EFFECTS OF DIMENSIONS OF AGAR AND GELATIN GELS ON PALATAL PRESSURE PATTERNS

Eating of agar and gelatin gels in the mouth was studied dynamically in detail. The palatal presures on agar and gelatin gels of various concentrations and dimensions were detected by pressure transducers installed at three locations of the palate. For each of the gels, Pm (the maximum palatal pressure at the initial stage of mastication), P (the mean palatal pressure), W (work), and T (retaining time in the mouth) changed significantly when their concentrations increased. Moreover, gel dimensions also affected Pm, P and W. For a bite-size gel, Pm, P and W increased or remained constant, while for a finer sized gel, Pm, P and W were nearly constant regardless of the increase in rupture strength or gel concentration.     

EFFECTS OF LONG-TERM STORAGE OF FOODS ON QUALITY OF PROCESSED FOODS II.

The effects of long-term storage at 4.4, 21.1, and 37.8°C on physicochemical characteristics, nutritional and organoleptic qualities of freeze-dehydrated ration items from Packet Long Range Patrol were studied. The items included beef hash, beef stew, chicken stew, spaghetti with meat sauce, chili con carne with beans, chicken and rice, pork with escalloped potato, and beef and rice. The freeze-dehy drated foods were stable in quality during storage at 4.4, 21.1, and 37.8°C. After 44 months of storage all freeze-dehy drated ration items were in acceptable condition.     

EFFECTS OF LONG-TERM STORAGE ON QUALITY OF PROCESSED FOODS

Experiments were conducted on the effects of long-term storage at 4.4, 21.1, and 37.8°C temperatures on nutritional quality, physicochemical characteristics and organoleptic quality of 8 food packets (ready to eat individual ration items processed in flexible retortable pouches) of ham and chicken loaf, beef steak, beef stew, frankfurters, fruit cake, pineapple slices, cheese spread, and chocolate brownies. At 37.8°C storage life of cheese spread, pineapple slices, beef stew, chocolate brownies and fruit cake was 12, 12, 30, 30 and 30 months respectively. Ham and chicken loaf, beef steak, and frankfurters were acceptable after 37.8°C storage for 54 months, but frankfurters were near the borderline of rejection. The browning is usually associated with the high temperature storage of high sugar foods. Meat products except beef stew are apparently more stable than others at high temperature storage. The high temperature storage resulted in drastic loss of thiamin and ascorbic acid, significant loss of riboflavin and niacin, and discoloration and rancidity. Despite the losses of quality observed in all food packets stored at 21.1°C for 54 months, they were acceptable. Storage at 4.4°C for 54 months had very little effect on quality of the food packets and were highly acceptable.     

PALATAL PRESSURE PATTERNS OF GELATIN GELS IN THE MOUTH

Palatal pressures of gelatin gel at various concentrations were detected by pressure transducers set at three locations in the palate. The following parameters were derived from the palatal pressure patterns: P, mean of palatal pressure from the beginning of eating to the end of swallowing; S, the last pulse of swallowing; T, retaining time of the sample in the mouth and W, energy consumed in the course of time until swallowing. P and W increased as the gelatin concentration increased from 1.0–4.0% and then they decreased as the gelatin concentrations exceeded 4.0%. T increased linearly over the whole range of gelatin concentrations. Changes in gelatin concentration had little effect on S. It was concluded that oral action changed primarily from crushing by the tongue against the palate to biting by the teeth as the toughness of the gelatin gel increased.     

EFFECTS OF SAMPLE DIMENSIONS ON THE SNAPPING FORCE OF CRISP FOODS *

Abstract. According to well-known formulae for the mechanics of flexure stresses, the force required to snap a test specimen of uniform rectangular cross-section is inversely proportional to its length and directly proportional to the width and the square of the thickness. For a specimen of circular cross-section, the snapping force is directly proportional to the cube of its radius and inversely proportional to its length. In order to test the validity of the theoretical models for foodstuffs, three snappy foods (cookie, beet, carrot) were fashioned into bars of rectangular or circular cross-section in lengths varying from 2.0 to 5.8 cm. The rectangular bars ranged from 0.4 to 1.0 cm in thickness and 1.5 to 3.0 cm in width. The cylindrical bars ranged from 0.253 to 0.578 cm in diameter. The bars were snapped in two by mounting them in a horizontal plane on two fixed vertical supports and applying force to fracture by means of a descending beam centered between the supports in a snapping rig mounted in an Instron Universal Testing machine. Experimental data for the commodities tested were in satisfactory agreement with the theoretical model.     

RHEOLOGY OF LIQUID FOODS - A REVIEW1

Liquid foods are classified and their properties discussed under various types of rheological behavior: Newtonian, pseudoplastic, shear thickening, thixotropic, and viscoelastic. Rheological data on selected liquid foods are summarized in either tabular form or in the form of equations. Wherever possible the influence of temperature, constituents, and structure on the rheological behavior is detailed. Because many foods are suspensions, the measurement of flow properties of suspensions and factors influencing their rheological behavior are also covered. Finally, the relationship between the flow behavior and the sensory evaluation of mouth feel and viscosity is discussed.     

ORAL PERCEPTION OF VISCOSITY IN FLUID FOODS AND MODEL SYSTEMS

The perceived in-mouth thickness ( T ) of a range of fluid foods and model systems was assessed by a trained sensory panel, using a ratio scaling technique, and correlated with objective measurements of viscosity (η_N). For Newtonian samples a simple linear correlation (r²= 0.98) is observed between log T and log η with exponent η= 0.22. The linear relationship between log T and log η for Newtonian materials was used to calculate the equivalent Newtonian viscosity (η_N) from subjective panel scores for the non-Newtonian samples studied. The shear rate at which observed viscosity is equal to η_N decreases with η_N, as reported previously by Shama and Sherman, but also decreases with increasing shear-rate dependence of viscosity. This implies oral perception of viscosity over a range of shear rates. Comparison of flow curves for samples assigned similar thickness scores, but showing very different shear thinning behaviour, suggests that the perceived thickness of extremely shear-thinning materials is dominated by their high viscosity at low rates of shear. As a simple practical index, viscosity at 10 s⁻¹ shows a better correlation (r²= 0.95) with the perceived thickness of the samples studied than values calculated by the methods suggested by Wood, or by Shama and Sherman (r²= 0.90 in both cases). The close agreement between panel scores for perceived thickness and perceived stickiness previously observed for concentrated solutions of random coil polysaccharides does not apply for several of the food systems studied, or for very concentrated solutions of xanthan.     

WATER ABSORPTION EFFECTS ON BIAXIAL EXTENSIONAL VISCOSITY OF WHEAT FLOUR DOUGH

Biaxial extensional viscosities of wheat flour dough at three water absorption levels were determined as a function of biaxial strain rates using lubricated squeezing flow. The shape of the curves obtained in this study showed a sharp increase followed by a gradual increase which could indicate the presence of viscoelastic effects, which is not the usual case reported in the published literature for other products when using this technique. Plasticizing effect of water coupled with the effect of the starch and the interaction among the other components of wheat flour dough could explain the rheological behavior of flour dough during lubricated squeezing flow testing. Values of biaxial extensional viscosities of wheat flour dough for the three water absorption levels obtained in this study showed significant differences in the entire deformation range (P < 0.05).     

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.     

EFFECTS OF HYDROSTATIC PRESSURE ON ALPHA-MACROGLOBULIN AND SELECTED PROTEASES

The enzymes, chymotrypsin, trypsin, collagenase and cathepsin C, as well as the protease inhibitor, α₂-macroglobulin, have been shown to be susceptible to hydrostatic pressure inactivation. a₂-Macroglobulin lost about 15% activity at a pressure of 2,000 atm and as much as 80% at 3,000 atm pressure applied for 1 h in both cases. Thermal stability studies also indicated the protein to be completely denatured at about 75C. The enzymes were also inactivated to various extents depending on the amount of pressure and the duration of application, The degree of susceptibility to pressures ranging between 2,000–4,000 atm applied for time periods ranging from 5–60 min was found to be as follows: chymotrypsin < cathepsin < trypsin < collagenase. The hydrostatic pressure effects were irreversible when pressure-treated enzymes were stored at room temperature (20–25C), but showed various levels of reactivation when stored at refrigerated temperatures (4–7C).     

EFFECTS OF OVEN HUMIDITY ON FOODS BAKED IN GAS CONVECTION OVENS1

Bread, cakes, and cookies were baked in direct‐ and indirect‐gas fired, foodservice style convection ovens. Oven humidity was varied by including different numbers of perlite and water dummy loads during baking. Oven, product, and dummy temperatures were continuously recorded during baking, as was oven humidity. The properties of the finished baked foods were measured. Increased oven humidity resulted in products with higher yield, greater volume or spread, lighter color, and reduced firmness.     

超高压对食品品质的影响

综述超高压处理对内、奶、蛋及果蔬制品品质的影响,包括超高压对肉类食品的色泽、风味、纤维结构和嫩度的影响及超高压对乳制品中微生物、蛋白质及感官品质的作用效果;归纳了超高压下蛋类制品营养成分、感官品质、蛋白质凝结性和杀菌效果的改变及超高压下果蔬制品的香气成分、维生素含量和口感的变化.     

THE EFFECTS OF DESIGN AND OPERATING CONDITIONS ON PARTICLE MORPHOLOGY FOR SPRAY-DRIED FOODS

An experimental program was carried out in order to provide insight into the effects of the design and operating conditions of spray drying on the morphological behavior of the product. Single streams of uniform-size drops fell through a column in which air temperature profiles could be monitored and manipulated. Scanning electron microscopy and optical microscopy were used to measure shrinkage (or expansion) and to observe physical characteristics. The effects of varying the type of feed, the feed concentration, initial drop size, and air temperature history were investigated. Results are compared with previous investigations related to bulk density.     

EFFECTS OF HYDROCOLLOIDS AND ASPARTAME ON SENSORY VISCOSITY AND SWEETNESS OF LOW CALORIE PEACH NECTARS

Effects were studied of interactions between each of three hydrocolloids-xanthan gum, guar gum and methylcellulose- and aspartame on sweetness intensity and sensory viscosity of low-calorie peach nectars (60% fruit purée with no sucrose added). The flows of the nectars were characterized as near Newtonian without hydrocolloids, as Bingham plastic at lower hydrocolloids concentrations and as pseudoplastic at higher concentrations (Ostwald flow for guar and methylcellulose, and Herschel-Bulkley for xanthan). Hydrocolloids concentrations were selected to cover viscosity range of commercial whole nectars: 0.10 and 0.20% xanthan or guar, and 0.15 and 0.30% methylcellulose. Aspartame concentrations tested were derived from the calculation of equisweet concentration as referred to a control nectar sample with sucrose (14°Brix) and of the upper and lower limen value: 0.216, 0.360 (equisweet), 0.502, and 0.644 g/L. Addition of either guar or methylcellulose did not alter the perceived sweetness in aspartame-sweetened peach nectars. Xanthan addition, even at 0.10%, significantly lowered sweetness of samples sweetened with the highest aspartame concentration (0.644 g/L). Addition of aspartame did not modify the perceived viscosity in samples thickened with either xanthan or guar gums. At all methylcellulose concentrations tested, samples with the lowest aspartame concentration (0.216 g/L) were perceived as less viscous.     

DYNAMIC TURBULENCE PROMOTION IN REVERSE OSMOSIS PROCESSING OF LIQUID FOODS

SUMMARY– The phenomenon of concentration polarization operates to reduce the efficiency of solvent-solute separation in the processing of foods by reverse osmosis. The viscous nature of most food concentrates aggravates the problem. Disrupting the boundary layer by mechanically inducing turbulence in the fluid stream improves the permeation efficiency. Flux improvement of up to 3-fold is possible with dynamic turbulence promotion involving plastic spheres moving randomly with the orange juice concentrate. Concentrate (and sphere) movement is pulsed alternately from one end of the membrane flow channel to the other. The spheres are confined within the flow channel to avoid the problem of moving them through the recycling pumps. A net movement of concentrate results when the pump volume is greater in one direction than the other. The permeation rate with dynamic turbulence promotion does not drop off significantly with time. The long-term effects of sphere movement on the membrane surface are not known but are believed not to be serious.