Timothy P. Guinee

Salt in Cheese: Physical, Chemical and Biological Aspects

The use of salt (NaCl) as a food preservative dates from pre-historic times and, together with fermentation and dehydration (air/sun), is one of the classical methods of food preservation. So useful and widespread was the use of salt as a food preservative in Classical and Medieval times that it was a major item of trade and was used as a form of currency in exchange for goods and labour. It is perhaps a little surprising that Man discovered the application of salt in food preservation so early in civilization since, in contrast to fermentation and dehydration, salting is not a ‘natural event’ in foods but requires a conscious act. It is interesting that the three classical methods of food preservation, i.e. fermentation, dehydration and salting, are all exploited in cheese manufacture and in fact are interdependent. The fourth common method of food preservation, i.e. use of high and/or low temperatures, was less widespread than the others because the exploitation of low temperatures was confined to relatively few areas until the development of mechanical refrigeration about 1870 and, although heating was probably used to extend the shelf-life of foods throughout civilization, its controlled use dates from the work of Nicolas Appert (1794) and Louis Pasteur (c.1840). In modern cheese technology, temperature control complements the other three methods of food preservation.

Autolysis and proteolysis in different strains of starter bacteria during Cheddar cheese ripening

Autolysis of and proteolysis by various Lactococcus lactis subsp. cremoris strains were monitored in cheese ‘juice’ extracted by hydraulic pressure up to 63 d ripening. Viability was lowest for strain AM2 (non-bitter), intermediate for strain HP (bitter) and highest for the defined mixed strains G11/C25 (non-bitter). Autolysis monitored by the levels of the intracellular marker enzymes lactate dehydrogenase (EC 1.1.1.27), glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and post-proline dipeptidyl aminopeptidase proceeded in the order AM2 > G11/C25 > HP. Differences in autolysis between strains did not appear to be due to differences in stabilities of the marker enzymes, populations of non-starter lactic acid bacteria or levels of the marker enzymes in the strains. Proteolysis, as measured by gel permeation FPLC and free amino acid analysis of the cheese juice was highest for AM2, intermediate for G11/C25 and lowest for HP. The results of this study provided some evidence that different Lactococcus strains used for cheesemaking had different autolytic patterns during ripening, the effects of which on ripening and flavour development have not yet been clearly demonstrated.

Cheese: Physical, Biochemical, and Nutritional Aspects

Publisher Summary This chapter discusses the physical, biochemical, and nutritional aspects of cheese. Cheese is the most diverse, most scientifically interesting, and most challenging group of dairy products. While most dairy products, if properly manufactured and stored, are biologically, biochemically, and chemically very stable, cheeses are biologically and biochemically dynamic and, consequently, inherently unstable. Cheese manufacture and ripening involves a complex series of consecutive and concomitant microbiological, biochemical, and chemical events, which, if synchronized and balanced, lead to products with highly desirable flavors, but when unbalanced, result in off-flavors. Considering that a basically similar raw material (milks from a very limited number of species) is subjected to a generally common manufacturing protocol, it is fascinating that such a diverse range of products can be produced.

Development and application of confocal scanning laser microscopy methods for studying the distribution of fat and protein in selected dairy products.

Confocal scanning laser microscopy (CSLM) methods were developed to identify fat and protein in cheeses milk chocolate and milk powders. Various fluorescent probes were assessed for their ability to label fat or protein in selected food products in situ. Dual labelling of fat and protein was made possible by using mixtures of probes. Selected probes and probe mixtures were then used to study (a) structure development of Mozzarella cheese during manufacture and ripening, and (b)) the distribution of fat and protein in milk chocolate made with milk powders containing varying levels of free fat. Microstructural changes in the protein and fat phases of Mozzarella cheese were observed at each major step in processing. Aggregation of renneted micelles occurred during curd formation; this was followed by amalgamation of the para-casein into linear fibres during plasticization. Following storage, the protein phase of the Mozzarella became more continuous; entrapping and isolating fat globules. Chocolate made with a high free-fat spray-dried powder blend showed a homogeneous fat distribution, similar to that of chocolate made with roller-dried milk. Chocolate made with whole milk powder containing 10 g free fat/100 fat showed a non-homogeneous fat distribution with some fat occluded within milk protein particles. These differences in fat distribution were related to Casson yield value and Casson viscosity of the chocolates.

Factors which may influence the determination of autolysis of starter bacteria during cheddar cheese ripening

Abstract An investigation of the factors affecting the determination of autolysis of the starter strain Lactococcus lactis subsp. cremoris G11 during Cheddar cheese ripening was undertaken. Autolysis was monitored by determining the activities of intracellular marker enzymes, lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G6PDH) and post-proline dipeptidyl aminopeptidase (PPDA), in cheeses which were extracted under hypo- and hypertonic conditions. Increased salt-in-moisture levels in the cheese, in the range 0·4–5·0%, were accompanied by increases in the activities of LDH and G6PDH and decreases in the activity of PPDA. The activities of LDH, G6PDH, and in some cases PPDA, increased in cheeses ripened at 4 or 10°C for up to 60 days; thereafter, activities reached a plateau or decreased to various degrees. Addition of sucrose or NaCl to the assay cuvette also affected the activity of all marker enzymes; increasing the concentration of NaCl resulted in increased activity of all enzymes while increasing concentrations of sucrose in the cuvette reduced LDH activity but increased the activities of PPDA and G6PDH. Holding the enzymes prepared from a cell free extract (CFE) for 4 h at 4°C resulted in about 20% decrease in the activities of LDH and PPDA. while in the case of G6PDH a 40% decrease in activity was noted. Addition of a CFE containing the marker enzymes to a cheese-like environment indicated that LDH activity appeared to be the most stable (40% of original activity remained after 500 h at 4°C) while G6PDH or PPDA activities had disappeared after 48 or 24 h, respectively.

Influence of κ-casein genetic variant on rennet gel microstructure, Cheddar cheesemaking properties and casein micelle size

Cheddar cheese was manufactured on three separate occasions over a two week period from milk collected from two mid-lactation, spring-calving, Holstein–Friesian herds (n=11) containing similar casein levels, having phenotype AA or BB for κ-casein genetic variant. κ-Casein variant did not significantly (P>0.05) influence the casein content or gross composition of milk. κ-Cas ein BB milk had significantly smaller average casein micelle diameter and superior rennet coagulation properties than that of the AA milk. Pilot-scale Cheddar cheesemaking studies showed that the κ-casein BB milk resulted in significantly higher fat recoveries into cheese and higher actual and moisture-adjusted cheese yields. Cheese produced from κ-casein BB variant milk had higher concen trations of fat and lower protein levels than that produced from the AA variant. κ-Casein variant had no significant effect on prote olysis or on the acceptability scores awarded to the cheeses.

Effect of milk protein standardization, by ultrafiltration, on the manufacture, composition and maturation of Cheddar cheese

Skim milks were pre-acidified to pH 6·4 and concentrated by ultra-filtration to give retentates with protein levels of 210 g/1. Retentates were blended with skim milk and cream to give standardized milks with protein levels ranging from 30 to 82 g/1. These were used for the manufacture of Cheddar cheese in conventional equipment. Increasing milk protein level resulted in reduced gelation times, increased curd firming rates and a decrease in the set-to-cut time when cutting at equal firmness values (i.e. elastic modulus, G′, ∼ 16 Pa). As the curd firming rates increased with milk protein level, it became increasingly difficult to cut the curd cleanly, without tearing, before the end of the cutting cycle. Reflecting the tearing of curd, and consequent curd particle shattering, fat losses in the running wheys were greater than those predicted on the basis of volume reduction (due to ultrafiltration) for milks with protein levels > 50 g/1. Reduction of setting temperatures, in the range 31–27 °C, and the level of added rennet brought the set-to-cut times and curd firming rates of concentrated milks closer to those of the control milk. While increasing milk protein level in the range 30–70 g/1 had little effect on cheese composition, it resulted in slower proteolysis and maturation.

The effect of high pressure treatment on the functional and rheological properties of Mozzarella cheese

Abstract Low-moisture Mozzarella cheese (LMMC) was high pressure (HP) treated at different stages of storage at 4°C and analysed immediately post HP treatment. Confocal laser scanning microscopy of the unheated cheese indicated that HP treatment enhanced the development of age-related swelling of the paracasein matrix. This microstructural change coincided with a reduction in the level of serum expressed on centrifugation and suggests that HP results in an increase in the water holding capacity of the paracasein matrix. Proteolysis, as measured by urea polyacrylamide gel electrophoresis (urea-PAGE), pH 4.6 water soluble nitrogen and total levels of free amino acids (FAA), was largely unaffected by HP treatment of LMMC. HP treatment resulted in an increase in the flowability and a reduction in the melt time on heating at 280°C, especially at storage times ≤15 days. Dynamic measurement of the viscoelastic changes on heating the cheese from 20 to 82°C showed that HP treatment resulted in an increase in the fluidity of the heated cheese, as measured by phase angle, especially in 1-day-old cheese. Thus, accelerated ripening of LMMC was induced by HP treatment, which may lead to the development of an industrial process if cost effective commercial HP equipment were available.

An investigation of the autolytic properties of three lactococcal strains during cheese ripening

Cheddar cheeses were manufactured using Lactococcus lactis ssp. cremoris AM2 (a non-bitter strain), HP (a bitter strain) or 303 (a commercial starter). Lysis was monitored in the cheese at various intervals over a 10-week ripening period by measuring the activities of intracellular marker enzymes [lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G6PDH) and post-proline dipeptidyl aminopeptidase (Pep X)] in the cheese juice. On day 1 of ripening, starter cell counts in cheeses manufactured using strain HP or 303 were in the range 109 − 1010 cfu g−1 cheese compared to 108 for AM2. Viability of starter strains during ripening decreased in the order: 303 > HP ⪢ AM2. Autolysis of the different strains, as indicated by the release of the marker enzymes, during cheese ripening decreased in the order: AM2 ⪢ 303 > HP. The degree of secondary proteolysis followed a similar trend to autolysis. Neither NSLAB numbers nor inter-strain variations in the specific activity of intracellular marker enzymes appeared to influence the activity of marker enzymes in Cheddar cheese during a 10-week ripening period.

Effect of exopolysaccharide produced by isogenic strains of Lactococcus lactis on half-fat Cheddar cheese.

Fat-reduced cheeses often suffer from undesirable texture, flavor, and cooking properties. Exopolysaccharides (EPS) produced by starter strains have been proposed as a mechanism to increase yield and to improve the texture and cooking properties of reduced-fat cheeses. The objective of this work was to assess the influence of an exopolysaccharide on the yield, texture, cooking properties, and quality of half-fat Cheddar cheese. Two pilot-scale half-fat Cheddar cheeses were manufactured using single starters of an isogenic strain of Lactococcus lactis ssp. cremoris (DPC6532 and DPC6533) that differed in their ability to produce exopolysaccharide. Consequently, any differences detected between the cheeses were attributed to the presence of the exopolysaccharide. The results indicated that cheeses made with the exopolysaccharide-producing starter had an 8.17% increase in actual cheese yield (per 100 kg of milk), a 9.49% increase in moisture content, increase in water activity and water desorption rate at relative humidities <or=90%, significant differences in the cheeses microstructure, and a significant improvement in both textural and cooking properties, without negatively affecting the flavor profiles of the cheeses.