ASSESSMENT OF THE EXTENT OF CONSISTENCY LOSS IN SEMILIQUID FOODS BY COMPRESSION AND SHEAR1

The consistency of commercial mayonnaise, mustard and tomato paste samples was assessed by squeezing flow before and after compression or stirring, by hand and with a domestic blender which caused intensive shearing. The specimens before and after these treatments were squeezed between Teflon® coated parallel plates mounted on an Instron UTM model 5542 to a final height of 0.8mm and had been let to relax before the crosshead was withdrawn. Their consistency was assessed in terms of their apparent stress at three heights, and after relaxation for 1 and 2 min at 0.8mm height. Compression of the specimen prior to its testing (1–3 times) has very little effect on the specimen's consistency which supports the view that there was little friction between the Teflon® coated plates and the samples. Shearing caused measurable loss of consistency in the mustard and tomato paste which was not fully restored even after three hours. The sheared mayonnaise restored much of its consistency after about an hour as judged by the apparent stress at a given height, and almost fully recovered it if judged by the apparent residual stress after relaxation.     

A VIDEO-BASED METHOD FOR DETERMINATION OF AVERAGE STRESS-STRAIN RELATIONS IN UNIAXIAL COMPRESSION OF SELECTED FOODS

A video-based method was applied to evaluate average stress-strain relationships during uniaxial compression experiments of selected food materials. The determination of apparent Poisson ratios of Gouda cheese resulted in numbers close to the theoretical value for incompressible materials of 0.5. In case of such foodstuffs, mathematically corrected compressional stress based on the consideration of constant specimen volume showed almost similar results to stress values estimated on the basis of the true cross-sectional area measured from lateral extension. For compressible materials such as apples or bread, which show a certain reduction of volume under stress or strain, the apparent Poisson ratios were strain-dependent. Average stress values calculated from compressional force and actual specimen diameter were found to be different from either engineering stress and corrected stress.     

BEHAVIOR OF DIFFERENT FOODS IN THE STANDARD SHEAR COMPRESSION CELL OF THE SHEAR PRESS AND THE EFFECT OF SAMPLE WEIGHT ON PEAK AREA AND MAXIMUM FORCE

Abstract Twenty-four foods (encompassing fruits, vegetables, meat, bread, cheese and rice) were tested in the Allo Kramer Shear Press at various weight levels ranging from those needed to cover the bottom of the cell to those required for a complete fill. The relationship between maximum force values and sample weight was found to be different for different foods. Products could be grouped into three general categories: those exhibiting a constant force to weight ratio (e.g. white bread, sponge cake), those exhibiting a continuously decreasing force to weight ratio (e.g. raw apples, cooked white beans), and those exhibiting a constant force, independent of sample weight, beyond a certain cell fill level (e.g. canned beets, canned and frozen peas). Fitting the observed behavior into mathematical models allows to infer that extrusion, in addition to the previously recognized shear and compression, plays an important role in the behavior of foods in the standard cell of the Shear Press, and that most foods are subject to various combinations of these forces. The contribution of extrusion was confirmed by actual extrusion tests. Peak areas showed an exponential relationship to sample weight following the equation A = l0^aW^b. Some evidence was obtained that exponents a and b are related to the amount and the general type of resistance offered by the food.     

GENERAL APPLICABILITY OF A METHOD FOR OBTAINING YEAST PROTOPLASTS USING A LYTIC PREPARATION FROM STREPTOMYCES

The ability of a lytic preparation from Streptomyces WL-6 to produce yeast protoplasts was analysed. True protoplasts were found to be produced from strains of the following yeasts: Trigonopsis variabilis, Toruiopsis stellata, Candida puicherrima, Saccharomyces carisbergensis, Saccharomyces cerevisiae and Saccharomyces meilis. The time necessary to obtain 100% protoplasts varied from 35 to 50 min.     

A RAPID AND REPRODUCIBLE METHOD FOR OBTAINING YEAST PROTOPLASTS

Protoplasts were prepared from exponentially growing yeast cells with a lytic preparation of Streptomyces WL-6. The following yeast strains were studied: Saccharomyces chevalieri, Candida albicans, Schizosaccharomyces pombe and Sacch. cerevisiae. True protoplasts were obtained in 100% yield after 15 min. incubation with the lytic preparation from Sacch. chevalieri and after 90 min. from Sacch. cerevisiae. For Schizosacch. pombe 10% of the cells were converted into protoplasts in the best conditions. Only spheroplasts were obtained from C. albicans.     

TEXTURE PROFILE ANALYSIS OF PROCESSED FOODS USING THE TENSIPRESSER AND THE MULTI-POINT MENSURATION METHOD

This paper reviews a considerable amount of research that has been performed in Japan on the development and application of a modified Texture Profile Analysis (TPA) system using a new instrument. Most of this work has heretofore only been available in Japanese. The Tensipresser is an instrument that has some special features that allow it to perform TPA rather easily. The multi-point mensuration method is a form of TPA that uses several variable degrees of compressions or bites on each piece of food. In ordinary work, two successive compressions or bites at predetermined clearances are applied to the sample. It is shown that the type of compressing or biting plunger plays an important role i n the shape o f the TPA curve. Examples of the use o f the Tensipresser and the multi-point mensuration method are given using breads and other baked goods, cooked rice, bean curd, pudding, sweet potato, noodle dough and cooked noodles.     

SHEAR RATES DURING ORAL AND NONORAL PERCEPTION OF VISCOSITY OF FLUID FOODS

Relationships were established for five sensory methods of oral and nonoral viscosity evaluation between viscosity scores and instrumentally measured dynamic viscosity for model and real Newtonian fluid foods. These relationships were then used to predict the effective shear rates under which the sensory tests were performed. The highest shear rates were predicted for viscosity perception by compression of samples between tongue and palate, and the lowest for pouring the fluid foods from a teaspoon. Mixing with a teaspoon, slurping and swallowing exhibited nearly the same dependencies of apparent shear rates on equivalent instrumental viscosity. All relations were of the hyperbolic type. The resulting relationships between the apprent shear rates and equivalent instrumental viscosity are in good agreement with a similar relationship predicted by Shama and Sherman (1973a) (see Cutler et al. 1983) for oral perception.     

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.     

SLUSH EVAPORATION: A NEW METHOD FOR CONCENTRATION OF LIQUID FOODS

Slush evaporation involves removal of water by combined evaporation and sublimation from the partly frozen state. It provides dehydration rates considerably greater than those attainable with freeze drying, but at the same time gives very good retention of volatile flavors and aroma. Experiments are reported which quantitatively examine the retention of natural volatile compounds during slush evaporation, as a function of temperature, drying rate, mode of drying, sample thickness, initial concentration, the fraction of water removed and the presence or absence of foam. A second set of experiments investigated the effect of these variables upon dissolved-solids loss, with losses of 0.1–0.5% being found under typical conditions for concentration.     

DIRECT SAPONIFICATION: A SIMPLE AND RAPID METHOD FOR DETERMINATION OF TOTAL CHOLESTEROL AND FATTY ACID COMPOSITION OF AQUATIC FOODS

Total cholesterol in aquatic foods was determined by direct saponification coupled with gas chromatography without derivatization. The direct saponification was compared with an AOAC extraction procedure and a culture tube extraction technique, both using chloroform:methanol (1:2, v/v) for extraction. Gas chromatography, high-performance-liquid-chromatography with UV detection of conjugated enone of cholesterol at 240 nm, and spectrophotometric o-phthalaldehyde method at 550 nm were compared to determine their effectiveness in cholesterol measurement. Direct saponification generally gave higher contents of cholesterol than the AOAC and culture tube extraction procedures, while quantification by the GC procedure appears to be the simplest method without sacrificing accuracy. Average percentage recoveries of cholesterol estimated with direct saponification-GC analysis in spiked fat-free catfish matrix and spiked fresh catfish muscle were 101.8 ± 9.6% and 101.7 ± 1.9%, respectively. The method may also be adaptable to food ingredients other than sterols such as the determination of fatty acid composition as demonstrated in this paper.     

DEFINITION OF OUTLIERS USING UNSUPERVISED PRINCIPAL COMPONENT SIMILARITY ANALYSIS FOR SENSORY EVALUATION OF FOODS

ABSTRACT

As unsupervised classifications, principal component similarity (PCS) and cluster analysis (CA) were compared for outlier detectability in panel evaluation. By rotating the reference, PCS can define outlying panelists based on the similarity of their evaluation patterns with that of the reference panelist. As a result, the outliers detected on PCS scattergrams are dependent on the reference selected, whereas, outliers detected by CA are based on dissimilarity, thus being rather unilateral. The definition of outliers in PCS is new as it is different from the currently most popular definitions based on dissimilarity. For verifying the outliers thus obtained, random-centroid optimization (RCO) was applied for selecting the best samples by each cluster of panelists. This combination of PCS/RCO may be useful in finding the likeness distribution among consumers and then in creating food products to correctly respond to the demands of different consumer groups.     

原子吸收光谱法在婴幼儿食品检测中的应用

对应用原子吸收光谱法分析婴幼儿食品中某些金属元素的应用范围、样品的制备方法进行了较详细的阐述,并列举了一些金属元素测定方法的实例。