Reduction of microorganisms in ground beef using multiple intervention technology

The effectiveness of multiple antimicrobial interventions on ground beef microbial, instrumental color and sensory characteristics through display was studied. Beef trimmings were inoculated with Escherichia coli (EC) and Salmonella typhimurium (ST) then treated with either: (1) 5% acetic acid followed by 0.5% cetylpyridinium chloride (AC); (2) 200 ppm chlorine dioxide followed by 0.5% cetylpyridinium chloride (CC); (3) 0.5% cetylpyridinium chloride followed by 10% trisodium phosphate (CT); or (4) control (C). Trimmings were ground, packaged and sampled through display for EC, ST, coliforms (CO), aerobic plate count (APC), and sensory color and odor characteristics. All treatments reduced (P<0.05) all bacterial types monitored through display. Ground beef from the CC treatment was similar (P>0.05) in redness (a*) to C. The CT treatment remained (P<0.05) redder (a*) in color, contained more (P<0.05) oxymyoglobin and had less (P<0.05) overall, worst point and percentage discoloration than C by day 7 of display.     

Microstructure alterations in beef intramuscular connective tissue caused by hydrodynamic pressure processing

Scanning electron microscopy (SEM) was utilized to evaluate microstructural changes in intramuscular connective tissue of beef semimembranosus muscle subjected to hydrodynamic pressure processing (HDP). Samples were HDP treated in a plastic container (HDP-PC) or a steel commercial unit (HDP-CU). Control and HDP samples were obtained immediately post-treatment and after 14 days of aging for SEM and Warner–Bratzler shear force (WBSF) analysis. Immediately post-treatment, HDP treated samples exhibited lower (P < 0.01) WBSF than did controls. After aging, HDP-PC samples had lower (P < 0.01) WBSF than that of aged controls. SEM analysis indicated that HDP-PC treatment disrupted the integrity of the collagen fibril network of the endomysium in both the non-aged and aged samples. Aging effects on the intramuscular connective tissue were observed in the HDP-PC and control samples. Both WBSF and connective tissue changes were greater in the HDP-PC than in the HDP-CU treated samples. Data suggest that shockwave alterations to connective tissue contribute to the meat tenderization of HDP.     

鲜剥大蒜中腐败微生物的分离纯化及鉴定

对鲜剥大蒜霉变部分的腐败微生物进行分离纯化,观察待测菌株的菌落形态特征、菌丝显微结构,并进行分子生物学分析。结果表明,经过分离纯化后一共得到4株菌,通过对其菌落形态特征和菌丝显微结构观察,初步判定为青霉、根霉、赤霉及曲霉;通过聚合酶链式反应（PCR）扩增、产物测序和序列分析,最终鉴定4株菌分别为：桔青霉（Penicillium citrinum）、匍枝根霉（Rhizopus stolonifer）、赤霉（Gibberella intermedia）、赭曲霉（Aspergillus ochraceus）。     

Alterations in the sarcoplasmic protein fraction of beef muscle with postmortem aging and hydrodynamic pressure processing

Abstract: Capillary electrophoresis (CE) and reversed‐phase high performance liquid chromatography (RP‐HPLC) analyses were utilized to detect differences in the sarcoplasmic protein fractions of beef strip loins subjected to aging and hydrodynamic pressure processing (HDP) treatments. At 48 h postmortem, strip loins (n= 12) were halved and subjected to control or HDP treatments. Following treatment, each half was divided into 3 portions which were aged for 0, 5, and 8 d. After each aging period, steaks were removed for Warner–Bratzler shear force (WBSF) analysis and for the extraction of sarcoplasmic proteins which were analyzed by CE and RP‐HPLC. Aging by HDP interactions were not detected using either separation technique. With CE analysis, no HDP effects were observed; however, the relative peak area of 8 protein peaks ranging in size from 17 to >200 kDa were influenced by postmortem aging. Separation of proteins by RP‐HPLC demonstrated that HDP influenced the relative size of 2 protein peaks while postmortem aging effects were observed in 6 peaks. Alterations in the sarcoplasmic protein fractions detected by both CE and RP‐HPLC were correlated to WBSF measurements. Overall, data demonstrate that HDP has minimal effects on sarcoplasmic proteins and that aging related changes in the water soluble protein fractions of muscle may be useful as indirect indicators of beef tenderness. Practical Application: Using 2 different postmortem tenderization techniques, aging and hydrodynamic pressure processing, this study demonstrates that postmortem changes in the soluble protein fraction of beef may be useful as potential indicators of meat tenderness.     

乳酸在生鲜牛肉加工中的应用

主要论述乳酸在生鲜牛肉加工中的作用,其中胴体减菌作用、保鲜作用、护色作用、嫩化作用得到重点的阐述。希望为冷鲜牛肉的生产、品质的改善提供理论依据和技术支持。     

Inhibition of metmyoglobin formation in fresh beef by pressure treatment

Application of pressures of 80-100 MPa for 20 min improved the colour stability, as measured by rate of metmyoglobin formation, of longissimus dorsi and psoas major beef muscles exposed to air 2 days post-slaughter. However, pressure treatment of these muscles at 7-20 days post-slaughter did not improve their colour stability. It is suggested that pressure inhibits, at least partially, the mechanism(s) responsible for the low colour stability of very fresh beef.     

Inactivation of food spoilage microorganisms by hydrodynamic cavitation to achieve pasteurization and sterilization of fluid foods

ABSTRACT:  Hydrodynamic cavitation is the formation of gas bubbles in a fluid due to pressure fluctuations induced by mechanical means. Various high-acid (pH ≥ 4.6) fluid foods were processed in a hydrodynamic cavitation reactor to determine if commercial sterility can be achieved at reduced processing temperatures. Sporicidal properties of the process were also tested on a low-acid (pH < 4.6) fluid food. Fluid foods were pumped under pressure into a hydrodynamic cavitation reactor and subjected to 2 rotor speeds and flow rates to achieve 2 designated exit temperatures. Thermal inactivation kinetics were used to determine heat-induced lethality for all organisms. Calcium-fortified apple juice processed at 3000 and 3600 rpm rotor speeds on the reactor went through a transient temperature change from 20 to 65.6 or 76.7 °C and the total process lethality exceeded 5-log reduction of Lactobacillus plantarum and Lactobacillus sakei cells, and Zygosaccharomyces bailii cells and ascospores. Tomato juice inoculated with Bacillus coagulans spores and processed at 3000 and 3600 rpm rotor speeds endured a transient temperature from 37.8 to 93.3 or 104.4 °C with viable CFU reductions of 0.88 and 3.10 log cycles, respectively. Skim milk inoculated with Clostridium sporogenes putrefactive anaerobe 3679 spores and processed at 3000 or 3600 rpm rotor speeds endured a transient temperature from 48.9 to 104.4 or 115.6 °C with CFU reductions of 0.69 and 2.84 log cycles, respectively. Utilizing hydrodynamic cavitation to obtain minimally processed pasteurized low-acid and commercially sterilized high-acid fluid foods is possible with appropriate process considerations for different products.     

Heat resistance of juice spoilage microorganisms

The heat resistance of various yeasts (Saccharomyces cerevisiae, Rhodotorula mucilaginosa, Torulaspora delbrueckii, and Zygosaccharomyces rouxii), molds (Penicillium citrinum, Penicillium roquefortii, and Aspergillus niger), and lactic acid bacteria (Lactobacillus fermentum and Lactobacillus plantarum) obtained from spoiled acid or acidified food products was determined in 0.1 M citrate buffer at pH values of 3.0, 3.5, and 4.0. S. cerevisiae was the most heat resistant of the microorganisms in citrate buffer, and its heat resistance was further evaluated in apple, grapefruit, calcium-fortified apple, and tomato juices as well as in a juice base with high fructose corn syrup. Decimal reduction times (D-values) and changes in temperature required to change the D-value (z-values) for S. cerevisiae were higher in the juices than in citrate buffer at all pH values tested. The D57 degrees C(135 degrees F)-values varied from 9.4 min in the juice product with pH 2.8 to 32 min in a calcium-added apple juice with pH 3.9. The S. cerevisiae strain used in this study can be used in thermal-death-time experiments in acidic products to calculate process conditions and in challenge tests to validate the calculated temperatures and hold times during processing.     

Utilization of image processing to quantitate surface metmyoglobin on fresh beef

Ground beef patties were manufactured with various combinations of ascorbic acid and mechanically recovered neck bone lean (MRNL) to study the use of image processing in predicting percentage surface metmyoglobin (metMb) on fresh beef. Ascorbic acid and MRNL cause various color phenomena that resulted in a wide range of variation in surface color. Patties were also stored over six days of retail display to cause further color changes. Surface color was assessed by several different accepted methods. A prediction equation for percentage surface metMb included mean values for hue, saturation and intensity. Root mean square error, R-square and Mallow's Cp statistic were used as selection criteria for choosing the best predictive model. Image processing hue, saturation and intensity accounted for 93% of the variation in percentage surface metMb. Since hue, saturation and intensity each contribute to overall color profile it is logical that these parameters are good predictors. These data indicate that image processing is capable of objectively measuring percentage surface metMb.     

超高压技术在酱牛肉保鲜中的应用

为探究超高压技术应用于肉制品保鲜中的可行性,对真空包装的酱牛肉采用600MPa,5、10、15min的超高压处理并与热处理(85～90℃,10min)及未处理组对照,分别在0、2、4、6、8周测定了4℃冷藏条件下的菌落总数、乳酸菌数以及pH、色泽、脂肪氧化值、挥发性盐基氮等理化指标。结果表明,高压处理能够显著降低酱牛肉的初始菌数(p<0.05),抑制细菌的生长,5min和10、15min组分别在第4、第6周超过80000cfu/g;处理组均出现脂肪氧化值升高的现象,高压组pH略有升高,热处理组储藏末期红度值显著降低(p<0.05),其他理化指标没有显著变化。综合考虑,超高压技术可用于真空包装酱牛肉的保鲜中,延长产品货架期。     

Effect of modified atmosphere packaging on the growth of spoilage microorganisms and Listeria monocytogenes on fresh cheese

Queso Fresco has a limited shelf life and has been shown to support the rapid growth of Listeria monocytogenes during refrigerated storage. In addition to improving quality and extending shelf life, modified atmosphere packaging (MAP) has been used to control the growth of pathogenic microorganisms in foods. The objectives of this study were to determine the effects of MAP conditions on the survival and growth of spoilage microorganisms and L. monocytogenes during storage of Queso Fresco manufactured without starter cultures. For L. monocytogenes experiments, cheeses were surface inoculated at ～4 log₁₀ cfu/g before packaging. Inoculated and uninoculated (shelf life experiments) cheeses were placed in 75-µm high-barrier pouches, packaged under 1 of 7 conditions including air, vacuum, or combinations of N₂ and CO₂ [100% N₂ (MAP1), 30% CO₂:70% N₂ (MAP2), 50% CO₂:50% N₂ (MAP3), or 70% CO₂:30% N₂ (MAP4), 100% CO₂ (MAP5)], and stored at 7°C. Samples were removed weekly through 35 d of storage. Listeria monocytogenes counts were determined for inoculated samples. Uninoculated samples were assayed for mesophilic and psychrotolerant counts, lactic acid bacteria, coliforms, and yeast and mold. In general, cheeses packaged under conditions consisting of higher contents of CO₂ had lower pH levels during storage compared with those stored in conditions with lower levels or no CO₂ at all. Similarly, the antimicrobial efficacy of MAP in controlling spoilage microorganisms increased with increasing CO₂ content, whereas conditions consisting of 100% N₂, vacuum, or air were less effective. Mean L. monocytogenes counts remained near inoculation levels for all treatments at d 1 but increased ～2 log₁₀ cfu/g on cheeses packaged in air, vacuum, and 100% N₂ (MAP1) conditions at d 7 and an additional ～1.5 log₁₀ cfu/g at d 14 where they remained through 35 d. In contrast, treatments consisting of 70% CO₂ (MAP4) and 100% CO₂ (MAP5) limited increases in mean L. monocytogenes counts to <1 log₁₀ cfu/g through 14 d and ～1.5 log₁₀ cfu/g by d 21. Mean L. monocytogenes counts increased to levels significantly higher than inoculation (d 0) on cheeses stored in MAP2 and MAP3 on d 21, on d 28 for MAP4, and on d 35 for cheeses stored under MAP5 conditions. Overall, significant treatment × time interactions were observed between air, vacuum, and MAP1 when each was compared with MAP2, MAP3, MAP4, and MAP5. These data demonstrate that packaging fresh cheese under modified atmospheres containing CO₂ may be a promising approach to extend shelf life while limiting L. monocytogenes growth during cold storage.     

Antagonistic action of cells of Lactobacillus delbrueckii subsp. lactis against pathogenic and spoilage microorganisms in fresh meat systems

Cells of Lactobacillus delbrueckii subsp. lactis RM2-5 were added to various meat model systems that had been inoculated with Escherichia coli O157:H7 or Salmonella Typhimurium to determine whether these lactobacilli were antagonistic to the pathogens during storage at 5 degrees C. Experiments in which L. delbrueckii subsp. lactis RM2-5 was directly applied to the surfaces of beefsteaks resulted in significant (P < 0.05) reductions in the growth of psychrotrophs and coliforms plus a slight decrease in the numbers of E. coli O157:H7 over time relative to those for control samples to which no lactobacilli had been added. Experiments involving the direct application of L. delbrueckii subsp. lactis RM2-5 to the surfaces of freshly slaughtered beef and pork carcass samples inoculated with either E. coli O157:H7 or Salmonella Typhimurium showed significant (P < 0.05) declines in numbers of the pathogens as well as a reduction in the growth of psychrotrophs during storage at 5 degrees C for 6 days. The results of the experiments suggest that lactobacillus cultures have potential for use in an intervention technology for the control of foodborne pathogens, especially on the surfaces of beef and pork carcasses. The results of this study also suggest that an extension of the shelf life of meat can result from the decreased growth of psychrotrophic spoilage organisms.     

面筋中腐败微生物的分离和鉴定的研究

该实验对变质面筋中腐败微生物进行分离,分离出的18株微生物全部为细菌,并对其进行面筋腐败验证试验,所有菌株均能在24 h内引起面筋变质。对面筋中腐败微生物进行分离纯化以及生理生化试验,初步鉴定引起面筋变质的腐败微生物主要为地衣芽孢杆菌（Bacillus licheniformis）,枯草芽孢杆菌（Bacillus subtilis）,巨大芽孢杆菌（Bacillus megaterium）以及蕈状芽孢杆菌（Bacillus mycoides）。     

Inactivation of spoilage microorganisms in apple cider using a continuous flow pulsed electric field system

The effect of pulsed electric field (PEF) in inactivating naturally occurring microorganisms (yeast and molds) in freshly squeezed apple cider was investigated in a continuous flow system. The microbial count decreased with an increase of applied pulses (17.6-58.7 total) and treatment temperature (45-50 °C), and a decrease of flow rate (3-10 l/h). At field strength of 27-33 kV/cm (3 mm electrode gap in a concentric chamber), 200 pulses/s, 3 l/h flow rate, and 50 °C process temperature, there was a 3.10 log reduction in microbial counts. By PEF treatment in the presence of a mixture of nisin and lysozyme (27.5 U/ml for nisin and 690 U/ml for lysozyme), there was an increase in the microbial count from 1.12 to 1.78 log reductions for 10 l/h flow. When cider samples were treated in the presence of clove oil (3 or 5 ml/100 ml), an additive reduction of 1.99 log cycles in microbial counts was observed.     

超高压处理对冷却牛肉色泽稳定性的影响

选取牛肉半腱肌为原料,研究室温条件下,常压以及200、400、600MPa超高压处理10min对牛肉色泽稳定性的影响,测定色差值、肌红蛋白含量、高铁肌红蛋白还原酶活性(MRA)、烟酰胺腺嘌呤二核苷酸(NADH)含量、耗氧率(OCR)等指标。结果表明:高压处理后牛肉的L*值升高,a*、b*值降低,OCR降低。MRA在400MPa左右达到最高,削弱高铁肌红蛋白(Met Mb)的积累,NADH含量与MRA相关。贮藏期间,各组MRA、NADH含量均降低,但高压处理组比对照组Met Mb积累速度慢,说明高压处理虽然可使肉色变浅,但贮藏期间肉色稳定性提高。      

超高压处理对冷却牛肉色泽稳定性的影响

选取牛肉半腱肌为原料,研究室温条件下,常压以及200、400、600MPa超高压处理10min对牛肉色泽稳定性的影响,测定色差值、肌红蛋白含量、高铁肌红蛋白还原酶活性(MRA)、烟酰胺腺嘌呤二核苷酸(NADH)含量、耗氧率(OCR)等指标。结果表明:高压处理后牛肉的L*值升高,a*、b*值降低,OCR降低。MRA在400MPa左右达到最高,削弱高铁肌红蛋白(Met Mb)的积累,NADH含量与MRA相关。贮藏期间,各组MRA、NADH含量均降低,但高压处理组比对照组Met Mb积累速度慢,说明高压处理虽然可使肉色变浅,但贮藏期间肉色稳定性提高。     

Potential prediction of the microbial spoilage of beef using spatially resolved hyperspectral scattering profiles

Spoilage in beef is the result of decomposition and the formation of metabolites caused by the growth and enzymatic activity of microorganisms. There is still no technology for the rapid, accurate and non-destructive detection of bacterially spoiled or contaminated beef. In this study, hyperspectral imaging technique was exploited to measure biochemical changes within the fresh beef. Fresh beef rump steaks were purchased from a commercial plant, and left to spoil in refrigerator at 8 °C. Every 12 h, hyperspectral scattering profiles over the spectral region between 400 and 1100 nm were collected directly from the sample surface in reflection pattern in order to develop an optimal model for prediction of the beef spoilage, in parallel the total viable count (TVC) per gram of beef were obtained by classical microbiological plating methods. The spectral scattering profiles at individual wavelengths were fitted accurately by a two-parameter Lorentzian distribution function. TVC prediction models were developed, using multi-linear regression, on relating individual Lorentzian parameters and their combinations at different wavelengths to log₁₀(TVC) value. The best predictions were obtained with r² = 0.95 and SEP = 0.30 for log₁₀(TVC). The research demonstrated that hyperspectral imaging technique showed potential for real-time and non-destructive detection of bacterial spoilage in beef.     

A modified hot processing strategy for beef: effects on fresh meat quality

A modified hot processing (MHP) strategy for beef carcasses using known chilling technology to maintain quality in the higher priced cuts while retaining lower value cuts for further, immediate hot processing was evaluated. Following high voltage electrical stimulation, paired sides from 36 carcasses were either conventionally processed (CP) or reduced in a manner similar to the French pan traité cut. The sides were help in a pre-chiller for 1 h prior to blast chilling at −20°C for 3 h at an air speed of 2·3 m s⁻¹, followed by chilling at 2°C for the remainder of the 24 h period. Overall, MHP of beef carcass sides had minimal effects on fresh meat quality in the longissimus thoracis et lumborum (LTL) and the semimembranosus (SM) muscles despite removing over 50% of the carcass side weight in the form of lower value cuts. Sarcomere length was significantly shorter (P ≤ 0·05) in the anterior (AL) and posterior (PL) LTL which was attributed to the removal of skeletal restraint and carcass weight. The increase in shear value in the AL, location of MHP sides although statistically significant (P ≤ 0·05) would not likely be percieved by consumers. Hence a non-traditional method of processing carcasses by treating low value and high value primal cuts separately, may be viable.     

超高压加工生鲜牡蛎的研究

研究了超高压处理对牡蛎的杀菌效果及其对产品感官性质的影响。研究结果表明,当超高压达到500MPa后,牡蛎达到商业无菌。600MPa处理的牡蛎在4℃冷藏21d后,总菌落数小于6个对数,仍然符合生鲜牡蛎细菌总数的要求。超高压对牡蛎中不同蛋白酶具有不同的影响。超高压处理使牡蛎的硬度、弹性、咀嚼度、粘结性和恢复力均表现出不同程度的下降,而且超高压处理对牡蛎的色泽产生了一定影响。超高压处理可引起TBA值显著升高,表明超高压引起了牡蛎中脂肪的氧化。