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UF cheese yields Methods by which UF cheesemaking can increase yields Whey protein retention and yield Fat retention and yield Problems in assessing the yield of UF cheeses Explanations for the success of certain commercial UF cheeses Non-ripened cheeses (UF Quarg, UF Ricotta, UF Cream) Mozzarella-type cheeses Ripened varieties in which factors other than proteolysis are important (UF Feta, UF Blue, UF Camembert) Ripened varieties in which proteolysis is mainly responsible for product characteristics (UF Havarti, UF Cheddar) Varieties where UF cheesemaking is most successful Conclusion References

SummaryComparisons were made of the flavour, free fatty acids and bacterial flora of commercial cheese made at different factories and experimental cheese made under aseptic conditions: (i) with δ-gluconic acid lactone instead of starter, (ii) with starter only, (iii) with starter and added floras derived from the curd of the commercial cheeses (reference flora cheeses).Comparison of the bacterial flora of commercial and reference flora cheeses showed that replication of organisms was better with some reference floras than with others. In all the cheeses the lactobacilli increased in numbers during maturation, whilst other groups of organisms died out.The amount of acetic acid present was influenced by the starter and by the lactobacilli. Single-strain starters produced some acetic acid, most of which was lost in the whey; commercial starters produced considerably more, due to the presence in them of Streptococcus diacetilactis. Later in maturation lactobacilli increased the acetic acid content, a greater increase being observed with homo-than with heterofermentative strains.The initial levels of butyric and higher fatty acids in the milk varied with source of the milk and with the season, summer milk having higher levels than winter milk. During cheese-making a slight increase of these acids occurred in every cheese made with starter and a further small increase occurred during ripening. However, there was no increase in the content of these acids in the cheese made with δ-gluconic acid lactone, indicating that lactic acid bacteria were weakly hydrolysing the milk fat.Flavour trials showed that Cheddar flavour was present not only in the reference flora and commercial cheese, but also in the cheese made with starter only. Different starters produced different intensities of flavour; one strain produced an intense fruity off-flavour. Cheeses made with δ-gluconic acid lactone were devoid of cheese flavour.

The production of enterotoxins A, B, and C by nine strains of Staphylococcus aureus has been studied under controlled conditions in a fermenter. The strain to strain differences between staphylococci producing a specific enterotoxin were very marked. Increasing aeration in shake flasks improved both growth and production of all extracellular proteins measured other than that of enterotoxin C, the yield of which was decreased in one strain at high aeration. Silicone antifoam decreased the production of extracellular proteins, although enterotoxin A production from three strains was much less affected than that of enterotoxins B and C. In a detailed study of three strains, production of enterotoxins A and C was considerably greater in a defined amino acid medium than in a casein hydrolysate medium and was optimal for all three enterotoxins between pH 6.5 and 7.3. Changes in the pH or medium used in the fermenter that led to increased enterotoxin production could generally be correlated with a change in growth pattern, showing an extended transition period from exponential to stationary phase. Three out of five enterotoxin-A producing strains produced significantly more enterotoxin at a controlled pH of 6.5 in the fermenter than in shake-flask cultures. The yields with strain 100 were about five times greater than hitherto reported. Since many foods are buffered at pH 6 to 6.5, some strains may, therefore, produce sufficient enterotoxin A to cause food poisoning, although little or none may be produced when grown under normal testing procedures.

SUMMARYExtracellular lipase production was a constitutive property of the micrococcus and pseudomonad studied but was considerably influenced by nutritional and physical conditions. The lipase in culture supernatant fluids of the micrococcus was markedly heat resistant but became increasingly more thermolabile with the degree of purification obtained. The hydrolytic activity of partially purified extracellular lipase preparations from each organism was due to a single protein which was identical with a hydrolytic enzyme also found in cell-free extracts of each organism. The lipases from both organisms had general specificity towards ester linkages although the lipase from the micrococcus was markedly more active towards esters containing short chain fatty acids and comparatively less active towards trigylcerides containing long chain acids than was the pseudomonal lipase. The activity of both lipases showed an optimum for all substrates at pH 8-0-8.5 and did not decrease at higher pH values, indicating the involvement of an acidic group in the enzyme/ substrate binding. The results of inhibition studies were consistent with the view that both lipases possess a serine-imidazole active centre and are therefore similar to esterolytic enzymes in mammalian systems.