Identification and kinetics of oxidized compounds from phosphatidylcholine molecular species

Heat-induced oxidative modifications of two phosphatidylcholine molecular species as potential functional food components were evaluated. 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) and 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine (SLPC) were chosen as models. The optimal temperature for hydroperoxide formation was determined by MS for each standard: 125 °C for SLPC and 150 °C for SOPC. Oxidation was performed at these temperatures and degradation products were identified using LC–ESI-MS combined to an acid treatment. Kinetics of formation of oxidation products from SOPC and SLPC were monitored over 120 min and curves were drawn for each identified structure. Results showed that native phospholipids rapidly decreased with heat and that oxidation products showed functions, such as hydroxyl, oxo or epoxy groups. Kinetics pointed out that some of these quite stable oxidation products are likely to be found in sizable amounts in processed foods containing phospholipids.     

大豆多酚氧化酶、过氧化物酶的酶学特性研究

对大豆氧化还原酶系中的多酚氧化酶和过氧化物酶的酶学特性进行了较深入系统地研究,其中包括酶活力、酶热稳定性、pH值的影响,以及大豆卵磷脂、二巯基丙醇对酶活力的抑制作用.结果表明多酚氧化酶在120℃时,酶活力值已达到不可逆失活状态,pH6～7时酶活力最大,当二巯基丙醇的浓度为1.5mmol/L时其酶活力降至6%以下.过氧化物酶具有较高的耐热性,酶活力最适的pH值为5.5左右,大豆卵磷脂浓度达到80mg/L时其酶活力可降至20%左右.     

Thermal stability of soy protein isolate and hydrolysate ingredients

The objective of this study was to characterize the effects of pH, protein concentration and calcium supplementation on thermal stability, at 140 °C, of soy protein isolate (SPI) and soy protein hydrolysate (SPH) ingredients. Increasing pH between 6.4 and 7.5 led to significantly (p < 0.05) higher mean heat coagulation times (HCTs) at 140 °C, for all soy protein ingredients at 1.8, and 3.6% (w/v) protein. Increasing protein concentration from 1.8 to 7.2% (w/v) led to shorter HCTs for protein dispersions. Calcium supplementation up to 850 mg/L, except in the case of supplementation of SPI 1 with calcium citrate (CaCit), decreased HCT for soy protein ingredient dispersions, at pH 6.4 – 7.5. No significant differences (p < 0.05) were found in mean HCT for dispersions supplemented with calcium chloride (CaCl₂) and those supplemented with CaCit at 450, 650 and 850 mg/L Ca²⁺, in the pH range 6.4–7.5.     

Quantitative Evaluation of Thermal Inactivation Kinetics of Free-Floating Versus Surface-Attached Listeria innocua Cells

Surface pasteurization is one of the decontamination treatments that can contribute to better preservation of meat products retaining most of their quality characteristics relatively intact if compared with the raw products. The current research compares the kinetics of free-floating and surface attached Listeria innocua cells by using integrated microbial and heat transfer modelling approaches. Surface pasteurization treatments are applied on a (abiotic) Teflon® model system in a novel steam surface decontamination rig. The experimental set-up prevented following four technological aspects to occur, (1) cold purge migration to the surface during the heating process, (2) inactivation kinetics of a cocktail of microbes, (3) protective effect of food components, and (4) physical distribution of bacteria throughout the depth of the product skin. Microbial load predictions are performed based on the inactivation parameters obtained during free-floating cell experiments. These predictions, when compared with the microbial data of the surface treatments, prove that the surface attached cells were much more heat resistant, despite the experimental set-up preventing the aforementioned (technological) events to occur. Indeed, surface attached cells can have different physiological/phenotypical/genetical characteristics, such as cell aggregations, colony formations, presence of flagella. In a final step, three techniques are implemented to evaluate mathematically the kinetics of the surface attached cells. Overall, this research’s significance is lying in the quantitative assessment of microbial heat resistance. The technological reasons underlying the increased microbial heat resistance on biotic and abiotic surfaces should be reevaluated, taking into account possible physiological/phenotypical/genetical characteristics.     

Stability of the Fusarium mycotoxins nivalenol, deoxynivalenol and zearalenone in ground maize under typical cooking environments

The effects of moisture, pH and heat on the stability of nivalenol (NIV), deoxynivalenol (DON) and zearalenone (ZEN) present as natural contaminants of ground maize were measured for different periods. Standard solution tests were also performed to measure pH, salt and temperature effects on NIV and DON. The solution tests showed NIV and DON to be relatively stable in buffer solutions over the pH range 1-10. Quite harsh conditions (pH 12, high salt concentration, 80°C, prolonged exposure) were needed to give substantial breakdown. In the ground maize substrate, these toxins were further stabilized relative to the solution tests. NIV and DON were both reduced (range 60-100%) by treatment with aqueous bicarbonate solution at 10, 20 or 50% of the ground maize dry weight, and subsequent heating at 80 or 110°C for 2 and 12 days. There was no measurable reduction at lower test temperatures (20, 40°C). NIV (but not DON) also showed some reduction following addition of water and heating at 80 or 110°C for 12 days. ZEN content was not reduced even by 12 days of heating at 110°C after treatment with a sodium bicarbonate solution.     

The impact of the postharvest environment on the viability and virulence of decay fungi

Postharvest decay of fruits, vegetables, and grains by fungal pathogens causes significant economic losses. Infected produce presents a potential health risk since some decay fungi produce mycotoxins that are hazardous to human health. Infections are the result of the interplay between host resistance and pathogen virulence. Both of these processes, however, are significantly impacted by environmental factors, such as temperature, UV, oxidative stress, and water activity. In the present review, the impact of various physical postharvest treatments (e.g., heat and UV) on the viability and virulence of postharvest pathogens is reviewed and discussed. Oxidative injury, protein impairment, and cell wall degradation have all been proposed as the mechanisms by which these abiotic stresses reduce fungal viability and pathogenicity. The response of decay fungi to pH and the ability of pathogens to modulate the pH of the host environment also affect pathogenicity. The effects of the manipulation of the postharvest environment by ethylene, natural edible coatings, and controlled atmosphere storage on fungal viability are also discussed. Lastly, avenues of future research are proposed.     

铜精炼阳极转炉氧化期烟气的传热特性

根据能量平衡原理,建立烟气对铜液的传热模型,并对不同空气过剩系数下的烟气平均温度和传热强度进行计算。结果表明:随着空气过剩系数的增大,烟气平均温度和传热强度均有明显下降。为增强烟气对铜液的传热能力,必须适当地减小空气过剩系数。此外,针对燃烧室排烟温度较高的问题,提出采用余热装置回收烟气余热的合理建议。     

REMARKS ON HEAT AND WORK TRANSFERS IN SYSTEMS WITH UNIFORM INTENSIVE PROPERTIES

The differential forms of heat and work, owing to their dependence upon parameters characterizing the interaction between system and environment (and not only upon the state functions of the system), differ basically from the usual non-exact differentials.

The main aim of this paper is to examine these differences considering quasi-static irreversible processes with the uniformity of internal temperature and pressure. Besides, the specific heat is defined referring only to the properties of the system and to the path of the process and not to the actual heat transfer     

Heat and anaerobic treatments affected physiological and biochemical parameters in tomato fruits

The aim of the present work was to evaluate the effect of thermal and anaerobic treatments on physiological and biochemical parameters in a variety of tomatoes (Lycopersicon esculentum Mill. cv. Colt 45). Treatments applied to mature green tomatoes were: (A) heat treatments by water immersion at 42 °C for 30 min (HS30′) or for 60 min (HS60′); or by air at 38 °C for 72 h (HS72h); and (B) anaerobic treatments carried out at 20 °C under humidified nitrogen atmosphere for 3 days (ANA3d) or 6 days (ANA6d). After treatments, fruits were stored at 2 or 14 °C. Parameters evaluated were: colour, total acidity, major organic acids, firmness, and ethanol and acetaldehyde concentration. Anaerobic and long-term heat shock treatments inhibited colour development irrespective of storage temperature. Air heat treatment reduced tritratable acidity by increasing malic acid metabolism. Anaerobic treatments induced ethanol accumulation, which could be reversed during storage for the short treatment (3 days), but not for the longer treatment (6 days). Acetaldehyde concentration was increased by anaerobic treatments, but also by immersion in hot water for 60 min, which would produce a “low-aerobic” environment.     

Measurement and targeting of thermophysical properties of carrot and meat based alginate particles for thermal processing applications

The objective of the study was to investigate the thermo-physical properties of meat and carrot based alginate particles as influenced by the formulation variables. A response surface methodology (RSM) was used to study the effect of sodium alginate concentration, calcium chloride concentration and dipping time in the calcium chloride solution, at five levels each, on the thermo-physical properties of the fabricated particles (9 mm in diameter and 9 mm in height). Density was similar for all conditions. Increasing sodium alginate concentration resulted in a significant decrease in the heat capacity and thermal conductivity values. These changes were primarily attributed to the lowering of moisture content of the particles resulting from the treatment. Using RSM, optimum conditions for fabricating particles having similar thermo-physical properties to real foods were obtained as 5.3% and 4.9% sodium alginate, 2.2% calcium chloride and 14.2 and 36.0 h immersion in the calcium chloride solution for meat and carrot alginate particles, respectively.