Food Science Commons^™

Practical Aspects Of Electron Microscopy In Dairy Research, Miloslav Kalab

Food Structure

Milk products are based mostly on casein micelles, fat globules, and whey proteins. The former two constituents are corpuscular and whey proteins become corpuscular when coagulated. Structural changes in these basic constituents during processing have been studied by electron microscopy. This review discusses the structures of yoghurt, curd, cheeses (hard cheeses, mould-ripened cheeses, cream cheeses, and process cheese), cream, milk powders, and nontraditional dairy products. Defects and deviations from traditional structures of these products are explained where the causes are known. Examples of such causes are foaming of milk, presence of unusual ingredients (bacterial polysaccharides, whey protein concentrates), and alterations …

Structure Of Margarines Made With Low Erucic Acid Rapeseed Oil, J. Hojerova, S. Schmidt, J. Krempasky

Food Structure

Margarine based on hydrogenated low erucic acid rapeseed oil shows a strong tendency to produce an unacceptable grainy structure. This is caused by rapid transition of the B-form into the B-form of fat crystals. Sorbitan esters, monoacylglycerols, and a blend of acylglycerols were investigated as possible B-stabilizers. Polymorphic transitions were evaluated by visual assessment, examination by polarized light microscopy, and x-ray diffraction analysis in margarines prepared on a laboratory scale and containing varying amounts of stabilizers. The evaluation was extended over a 7-week period of storage at 10 C. Sorbitan esters of fatty acids were found to be the most …

Functional Properties And Microstructure Of Chicken Breast Salt Soluble Protein Gels As Influenced By Ph And Temperature, S. F. Wang, D. M. Smith

Food Structure

The effects of different pH's (4 .5 , 5.5, 6.5 and 7.5) and temperatures (30-80 •c) on the functional properties and microstructure of chicken breast salt soluble protein (SSP) in 0.6 M NaCI were investigated. Protein solubility decreased from 98% at pH 6.5 to less than I% at pH 4.3 and below. Salt soluble protein at pH 4.5 produced a discontinuous gel which could not be measured by back extrusion and had an expressible moisture above 80% at all heating temperatures . Aggregated globular microstructures were observed at pH 4.5 by scanning electron microscopy (SEM). Thin-sectioned images as seen by …

Scanning Electron Microscopy Studies Of A Typical Spanish Confectionery Product: "Xixona Turron", M. A. Lluch, M. J. Galotto, A. Chiralt

Food Structure

The microstructure of "Xixona turron" , a typical Spanish confectionery product, made with toasted almonds, sugar and honey, was elucidated, in order to confirm the nature of those physical changes occurring in its manufacturing process, which has not been previously studied. The effect of the major components of "Xixona turron" (oil, proteins and sugar) on its structural c!Jange was established. The initial oil suspension of sugar syrup drops and proteins undergoes a phase inversion , becoming an oil /water emulsion when hot, and a solid-like structure, when the aqueous sugar continuous phase solidifies at room temperature. In order to determine …

Effect Of Chemical Modifications On The Stability, Texture And Microstructure Of Cooked Meat Batters, Andre Gordon, Shai Barbut

Food Structure

The effects of five chemical agents on the stability, texture and microstructure of cooked comminuted meat batters were studied. B-mercaptoethanol (/3-ME), hydrogen peroxide (H20~, ethylenediaminetetraacetic acid (EDT A), urea, and polyoxyetbylene sorbitan monooleate (fween 80) were used. The reduction of disulphide bonds by 8-ME or the oxidation of free sulphydryls by H20 2 prior to cooking did not affect liquid and fat losses during cooking as compared to the control (2.5% NaCI). However, texture profile analysis (fPA) showed that treatment with H20 2 resulted in a harder, more cohesive product than the control and ,8-ME treatments because a more fine-stranded, …

Effect Of Lactose And Protein On The Microstructure Of Dried Milk, V. V. Mistry, H. N. Hassan, D. J. Robison

Food Structure

Skim milk of approximately 3% total protein was ultrafiltered to 16.2% protein and 4.1 % lactose, and then diafiltered to reduce lactose to 2.1% and 0.9%. Total protein con ten t was maintained at approximately 17%. A ponion of the skim milk was condensed in a rising film evaporator to 14.7% protein and 15.7% lactose . All concentrates were spray dried at 120 to 125 °C inlet air temperature and 75 to 80 C outlet temperature using a rotary atomizer in a pilot plant spray dryer . Moisture content of the powders were 4.7 to 6.3% and lactose content ranged …

Distribution Of Amylose And Amylopectin In Potato Starch Pastes: Effects Of Heating And Shearing, K. Svegmark, A. M. Hermansson

Food Structure

The microstructure of potato starch pastes and gels in the concentration range 5-10% (w/w) was studied as a function of shear and heat treatment usi.ng light microscopy. Heating induced extensive swelling of potato starch granules, and the swollen granules filled the whole volume of the starch pastes that were subjected to a minimum of shear. The volume of the aqueous phase outside and in the center of the swollen granules is practically negligible compared to the volume occupied by the walls of the swollen granules. The granules with the lowest gelatinization temperatures swelled quickly without restrictions, so that less water …

Effect Of Extruder Die Temperature On Texture And Microstructure Of Restructured Mechanically Deboned Chicken And Corn Starch, V. B. Alvarez, D. M. Smith, S. Flegler

Food Structure

Proximate composition, textural properties and microstructural changes of mechanically deboned chicken/15% corn starch extrudates were evaluated when restructured at die temperatures of 25, 71, 82, 93 , 104 and ll5°C in a twin-screw extruder. Total sol ids and fat content decreased, whereas protein content increased die temperatures were increased. When die temperature was increased from 71°C to 104°C, apparent stress at failure of extrudates increased by 44 kPa , but decreased at a die temperature of 115°C. Changes in the protein matrix, fat globules and starch granules due to changes i n extruder die temperature were observed by scanning electron …

Relationship Between Microstructure And In Vitro Digestibility Of Starch In Precooked Leguminous Seed Flours, Juscelino Tovar, Alicia De Francisco, Inger Bjorck, Nils-Georg Asp

Food Structure

Precooked flours (PCFs) were prepared by milling boiled and freeze-dried red kidney beans, white beans and lentils. As demonstrated by scanning electron microscopy, PCFs were rich in relatively large particles which contained cell structures filled with starch. In contrast, flours from raw seeds contained a large number of free starch granules. The in vitro a-amylolysis rate ofPCFs was remarkably low, but increased after physical and chemical treatments of the flours. Homogenization resulted in the largest increase of hydrolysis rate. The susceptibility to enzymatic hydrolysis was also enhanced when PCFs were preincubated with pepsin or submitted to additional boiling. These treatments …

Comparison Of The Effects Of Three Different Grinding Procedures On The Microstructure Of "Old-Fashioned" Non-Stabilized Peanut Butter, Clyde T. Young, William E. Schadel

Food Structure

Three different grinding procedures were utilized to prepare "old-fashioned" non-stabilized peanut butters. A leading commercial brand of stabilized peanut butter was used for comparison. The microstructure of each non-stabilized peanut butter was then evaluated with light microscopy and compared to the microstructure of the commercial brand of stabilized peanut butter. Major findings include: (1) dense spatial relationships of protein bodies, starch grains, and cell and tissue fragments that exist in "old-fashioned " non-stabilized peanut butter as compared to the well-dispersed spatial relationships which exist in commercially prepared stabilized peanut butter; and (2) degree of homogenization in the nonstabilized peanut butters …

Textural And Microstructural Properties Of Frozen Fish Mince As Affected By The Addition Of Nonfish Proteins And Sorbitol, K. S. Yoon, C. M. Lee, L. A. Hufnagel

Food Structure

Changes in textural and microstructural properties of washed and unwashed frozen fish mince were studied as affected by the addition of non fish proteins (soy protein isolate, milk protein isolate, egg white, and wheat gluten at 2 , 4 or 6%) and 6% crystalline sorbitol. Soy and milk proteins and sorbitol reduced the hardness of frozen fish mince, while egg white and wheat gluten made the texture firmer without rubberiness developing after frozen storage. All nonfish proteins and sorbitol stabilized the myofibrillar organization by reducing freeze-induced contraction of myofibrils.

The mechanisms of reducing texture hardening appear to be different between …

The Microstructure Of Raw Meat Batters Prepared With Monovalent And Divalent Chloride Salts, Andre Gordon, Shai Barbut

Food Structure

Cold stage scanning electron microscopy (cryo-SEM), transmission electron microscopy (TEM) and light microscopy (LM) were used to examine the effect of NaCl (2.5%), MgC1₂ , CaC1₂ , KCl, LiCl (calculated ionic strength, IS = 0.43) and 1.5% NaCl (IS = 0.26) on the microstructure of comminuted raw meat batters (fat added) and comminuted meat mixes (no fat added). Cryo-SEM revealed that comminuting the lean meat with different chloride salts resulted in the formation of different types of gel structures. Differences were mainly in gel strand thickness, the degree of interlinking between strands and the size of pores within …

Light And Scanning Electron Microscopy Of The Peanut (Arachis Hypogaea L. Cv. Florunner) Cotyledon After Roasting, Clyde T. Young, William E. Schadel

Food Structure

Changes in the microstructure of peanut (Arachls ~ L. cv Florunner) cotyledons after roasting at a temperature of 160°C (16 min) were investigated with light and scanning electron microscopy. Major changes included: (1) pitting and pock -marking of the epidermis of the cotyledons caused by the escape of steam and on released during roasting; (2) loss of cellular organization of the cytoplasmic network surrounding the Jipid bodies, protein bodies, and starch grains ; (3) alteration of the structures of cytoplasmic network. lipid bodies, and protein bodies; and (4) heat destruction of some middle lamellae of cell - t o-cell junctions.

Microstructure And Firmness Of Processed Cheese Manufactured From Cheddar Cheese And Skim Milk Powder Cheese Base, A. Y. Tamime, M. Kalab, G. Davies, M. F. Younis

Food Structure

Processed cheese (10 different types) was made from Cheddar cheese and a cheese base produced from reconstituted skim milk powder by blending and melting with commercial emulsifying salts at 9Q<>C. In one experiment, the cheese base was subjected 10 accelerated cheese ripening by added enzyme. The finished products had 50.1- 53.5% total solids, 18.2-19.3% protein, 47.4-49.7% fat in dry matter, and 2.7-3.0% salt in water; pH was 5.3-5.4 after three months of storage at 10 C and 30 C.

The experimental cheeses were markedly firmer than the control cheeses. All processed cheeses exhibited a similar pattern of firmness whereby …

The Role Of The Interfacial Protein Film In Meat Batter Stabilization, A. Gordon, S. Barbut

Food Structure

The microstructure of meat batters made with equal ionic strengths of NaCl, MgC1 2 , CaCl2 and KCl (IS- 0.43) and a reduced-NaCl batter (IS- 0.43) were examined by scanning and transmission electron microscopy. Micrographs revealed that fat globules with smooth and rough protein coats were present in all treatments. The roughly-coated globules were prevalent in the unstable batters. Pores were observed in the interfacial protein film (IPF) surrounding the globul es and were more prevalent in the globules with rough protein coats. Fat was seen to exude from the pores in both types of globules, Fat globules were shown …

A Method For The Examination Of The Microstructure Of Stabilized Peanut Butter, Clyde T. Young, William E. Schadel

Food Structure

A method for light and scanning electron microscopy of damaged resting peanut seed tissue was adapted as a research tool for evaluating the microstructural features of commercially available stabilized peanut butter. This method was used in the present study to evaluate the degree of homogenization of stabilized peanut butter by examining the spatial relationship which exists among the microstructural features. Light and scanning electron microscopy of three commercially available stabilized peanut butters revealed varying degrees of homogenization of broken cell and tissue fragments, protein bodies, and starch grains within a matrix of stabilized oil.

Image Analysis Of The Fat Dispersion In A Comminuted Meat System, Peter A. Koolmees, Piet C. Moerman, Monique H.G. Zijderveld

Food Structure

In a series of experiments on a comminuted meat system, image analyses were conducted to quantify changes in structure as affected by polyphosphate, fat level, and chopping time and temperature. Four batches of comminuted meat were investigated which contained neck beef, pig head meat, rino, ice, salt (2%), fat at a level of either 27 or 40%, and polyphosphate at a level of either 0 or 0. 5%. Structural changes in different stages of comminution coincided with a shift in size distribution, shape factor, density and area percentage of fat particles. The density of the protein matrix (matrix defined as …

Microstructure And Texture Of Meat Emulsions Supplemented With Plant Proteins, Allan T. Paulson, Marvin A. Tung

Food Structure

A model meat emulsion system was used to evaluate the effects of cooking time and temperature on texture, microstructure and cook stability of meat emulsions containing soy or canola protein isolate. The plant proteins were incorporated either dry or rehydrated at replacement levels of 33.3% and 66.7% of the meat protein, and the emulsions were cooked at 70 or 95 C tor 25 or 50 min. Texture of the cooked emulsions was assessed by an instrumental texture profile analysis (TPA) using an lnstron tester . Analysis of TPA and stability data revealed several complex Interactions between experimental variables; however, level …

Heat-Set Gels Based On Oil/Water Emulsions: An Application Of Whey Protein Functionality, R. Jost, F. Dannenberg, J. Rosset

Food Structure

The microstructure of portein/lipid gels produced by heat treatment of whey protein stabilized oil-in-water(O/W) emulsions was studied. Scanning electron microscopy as well as transmission electron microscopy was performed on glutaraldehyde/osmium tetroxide fixed, and critical point-dried samples. Microstructure analysis showed that in the case of homogenized O/W emulsions, extensive coating of the fat globule surface with coagulated protein led to a "cauliflower - like" structure. In such gels, uncoated fat globules having smooth surfaces were not present. This specific microstructure was not obtained with protein/lipid gels in which whey protein was added in the continuous phase and mixed with a O/W …

Structural Characteristics Of Pennisetum Americanum (Pearl Millet) Using Scanning Electron And Fluorescence Microscopy, C. M. Mcdonough, L. W. Rooney

Food Structure

Fluorescence bright field and scanning electron microscopy were used to characterize the structure of selected mature pearl millet caryopses from the World Germplasm Collection. Kernel shape (globose, lanceolate, obovate and hexagonal). kernel endosperm color (while. yellow and grey) and external appearance (color) of the samples were documented for 96 varieties. Color of the pearl millet kernel was due to the combined effects of pigmentation in the pericarp. aleurone and endosperm. as well as the pericarp thickness. White kernels had few pigmented areas. yellow kernels had pigments primarily in the epicarp and endosperm. and brown kernels had pigments in the epicarp. …

Microstructure Of Extruded Mixtures Of Cereals And Oil Seed Processing Residues, A. Salgo, Sz. Torok, Sz. Sandor

Food Structure

The utilization of valuable by-products of seed processing residues as coextrusion materials was investigated. By mixing sunflower, pumpkin, corn or rice germ presscake with cereals (wheat, corn, rice), the good protein quality of the former group might improve the biological value of the resulting coextrudates. The microstructure of such coextruded products was analysed with reference to their chemical compositions, nutritional characteristics and functional properties. As seed processing residue was increased, the microstructure of the products became more compact and uniform and the air/solids ratio decreased considerable. The results showed that the highest acceptable concentration of the additive was not more …

The Effect Of Chloride Salts On The Texture, Microstructure And Stability Of Meat Batters, A. Gordon, S. Barbut

Food Structure

The stability, texture and microstructure of six mechanically deboned chicken meat bat.ters prepared with NaCL (1.25 and 2.5%) and replacement of the 2. 5 NaCl with HgC12 , CaC12 , KCl and LiCl based on isoionic strength were examined . The uncooked HgCL2 batter showed the poorest fat binding, The monovalent chloride salts produced stable cooked batters, whereas both divalent salts did not, CaC12 produced a more unstable batter than MgC1 2 High correlation was found between water and fat loss and total cookout losses from cooked batters. Texture was significantly affected by the type of chloride salt used. The …

Microstructure Of Shortenings, Margarine And Butter - A Review, A. C. Juriaanse, I. Heertje

Food Structure

Fat spreads are composed of liquid oil, fat crystals and water. The fat crystals in these products give the product the required consistency and stabilize the water droplets. Shortenings are waterfree products , the rheology of which depends on the solid fat content and interactions between fat crystals. Size and interaction between crystals is influenced by both composition and processing. Crystals form a three - dimensional network. Recrystallization phenomena, especially formation of large beta- crystals , can create product defects like sandiness. Margarines and halvarines are water- in - oil emulsions and have a relatively simple product structure. Because of …

Functional And Microstructural Effects Of Fillers In Comminuted Meat Products, Frederick W. Comer, Paula Allan-Wojtas

Food Structure

Fillers are used in comminuted meat products such as wieners to increase yield, improve stability, and modify textural properties. Light microscopy, scanning electron microscopy and transmission electron microscopy show that comminutred meat products are mechanical mixtures in which the microstructural features of starch and insoluble protein ingredients are largely retained. The water absorption and gelation properties of these ingredients contribute to the stability and textural firmness. Soluble proteins may improve stability through emulsion formation but the role of emulsion formation i s clearly secondary to that of gelation. The characteristic springy gel structure of wieners is determined by the gelation …

The Microstructure Of Spray-Dried Microcapsules, M. Rosenberg, Y. Talmon, I. J. Kopelman

Food Structure

A newly developed technique for SEM sample preparation has been applied in the study of the effects of process parameters on the microstructure of gum arabic spray-dried microcapsules. The technique, that employs embedding in an apolar resin and partial polymerization makes it possible to simultaneously observe the inner and outer structure of microcapsules. Our results show how the core material is organized in the solid wall matrix, existence of one or more internal voids in the microcapsule, indentation and caps in the exterior of the microcapsules, and how these microstructural features are affected by solids concentration in the sprayed emulsion, …

The Effect Of Processing On Some Microstructural Characteristics Of Fat Spreads, I. Heertje, J. Van Eendenburg, J. M. Cornelissen, A. C. Juriaanse

Food Structure

The processing and the composition of fat spreads determine to a large extent the final product properties such as hardness, spreadability, mouthfeel, emulsion stability and salt release. In establishing the relation between composition, processing and final product properties, microstructural studies play an important role. In this context the influence of some process parameters in the production of shortenings and 80% fat spreads on microstructure and product properties has been investigated. Shear, cooling regime and crystallization conditions influence both the emulsion structure and the fat crystalline matrix. In general, working leads to softer products with a more granular crystalline fat matrix, …

The Effect Of Storage, Processing And Enzyme Treatment On The Microstructure Of Cloudy Spartan Apple Juice Particulate, D. L. Mckenzie, T. Beveridge

Food Structure

The effect of blanching, post-harvest refrigerated (4C) storage and enzyme treatment with poly-galacturonase on the microstructure of Spartan apple juice was examined by thin sectioning and negative staining transmission electron microscopy. Particles were categrized as granules (3-54 nm), spheres (20-368 nm) and aggregates (12-2519 nm). Enzyme treatment with polygalacturonase significantly decreased granule size (P < 0.01). Storage of apples significantly decreased both granule size (p < 0.01) and aggregate length (p < 0.05) and also resulted in a web-like aspect in the microscopic appearance of juice particulate. The web-like aspect of the particulate was removed either through enzyme treatment with polygalacturonase or by blanching. Blanching of puree significantly increased granule (p < 0.05) and sphere size (p < 0.01) while significantly decreasing aggregate length (p < 0.01). In addition, blanching stabilized suspended particulate by what appeared to be the formation of a protective colloid which prevented particle aggregation through electrostatic repulsion.

The Size Distribution And Shape Of Curd Granules In Traditional Swiss Hard And Semi-Hard Cheeses, M. Ruegg, U. Moor

Food Structure

Curd granule junction patterns in hard (Emmentaler, Gruyere, Sbrinz) and semi-hard cheeses (Appenzeller , Tilsiter, Raclette) were visualized on slices and examined using light microscopy and digital image analysis. Horizontal and vertical sections were cut in different zones of the loaves, in order to obtain information on the orientation of the flattened curd granules.

The frequency histograms of the cross section areas could in most cases adequately be described as a log-normal distribution. The median values ranged from 0.97 to 1.15 mm2 and, from 1.31 to 1.68 mm2 for hard and semi-hard cheeses, respectively.

An elliptical form factor was used …

Microstructural Studies Of Texturized Vegetable Protein Products: Effects Of Oil Addition And Transformation Of Raw Materials In Various Sections Of A Twin Screw Extruder, S. Gwiazda, A. Noguchi, K. Saio

Food Structure

In high-temperature short- time extrusion cooking with a twin screw extruder , effects of oil addition to defatted soybean flour and microstructural transformation of full - fat soybean flour during cooking , were investigated by use of a light microscope. At levels up to 15% , soybean oil was distributed in the protein and carbohydrate matrix as small, spherical drops under the experimental conditions used in this study. However , oil contents above 15% significantly prevented formation of well-aligned fibrous structures in the extrudates . During extrusion cooking , the starting materials began to break down by shearing and kneading …

Textural Properties And Microstructure Of Process Cheese Food Rework, Miloslav Kalab, Joseph Yun, Suk Hing Yiu

Food Structure

Process cheese food was made using sodium citrate (2.7%) or trisodium phosphate (TSP, 2.7%) as emulsifying agents. No precooked cheese (rework) was used in some samples whereas in others the rework (20%) consisted of a cheese blend emulsified with sodium citrate (2.7%) and (a) briefly heated to 82 degrees C, (b) heated to 82 degrees C for 1 h, (c) heated to 82 degrees C for 5 h, and (d) heated to 82 degrees C for 5 h, frozen at -10 degrees C for 24 h, and thawed at +4 degrees C. Heating for extended periods of time produced so-called …