Heat Transfer to Non-Newtonian Fluid Foods under Laminar Flow Conditions in Horizontal Tubes

This paper presents a study of rates of heat transfer to non-Newtonian fluid foods: mango and papaya nectars, passing through horizontal tubes of circular cross section under laminar flow conditions. Determination of the flow and thermal properties of the fluids under study was performed to adequately explain heat transfer experiences. A laminar mixed convection equation was used for describing experimental heat transfer coefficients: Nu = 1.75 [Gz + 0.0083 (Gr_w . Pr_W)^0.75]^1/3 . δ^1/3 . (K_b/K_w)^0.14 The experimental data covered Graetz numbers between 500 and 7000, and were correlated with a mean deviation of 8.4%. The results should be helpful for interpreting heat transfer to pseudoplastic materials in the design of double tube heat exchangers.     

FLOW CURVES, STRESS RELAXATION AND CREEP MEASUREMENTS OF STARCH GELS

Flow curves, stress relaxation, and creep compliance were measured for various types of corn starch gel that underwent different degrees of modification. The four starches were native corn starch, medium hydroxypropylated distarch phosphate, highly hydroxypropylated distarch phosphate, and distarch phosphate. All the starches exhibited pseudo-yield stress behavior at low shear rates and shear-thinning at higher shear rates. Stress relaxation data at different strains indicated strain-softening phenomenon for all starches. Higher degrees of cross-linking decreased the half relaxation time due to the addition of rigid filler into the matrix. Increasing the concentration increased the relaxation modulus for all starches. Creep compliance and recovery measurements were conducted over the range of 3.2 Pa-320 Pa. In the linear viscoelastic region, the compliance data were not dependent on the magnitude of stress applied. As concentration increases, higher stress magnitude leads to nonlinear behavior. The creep compliance data were fitted into the Ninomiya and Ferry relation from dynamic viscoelastic data and the Maxwell-Voigt model. Ninomiya and Ferry overpredicted the relaxation data while the Maxwell-Voigt model fitted the data reasonably well.     

Cryopreservation of <i>Cyrtopodium hatschbachii</i> Pabst (Orchidaceae) immature seeds by encapsulation-dehydration

The aim of the present study was to investigate the efficiency of the encapsulation-dehydration technique for cryopreservation of Cyrtopodium hastchbachii Pabst seeds. Immature seeds of this species were cryopreserved by an encapsulation-dehydration technique. Seeds of five immature pods, 120 days after pollination, were encapsulated in 3% calcium alginate matrix and pretreated in liquid medium supplemented with 0.08 M sucrose (24 h), 0.15 M sucrose (24 h), 0.25 M sucrose (48 h), 0.5 M sucrose (24 h) and 0.75 M sucrose (24 h) in shaker at 60 rpm. Alginate beads were dehydrated 5 h in silicagel and immersed in liquid nitrogen for 12 h. Cryopreserved beads were thawed at 30°C for 1 min, rehydrated using the same liquid mediums [0.75 M sucrose (24 h), 0.5 M sucrose (24 h), 0.25 M sucrose (48 h) and 0.15 M sucrose (24 h)] and cultivated in half strength Murashige & Skoog medium (1962) with the addition of 2 g/L activated charcoal. Sixty four percent of seeds survived and developed into acclimatized plants after being cryopreserved. In this work, the encapsulation-dehydration technique was employed for first time in Cyrtopodium hatschbachii.     

Proton NMR and Dielectric Measurements on Sucrose Filled Agar Gels and Starch Pastes

Low-field proton NMR and high-frequency dielectric measurements were performed on sucrose-filled agar gels of 0 to 1.2g sucrose/g water and starch pastes of concentrations between 0.2 and lg starch/ g water. The dielectric constant decreased linearly with increasing concentration for both. The dielectric loss of sucrose-filled agar gels showed two regions, first increasing and then decreasing with concentration. The dielectric loss data for starch pastes showed a constant value close to that of pure water throughout the concentration range. Dielectric data were related to hydration models derived from proton NMR measurements.     

Chemical composition and microbial evaluation of Argentinean Corrientes cheese

The chemical and microbial composition of an artisanal cheese made from raw cow's milk produced and consumed in the province of Corrientes (north-eastern Argentina) was evaluated using standard methods. Corrientes cheese has high moisture content (50–60%), normal protein and fat contents (21–27 and 22–26% respectively), and is low in salt (0.5–2.0% w/w). Microbial counts also varied significantly between samples (colony-forming units per gram ranges covering logs of 5–11), probably due to environmental contamination in the raw material. These results will help produce higher quality Corrientes cheeses with well-defined characteristics.     

PHYTIC ACID HYDROLYSIS AND BEAN SUSCEPTIBILITY TO STORAGE INDUCED HARDENING1

Two bean cultivars were stored over a 33-day period (75% RH and 41°C). After this period, cooked hardness, levels of phytate, phytase activity and integrity of protein bodies were monitored. The Michigan cultivar, which was the most susceptible to hardening, showed higher initial content of phytate which decreased by 20.7% after 30 days of storage. In contrast, Ojo de cabra, the cultivar less susceptible to hardening, presented lower initial content of phytate and a marked drop of 66.1% in its level during the same period of time. The phytase activity and the autolytic protein body destruction were higher in the last one than those in the former one. These results suggest that the contents of phytate or its rate of hydrolysis are not the major contributor to the seed susceptibility to storage induced hardening of different bean varieties.     

An Examination of the Minimal Water Activity for Staphylococcus aureus ATCC 6538 P Growth in Laboratory Media Adjusted with Less Conventional Solutes

Present work investigated whether or not Staphylococcus aureus ATCC 6538 P growth may occur below a_w 0.86 in laboratory media adjusted by addition of less conventional a_w controlling solutes. Solutes examined included, 1-proline, 1-lysine, β-alanine, sorbitol, KC1, sodium lactate and polyethylene glycols. No growth was observed in any case at or slightly below a_w 0.86; thus Scott's (1953) general conclusion on the lowest limit for S. aureus growth remains unchallenged. Results obtained also showed that polyethylene glycols (M.W. 200 and 400) have a significant inhibitory effect on S. aureus ATCC 6538 P growth independent of a_w lowering.