Sensory, Microbial and Chemical Characteristics of Fresh Aerobically Stored Ground Beef Containing Sodium Lactate and Sodium Propionate

Hamburger patties with sodium lactate (NaL; 0, 3, or 4%) with or without sodium propionate (NaP; 0.1, or 0.2%) were stored aerobically at 4°C for 0, 1, 2, or 3 days, and evaluated for sensory attributes, Aerobic Plate Counts (APCs), lipid oxidation, pH, and water activity. NaL slowed microbial growth; addition of 0.2% NaP to 3% NaL increased antimicrobial effects equal to that of 4% NaL. NaL in combination with NaP reduced lipid oxidation over control or NaL patties. Patties with NaL had higher beef/brothy and beef fat scores and were sweeter, springier, more cohesive, and less crumbly than control patties and addition of 0.2% NaP increased juiciness.     

Proteolytic and Lipolytic Changes in Beef Inoculated with Spoilage Microorganisms and Bioprotective Lactic Acid Bacteria

Abstract

The use of a controlled lactic fermentation has been studied by several authors as a means to extend meat shelf‐life without notably altering its sensory quality. Growth and metabolite production by spoilage microorganisms as well as by bioprotective strains are influenced by storage conditions. The objective of this work was to study the effect of temperature and storage time upon the growth and metabolite production of four spoilage bacteria and three bioprotective lactic acid strains in vacuum packaged, finely cut beef. Lipolysis was mainly due to the presence of Brochothrix thermosphacta at 4°C and at 20°C, whereas proteolysis was mainly caused by pseudomonads. Presence of Lactobacillus minor, a heterofermentative strain, did not promote proteolysis nor lipolysis at either temperature. No considerable lipolysis was observed until day 8 of storage in samples inoculated with bioprotective strains, but increased at day 12 when stored at 20°C; no proteolysis was observed at any storage temperature.     

Comparison of HPLC and GC Methods for Measuring Lactic Acid in Ground Beef

A rapid method for measurement of lactic acid in refrigerated ground beef was developed using high performance liquid chromatography (HPLC) with an Aminex HPX-87H ion exclusion column. The method was compared with an existing gas chromatography procedure. Nine samples of ground beef, consisting of three grades based on fat content, were tested over six days of aerobic and two weeks of anaerobic storage. No significant difference was found in reproducibility between the two methods as measured by their variance. There also was no significant difference between the variances for grade of beef or for duration of aerobic or anaerobic storage. The following equation was developed to relate the two methods: GC =−138.43 + 1.1254 (HPLC).     

Bacteria and Volatile Compounds Associated with Ground Beef Spoilage

Ground beef (GB) samples were maintained in atmospheres of 2 or 18% oxygen. Similar putrid spoilage occurred at both concentrations, although the microflora differed. Two of 10 isolates from fresh and spoiled GB, nonfluorescent pseudomonads, produced putrid aromas but only 4 volatile compounds in common when inoculated into sterile GB. A Moraxella isolate produced a pronounced estery, decayed vegetable odor while others produced a decayed straw, ammoniacal or sour aroma. Differences in spoilage aromas apparently were not characterized by individual compounds but rather by the concentration of sulfur compounds and their ratio to other compound classes. Acetone, methyl ethyl ketone, dimethyl sulfide and dimethyl disulfide were indexes of microbial spoilage.     

稻谷储藏危害真菌生长与CO2浓度的相关性

采用危害真菌孢子计数法和便携式储粮危害生物快速检测仪法,研究了稻谷储藏过程中危害真菌生长与CO2浓度的关系。选择不同水分的稻谷样品,在不同温度下储藏60 d,采用两种方法对各稻谷样品真菌生长与CO2浓度进行检测,并对检测结果进行相关性分析,其相关系数分别为,r2=0.959 1(25℃)和r2=0.943 9(30℃)。在我国南方某地,选择了3个储藏稻谷的平房仓作为实验仓,每仓设30个采样点,采样深度为0.35 m,对各采样点的真菌生长与粮堆和仓内环境中CO2浓度进行了研究,并对检测结果进行相关性分析,相关系数分别为r2=0.998 4和r2=0.988 7。研究表明,稻谷储藏过程中危害真菌的生长与CO2浓度具有良好的相关性。     

Inhibition of Spoilage Bacteria by Acidification of Soy Extended Ground Beef

Bacterial isolates from soy extended ground beef were used to test the effect of pH on their growth in trypticase soy broth (TSB), ground beef, and ground beef + 20% textured soy protein (TSP). Growth was measured in TSB acidified with hydrochloric, citric, lactic, or acetic acids at pH levels from 5.4–6.2. After incubation at 4°C for 7 days, acetic acid was determined to inhibit growth to the greatest extent with no growth at or below pH 5.8. Growth response was studied in meat blends at pH levels of 5.4, 5.7, 6.0, and 6.3. Growth was suppressed in ground beef initially at pH 5.4 and in ground beef + 20% TSP initially at pH 5.4 and 5.7. This resulted in an increased shelf life of 2 days in acidified blends.     

Reducing Microbial Populations on Beef Tissues: Concentration and Temperature of an Acid Mixture

A mixture of 2% acetic, 1% lactic, 0.25% citric and 0.1% ascorbic acid was applied to beef core samples of muscle inoculated with bacteria. Experimental variables were concentration and temperature of mixed acids and type of microorganism. Overall, an increase in either mixed acids concentration (0 to 3%) or temperature (20 to 70°C) resulted in reductions in counts of about one logi₀ for aerobic bacteria and S. ryphimurium, less than one log₁₀ for Enterobacteriaceae, and about one-half log₁₀ for E. coli. Initial meat surface pH dropped to 4.3 after treatment with 3% mixed acids solution but rose to 5.2 after 24 hr. Overall, this mixture of acids performed about the same as acetic acid or lactic acid under the same conditions.     

Antioxidative/Antimicrobial Effects and TBARS in Aerobically Refrigerated Beef as Related to Microbial Growth

Ground beef muscle-pretreated (PT) with 60 ppm chlortetracycline/0.2% potassium sorbate or nonpretreated (NPT)-was mixed with sodium lactate (3%), ascorbate (0.05%), tripolyphosphate (0.5%), citrate (0.5%), or water only and aerobically refrigerated for 0–18 days. More TBA-reactive substances (TBARS) were accumulated in PT than in NPT samples. Only lactate was antimicrobial and resulted in higher TBARS in the NPT. Ascorbate and citrate resulted in lower TBARS in both PT and NPT meat. TBARS correlated with 18:2 fatty acid losses only in microbially controlled (PT) samples. Ascorbate and citrate reduced overall off-odor scores in the PT and discoloration in both NPT and PT samples.     

啤酒污染乳酸菌PCR引物的设计

根据细菌16s rDNA序列的特点，通过对啤酒污染菌16s rDNA序列进行分析，设计合成了针对啤酒污染乳酸菌的引物，在16srDNA基因水平证明了该引物对乳酸菌的特异性，该引物的特异性是PCR检测技术在啤酒厂推广应用的前提，同时反映了16s rDNA在微生物鉴定中所起的重要作用。     

Haze Development in Aerobically or Anaerobically Produced Clarified Apple Juices

Haze production in aerobically or anaerobically produced Red Delicious apple juice was assessed following heating, aeration, and protein addition. Stored aerobic juice produced haze in 6 wk, but anaerobic juice was haze-free unless oxygen was introduced. Phenolic material was incorporated into haze in both systems. HPLC (detection at 420 nm) of concentrated juice and addition of 100 mg/L BSA suggested the presence in both juices of ‘reactive’ material which could complex and precipitate during storage. Phenolic compounds, heating, and especially oxidation during processing (and storage) appear to be major determinants of ‘haze potential’ in clarified apple juice.     

Processing, Microbial and Sensory Characteristics of Cooler and Freezer Stored Hot-Boned Beef

Weiners were prepared from preblended hot-boned (prerigor) beef raw materials stored up to 21 days at 2°C and up to 28 days at -10°C. The addition of salt was necessary for maintenance of desirable sausage-making characteristics of hot-boned beef stored at 2°C for 7 days. The addition of salt for the maintenance of desirable functional properties does not appear to be necessary, if the prerigor materials are stored at freezer temperatures (-10°C). Flavor problems may develop in products from preblended raw materials stored at -10°C beyond 14 days postmortem.     

小麦储藏危害真菌生长规律的研究

采用真菌孢子计数法,对不同含水量的小麦在储藏期间,危害真菌生长的规律进行了研究.结果表明:在30℃,13.3%、14.2%、15.7%、16.4%四个水分的小麦样品,除13.3%水分储藏90 d未检出有危害真菌生长外,14.2%水分储藏80 d时,可检出有真菌生长迹象,但生长很慢.15.7%和16.4%两个水分,储藏20 d时,检出有真菌生长,这些真菌初期生长速度较快,当达到一定的值时,生长逐步减缓,整个生长呈动态变化过程,即:孢子-菌丝-孢子;经初步鉴定表明:在本试验中以灰绿曲霉生长为主,另外还有少量的白曲霉和青霉.整个试验期间样品的水分变化幅度为0.3%～0.9%,温度变化幅度为0.3～1.1℃,其变化大小与危害真菌生长有明显的关系;本方法与感染粒法比较,两者研究的结果具有良好的相关性.     

稻谷储藏危害真菌生长规律的研究

采用真菌孢子计数法,模拟不同含水量的稻谷,对储藏期间主要危害真菌的生长规律进行了研究.结果表明:在30℃,13.5%、14.1%、15.0%、16.1%、16.7%5个水分的试验稻谷样品,其中13.5%水分的样品储藏80 d时,发现有危害真菌生长迹象,但其生长速度很慢;14.1%和15.0%水分的样品,危害真菌感染时间为20 d,其生长速度较为缓慢;而16.1%和16.7%水分的样品,危害真菌10 d即可检出,且生长迅速.稻谷储藏期间主要危害真菌,以灰绿曲霉和白曲霉为主,储粮水分在16.0%左右时,为两种曲霉生长优势的转折点,灰绿曲霉生长由强变弱,白曲霉生长由弱变强,它们的生长是一个动态的变化过程.在本试验期间,样品水分的变化与真菌的生长有关系.     

玉米储藏主要危害真菌生长规律的研究

采用储粮真茵孢子计数法,对不同含水量的玉米在储藏期间,主要危害真菌生长规律进行了研究.将新玉米清理、除杂后,采用喷雾法将水分调至14%、15%、16%、17%、18%五个梯度,于30℃恒温恒湿箱中储藏,定期取样,检测孢子数、水分、温度等指标,实验为期60 d.结果表明:在本实验条件下玉米储藏危害真菌以灰绿曲霉和白曲霉为主;在水分16%下,以灰绿曲霉生长为主,随着水分和储藏时间增加,与其危害程度有明显的规律性;在水分17%、18%时,以白曲霉生长为主,其对储粮的危害与储藏时间和水分有明显的相关性;两种曲霉具有典型的储粮真茵生长特征,即孢子-菌丝-孢子,随着储藏时间延长,孢子呈动态上升趋势,与玉米危害程度有明显的相关性.     

Potential of Lactic Acid Bacteria to Inhibit Rope Spoilage in Wheat Sourdough Bread

The ability of selected lactic acid bacteria to inhibit the growth of rope-forming Bacillus strains in laboratory experiments and in wheat bread was investigated. Growth of Bacillus subtilis and Bacillus licheniformis was inhibited by Lactobacillus plantarum VTT E-78076 and Pediococcus pentosaceus VTT E-90390 in an automated turbidometry assay and in test bakings. Rope spoilage of wheat bread was inhibited by adding 20-30 g of sourdough/100 g of wheat dough if the sourdough was fermented with Lactobacillus plantarum VTT E-78076,Pediococcus pentosaceus VTT E-90390 or Lactobacillus brevis (commercial starter culture) and the pH values of sourdoughs were adjusted below 4.0 and the amount of total titratable acidity value was >12. Addition of lactic acid alone in concentrations comparable with those formed in sourdoughs did not prevent rope spoilage.     

啤酒污染乳酸菌PCR引物的设计与验证

根据细菌16SrDNA序列的特点,对啤酒中常见污染乳酸菌16SrDNA序列进行分析,设计合成了针对啤酒污染乳酸菌的特征引物。并用该引物对从啤酒厂分离到的7种乳酸菌进行了检测,PCR结果表明该引物能够准确检测到啤酒中常见的乳酸菌。     

Microbial and Oxidative Changes in Low-Fat Ground Beef During Simulated Retail Distribution

A low-fat ground beef product containing water, carrageenan, encapsulated salt and hydrolyzed vegetable protein (carrageenan-based) was compared to a low-fat, all-beef control during simulated commercial manufacturing and retail distribution. Few differences were found in oxidative stability and microbial growth of the two. No differences (P>0.05) were found in aerobic plate counts, populations of psychrotrophs or mold and yeast populations for the two products. Hunter color ‘a’ values (redness) and overall color scores for surface color were higher (P<0.05) for the carrageenan-based product than the all-beef product. Retail display of low-fat products in aerobic packaging resulted in greater (P<0.05) product discoloration than anaerobic retail display.     

Effects of Phage Concentration, Bacterial Density, and Temperature on Phage Control of Beef Spoilage

Retail beef steaks, inoculated with graded amounts of a Pseudomonas spp. and homologous phage, were subjected to a range of retail case temperatures to assess the significance of any interactive effects upon retail case life. The potential of phage to increase the case life of beef was unaffected by temperature within the range 1–10°C but was significantly influenced by the interactive effects of initial bacterial density and phage concentration. A maximum increase in the retail case life of beef, from 3.4 to 6.4 days, required initial bacterial densities of 4.6 × 10³ CFU/cm² and phage concentration of 9.7 × 10⁷ PFU/ cm².