Factors affecting composition variations

Factors affecting the integrity of spectroscopic data include the variations in sample chemistry, the variations in the physical condition of samples, and the variation in measurement conditions. Calibration data sets must represent several sample spaces to include compositional space, instrument space, and measurement or experimental condition space (e.g., sample handling and presentation spaces). Interpretive spectroscopy where spectra-structure correlations are understood is a key intellectual process in approaching spectroscopic measurements if one is to achieve an understanding in the X and Y relationships of these measurements. 

The gross composition of bovine milk has been reviewed many times (Rook 1961 Laben 1963 Jenness 1974 Johnson 1975 Moore and Rook 1980). These reviews have delineated thoroughly the extent of the variation and factors affecting it. One of the reviews is presented in a previous edition of this volume (Johnson 1975). Consequently, the present discussion is somewhat abbreviated. 

The normal levels of the major mineral constituents of cow s milk are listed in Table 5-1. These are average values there is a considerable natural variation in the levels of these constituents. A number of factors influence the variations in salt composition, such as feed, season, breed and individuality of the cow, stage of lactation, and udder infections. In all but the last case, the variations in individual mineral constituents do not affect the milk s osmotic pressure. The ash content of milk is relatively constant at about 0.7 percent. An important difference between milk and blood plasma is the rela-... 

The unique flavors of wines are due not only to grape flavors but also to those formed during the primary yeast fermentation and any secondary bacterial or yeast fermentation that can occur. Many of the factors affecting fermenta-tions-related flavors remain controversial (e.g., spontaneous versus inoculated yeast fermentations) or are still not well understood. The effects of grape composition, seasonal variations, and the identification of odor impact compounds need much more investigation. However, novel enzymatic syntheses are leading to an increased understanding of the pathways by which fermentation flavors are formed. These topics are discussed in Chapters 6-9. 

Consequently, two major factors affect the rheological properties of the mixture during phase separation (i) the change of composition in the epoxy-rich matrix and (ii) the variation of viscoelastic behavior of the phase-separated blend. The authors employed a two-phase suspension model as proposed by Graebling and Palierne [52] to explain the effect of viscoelastic behavior on the phase-separated mixture ... 

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