The effect of sodium reduction with and without potassium chloride on the survival of Listeria monocytogenes in Cheddar cheese

Sodium chloride (NaCl) in cheese contributes to flavor and texture directly and by its effect on microbial and enzymatic activity. The salt-to-moisture ratio (S/M) is used to gauge if conditions for producing good-quality cheese have been met. Reductions in salt that deviate from the ideal S/M range could result in changing culture acidification profiles during cheese making. Lactococcus lactis ssp. lactis or Lc. lactis ssp. cremoris are both used as cultures in Cheddar cheese manufacture, but Lc. lactis ssp. lactis has a higher salt and pH tolerance than Lc. lactis ssp. cremoris. Both salt and pH are used to control growth and survival of Listeria monocytogenes and salts such as KCl are commonly used to replace the effects of NaCl in food when NaCl is reduced. The objectives of this project were to determine the effects of sodium reduction, KCl use, and the subspecies of Lc. lactis used on L. monocytogenes survival in stirred-curd Cheddar cheese. Cheese was manufactured with either Lc. lactis ssp. lactis or Lc. lactis ssp. cremoris. At the salting step, curd was divided and salted with a concentration targeted to produce a final cheese with 600 mg of sodium/100 g (control), 25% reduced sodium (450 mg of sodium/100 g; both with and without KCl), and low sodium (53% sodium reduction or 280 mg of sodium/100 g; both with and without KCl). Potassium chloride was added on a molar equivalent to the NaCl it replaced to maintain an equivalent S/M. Cheese was inoculated with a 5-strain cocktail of L. monocytogenes at different times during aging to simulate postprocessing contamination, and counts were monitored over 27 or 50 d, depending on incubation temperature (12 or 5°C, respectively). In cheese inoculated with 4 log₁₀ cfu of L. monocytogenes/g 2 wk after manufacture, viable counts declined by more than 3 log₁₀ cfu/g in all treatments over 60 d. When inoculated with 5 log₁₀ cfu/g at 3 mo of cheese age, L. monocytogenes counts in Cheddar cheese were also reduced during storage, but by less than 1.5 log₁₀ cfu/g after 50 d. However, cheese with a 50% reduction in sodium without KCl had higher counts than full-sodium cheese at the end of 50 d of incubation at 4°C when inoculated at 3 mo. When inoculated at 8 mo postmanufacture, this trend was only observed in 50% reduced sodium with KCl, for cheese manufactured with both cultures. This enhanced survival for 50% reduced-sodium cheese was not seen when a higher incubation temperature (12°C) was used when cheese was inoculated at 3 mo of age and monitored for 27 d (no difference in treatments was observed at this incubation temperature). In the event of postprocessing contamination during later stages of ripening, L. monocytogenes was capable of survival in Cheddar cheese regardless of which culture was used, whether or not sodium had been reduced by as much as 50% from standard concentrations, or if KCl had been added to maintain the effective S/M of full-sodium Cheddar cheese.     

The Influence of Sodium Chloride on the Activity of Yeast in the Production of Single Cell Protein in Whey Permeate

Whey can contain substantial amounts (6 to 10%) of sodium chloride, such as whey from the pressing of hard cheese or when from making Domiati cheese where salt is added to milk prior to renneting. Nine different lactose-fermenting yeasts were cultured in shake flasks using Cheddar cheese whey permeate as the fermentation medium. The pH and temperature of growth media were kept at 5 and 32°C, respectively. We studied the effect of 3, 6, or 9% concentrations of sodium chloride on the ability of yeasts to convert whey into biomass.Kluyveromyces marxianus var. marxianus ATCC 28244 and Candida tropicalis ATCC 20401 were more efficient in producing cell mass from 0 to 9% salt permeate than the other strains.     

Texture,flavor, and sensory quality of buffalo milk Cheddar cheese as influenced by reducing sodium salt content

The adverse health effects of dietary sodium demand the production of cheese with reduced salt content. The study was aimed to assess the effect of reducing the level of sodium chloride on the texture, flavor, and sensory qualities of Cheddar cheese. Cheddar cheese was manufactured from buffalo milk standardized at 4% fat level by adding sodium chloride at 2.5, 2.0, 1.5, 1.0, and 0.5% (wt/wt of the curd obtained). Cheese samples were ripened at 6 to 8°C for 180 d and analyzed for chemical composition after 1 wk; for texture and proteolysis after 1, 60, 120, and 180 d; and for volatile flavor compounds and sensory quality after 180 d of ripening. Decreasing the salt level significantly reduced the salt-in-moisture and pH and increased the moisture-in-nonfat-substances and water activity. Cheese hardness, toughness, and crumbliness decreased but proteolysis increased considerably on reducing the sodium content and during cheese ripening. Lowering the salt levels appreciably enhanced the concentration of volatile compounds associated with flavor but negatively affected the sensory perception. We concluded that salt level in cheese can be successfully reduced to a great extent if proteolysis and development of off-flavors resulted by the growth of starter and nonstarter bacteria can be controlled.     

Development of a validated model to describe the individual and combined water activity depressing effects of water soluble salt, sugar and fat replacers

The relationship between water activity (a_w) and concentration of NaCl, sucrose and various simple and commercial salt, sugar and fat replacers was determined. The model originally developed by Favetto and Chirife (1985) and extended by Roa and Tapia (1998) was successfully used to model the relationship between a_w and molality of the binary and multi-component aqueous solutions. These models were then reparameterized to enable the a_w to be modeled as function of the water phase concentrations of binary and multi-component solutions. This reparameterization enables the modeling of the a_w depressing effects of compounds for which sufficient data required to calculate the molecular weight cannot be obtained. Both models were successfully used to predict the a_w of some food products including meat and fish products and mayonnaises with average deviations of 0.0052 from the measured a_w, and bias and accuracy factors of 0.995 and 1.0057, respectively.     

Short communication: Little change takes place in Camembert-type cheese water activities throughout ripening in terms of relative humidity and salt

Water activity (a_w) affects the growth and activity of ripening microorganisms. Moreover, it is generally accepted that a_w depends on relative humidity (RH) and salt content; these 3 variables were usually measured on a given day in a cheese without the microorganism layer and without accounting for a distinction between the rind, the underrind, and the core. However, a_w dynamics have never been thoroughly studied throughout cheese ripening. Experimental Camembert cheeses were ripened under controlled and aseptic conditions (temperature, gaseous atmosphere, and RH) for 14 d. In this study, only RH was varied. Samples were taken from the cheese (microorganism layer)–air interface, the rind, and the core. The a_w of the cheese–air interface did not change over ripening when RH varied between 91 and 92% or between 97 and 98%. However, on d 5, we observed a small but significant increase in a_w, which coincided with the beginning of growth of Penicillium camemberti mycelia. After d 3, no significant differences were found between the a_w of the cheese–air interface, the rind, and the core. From d 0 to 3, cheese rind a_w increased from 0.94 to 0.97, which was probably due to the diffusion of salt from the rind to the core: NaCl content in the rind decreased from 3.7 to 1.6% and NaCl content in the core increased from 0.0 to 1.6%. Nevertheless, a_w did not significantly vary in the core, raising questions about the real effect of salt on a_w.     

SOLUBILITY OF CALCIUM LACTATE IN AQUEOUS SOLUTION

The presence of calcium lactate (CaL₂) crystals on the surface of Cheddar cheese is an appearance defect that consumer often attributes to mold. This problem is widespread in the cheese industry. The solubility of CaL₂in water determines the likelihood of formation of CaL₂crystals on the surface of Cheddar cheese. Very little fundamental work has been done to measure the solubility of CaL₂at conditions appropriate to storage of cheese. CaL₂is a moderately-soluble salt, with saturation concentrations that increase from about 2 g anhydrous CaL₂/g water at 0°C to about 50 g anhydrous CaL₂/g water at 60°C. The substantial variability in data available in the literature attests to the difficulties in accurately measuring solubility concentrations. The limited amount of data available in the literature suggest that a decrease in pH through addition of lactic acid leads to a decrease in solubility, and that addition of salt (NaCl) has no effect on solubility.     

Clarification of Cheese Whey by Aqueous Two-Phase Systems

Aqueous two-phase systems comprising a pair of a polymer and a salt were investigated as a means to clarify Cheddar cheese whey. Fat in cheese why could partition exclusively into the bottom phase of a polyethylene glycol/KH₂PO₄ aqueous two-phase system, resulting in a clear top phase containing whey proteins. Several parameters have been studied to optimize the recovery of whey proteins in such a system. Decreasing solute concentrations to 11.7% polyethylene glycol/10% KH₂PO₄, lowering pH to 3.8, and lowering temperature to 7°C all contributed to enhance the yield. This method should be able to remove ca. 98% fat in Cheddar cheese whey and to recover > 90% whey proteins.     

Modeling incidence of lipid and sodium chloride contents on sorption curves of gelatin in the high humidity range

Water mobility and availability are predominant factors in controlling organoleptic and biological quality in food. To characterize and quantify the role of protein macromolecular mesh, sodium chloride and fat on the water retention in the high humidity range, sorption isotherms were measured at 20 °C. A specific method was used which provides rapid equilibrium and many experimental points in comparison with the standard saturated salt solution method. Experiments were carried out on gelatin gels to which either sodium chloride (0-45% w/w on an anhydrous gelatin basis) or vegetal hydrogenated fat (0-50% w/w on total sample mass) was added. Desorption isotherms of 40 points each were measured for each sample for a_w values in a range from 0.60 to 0.99. Results precisely show the specific behavior of water in a protein-sodium chloride mix for a_w values between 0.65 and 0.75. Water activity was then predicted from sample composition. Good agreement with measurements was obtained (1) assuming no incidence of lipids on water-holding capacity and (2) adapting a Ross-type model considering crystallization and introducing an interaction factor related to sodium chloride content.     

Reduced‐sodium cheeses: Implications of reducing sodium chloride on cheese quality and safety

Sodium chloride (NaCl) universally well‐known as table salt is an ancient food additive, which is broadly used to increase the storage stability and the palatability of foods. Though, in recent decades, use of table salt in foods is a major concern among the health agencies of the world owing to ill effects of sodium (Na) that are mostly linked to hypertension and cardiovascular diseases. As a result, food scientists are working to decrease the sodium content in food either by decreasing the rate of NaCl addition or by partial or full replacement of NaCl with other suitable salts like potassium chloride (KCl), calcium chloride (CaCl₂), or magnesium chloride (MgCl₂). However, in cheese, salt reduction is difficult to accomplish owing to its multifaceted role in cheese making. Considering the significant contribution in dietary salt intake (DSI) from cheese, researchers across the globe are exploring various technical interventions to develop reduced‐sodium cheeses (RSCs) without jeopardizing the quality and safety of cheeses. Thus, the purpose of this study is to provide an insight of NaCl reduction on sensory, physicochemical, and technofunctional attributes of RSCs with an aim to explore various strategies for salt reduction without affecting the cheese quality and safety. The relationship between salt reduction and survival of pathogenic and spoilage‐causing microorganisms and growth of RSCs microflora is also discussed. Based on the understanding of conceptual and applied information on the complex changes that occur in the development of RSCs, the quality and safety of RSCs can be accomplished effectively in order to reduce the DSI from cheese.     

A Study of Staphylococcus Aureus Growth in Model Systems and Processed Cheese

A survey of a_w and pH in commercial samples of processed cheese produced in Argentina, indicated the a_w varied between 0.950–0.978 and pH ranged from 5.2–6.1 Staphylococcus aureus growth studies in model systems (laboratory media with added NaCl) with a_w and pH adjusted to resemble that of commercial samples of processed cheese showed that S. aureus grows very well at a temperature of 30°C, but complete growth inhibition occurs at refrigerator temperature. The results obtained with model systems were confirmed by S. aureus growth experiments in inoculated cheese.     

Physical and Sensory Properties of Block Processed Cheese with Formulated Emulsifying Salt Mixtures

Abstract

Various emulsifying salt mixtures were used in making block type processed cheeses. Ras cheese was used as the cheese base with two salt mixtures: (i) Na-diphosphate + Na-polyphosphate + Na-tripolyphosphate and (ii) Na-poly-phosphate + Na-citrate + Na-orthophosphate + Na-diphosphate comparing to commercial salts Joha SE and PZO respectively. The resultant processed cheeses were analyzed when fresh and monthly during storage at 7 and 20°C for water activity (a _w ), oil separation, meltability, flow behavior, color parameters, and sensory properties. There were no significant differences in water activity values among all treatments. The differences were significant in oil index and meltability values. The samples exhibited different shear stress values and it was highest in treatments with commercial salts. Consistency coefficient (k-value) of processed cheese samples was affected by emulsifying salt mixture being almost two folds higher with salt mixtures (i) than those of salt mixtures (ii). The color parameters L, a, b, Chroma and hue angle showed slight differences among treatments and the cheese was shinier and whiter with increasing pyrophosphate content in the salt mixture. The stored samples became less white especially when stored at room temperature (20°C). Sensory evaluation showed that all cheeses were acceptable but the most acceptable samples were produced with mixtures in the ratio of (i) 30:40:30 and (ii) 50:20:20:10.     

Effect of NaCl reduction and replacement on the growth of fungi important to the spoilage of bread

The effect of NaCl and various NaCl replacers (CaCl₂, MgCl₂, KCl and MgSO₄) on the growth of Penicillium roqueforti and Aspergillus niger was evaluated at 22 °C. In addition, challenge tests were performed on white bread to determine the consequences of NaCl reduction with or without partial replacement on the growth of P. roqueforti. From the results obtained it can be concluded that at equivalent water phase concentrations the isolates exhibited differing sensitivities to the salts evaluated with NaCl and MgCl₂ having the greatest inhibitory action on the growth of A. niger and P. roqueforti, respectively. MgSO₄ had the least antifungal activity. At equivalent molalities, CaCl₂ had in general the largest antifungal activity. Although the water activity (a_w) lowering effects of the compounds studied play a large role in explaining the trends observed, at equivalent water phase concentrations MgCl₂ was found to have a smaller inhibitory effect on A. niger than that expected from its a_w depressing effect. The challenge tests revealed that no difference occurred in the growth of P. roqueforti on standard white bread, bread with 30% less NaCl and bread in which 30% of the NaCl has been partially replaced by a mixture of KCl and Sub4Salt. These results are of importance in assessing the possible microbiological consequences of NaCl reduction or replacement in bread and similar bakery products.     

A Comparison of Available Methods for Determining Salt Levels in Cheese

Comparative salt analyses were run on seven different types of cheese using each of four methods: Mohr, Volhard, ion selective electrode, and chloride analyzer. The results of Volhard, Mohr, and chloride analyzer methods were similar for unaged cheese varieties, i.e., Mozzarella, Cheddar, Ricotta, Romano, and Provolone, but concentrations detected with the ion selective electrode were lower than the other three methods. Results were similar with aged Cheddar and process cheeses except the Mohr procedure proved unreliable. A constant correction factor could be used to make the ion selective electrode results similar to that obtained with the Volhard procedure.     

Effect of Temperature on the Moisture Sorption Isotherms and Water Activity Shift of Two Dehydrated Foods

The water activity (a_w) of eight salt solutions was determined at three temperatures (25, 30, 45°C) using a pressure transducer-vapor pressure manometer. The a_ws of the salts showed a decrease with increasing temperature, which was explained with the help of a thermodynamic equation. This is opposite to the increase in a_w with increase in temperature for foods. Moisture sorption data for fish flour and cornmeal were obtained at 25–65°C. The Guggenheim-Anderson-deBoer model was evaluated and shown to be comparable to the Brunauer-Emmett-Teller model for prediction of the monolayer. Product was equilibrated at different a_ws at 25°C then subsequently shifted to 30°C and 45°C in a sealed chamber. The resultant a, change, measured on the Kaymont-Rotronics, was predictable from the isotherm at each temperature using the Clausius Clapeyron relationship.     

Impact of Fat Replacers on the Rheological,Tribological, and Aroma Release Properties of Reduced-Fat Model Emulsion Systems and Processed Cheese

Due to the increasing prevalence of overweight and obesity and their associated health problems, the demand for low-calorie and low-fat foods is growing worldwide, especially in the fast food and convenience sectors. However, fat- or calorie-reduced products are often accompanied by sensory deficiencies. Although fat reduction in foods has been addressed in literature, an ideal fat replacer has not been identified due to the variety of fats, their multifarious functions in foods, and the wide range of food products. The aim of this work was to investigate the influence of selected fat replacers on the properties of reduced-fat model emulsion systems and processed cheese. The use of dietary fibers as fat replacers was of particular interest due to their intrinsic health benefits. In addition, both new and established methods of measurement of sensory attributes were applied and compared to determine correlations of findings between different methods of measurement. Chapter 1 addresses the influence of fat replacers on attributes such as energy density, flowability, and firmness in a real food product, processed cheese. To this end, microparticulated whey protein (MWP), which has been widely used as a fat replacer, and three dietary fibers (corn dextrin (CD), inulin, and polydextrose), were used in reduced-fat processed cheese slices. A reduction in energy density of about 30 to 40% was achieved using a fat replacer compared to standard commercial full-fat processed cheese. Higher CD and inulin concentrations reduced the flowability of the cheese slices upon heating, but only had a minor impact on the firmness of the unheated cheese. The addition of MWP resulted in firmer cheese slices with higher flowability compared to the other fat replacers. However, changes in the MWP concentration had little effect on either property. The results demonstrated that different fat replacers with varying concentrations need to be applied to achieve desired attributes for specific conditions of use, e.g., unheated cheese in sandwiches or heated cheese in cheeseburgers. To evaluate newly developed reduced-fat foods, the impact of fat replacers on sensory properties and aroma release also needs to be investigated, which is addressed in chapters 2 to 4. Due to the complex composition of cheese, systematic investigation of the mode of action of fat replacers is difficult. Therefore, emulsion-based model foods were used to eliminate interfering factors and natural variations of ingredients. The second study (chapter 2) focused on developing and validating appropriate methods to investigate the effects of fat, fat reduction and the use of fat replacers on emulsion systems. Tribology, a comparatively new method in food research, was used to instrumentally analyze selected aspects of food mouthfeel. Reduced-fat salad mayonnaises were prepared as separate samples containing different CD concentrations, and characterized using textural, rheological and tribological analyses together with measures of spreadability and human-sensory analysis. The results showed a very high correlation between tribological measurements and the sensory evaluation of the attribute stickiness. In addition, it was shown that some correlations between instrumental and sensory data were best described by a non-linear correlation (Stevens’ power law), such as the relationship between Texture Analyzer measurements and sensory sensations of firmness. Furthermore, the Kokini oral shear stress correlated very well with the sensory attribute creaminess. Hence, the instrumental analytical methods used showed the potential to predict elements of the sensory analysis and reduce the overall analytical effort. While aroma release plays a key role in consumer acceptance, the influence of fat replacers on this attribute has rarely been studied. The third study (chapter 3) therefore investigated not only techno-functional properties but also the release of typical cheese aromas using a liquid emulsion as a model food. While both MWP and CD exhibited a retarding effect on the release of lipophilic aroma compounds, MWP also reduced the release of hydrophilic aroma compounds. It was also shown that aroma release is not only influenced by a change in viscosity, but also by interactions between aroma compounds and fat replacers. In this context, CD exhibited a similar ability to interact with aroma compounds as fat, which is desirable for the development of low-fat foods. In the final study (chapter 4), the findings and methods developed in chapters 1-3 of this work, supplemented with additional methods, were used to investigate the effect of fat reduction and CD concentration on a model processed cheese spread (PCS). By replacing 50% of fat completely with CD, the fat content of the PCS could be reduced without causing any significant changes in properties compared to the full-fat version, e.g. in firmness, flowability upon heating and aroma release. CD was determined to be a promising fat replacer, mimicking important properties of fat. Additional correlations, such as those between the parameters of Winter's critical gel theory (gel strength and interaction factor) and spreadability and lubrication properties were identified and can help to further reduce the analytical effort. In conclusion, CD has been confirmed as a promising fat replacer in both liquid and semi-solid food emulsion products. Furthermore, this work contributes to closing the research gap in the instrumental measurement of sensory attributes by outlining correlations, for example, between tribological methods and mouthfeel sensations. Thus, the evaluation tools of this work can help to assess the potential applications of new fat replacers without extensive application and sensory testing which significantly shortens the development time for food manufacturers. In addition, the results contribute to a better understanding of the interactions between fat, fat replacers and aroma compounds in food matrices. This facilitates the systematic development of reduced-fat processed cheese and other dairy- and emulsion-based products which meet consumer preferences and accelerate the trend towards healthy eating.     

Study of taste-active compounds in the water-soluble extract of mature Cheddar cheese

The chemical composition of the water-soluble extracts of mature Cheddar cheese were identified, with the emphasis on understanding the interplay of compounds contributing to the savoury taste in Cheddar. The ultra-filtered water-soluble extracts of two mature Cheddar cheeses were fractionated by gel permeation chromatography (GPC). By sensory evaluation, two taste-active GPC fractions were identified from each cheese. On the basis of chemical profiling of these fractions, aqueous model tastant mixtures were prepared and sensory omission tests carried out. Glutamic acid, organic acids and mineral salts were the main tastants, whereas the other amino acids had a limited impact on taste. The characteristic umami taste was explained by a synergistic effect of glutamic acid and salts. Matching umami taste intensities were obtained from different concentrations of glutamic acid and salts. Unmasking of a bitter or sweet taste from mixtures of sub-threshold concentrations of amino acids without glutamic acids was also observed.     

Water Activity – Concentration Models for Solutions of Sugars, Salts and Acids

A semi-empirical model of water activity changes due to solute concentrations increase in solutions of electrolytes and nonelectrolytes was developed based on an extension of Raoult's law. Comparisons between predicted and observed a_w data for a variety of sugars, salts and acids indicated the proposed model fitted the a” data with accuracy to ±0.001 a_w up to 4–14 molalities depending upon the solutes. Percent weight concentrations of some solutes for various a” values at 25°C were presented for practical applications.     

Use of a β-glucan hydrocolloidal suspension in the manufacture of low-fat Cheddar cheese: manufacture, composition, yield and microstructure

Low‐fat Cheddar cheese was manufactured using a β‐glucan, hydrocolloidal fat replacer denoted as Nutrim. The composition, production efficiency, microstructure, and utility of replacing fat with Nutrim were examined. Cheese samples (designated as Nutrim‐I, and Nutrim‐II) containing Nutrim were produced with mean fat levels of 6.84 and 3.47%, respectively. A low‐fat cheese was also produced as a control with a mean fat level of 11.2%. Nutrim‐II cheese had significantly higher moisture, salt, and ash contents as compared with the low‐fat control cheese. The low‐fat control cheese had a higher yield normalized for 54% moisture and 1.5% salt content as compared with the Nutrim‐II cheese. Scanning electron microscopy revealed smaller and more uniform fat droplet voids in the Nutrim cheese than the low‐fat control, and a more dense, noncontinuous background protein matrix with globular clusters suggesting a physical buffering afforded by the presence of the β‐glucan hydrocolloid or its associated water.     

The impact of reduced sodium chloride content on Cheddar cheese quality

The effect of varying salt (sodium chloride) addition levels of 0.50%, 1.25%, 1.80%, 2.25%, 2.50% and 3.00% (w/w) on the quality of Cheddar cheese was assessed. Reducing the salt adversely impacted Cheddar flavour and texture. The key compositional parameters of moisture-in-non-fat-substances and salt-in-moisture were most affected. Decreasing salt resulted in a concomitant reduction of pH, a slight reduction in buffering capacity and an increase in water activity and growth of starter and non-starter lactic acid bacteria that resulted in enhanced proteolysis. Lipolysis was not impacted by salt reduction. To produce quality reduced salt Cheddar cheese cognisance must be taken on how to reduce proteolysis, limit growth of NSLAB, reduce water activity, achieve pH 5.0–5.4 by modifications to the cheese making procedure to create a more appropriate environment for selected starter and/or adjunct cultures to generate acceptable Cheddar flavour and texture.