Food Science Commons^™

Freeze Texturation Of Proteins: Effect Of The Alkali, Acid And Freezing Treatments On Texture Formation, Frisco I. Consolacion, Paul Jelen

Food Structure

The effects of alkali extraction, isoelectric precipitation, and rate of ice crystal formation on protein interaction in the freeze texturization process were studied , The protein isolate was obtained from mechanically deboned poultry meat residues by extraction with NaOH at pH 10.5 and precipitation by HCl at pH 5, 0, The presence of large molecular weight subunits in the protein isolate was revealed by SDS-polyacrylamide gel electrophoresis. Scanning electron microscopy demonstrated the nature of the fiber formation and protein cross-linking as affected by freezing at -25'C or -196'C. The transformation of the level of protein organization from the lumpy or …

Action Of Polyphosphates In Meat Products, D. F. Lewis, Kathleen H.M. Grooves, J. Hilary Holgate

Food Structure

The action of polyphosphates on meats has been examined in studies using different meats and has been compared with other treatments. The results were monito red by recording cooked yield and observing changes in structure by electron microscopy. Four possible characteristics of polyphosphates are considered: pH, sequestering action, ionic strength and as an ATP (adenosine triphosphate) analogue. In the conditions used in these experiments, the pH-buffering effect of polyphosphates is found as the principal characteristic in meat products.

Some meats were found to be more affected by polyphosphates than others and:. hypothesis is developed to explain this. It is proposed …

Microscopal Observations On The Structure Of Bacon, C. A. Voyle, P. D. Jolley, G. W. Offer

Food Structure

Commercially processed salt-treated pig longissimus dorsi muscle, in the form of bacon slices, sometimes shows localized variations in the light-scattering properties of the tissue. The phenomenon is described as 'tiger-stripe'. A study of areas of tissue showing such variations, using electron microscopy, has revealed differences in the structure at the myofibrillar level. Areas which appear dark when viewed by incident illumination show ordered myofibrillar structure, whereas areas which appear light under similar viewing conditions appear to be disordered.

Rheological And Particle Size Changes In Corn Oil-In Water Emulsions Stabilized By 7s Soybean Proteins, M. Reeve, P. Sherman

Food Structure

The viscoelastic properties and mean drop size (Om) of corn oil-in-water emulsions stabllized by 0.5-1.5% (wt/wt) 7S soybean proteins have been examined at various pH•s . Changes 1n these parameters when the ernul sions were stored at 4-5°C were measured also. Viscoelasticity ~arameters were derived from time-dependent strain behaviour at a constant low shear stress of 41 .7 dyne cm- 2. Although each emulsion showed a continuous increase in D during storage, due to drOIJ coalescence, 1l"s instantaneous elastic modu l us (G) rose initially over several days to an op£imum value and then subsequently decreased, The trends in D …

Ultrastructure Of Maize Starch Granules. A Review, Daniel J. Gallant, Brigitte Bouchet

Food Structure

History of starch granule ultrastructure and the principal data obtained on maize starch granules are analyzed. New results are developed: i) growth and development of the maize starch granules during maturation depend on the maize varieties and the tissue site in the kernel, especially the horny and flloury endosperms; ii) cytochemical studies of the starch granules differing from their amylose/amylopectin ratio show important differences in the distribution of their crystalline and amorphous zones that explain their behaviour under some hydrolytic treatments; iii) complexing between colloidal gold labelled concanavalin-A and starch (amylopectin) permits new and greater specificity to ultrastructural study of …

Observations On The Microstructure And Rheology Of Ovalbumin Gels, I. Heertje, F. S.M. Kleef

Food Structure

Understanding the gelation behaviour of proteins is of importance in order to be able to influence the properties of many food systems and it may lead to proposals for product or process improvement . In this context the formation of heat-set ovdl bumin gels. in different media , has been studied by microstrucmral. rheological and conformational observations. An oval bumin/ water geL prepared at pH 5, shows a granular. inhomogeneous microstructure. At this pH the re are both many interand intramolecu lar interactions. and network formation occurs via aggregates of folded, globular protein chains. On the other hand , gels …

Changes In The Microstructure Of Skipjack Tuna During Frozen Storage And Heat Treatment, L. E. Lampila, W. D. Brown

Food Structure

Samples of fresh, frozen and heat- treated skipjack tuna muscle were observed by scanning electron mieros copy. The photomicrographs were used to assess changes in the microstructure of fish muscle during frozen storage and thermal processing . Differences noted in frozen tissue could be related to the formation of gaps between fibers and the deformation of muscle fibers . No freeze mediated damage to the cell wall was observed at the lower limits, 20,000x, of high resolution scanning electron microscopy. The degree of muscle fiber shrinkage and erosion and the behavior of certain protein fractions was found to be affected …

Cryo-Scanning Electron Microscopy Of Microorganisms In A Liquid Film On Spoiled Chicken Skin, T. A. Mcmeekin, D. Mccall, C. J. Thomas

Food Structure

Cryo-scanning electron microscopy was used to examine bacteria which had grown in a liquid film on the skin surface of poultry carcasses. Pits or void zones surrounding bacteria on ethanol-dehydrated, critical point dried (CPD) samples were not found on washed or untreated specimens frozen prior to examination by scanning electron microscopy (SEM). However, pits equivalent to those produced during chemical fixation and dehydration were formed when skin tissue was treated with ethanol prior to freezing. We conclude that the pits are dehydration artifacts caused by the chemical preparative methods employed rather than the result of degradation of film proteins by …

Structural Characteristics Of Eleusine Corocana (Finger Millet) Using Scanning Electron And Fluorescence Microscopy, C. M. Mcdonough, L. W. Rooney, C. F. Earp

Food Structure

The objective of this study was to document the microstructure of finger millet wlth scanning electron and fluorescence microscopies. Finger millet is an utricle which is spheri ca 1 and about 1 . 5 ITlT1 in diameter. The membranous peri carp of finger millet was loosely associated with the seed at maturity. Beneath the loose pericarp wa s a five-layered testa that varied from red to purple in color. The outer layer was the only testa layer that autofl uoresced, suggesting the presence of phenolic acids, i .e., ferulic acid. The aleurone layer was beneath the testa , and was …

Lipolytic Changes In The Milk Fat Of Raw Milk And Their Effects On The Quality Of Milk Products, E. Kirst

Food Structure

Lipolytic changes in milk rat affect sensory attributes and techno logicaI properties of milk and milk products. They are affectcd by physiologal, thermal . and biochemical factors as well as by the mechanics of fluids Lipolytic processes in milk are intensified by modern processing methods.

In this review. special attention has been paid to runinant- related feeding of dairy cows. foaming of milk. mechanical and thermal influences and the growth of psycllrotrophic bacteria.

Feeds deficient in energy affect the chemical composition of the milk fat. Tests have shown that on an average. approximatey 55% of free fatty acids in the …

Current Concepts Of Muscle Ultrastructure With Emphasis On Z-Line Architecture, M. Yamaguchi, H. Kamisoyama, S. Nada, S. Yamano, M. Izumimoto, Y. Hirai, R. G. Cassens, H. Nasu, M. Muguruma, T. Fukazawa

Food Structure

Invertebrate striated muscle, the Z-line, which defines the sarcomere length, presents diverse structural patterns both in cross section and in longitudinal section. Conflicting models have been proposed to explain the microscopic observations. The protein composition of the Z- line structure is unresolved. o: -Actin in is widely accepted as a Z-line component, and actin filaments extend into wide Z-lines. Based on recent findings from our laboratory and others, we developed a new model applicable to wide and narrow Z-lines. The model allowed the observed ultrastructural patterns of Z-lines to be simulated. Improved electron microscopic techniques should allow further progress to …

Microstructure Of Lentil Seeds (Lens Culinaris), Joe S. Hughes, Barry G. Swanson

Food Structure

Scanning electron microscopy (SEM) was used to investigate the microstructure of five cultivars of lentil seeds (Lens culinaris). Lentil cot yledons contain sphericai starch granules surrounded by protein bodies similar to starch granules and protein bodies observed in cotyledons of other food legumes. Examination of the lentil seed coat in cross - section revealed outer palisade and inner parenchyma layers characteris tic of legumes. The subepidermal layer, however, is comprised of hourglass cells and is found primarily in the area surrounding the hilum and the entire lentil seed coat is thinner than the seed coat s of most other food …

The Skinned Fiber Technique As A Potential Method For Study Of Muscle As A Food, R. G. Cassens, T. J. Eddinger, R. L. Moss

Food Structure

Skeletal, smooth and cardiac muscle cells can be skinned by physical means or a variety of chemical techniques. The skinned fibers have been used to study the molecular mechanisms of contraction and the regulation of contraction by ca++. Skinned fiber preparations are also useful for study of muscle as a food. For example, it is now possible to determine fiber type of skinned fibers following study of their physical properties.

Microstructure Of Mealy And Vitreous Wheat Endosperms (Triticum Durum L.) With Special Emphasis On Location And Polymorphic Behaviour Of Lipids, A. Al Saleh, D. Marion, D. J. Gallant

Food Structure

Dark inclusions observed in osmiophilic zones, already described in mature wheat endosperm using transmission electron microscopy, were confirmed by freeze-fracture electron microscopy to be lipids. The polar lipids (glycolipids, phospholipids, free fatty acides, monoglycerides) were organized in a liquid crystalline phase. The reversed hexagonal or HII phase should be the main lattice which might arise from the transition of lipids present in membranous structures as a lamellar phase. This transition was caused by dehydration occurring during maturation. It is suggested that the water-dependent lamellar hexagonal phase transitions are of considerable importance in cereal food technology.

Features Of Food Microscopy, D. F. Lewis

Food Structure

The value of food microscopy is judged by its practical application to food handling. Hence microscopists must explain the relevance of their findings to food technologists. The food microscopist has to deal with materials that are particularly difficult to prepare for microscopy because they often contain high levels of fat, air, sugar, salt, starch or acid. Sometimes the methods used are unorthodox and could be regarded as questionable by microscopists in more traditional disciplines. This paper considers the relationship between food microscopists, food technologists and other microscopists. An approach to interpretation of images is based on the following features. 1) …

Texture And Microstructure Of Soybean Curd (Tofu) As Affected By Different Coagulants, J. M. Deman, L. Deman, S. Gupta

Food Structure

The coagulating properties of five coagulants and the nature of the curd obtained from soymilk was investigated . Viscosity changes during coagulation were studied using a Namctrc Vibrating Sphere Viscometer and texture measurements were made by compression and computer assisted analysis. pH and amount of solids in the whey were determined. The microstructure of the tofu was examined by sca nning electron microscopy. It was observed that CaCI2.2H20 and MgCI2.6H20 coagulaled the milk in stantl y while CaS04 .1/2H20. glucono delta l a~tonc (GOL) and MgS04 .7H20 acted comparatively slowly. The t exture of the curd was greatly influenced by …

Mucilage In Yellow Mustard (Brassica Hirta) Seeds, I. R. Siddiqui, S. H. Yiu, J. D. Jones, M. Kalab

Food Structure

Release of mucilage from yellow mustard (brassica hirta, also known as Sinapis alba) seed coats (hulls) was studied by optical and scanning electron microscopy. Micrographs were obtained of the mucilage which had exuded from briefly moistened seeds and dried subsequently in the form of small droplets on the seed surface.

The mucilage collected from the seed surface and mucilage isolated on a larger scale from seed hulls was hydrolyzed with sulfuric acid and the hydrolyzates were analyzed for sugar composition. Galactose, glucose, and galacturonic acid were found to be major components and mannose, arabinose, xylose, and rhamnose were minor components. …

The Development Of Structure In Whipped Cream, B. E. Brooker, M. Anderson, A. T. Andrews

Food Structure

Interfacial changes occurring during the formation of whipped cream were followed using transmission and scanning electron microscopy. During the initial stages of whipping, air bubbles were stabilized by adsorbed 8-casein and whey proteins with little involvement of fat globules. The adsorption of fat to a i r bubbles occurred ~.then the globule membrane coalesced with the protein a ir-water i nterface . As a res ult, fat was brought into direct contact with air but only rarely did it spread at the ai.r-fat interface. The crosslinking of fat globules adsor bed t o adjacent air bubbles by chains of coalesced …

The Structure Of Gluten Gels, A. M. Hermansson, K. Larsson

Food Structure

This paper reports on a combined electron microscopy and X-ray diffraction study of gluten gel, in which conventional gluten, a delipidized gluten sample and a storage protein fraction obtained by salt-fractionation were used. It can be concluded that the gluten gel is a continuous phase of densely packed protein units. Other structural components such as air ce lls, lipid droplets, liposomes, fiber residues, starch granules etc. are dispersed in the continuous matrix. The space available for water is strictly limited in the continuous phase due to the dense packing of protein molecules. Water that is not completely separated from the …

Mechanical Properties Of Cheese, Cheese Analogues And Protein Gels In Relation To Composition And Microstructure, M. L. Green, K. R. Langley, R. J. Marshall, B. E. Brooker, A. Willis, J. F. V. Vincent

Food Structure

Samples of commercial Cheddar cheese, experimental Cheddar cheeses made from heated, ultrafiltration-concentrated mllks, processed cheese analogues and whey protein gels of defined composition were examined microscopically and some fracture and deformation properties were determined. Surfaces of cheese prepared by critical point drying and those examined frozen were comparable in microstructure. As the concentration factor of the milk used for experimental c heesemaking increased, the cheese became more resistant to reversible deformation, the work required to cut with a wire or break wf th a hammer increased and the microstructure showed that the protein matrix was coarser. The force to deform …

Relationship Between Microstructure And Susceptibility To Syneresis In Yoghurt Made From Reconstituted Nonfat Dry Milk, V. R. Harwalkar, Miloslav Kalab

Food Structure

Increase in the density of protein matrices i n yoghurt samples conta ining 10 to 30% total milk sol ids was studied by scanning electron micros copy and was corr e lated with a decrease in syneresis. Casein particles which formed chains and clusters in the protein matrix were largest in the 10% total solids yoghurt and their dimensions were decreased as the total solids contents were increased. This observation was confirmed by transmission electron microscopy of thin sections. An attempt has been made to explain the discrepancy between results on syneresis obtained by a drainage and a centrifugation method …

Ultrastructural Studies On The Cultivation Processes And Growth And Development Of The Cultivated Mushroom Agaricus Bisporus, D. A. Wood, G. D. Craig, P. T. Atkey, R. J. Newsam, K. Gull

Food Structure

Scanning electron microscopy (SEM) , transmission electron microscopy and light microscopy have been used to study various processes in the cultivation of the edible mushroom Agaricus bisporus . Mushrooms are cultured on composted wheat straw. The microbial degradation processes during composting have been visualised by TEM and SEM and correlated with microbiological studies . Various modes of attack by the microorganisms on the plant cell walls can be seen. Most rapid degradation occurred on the cuticle and phloem and spread to other cell types. Microbial attack was found to be nonuniform between tissue types and individual cells. The mycelium of …

The Size Distribution Of Bovine Casein Micelles: A Review, C. Holt

Food Structure

This review considers the average size and size distribution of bovine casein micelles as measured by electron microscopy, light scattering and controlled pore glass chromatography, and the origin and biological function of the size distribution.

Recent work by electron microscopy has given average sizes in reasonable agreement with measurements on the same milk sample by light scattering . It is suggested that natural variations in averaqe micelle size and overestimation of micelle radii by light scattering methods as well as deficiencies in electron microscopical methodology were responsible for past discrepancies.

Electron microscopy and controlled pore glass chromatography provide evidence that …

Structure Of Coarse And Fine Fractions Of Corn Samples Ground On The Stenvert Hardness Tester, Y. Pomeranz, Z. Czuchajowska

Food Structure

Kernels from a pair of isogenic lines (with regard to hardness) and two commercial hybrids of dent corn (that varied in hardness) were ground on the Stenvert Hardness Tester and separated by sieving into coarse (>0.710 mm) and fine (<0.500 mm) fractions. The corn samples differed little in oil contents. The coarse particles from the hard corn samples were angular and sharp-edged; those from the soft corn samples were rounded. The yield of coarse particles was higher and they contained less oil in hard than in soft corn. Fine particles from all four corn samples had higher oil content than the coarse particles. Visual examination, observation at low magnification under a light microscope, and use of a scanning electron microscope revealed consistent differences in the extent and mode of corn kernel breakdown during grinding. Particles in the coarse fraction from hard kernels were to a large extent intact with little exposure of their contents. In the soft kernels, particles in the coarse fraction were broken extensively and their contents exposed. It is postulated that differences in the extent of mechanical breakdown and oil content are related to differences in shelf life of corn grits.

Relation Between Microstructure, Destabilization Phenomena And Rheological Properties Of Whippable Emulsions, W. Buchheim, N. M. Barfod, N. Krog

Food Structure

The structure of spray-dried whippable emulsions (toppings) containing different types of lipid surfactants, was investigated by electron microscopy using the freeze-fracture technique. The size distribution of the lipid particles within the powders varied with the type of the surfactant used. After reconstitution of the topping powders in water. a strong destabilization phenomenon took place to an extent depending on the type of the surfactant. Simultaneously a crystallization of coalesced lipid particles occurred along with an increase in viscosity of the emulsions. The degree of crystallization was measured by p-NMR. It has been concluded that these phenomena are closely related to …

Thermal Analysis Microscopy For The Study Of Phase Changes In Fats, J. M. Deman, A. N. Mostafa, A. K. Smith

Food Structure

An investigation was carried out using the Mettler FPBOO Thermosystem to study polymorphic transitions of several monoacid triglycerides and hydrogenated Canola oil. The system includes a central processing unit connected with a thermal microscopy hot stage that allows the measurement of heat flow to the scrnple . Scanning electron microscopy was also used to examine the same samples after osmium tetroxide fixation . The results obtained relate phase transitions occurring during heating and cooling with the morphology of the various crystal structures.

Ultrastructural Ultilization Of Plants By Herbivores, L. H. Harbers

Food Structure

Study of the patterns of ruminal digestion of forages enhances the nutritional knowledge of how specific plant tissues are digested and adds its own dimension by characterizing the specific cells and the complex interactions of ruminal microflora with those tissues. A common pattern of digestibility exists for mono- and dicotyledon leaves: mesophyll and phloem are degraded readily, and sclerenchyma slowly, whereas cuticle and the remaining vascular tissues are rarely utilized . Digestion of stems is limited to parenchymal tissues in monocotyledons and to cortex and parenchyma in dicotyledons. Epidermal silica and cuticle are undigestible and restrict microbial entrance. Calcium oxalate …

Scanning Electron Microscopic Study Of Rockfish Preserved At Either Ambient Temperature Or By Isothermal Freeze-Fixation, L. E. Lampila, V. Mohr, D. S. Reid

Food Structure

Fresh rockfish (Bocaccio, Sebastus paucispinis) fillets were blast frozen and stored at either -5 °C or -20 °C for 60 days . At defined sampling intervals, speci mens were removed and chemically fixed at either ambient temperature or isothermally, at the respective storage temperatures (-5 °C or -20°C) . The results indicated that isothermally freeze - fixed specimens showed a degree of crushing and/or distortion of the muscle fiber, the deposition of presumed ice crystals in the cell membrane, the multi-dimensionality of connective tissue and the preservation of fine detail . In specimens fixed at ambient temperatures , structura l …

Early Research On The Fibrous Microstructure Of Meat, H. J. Swatland

Food Structure

The older scientific literature on the histology of skeletal muscle describes the trans verse fragmentation of myofibrils to form sarcomere disks and the attachment of Z lines to the sarcolemma in contracted muscle. These phenomena may now be explained by recent research on the cytoskeletal framework of muscle fibers, particularly desmin and vinculin. The formation of sa rcomere disks might be developed as a simple method to study cytoskeletal integrity in meat. In early research, contraction bands and the disappearance of transverse striations during contraction caused considerable confusion with ordinary light microscopy. These problems were largely resolved by the use …

Changes In Typical Organelles In Developing Cotyledons Of Soybean, K. Saio, K. Kondo, T. Sugimoto

Food Structure

Soybean cotyledonary cells harvested every 5-10 days at 15 to 60 days after flowering (OAF), were investigated by means of light and transmission electron microscopy. In the early developing stages (15-20 OAF) most of the cells were occupied by large, centrally located vacuoles while the cytoplasm was restricted to a thin layer against the cell wall and contained numerous ribosomes, mitochondria, plastids, small amounts of endoplasmic reticulum (ER) and minute lipid bodies. At about 25 OAF, spherical organelles which contained protein, lipid and sugar (PLS bodies), appeared and then increased in number and in size. Vacuoles had protein deposits lining …