Compositional characteristics and volatile organic compounds of traditional PDO Feta cheese made in two different mountainous areas of Greece

The compositional characteristics of Feta cheese manufactured in two mountainous areas from raw milk, from sheep fed by grass, and the forages’ volatile organic compounds (VOC) were studied, to differentiate the Feta cheese. Although the main compositional features did not vary greatly, the proteolysis mode was altered. The VOC profiles of the cheeses varied. While some VOCs were common to both groups of cheeses, others were discriminatory for each production area. There were common terpenes in both the bulk forage and the mature cheeses. Overall, the VOC composition of Feta could provide a basis for identification with regard to its region of origin.     

Effects of γ-irradiation on Listeria monocytogenes population,colour, texture and sensory properties of Feta cheese during cold storage

Feta, a white brine cheese, was produced and contaminated with Listeria monocytogenes. Contamination occurred either at the beginning (pre-process contamination) or at the end of Feta manufacturing (post-process contamination). In the first case the milk was contaminated with 10³ cfu/ml, and 2 months later, in the final product, the L. monocytogenes population was approximately 10⁵ cfu/g. In the second case, the brine (NaCl, 7% w/v), in which the Feta was packaged, was contaminated with 10³ cfu/ml. Contaminated Feta samples were vacuum-packaged and exposed to irradiation doses of 1.0, 2.5 and 4.7 kGy and stored at 4 °C for a month. In the pre-process contaminated samples none of the irradiation doses eliminated L. monocytogenes; however the highest dose reduced the viable population to a level which is in compliance with EC regulations. In the post-process contamination, the 2.5 kGy and 4.7 kGy doses reduced L. monocytogenes counts below the detection limit. Irradiation had no effect on the texture of Feta. Irradiation at 4.7 kGy increased Feta's redness and decreased its yellowness and lightness. Sensorial analyses showed that at the 4.7 kGy dose, the aroma profile of Feta was temporarily affected, since it was restored after 30 days of cold storage.     

Study of organic acids, volatile fraction and caseins of a new Halloumi-type cheese during ripening in whey brine

Organic acids, fat hydrolysis, volatile compounds and sensory characteristics of a new brine cheese which combines characteristics of Halloumi and Feta cheeses during its ripening in whey brine (100g NaCl L⁻¹) were studied. Thermotolerant protease of Mucor miehei as a coagulant enzyme and a mixture of thermotolerant starter cultures Enterococcus faecium 0165 (0.5% w/w) and Lactobacillus casei 80 10D were used. Good quality new Halloumi-type cheese was produced with higher proteolysis than traditional Halloumi cheese kept in whey brine. The volatile compounds identified comprised alcohols, aldehydes, ketones, acids, esters, hydrocarbons and sulphur compounds. Ethanol was the dominant volatile compound determined. Lactic acid was the dominant acid produced; its concentration increased during ripening, reaching a maximum value of 9929 mg kg⁻¹ at day 30. Acetic acid was also found in high amounts, which increased during cheese ripening. Lipolysis of cheese was not intense. The most abundant acids of the mature cheese were palmitic, oleic and acetic acid. The Halloumi-type cheese scored higher in the sensory analysis when fresh than did the mature cheese.     

Assimilation of cholesterol by yeast strains isolated from infant feces and Feta cheese

Eight yeast strains isolated from infant feces and the traditional Greek Feta cheese, selected for their probiotic properties, were tested along with a commercially available strain of Saccharomyces boulardii for their ability to remove cholesterol from a growth medium (yeast extract glucose peptone broth) supplemented with 0.3% Oxgall. The amount of cholesterol removed during 72 h of growth at 37 degrees C revealed significant variations among the yeast strains examined. Two isolates from infant feces, namely Saccharomyces cerevisiae KK1 and Isaatchenkia orientalis KK5.Y.1 and one isolate from Feta cheese, namely S. cerevisiae 832, along with the commercial strain S. boulardii, were able to remove cholesterol from the growth medium after 48 h of incubation at 37 degrees C. However, Saccharomyces strains proved to be able to remove cholesterol even after 24 h of growth at 37 degrees C. The cholesterol removed from the growth medium was not metabolically degraded but was rather assimilated into the yeast cells. The ability to assimilate cholesterol in vitro and to tolerate low pH levels, gastric juice, and bile indicate that S. cerevisiae 832, and especially S. cerevisiae KK1 and I. orientalis KK5.Y.1 (being more bile and gastric juice tolerant because of their human origin) may be promising candidate strains for use as probiotics.     

Proteolysis in reduced sodium Feta cheese made by partial substitution of NaCl by KCl

Feta cheeses (five trials) of different sodium content were made, using ewes’ milk, from split lots of curd by varying the salting procedure, i.e. dry salting with NaCl (control) or mixtures of NaCl/KCl (3:1 or 1:1, w/w basis) and filling the cans with brine made with NaCl or the above NaCl/KCl mixtures, respectively, in order to study the influence of the partial substitution of NaCl by KCl on the proteolysis during cheese ripening. The extent and characteristics of proteolysis in the cheeses were monitored during aging by using Kjeldahl determination of soluble nitrogen fractions (water-soluble nitrogen, trichloroacetic acid-soluble nitrogen, phosphotungstic acid-soluble nitrogen), the cadmium–ninhydrin method for the determination of total free amino acids (FAA), urea–polyacrylamide gel electrophoresis of cheese proteins followed by densitometric analysis of the α_s1- and β-casein fractions, reverse-phase HPLC analysis of the water-soluble extracts of cheeses, and ion-exchange HPLC analysis of FAA. The results showed that proteolysis was similar in control and experimental cheeses at all sampling ages, indicating that the partial substitution of NaCl by KCl in the manufacture of Feta cheese had no significant effect on the extent and characteristics of proteolysis during cheese aging.     

Effects of salting method and storage time on composition and quality of feta cheese

Feta cheese was manufactured by using five different salting methods (dry salting for one day followed by addition of 6% NaCl brine, dry salting for 1,2 or 3 days followed by addition of 7% NaCl brine and dry salting for 3 days followed by addition of 8% NaCl brine). The effects of salting method and storage time on the composition, physicochemical, organoleptic and rheological properties of feta cheese were studied. It was found that moisture was not affected by salting method or storage time. The salting method but not the storage time had a significant effect on salt content. As the salt content of cheeses increased or the storage time was prolonged the moisture decreased. pH and cheese yield were not influenced by salting method but did decrease with storage time. Protein content was not affected by salting method or storage time, whereas fat content was affected by both factors. Proteolysis, lipolysis, organoleptic and rheological properties of cheeses were not influenced by the salting methods applied. On the other hand, storage time had a significant effect on proteolysis, lipolysis, cheese appearance, fracturability and percentage compression at the yield point. Dry salting of cheese for one day and preservation in 7% NaCl brine was considered as the most appropriate salting method for practical application.     

利用盐湖高钙含钾卤水制取氯化钾工艺试验研究

青海盐湖部分氯化物型卤水中,由于钙的循环积累,其浓度不断增高,这可能对从卤水中提取氯化钾带来一定影响。实验研究了该类型高钙含钾卤水对4#工艺制取氯化钾的影响,研究结果表明卤水中钙含量对4#工艺制取氯化钾影响较小。     

Effect of calcium reduction on the properties of half-fat Cheddar-style cheeses with full-salt or half-salt

Standard-calcium (SCa) and reduced-calcium (RCa) half-fat (16%) Cheddar-style cheeses with full-salt (1.9%) or half-salt (0.9%) were made in triplicate, ripened for 270 d, and analysed for composition and changes in lactose metabolism, pH, proteolysis, water-sorption, fracture properties and heat-induced flowability during maturation. The pressing load applied to the moulded cheese was modified to ensure equal moisture in all cheeses despite the differences in salt and calcium levels. The RCa cheeses were characterised by higher primary proteolysis (α_S1-casein degradation, pH 4.6-soluble N development), lower secondary proteolysis (concentration of free amino acids), higher water-holding capacity on reducing relative humidity from 85 to 5%, lower fracture stress and strain, and more extensive flow on heating. Overall, calcium reduction, when used in conjunction with moisture normalisation, proved an effective means of counteracting the adverse effects of fat reduction on texture and cooking properties in half-fat, half-salt cheese.     

Probiotic white cheese with Lactobacillus acidophilus

The objective of the present study was to determine the effects of Lactobacillus acidophilus on the sensory attributes, ripening time, and composition of Turkish white cheese and to investigate the survival of L. acidophilus during ripening of the cheese stored in vacuum or in brine. Two types of white cheeses, traditional cheese (control, made with Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris) and probiotic cheese (made with Lactococcus lactis ssp. lactis, Lactococcus lactis ssp. cremoris and L. acidophilus 593 N), were produced and ripened in vacuum pack or in brine at 4°C for 90 days. Cheese samples were assessed for microbiological and compositional properties, proteolysis, and sensory evaluation at different ripening stages. On ripening in vacuum pack, L. acidophilus survived to numbers >10⁷ cfu g⁻¹, which is necessary for positive effects on health. Protein, dry matter, salt content, and percentage of lactic acid in the vacuum-packed and brine-salted probiotic cheeses were significantly different. Also, the lactic acid content of probiotic cheeses was slightly higher than that of the controls for both vacuum- and brine-packed cheeses. Vacuum-packed probiotic cheese had the highest levels of proteolysis and the highest sensory scores of all cheeses. Consequently, L. acidophilus could be used for the manufacturing of probiotic white cheese to shorten ripening time and vacuum packaging is the preferred storage format.     

Influence of residual rennet and proteolysis on the exudation of whey from Feta cheese during storage

A change in the quantity of rennet added to the cheesemilk resulted in a corresponding change in the level of residual rennet in Feta cheese. Casein proteolysis and exudation of whey from Feta cheese during storage were proportional to the quantity of residual rennet in the cheese. It is likely that with proteolysis, the three-dimensional casein network becomes weaker and gradually disintegrates. The water-holding ability of the casein gels is thereby greatly reduced and moisture is released from the interstices of the casein gel. This free moisture and soluble material, including peptides and amino acids formed during proteolysis, are released as exudate during the storage of Feta cheese.     

Migration of water-soluble nitrogenous compounds of Feta cheese from the cheese blocks into the brine

The migration of water-soluble nitrogenous compounds of Feta cheese from the cheese into brine was monitored over a 5-month period, and the nature of the compounds diffusing into the brine was investigated. Reversed-phase high-performance liquid chromatography analysis of the water extract of Feta cheese and of the brine showed that both contained serum proteins and various peptides; the chromatographic profiles changed with the age of the cheese. Also, differences between chromatograms of the water extract of the cheese and the brine at the same age were observed. It seems likely that the parameters driving the solubility of peptides in 120 g L⁻¹ trichloroacetic acid (size and hydrophobicity) also determine their potential for diffusion into the brine. Amino acids also migrate into the brine, with the hydrophobicity and shape of the side chain governing their diffusing ability.     

两步法钙镁泥脱盐技术可行性研究和探讨

一种两步法钙镁泥脱盐方法,将卤水净化一级、二级反应产生的含盐钙镁泥经过两步法脱盐,使含有高盐分钙镁泥变废为宝,钙镁泥盐分可达到0.5%以下,甚至更低。一级反应产生的含盐石膏经脱盐后既可以出售给水泥厂用作水泥缓凝剂,又可作为制砖的添加剂。二级反应碳酸钙废渣经脱盐后由于含量较高其用途及前景更广。     

提高氢氧化镁质量的几项措施

运城盐湖卤水中含有大量的有机质和一些无机杂离子,文章通过将盐湖卤水絮凝、活性炭吸附精制后,与硫氢化钡反应,再通过调节溶液pH值降低产品中的硼含量、反应完后利用母液保温沉化降氯离子后,可提高氢氧化镁的质量,使其达到高纯氢氧化镁的要求.     

Composition, microstructure, and surface barrier layer development during brine salting

The goal of this study was to characterize the changes in chemical composition, porosity, and structure that occur at the surface of a block of brine-salted cheese and their relationship to the rate at which salt is taken up from the brine. To create a difference in composition, salt uptake, and barrier layer properties, identical blocks of Ragusano cheese were placed in saturated and 18% salt brine at 18°C for 12 d. The overall moisture content and porosity decreased, whereas salt and salt in moisture content increased near the surface of blocks of brine-salted Ragusano cheese for all treatments. The general appearance of the microstructure of the surface of the blocks of brine-salted cheese was much more compact than the microstructure 1 mm inside the block at both brine concentrations. Large differences in porosity of the barrier layer were produced by brine-salting cheese in 18% vs. saturated brine, with cheese in saturated brine having much lower porosity at the surface and taking up much less salt during brining. The macro network of water channels within the microstructure of the cheese was less open near the surface of the block for cheese in both saturated and 18% brine after 4 d. However, no large differences in the size of the macro channels in the cheese structure due to the difference in brine concentration were observed by scanning electron microscopy. It is possible that the shrinkage of the much smaller pore structure within the casein matrix of the cheese is more important and will become more limiting to the rate of salt diffusion. Further microstructure work at higher resolution is needed to answer this question. The calculated decrease in porosity at the exterior 1-mm portion of the block was 50.8 and 29.2% for cheeses that had been in saturated vs. 18% brine for 12 d, respectively. The difference in brine concentration had a very large impact on the salt in moisture content of the cheese. The exterior of the cheese in 18% brine reached a salt in moisture content almost identical to that of the brine very quickly (17.3% at 4 d), whereas the salt in moisture content at the surface of the cheese block in saturated brine was only 11.9% at 4 d. There appears to be some critical concentration of salt in brine above which there is a large negative impact on salt uptake due to the creation of a barrier layer at the surface of the block of cheese.     

江汉油田卤水输送管道中碳酸钙结垢趋势预测

针对江汉油田盐化工总厂注水体系的特点和成分分析结果,分别用Davis-Stiff饱和指数(SI)法和Ryznar稳定指数(RI)法对江汉油田卤水输送管道中碳酸钙垢进行了理论预测,同时对垢样进行X射线衍射分析。理论预测结果表明,输送管道中的卤水具有形成碳酸钙垢的趋势,且其pH值越高结垢越严重。实验为江汉油田注、采卤系统的结垢预测、阻垢条件选择提供了依据。     

Influence of presalting and brine concentration on salt uptake by Ragusano cheese

The impact of presalting and nonsaturated brine on salt uptake by Ragusano cheese was determined. The study included four treatments: 1) the traditional method using no presalting and saturated brine, 2) presalting and saturated brine, 3) no presalting and 18% brine for 8 d followed by 16 d in saturated brine, and 4) presalting and 18% brine for 8 d followed by 16 d in saturated brine. Cheese blocks were weighed and sampled before brine salting (time 0) and after 1, 4, 8, 16, and 24 d of brining for each treatment. Presalting delivered 60% of the normal level of salt in the center of the block prior to brine salting without decreasing the rate of uptake of salt from either saturated or 18% brine. Use of 18% salt brine for the first 8 d of 24 d of brine salting increased the rate of salt uptake, compared with 24 d in saturated brine. The increased rate of salt uptake with 18% brine compared with saturated brine was related to the impact of salt brine on the moisture content and porosity of the cheese near the surface of the block. Brine with higher salt content causes a rapid loss of moisture from cheese near the surface of the block. Moisture loss causes shrinkage of the cheese structure and decreases porosity, which impedes moisture movement out and salt movement into the block. The use of 18% salt brine for the first 8 d delayed the moisture loss and cheese shrinkage at the exterior of the block and allowed more salt penetration.     

Modeling of proteolysis and lipolysis in Iranian white brine cheese

The simultaneous effects of processing variables such as ripening time (20–60 days), ripening temperature (6–10 °C), level of rennet added (1–2 g/100 kg milk) and brine concentration (8–14%, w/v) on the proteolysis, lipolysis and sensory score of Iranian white brined cheese (Feta type) were explored by the means of response surface methodology. The most important effect in proteolytical terms was produced by ripening temperature and ripening time in linear form, but level of rennet added and brine concentration were also significant at the 5% level. In terms of lipolysis, ripening time was dominant factor in both linear and quadratic forms; quadratic effect of ripening temperature was greater than its linear effect.     

钙液脱硝后卤水输送管道结垢趋势研究

通过氯化钙溶液脱硝试验,研究了卤水钙液脱硝前后结垢成分、硫酸钙过饱和度变化;结合硫酸钙结垢因素的分析,探讨了卤水钙液脱硝后,卤水输送管道的结垢趋势,对井下钙液脱硝采卤(或井上输卤源头钙液脱硝)对输卤管道结垢的影响进行预测。     

石膏型卤水体系硫酸钙结晶过程研究

石膏型卤水体系真空蒸发制备NaCl过程中,CaSO4.2H2O对NaCl产品的纯度影响较大。研究了石膏型卤水体系中CaSO4.2H2O的结晶过程。实验研究了搅拌速率、停留时间、晶种量、温度等条件对石膏型卤水体系二水硫酸钙结晶过程的影响。研究结果表明:晶体的粒度开始随搅拌速率的增大不断增大,当搅拌速率达250 r/min时,晶体粒度达到最大值77.24μm;晶体粒度同样开始时随停留时间的增大而增大,当停留时间为120 min时达到最大值,此时平均粒径为70.39μm。CaSO4.2H2O晶体粒度随晶种量的增加而减小;在40℃～70℃范围内,晶体粒度开始随温度的升高而增大,在60℃时达到最大值,此时晶体的平均粒径为70.39μm,随后随温度的升高晶体的粒度逐渐降低。采用正交实验确定了石膏型卤水体系对二水硫酸钙生长影响的最佳实验条件为:温度为70℃、搅拌速率为250 r/min,停留时间为120 min,晶种量为3 g。此时的晶体的线生长速率为2.508×10-9 m/s。     

Role of salt in Iranian ultrafiltered Feta cheese: Some textural and physicochemical changes during ripening

The effect of NaCl (0–4%) on the ripening of Iranian ultrafiltered (UF)‐Feta cheese was assessed over 120 days of ripening at 4 °C. Whey percentage, whey salt, whey pH, cheese pH and textural properties of hardness and cohesiveness were monitored, and experimental modelling performed using response surface methodology. Texture, pH and whey percentage were significantly affected by NaCl and ripening. The maximum whey of 22% was recorded at the end of ripening period. Texture of this cheese becomes harder during ripening confirming cheese pH and whey percentage being the major determining factors. Cheese samples were more elastic than viscous with cohesiveness values of 0.6–0.9.