OPTIMIZATION OF GUAVA JUICE AND POWDER PRODUCTION

Enzyme treatment of guava puree was optimized for yield and clarity by first determining the most effective concentration, then varying both incubation time and temperature. Application of Pectinex Ultra SP-L® was optimal using 700 ppm enzyme for 1.5 h at 50C. Clarified guava juice was clearer (89.6%) when prepared using ultrafiltration (MW cut-off 40–60 kDa) rather than plate and frame filtration (82.8%); however, the latter was higher in both soluble solids and ascorbic acid. Clarified guava juice powders were made using freeze-drying, spray drying and tunnel drying. The freeze-dried product had superior quality; however, the spray-dried product was stable and may be more economical. Sensory panelists ranked the cloudy juice prepared from aseptic guava puree highest, and there were no significant differences between the juices from pasteurized, clear nectar, freeze-dried puree powder or juice powder.     

THERMOPHYSICAL PROPERTIES OF FRESH AND ROASTED COFFEE POWDERS1

The present work deals with experimental determination of bulk specific heat, bulk thermal conductivity, bulk and true density and moisture content of Columbian and Mexican coffee bean powders. Specific heat was determined by DSC, thermal conductivity by modified Fitch apparatus, density by stereopycnometer and moisture contents by standard vacuum oven method. Specific heat values showed marginal rise over the temperature range (45 to 150C) studied. Thermal conductivity values, determined in the temperature range of 20–60C were not found to have any definite trend with rise in moisture in the experimental range of 4.8 to 9.8% moisture (dry basis). Bulk density of powders varied appreciably (1.298 to 0.882 g.cm^?3), while the change was negligible for true density (1.361 to 1.092 g.cm^?3) with the degree of roasting. Statistical analysis of the data shows the reliability of the experimental determinations. Suitable correlations were developed to determine bulk specific heat and bulk density.     

PREDICTION OF DIELECTRIC PROPERTIES IN OIL-WATER AND ALCOHOL-WATER MIXTURES AT 3,000 MHz, 25°C BASED ON PURE COMPONENT PROPERTIES

Measurements of oil-water emulsions show that dielectric properties are predicted at 3,000 MHz, 25°C by the noninteractive Fricke model for complex conductivity of colloidal suspensions. Similar measurements for methanol-water and ethanol-water show that dielectric properties are predicted at 3,000 MHz, 25°C by an empirical combination, designated as the interactive Fricke model, of the noninteractive Fricke model and the Debye models for pure polar liquids with single relaxation times. A tentative physical-chemical basis for prediction of dielectric properties in liquid food systems is suggested, which involves concepts of relative dielectric activities of major chemical constituents, extent of solvation and colloidal content and is based on mechanisms of dielectric behavior observed in aqueous mixtures at microwave frequencies.     

PHYSICOCHEMICAL AND SENSORY PROPERTIES OF MUSCADINE GRAPE JUICE AND CONCENTRATES

Juices from bronze and red muscadines were concentrated by low-temperature vacuum evaporation. Half of each of the lots was treated with a mixture of pectinolytic and cellulolytic enzymes and the other half untreated. Red juice was higher in soluble solids and Brix-to-acid (BTA) than bronze, but pH, acid, and viscosity were similar. When concentrated to 68° Brix, the BTA was the same regardless of juice type. Enzyme treated samples were not different from their nontreated counterparts, except for slightly higher pH of treated red juice. Hue angle for bronze concentrate shifted from about 100 to 78 while chroma increased. Hue for the red juice shifted from about 40 to 95, while chroma remained constant. Fructose and glucose were the major sugars with sucrose averaging less than 1%. Panelists rated the bronze reconstituted juices lower in color intensity, aroma intensity, sweetness, acidity, and flavor than the single-strength juice. However, the red reconstituted juices were rated higher in color intensity than their single-strength counterparts. Panelists rated reconstituted juices higher when reconstituted with essence recovered plus water than with water only.     

CONTINUOUS PASTEURIZATION OF EGG YOLK: THERMOPHYSICAL PROPERTIES AND PROCESS SIMULATION

This article presents empirical correlations to predict the density, specific heat, thermal conductivity and rheological power–law parameters of liquid egg yolk over a temperature range compatible with its industrial thermal processing (0–61C). Moreover, a mathematical model for a pasteurizer that takes into account the spatial variation of the overall heat transfer coefficient throughout the plate heat exchanger is presented, as are two of its simplified forms. The obtained correlations of thermophysical properties are applied for the simulation of the egg yolk pasteurization, and the obtained temperature profiles are used for evaluating the extent of thermal inactivation. A detailed simulation example shows that there is a considerable deviation between the designed level of heat treatment and that this is predicted through process simulation. It is shown that a reliable mathematical model, combined with specialized thermophysical property correlations, provide a more accurate design of the pasteurization equipment that ensures effective inactivation, while preserving nutritional and sensorial characteristics.     

WHITE GUAVA FRUIT AND PUREES: TEXTURAL AND RHEOLOGICAL PROPERTIES AND EFFECT OF THE TEMPERATURE

This study focuses on the effect of temperature on the rheological properties of white guava puree. The results of the textural analysis on the whole guava as well as the rheological analysis on the puree made from it showed different behaviors depending on whether the fruit was unripened or ripened. A relationship was observed between the textural properties of the whole guava and the rheological parameters of its puree. The behavior of white guava puree was thixotropic and pseudoplastic, and its rheological properties were dependent of the temperature. Its consistency coefficient decreased and its flow behavior index increased with an increase in temperature. Experimental data were fitted by the power law, and the activation energy of the process was calculated from the Arrhenius equation. Oscillation test data showed that the viscoelasticity for the guava puree was also affected by temperature.

PRACTICAL APPLICATIONS

Knowledge of the rheological properties of foods is useful for quality control, and design and evaluation of process equipment. In this study, it has demonstrated the relationship between textural properties of whole white guava fruit and rheological properties of the purees obtained from these fruits.     

THERMOPHYSICAL PROPERTIES OF COCONUT WATER AFFECTED BY TEMPERATURE

The effect of temperature on the thermophysical properties of coconut water was investigated from 5 to 80C, taking density, Newtonian viscosity, thermal diffusivity and thermal conductivity into consideration, besides specific heat. The validation of existent models of other foodstuffs, as well as the proposal of new models, was also investigated. It was verified that temperature significantly affected these properties, presenting in general a linear behavior, except for Newtonian viscosity, which presented an exponential behavior. Among the existent equations, results from the multiple linear model were appropriated to predict the density, thermal diffusivity and thermal conductivity values, while the model, which depended on solids fraction, was the best one for specific heat value, and the exponential model was the best in relation to Newtonian viscosity values. The proposed models fitted well, and were simple and easy to use.

PRACTICAL APPLICATIONS

Most of the known values of thermophysical properties of fluid foods typically concern products from subtropical and cold areas. Until today, there was little information concerning tropical products such as coconut water. Food composition and temperature are important factors that affect thermal properties. In order to create and adapt specific equipment, optimize processes that involve pumping and heat transfer, contributing to an effective design of food-processing equipment for tropical fluid foods, it is important to know the factors. Besides, the evaluation of existent models and equations, and the introduction of new equations is important to allow an adequate prediction of studied properties, thus saving time, material and money.     

PROCESSING AND STORAGE OF CARBONATED GUAVA BEVERAGE

Guava cv.'Allahabad Safeda'was crushed and treated with pectic enzymes at 0.1% concentration (w/v), incubated for 1 h at 40–50C and the liquefied juice having 10.8 Brix and 0. 65% acidity was used for carbonation. The juice was converted into sugar syrup base having 40% guava juice at 40 Brix and 1% acidity. After dosing 50 ml of it into a glass bottle (200ml capacity) filled with chilled (4-6C) carbonated water at 80 psi pressure of CO₂ gas, the bottle was sealed with crown cork and heat processed at 60C for 30 min. The carbonated guava beverage could be stored for 3 months at room (23-41C) and low (3-5C) temperatures and was found acceptable with respect to color, flavor and overall quality. Heat processing improved the flavor of the carbonated guava beverage, and the beverage contained no detectible microbes.     

RHEOLOGICAL PROPERTIES OF CLOUDY AND CLARIFIED JUICE OF MALUS FLORIBUNDA AS A FUNCTION OF CONCENTRATION AND TEMPERATURE

The rheological behaviour of cloudy and clarified juice of Malus floribunda was studied as a function of solid concentration, in a range of 45–70 Brix, at nine temperatures (5–50C). Cloudy and clarified juices are slightly thixotropic at 65–70 Brix and 5–10C. At lower concentrations and higher temperatures the thixotropy is low and can easily be eliminated by shearing. The power law model was applied to fit the pseudoplastic behaviour depending on the concentration level. Cloudy juice has pseudoplastic behaviour for concentrations higher than 45 Brix. Clarified juice is pseudoplastic at 65 Brix for temperatures lower than 25C and Newtonian at higher temperatures and for solid concentrations lower than 60 Brix. The activation energy for flow evaluated with the Arrhenius-Guzman equation, increases with solid concentration and ranged from 10.8 to 3.45 kcal gmol⁻¹ for cloudy juice and 15.3 to 7.9 kcal gmol⁻¹ for clarified juice. A nonlinear correlation accounting for temperature and concentration effects on the consistency coefficient was identified.     

THERMAL CONDUCTIVITY OF CHICKEN MEAT AT TEMPERATURES BETWEEN −75 AND 20°C

Effects of temperature and time postmortem on the thermal conductivity of white and dark chicken meat were studied using a line heat source thermal conductivity probe to measure thermal conductivity. The effect of time postmortem was determined at body temperature and 20° C by leaving probes in whole birds for periods of 1–2 days; time postmortem had no significant effect. The effect of temperature was studied at temperatures of 20, 10, 0, −10, −20, −40 and −75°C using cylindrically shaped samples 3/4 in. in diam × 11/2 in. long. 48 samples were used from 24 7-lb cockerels. Three thermal conductivity measurements were made on each sample at each temperature level. The effect of temperature was similar to that reported in the literature for other meats. The following equations may be used to express the results obtained for white meat: k(Watt/m-°C) = 0.476 + 0.00060T(°C) (0–20°C) and k(Watt/m-°C) = 1.07 − 0149T − 1.04 × 10⁻⁴T²(−75 to −10°C). Similar expressions were obtained for dark meat.