SUBMICRON MAGNETIC PARTICLE SEPARATION

ABSTRACT

The control, collection or separation of particles on the basis of Their magnetic moment relative Co the carrier fluid has been demonstrated in many applications. Usually the particle sizes are larger than one micron and the magnetic susceptibility at least moderately paramagnetic. Recently, particle separation techniques have been developed for both diamagnetic and submicron particles. These techniques have found application in mineral beneficiation, nuclear reactor coolants, biology and medicine. Such developments require an understanding of flow forces in liquids and gases, diffusion and Brownian motion, and of magnetic properties which range from the strong magnetic moments of ferromagnetic and superparamagnetic particles down orders of magnitude to those of diamagnetism.     

WHAT IS “URBAN STUDIES”? CONTEXT,INTERNAL STRUCTURE,AND CONTENT

ABSTRACT: The record of learned concern with cities is nearly as old as the city itself. In the past several decades, however, a distinct academic field of “Urban Studies” has emerged. This article characterizes the context, internal structure, and content of the field through interviews with leading scholars, probabilistic multidimensional scaling analyses of survey data, and a content analysis of a leading journal. The article concludes that although Urban Studies is in some respects not a bounded “academic discipline,” it is an intellectually coherent, distinctively structured, and promising field of inquiry steered by complex, ever‐changing, and often‐large‐scale realities and real‐world problems of evolving human settlements.     

Softening of Canned Apricots: A Chelation Hypothesis

Infiltration of apricot (Prunus armeniaca L.), Patterson cultivar fruits, which are susceptible to rapid softening, with calcium chloride before processing resulted in definite firming of the canned apricots. Non-susceptible fruits treated with citrate buffers (pH 3.7) showed dramatic post-process softening. In individual, untreated, early, green fruit, firmness after processing was directly correlated with the bound calcium:citrate ratio. Based on a chelation hypothesis, it was proposed that softening was accelerated when chelators such as organic acid anions removed structural calcium from the cell wall once cell membranes were lysed by heating.     

Effects of Variety, Maturity and Processing on Pear Juice Quality and Protein Stability

?Anjou, Comice, and Bartlett pears were processed into clarified juices from hard green and soft ripened fruits. Processing trials with and without SO₂ were conducted. Effects of variety, maturity and processing on browning, turbidity, proteins, and stability were investigated. Browning increased with heat treatment, and was reduced by processing with SO₂. Total soluble protein content increased with fruit maturity and processing with SO₂. Protein fractions from a clarifying enzyme preparation (mainly arabinase and amylase) with MW in the range of 64,000–92,000 and containing glycoproteins were not removed by fining/clarification. They contributed to protein instability in the clarified pear juices, but could be removed by heat treatment (pasteurization) prior to final filtration and bottling. Our results indicate some enzymes added for clarification during processing may contribute to post-clarification haze and sediment formation.     

THE 7S PROTEIN FROM BRAZIL NUT1

The 7S (6.2S) protein of Brazil nut (Bertholletia excelsa) was isolated by ammonium sulfate solubilization from a high molecular weight fraction which contained primarily the major 11S (10.5S) nut globulin excelsin. Electrophoretic characterization of the protein showed that, in addition to sedimenting more slowly, it differed from excelsin in size, being smaller, and in subunit composition.     

c4-Heptenal: An Influential Volatile Compound in Boiled Potato Flavor

Analysis of headspace volatile concentrates from freshly boiled Russet Burbank potatoes revealed a variety of lipid oxidation products including t2,c6-nonadienal which is further degraded to c4-heptenal through a water-mediated retro-aldol condensation reaction. Dilute aqueous solutions of c4-heptenal exhibited boiled potato-like aromas, and at relatively high concentrations (greater than 0.7 ppb) added c4-heptenal contributed distinct staling-type flavor defects to both fresh, mashed potatoes and reconstituted dehydrated potatoes. When added at levels between 0.1–0.4 ppb, c4-heptenal enhanced overall earthy, potato-like flavors in freshly boiled mashed potatoes, but these levels caused stale flavors in reconstituted dehydrated potatoes.     

Controlled Low-Temperature Vacuum Dehydration–A New Approach for Low-Temperature and Low-Pressure Food Drying

The processes of freeze-drying, vacuum drying and controlled low-temperature vacuum dehydration (CLTV) were used to dry clam paste and a gelatin-microcrystalline cellulose model food system. CLTV was carried out as cold as possible without freezing the product. Much less drying time was required for CLTV and vacuum drying than for freeze-drying. The mass transfer resistance for both freeze-drying and CLTV was less than that of vacuum drying. Functional properties were closer to those of freeze-drying than to vacuum drying. CLTV versus freeze-drying showed a 30% reduction in enthalpy change and 40% reduction in running cost. Microbiological analysis, used to monitor the safety of processing clam paste, showed that the process was satisfactory relative to common parameters.     

Effects of Fatty Acids on the Oxidative Stability of Soybean Oil

Effects of 0, 0.5, and 1.0% levels of stearic, oleic, linoleic or linolenic acid or octadecane on the oxidative stability of soybean oil were determined by a combination of peroxide values and measurements of volatile compounds and oxygen in the headspace of samples by gas chromatography. These fatty acids showed similar prooxidant activities which were not statistically different at α= 0.05. However, octadecane which had the same number of carbons as stearic, oleic, linoleic or linolenic acid but no carboxylic group, did not show prooxidant activity.     

EXTENDED VALIDATION OF A SIMPLIFIED EXTRACTION AND GRAVIMETRIC DETERMINATION OF TOTAL FAT TO SELECTED FOODS

A simplified method for chloroform/methanol extraction and gravimetric determination of total fat previously published for diet composites was tested on additional foods, including milk, cheese, fried snack foods, nuts/seeds, salad dressings, baked goods, meat, fish/shellfish and fruits/vegetables. Homogenized food composites and certified reference materials (CRMs) were analyzed using the existing method involving, briefly, orbital shaking of a subsample with chloroform/methanol/buffer in specific proportions, then recovery of total lipid in the chloroform extract. For meat, fish, shrimp, cheese and fried plantains, total fat recovery was low and/or variability was high with the unmodified assay versus results from other standard total fat methods (e.g., ether extraction, acid hydrolysis) or to CRM assigned values. Reducing the sample size or adding a homogenization step during extraction resulted in relative standard deviations of < 3% for all matrices and also values consistent with those generated by other standard total fat methods and within assigned ranges for total fat in most CRMs.

PRACTICAL APPLICATIONS

The method allows for routine batch analysis of multiple samples of a range of food types with minimized hands-on time, using commonly available laboratory equipment. The resulting total lipid extract can be subdivided for analysis of various specific lipid analytes as well as for gravimetric measurement of total fat.     

QUENCHING MECHANISMS AND KINETICS OF CAROTENOIDS IN RIBOFLAVIN PHOTOSENSITIZED SINGLET OXYGEN OXIDATION OF VITAMIN D2

The oxidation of vitamin D₂ in a solution of 12% water, 88% acetone and 15 ppm ribqflavin under light or dark was studied by measuring the headspace oxygen. Ribofiavin accelerated the oxidation of vitamin D₂ by singlet oxygen under light, but did not affect vitamin D₂ oxidation under dark. Quenching mechanisms and kinetics within the range of 0–20 ppm β‐cawtene or fucoxanthin and with 0–80 ppm retinyl acetate or retinol on 15 ppm riboflavin photosensitized singlet oxygen oxidation of vitamin D₂ were also studied. The rate of singlet oxygen formation by 15 ppm riboflavin was 1.78 umole oxygen/mL headspace‐hour. The reaction rate constant of vitamin D₂ with singlet oxygen was 2.2 times 10⁷ M^?1A s^?1. The carotenoids minimized the oxidation of vitamin D₂ by quenching singlet oxygen. The total quenching rate constants of retinol, retinyl acetate, jucoxanthin and ft‐carotene were in the order of 1.22 times 10⁸, 5.98 times 10⁸, 1.78 times 10⁹ and 5.00 times 10⁹M^?1. s^?1 respectively, which suggests that as the number of double bonds of carotenoids increases, the quenching rate constant ofcarotenoid increases.