Sodium Retention in Prerigor and Postrigor Ground Pork

Sodium retention in pre- and postrigor ground pork was studied. Pork of different ionic strengths was prepared by mixing meat with various amounts of water and NaCl, and was separated into two fractions: supernatants and pellets. Na⁺ retention in supernatants increased with increasing percent NaCl (0–5%). Supernatants of prerigor ground pork contained less Na⁺ than those of postrigor ground meat. Na⁺ retention in pellets also increased with increasing percent NaCl (0–5%). Na⁺ retention was higher in pellets of prerigor ground pork than in those of postrigor ground meat. Muscle proteins were not able to bind added Na⁺, as demonstrated by a dialysis method, regardless of rigor state and fraction.     

Iron Catalyzed Oxidative Rancidity in Prerigor Ground Pork

Lipid oxidation in prerigor ground porcine muscles as affected by ethylenediaminetetraacetic acid (EDTA) and FeCl₃ was studied over a 12-day storage period. Concentrations of total, soluble-protein bound and free iron in prerigor and postrigor ground muscles were determined at 24 hr postmortem. Increasing EDTA concentrations from 0.02 to 2.0% in the presence of 0.009% FeCl₃ produced increasing inhibitory effects on oxidation as measured by thiobarbituric acid numbers. Extremely low concentrations of EDTA (0.002%) in the presence of added FeCl₃ enhanced the rate of oxidation. Iron content analyses showed that postrigor ground muscle had a slightly higher free iron content than prerigor ground muscle.     

Sensory Properties and Lipid Oxidation in Prerigor Processed Fresh Pork Sausage

Fresh pork sausage prepared from prerigor ground and salted meat had higher pH, lower cooking losses, higher juiciness scores, and less easily fragmented cooked patties than that prepared from post-rigor ground and salted meat. Sausage from prerigor ground-post-rigor salted meat was intermediate in these properties to prerigor ground and salted and postrigor ground and salted products. Prerigor grinding and salting reduced the rate of autoxidation (TBA number) during storage at 0°C contrasted to oxidation in sausage that was salted postrigor after either prerigor or postrigor grinding.     

Production of Glycosidases by Psychrotrophic Bacteria

Six of 19 psychrotrophic bacteria common in milk and meat hydrolyzed large amounts of p-nitrophenyl-glycosides during 48 hr in minimal growth broth at 20°C. Four of the 19 were inactive against the four glycosides used in the screening tests, and nine were weakly active. In tests of the six active cultures against 11 p-nitrophenyl-glycosides, strains of Enterobacter had more glycosidase activity than strains of Pseudomonas, β-anomers were hydrolyzed more rapidly than α-anomers, more p-nitrophenol was released from the β-D-galactoside than from other substrates, there was activity against the D form but not the L form of fucoside, and p-nitrophenyl-β-D-glucoside was hydrolyzed at about the same rate by each culture.     

Oxidative Stability of Batter-Breaded Restructured Nuggets Processed from Prerigor Pork

Restructured pork slices made with either prerigor or postrigor meat, with or without 1.5% of defatted glandless cottonseed flour (GCF). were batter-breaded with or without GCF in predust and batter-mix: Prerigor products had less cooking losses than postrigor products; GCF in the meat or coating reduced cooking losses. Prefried prerigor products were more susceptible to lipid oxidation and warmed-over flavor development than prefried postrigor products. GCF in the meat or coating markedly reduced the oxidative deterioration in nuggets stored at 4°C or ?20°C regardless of the rigor state of meat used for restructuring. Little lipid oxidation occurred in vacuum-packaged raw nuggets stored at ?20°C.     

Konjac Flour Gel as Fat Substitute in Low-fat Prerigor Fresh Pork Sausage

Prerigor trimmings from four lean cuts of pork carcasses (n = 3) were used to manufacture three replications of low-fat (10%) fresh pork sausage containing konjac flour gel, at 0, 10 or 20% levels and compared to a 40% fat control. Treatment sausages showed equal or improved cooked yields, slightly higher shear force (kg/g) and sensory textural attributes, but rated slightly lower in juiciness. As konjac flour gel levels increased, shear force and sensory textural attributes became more like the control. Storage time had minimal effect on quality and shelf life. Acceptable low-fat, prerigor pork sausage can be produced with 10–20% incorporation of konjac flour gel.     

Rapid Detection of Psychrotrophic Bacteria in Relation to Retail Beef Quality

Media and incubation conditions were compared to establish a rapid method for the detection of psychrotrophic bacteria from retail beef Of the methods tested, incubation of plate count agar (PCA) at 25°C for 24 hr gave the most accurate measure of the psychrotrophic bacterial population when compared to the recommended procedure (7°C, 10 days). Moreover, the initial bacterial load as determined following 25°C (24 hr) incubation was directly related to the retail case life of steaks. Increasing the temperature of incubation of PCA to 25°C results in a substantial reduction in the time required for psychrotroph enumeration, without loss of precision, and thereby provides a more useful estimate of retail beef keeping quality.     

Photosensitized Lipid Peroxidation in Ground Pork and Turkey

The initiative role of singlet oxygen (¹O₂) in hydroperoxide production in ground pork and turkey was studied. Ground meats treated with or without various antioxidants and illumination (350 ft-c, 4°C) were monitored for lipid peroxidation by peroxide value (POV). Ground turkey breast meat developed higher (P < 0.01) POV during illumination than did thigh meat. In both pork and turkey, light exposure resulted in higher (P < 0.01) POV than samples kept in the dark. The prooxidant effect of light was reduced (P < 0.01) by a ¹O₂ quencher (2,2,6,6-tetramethy1-4-piperidone) in turkey meat, and by another ¹O₂ quencher (N,N,N′,N′-tetramethylethylene diamine, TMEDA), a free radical scavenger (butylated hydroxyanisole, BHA) and TMEDA + BHA in pork.     

嗜冷茵对UHT奶品质影响的研究

嗜冷菌产生耐热蛋白酶和脂肪酶是UHT奶在长期存放过程中产生劣变的主要原因之一。原料乳中蛋白酶、脂肪酶的活性与产品长期保存时的品质呈负相关。通过控制原料奶乳中嗜冷菌数,测定蛋白酶和脂肪酶活力,对原料奶进行分级和评价是确保UHT奶品质的一种有效手段,本实验为乳品企业嗜冷菌的检测提供了理论依据。     

解冻猪肉中优势腐败菌致腐能力研究

将解冻猪肉中的优势腐败菌(假单胞菌属、热死环丝菌和肠杆菌科)接种到灭菌肉上研究其在不同温度贮藏过程中腐败的特点。在贮藏期间每天进行感官评价,测定各腐败菌的菌落数(CFU)、挥发性盐基氮(TVB-N)、脂肪氧化值,并以产生腐臭味时的TVB-N产量因子Y(TVB-N/CFU)作为各优势腐败菌腐败能力的定量指标。研究结果表明：至贮藏期第5天时解冻猪肉已产生强烈的腐臭味,热死环丝菌菌数在4、0℃和－5℃贮藏时分别达11.28lg(CFU/g)、9.63lg(CFU/g)和6.62lg(CFU/g),而相应的TVB-N值分别达14.92、14.50mg/100g和9.10mg/100g;与之类似,假单胞菌属菌数4、0℃和－5℃贮藏时分别达9.46lg(CFU/g)、8.87lg(CFU/g)和5.37lg(CFU/g),TVB-N值分别达21.59、14.49mg/100g和8.97mg/100g。研究表明热死环丝菌和假单胞菌属导致解冻猪肉腐败能力较强。     

解冻猪肉的有害菌鉴定及其再生长研究

采用选择性培养基对－18℃冻藏5d后解冻的猪肉中有害菌进行计数,并对各选择性培养基上的典型菌落进行分离纯化和初步鉴定,进而对各种有害菌在4、0、－5℃的再生长进行研究。结果表明假单胞菌属、热死环丝菌、肠杆菌科是解冻猪肉中存在的优势有害菌。在4℃和0℃贮藏的过程中各有害菌均有增长,假单胞菌和热死环丝菌增长最快,菌数最多;－5℃贮藏过程有害菌增长缓慢,甚至有所减少。     

Lnsolubilization of Orthophosphates in Fresh or Cooked Ground Pork

The insolubilization of added orthophosphate (1000–10000 ppm, equivalent to 0.1–1 .0% w/w) and of orthophosphate generated through enzymatic hydrolysis of added sodium acid pyrophosphate (SAPP) was studied in fresh and in cooked (65.5°C) ground pork held at 5°C for 6 days. Fresh and cooked pork linearly absorbed or otherwise insolubilized orthophosphate added directly to the meat or generated through enzymatic hydrolysis of added SAPP. Orthophosphate insolubilization was constant throughout the range of addition studied and equivalent to 70–80%. Soluble orthophosphate measurements, therefore, could not be used to estimate the proportion of added pyrophosphate that was hydrolyzed in the meat or, by difference, the proportion of residual, unhydrolyzed SAPP.     

Analysis of Vacuum Packed Beef Regarding Psychrotrophic Bacteria Growth and Biogenic Amines Content

It has been recognized that biogenic amines (BA) content in meat can be considered a freshness marker. Considerable amounts of some BAs can appear during food storage under certain conditions, according to the handling of the raw material, technology applied, storage temperature and time, packaging condition, mainly if amino acid - decarboxylase positive microorganisms are present. The aim of this study was to evaluate the psychrotrophic bacteria growth and metabolic production of BAs during chill storage of beef. The vacuum packed beef cuts (Longissimus dorsi muscle) were analyzed during storage at 7 °C at 0, 15, 30, 45, and 60 d, to determine the psychrotrophic bacteria growth and the BAs amount. The BAs considered were: putrescine, cadaverine, histamine, spermidine, and spermine. The BAs quantitative determination was carried out by reversed phase high-performance liquid chromatography (HPLC) with UV detection. Statistic procedures were performed using SAS statistical software. The growth parameters of psychrotrophic bacteria including lag phase, maximum specific growth rate, maximum bacterial cell density, initial population, mean square error, and coefficient of determination were determined according to Baranyi and Roberts model. The values of histamine and spermidine increased significantly (P < 0.0001) during storage time, while the levels of spermine decreased (P < 0.0001). Psychrotrophic bacteria counts increased significantly (P < 0.0001) reaching 7.6 log cfu/g over time. The counts of this group positively correlated to histamine and spermidine (r = 0.68 and 0.61, respectively), while spermine showed a negative correlation (r = -0.70). Conversely, no significant correlation was found between psychrotrophics counts and putrescine or psychrotrophics counts and cadaverine.     

Properties of Crude Ethylester-forming Enzyme Preparations from Some Lactic Acid and Psychrotrophic Bacteria

Ester-forming enzyme preparations were obtained from 48 h cultures of Streptococcus diacetilactis ATCC 15346, S. lactis ML3, Lactobacillus No. 81 and two strains of psychrotrophic bacteria belonging to the genus Pseudomonas (Strains No. 50 and 53).Optimum pH's of the enzyme preparations of Lactobacillus No. 81 and two strains of the lactic streptococci for the production of ethylbutyrate and ethylhexanoate were 6.5 and 7.0 to 7.5, respectively. Enzymes of Strains No. 50 and 53 had their maximum activities at pH 8.0. The optimum temperature was 32 C for all strains. Enzymes were generally stable below 35 C at pH 7.0, but their activities were rapidly lost at higher temperature. When the esterases were incubated at 4 C for 24 h, Lactobacillus No. 81, the lactic streptococci (Strains ML3 and ATCC 15346), and the psychrotrophic bacteria (Strains No. 50 and 53) were most stable at pH 6.0, 7.0, and 8.0, respectively. Copper, manganese, and cobalt salts inhibited all the enzymes. The inhibitory effect of cobalt on enzyme activities of Strains ML 3, No. 50 and 53 and that of copper on Strain No. 81 were especially significant.     

Effect of Nitrogen Flushing on the Production of Proteinase by Psychrotrophic Bacteria in Raw Milk

Raw milk was flushed with 100 ml N₂ min ^-1 during storage at 4°C. Microflora (total psychrotrophs, proteolytic psychrotrophs, lactic acid bacteria) in nitrogen-flushed milk exhibited a longer lag phase and slower growth rates than those in milk stored aerobically at 4°C. Although proteolytic psychrotrophs grew in nitrogen-flushed milk, proteinases could not be detected in these milk samples. Proteinase assays and electrophoresis showed extensive proteolytic activity and hydrolysis of β-casein in control milk but no detectable casein degradation in nitrogen-flushed milk, even after storage for 18 days at 4°C. This study shows the potential of controlled atmosphere storage of raw milk for inhibition of the accumulation of proteolytic enzymes from psychrotrophic bacteria.     

鲜猪肉在保藏中的主要腐败菌分析

为确定市售鲜猪肉的货架期,通过分析肉品分别在4 ℃和25 ℃条件下保藏销售过程中的感官指标、挥发性盐基氮（total volatile base nitrogen,TVB-N）值、细菌总数和腐败菌的变化情况对其腐败临界点进行研究,并采用皮尔逊相关系数分析腐败菌与肉样腐败品质间的相关性。结果显示：鲜猪肉在4、25 ℃保藏条件下出现明显腐败品质特征的时间分别为96、24 h,其TVB-N值分别为（19.28±0.22） mg/100 g和（20.14±0.21）mg/100 g,细菌总数分别为（8.11±0.29）（lg（CFU/g））和（7.91±0.23）（lg（CFU/g））;4 ℃保藏条件下肉样的假单胞菌数与细菌总数和TVB-N值的相关性分别为0.955（P＜0.01）和0.901（P＜0.01）,均高于肠杆菌的0.914（P＜0.01）和0.871（0.01＜P＜0.05）,而25 ℃保藏条件下肉样的肠杆菌数与细菌总数和TVB-N值的相关性分别为0.989（P＜0.01）和0.963（P＜0.01）。结果表明,鲜猪肉在4 ℃和25 ℃保藏条件下的销售货架期分别为96 h和24 h,其TVB-N值、细菌总数在货架期终点均与其感官指标基本一致,且4 ℃保藏肉样的致腐菌以假单胞菌为主,其次为肠杆菌,而25 ℃保藏肉样的致腐菌以肠杆菌为主。     

Inhibition of Oxidative Rancidity in Salted Ground Pork by Carnosine

Carnosine (0.5 and 1.5%) effectively inhibited formation of lipid peroxides and thiobarbituric acid reactive substances (TBARS) in frozen (? 15°C) salted ground pork during up to 6 mo storage. Inhibition of TBARS formation by carnosine (1.5%) was better than sodium tri-polyphosphate (0.5%), ot-tocopherol and butylated hydroxytoluene (0.02% of fat content). Carnosine was the most effective at preventing oxidative rancidity and color changes as determined by sensory panel, in salted ground pork after 1 mo frozen storage (?15°C). These data suggested that carnosine could be used as a “natural” antioxidant in muscle foods.     

Antibiotic Resistance Patterns of Gram‐Negative Psychrotrophic Bacteria from Bulk Tank Milk

Bacterial resistance to antibiotics is a major global health problem and resistance of Pseudomonadaceae and Enterobacteriaceae is a serious concern. We investigated the prevalence of drug‐resistance in a total of 80 psychrotrophic strains from bulk milk belonging to Pseudomonas genus (n. 63) and Enterobacteriaceae group (n. 17). All the strains were tested against 16 antibiotics. Pseudomonas were further investigated for their sensitivity against 12 additional antibiotics. Pseudomonas showed a high susceptibility toward fluoroquinolones, aminoglycosides, and piperacillin and, to a lesser extent, to imipenem, ceftazidime, cefepime. Thirty‐five out of 63 Pseudomonas strains were susceptible to meropenem, while among antibiotics for which recommended breakpoints are not yet available, 55% of Pseudomonas strains had no inhibition halo in presence of nitrofurantoin, highlighting a resistance toward this drug. The results obtained in this study indicate a high efficiency of fluoroquinolones, chloramphenicol (94%), and kanamycin (76%) for Enterobacteriaceae while a high prevalence of resistant strains was found to ampicillin (13/17). Serratia marcescens is highly susceptible to fluoroquinolones, chloramphenicol, and kanamycin. Moreover, mupirocin seems to be the new antibiotic with the less efficacy for Enterobacteriaceae, with 41% of strains without halo, pointing out an important resistance. Further knowledge on resistance to known and new antibiotics among Pseudomonas species and Enterobacteriaceae of milk origin was acquired.     

原料乳中嗜冷菌计数及产脂肪酶特性的研究

本文主要对乳中的嗜冷菌数的检测方法进行了初步研究。同时,考虑到嗜冷菌能在乳中产生大量的耐热性脂肪酶,力求在脂肪酶活与菌数之间建立联系。即对不同时间测得的酶活与菌数之间的关系进行初步探讨。     

Characterization of Gram‐Negative Psychrotrophic Bacteria isolated from Italian Bulk Tank Milk

Eighty psychrotrophic bacterial strains, isolated from different northwest Italian bulk tank milks destined for Grana Padano cheese production, were identified by 16S rRNA gene amplification and partial sequence analysis of the rpoB gene. Pseudomonas spp. were the most commonly occurring contaminants, P. fluorescens being the predominant isolated species, along with Enterobacteriaceae, primarily Serratia marcescens. RAPD‐PCR was used to study genetic variability and distinguish closely related strains; a high degree of genetic heterogeneity among the strains was highlighted. All the strains were characterized for their ability to produce proteases, lipases and lecithinases at different temperatures (7, 22, and 30 °C). Forty‐one of the psychrotrophic strains were positive for all the enzymatic activities. The highest number of positive strains for all the incubation temperatures was found for lipolytic activity (59), followed by proteolytic (31) and lecithinase (28) activities, and the enzymatic traits varied among the Pseudomonas and Enterobacteriaceae strains. The proteolytic psychrotrophic strains were screened for the presence of the aprX gene, coding for a heat‐resistant metalloprotease in Pseudomonas spp. The aprX gene was detected in 19 of 63 Pseudomonas strains, and was widespread in the P. fluorescens strains (14/19).