oxides. This competition may have consequences for the transport of both compounds in soil and hence for the contamination of groundwater. We present and evaluate six simple, kinetic models that only take time and concentrations into account. Three of the models were found suitable to describe the competition in soil. These three models all assumed both competitive and additive adsorption, but with different equations used to describe the adsorption. For the oxides, three additional models assuming only competitive adsorption were also found suitable. This is in accordance with the observation that the adsorption in soil is both competitive and additive, whereas the adsorption on oxides is competitive. All models can be incorporated in transport models such as the convection-dispersion equation.