A MEDIUM FOR THE CULTIVATION OF LACTOBACILLI

SUMMARY: An improved growth medium for lactobacilli is described. It supports good growth of lactobacilli generally and also is particularly useful for a number of fastidious strains which grow only poorly in other general media. In addition, tomato juice, a highly variable material, is not required. In a slightly modified form, it can also be used as a basal medium for fermentation tests.     

A NOTE ON THE USE OF ROGOSA AND MODIFIED ROGOSA MEDIA FOR THE ENUMERATION AND CULTURE OF LACTOBACILLI

SUMMARY: The modified Rogosa media (acetate broth and acetate agar) developed by Mabbitt & Zielinska (1956) have been compared with tomato juice media for the growth of representative Lactobacillus species.
Most of the species tested grew markedly better in acetate broth than in tomato dextrose broth, but some cultures did not grow well in the acetate broth although they grew normally in tomato dextrose broth. The acetate agar was satisfactory for counting those lactobacilli cultured at 30° but was inferior to tomato dextrose agar for counting those grown at 37°.     

THE SELECTIVE ACTION OF THALLOUS ACETATE FOR LACTOBACILLI

SUMMARY: The effect of thallous acetate has been examined on the growth of 23 strains of lactobacilli representing 13 different species. All strains grew satisfactorily in both broth and agar media containing 0.1% of thallous acetate. Of the 18 other organisms also examined the growth of the streptococci was unsuppressed, staphylococci, a micrococcus, B. licheniformis and Pr. mirabilis were partially inhibited and strains of Bact. coli, B. cereus, Chr. prodigiosum and Ps. fluorescens were almost completely inhibited by that concentration. By its use a valuable selective medium for isolating lactobacilli from natural habitats of mixed flora was obtained, other organisms, with the exception of streptococci, being almost completely eliminated.     

THE ENUMERATION OF LACTOBACILLI ON GRASS AND IN SILAGE

SUMMARY: For the enumeration of lactobacilli on grass and in silage the following medium has shown promise: peptone, meat extract and glucose, 10 g. each; tomato extract, 200 ml.; yeast autolysate, 50 ml.; Tween 80, 0.5 ml.; agar, 15 g., in a final volume of 1 1. and containing acetic acid/sodium acetate buffer in 0.2M concentration; pH 5–4. The medium was adjusted to pH 5–4 before sterilization and the requisite amount of concentrated pH 5.4 acetate buffer added just before plating. Double laver plates were used.
The only other silage organisms which in this medium formed colonies comparable in size with those of lactobacilli were heterofermentative streptococci and a micrococcus.     

TASTE COMPONENTS OF CHEDDAR CHEESE: FRACTIONATION AND OPTIMIZATION OF CHEDDAR CHEESE TASTE IN WATER

To determine the taste components of Cheddar cheese, we fractionated one mild Cheddar cheese and one aged Cheddar cheese by water extraction, freeze‐drying and gel filtration. Salty, sour and umami were the three predominant tastes present in the fractions. Neither trigeminal sensations nor astringency was perceived. We used response surface methodology to reconstruct a mild Cheddar cheese taste and an aged Cheddar cheese taste in water. Less salt and less acid were needed to simulate the taste of mild Cheddar cheese, compared with aged Cheddar cheese. Our optimized water solutions (containing sodium chloride, lactic acid and monosodium glutamate) were as similar to the real cheese samples as were the water extracts of the standard cheeses. However, neither our optimized solutions nor the water extracts matched the taste of the actual cheeses.     

CROSS VALIDATION OF A SENSORY LANGUAGE FOR CHEDDAR CHEESE

Communication and replication of sensory data from different sites are important to track progress on fundamental research issues and to ensure that research efforts are not duplicated. A uniform anchored Cheddar cheese sensory language has previously been identified and refined. The objective of this study was to demonstrate application of the defined sensory language for Cheddar cheese for communication between sensory panels at three different sites. The defined and referenced sensory language for Cheddar cheese was disseminated to panel leaders at the three sites and sensory panels (n ≤ 8) were trained for 40 to 80 h at each site. Ten forty-pound blocks of Cheddar cheese representing different ages were collected and evaluated by the panels. Cheeses were differentiated by the three panels by univariate and multivariate analysis (P<0.05). Cheeses were differentiated by the three panels in a similar manner. Results indicate that it is possible to calibrate panels using a standardized defined sensory language.     

CHANGES IN THE PERCEIVED TEXTURAL PROPERTIES OF CHEDDAR CHEESE DURING MATURATION

The perceived textural attributes of an English Cheddar were measured by a trained panel at various intervals during ripening, including those corresponding to mild and medium maturation times for this variety. The moisture content and pH were also monitored. After the recommended ripening period of 50 weeks the matured cheese was significantly less springy, firmer, harder, crumblier and creamier, indicating that textural attributes are related to the age of the Cheddar. Measures beyond the recommended maturation period revealed further significant differences. Comparisons of the measures taken at mild, medium and full maturity also revealed differences in the textural properties of the different classes of Cheddar. Significant correlations (p ≥0.01) between pH and springiness, crumbliness by fingers and creaminess suggested a strong relationship between these textural attributes and the extent of proteolysis. The results of this study revealed a strong relationship between age and the textural attributes of cheddar when restricted to one particular variety.     

A SELECTIVE MEDIUM FOR BACILLUS CEREUS IN MILK

SUMMARY: A medium is described by means of which cells of Bacillus cereus in milk may be estimated without the prior use of a heat treatment. Into a nutrient agar are incorporated: egg yolk, to demonstrate production of the characteristic opacity; citrate, to render the inoculated medium more transparent; lithium chloride and polymyxin, to reduce the growth of other bacteria. A cover of water agar limits the development of certain spreading organisms. The medium has proved of value in a survey of samples of raw milk, providing information additional to that obtained by plating after a heat treatment.