Growth of Staphylococcus aureus as Related to 17O NMR Water Mobility and Water Activity

¹⁷O NMR data were determined for three solute-BHI (Brain Heart Infusion) mixtures. For each solute, NaCl, raffinose and glycerol, NMR data (linewidths and signal intensity) were determined as well as water activity (a_w), moisture contents, and effects on growth of Staphylococcus aureus in media of various moisture contents. Liquid (highly mobile) water content in all media tested was determined by NMR. This mobile water was important and had a stronger correlation with S. aureus growth rate than did a_w or moisture content, although solute effects limited empirical prediction. NMR linewidth also correlated with lag phase.     

Impact of salted duck egg albumen powder on proteolysis and gelling properties of sardine surimi

The influences of salted duck egg albumen powder (SDEAP) as salt replacer at various levels (0.5–2.5%) on autolysis and gelling properties of sardine surimi were investigated. SDEAP had high salt (33.67%) and protein contents (64.52%) with trypsin inhibitory activity of 5,975 kunits/g solid. SDEAP was white in color with L*‐value of 96.72. It had low moisture content (3.98%) and water activity (0.38). Autolysis of sardine surimi was drastically inhibited when SDEAP was incorporated with increasing levels as indicated by the more retained myosin heavy chain and the reduced trichloroacetic acid‐soluble peptide content. Breaking force and deformation of surimi gel increased, while expressible moisture content decreased as the levels of SDEAP added were increased (p < .05). Gumminess, hardness, chewiness, springiness, and cohesiveness of surimi gels also increased as SDEAP levels increased (p < .05). Lightness and whiteness were higher in all surimi gels incorporated with SDEAP than the control (p < .05). For microstructure, surimi gels incorporated with SDEAP at all levels used had finer gel network with smaller voids and more connectivity than the control gel. Thus, SDEAP could be used as a salt replacer for sardine surimi gel preparation and it could improve the properties of resulting gel.     

Evolution of Moisture Distribution During Storage in a Composite Food Modelling and Simulation

In order to predict moisture transfer in a composite food, a mathematical model was developed and tested on a 2‐components system constituted of a sponge‐cake in contact with a fresh wet filling. Using independent sorption kinetic experiment, a power law was found as representative of the effect of moisture content on water effective diffusivity of sponge‐cake. The parameters of power law was then adjusted using the model optimization procedure on moisture profiles measurements of sponge‐cake in contact with a 0.99 water activity agar gel at 20°C. The model was validated with 0.95 and 0.90 water activity agar gels and successfully used to predict moisture transfer in a real food (processed cheese/sponge‐cake system).     

Characterization of water distribution in xanthan-curdlan hydrogel complex using magnetic resonance imaging, nuclear magnetic resonance relaxometry, rheology, and scanning electron microscopy

Abstract: Xanthan‐curdlan hydrogel complex (XCHC) has been shown capable of retaining moisture up to 5 freeze‐thaw cycles (FTCs); however, moisture distribution in the complex in relation to the hydrogel composition and structure remains uncharacterized. In the present study, magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR) relaxometry, rheology, and scanning electron microscopy (SEM) were used to examine the effect of water distribution and interaction with 2.0% aqueous solutions of xanthan, curdlan, and XCHC consisting of equal amounts of both polysaccharides. A gel structure with an indication of syneresis was clearly seen in the MR image of curdlan alone, whereas the distribution of protons throughout xanthan and XCHC samples remained homogeneous and showed no detectable syneresis. The three‐dimensional network, indicated by frequency sweeps, of curdlan was responsible for curdlan's gel structure. The frequency sweep and slope of the storage modulus (G′) of XCHC was significantly closer to curdlan with higher elasticity and less dependency upon angular frequency than xanthan alone. The reduction in XCHC dynamic moduli (G′ and G″) compared to curdlan could be attributed to the formation of wavy layers instead of a fully cured three‐dimensional structure. Addition of xanthan to curdlan restricted XCHC spin–spin relaxation time (T₂) to intermediate and slower exchange regimes, namely approximately 110 and 342 ms, respectively, promoting the polymer's interaction with water while inhibiting interpolymer interactions found in curdlan. A 3rd proton pool with the slowest T₂ seen in curdlan was not found in XCHC, correlating to the absence of syneresis. Practical Application: The combination of texture measurements and discrete noninvasive techniques was found capable of providing insightful understanding of water distribution in a gel system. These techniques may be applied to other hydrogel complexes. The XCHC system investigated has the potential to enhance freeze‐thaw stability in frozen food products by minimizing syneresis due to undesirable temperature fluctuations during distribution and consumer application.     

Influence of Water Activity on Thermal Resistance of Microorganisms in Low‐Moisture Foods: A Review

A number of recent outbreaks related to pathogens in low‐moisture foods have created urgency for studies to understand the possible causes and identify potential treatments to improve low‐moisture food safety. Thermal processing holds the potential to eliminate pathogens such as Salmonella in low‐moisture foods. Water activity (a_w) has been recognized as one of the primary factors influencing the thermal resistance of pathogens in low‐moisture foods. But most of the reported studies relate thermal resistance of pathogens to a_w of low‐moisture foods at room temperature. Water activity is a thermodynamic property that varies significantly with temperature and the direction of variation is dependent on the product component. Accurate methods to determine a_w at elevated temperatures are needed in related research activities and industrial operations. Adequate design of commercial thermal treatments to control target pathogens in low‐moisture products requires knowledge on how a_w values change in different foods at elevated temperatures. This paper presents an overview of the factors influencing the thermal resistance of pathogens in low‐moisture foods. This review focuses on understanding the influence of water activity and its variation at thermal processing temperature on thermal resistance of pathogens in different low‐moisture matrices. It also discusses the research needs to relate thermal resistance of foodborne pathogens to a_w value in those foods at elevated temperatures.     

Physicochemical properties, gel-forming ability and myoglobin content of sardine (Sardinella gibbosa) and mackerel (Rastrelliger kanagurta) surimi produced by conventional method and alkaline solubilisation process

Characteristics and gel properties of sardine and mackerel surimi produced by conventional washing process and alkaline solubilising process were investigated. The decrease in Ca²⁺-ATPase activity with the changes in the surface hydrophobicity was found in surimi produced by alkaline solubilising process (p<0.05), suggesting the denaturation of protein induced by this process. The alkal-ine solubilising process with prewashing could remove myoglobin most effectively from sardine muscle, whereas the process without prewashing resulted in the greatest myoglobin removal in mackerel muscle (p<0.05). Surimi conventionally prepared by water or NaCl washing showed the gel with greater breaking force and deformation than that from alkaline solubilising process (p<0.05). The hig-her expressible moisture was found in the gels of surimi pre-pared by alkaline process, indicating the poor water holding capacity of the gel matrix. The highest whiteness was found in the gel of sardine surimi produced by alkaline process with prewashing but the highest whiteness was obtained in the gel of mackerel surimi washed with distilled water.     

Effect of laver powder on textual,rheological properties and water distribution of squid (Dosidicus gigas) surimi gel

In order to ameliorate the gel quality of Dosidicus gigas surimi, the effects of laver powder on gel properties, rheological properties, and water-holding capacity (WHC) were investigated. Results indicated that the addition of laver powder could significantly increase the hardness, chewiness, and breaking force of surimi gels. However, the texture indexes and gel strength began to decline when additional amount exceeded 0.6%. Rheological results demonstrated that the addition of laver powder increased the storage modulus (G′) and viscosity of surimi, prolonged protein denaturation temperature in surimi gels. Moreover, the WHC of surimi gel was improved with the increase of laver powder. Further analyses in low-field nuclear magnetic resonance revealed that laver powder could shorten the transverse relaxation time, enhanced the combination with water, and altered the distribution of different water categories. The proportion of bound water and immobilized water reached its maximum and minimum at 0.6% of laver powder, respectively. Correlation analyses showed that WHC of surimi gel was negatively correlated well with the proportion of loose-bound water, but positively correlated with the strong-bound water and free water. In conclusion, the results supported that 0.6% was the optimal additional amount of laver powder for the squid-based surimi production based on the current ingredients of surimi products.     

水分状态对鱼糜凝胶高温处理热稳定性的影响

探讨不同水分含量及状态对鱼糜凝胶高温处理热稳定性的影响。将鱼糜中添加不同保水剂制成凝胶,经冷风干燥一定时间后进行高温处理,测量冷风干燥不同时间后水分含量、水分活度和水分状态的变化,通过5分法评分标准评定高温处理后鱼糜凝胶的凝胶特性。结果表明:随着冷风干燥时间的延长,空白组及添加保水剂组的鱼糜凝胶的水分含量均呈现相同的下降趋势,水分活度也呈现一定的下降趋势,但下降幅度不尽相同,鱼糜凝胶中的不易流动水和自由水的含量均有一定程度的变化,另外,高温处理后鱼糜凝胶的凝胶特性呈现上升的趋势。说明降低水分含量可有效提高高温处理鱼糜凝胶的凝胶特性,同时可通过添加保水剂改变水分活度和水分状态从而进一步提高鱼糜凝胶的高温处理热稳定性。     

Studies on Disinfection Mechanism of Electrolyzed Oxidizing Water on E. coli and Staphylococcus aureus

Abstract: Suspension quantitative germicidal test showed that electrolyzed oxidizing water (EO water) was an efficient and rapid disinfectant. Disinfection rates towards E. coli (available chlorine concentration ACC: 12.40 mg/L) and Staphylococcus aureus (ACC: 37.30 mg/L) could reach 100% at 1 and 3 min, respectively. Disinfection mechanism of EO water was investigated at a molecular biological level by detecting a series of biochemical indices. The results showed that the dehydrogenase activities of E. coli and S. aureus decreased rapidly, respectively, at the rates of 45.9% and 32% in the 1st minute treatment with EO water. EO water also improved the bacterial membrane permeability, causing the rise of conductivities and the rapid leakages of intracellular DNA, K⁺, and proteins in 1 min. The leakages of DNA and K⁺ tended to slow down after about 1 min while those of proteins began to decrease a little after reaching the peak values. The sodium dodecyl sulfonate polyacrylamide gel electrophoresis (SDS-PAGE) showed that EO water destroyed intracellular proteins. The protein bands got fainter and even disappeared as the treatment proceeded. EO water's effects on the bacterial ultrastructures were also verified by the transmission electronic microscopy (TEM) photos. The disinfection mechanism of EO water was composed of several comprehensive factors including the destruction of bacterial protective barriers, the increase of membrane permeability, the leakage of cellular inclusions, and the activity decrease of some key enzymes. Practical Application: Large-scale communicable diseases have often occurred due to the infectious pathogenic microorganism. EO water is a novel environment-friendly disinfectant characterized by its high efficiency, broad spectrum, and no side effects. It has been greatly used in agriculture, food industry, and medicine. Our research lays the foundation for further research of EO water and we can predict that EO water will continue to be broadly used in daily life, health care, sanitation, and so on.     

Effects of Electrolyzed Oxidizing Water on Inactivation of Bacillus subtilis and Bacillus cereus Spores in Suspension and on Carriers

Spores of some Bacillus species are responsible for food spoilage and foodborne disease. These spores are highly resistant to various interventions and cooking processes. In this study, the sporicidal efficacy of acidic electrolyzed oxidizing (EO) water (AEW) and slightly acidic EO water (SAEW) with available chlorine concentration (ACC) of 40, 60, 80, 100, and 120 mg/L and treatment time for 1, 2, 3, 4, 5, and 6 min were tested on Bacillus subtilis and Bacillus cereus spores in suspension and on carrier with or without organics. The reduction of spore significantly increased with increasing ACC and treatment time (P < 0.05). Nondetectable level of B. cereus spore in suspension occurred within 2 min after exposure to both EO waters containing 120 mg/L ACC, while only SAEW at 120 mg/L and 2 min treatment achieved >6 log reductions of B. subtilis spore. Both types of EO water with ACC of 60 mg/L and 6 min treatment achieved a reduction of B. subtilis and B. cereus spores to nondetectable level. EO water with ACC of 80 mg/L and treatment time of 3 min on carrier test without organics addition resulted in reductions of B. subtilis spore to nondetectable level. But, addition of 0.3% organics on carrier decreased the inactivation effect of EO water. This study indicated that EO water was highly effective in inactivation of B. subtilis and B. cereus spores in suspension or on carrier, and therefore, rendered it as a promising disinfectant to be applied in food industry.     

挤压加工对苦荞粉理化性质的影响

为了阐明挤压加工技术对苦荞粉理化性质的影响,分别研究了不同挤压温度、物料水分和螺杆转速对挤压苦荞粉的吸水性指数、水溶性指数、膨胀势、糊化及凝胶特性的影响规律。结果表明:与未挤压苦荞粉相比,经挤压改性后的苦荞粉在30℃水浴时有更好的吸水性和水溶性;在100℃水浴时的水溶性增大,吸水性减小;膨胀势、糊化特征值及凝胶特征值均明显升高。随挤压温度升高,挤压苦荞粉的峰值粘度、衰减值增大,谷值粘度、回生值降低,制成的凝胶品质更好;随物料水分升高,吸水性指数、膨胀势、各糊化特征值显著增大,水溶性指数明显降低,低物料水分形成的凝胶品质较好;随螺杆转速升高,水溶性指数增大,吸水性指数和峰值粘度、谷值粘度、衰减值稍降低,膨胀势先增大后减小,转速越高的苦荞粉的凝胶品质越好。综合而言,物料水分变化对挤压苦荞粉的各理化性质影响最大。吸水性指数和水溶性指数与糊化特性、凝胶特性都有显著相关性(P0.05);膨胀势与糊化特性极显著正相关(P0.01),与凝胶特性没有显著相关性。     

金黄色葡萄球菌便携式计数测试片的研制

为了研制新型便携式计数测试片检测食品中金黄色葡萄球菌,本文通过正交试验对金黄色葡萄球菌测试片中培养基成份进行优化;研究冷水可溶性凝胶的复配比例,以及优化后的表面活性剂对复配凝胶质构特性的影响。结果表明,金黄色葡萄球菌测试片中培养基组分为胰蛋白胨10 g/L,牛肉膏5 g/L,酵母膏1 g/L,甘氨酸12 g/L,氯化锂5 g/L,尿素0.2 g/L,亚碲酸钾10 mg/L,卵黄粉6 g/L,表面活性剂最优添加量为D-甘露醇4 g/L,丙酮酸钠5 g/L;冷水可溶性凝胶复配比例为瓜尔胶:聚丙烯酸钠=7:3;添加优化后的D-甘露醇和丙酮酸钠的复合冷水可溶性凝胶可获得最优的凝胶质构,其硬度和黏性分别为1362.04 g和630.41 g。将本研究的测试片与国标平板计数方法相比,其检测结果相关性良好(R^2=0.995),可达到相同水平的检出限2CFU/m L和灵敏度(100%)。本文研究的金黄色葡萄球菌测试片可应用于食品中金黄色葡萄球菌的定量检测。     

Ohmic Heating Maximizes Gel Functionality of Pacific Whiting Surimi

Surimi without enzyme inhibitors containing 78% moisture and 2% NaCl was heated conventionally and ohmically to 90°C after holding at 55°C for 0, 1, 3 and 5 min. Gels heated slowly in a water bath exhibited poor gel quality, while the ohmically heated gels without holding at 55°C showed more than a twofold increase in shear stress and shear strain over conventionally heated gels. Degradation of myosin and actin was minimized by ohmic heating, resulting in a continuous network structure. Ohmic heating with a rapid heating rate was an effective method for maximizing gel functionality of Pacific whiting surimi without enzyme inhibitors.     

PHYSICOCHEMICAL PROPERTIES OF TEXTURIZED MEAT ANALOG MADE FROM PEANUT FLOUR AND SOY PROTEIN ISOLATE WITH A SINGLE‐SCREW EXTRUDER 1

The objective of this study was to establish conditions for the texturization of soy protein isolate and peanut flour mixture using a single‐screw extruder. The effects of feed moisture, screw‐speed, and barrel temperature on the characteristics of the texturized products were studied. Feed moisture was the most important factor affecting the texture. Feeding ingredients with 22% moisture had the highest water absorption and expansion indices, and Hunter L value (P < 0.05). When the screw speed was above 180 RPM, the meat analog had a 12% decrease in the expansion index and a 5% decrease in moisture content (P < 0.05). When the barrel temperature was increased to 165C, there was a 12% decrease in the water absorption index, and a 23% decrease in the expansion index of the meat analogs (P < 0.05). Overall, an acceptable meat analog could be successfully produced with 22% moisture in the raw ingredient, screw speed at 140 RPM, and barrel temperatures at 150, 155, and 160C for the three temperature zones respectively.     

漂洗过程中锌离子对鲢鱼鱼糜凝胶特性的影响

以鲢鱼鱼糜为研究对象,通过测定凝胶强度、持水性、蒸煮损失率、色度、质构特性、水分分布状态、微观结构和蛋白质分子质量分布指标,分析了漂洗过程中锌离子对鲢鱼鱼糜凝胶特性的影响。结果表明,用含有锌离子的漂洗液漂洗较用清水漂洗和质量分数0.15%Na Cl漂洗对鲢鱼鱼糜凝胶性能有较大改善,其中,当锌离子浓度为6μmol/L时,鲢鱼鱼糜凝胶的凹陷距离、凝胶强度和咀嚼度均处于最大值(8.47 mm、2 325.90 g·mm、2 752.12 g·mm);破断力为274.74 g,较清水漂洗提高了14.95%;该浓度条件下凝胶对水的束缚能力增强,持水性达到最大值(83.13%),并且蒸煮损失率和横向弛豫时间T23为最小值(分别为9.39%、45.47 ms);白度得到提升。在锌离子的作用下,肌球蛋白重链通过交联作用形成较大聚集体,且凝胶微观结构均匀致密。     

Anti-Fenton reaction activity of three taxa of water yam (Dioscorea alata L.)

In the present study, we compared the anti‐Fenton reaction activity of three taxa of water yam (Dioscorea alata L.): DS2, TN2 and PSY [D. alata L. var. purpurea (Roxb.) M. Pouch]. Anti‐Fenton reaction activity was evaluated by measuring the damage inflicted on calf thymus DNA by copper ions combined with hydrogen peroxide with the use of an ethidium bromide binding assay and agarose gel electrophoresis. We found that extracts of tuber pulp from all three taxa of yam had significant anti‐Fenton reaction activity. The protection pattern of the three tuber pulp extracts was similar to that of EDTA, a typical divalent metal ion chelator, which displayed a significant protection lag‐phase. With the use of thin‐layer chromatography, we found that a common, major ansialdehyde‐sulphuric acid stained spot (possibly a polysaccharide mucilage) with an R_f of 0.09 may be the most likely contributor to the anti‐Fenton reaction activities of the yam tuber extracts investigated. The present study identifies the mechanism of the health benefit of the Dioscorea family. The copper‐chelating and absorbing capability of yam tuber pulp extracts may be useful in functional screening.     

含水量对湿热处理荸荠淀粉性质的影响

为有效开发利用荸荠淀粉,以荸荠淀粉为原料,将荸荠淀粉的含水量分别调节为20%、25%、30%、35%,利用鼓风干燥烘干箱在105℃下湿热处理2 h,研究湿热处理对荸荠淀粉糊化特性、流变特性、溶解度与膨胀度的影响。结果表明:随着湿热处理淀粉含水量的增大,淀粉糊峰值黏度和衰减值均有所降低;谷值黏度有所升高,淀粉颗粒的溶解度和膨胀度均有一定程度的下降;剪切稀化现象减弱;损耗角正切值越来越小,荸荠淀粉在湿热处理后所形成的凝胶为弱凝胶。     

烟酰胺水分测定方法的筛选

为确定一种误差小、精密度高且能测定烟酰胺产品水分含量的方法,比较卡尔费体容量滴定法、不带鼓风电热恒温干燥箱法、带鼓风电热恒温干燥箱法与硅胶为干燥剂干燥器法测定酰胺产品失水率的差异.结果表明:使用不带鼓风和带鼓风电热恒温干燥箱的检测结果分别比容量滴定法高出0.295%～0.5%和0.365%～1.12%;使用带鼓风的比不带鼓风的电热恒温干燥箱检测结果高出0.10%～0.62%;而硅胶为干燥剂的干燥器法测定的结果低于产品实际含水量.综合而言,卡尔费休容量滴定法的重复操作性强,结果准确,测定烟酰胺产品水分含量可优选卡尔费休容量滴定法.     

Mechanical and barrier properties of sodium caseinate–anhydrous milk fat edible films

Edible films were cast from solutions of sodium caseinate (NaCAS) and from emulsions of this protein with anhydrous milk fat (AMF). The moisture sorption isotherms, mechanical properties [tensile strength (TS) and elongation] and water vapour and oxygen permeabilities were determined for films based on NaCAS as a function of AMF concentration. AMF concentration significantly affected TS (P < 0.001) and elongation (P < 0.05). The increase of lipid content led to a loss of mechanical efficiency, but had little influence on water vapour barrier properties. No significant difference (P > 0.05) occurred between oxygen permeability of films at each lipid concentration.     

Physical Stability of Octenyl Succinate–Modified Polysaccharides and Whey Proteins for Potential Use as Bioactive Carriers in Food Systems

The high cost and potential toxicity of biodegradable polymers like poly(lactic‐co‐glycolic)acid (PLGA) has increased the interest in natural and modified biopolymers as bioactive carriers. This study characterized the physical stability (water sorption and state transition behavior) of selected starch and proteins: octenyl succinate–modified depolymerized waxy corn starch (DWxCn), waxy rice starch (DWxRc), phytoglycogen, whey protein concentrate (80%, WPC), whey protein isolate (WPI), and α‐lactalbumin (α‐L) to determine their potential as carriers of bioactive compounds under different environmental conditions. After enzyme modification and particle size characterization, glass transition temperature and moisture isotherms were used to characterize the systems. DWxCn and DWxRc had increased water sorption compared to native starch. The level of octenyl succinate anhydrate (OSA) modification (3% and 7%) did not reduce the water sorption of the DWxCn and phytoglycogen samples. The Guggenheim–Andersen–de Boer model indicated that native waxy corn had significantly (P < 0.05) higher water monolayer capacity followed by 3%‐OSA‐modified DWxCn, WPI, 3%‐OSA‐modified DWxRc, α‐L, and native phytoglycogen. WPC had significantly lower water monolayer capacity. All Tg values matched with the solid‐like appearance of the biopolymers. Native polysaccharides and whey proteins had higher glass transition temperature (Tg) values. On the other hand, depolymerized waxy starches at 7%‐OSA modification had a “melted” appearance when exposed to environments with high relative humidity (above 70%) after 10 days at 23 °C. The use of depolymerized and OSA‐modified polysaccharides blended with proteins created more stable blends of biopolymers. Hence, this biopolymer would be suitable for materials exposed to high humidity environments in food applications.