Arnott Test Correlates with Dynamic Rheological Properties for Determining Cheddar Cheese Meltability Z. USTUNOL, K. KAWACHI and J. STEFFE ABSTRACT Cheddar cheesewith six different fat levels (34.3, 31.5, 26.8, 20.5, 12.6 and Cl%) were manufactured and allowed to ripen 4 mo at 7°C. Melting characteristics of the cheeseswere studied by the Arnott test and dy- namic rheological testing. Meltability of Cheddar cheese was signifi- cantly influenced by its fat content as determined by the Arnott test. A significant correlation (r = -0.80) occurred between the minimum com- plex modulus G* and meltability of Cheddar cheese.Minimum complex modulus G* may be a useful predictor of cheesemeltability. Key Words: meltability, Cheddar cheese,Arnott method, dynamic rhe- ological test IN’iRODUCTION MELTING CHARACTERISTICS OF CHEESE, particularly varieties such as Mozzarella, Cheddar and process cheese, are important factors in determining quality and application. The dairy indus- try has needed objective methods to assess melting properties of cheese (Amott et al., 1957; Kosikowski, 1982; Park et al., 1984;. Kindstedt et al., 1989). However, such determination of cheese meltability has been somewhat complicated because cheese meltability is determined both by thermal phase change characteristics of the solid cheese and the rheological or flow properties of the melt, which are interdependent (Park et al., 1984). The Schreiber (Kosikowski, 1982) and the Amott (Amott et al., 1957) methods have been most commonly used in the industry. Both are simple, empirical methods. Attempts have been made to define meltability in specific, objective, physical terms (Lee et al., 1978, Smith et al., 1980) but none have been totally successful. Differential scanning calorimetry (DSC) has been used to study melting characteristics of cheeses. However, DSC did not reveal differences useful for predicting cheese melting behavior (Park et al., 1984). A capillary rheometer was used to study flow curves of melted cheese, but slippage and strong viscoe- lastic effects made results invalid (Smith et al., 1980). Objective methods for the assessment of meltability that are reproducible are still much needed. Dynamic rheological testing has many applications in the food industry (Steffe, 1992; Rao and Steffe, 1992) and has been used with cheese. Nolan et al. (1989) studied the dynamic rhe- ological properties related to meltabilities of natural and imita- tion low-moisture part-skim Mozzarella cheese. Measurements of viscoelastic moduli and dynamic viscosities helped provide an objective basis for distinguishing between imitation and nat- ural Mozzarella cheeses. Taneya et al. (1979) measured the dy- namic properties of Gouda, Cheddar and process cheese. Tunick et al. (1990) examined viscoelastic properties of Cheddar and Cheshire cheeses. These two varieties are very similar in com- position ,and in several physical properties, thus more specific methods are needed to identify them. Tunick et al. (1990) re- Author Ustunol is affiliated with the Dept. of Food Science & Hu- man Nutrition, Michigan State Univ., 165 S. Anthony Hall, E. Lan- sing, MI 48824. Author Kawachi’s current address: Snow Brand Milk Products Co., Ltd., 1-2, Minamidai, I-Chome, Kawagoe, Sai- tame, Japan. Author Steefe is the the Dept. of Agricultural Engi- neering, Michigan State Univ. E. Lansing, Ml. ported, at 0.1% strain, the values of G’, G” and q* of Cheddar was almost twice that of Cheshire. They suggestedthis method may be used in the identification of these two cheesesto avoid mislabeling. Nolan et al. (1990) compared properties of Cheddar and pasteurized process American cheeses by dynamic rheolog- ical properties. The dynamic viscosity of both cheeses followed an Arrhenius-type relationship. Dynamic rheological testing has many possible applications in cheese research. Our objective was to determine whether dynamic rheological properties could be used as an index of meltability in cheese. Melting properties of Cheddar cheese with varying fat content were determined using dynamic testing and correlated with the Amott test, a traditional test for meltability. MATERIALS & METHODS Cheese manufacture Cheddar cheese with varying fat levels (34.3, 31.5, 26.8, 20.5, 12.6 and < 1% fat) was manufactured from milk standardizedto the appro- priate fat levels. Standardizedmilk was warmed to 31°C and inoculated with 0.02% DVS (Direct Vat Set) culture (DVS #BSO, Chr. Hansen’s Laboratory Inc., Milwaukee, WI). Milk was ripened for 1 hr, and 0.01% double-strengthchymosin (Chymax-Double strength, Pfizer, Milwaukee, WI) was added to clot milk in 30 min. Cheddar cheese was manufactured by the standard procedure outlined by Kosikowski (1982). Curd was salted, hooped and pressed for 18 hr. Manufactured cheeses were vac- uum-packaged the next day and ripened at 7°C for 4 mo. Amott method Meltability of the manufactured cheeses was determined by the Arnott test (Arnott et al., 1957). Cheese samples were cut into cylinders (22 mm in diameter and 17 mm in height) with a corkborer and a knife. Each specimen was placed in the center of a glass Petri dish. The Petri dish was heated in a laboratory convection oven at 100°C for 15 min. After cooling to room temperature for 30 min, the height and diameter of the melted cheese sample were measured. The meltability of the cheese was calculated by averaging the height and diameter of the melted ‘cylinders’ and reported the resulting dimensions in cm. Rheological behavior A Rheometrics fluid spectrometer (8400 Rheometrics Inc., Piscataway, NJ) was used to characterize rheological properties of all Cheddar cheese samples. Tests were performed at a constant frequency of 1 radlsec and a constant strain of 0.1% in a parallel plate apparatus (2.5 cm radius). Cheese samples were cut at 5°C to provide disks w 6 cm in diameter and 1 mm to 2 mm in height using a meat slicer (Model 512, Hobart Co., Troy, OH) and a cookie cutter. The cheesesamples were cut larger than the plate because of shrinkage causedby dehydration of the sample during the heating process. Temperature of the samples was controlled by a programmer (MPT-microprocessor, Neslab Instruments, Inc., New- ington, NH) using silicon oil (polydimethyl siloxane, Dow Coming 200, Dow Coming Co., Midland MI) as the medium. The temperature was increasedfrom 25 to 90°C at 2”C/min during the test. The data obtained included the elastic (or storage) modulus, G’, and viscous (or loss) mod- ulus, G”, which are components of the complex modulus, G*, loss tan- gent, tan S, and complex viscosity, q*. These parametersare related as follows: (G*)2 = (G’)* + (G”)2, tan S=G”/G’ and q*=G*/o (where o is the frequency in rad/sec). 97&-JOlJRNAL OF FOOD SCIENCE-Volume 59, No. 5, 1994 / ,/’