Search

Changes in the water activity (aw) of experimental Cheddar cheeses with different compositions were measured over a 270 d ripening period. The ranges of key compositional parameters were typical of those found in commercial Cheddar cheese: moisture (35.6–38.6%), fat (29.9–33.4%), salt (1.4–2.0%), salt-in-moisture (3.8–5.2%), moisture-in-non-fat substances (MNFS, 52.4–56.3%) and pH (5.0–5.7). Linear regression analysis indicated that at ripening times ≤30 d, the aw was inversely correlated with salt-in-moisture, while at 270 d it was positively correlated with levels of moisture and MNFS, but negatively with fat content. The aw decreased significantly (P

The objective of this study was to examine the effects of lowering protein content of a model infant formula on its processing characteristics and physical stability. Formulations containing five different protein:fat ratios (0.21–0.43) were investigated. Increasing protein:fat ratio increased viscosity and decreased fat globule size. Fat globule size increased significantly upon evaporation ( P P τ ) did not differ significantly between treatments. Increasing protein:fat ratio resulted in decreased creaming rates and improved emulsion stability. In conclusion, decreasing the protein:fat ratio of the formulae, particularly to 0.21, reduced the physical stability of the emulsions.

The microbiological status of thirty herb and spice preparations used in the manufacture of ready meals was determined. The effect of a simulated manufacturing process with subsequent cold storage was evaluated on spices having highest microbial loads either suspended in water, or added to a ready meal. Total aerobic mesophilic bacteria count indicated that 20% of the spices had >6 log CFU/g. Spore-forming bacteria and thermophiles (2–6 log CFU/g) were detected in 80% of samples. Pseudomonas spp. and Enterobacteriaceae (2–6 log CFU/g) were detected in 33% or 23% of spices, respectively. Molds were detected in 50% of samples (1–3 log CFU/g), while yeasts were detected in two samples only. Bacillus cereus was detected only in samples of marjoram. The simulated manufacturing treatment with subsequent cold storage indicated a degree of bacterial survival with a possible protective effect of the food matrix. Overall, the heat processing steps applied during manufacture of chilled ready meals may not always be sufficient to eliminate the indigenous microflora especially in spices of poor microbiological quality.

Ten commercial Cheddar cheeses of variable quality differing in fat content and age were subjected to compositional, proteolytic, lipolytic and sensory analyses. The compositional parameters of the full-fat cheeses were predominantly outside those typically associated with good-quality cheese. Sensory analysis discriminated the full-fat cheeses predominantly by age, with the longer ripened cheeses associated with more negative attributes, some which appeared to be due to excessive lipolysis and/or β-casein breakdown. Both proteolysis and lipolysis appear to be age dependent. The two reduced-fat cheeses were clearly discriminated from the eight full-fat cheeses by sensory analysis that appeared to be due to differences in composition and the extent of lipolysis.

Cheddar cheese was manufactured using a standard procedure from early-, mid- and late-lactation (LL) milk from a spring calving herd. All cheeses were within acceptable quality thresholds, although some statistically significant compositional differences occurred. The rate of proteolysis over ripening was highest in cheeses made from LL milk and lowest in cheeses made from early-lactation (EL) milk. The level of free fatty acids (FFAs) in all cheeses was primarily influenced by levels of FFAs in the milk, which were highest in LL and lowest in EL. Lipolysis occurred during ripening, but was not influenced by stage of lactation (SOL). Volatile analysis generally discriminated the cheeses based on SOL, but sensory descriptive analysis clearly discriminated the cheeses based on extent of lipolysis. This study has demonstrated that a seasonal milk supply causes significant biochemical and compositional differences in Cheddar cheese, which in turn influence their sensory and volatile character.

The effect of protein content (6.68-11.88 g protein 100 g-1 powder) on the microstructure and physical stability of dry infant formula was investigated at relative humidities (RH) of 0 and 54.4%. Time-dependent lactose crystallisation of powders occurred at lower water contents as protein level decreased. Surface composition of powders stored at 0% RH were significantly (P < 0.05) different to their bulk composition, with fat extensively covering the surface of powder particles. Increasing RH to 54.4% increased surface lactose levels due to lactose crystallisation. Reducing protein level increased levels of free fat in powders stored at 0% RH for 14 days. Glass transition temperatures of powders decreased only at the lowest protein level studied (6.68 g 100 g-1). Reducing the protein content of infant formulae resulted in altered powder particle surface composition, free fat levels and time-dependent lactose crystallisation properties. © 2012 Elsevier Ltd.

A detailed investigation was undertaken to determine the effects of four single starter strains, Lactococcus lactis subsp. lactis 303, Lc. lactis subsp. cremoris HP, Lc. lactis subsp. cremoris AM2, and Lactobacillus helveticus DPC4571 on the proteolytic, lipolytic and sensory characteristics of Cheddar cheese. Cheeses produced using the highly autolytic starters 4571 and AM2 positively impacted on flavour development, whereas cheeses produced from the poorly autolytic starters 303 and HP developed off-flavours. Starter selection impacted significantly on the proteolytic and sensory characteristics of the resulting Cheddar cheeses. It appeared that the autolytic and/or lipolytic properties of starter strains also influenced lipolysis, however lipolysis appeared to be limited due to a possible lack of availability or access to suitable milk fat substrates over ripening. The impact of lipolysis on the sensory characteristics of Cheddar cheese was unclear, possibly due to minimal differences in the extent of lipolysis between the cheeses at the end of ripening. As anticipated seasonal milk supply influenced both proteolysis and lipolysis in Cheddar cheese. The contribution of non-starter lactic acid bacteria towards proteolysis and lipolysis over the first 8 months of Cheddar cheese ripening was negligible.

The evolution of free fatty acids (FFA) was monitored over 168 d of ripening in Cheddar cheeses manufactured from good quality raw milk (RM), thermized milk (TM; 65 degrees C x 15 s), and pasteurized milk (PM; 72 degrees C x 15 s). Heat treatment of the milk reduced the level and diversity of raw milk microflora and extensively or wholly inactivated lipoprotein lipase (LPL) activity. Indigenous milk enzymes or proteases from RM microflora influenced secondary proteolysis in TM and RM cheeses. Differences in FFA in the RM, TM, and PM influenced the levels of FFA in the subsequent cheeses at 1 d, despite significant losses of FFA to the whey during manufacture. Starter esterases appear to be the main contributors of lipolysis in all cheeses, with LPL contributing during production and ripening in RM and, to a lesser extent, in TM cheeses. Indigenous milk microflora and nonstarter lactic acid bacteria appear to have a minor contribution to lipolysis particularly in PM cheeses. Lipolytic activity of starter esterases, LPL, and indigenous raw milk microflora appeared to be limited by substrate accessibility or environmental conditions over ripening.

To assess the contribution of starter lactic acid bacteria (LAB) to lipolysis in Cheddar cheese, the evolution of free fatty acids (FFAs) was monitored in Cheddar cheeses manufactured from pasteurized milks with or without starter. Starter-free cheeses were acidified by a combination of lactic acid and glucono-δ-lactone. Starter cultures were found to actively produce FFAs in the cheese vat, and mean levels of FFAs were significantly higher in starter cheeses over ripening. The contribution of nonstarter LAB toward lipolysis appears minimal, especially in starter-acidified cheeses. It is postulated that the moderate increases in FFAs in Cheddar cheese are primarily due to lack of access of esterase of LAB to suitable lipid substrate. The results of this study indicate that starter esterases are the primary contributors to lipolysis in Cheddar cheese made from good quality pasteurized milk. Keywords: Cheddar; lipolysis; starter-free cheese; glucono-δ-lactone

The objective of this study was to determine and quantify the influence of various food components (carbohydrates, fat, protein or NaCl contents) or chemical properties (pH, water activity levels) on the antimicrobial efficacy of oregano and clove essential oils (EOs). Growth of Listeria innocua or Escherichia coli treated with oregano or clove EOs was monitored following separate addition of various food components. Antimicrobial activity of EOs was enhanced in presence of NaCl (? 0.5 g/100 ml), or in media with low pH values (? 5.0), especially when adjusted with organic acids. Enhanced antimicrobial activity was observed following reduction in water activity, which appeared related to the nature of solute used. Antibacterial activity of EOs was reduced in presence of vegetable oil (? 1 ml/100 ml), protein (? 1 g/100 ml) or starch (? 10 g/100 ml). Based on data obtained, the composition of vegetable soup was altered to optimise the efficacy of EOs, by lowering the pH to 5.0 using citric acid. A combination of oregano EO and acidification appeared to control growth of L. innocua and E. coli during storage at 4 or 10 ºC. Thus, reformulation treatments including EO addition should be considered to improve the shelf-life of chilled ready meals.

The aim of this study was to evaluate and compare the antimicrobial properties of extracts of thirty commercial herbs and spices commonly used in the production of ready meals. Various extracts of spices were evaluated for their antimicrobial activities against Escherichia coli, Listeria innocua, Staphylococcus aureus and Pseudomonas fluorescens using a microdilution broth method. Ethanol and hexane extracts of oregano, clove, sage, rosemary and celery showed relatively strong antimicrobial activities against all bacteria tested. In contrast, water extracts displayed little or no antimicrobial activity. Flow cytometry revealed that cell membrane structures were damaged by spice and herb active extracts, while analysis of intra- and extracellular ATP contents of bacteria indicated that an increase in extracellular ATP was partially due to intracellular leakage. Extract combinations assessed using the checkerboard method did not display synergistic effects, however, some additive effects were observed when oregano was combined with sage or rosemary against L. innocua or S. aureus. This study has demonstrated that some commercial spice extracts have antimicrobial activity against food-borne bacterial species and may be considered as potential antibacterial agents for addition to ready meals.