The effect of time that processed cheese was held ex- posed to heat alone or with agitation, the level of rework cheese, and the type and level of emulsifying salt were evaluated by determining finess of emulsion based on scanning electron microscopy measurements, meltability, and rheological measurements using a Universal Testing Machine. Process cheese held in the cooker at 82°C for up to 4o minutes became less meltable and more firm and the emulsion became finer while that held at 82°C outside of the cooker without agitation was only slightly affected. Loss of meltability and increased firmness associated with pro-longed cooking of process cheese is associated with the state of the fat emulsion and not with the effect of heat on the proteins per se. The level of rework cheese had a great influence on the cheese rheological properties as well as on the microstructure of process cheese. There was a poor emulsion when no emulsifying salt was used regardless of the percent rework cheese added. The emulsion became finer as the per- cent rework cheese was increased if emulsifying salt was also present except after 20% rework cheese addition where the emulsion became coarse again. Process cheese lost meltability during storage at 4°C after 53 days when 1.0 or 0.0% emulsifying salt is used or when rework cheese is present at 0.0 or 5%, but no effect was noticed in meltability values if the 2.5% emulsifying salt was used with no rework cheese.

Problem and its importance: Starter is the "heart" of the cheese making industry. only by proper handling of starter can good quality cheese be made. The economic loss from contaminated starter may prove disastrous to a cheese plant if proper corrective measures are not taken. Milk usually contains a variety of bacteria. Under plant conditions some of these bacteria get into the mother starter or bulk starter unless extreme caution is used. Comparatively little is known about how one organism influences another when grown in milk. This problem is important in the cheese industry. Purpose: The purpose of this research project is to determin the effect of some common contaminants on cheese starters. Some of the off flavors and slow acid production found in cheese making may be due to the results of contaminant organisms growing with the starter organisms. If this be true, more information on this subject will prove valuable. Some organisms have detrimental effects on milk. The question arises: What will two different organisms do when grown together in milk? Streptococcus lactis is important in the cheese industry because it satisfactorily produces the acid necessary in cheese making. If some organism inhibits or stimulates this acid production when grown with Streptococcus lactis, it is important that the cheesemaker know this. Scope: Only those contaminants commonly found in dairy products are considered in this project. Simulated plant conditions are used; that is, the starter being tested is contaminated one evening and the results checked and read the next day. Commercial lactic acid cheese starter from the Hansen's Laboratories and milk from the Utah State Agricultural College Creamery are used to propagate the starter. Different percentages of the contaminant are added to the starter to determine the effects of varying numbers of the contaminant on the starter organisms. A control starter is incubated and tested along with the contaminated starter. After the starters have been incubated at 70°F. Overnight, the following tests are run on each one: activity, acidity, pH, creatine, odor and appearance, and microscopic count. Starter vitality may be determined by the above tests; however, these do not indicate how the contaminant organisms affect cheese when carried on into the cheese making process. Therefore, this project is limited to the effects of contaminants on the starter and not on cheese. This latter problem is reserved for future investigators.

Attempts were made to adapt the microtiter hemagglutination inhibition assay technique for the assay of enterotoxin A. The presence of a potent hemagglutinin in crude and partially purified preparations and the instability of sensitized erythrocytes prevented its use for routine analysis of enterotoxin from culture media and foods. A capillary tube immunological assay was developed in which 1 μ g of enterotoxin/ml was detected in less than 1 hr . Interfacial reaction of antisera and enterotoxin solutions in a 1 mm internal diameter capillary tube allowed rapid detection and serological typing of enterotoxins. Staphylococcus aureus growth and enterotoxin A development in Cheddar cheese slurry was evaluated. S. aureus growth and enterotoxin production occurred at 32 C. in 45 and 60% moisture cheese slurries following inoculation with 10 3 to 10 5 bacteria/gram. Hydrogen peroxide (0. 5%) treatment of slurry at 37 C did not inhibit S. aureus and enterotoxin A development. Heating slurry at 72 C for 30 min eliminated staphylococci but reinoculation with ripening organisms was essential. Addition of sorbic acid (0. 2 to 0. 3%) to a slurry adjusted to pH 5. 0 with lactic acid, inhibited staphylococci. in milk and slurry. Cheese flavor development was retarded due to inhibition of micrococci and lipolysis. Non-protein nitrogen increases paralleled that of sorbate-free controls. Sorbate treatment was preferred over other treatments .

The objective of this study was to evaluate the effects of using food grade coatings and nettings formulated with xanthan gum and propylene glycol (PG) or carrageenan (CG), propylene glycol alginate and PG on aged Cheddar cheese to control Tyrophagus putrescentiae growth at temperatures of 10°C, 15°C, and 20°C and relative humidity’s of 75% and 85%. Cheddar cheese cubes with treated nets and coatings inhibited mite growth at all temperature and relative humidity combinations. Control cheese cubes either without coatings or in untreated nets had fewer mites (P<0.05) at 10°C than at 15°C or 20°C. The sensory properties of the cheese were not affected by the coatings and nettings at 10°C and 75 % RH. However, all other temperature and RH combinations with the exception of the CG netting at 15°C at 75 % and 85 % RH caused sensory flavor differences (P<0.05).

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