Effect of Water Activity of Milk upon Growth and Acid Production by Mixed Cultures of Streptococcus thermophilus and Lactobacillus bulgaricus

Acid production and growth rates were determined in pure cultures of Streptococcus thermophilus and Lactobacillus bulgaricus and cocci/ bacilli ratios in mixed cultures of both species, using milk with modified a_w as culture medium. Maximal growth rates were always at a_w lower than 0.992 for all strains whcn a_w of milk was adjusted with glycerol, while maximal acid production rates were at a_w 0.992-0.983. Glucose had an inhibitory effect additional to that caused by lowering a_w. The cocci/bacilli ratio in mixed cultures increased as a_w decreased in most cases, because of the higher susceptibility of L. bulgaricus to a_w decrease. The behavior of a mixed culture could not always be predicted from data of the component strains in a pure culture, showing some kind of symbiotic compatibility between species.     

SPINNING DISC MEASUREMENT OF TWO-STAGE CLEANING OF HEAT TRANSFER FOULING DEPOSITS OF MILK

The efficient and effective cleaning of milk protein – based deposits from heat transfer equipment is essential in the dairy industry. The aim of this study was to evaluate the effectiveness of two‐stage cleaning using acid and caustic. Stainless steel discs were fouled during heat transfer by skimmed milk and whey protein. The discs were then cleaned with acid and sodium hydroxide solutions under controlled mass transfer conditions using spinning disc techniques. The use of 0.5% nitric acid, and a commercial acid known as Triplex, as a rinse before caustic cleaning increased the cleaning rate by 2.5 times. The foulant was found to swell about 40% and calcium was leached out within 5 min after exposure to acid. The acid treatment is believed to cause a reduction in the viscosity, and hence an increase in dissolution, of the gel layer formed when caustic cleaning takes place.     

Thermal satellite imagery applied to a littoral macrobenthos investigation in the Gulf of Maine

The application of satellite imagery to oceanographic problems has grown in recent years. Its use in biological oceanography, however, has been largely limited to studies of primary productivity. The ability of thermal satellite imagery to identify coastal oceanic fronts suggests that there may be an application to macrobenthos investigations. This communication describes how thermal satellite imagery was applied to the study of sand-beach community distribution in the Gulf of Maine.     

Interaction of Antibiotics and Water Activity on Streptococcus thermophilus and Lactobacillus bulgaricus

Acid production was determined in cultures of Streptococcus thermophilus and Lactobacillus bulgaricus in the presence of penicillin and gentamycin in milks with water activity adjusted between 0. 992 and 0.943 by adding glycerol, glucose or sucrose. Resistance of S. thermophilus A TCC 19258 and CRL 410 to penicillin increased when a_w was lowered with glycerol from 0.992 to 0.995, and from 0.992 to 0.985 in L. bulgaricus ATCC 11842. Susceptibility to gentamycin increased in both species with reduction of a_w. Susceptibility of S. thermophilus CRL 410 to penicillin increased in most cases when a_w was adjusted with glucose, while acid production at a a_w of 0.985 was always higher than that of the controls (a_w 0.992) when sucrose was used. With L. bulgaricus CRL 420, lower acid production was observed at all penicillin concentrations, whether glucose or sucrose was used as the humectant.     

Biochemical Changes and Sensory Quality of Shredded and MA-Packaged Iceberg Lettuce

Cultivars of shredded iceberg lettuce (Lactuca sativu L.) ‘Saladin’, ‘Santis’, ‘Telda’ and ‘Roxette’ responded in a parallel way to four modified atmosphere (MA) packaging treatments. Moderate vacuum packaging (mvp) in 80 μm polyethylene (PE) inhibited enzymatic browning over 10-day storage at 5°C. When lettuce was packaged in 80% O₂, 20% CO₂ (80/20), more browning occured in SL3-bags (59 μm multilayer coextruded film) than in PE-bags. Polyphenol oxidase activity declined during storage in all 4 atmospheres, with lowest activity in PE-80/20. Endogenous ascorbic acid (AA) did not act as an efficient antioxidant in delaying browning. Total carbohydrate content (TC) declined slightly during storage. Tristimulus color measurements correlated highly with visual ratings.     

DIFFERENTIATION OF MYOFIBRILLAR AND CONNECTIVE TISSUE STRENGTH IN BEEF MUSCLES BY WARNER-BRATZLER SHEAR PARAMETERS

Heat induced changes in aged bovine m. longissimus dorsi (LD) and m. biceps femoris (BF) were studied by water bath cooking to 60, 70 or 80°C at slow (.12°C/min) and fast (.6°C/min) heating rates. Forcedeformation curves from the Warner-Bratzler (WB) shear device were used to evaluate specific changes in the myofibrillar (WB M-force) and connective tissue component (WB C-force) of tenderness. Other measurements include WB peak force value, cooking loss, collagen solubility and sensory evaluations. Differences due to muscle type were significant in all parameters except collagen solubility. Both WB M- and WB C-force were reduced by slow heating rate but for samples heated to 80°C, WB M-force was affected only by heating rate below 60°C while WB C-force was most influenced above 60°C. Effect of final temperature resulted in higher WB M-force from 60°C to 70°C, whereas WB C-force was most affected from 70°C to 80°C. On the contrary, WB peak force was less affected by final temperature. Due to concomitant and opposing changes in myofibrillar and connective tissue strength with increasing end point temperature, it is concluded that improvements in interpretations with regard to heat-induced changes and response of heat treatment in various muscles may be increased by measurement of WB M-force and WB C-force from shear force-deformation curves.     

Probabilistic sensitivity analysis in life-prediction of an α+β titanium alloy

Probabilistic sensitivities using the score function method are developed for a lifing analysis of an α+β titanium alloy in a round bar under axial fatigue load. Sensitivities with respect to the statistical inputs of the crack initiation size ( a ), and Paris crack growth intercept ( C ) and exponent ( m ) are developed with consideration of the correlation between C and m . The sensitivities are obtained using a single Monte Carlo sampling analysis and do not involve finite difference approximations. The sensitivities indicate the importance of the random variable input parameters on the mean life and standard deviation of life and can be used as a basis for determining constructive data collection efforts. For this example, the crack growth intercept ( C ) is the dominant variable that affects mean-life and standard deviation of life, indicating that improved confidence in the results can be obtained most efficiently by improving the statistical characterization of C .     

Preparation, Characterization, and Melting Point of High-Purity Lithium Oxide

High-purity lithium oxide was synthesized by thermal decomposition of the peroxide at temperatures up to 1070 K under dynamic vacuum. Analyses of typical preparations gave carbonate 0.01 to 0.02%, hydroxide 0.0 to 0.2%, sodium 0.002%, manganese 0.0004%, and lithium oxide 99.8 to 100.0%. The corrected melting point was measured as 1711±5 K based on the thermal arrest observed when molten specimens were cooled.