Biomedical subjects

R C Reid

Publications and source records attributed to R C Reid.

44 records · Page 3Linked to original sources

PubMed1987

Migration of BHT and Irganox 1010 from low-density polyethylene (LDPE) to foods and food-simulating liquids.

The most widely used food-wrapping material is low-density polyethylene (LDPE). Food-wrap grades contain antioxidants to minimize degradation during processing and, in the final films, such additives are normally present at levels of several hundred ppm. During use, the antioxidants may migrate into food stored in LDPE wraps. Two typical antioxidants, BHT and Irganox 1010, were radiolabelled to allow accurate analytical measurement of the extent of their migration into foods and food-simulating liquids (FSL). The results show that BHT, a much smaller and more volatile molecule than Irganox 1010, migrates more rapidly into foods, but the differences are less for FSL. In most instances, migration appears to be controlled by diffusion of the antioxidant in the polymer, and the quantity lost can be correlated in a linear fashion with the square root of time. With aqueous FSL, and, presumably aqueous-type foods, however, anomalies result; the migration is often erratic, but is more closely related to time than to the square root of time. A tentative model developed to explain these facts assumes that the antioxidants decompose in aqueous media and the net migration rate is controlled largely by the rate of chemical decomposition. It is also shown that dry foods can be surprisingly effective sinks for antioxidants under typical storage conditions.

Butylated Hydroxytoluene↗

PubMed1987

Migration of Irganox 1010 from ethylene-vinyl acetate films to foods and food-simulating liquids.

In a series of experiments on the migration of the antioxidant Irganox 1010 from ethylene-vinyl acetate (EVA) films into food-simulating liquids and foods, the antioxidant was found to migrate rapidly from EVA film into n-heptane, 100% ethanol and corn oil. The rate of migration into these media was greater from EVA than from low-density polyethylene (LDPE) under comparable conditions. In contrast, little migration of Irganox 1010 was recorded on exposure of the EVA film to aqueous media, whereas migration from LDPE into such media was relatively high.

Butylated Hydroxytoluene↗

PubMed1987

Linear mechanisms of directional selectivity in simple cells of cat striate cortex.

The role of linear spatial summation in the directional selectivity of simple cells in cat striate cortex was investigated. The experimental paradigm consisted of comparing the response to drifting grating stimuli with linear predictions based on the response to stationary contrast-reversing gratings. The spatial phase dependence of the response to contrast-reversing gratings was consistent with a high degree of linearity of spatial summation within the receptive fields. Furthermore, the preferred direction predicted from the response to stationary gratings generally agreed with the measurements made with drifting gratings. The amount of directional selectivity predicted was, on average, about half the measured value, indicating that nonlinear mechanisms act in concert with linear mechanisms in determining the overall directional selectivity.

Action Potentials↗

PubMed1987

Indirect food additive migration from polymeric food packaging materials.

Many foods contact polymeric packaging materials which contain residues of the polymerization process or additives employed to facilitate processing. The extent of migration of such materials from the packaging to foods is the focus of the present article. A major experimental program using eight polymer-migrant systems is described. Migration was measured to food-simulating liquids (FSL) and to foods. Accelerated tests were conducted with FSL under FDA guidelines conditions so as to develop correlations between such data and those found using foods under normal storage temperatures and shelf lives. In the majority of tests, the migration was found to be approximately proportional to the square root of time, to increase significantly with a rise in temperature, and to be proportional to the initial concentration of migrant in the polymer. Stirring in the FSL or food phase was generally not important except for the system involving dioctyl adipate migrating from polyvinyl chloride film. In some instances, after a period of time, migration rates became very low, and this effect was attributed to saturating the FSL or food phase with migrant. The foods comprised a variety of types, including liquid, semisolid, solid, and dry; both oily and aqueous foods were included. The physical steps involved in migration include the diffusion of the migrant from the interior of the film to the surface, where it can dissolve in the external FSL or food phase. The nature of the FSL or food is shown to be very important in that components can penetrate the polymer and dramatically increase migration rates. Consistent with the FDA guidelines in effect at the time of this study, testing was performed with five FSL (water, 3% acetic acid, 8% and 50% ethanol, and n-heptane) at 49 degrees C. Detailed comparisons were made between the migrations to foods and to FSL; following are the more relevant conclusions. (1) Three percent acetic acid showed no advantage over water as a food simulant even in those cases where the food could be considered acidic in nature. (2) Water, when used as an FSL at 49 degrees C for 5 days, overestimated migration in aqueous foods in about 75% of the cases. In some instances, however, the water phase became saturated with migrant. In other situations, this test protocol underpredicted migration--especially in those cases where there were components in the food that were able to penetrate into the polymer and enhance migration (such as orange juice).(ABSTRACT TRUNCATED AT 400 WORDS)

Chemical Phenomena↗

PubMed1985

Contrast and assimilation in the perception of brightness.

The rapid estimation of the brightness of objects is one of the nervous system's major visual tasks. Exactly how the eye and brain perform this basic task is still not understood. Two mechanisms that contribute to human perception of the brightness of objects have been identified previously: (i) the visual response to physical contrast and (ii) assimilation. Use of a unique visual display device allowed us to measure the relative importance of these two mechanisms. The present results reveal that assimilation is about half as effective as physical contrast in determining the apparent brightness of objects. These results imply that previous theories of vision--for instance, the retinex theory--will have to be revised; the importance of physical contrast must be weighted more strongly.

Acculturation↗

PubMed1982

Plasticizer migration from polyvinyl chloride film to solvents and foods.

Polyvinyl chloride (PVC) films used for food wraps contain significant concentrations of plasticizers, along with other additives. The rate of migration of these plasticizers to foods and food-simulating solvents is the principal concern of this paper, which reviews prior experimental studies and presents new data for radiolabelled dioctyl adipate. Analytical models are described to correlate many of the data, criteria are presented for identifying the controlling step in the mechanism of transfer of plasticizer from PVC films into foods and food-simulating solvents, and tentative recommendations are offered for the selection of food simulants and for the type of experiment necessary to allow an unambiguous interpretation of the data.

Diffusion↗

PubMedDate not supplied

The use of m-sequences in the analysis of visual neurons: linear receptive field properties.

We have used Sutter's (1987) spatiotemporal m-sequence method to map the receptive fields of neurons in the visual system of the cat. The stimulus consisted of a grid of 16 x 16 square regions, each of which was modulated in time by a pseudorandom binary signal, known as an m-sequence. Several strategies for displaying the m-sequence stimulus are presented. The results of the method are illustrated with two examples. For both geniculate neurons and cortical simple cells, the measurement of first-order response properties with the m-sequence method provided a detailed characterization of classical receptive-field structures. First, we measured a spatiotemporal map of both the center and surround of a Y-cell in the lateral geniculate nucleus (LGN). The time courses of the center responses was biphasic: OFF at short latencies, ON at longer latencies. The surround was also biphasic--ON then OFF--but somewhat slower. Second, we mapped the response properties of an area 17 directional simple cell. The response dynamics of the ON and OFF subregions varied considerably; the time to peak ranged over more than a factor of two. This spatiotemporal inseparability is related to the cell's directional selectivity (Reid et al., 1987, 1991; McLean & Palmer, 1989; McLean et al., 1994). The detail with which the time course of response can be measured at many different positions is one of the strengths of the m-sequence method.

Animals↗

PubMedDate not supplied

High-temperature migration of antioxidants from polyolefins.

Migration rates of radiolabelled antioxidants, Irganox-1010 (I-1010) and Irganox-1076 (I-1076), were measured from low- and high-density polyethylenes (LDPE, HDPE) and polypropylene (PP) at temperatures up to 135 degrees C. Water, 8 and 95 per cent aqueous ethanol and corn oil were employed as food simulating liquids (FSL). The experiments were conducted in a high-pressure cell in a manner that allowed contact between the polyolefin plaque and the FSL only during the test period and not while being heated. The migrations of the antioxidants varied with the square root of time, and the Fickian diffusion coefficients could be correlated with temperature in an Arrhenius fashion. Under comparable test conditions, antioxidant migrations were largest from PP for aqueous simulants, but for non-aqueous simulants the highest losses were from LDPE. In both instances lowest losses were from HDPE. In most instances there was little difference between the migration behaviour of I-1010 and I-1076. A few tests were conducted to measure the antioxidant migrations to foods. The losses were usually larger than those to water but below those to corn oil.

Antioxidants↗