INFLUENCE OF ANTIMICROBIAL COMPOUND(S) EXTRACTED FROM MILK FERMENTED BY STREPTOCOCCUS THERMOPHILUS ON KEEPING QUALITY OF MEAT AND MILK

The potential of a methanol-acetone (M-A) extract prepared from milk fermented by Streptococcus thermophilus in extending the shelf-life of meat and milk was investigated. In experiment I, increasing amounts (0, 0.1, 0.2 and 0.3 ml) of M-A extract with or without ascorbic acid were added to 20 g aliquots of ground beef subsequently stored at 5–7° C for 0, 3 and 6 days. Total and gramnegative bacterial counts and pH in ground beef treated with M-A extract were significantly (P<0.01) less than the corresponding values in control beef on days 3 and 6 for all dose levels tested with significant (P<0.01). In experiment II, rib-eye steaks were sprayed with H₂O or 0.1, 0.2 and 0.3 ml of M-A extract and stored at 5–7° C for 0, 3 and 6 days. The total and gram-negative bacterial counts on the surface of steaks sprayed with M-A extract were significantly (P<0.01) lower than the counts in control steaks. Also, in experiment III, inhibition of bacterial growth by M-A extract was significant (P<0.01 or 0.05) both in milk stored at either room temperature or 5–7° C. M-A extract inhibited the growth of Pseudomonas fluorescens inoculated into milk.     

EFFECT OF A BACTERIOCIN-LIKE SUBSTANCE (BLS) PRODUCED BY STREPTOCOCCUS THERMOPHILUS STRAINS ON LISTERIA SPP. STRAINS

In this study, fifty-two strains of Streptococcus, isolated from Turkish yogurt were tested for their ability to inhibit Listeria strains. Only two isolates exhibited antimicrobial activity (CFF; cell-free filtrate) against eight strains of Listeria innocua, four strains of Listeria monocytogenes and one strain of Listeria welshimeri by agar diffusion. However, bacteriocin-like substance (BLS) producing strains were determined under conditions with the effects of organic acids and hydrogen peroxide eliminated. Inhibitory activities of Streptococcus thermophilus ET5 and S. thermophilus H22 were due to BLS. BLS of S. thermophilus ET5 was observed to exhibit more significant inhibition to the Listeria strains than BLS of S. thermophilus H22.
Inhibitory effect of nisin in 50, 100, 150, 200, 250 and 300 ppm concentrations was compared with BLS producing S. thermophilus strains against Listeria spp. strains. While all Listeria strains were resistant to 50 and 100 ppm concentrations of nisin, some strains of Listeria spp. were only sensitive to 150, 200, 250 and 300 ppm concentrations. The inhibitory activity of S. thermophilus ET5 was more effective against Listeria strains than the inhibitory activity of nisin. It appears that BLS of S. thermophilus ET5 could provide greater potential and usefulness as bacteriocin than nisin. These results indicate that the potential application of antimicrobial-production of S. thermophilus ET5 and H22 as bio-preservatives against Listeria contamination on dairy products could be suggested.     

牛奶中大肠杆菌和无乳链球菌的快速检测

大肠杆菌和无乳链球菌是两种导致奶牛乳房炎的重要致病菌,这两种致病菌的检测有助于及时诊断和治疗奶牛乳房炎,从而有效控制牛奶质量.利用16S-23S rDNA间区作为检测靶点,建立牛奶中大肠杆菌和无乳链球菌的快速PCR检测方法,并对该检测方法的灵敏度和特异性进行了确认.结果显示,该方法对于牛奶中大肠杆菌和无乳链球菌的检出限均能够达到1 cfu/mL,并且与其它7种对照菌株均无交叉反应,整个检测过程可在20 h内完成.     

电流对运动电荷的电场力作用

从狭义相对论的角度出发导出了电流对运动电荷的电场力作用公式，揭示了电场与磁场可构成一个统一的实体——电磁场．     

EFFECT of SALT and CITRIC ACID ON ELECTRICAL CONDUCTIVITIES and OHMIC HEATING of VISCOUS LIQUIDS

Four hydrocolloid solutions (starch, 4.3%; carrageenan, 1.7%; xanthan, 2%; pectin, 2.5%) were prepared in water with varying amounts of NaCl (0.25, 0.5, 0.75 and 1%). Hydrocolloid concentrations were adjusted to result in an apparent viscosity of 0.2 Pa.s at 20C and 300 s^-1. A voltage of 150 V was applied in a static ohmic heating cell to study the effect of hydrocolloid and salt on electrical conductivity (EC) and temperature profile at their pH. the pH levels were modified by citric acid addition and the combined effect of hydrocolloid, salt and citric acid was investigated. At low salt concentration, carrageenan and xanthan had shortest heating times and highest ECs. This was followed by pectin. Starch was the least effective, having slowest heating rates and lowest ECs. At 1% concentration, the salt effect overcame that of hydrocolloid giving similar temperature profiles and ECs. the effect of citric acid addition was present but negligible.     

THE EFFECT OF EEC REGULATIONS ON THE MARKETING OF MILK AND MILK PRODUCTS IN THE UK

The effect on the dairy industry of membership of the EEC and the distinction between its regulations and directives as set out in the Treaty of Rome are described. Over 3,000 regulations were issued in 1974, 250 of which dealt with milk and dairy products and a list of the main regulations is given in an appendix. The advantages of price reviews more than once a year and possible seasonal milk pricing are discussed. The marketing field is described and the need for products with the greatest earning potential stressed. Developments in liquid milk markets are shown and their importance in the United Kingdom emphasized. Possible standardization in the liquid milk market, and the difficulties involved in the operation of milk marketing boards is considered. {Editor's summary).     

EFFECT OF PROTEIN CONTENT OF MILK ON THE STORAGE AND LOSS MODULI IN RENNETING MILK GELS

A series of skim milks was made up with protein levels in the range 3 to 5 g/100g using ultrafiltration. The rheometric behavior during renneting was measured using low-amplitude oscillatory shear. Gel times were determined in terms of storage modulus G′, loss modulus G″ and tan δ (=G”/G′), respectively and were modelled in terms of protein level and enzyme level. Coagulum cutting time was defined in terms of G′. A prediction equation was developed for coagulum firming time in terms of gel time and protein level. The consistency of ultimate tan δ, over the range of protein and milks, showed that G″ at coagulum cutting was related to G′ and hence an on-line system could monitor coagulum firming rate by sensing either G′ or G′, or any related parameter, such as viscosity or complex modulus.     

牛乳中微生物的微波致死特性试验研究

牛乳营养丰富,是微生物的优良培养基.而这些微生物却是造成牛乳腐败变质的主要原因.为了探讨牛乳中微生物的微波致死特性,本文进行了不同功率下的牛乳微波杀菌试验.通过试验表明,牛乳中的微生物在微波功率为600w时致死特性最显著,同时也表明随着微波功率的变大,微波致死时间呈双曲线型下降,而生产效率呈线性逐渐增加.     

EFFECT OF MILK PROTEINS AND STABILIZER ON ICE MILK QUALITY

Ice milk mixes were made with and without stabilizer/emulsifier as well as with and without milk protein isolate (sodium caseinate or whey protein isolate). The mixes were evaluated for rheological, freezing, melting, and sensory properties. Adding a stabilizer/emulsifier blend to ice milk changed its physical properties more than adding milk protein isolates. The mixes with stabilizer/emulsifier exhibited increased viscosity and chewiness and decreased drainage rate, iciness, and vanilla flavor intensity. The mixes with added caseinate exhibited increased viscosity compared with those with added whey protein isolate. Overall, the quality of ice milk mix was more dependent on stabilizer/emulsifier addition than on milk protein isolate addition.     

EFFECT OF DRUG RESIDUES ON RENNET COAGULATION OF MILK

The aim of this study was to consider the problem of residual drugs in cow's milk and to define the influence of such residues in the milk coagulation process, including the case in which the concentration is below the lowest limits permitted by law. Compounds that have EU maximum residue levels (MRLs) were selected. Through milk dynamographic analysis, the chemical and rheological parameters (r, k₂₀ and a₃₀) were determined in relation to the different quantities of drug additions. Effects on coagulation were demonstrated for high concentration. The only residue that demonstrated significant effects at MRL value was trimethoprim. These results were confirmed using electron microscopy, rheological studies and near‐infrared spectral analysis.     

EFFECT OF MICROWAVE HEATING ON SURVIVAL OF SALMONELLA TYPHIMURIUM IN ARTIFICIALLY CONTAMINATED READY-TO-EAT FOODS

This research evaluated the destruction of Salmonella typhimurium during reheating of foods in two different types of microwave ovens: a conventional 750W oven and 700W oven with preset controls. The heating times in the conventional microwave oven were established as 50 s for baby food and 75 s for mashed potatoes as well as for the beef stroganoff samples, while for the preset oven those periods of time were determined by a built-in temperature sensor. The percentage of food samples positive for S. typhimurium in conventional microwave was 47.8% while in microwave with preset controls it was 93.3%. Our results suggest that reheating contaminated foods in microwave ovens may, therefore, not be sufficient to destroy S. thyphimurium in order to assure food safety .