EFFECT OF RIPENING AND TYPE OF RENNET ON THE MINERAL CONTENT OF LOS PEDROCHES CHEESE

The changes in the macro and micromineral contents (Ca, P, Na, K, Mg, Fe, and Zn) of Los Pedroches cheese, manufactured with pure ewe's milk, were investigated during 100 days' ripening. The effect of the rennet type used (animal or vegetable) on these minerals was investigated too. Using these mineral values, expressed as a function of the dry matter, an analysis of covariance was applied. The rennet type had an influence on the P and Zn contents of the cheeses. There was a significant decreasing trend in the levels of P, Zn and Na values during ripening.     

EFFECT OF SOME HERB ESSENTIAL OILS ON LIPOLYSIS IN WHITE CHEESE

The influence of some herb essential oils on the lipolysis of white cheese was examined. The essential oils of Sirmo (wild Allium sp.), thyme (wild Thymus sp.) and mint (wild Mentha sp.) were added individually or in combinations to cheeses. The cheese samples were ripened for 90 days at 5C. Lipolysis rate increased from the beginning to the sixtieth day of ripening, then decreased up to 90 days in cheese samples. The highest lipolysis rate was observed in the control sample while the lowest was in thyme and sirmo-thyme added samples. Differences between cheese samples and ripening periods were found to be statistically significant (P<0.01) in terms of fatty acids production rates. Sirmo and mint essential oils did not affect the lipolysis of white cheese. The sensory acceptability ofsirmo and mint essential oils added cheeses was superior to that of other samples.     

EFFECT OF FERMENTED WHEY PROTEIN CONCENTRATE ON TEXTURE OF IRANIAN WHITE CHEESE

The influence of fermented whey protein concentrate (FWPC) added before and after formation of cheese curd on the textural characteristics of Iranian white cheese was studied. The FWPC, prepared from whey obtained during cheese making, was added at different levels 5, 10, 15 and 20% (v/v) after (A) or before (B) cheese curdling. The changes in rheological parameters of cheeses were determined before and after 1 month of ripening. It was found that both incorporation level and stage of addition of FWPC (A and B) caused significant effects on texture profile analysis of cheeses. Increasing the level of FWPC in B group, except samples containing 10% FWPC, in contrast with A cheeses led to considerable increase in moisture and decrease in hardness and chewiness. Samples containing more than 15% FWPC had undesirable texture and were too soft. All experimental cheeses exhibited a decline in values for each rheological parameter after 1 month of ripening.

PRACTICAL APPLICATIONS

Perhaps the biggest story in the dairy industry in the past couple of decades has been the rise of new applications for whey and whey proteins. Once considered a waste product in the cheese manufacturing process, whey and whey protein products today are used for a wide range of functional and nutritional properties. In the cheese industry, particularly in soft cheese varieties, whey proteins have shown good applications to replace caseins as they act as fat replacer and bind more water than caseins, which results in softer cheeses. Therefore, this study was attempted to investigate the impact of fermented whey protein concentrate on textural attributes of Iranian white cheese.     

EFFECT OF MYOGLOBIN ON THE MUSCLE LIPASE SYSTEM

The effect of different concentrations of myoglobin on the enzyme systems involved in lipid degradation were determined. Lipases, including both acid and neutral lipases and acid phospholipase, were inhibited by myoglobin. The neutral lipase was more susceptible to the inhibitory effect of myoglobin (35% of its initial activity at 1 mg/mL of myoglobin), followed closely by acid phospholipase; acid lipase activity was affected to a lesser extent (less than 20% inhibition). This inhibition was also observed on the esterase activities, being greater on the neutral esterase activity (38% of its initial activity at 1 mg/mL of myoglobin) than on the acid one. In view of these results, myoglobin could be considered as an endogenous inhibitor which would determine the lipolytic activity in different type of muscles and therefore, the rate of generation of the free fatty acids.     

THE FORMATION OF HISTAMINE IN HERBY CHEESE DURING RIPENING

The purpose of this study is to observe the formation of histamine throughout the period of ripening in herby cheese. Herby cheese samples were made from raw milk and buried in soil where they mature in 3 months. Samples were taken on the first, seventh, 15th, 30th, 60th and 90th days of ripening. The moistness, content pH, salt and (total aerobic mesophile bacteria, lactic acid bacteria, coliform bacteria and yeasts and mold) changes were observed. The concentration of histamine are 2.19 mg/100 g on the first day of ripening. It gradually increased and reached 4.62 mg/100 g on the 90th day. Consequently, the histamine that was observed in herby cheese during the ripening appears to be not important for public health.     

CHANGES IN VISCOELASTIC PROPERTIES DURING THE RIPENING OF ARZÚA-ULLOA CHEESE. EFFECT OF PROTEOLYSIS

Changes in viscoelastic properties during the ripening of three different batches of Arzúa-Ulloa cheese, a traditional Spanish variety, were studied. Proteolysis changes were determined in terms of the typical nitrogen fractions, these fractions were significantly correlated with the measured viscoelastic properties. Substantial changes in stress amplitude over the linear viscoelastic range were observed at 20C, as were significant differences in storage modulus (G') and viscous modulus (G") throughout the ripening period. Both moduli decreased markedly over the first two weeks, but exhibited an opposite trend from the third week. Mechanical spectra were recorded at 20, 25, 30 and 35C throughout the ripening period. The viscous component significantly increased compared to the elastic one as function of temperature and ripening time.     

EFFECT OF GAMMA IRRADIATION ON SOFTENING CHANGES AND ENZYME ACTIVITIES DURING RIPENING OF PAPAYA FRUIT

The aim of this work was to study the role of cell wall and ethylene related enzymes to papaya fruit firmness. Irradiation treatment was used as an imposed stress to cause changes in firmness. Physiologically mature papaya fruits were irradiated (500 Gy) and allowed to ripen at 22C and 90% RH. Polygalacturo‐nase (PG), pectinmethylesterase (PME), βgalactosidase, cellulose and 1‐aminocyclopropane‐1‐carboxylate oxidase (ACC‐oxidase) activities were followed during ripening and correlated to changes in firmness, skin and pulp color, respiration and ethylene production. The firmness of irradiated fruits was retained at least 2 days longer than in normal fruits and also had a slower rate of softening. Total soluble solids (d?Brix), cellulase activity and ethylene production were not altered by irradiation treatment. The activity patterns of PG, PME and β‐galactosidase were related to pulp softening and affected by irradiation. ACC‐oxidase activity was influenced by irradiation treatment, but its changes were not temporally related to those in firmness. It was concluded that irradiation had no direct effect on firmness but it acted by altering the ripening induced synthesis of cell wall enzymes, mainly PME.     

修饰发酵剂细胞促熟干酪的研究进展

修饰发酵剂细胞是采用各种物理、化学或基因修饰等方法使发酵剂(主要是乳酸菌)不能生长而不致产生过量的乳酸。同时在干酪中添加时细胞会完整存在，并能在成熟期间释放出活性胞内酶。修饰发酵剂的方法主要有热休克、冷休克、冷冻或喷雾干燥、溶菌酶处理、溶剂处理和基因修饰等。这些方法修饰乳酸菌(包括乳球菌，乳杆菌)与原发酵剂一并加入乳中，可加速干酪中的蛋白质降解和脂肪分解，缩短其成熟期，且增强风味(减少苦味)，在促熟干酪方面取得了较好的实验效果。综述了现有的修饰发酵剂细胞促熟干酪的方法，详述了热休克、冷休克这两种常用的方法，最后对修饰发酵剂细胞促熟干酪的应用前景作以展望。     

混合型大豆干酪成熟中蛋白质降解特性的研究

对混合型大豆干酪成熟过程中蛋白质的降解及感官特性变化进行了研究。检测了混合型大豆干酪成熟过程中pH4．6水溶性氮、12％三氯乙酸氮、5％磷钨酸氮和游离氨基酸含量的变化；在不同成熟时间下对混合型大豆干酪进行了感官评定。结果表明，随着成熟时间的延长，混合型大豆干酪的pH4．6水溶性氮、12％三氯乙酸氮、5％磷钨酸氮的含量增大；游离氨基酸含量变化较为显著；8℃下成熟30d时，混合型大豆干酪的感官特性最好。     

EFFECT OF HEATING AT DIFFERENT TEMPERATURES TO EXTEND THE SHELF LIFE OF VACUUM-PACKED WHITE CHEESE

The aim of this study was to determine the effects of heating applications on the shelf life of vacuum‐packed white cheese. Shelf life was evaluated for chemical, microbiological and organoleptic properties during the ripening period of 90 days. For this purpose, pickled white cheeses made with commercial starter cultures (Chr. Hansen R707 Lactococcus lactis subsp. lactis, L. lactis subsp. cremoris) were put in polyamide bags for vacuum packaging. During the ripening period, a water bath was used for heating applications at 65, 70 and 72C for 15, 10 and 5 min, respectively. In the ripening period, there were no changes in the values of dry matter in the control group. Dry matter values in control cheese were 40.02–42.09% (average value: 40.87%). Total acidity, protein (%), soluble nitrogen, ripening index (RI), tyrosine content and volatile fatty acid values all showed significant increases between the first and 90th days of the ripening period. However, in the heated cheese groups, dry matter showed no changes, but compared with the control group cheese total acidity, protein (%), soluble nitrogen, RI, tyrosine content and volatile fatty acid values increased but not as much as the control group.     

干酪成熟过程发酵剂的作用及快速成熟的研究进展

干酪的成熟过程,是在添加酶及各种微生物的协同作用下完成的.干酪中的微生物作用也包括人为添加发酵剂的作用.本文综述了干酪生产过程中发酵剂的使用和成熟过程所起的作用,主要有酸化、改善质构、形成风味物质.此外,本文也讨论了干酪的成熟机制,综述了目前用于促进干酪成熟所使用的一些方法和技术以及对它们的最新研究进展.     

EFFECT OF LUBRICATION ON THE COMPRESSION BEHAVIOUR OF CHEESE AND FRANKFURTERS

Cylindrical samples of cheese and frankfurters were subjected to a 50% uniaxial compression between flat plates and artificial molars, mounted on a Texture Analyser, operating at two speeds, with and without lubrication. At both speeds and with both types of probe the maximum force was less for the lubricated probes than the unlubricated probes. In all cases the maximum force recorded at the higher speed was greater than at the lower speed and greater when plates were used than when teeth were used. Through observations made during the testing and from photographs taken, it was concluded that the frictional effect of the cusps on the molar teeth was greater than the effect of lubrication. Observations made when samples were compressed between molar teeth in the mouths of panellists confirmed the conclusion that compression of foods in the mouth follows the nonlubricated pattern despite the lubrication provided by saliva.     

Camembert干酪成熟期间理化特性研究

对Camembert干酪成熟期间理化特性的研究表明:成熟前期水分含量减少,后期基本不变;外部和内部的pH值都呈先下降后上升的变化趋势;干酪成熟过程中由于乳酸菌和霉菌产生的蛋白酶的作用使蛋白发生强烈水解.pH4.6的可溶性氮、质量分数为12%的三氯乙酸可溶性氮和游离脂肪酸(FAA)含量都呈明显增加趋势;成熟过程中TPA各项指标均会有不同程度的下降.     

干酪促熟方法的研究进展

干酪成熟时间较长，费用较高，导致生产成本增加。因此干酪的促熟受到人们普遍关注。干酪促熟常用的方法有酶法、修饰发酵剂细胞、悬浮液系统、提高成熟温度、高压处理等。其中提高成熟温度和高压处理法不需要额外的干酪添加剂，是应用于生产中成本较低且易实现的方法。本文主要就以上两种方法促熟干酪作以详述。     

EFFECT OF ACID ADAPTATION AND DIFFERENT SALT CONCENTRATIONS ON SURVIVAL OF LISTERIA MONOCYTOGENES IN TURKISH WHITE CHEESE

ABSTRACT

Survival of acid‐adapted and nonacid adapted Listeria monocytogenes in Turkish white cheese with different salt concentrations (3.8 and 6.7% NaCl) was investigated. Cheese blocks were inoculated with L. monocytogenes and stored at 4C for 15 days. Samples were taken on different days and analyzed for the numbers of the pathogen, and the samples were challenged with simulated gastric fluid (SGF) for determining acid tolerance. There was no significant differences between the numbers of acid‐adapted and nonadapted L. monocytogenes cells regardless of the salt concentration on sampling days (P > 0.05). Challenge in SGF revealed that there was no significant difference between acid‐adapted and nonadapted bacteria in cheese with 3.8% NaCl throughout the storage period, while significant (P < 0.05) differences between those cells in cheese with 6.7% NaCl were found after day 5. These results suggest that acid‐adapted L. monocytogenes exposed to high salt concentration such as 6.7% may have an advantage in SGF.

PRACTICAL APPLICATIONS

Evaluation of potential stress responses of pathogens in food is important to understand the behavior of pathogens that can survive under stresses. As an environmental contaminant, Listeria monocytogenes may acquire adaptation to low acid conditions in cheese plants. Our results suggested that although there was no significant difference between acid‐adapted and nonadapted cells both in industrial (3.8% salt) and traditional (6.7% salt) white cheese, salt concentration significantly affected the survival of acid‐adapted cells in simulated gastric fluid (pH 2.3). These findings may indicate that L. monocytogenes, which is adapted to acid before contaminating high salt cheeses, may survive in stomach and cause infection. It can be said that increased salt concentration in cheese may not provide a barrier against acid‐adapted L. monocytogenes.