干酪质地及流变学特性的研究进展

介绍了有关干酪的成分及工艺过程对质地和流变学特性影响的研究。在干酪成分中，蛋白质是影响产品流变学特性的主要因素，酪蛋白空间形成的网状结构构成了干酪流变学的基础。在加工过程中，pH、温度、钙浓度、蛋白水解等所有对干酪成分分子产生变化的因素都可能使干酪的流变学特性和质地发生变化。因此，干酪流变学特性的研究对更好地控制质地，生产出质优价廉的干酪，具有重要的意义。最后，研究状况进行了展望。     

TEXTURE ANALYSIS OF CHEDDAR CHEESE MADE FROM ULTRAFILTERED MILK

The textural properties of Cheddar cheese made from ultrafiltered milk were assessed. Cheddar cheeses were prepared from 1.5- and 2.0-fold concentrated milk and ripened for three months. Textural characteristics of the UF cheeses were compared to control and commercial Cheddar cheeses by sensory and instrumental measures. The texture of cheese made from UF milk differed from the control commercial Cheddar cheeses. According to the trained sensory panel, the UF cheeses were harder and more rubbery, crumbly, chewy and grainy than the control and commercial Cheddar cheeses (P <0.01). The texture profile analysis (TPA), conducted using the Instron, did not correspond to the sensory measurements nor was it successful in discriminating among the cheese samples. Lack of agreement between the sensory and instrumental tests was attributed to differences in the testing conditions and procedures of the two methods. Instrumental tests should be validated against sensory measures in order to be useful as measures of palatability. Consumer preferences for the commercial, control and UF Cheddar cheeses were significantly different (P < 0.01), the UF cheeses being less preferred in terms of flavor, texture and overall acceptability.     

THE INFLUENCE OF VACUUM PRESSING ON THE TEXTURE OF CHEDDAR CHEESE*

A study was made of the influence of several factors on the texture of young and mature vacuum-pressed rindless cheese. Pressures greater than 26 lb/in² were required for maximum improvement in texture. A vacuum of 15 in was less effective than a vacuum of 25 in. Vacuum pressing of ‘dressed’ cheese for 5 min was almost as effective as vacuum pressing for 17 h; vacuum pressing after dressing was more effective than before dressing; transfer of vacuum-pressed cheese to a normal press for the completion of pressing did not affect texture. Vacuum treatment of curd before hooping and pressing in the normal way had no beneficial effect on texture; vacuum pressing improved the texture of cheese made with mixed-strain starters although this cheese was not as close as vacuum-pressed cheese made with single strain starters. The distinct improvement in cheese texture which resulted from some combinations of vacuum pressing condition was confirmed in commercial scale trials involving 2,540 rindless cheese. This improvement was evident when cheese were graded at two weeks and when regraded at maturity.     

RELATIONSHIPS BETWEEN SENSORY AND RHEOLOGICAL MEASUREMENTS OF TEXTURE IN MATURING COMMERCIAL CHEDDAR CHEESE OVER A RANGE OF MOISTURE AND pH AT THE POINT OF MANUFACTURE

Textural characteristics of 10 Cheddar cheeses with a range of moisture contents and pH values were investigated by sensory and instrumental methods, over a 9‐month maturing period. A trained panel of nine assessors described the sensory texture characteristics of the cheeses using 11 texture parameters. Instrumental parameters were derived using texture profile analysis. Relationships between sensory, instrumental, compositional and maturation properties of the cheeses were determined with the aid of principal component analysis and multiple linear regression. Nine sensory parameters significantly correlated with instrumental parameters, e.g., sensory rubbery correlated with instrumental firmness (R = 0.696, P < 0.001), chewiness (R = 0.679, P < 0.001), fracture stress (R = 0.669, P < 0.001) and springiness (R = 0.643, P < 0.001). Sensory firmness corresponded closely with instrumental firmness (R = 0.539, P < 0.001) and fracture stress (R = 0.518, P < 0.001). Sensory and instrumental texture parameters were significantly affected by changes in moisture content, pH and maturation.     

NATURAL CHEDDAR CHEESE TEXTURE VARIATION AS A RESULT OF MILK SEASONALITY

A set of standard testing conditions using the TA-XT2 Texture Analyser were established to monitor cheddar cheese texture variation. Cheddar cheese was produced in the standard commercial practice and sampled at monthly intervals throughout the milk production season (August - June), and monitored for textural and compositional changes occurring during ripening. The composition, based on fat and protein levels, of the cheese was relatively constant during the period, which was expected as the commercial process aims for that outcome. A reduction in the force and degree of compression at fracture with time, indicative of a reduction in cheese firmness and an increase in cheese crumbliness, was recorded as the milk production season progressed. The degree of proteolysis and changes in milk fat in late season milk are primarily responsible for the changes recorded in cheese texture. The differences observed between cheeses produced at different times during the season indicate that the current fat and protein standardization employed by cheese-makers is not adequate to provide cheddar cheese with consistent textural characteristics year round.     

THE EFFECTS OF pH AND TIME ON RHEOLOGICAL CHANGES DURING EARLY CHEESE MATURATION

Changes in rheological properties of cheese curd during the initial stages of ripening, with pH (5.45–6.05) and with time (2–14 days), were evaluated using a small strain oscillatory test and a newly designed large strain deformation test. The new test method developed for evaluation of grated cheese employed extrusion flow technique and was carried out using the Instron Universal Testing Machine. The values for the storage modulus (G') measured using the small strain test increased with an increase in the pH of cheese curds from 5.45 to 5.90. The results from the large strain test showed essentially similar trends. The samples of curd also showed an increased solid-like behaviour as the pH increased and appeared to become more elastic with time during the two-week period of analysis.     

契达酶改性干酪的研制

选择中性蛋白酶、风味酶以及脂酶Lipase R,将其添加到新鲜干酪浆中,水解到一定程度以生产出具有契迭风味的酶改性干酪.首先添加中性蛋白酶和风味酶,根据蛋白水解程度和感官评价,确定出具有最佳风味的初级水解产品.之后向此初级产品中分别添加Lipase R进行脂解以获得最终的EMC.最后将生产出的EMCs产品与新鲜干酪、天然成熟契达干酪进行比较,比较内容包括理化成分、蛋白水解程度、感官评价等.     

THERMAL PROPERTIES OF CHEDDAR CHEESE: EXPERIMENTAL AND MODELING

Thermal properties (thermal conductivity, thermal diffusivity and heat capacity) of Cheddar cheese were measured as a function of cheese age and composition. The composition ranged from 30–60% moisture, 8–37% fat, and 22–36% protein (wet basis). The thermal conductivity and heat capacity ranged from 0.354–0.481 W/m °C and from 2.444–3.096 kJ/kg °C. Both thermal conductivity and heat capacity increased with moisture and protein content and decreased with fat content. The thermal diffusivity ranged from 1.07×10^?7 ? 1.53 × 10^?7 m²/s. There was no significant relationship between thermal diffusivity and moisture, fat and protein content of cheese. No statistically significant effect (at the 10% level) of age (0 to 28 wk) on thermal properties was observed. Models predicting thermal properties as a function of cheese composition were developed and their predictive ability was compared with that of empirical models available in the literature. In addition, several theoretical thermal conductivity models were evaluated for their usefulness with Cheddar cheese. Published thermal conductivity models cannot accurately predict (mean error was from 3.4 to 42%) the thermal conductivity of Cheddar cheese.     

RHEOLOGICAL AND CHEMICAL PROPERTIES OF MOZZARELLA CHEESE

Dynamic viscoelastic parameters and chemical properties of Mozzarella cheese produced using a "no-brine" cheese making method with 3 different cooking temperatures (38, 41, and 44C) were determined. Samples were stored for 3 weeks at 4C before dynamic mechanical analysis at 22C. G', G" and tan δ were 5.8 – 6.4 × 10⁵ dyne/cm², 1.9 – 2.1 × 10⁵ dyne/cm², and 0.33 – 0.35, respectively, at 1% strain and 10 rad/s. The percentage of intact α_s-casein and β-casein were 38–40% and 33–35% of total protein in the cheese, respectively. The range of cooking temperatures used in this experiment had little effect on dynamic viscoelastic properties or the amount of intact protein for the cheese.