FLOW BEHAVIOR OF CLARIFIED ORANGE JUICE AT LOW TEMPERATURES

This paper presents a study of the rheological behavior of clarified and depectinated orange juices, with different soluble solid contents, at temperatures just above their freezing point. The rheological behavior of depectinated and clarified orange juice was determined for a wide range of soluble solid contents (10–65.8° Brix) and temperatures ( − 15 to 30C). The results indicated that the samples behave like a Newtonian fluid. The effect of temperature on the juice can be described with an Arrhenius-type equation. It was found that the activation energy for viscous flow was in the range of 9.4 to 59 kJ/mol, depending on the concentration. The effect of the soluble solid content can be described by an exponential-type equation. Finally, an equation in which dynamic viscosity depends on temperature and soluble solids content gives the following expression: η =  1  ×  10 ^{- 15} exp(0.12C  +  9021/T), where T in Kelvin, C in °Brix, and viscosity in mPa·s.

PRACTICAL APPLICATIONS

It is necessary to know the relationship between viscosity with temperature and concentration, since knowledge of these parameters is of vital importance in the manipulation, calculation and design of all those unit operations during the process, mainly those based on heat and quantum transfer.     

NONENZYMATIC BROWNING IN CLARIFIED APPLE JUICE AT HIGH TEMPERATURES: A RESPONSE SURFACE ANALYSIS

The effect of temperature and soluble solids on nonenzymatic browning in clarified and concentrated apple juice was analyzed by response surface methodology. Color development at 20, 40 and 60 Brix and temperatures ranging from 70–90C were compared over a time range of 30–180 min. the browning reaction was found to be dependent on soluble solid content as well as on the reaction conditions such as temperature and time. the model combines the effect of temperature, soluble solids content and time on color change due to nonenzymatic browning.     

RHEOLOGICAL BEHAVIOUR OF CLARIFIED MANGO JUICE CONCENTRATES

The rheological behaviour of clarified mango juice was measured at temperatures 15–85C and concentrations 15–66 °Brix, using a rotoviscometer. Mango juice free of pectin and pulp behaves as a Newtonian fluid. The effect of temperature can be described by an Arrhenius-type equation. The activation energy for viscous flow was in the range of 1.64–8.44 kcal/g-mol, depending on the concentration. The effect of concentration was modelled better by an exponential relationship than a power-law relationship. Simple equations are proposed for describing the combined effect of temperature and soluble solids content on the juice viscosity.     

RHEOLOGICAL BEHAVIOUR OF KIWI FRUIT JUICE CONCENTRATES

The rheological behaviour of diluted kiwi concentrates (22.5–63.0 °Brix) over the temperature range 4 to 70C, was studied. The values below 55.7 °Brix fit the power law while above 55.7 °Brix fit the Herschel-Bulkley equation. Maximum and minimum consistency index values were 62225 and 16 mPa. s ⁿ . Concentrates showed a yield stress at 55.7 °Brix, from 5 to 11 Pa, and 63.0 °Brix, from 19 to 53 Pa. Yield stress was correlated with temperature by means of a linear equation. Arrhenius activation energies were in the range of 28.97 to 33.89 kJ/mol. The average value of the flow behaviour indexes varied from 0.85 (sample at 22.5 °Brix) to 0.59 (sample at 63.0 °Brix). Simple equations are proposed to describe the combined effect of temperature and soluble solids content on consistency index and rheological behaviour index.     

REDUCTION OF PATULIN IN APPLE JUICE CONCENTRATES DURING STORAGE

In this study, the reduction of patulin content in apple juice concentrates during 6 months of storage at 22 and 30C was investigated. Results demonstrated that reduction in patulin content was dependent on the storage temperature and time. Patulin reductions after 1 month of storage at 22 and 30C were in the ranges of 45–64% and 66–86%, respectively. Levels of patulin were below detectable limits after 4 months of storage at 22 and 30C.     

INCREASED INACTIVATION OF BACTERIAL SPORES AT HIGH TEMPERATURES IN THE PRESENCE OF MONOGLYCERIDES12

The presence of monolauryl-glyceride (monolaurin) in the heating menstruum (phosphate buffer, reconstituted non-fat dry milk or cream style corn) of Bacillus stearothermophilus 1518 spores increased the rates of spore inactivation at 113–121°C by 2–3 fold. The ZD-values for the spores heated with and without monolaurin were 8.7 and 6.9°C, respectively. Rates of inactivation of B. subtilis A spores also were enhanced, but spores of Clostridium perfringens NCTC 879B, C. sporogenes PA 3679, C. botulinum 62A, or C. botulinum 213B were unaffected. Increasing the concentration of monolaurin from 0.4 mM to 3.6 mM increased the rate of inactivation, but concentrations higher than 3.6 mM did not appear to influence the effectiveness of monolaurin. All monoglyerides containing C8-C16 saturated fatty acids appeared to increase the inactivation of B. stearothermophilus spores, but the enhancement of spore inactivation declined as the fatty acid chain length increased beyond 10 carbon atoms. The influence of monolaurin on B. stearothermophilus spores did not appear to be pH dependent over the range of pH 6 to 8. The spore-monolaurin interaction was not due to heat-injury of the spores, although the interaction was dependent on the heat treatment. The increased inactivation appeared to be due to a heat enhanced chemical inactivation of the spores.     

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.     

砀山酥梨浓缩汁生产中的褐变类型研究

研究了浓缩砀山酥梨清汁生产的褐变类型。对70Brix的浓缩砀山酥梨清汁各加工工序中的色值、总酚，氨基酸态氮、5-羟甲基糠醛（5-HMF）、多酚氧化酶（PPO）相关指标进行检测，分析褐变机制。结果分析表明，在整个加工过程中，预浓缩工序之前的褐变主要是酶促褐变，预浓缩后至超滤之间的褐变是酶促褐变和非酶促褐变共同作用的结果，超滤之后的褐变则完全是非酶促褐变。     

EFFECT OF pH AND SOLUBLE SOLIDS ON THE SERUM VISCOSITY AND SERUM COLOR OF TOMATO JUICE AT ELEVATED TEMPERATURES1

Effects of heating time and temperature, pH, and soluble solid levels on serum viscosity and serum color of tomato juice were studied. The samples were canned in 18 mL TDT cans and exposed to processing temperatures of 88C, 102C, and 112C for 30, 60, and 120 min. Depending upon the time and temperature of heating, and initial viscosity of the serum, the losses in viscosity ranged from 3.0–55.6% being higher in serum with higher initial viscosity. Percent losses in serum viscosity during heating of juice increased (6–60%) with increase in pH (3.8–4.9) and soluble solids (6°–24°) in the juice. An increase in pH and soluble solids also enhanced heat induced browning in the serum with values varying from 0.1–2.69.     

DEBITTERING OF KINNOW MANDARIN JUICE BY COVALENTLY BOUND NARINGINASE ON HEN EGG WHITE

A protocol is optimised for the immobilization of naringinase on glutaraldehyde coated hen egg white (1 gHEW beads, 10 Uof naringinase, 37°C, pH 4.0 and 48 h) through 1% glutaraldehyde cross linking. The efficiency of immobilization was 140%, while soluble naringinase afforded 91% efficacy for the hydrolysis of standard naringinunder optimal conditions (5U/gHEW, pH3.0, 60°Cand 5 h). Its applicability for debittering Kinnow mandarin juice afforded 68% debittering efficiency.     

温度改变时的食品水分吸附平衡

为了简化计算和便于理论分析,食品物料湿含量平衡的动力学模型往往建立在等温条件下,而食品的实际加工处理过程中湿含量的平衡受到环境相对湿度的影响,等温是相对的.因而提出一种半经验非等温吸附平衡数学表达式,比较理想地预测了实际过程,其计算值与实验值吻合较好.     

REHYDRATION OF FREEZE-DRIED STRAWBERRIES AT VARYING TEMPERATURES

Strawberries (var. Seascape), cut in halves or 5‐mm slices, were freeze‐dried at a heating plate temperature of 55C for 28 h. Freeze‐dried products were then rehydrated at 0, 20, 40 and 80C in distilled water. The progression of the rehydration coefficient (RC) was followed as a function of time (up to 25 min). Less than 2 min were necessary to fully rehydrate the slices and less than 5 min for half strawberries. The results showed that halved and sliced freeze‐dried strawberries had higher RCs when rehydrated at a temperature near 0C. A simple diffusive‐type equation was used to represent water uptake during rehydration. Effective diffusion coefficients were modeled as a function of temperature using an Arrhenius‐type relationship.     

TRACE HYDROGENATION OF BUTTEROIL AT LOW TEMPERATURES

SUMMARY— The present investigation describes a process of selective trace hydrogenation of butteroil at low temperatures using palladium catalyst. Butteroil was selectively trace hydrogenated at low temperatures, in some instances in a semisolid state. The hydrogenated product had a remarkable flavor stability and without appreciable increase in trans-isomers and melting point. The hydrogenated butteroil also retained most of its desirable flavor and color.