No abstract

A family of nonlinear four-wave mixing techniques that are capable of site-selective organic spectroscopy are presented. Three lasers are used in the methods in order to achieve fully resonant mixing. Three lasers are shown to provide better sensitivity, selectivity, and versatility in the study of ground and excited electronic state vibrational spectroscopy. New approaches become possible in the establishment of resonances that translate the output signal from the normal Stokes or anti-Stokes side of the lasers to intermediate positions that are free of fluorescence interference. These new methods are divided into Multiply Enhanced Parametric Spectroscopy (MEPS) and Multiply Enhanced Nonparametric Spectroscopy (MENS), depending upon the spectroscopic characteristics for site-selective applications. The characteristics of MEPS and MENS are found to be quite different and depend upon the number and separation of the sites, the power of the lasers, the relative shifts of the levels, and the correlation effects in the inhomogeneous broadening. The feasibility of MENS and the site-selective capability of both CARS and MENS is demonstrated experimentally with the use of the pentacene: p-terphenyl system as a model.

1 SN-labelled nitrite was used to determine the amount of nitric oxide bound to unheated compared to heated myoglobin. Heated samples contained twice the amount of 1 5N as unheated samples. The globin portion was likely detached from the myoglobin by heating, and two sites for binding of nitric oxide were therefore made available.

Experiments were designed to determine the effect of the chemical state of myoglobin and presence of ascorbate on the conversion of nitrite to nitrate. In model systems, nitrate was not formed when nitrite was incubated in the presence of either metmyoglobin or ascorbate. However, most of the added nitrite was converted to nitrate when both ascorbate and metmyoglobin were present. It is suggested that ascorbate reduces metmyoglobin to myoglobin, and then, the myoglobin is oxidized simultaneously with nitrite to form nitrate. In cured meat products, a detectable level of nitrate was formed in the absence of ascorbate, but in the presence of ascorbate the level of nitrate formed was greater. The explanation suggested was that endogenous reductants in meat could play the same role as ascorbate in model systems. Such endogenous reductants were responsible for more than half of the nitrate formation in meat products containing sodium ascorbate.

When a cured meat model system was made from white muscle it contained less residual nitrite than if it were made from a red muscle; this effect is due to the lower pH of white muscle. If the pH of red and white muscle is similar then the slightly lower residual nitrite in products made from red muscle probably is due to the greater content of myoglobin in red muscle. INTIiODUCTION CONSIDERABLEATTENTION has been focused recently on the use of nitrite in foods. The reason for this is twofold. First, a potential exists for reaction of nitrite with amines or amides to form N-nitroso compounds which are carcinogenic. Second, the residual nitrite content of cured meats represents one source of nitrite consumed by humans. Since such residual nitrite is a known measurable source, it deserves some scrutiny in terms of not only significance but also in regard to procedures for influencing the level of residual nitrite in the finished product.Some of the nitrite added to meat for curing disappearsthat means it cannot be identified analytically as residual nitrite nor can it be accounted for via known reaction pathways. A review of work pertinent to the fate of nitrite has been made by Cassens et al. (1974), and a complete account of aspects regarding the use of nitrite in meat products is found in the proceedings of the Symposium edited by Krol and Tinbergen (1974).Muscles are composed of muscle fibers; muscle fibers consist of at least two distinctly different types known generally as red and white (Cooper et al., 1969).'The gross properties of a-muscle result from the ratio of the two types of fibers present. Visual color, for example, is a reflection of predominant fiber type within a muscle, and usually varies consistently among different muscles. This is readily apparent on the cross-sectional surface of a ham which shows several muscles of different degrees of color. Red muscle fibers have a higher myoglobin content, more lipid and higher activity of oxidative enzymes than do white fibers. White muscle fibers contain inore glycogen than red muscle fibers; therefore, postmortem glycolysis results in a lower pH in white muscle (predominance of white fibers) than in red muscle.The objective of the work reported herein was to determine the effect of muscle type on residual nitrite in a model cured meat system. The rationale was to develop information about the possibility of regulating residual nitrite in cured meat by utilizing the natural characteristics of the fresh meat selected for further processing. MATERIALS & METHODSLONGISSIMUS WAS used as a white muscle, Trapezius as a red muscle, and white and red portions were taken from the Semitendinosus (Beecher et al., 1965). All samples were excised from the carcass 1 day postmortem, frozen in liquid nitrogen and pulverized with a blendor. After pH was measured, 5 ml of solution containing sodium nitrite was added to log of muscle sample to make final 156 ppm nitrite and mixed well with a plastic rod. In other aliquots of some samples, pH was adjusted; lactic acid was us...