Effect of pH on Characteristics of Low‐Moisture Mozzarella Cheese during Refrigerated Storage

ABSTRACT: This study evaluated the effect of cheese pH on proteolysis, calcium distribution, and functional characteristics of Mozzarella cheese. On 4 occasions, cultured low‐moisture part‐skim Mozzarella cheeses were obtained from a commercial producer on the day after manufacture. Cheese blocks were randomly assigned to 2 groups. One group was shredded, subdivided, and exposed to either ammonia vapor to increase the pH or HCl vapor to decrease the pH. Samples were vacuum packaged, stored at 4 °C, and analyzed for pH 4.6 and 12% TCA soluble nitrogen, apparent viscosity, free oil, and water‐soluble calcium on days 5, 12, 22, and 40. The 2nd group was sectioned into 23‐mm thick slabs and similarly exposed to either ammonia vapor to increase the pH or HCl vapor to decrease the pH. The slabs were vacuum packaged, stored at 4 °C, and analyzed for pH 4.6 and 12% TCA soluble nitrogen, TPA hardness, springiness and cohesiveness, and meltability on days 17, 29, and 41. Data were analyzed by ANOVA according to a spilt‐plot design. Experimentally induced pH differences persisted and significantly affected TPA hardness, apparent viscosity, meltability, and water‐soluble calcium throughout 40 d of storage, but did not affect soluble nitrogen changes. Thus, cheese pH affected functional characteristics and calcium distribution but did not affect proteolysis rates. Higher cheese pH resulted in a harder cheese that required longer aging to develop desirable melting characteristics, whereas cheese with lower pH developed desirable melting characteristics more quickly but had a shorter functional shelf life.     

Time and Temperature Influence on Chemical Aging Indicators for a Commercial Cheddar Cheese

Cooling freshly formed Cheddar cheese requires close control for uniform and consistent flavor. Cheese in 18–kg blocks collected after pressing, at 30–35°C was used. Samples were cooled rapidly to 12 25°C as small pieces individually vacuum-wrapped at a local production site. The extent of proteolysis, total acidity, pH, lactose and organic acids was quantified after storage at these temperatures. Theoretical and empirical equations describing the influence of time and temperature on these chemical indicators were developed through nonlinear statistical methods. The kinetic expressions were applied to generate recommendations for the cooling rate and subsequent aging temperature of Cheddar cheese blocks.     

Rheological Behavior of Frozen and Thawed Low-Moisture, Part-Skim Mozzarella Cheese

Stress relaxation and dynamic profiles of low-moisture, part-skim (LMPS) Mozzarella cheese cylinders refrigerated 14 days (control), frozen and thawed, and stored frozen and refrigerated up to 90 days were compared. Samples were frozen at ?30°C and stored at ?20°C. Thawing and refrigerated storage were at 5°C. Stress relaxation tests were conducted at 20°C and dynamic spectrometry at 20°C and 60°C. The frozen and thawed Mozzarella cheese tested at 20°C became harder and more elastic with storage time, while refrigerated stored samples became softer and more elasticoviscous with time. Upon melting, both go-day-frozen and go-day-refrigerated cheeses were less elastic and less viscous than 14-day-refrigerated samples.     

Dynamic Rheological Properties of Process Cheese: Effect of Ca and P Content,Residual Lactose,Salt-to-Moisture Ratio and Cheese Temperature

Four treatments of Cheddar cheese with two levels (high and low) of calcium (Ca) and phosphorus (P), and two levels (high and low) of residual lactose were manufactured. Each treatment was subsequently split prior to the salting step of cheese manufacturing process and salted at two levels (high and low) for a total of eight treatments. After two months of ripening, each treatment of Cheddar cheese was used to manufacture process cheese using a twin-screw Blentech process cheese cooker. NFDM, butter oil, trisodium citrate (emulsifying salt), and water were added along with Cheddar cheese for process cheese formulation. All process cheese food formulations were balanced for moisture (43.5%), fat (25%), and salt (2%), respectively. Dynamic rheological characteristics (G′ and G″) of process cheese were determined at 1.5Hz frequency and 750 Pa stress level by using a Viscoanalyzer during heating and cooling, temperature ranges from 30°C to 70°C then back to 30°C. High Ca and P content, and high S/M (HHH and HLH) cheeses had the significantly higher elastic (G′) and viscous (G″) modulus than other cheeses during heating from 30°C to 70°C, and cooling from 70°C to 30°C. No significant difference was observed among the other process cheeses during heating and cooling. Viscoelastic properties of process cheeses were also determined in terms of transition temperature (where G′?=?G″), and tan δ during heating (30°C to 70°C). Cheeses with high Ca and P, high lactose, and high S/M content had higher transition temperature than low Ca and P, low lactose, and low S/M content process cheeses. Low Ca and P and low S/M content cheeses (LLL, LHH, LHL, HLL) exhibited more viscous characteristics than high Ca and P and high S/M content process cheeses (HHL, HLH, LLH, HHH) during heating from 30°C to 70°C. Low Ca and P, low lactose, low S/M content (LLL) process cheese was observed for highest tan δ values (0.39 to 1.43), whereas high Ca and P, high lactose, high S/M content process (HHH) had the least (0.33 to 1.06) during heating. This study demonstrates that different characteristics of natural cheese used in process cheese manufacturing have significant impact on process cheese rheological and viscoelastic properties.     

Effects of pH on the Textural Properties and Meltability of Pasteurized Process Cheese Made with Different Types of Emulsifying Salts

ABSTRACT: Functional properties of pasteurized process cheese (PPC) made with different types of emulsifying salts (ES) (2%, wt/wt) were investigated as a function of different pH values (from 5.3 to approximately 5.9). The ES investigated were trisodium citrate (TSC), disodium phosphate (DSP), sodium hexametaphosphate (SHMP), and tetrasodium pyrophosphate (TSPP). Meltability and textural properties were determined using UW‐MeltProfiler and uniaxial compression, respectively. All PPC samples exhibited an increase in degree of flow (DOF) determined at 45 °C when the pH was increased from 5.3 to 5.6, presumably reflecting greater Ca binding by the ES, increased charge repulsion and therefore greater casein dispersion. When the pH of PPC was increased from 5.6 to approximately 5.9, 2 types of ES (DSP and SHMP) exhibited no further increase in DOF at 45 °C; while DOF increased in 1 type of PPC (made with TSC) but decreased in another (made with TSPP). TSPP is able to form crosslinks with casein especially in the vicinity of pH 6, which likely restricted melt; in contrast TSC does not crosslink caseins and the increase in pH helped cause greater casein dispersion. Low pH samples (5.3) were not significantly harder than higher pH samples for all ES types but exhibited fracture. The PPC with the highest hardness values at pHs 5.3 and 5.6 were made with TSPP and TSC, respectively. The pH‐dependent functional behavior of PPC was strongly influenced by the type of ES and its physicochemical properties including its ability to bind Ca, the possible creation of crosslinks with casein and casein dispersion during cooking.     

Effect of Heating and Elevated Temperature Storage on Cheese Whey

The effect of heating and storage of sweet (pH 6.1–6.3) and acid (pH 4.75) cheese whey for up to 10 hr at 62.8°C (145°F) on pH, titratable acidity, total bacteria count and protein denaturation was investigated. Heating and elevated temperature storage reduced the total bacteria counts of both types of whey to ≤ 100 mL^?1 and stabilized their titratable acidity at 1.60–1.65%. These treatments resulted in up to 13.4% and 6.7% protein denaturation in sweet and acid whey, respectively, as measured by the pH 4.6 solubility method. SE- HPLC data confirmed that these elevated temperature treatments resulted in slight losses of major proteins.     

Effect of Nonuniform Cooling on Moisture,Salt, and pH Distribution in 290-Kilogram Blocks of Stirred-Curd Cheddar Cheese

Cheese samples representing six positions in each of 12 290-kg stirred curd Cheddar cheese blocks in stainless steel hoops were analyzed for salt, pH, and moisture after the blocks had been held at 6 or 22°C for 7 d after pressing. Analysis of variance was used to determine differences between vats, filling sequences, cooling treatments, and positions within cheese blocks. Temperature during cooling had a significant effect on pH, salt, and moisture distribution within the cheese. Mean differences between the centers and sides of all cheese blocks cooled at 5°C were .1% salt, .12 pH units, and 5.73% moisture. Differences between the centers and sides of cheese blocks cooled at 22°C were 0% salt, .03 pH units, and .96% moisture. After filling the hoops, moisture transferred from high temperature to low temperature areas in the cheese. Moisture differences in large cheese blocks were minimized when temperature differences within blocks were reduced.     

The Effect of pH and Temperature on Cabbage Volatiles During Storage

During storage of shredded cabbage, characteristic sulfurous volatile compounds are formed affecting cabbage aroma both negatively and positively. Selected ion flow tube‐mass spectrometry (SIFT‐MS) was used to measure the concentration of cabbage volatiles during storage. The volatile levels of cabbage samples were measured at pH 3.3 to 7.4 at 4 °C for 14 d, and pH 3.3 at 25 °C for 5 d in order to determine the effect of pH and temperature. Aroma intensity, best aroma, freshness, and off odor were evaluated in a sensory test of the samples at 4 °C. The desirable volatile allyl isothiocyanate was lower in high pH samples (pH 7.4 and 6.4), whereas higher concentrations were detected in low pH samples (pH 3.3 and 4.6). Lipoxygenase volatiles, which produce a fresh green and leafy aroma in cabbage, were generated in very low amounts at any pH value. High pH samples generated significantly higher concentrations of off odors such as dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, and methanethiol. Sensory tests showed that higher pH samples had significantly stronger off odor and lower desirable cabbage aroma than lower pH samples. Thus, sensory results matched the volatile results in that samples at higher pH levels formed the highest amount of undesirable volatiles and the least amount of desirable volatiles. Storage at 25 °C produced similar concentrations of allyl isothiocyanate, but significantly higher levels of off odors, than at 4 °C. Shredded cabbage products should be stored in low pH dressings to minimize formation of off odors and maximize formation of characteristic, desirable cabbage odor.     

Physicochemical Response of Palmita-type Cheese to Low-dose Irradiation

ABSTRACT: The physicochemical tolerance of Palmita‐type white cheese to low‐dose irradiation, as applicable to enhance shelf life, and hopefully food safety, was studied. The response of cheese to doses between 1 and 5 kGy was followed by both chemical analysis of substances important as indicators of quality and radiation effect, and sensory detection of modification. The experiment was replicated twice, and samples analyzed immediately after irradiation and after 21 d of storage at 11.9 ± 0.4 °C. Dose effects, though statistically significant for some substances, were small. Consequently, no objectionable sensory characteristics were detected. Palmita‐type cheese tolerated low radiation‐doses applicable for sanitizing food, which suggest the potential use of irradiation to control Palmita‐cheese food‐borne diseases.     

Effect of Modified Manufacturing Parameters on the Quality of Cheddar Cheese made from Ultrafiltered (UF) Milk

Cheddar cheese was made from milk concentrated twofold by ultrafiltration (UF). Lowering the cooking and cheddaring temperature from 39°C to 35°C resulted in faster acid development, promoted more proteolysis, caused faster degradation of lactose, and contributed smoother body and texture to the cheese. Starter culture at 2% by weight of unconcentrated milk in combination with low cooking and cheddaring temperature reduced pH at faster rate and shortened the cheese making time by approximately 45 min, compared to cheese made using the traditional temperature (39°C). For the traditional temperature (39°C) of cooking and cheddaring, the addition of 0.2 mL/ kg rennet of unconcentrated milk produced the same rate of proteolysis in both control and cheese made from UF retentate. Composition (fat, protein, salt and moisture) and yield of the UF cheeses with modified temperature treatments were not significantly different from control.     

Dynamic Headspace Analyses of Volatile Compounds of Cheddar and Swiss Cheese during Ripening

The volatile compounds of Cheddar and Swiss cheeses during ripening for 9 wks at 11°and 21°C, respectively, were analyzed by a dynamic headspace analyzer/gas chromatograph every week. The compounds were identified by a combination of retention times and mass spectra. The volatile compounds of Cheddar increased 5.6 and Swiss cheese 15 times as ripening increased from 0 to 9 wks. The amount of volatile compounds of Swiss cheese was 2.6 times greater than that of Cheddar cheese during ripening. The volatile compounds were ketones, alcohols, aldehydes, esters, acids, sulfur compounds, benzenes, and hydrocarbons. Ketones and alcohols accounted for 92% of volatiles from Cheddar cheese and 88% of those from Swiss cheese.     

Manufacture of Cheddar Cheese Using Proteinase-Negative Mutants of Streptococcus cremoris

Cheddar cheese was manufactured with a proteinase-negative mutant of Streptococcus cremoris UC 73 and from a commercial lactic culture blend. Soluble nitrogen was analyzed and the cheese graded at intervals to 365 d of age. The cheese made with proteinase-negative cultures graded equal to the control cheese up to 90 d. It was best in overall texture and body and lowest in cheese flavor and flavor intensity after 90 d. It also had significantly higher soluble nitrogen throughout storage. No significant differences in yields were found.Cheddar cheese made at a constant 39°C temperature with a 2% inoculum of proteinase-negative S. cremoris UC 73 increased manufacturing time by 40 min over cheese made by conventional cooking procedures. When inoculum was increased to 4% and the constant temperature to 42°C, manufacturing time was 3.6 h, which was 1 h less than with a 2% inoculum and conventional cooking. By providing a yeast extract carry-over of .0175% from the proteinase-negative bulk culture, it would be possible to produce Cheddar cheese within a normal time frame with only .7% inoculum.     

Effect of temperature on lipid‐derived volatile compounds in boiled potato during storage

BACKGROUND: The aroma of boiled potatoes is greatly appreciated by consumers. Although it is formed by 150 volatile compounds, only a few seem to actually contribute to the characteristic aroma. In addition, potatoes have to be stored at a low temperature after harvest to guarantee a year‐round supply. However, even at low temperatures, tuber volatile composition is modified during storage. The aim of the present study was to investigate the effect of storage temperature on boiled potato volatile constituents, mainly focused on lipid‐derived components, by considering different varieties stored at 4 °C and 8 °C. RESULTS: It was found that fewer lipid‐derived components were obtained when the potato tubers were stored at 4 °C rather than 8 °C. Specifically, the amounts of 2,4‐decadienal isomers and hexanal increased with the storage time, particularly at 8 °C. Similarly, pentanal and nonanal, which are autoxidation products, occurred to a greater extent at higher temperatures. In contrast, the levels of sugar‐derived compounds, in general, increased during storage at 4 °C rather than 8 °C as a result of higher content of sugars at low temperature. CONCLUSION: The effect of storage temperature on lipid‐derived volatile components in boiled potato appears to depend on the variety studied. Generally speaking, lower temperatures during storage promote sugar content and, as a consequence, sugar‐derived products. At the same time, lower temperatures result in less lipid oxidation and, therefore, a fewer lipid‐derived compounds. Copyright © 2009 Society of Chemical Industry     

Monitoring Chemical and Microbial Changes of Cottage Cheese using a Full-history Time-temperature Indicator

Cottage cheese (4% milkfat) was stored under three isothermal conditions (3, 9, and 15°C) and one varied temperature condition for the length of its useful shelf life–up to 32 days. Attached to each one-half pint carton were two full history, enzymatic based, time-temperature indicators (I-POINT models #4014 and #4021). Throughout the study quality attributes of the cottage cheese, as determined by chemical and microbial means, and the indicator progress were periodically monitored. The cheese spoiled due to growth of acid-forming bacteria under the warmer conditions and due to psychrotrophic bacteria under the coldest condition. Response of the I-POINT model 4014 was significantly related to changes in three of the quality attributes of the cottage cheese, specifically: pH, standard plate count when the cheese was stored at 8.8° C, and titratable acidity when the cheese was stored at 15.1° C.     

The effect of salt concentration on rancidity in Gaziantep cheese

Gaziantep cheese is a non‐fermented and enzyme clotted type cheese. The changes in oxidative and hydrolytic rancidity in the cheese were analysed during its storage. Storage conditions were selected as 4, 10 and 20°C and 90, 170, 200 and 230 g kg⁻¹ salt solutions by considering the traditional storage conditions. Oxidative rancidity increased with increasing temperature and NaCl concentration in the brine. Hydrolytic rancidity increased with increasing temperature and decreasing salt content of the cheese. The extent of oxidative rancidity was found to be higher than hydrolytic rancidity. The results of this study showed that the storage temperature should not be higher than 10°C and brine concentration must be higher than 90 g kg⁻¹ and lower than 230 g kg⁻¹ to minimize lipid oxidation. Gaziantep cheese was organoleptically examined after 2 months of storage at 20°C and in 90, 170 and 230 g kg⁻¹ salt solutions, and it was found that even at a peroxide value around 1 meq kg⁻¹, acceptable levels of changes in flavour were observed. Sensory analysis results showed that textural properties of Gaziantep cheese changed with salt concentration of the brine. © 1999 Society of Chemical Industry     

Linear Viscoelastic Properties of Regular- and Reduced-Fat Pasteurized Process Cheese During Heating and Cooling

The rheology of process cheese during heating and cooling was examined by measuring the transient and dynamic linear viscoelastic properties of regular fat, lower moisture and an 80% reduced-fat, higher moisture pasteurized process cheese from 10 to 50°C. The dynamic (stress and frequency sweep) and transient (creep and recovery) rheological properties of the reduced-fat process cheese were found to be higher than that of regular-fat process cheese, indicating that fat content changed rheological properties more than moisture content. The temperature-dependent frequency dispersions of storage and loss moduli (dynamic mechanical spectra) were fitted with a power-law model, and master curves (at a reference temperature of 30°C) and shift factors were obtained by shifting the temperature-dependent frequency dispersion of dynamic mechanical spectra. The relaxation spectra (moduli, viscosities and relaxation times) of both cheeses were obtained from the master curves using the generalized Maxwell model and nonlinear regression. The viscosity distribution of corresponding Maxwell model elements were higher for the reduced-fat cheese by a factor of 1.6–4.7 compared to the regular-fat cheese, indicating that the higher moisture content in the reduced-fat process cheese did not loosen the protein matrix or soften the cheese even though higher moisture is recommended to cheese manufacturers in order to compensate for some textural defects in reduced-fat cheeses.     

Quantifying Thermally Induced Flowability of Rennet Cheese Curds

Conversion of liquid milk to cheese curds is the first stage in cheese manufacture. Changing the rigidity of cheese curds through heating and pH control is an established method for preparing fresh curds, whereas a similar method to prepare fully coagulated curds is largely unknown. This study elucidated the effect of temperature variation on the viscoelastic moduli of fully coagulated curds under different pH conditions. The results showed that Rennet curds treated at pH 4.8 exhibited drastic changes in the viscoelasticity at 43°C, above which the degree of fluidity exceeded the degree of rigidity. The viscoelastic moduli exhibited exponential decay as a function of temperature, which was independent of pH.     

Prediction and Characterization of Normal and Vat-Failed Cottage Cheese

An acidification-heat-coagulation test has been developed for predicting cottage cheese vat-failure potential of milk. Milk is fist acidified to pH 5.06 at 10°C and then heated at a slow rate (1°C increment per min). Poor quality acidified milk (> 10⁴ CFU/ml) forms small curds at 37°C and below. Good quality acidified milk (< 10⁴ CFU/ml) will form small curds at higher temperatures. By this procedure cottage cheese vat-failure potential of milk containing different levels of psychrotrophs can be predicted. Normal and vat-failed cottage cheese curds are characterized by % of grit in cottage cheese and amount of curd fines in whey.     

Functional modification of vital wheat gluten with corn syrup using hydrothermal treatment

Functional properties of gluten modified using hydrothermal treatment were compared with those of vital wheat gluten (VWG). Gluten slurry was jet cooked under pressure in the presence of corn syrup (CS) at different temperatures (121 and 149 °C) for different times and then spray dried. Foaming properties for all samples (treated and untreated) at different pHs showed that, although the optimum pH was 5, at this pH the treated gluten samples displayed reduced foaming properties as compared with the control, whereas at all other pHs there was an increase in foaming properties. The sample treated with CS at 121 °C (JC121w/cs) showed the highest viscosity and elasticity increase among all treated samples. Emulsifying properties were adversely affected by an increase in temperature of treatment, whilst addition of CS helped to restore emulsion stability (ES). The sample VWG with CS (Cont.w/cs) at pH 3 showed maximum ES. In general, samples after treatment showed increased solubility. The hydrophilic but non‐ionisable sugar hydroxyl groups affected the functionality at lower pH. Molecular changes were followed by size exclusion high‐performance liquid chromatography (SE‐HPLC) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE). Samples subjected to the lower temperature (121 °C) showed a shift of the molecular weight distribution to higher values in the HPLC profile, consistent with higher viscosities for this treatment. For the same samples, SDS‐PAGE of the reduced protein exhibited a decrease in the intensity of bands corresponding to high‐molecular‐weight glutenin subunits, complementing the fact that large‐molecular‐size polymers are involved during protein modification. Copyright © 2005 Society of Chemical Industry     

Using High-Pressure Processing for Reduction of Proteolysis and Prevention of Over-ripening of Raw Milk Cheese

High-pressure-processing (HPP) at 400 or 600 MPa was applied to cheeses made from ewe raw milk, on days 21 or 35 after manufacturing, to reduce proteolysis and prevent over-ripening. The characteristics of HPP and non-pressurized (control) cheeses were compared during ripening at 8 °C until day 60 and further storage at 4 °C until day 240. HPP and control cheeses showed similar pH values throughout ripening, but on day 240 pH values remained 0.4–0.6 units lower for HPP cheeses than for the control cheeses. Casein degradation was significantly retarded in the 600 MPa cheeses. Their α-casein concentration was 48–52 % higher on day 60 and 30–33 % higher on day 240 than in the control cheeses while β-casein concentration was 25–26 % higher on day 60 and 100–103 % higher on day 240. No significant differences in para-κ-casein concentration between cheeses were found on day 60, but on day 240, it was 22–35 % higher in the 600 MPa cheeses than in the control cheese. Hydrophilic peptides, hydrophobic peptides and total free amino acids evolved similarly in HPP and control cheeses during the 60-day ripening period. However, on day 240 hydrophilic peptides were at 34–39 % lower levels in the 600 MPa cheeses than in the control cheeses, hydrophobic peptides at 7–16 % lower levels and total free amino acids at 25–29 % lower levels. Flavour intensity scores increased at a slower rate in HPP cheeses than in the control cheese. Flavour quality declined markedly in the control cheeses during refrigerated storage while it did not vary significantly in 600 MPa cheeses.