Handbook of Milk Composition

Bozzano G Luisa

• Editore: Academic Press
• Anno: 1995
• ISBN:
  9780080533117
• Argomento: Ciencias biológicas
• Categoria: Zoología

This informative treatise offers a concise collection of existing, expert data summarizing the composition of milk. The Handbook of Milk Composition summarizes current information on all aspects of human and bovine milk, including: sampling, storage, composition, as well as specific chapters on major and minor components such as protein, carbohydrates, lipids, electrolytes, minerals, vitamins and hormones. The book also features comprehensive coverage of compartmentation, host-defense components, factors affecting composition, composition of commercial formulas, and contaminants.* Reliable data on the composition of human and bovine milks.
* Discusses the many factors affecting composition.
* Composition tables make up 25-30% of the total book.
* Problems concerning sampling and analysis are described.
* Should appeal equally to industry and academia.
* Also of interest to developing countries in need of information on infant nutrition and agricultural development

CHAPTER 1

Introduction

ROBERT G. JENSEN

I. Purpose

Macy et al. (1953) in their classic publication, “The Composition of Milks,” summarized the data then available on the composition and properties of bovine, human, and goat milks. The effects of time postpartum (stage of lactation) were included. Macy’s (later Hoobler) results from her extensive research were published (Macy and Kelly, 1961). The composition of milks from many animals were collected by Jenness (1974). Listings of the components in infant formulas are available (Tsang and Nichols, 1988). However, since the publications of Macy and colleagues, there has been no effort to compile and summarize in one volume the composition and properties of the milks and infant formulas used for food nor of the milks from other mammals for which reliable data exist. There is no single source of this information for the workers who are interested in any aspect of milk. My primary purpose for preparing our book is to provide this source.

Advances in analytical methods provide another reason for publication of the “Handbook of Milk Composition.” Milk can be analyzed with sensitivity, resolving power, and speed that were impossible in years past. One of the results of improvement of sensitivity is that hitherto unknown or unrecognized compounds are detected. Thus, the complexity of milk as a system designed to deliver nutrients and nonnutritive messages to the neonate has increased.

An example of the impact of a new analytical procedure is the determination of bovine milk fatty acids by gas–liquid chromatography (GLC). The analysis which required weeks in the past is now routinely done in about 2 hr (Jensen et al., 1991). The identities and amounts of fatty acids in many samples can be quickly obtained. The new data are much more reliable and comprehensive.

My contributing authors were asked to report the data which in their opinions were the most reliable and to discuss problems with sampling, storage, and analysis which might influence composition. They were instructed to use, when possible, hours or days instead of colostrum, transitional, and mature to describe age postpartum. We prefer this term to the clumsy phrase, stage of lactation. They were required to report their data at wt/dl with use of SI units optional. Those who were gathering information on bovine milk were reminded that much of this is consumed in the pasteurized homogenized form although few data are available on this product. The length of the contributions varies, primarily because this was left to the discretion of the authors. Some sections are short, e.g., “Bovine Milk Proteins,” because comprehensive, current texts are available. Other sections, notably “Carbohydrates,” are long because there is no single source of information available on the subject. We have tried to provide the best data on composition that are now in the literature.

Since imitation is the highest form of flattery we will paraphrase from the preface of Macy et al. (1953). She recognized the importance of milk as a food for all age groups and mentioned the difficulties involved in gathering information (her group examined 1500 references) and the general inadequacy of knowledge of milk components. It was anticipated that the survey would be useful to investigators and those working directly on infant nutrition either with human milk or formulas. All of these reasons are valid today, perhaps even more so. This is because of the increased incidence of breastfeeding in Western countries, the recognition that human milk provides protection against diseases, e.g., diarrhea, endemic in the Third World, and that it may be needed for optimal growth and development of infants and their performance as adults.

II. General Description of Milks

Milks contain, with some exceptions, the nutrients required for the growth and development of the neonate. If the development time is short then the milk is nutrient dense. All milks contain specific proteins, fats designed to be easily digested, most have lactose, minerals, vitamins, and other components which may have important roles. These are organized as follows: lipids in emulsified globules coated with a membrane, proteins in colloidal dispersion as micelles, and most minerals and all lactose in true solution (Jensen et al., 1991).

For the guidance of the reader we present, in Table 1, proximate analyses of bovine, human, goat, and sheep milks.

TABLE I

Proximate Composition (WT%) of Bovine, Human, Goat, and Sheep Milks^a

^aJenness (1974).

References

Jenness, R., The composition of milk. Larson, B.L., Smith, V.R., eds. Lactation. New York: Academic Press; 1974;Vol. III:3–107.

Jensen, R.G., Ferris, A.M., Lammi-Keefe, C.J. The composition of milk fat. J. Dairy Sci. 1991;74:3228–3243.

Macy, I.G., Kelly, H.J., Human milk and cow’s milk in human nutrition. Kon, S.K., Cowie, A.T., eds. The Mammary Gland and Its Secretion. New York: Academic Press; 1961;Vol. II:265–304.

Macy, I.G., Kelly, H.J., Sloan, R.E. The Composition of Milks. National Academy of Science and National Research Council, Publication 254, Washington, DC. 1953.

Tsang, R.C., Nichols, B.L. Nutrient content of infant formulas. In: Tsang R.C., Nichols B.L., eds. Nutrition during Infancy. Philadelphia: Hanley and Belfus; 1988:418–424.

CHAPTER 2

The Structure of Milk: Implications for Sampling and Storage

A. The Milk Lipid Globule Membrane

THOMAS W. KEENAN and STUART PATTON

I. Intracellular Origin and Growth of Milk Lipid Globules

Membrane and membrane-associated material which surrounds the triacylglycerol-rich milk lipid globules commonly is referred to as the milk fat or milk lipid globule membrane (MLGM hereafter). This material originates from specialized regions of apical plasma membrane of mammary epithelial cells, and from endoplasmic reticulum (ER) and perhaps other intracellular compartments. That portion of the MLGM derived from apical plasma membrane, termed the primary membrane, has a typical bilayer or unit membrane appearance, with an electron-dense material on the inner membrane face. That component derived from ER lacks bilayer membrane structure, primarily is composed of proteins and polar lipids, and covers the surface of the lipid droplets within the cell. Constituents of this coat material mediate intracellular fusions through which droplets grow in volume and also may be involved in interaction of droplets with plasma membrane.

A. Droplet Formation

Earliest intracellular precursors of milk lipid globules appear to originate from ER. Triacylglycerols appear to accumulate at focal points on or in the ER membrane (Dylewski et al., 1984). Whether this accumulation of triacylglycerols is due to localized synthesis or accretion is unknown. It has been suggested that triacylglycerols accumulate between the halves of the bilayer membrane and are released from ER into the cytoplasm as droplets coated with the outer or cytoplasmic half of the ER membrane (Long and Patton, 1978; Scow et al., 1980). Some morphological evidence supporting this suggestion has been obtained (Patton and Keenan, 1975; Zaczek and Keenan, 1990), but information that would prove or disprove this hypothesis is lacking.

B. Growth of Droplets

By whatever mechanism they originate, milk lipid globule precursors first appear in the cytoplasm as small (diameters < 0.5 μm) droplets that have a triacylglycerol-rich core surrounded by a granular coat material lacking unit-like (or bilayer membrane structure, but that in localized regions appears thickened, with tripartite-like structure (Dylewski et al., 1984; Deeney et al., 1985). Small lipid droplets, termed microlipid droplets, appear to grow in volume by fusions with each other. Fusions give rise to larger droplets, termed cytoplasmic lipid droplets, operationally defined as those droplets with diameters > 1 μm.

In addition to observations made by electron microscopic examination of fixed and sectioned material, the nature of the surface coat material on intracellular lipid droplets has been explored through isolation and compositional analysis of droplets (Dylewski et al., 1984; D...