Phosphine resistance in stored-product insects collected from various grain storage facilities in Morocco

Despite heavy dependence on phosphine (PH₃) for fumigating stored products, the resistance status of insect pests in Morocco has never undergone a thorough investigation. Some control failures with PH₃ were reported in Morocco, and a previous study showed two field populations of Sitophilus oryzae to be highly resistant to phosphine.We surveyed phosphine resistance in field populations of three major insect pests of stored wheat in Morocco. Around 32% of the samples collected at different storage facilities were found to be infested with one or more species of stored-product beetles. First-generation adult beetles, cultured from the field samples, were subjected to a discriminating dose test for phosphine resistance using an FAO method. The results indicated that, with the exception of one population of S. oryzae, all samples tested contained phosphine-resistant individuals. Treatments at up to 1.8 g m⁻³ of phosphine for 20 h, or at 0.18 g m⁻³ for up to 5 days, indicated that a high degree of resistance was already selected in some of the insect populations.Tests using [³²P]-radiolabelled phosphine showed that the mechanism of resistance in the three insect species tested involved a reduced uptake of the fumigant. The study has highlighted an urgent need for reviewing current fumigation practices in Morocco to ensure effective use of phosphine and avoid further selection of resistance.     

HXD气流干燥过程工艺气流传热分析

为研究RCC-HXD气流干燥过程的运行规律,在热工原理分析的基础上,设定试验方案并进行数据采集处理,通过使用在线数据采集系统RSSQL并运用理论推导和统计分析方法对试验结果进行了分析。结果表明:①在干燥过程中,HXD喂料点前工艺气流与烟丝间的换热量可用干燥前后工艺气流温差的倒数来衡量;②在其它控制参数不变,只改变排潮模式(手动与自动)的情况下,设置为手动控制排潮时,干燥过程的换热量总是较低;③当设置为自动排潮且HXD蒸气注入量超过1800kg/h时,工艺气流的干燥能力随着注入量的增大而降低。     

Disparity of dietary effects on collagen characteristics and toughness between two beef muscles

Manipulation of growth rate and/or diet has been shown to affect protein turnover and may be used to improve beef quality. This trial was conducted to evaluate the effects of average daily gain (ADG) and diet on animal performance, collagen characteristics and beef quality of two different muscles; longissimus dorsi (LD) and semitendinosus (ST). Seventy six Hereford and Angus steers were assigned to three dietary management regimens for finishing: high grain diet based on corn (n = 28), alfalfa pasture (n = 22) and grass pasture (n = 26). Average daily gains were greater (P < 0.001) in Herefords vs. Angus and for corn- vs. pasture finished cattle. Overall, total collagen content was greater (P < 0.001) and the percentage of total collagen that was heat soluble was lower (P < 0.0001) for ST than for LD muscle. The lowest (P < 0.05) values for both total and heat soluble collagens were found in animals finished on corn. WBSF values for LD were greater (P < 0.01) in grass-fed vs. alfalfa- and grain-finished cattle while there was no difference in WBSF values for ST between grass- and corn-fed animals. No correlation between ADG and WBSF was observed for any muscle. ADG was not correlated with collagen solubility in ST, but was correlated (P < 0.05) with collagen solubility in LD. A key finding is that growth rate affected heat soluble collagen in the two muscles to a different extent. In conclusion, this study shows that different feeding strategies may not influence the tenderness of all muscles in a similar way.     

The effects of temperature,chlorine and acids on the survival of Listeria and Salmonella strains associated with uncooked shrimp carapace and cooked shrimp flesh

The purpose of this study was to assess the influence of the association of Listeria and Salmonella with shrimp surfaces on the effects of temperature, chlorine and acids on their survival. Planktonic, attached and colonized cells of Listeria monocytogenes Scott A, L. monocytogenes V7, Salmonella Senftenberg 1734b and S. Typhimurium ATCC 14028 were challenged with high (50°, 60° and 70 °C) and low (4 °C) temperature, 100 ppm sodium hypochlorite solution, and acetic, hydrochloric and lactic acids (pH 4.0). Attached and colonized Listeria and Salmonella showed significantly greater (p < 0.05) resistance to heat (∼1.3–2.6 fold increase in D-values), hypochlorite (∼6.6 ≥ 40.0 fold) and acids (∼4.0–9.0 fold) than their planktonic counterparts. There were no significant differences (p > 0.05) in the survival of planktonic, attached or colonized cells of Listeria and Salmonella stored under refrigerated conditions. The association of Listeria and Salmonella with shrimp surfaces enhances their resistance to heat, chlorine and acids. Both attachment to, and subsequent colonization of, shrimp surfaces by pathogens may reduce the efficacy of methods used in their control. Strategies to reduce attachment of these pathogens to shrimp are required to assure safety of this product.     

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.