警示录：剖析中非酒店的十大败因

成都某大型企业下属的中非酒店，原本是一家前途无量的酒店，然而却因为种种原因而陷入困境．亏损不说，还被成都一家餐饮管理公司告上法庭。分析其败走麦城的成因．对我们无疑具有警示作用。     

THE ANALYSIS OF STRESS RELAXATION DATA OF SOME VISCOELASTIC FOODS USING A TEXTURE ANALYZER*

Uniaxial compression test for dough and several commercial products like jello, mozzarella cheese, cheddar cheese, tofu and sausage (cooked and uncooked) was performed using a texture analyzer (TA). Percent stress relaxation (%SR ), k1 (initial rate of relaxation), k2 (extent of relaxation) and relaxation time (RT) were calculated and compared for different products. The TA software was used to convert the raw SR data into a linear form. Constants k1 and k2 were determined from the intercept and slope of the linear data. Higher values of %SR and k2 (90 and 9, respectively) indicated higher elasticity for jello, whereas wheat flour dough samples showed the lowest values (20–30) for %SR and 1 to 2 for k2. The RT and k1 values were not good indicators for differentiating different products based on their viscoelastic behavior. Measurement of RT was limited by the maximum time for which the data were collected, whereas k1, because of its mathematical form, needed careful interpretation. In this study, %SR was found to be a good measure to interpret viscoelasticity of different food samples.     

LINEAR VISCOELASTIC BEHAVIOR OF FRANKFURTERS

Normal creep and stress relaxation experiments were performed on seven commercial brands of frankfurters. A nonlinear procedure was used to determine the model best fitting the data for each test. Re assumption of linear viscoelasticity was tested by the equivalence of model parameters. Results showed fankfurters to be linear viscoelastic materials at strain levels up to 3.8%.     

EFFECTS OF TEMPERATURE AND MOISTURE CONTENT ON THE VISCOELASTIC BEHAVIOR OF COWPEAS

The viscoelastic parameters of cowpeas (Vigna unguiculata) were studied at different temperature and moisture content combinations. Cowpeas were tested at temperatures of 25°, 45° and 70°C and moisture contents of 13.9, 19.6 and 22.4% dry basis on an Instron Universal Testing Machine using stress relaxation techniques. The response of cowpeas was characterized by two Maxwell bodies in parallel without the incorporation of a residual spring. The relaxation curves (uniaxial modulus versus time) were used to calculate temperature and moisture shift factors, which subsequently led to the construction of a single master response curve. Cowpeas are both thermo-rheologically and hydro-rheologically simple biological materials.     

VISCOELASTIC AND THERMAL CHARACTERISTICS OF VEGETABLE PUREE-BASED BABY FOODS

Viscoelastic properties of three commercial vegetable puree‐based baby foods (pea, corn and wax bean) were evaluated in the temperature range of 20 to 80C using dynamic oscillatory viscometry, and the thermal properties were evaluated using a standard differential scanning calorimeter (DSC) (?10 to 100C). Test samples behaved like viscoelastic fluids with consistently higher magnitudes of storage modulus (G′) as compared to loss modulus (G″) in an oscillatory frequency (ω) range between 0.628 and 62.800 rad/s. Both G′ and G″ versusωdata were well fitted by a power‐type relationship at all temperatures employed in the study. However, the derived power‐law parameters of G′ and G″ showed no consistent trends with temperature. Both pea and wax bean purees exhibited similar viscoelastic patterns with an increase in both G′ and G″ at 50C, somewhat coinciding with the initiation of starch gelatinization. However, the corn puree exhibited a stronger elastic characteristic with starch gelatinization occurring around 80C. The rheological measurements were well supported by the calorimetric data from the DSC.     

MODIFICATIONS AND APPLICATIONS TO FOODS OF THE GENERAL FOODS SENSORY TEXTURE PROFILE TECHNIQUE

The primary attributes of the General Foods sensory texture profile technique are standardization, reproducibility, and ease of correlation with instrumental measurements. Since the original publication in 1963, the method has undergone modifications and refinements such as: addition of an initial stage for evaluation of surface properties, evaluation of certain mechanical characteristics of elasticity and cohesiveness on specific products, and development of texture profile techniques and terminology for the evaluation of semi-solids. Application of this expanded texture profile method is demonstrated using foods such as vanilla cookies, frankfurters, and whipped toppings.     

AN ATTEMPT TO IDENTIFY AND MODEL TRANSIENT VISCOELASTIC FLOW IN FOODS2

Shear stress development data for commercial ketchup, mustard, mayonnaise, apple butter, butter, margarine and canned frosting were obtained using the cone and plate geometry of the Rheometrics Mechanical Spectrometer. At sudden imposition of four shear rates, .1, 1, 10, and 100 s^?1, shear stresses displayed different degrees of overshoots with margarine exhibiting a maximum overshoot of 320% that of the steady-state value at a shear rate of 100 s^?1. The actual extent of overshoot depended on the particular food and the particular shear rate applied. An attempt was made to explain observed transient shear stresses with the Bird-Leider equation, a four parameter empirical model which incorporates both steady viscous and elastic properties of food materials. This model assumes both the steady viscosity function, η, and the steady primary normal stress coefficient Ψ to have a prominant power-law region with increasing shear rate. This assumption is shown to be justified for all foods studied between shear rates of .1 s^?1 and 100 s^?1. When this assumption is justified a time constant Λ can be constructed. This time constant is found to be an approximate indicator of relative stress overshoot for the foods studied. It is found that the Bird-Leider equation provides a moderately good prediction of peak shear stresses and peak times and only a crude prediction of shear stress decay. Nevertheless, the model is a definite improvement over time independent models such as the power-law model.     

USING BROOKFIELD DATA AND THE MITSCHKA METHOD TO EVALUATE POWER LAW FOODS

Mitschka proposed a simple technique to calculate average shear stress and average shear rate from data obtained with Brookfield viscometers. It allows for estimation of the apparent viscosity, the flow behavior index, and the consistency coefficient of power law fluids. This method was evaluated for typical shearthinning foods (banana puree, salad dressing, enchilada sauce, and pancake syrup) and found to have excellent potential for quality control testing in the food industry. Results compared favorably with those obtained with a standard cone and plate viscometer.     

VISCOELASTIC BEHAVIOR OF ARZÚA-ULLOA CHEESE

A study of the viscoelastic properties of ten samples of commercial Arzúa-Ulloa cheeses produced according to the regulations of the designation of origin is reported. The linear viscoelastic range at 20C was determined from stress sweep tests and later confirmed by transient tests. The shear creep compliance curves were analyzed in the framework of the generalized Burgers model. Mechanical spectra at 20C obtained from frequency sweep tests completed the study. The results thus obtained were highly consistent themselves and they manifested the structural differences among the samples. Some correlation between the dry extract content and the viscoelastic behavior was found.     

VISCOELASTIC BEHAVIOR OF FRIED POTATO CRUST*

A restructured potato model system was fried for 5, 10 or 15 min at 170, 180, or 190C and tested in a dynamic mechanical analyzer. Stress relaxation phenomena was described by a two‐element Maxwell model with a parallel spring. The viscoelastic behavior of the crust resulted from its porous structure of open and closed foam cells embedded in oil. Relaxation of stress in the fried crust was a result of slippage of the dispersed oil through the crust and from rearrangements of the air cells. Elastic modulus of the fried crust increased for higher frying times and temperatures and were the most significant elements in distinguishing between samples.     

CONSIDERATIONS OF A GENERAL RHEOLOGICAL MODEL FOR THE MECHANICAL BEHAVIOR OF VISCOELASTIC SOLID FOOD MATERIALS*

A model describing the rheological behavior patterns of solid foods is suggested and discussed. It consists of a parallel array of a generalized Maxwell body in which the Maxwell elements have been modified by incorporation of two fracture elements. The model enables the anticipation of response patterns of real food materials under various force—deformation histories without becoming inconsistent. It also predicts the viscoelastic phenomena of materials after their failure and does not exclude the elastic deformation stage. The effects of experimental conditions, differences between various types of foods, as well as variations and changes in the same food can be expressed or explained in terms of model components and their relative distribution. The application of the model is demonstrated with a small number of representative elements.     

NONLINEAR RHEOLOGICAL BEHAVIOR CHARACTERIZATION OF SOLID FOODS

Nutting's general law of deformation was used to characterize the nonlinear rheological behaviour of bread. A simple experimental technique submits a sample of regular geometry to a sequence of compression runs in which the ultimate strain, or the ultimate load, was kept constant. In order to avoid sample failure as a consequence of mechanical fatigue an ultimate strain as low as 5% and an ultimate load of 150 g were chosen. An extremely good agreement (correlation coefficient 0.9997) between the model prediction of bread stress-strain behaviour and the experimental results was found up to 80% compression. This result appears quite promising since it provides a simple way to predict and compare material performances under very large deformations.     

TIME-TEMPERATURE BEHAVIOR OF DEEP-FROZEN READY-TO-SERVE ETHNIC FOODS FROM THE MIDDLE EAST REGIONS

Since in the Middle East no production of deep-frozen foods of any significance has been established, all products have to be imported. This implies that the entire product spectrum consists of products adapted to the requirements of European consumers. Foods prepared according to the preferences of the people of the Middle East have not yet been offered commercially. To collect initial experiences with food prepared to meet the preferences of people living in the Middle East, three dishes were prepared and kept under cold storage conditions suitable also for the existing frozen food chain in the Middle East. The ready-to-serve food products were evaluated sensorily.     

黄金分割法在焙烤食品中的应用研究

主要介绍了黄金分割法在焙烤食品开发中单因素及单因素复配优选的问题上的应用,这种简单的科学方法在焙烤领域很值得推广.