Observations on the Air-Serum Interface of Milk Foams

A new rapid method for the preparation of milk foams for transmission electron microscopy is described . The air-serum interface of foams made from skimmed milk consists of a uniform electron dense layer (5 nm thick) to which casein micelles become secondarily attached . Changes in bubble volume lead to the formation of folds of excess interfacial material which project into the aqueous phase. Using collapsed bubble ghosts to study the attachment of micelles to the airserum interface it was concluded that neither disulphide bridge formation nor hydrophobic interactions were of major importance. Similar preparations of interfacial material but without casein micelles attached were prepared from milk plasma and solutions of ~- lactoglobulin. The former fragmented slowly into small particles at room temperature but very rapidly when heated to 55° C whereas material derived from~- lactoglobulin was quite stable. The destruction of bubble ghosts in skimmed milk by heating is attributed to interface breakdown rather than to micelle detachment. The air-serum interface, of which casein micelles do not form an integral part, probably consists of a mixture of globular whey proteins and some soluble caseins . Thus, using high pressure liquid chromatography, foamed milk plasma from which bubble ghosts had been removed was shown to be depleted in both a- lactalbumin and ~- lactoglobulin

Recent Developments in the Application of X-ray Microanalysis to the Study of Food Systems

Low temperature scanning electron microscopy in conjunction with X-ray microanalysis can be used to study not only the internal structure of intact bulk food systems but also the distribution of their constitutive chemical elements. However, the considerable practical problems that are usually encountered when performing X-ray analysis on frozen samples include: a) the controlled deposition of a good quality carbon film to prevent charging, b) producing digital elemental distribution maps of elements whose X-ray spectral energy peaks partially or completely overlap and c) controlling the plane of fracture through the specimen and ensuring that the resulting topography allows meaningful analysis to be performed. The quality and control of carbon film deposition is greatly improved by the inclusion of a turbomolecular pump in the vacuum system and by using thickness monitoring of the carbon film during deposition. However, the complications of energy peak overlap in digital X-ray mapping can only be overcome by using a procedure which produces maps corrected for all of the spectrum processing routines normally available in quantitative programmes. Another advantage of this approach is that statistics such as FIT index {see appendix) and standard deviation are available for each pixel. Problems associated with fracturing are avoided if the internal structure of materials is revealed using cryo-mi11ing. This procedure uses a rotating diamond cutting tool to produce a very flat surface on the frozen specimen which is ideal for X-ray analysis and for image analysis of structural components. Quantitative X-ray mapping of milled cocoa beans shows that this preparation procedure does not cause smearing of the chemical components across the surface of the specimen

The Crystallization of Calcium Phosphate at the Surface of Mould-Ripened Cheeses

Samples of several different types of mouldripened cheese were examined by light and electron microscopy for evidence of calcium phosphate crystallization near their surfaces , which, it was predicted , should result from the pH changes that take place in the rind during ripening . Transmission electron microscopy showed that characteristic convoluted crystals appeared in the rind as mould growth developed and that there was good evidence that at least some of the crystal nucleation was taking place inside effete hyphae. Light microscopy showed that this coincided with the appearance of birefringent, phosphate-rich crystals in the cheese rind which were tentatively identified as calcium phosphate. This was confirmed by a ser ies of experiments in which frozen and fractured cheese was examined by scanning electron microscopy in conjunction with digital X-ray spectrometry . This showed that the rind contained very high levels of calcium and phosphorus which could not be attributed to surface drying because in the same area, there was no corresponding concentration of other elements, such as chlorine. It is proposed that the high pH generated by the surface flora causes the precipitation of calcium phosphate from the continuous aqueous phase . In addition, the inhibitory effect of casein on the phase transformation to crystalline calcium phosphate is probably removed by the action o f extracellular proteases from the mould. The resulting depletion of calcium phosphate in the aqueous phase establishes a gradient which is responsible for the diffusion of more of the salt from deeper parts of the cheese and the progressive concentration in the rind

HOUSEHOLD NUTRIENT DEMAND: USE OF CHARACTERISTICS THEORY AND A COMMON ATTRIBUTE MODEL

A characteristics model, which assumes goods generate a common set of attributes but no unique attribute, is described. The model yielded two equations which were estimated. One was a set of hedonic price equations in which the price paid for each food purchased was a function of imputed attribute prices. This set of equations was estimated at the household level. Nutrient demand equations were estimated across households. Imputed prices, income, and household characteristics including location, size, education, age distribution, and race affected nutrient demand levels.Consumer/Household Economics,

The Adsorption of Crystalline Fat to the Air-Water Interface of Whipped Cream

The interfacial structure of air bubbles in normal and defective whipped creams were compared, using freeze fracturing and transmission electron microscopy , in an attempt to understand the underlying mechanism of t he observed gross differences in their whipping times and overruns . In normal whipped creams sparsely distributed fat crystals were found to have penetrated some of the bubbles and were lying in the plane of the air/water interface. In defective whipped creams , large numbers of needle-like crystals had penetrated the air/water interface of every bubble and, as a consequence, reduced numbers of fat globules were found to have adsorbed . There was also morphological evidence that the crystals reached the interface before the milk fat globules during the whipping process . The presence of large masses of free fat in the aqueous phase of whipped cream, on whose surface arrays of very long fat crystals were found, suggested that the needle-like crystals were dislodged by the shear forces generated during whipping and were then free to adsorb to bubbles . The detection of such large amounts of free fat indicated a large scale damage to fat globules during processing with the consequent escape of both crystalline and liquid fat. Possible mechanisms to account for the low overrun and long whipping times in defective creams are discussed

The Stabilisation of Air in Foods Containing Fat - A Review

Foods containing aqueous solutions of proteins readily foam when air is introduced into them. When fat is also present, interaction between the two components at the air/water interface may produce a stable foam with characteristic bulk properties. In the case of dairy foams (such as whipped cream), bubbles produced in the whipping process are initially stabilised by the adsorption of protein at the air/water interfaces. Commonly encountered defects in whipping cream arise when large triglyceride crystals, formed in masses of free fat, adsorb to the air/water interface during whipping at the expense of fat globules. In other food systems , fat crystal adsorption is part of the normal stabilizing mechanism. In cake batters produced by \u27creaming\u27 with shortening, air is held in the fat phase and stabilised by .B\u27-gystals; however, bubbles move into the aqueous phase during cooking. Studies with batters in which the air is in the aqueous phase have shown the importance of both protein and .B\u27 -crystals in air stabilisation. The added importance of fat crystals is that they provide extra protein air/water interface for the bubbles as they expand during cooking and, thereby, help to preserve the texture of the final product. The fat protein interactions observed at the air/ water interface of several different foams, provide a unifying mechanism for the stabilisation of air in many diverse food systems

A MARKETING-SYSTEM APPROACH TO REMOVING DISTRIBUTION BARRIERS CONFRONTING SMALL-VOLUME FRUIT AND VEGETABLE GROWERS

Marketing,

State Department of Agriculture Participation in Fresh Produce Marketing in Georgia, Kentucky, North Carolina, and Tennessee

Agricultural and Food Policy,

Removing Distribution Barriers Confronting Small-Volume Fruit and Vegetable Growers: Results of the Tennessee Extension Service Survey

Crop Production/Industries, Teaching/Communication/Extension/Profession,

Produce Growers and Market Development: A Four-State Comparison

Crop Production/Industries,