STARCH AND PECTIC SUBSTANCES AS AFFECTED BY A FREEZE-THAW POTATO GRANULE PROCESS

Changes in total content and fractions of pectic substances and starch were studied in a freeze-thaw process for potato granule production consisting of peeling, steam cooking, hot mashing, freezing and thawing, pre-drying, granulation, drying, cooling and sifting. Pectic substances in raw potatoes (expressed as mg uronide/netted Gem 100g dry wt) were 202.4 for water soluble and only 80 for the calgon-soluble fractions. Water soluble pectic substances increased sixfold after cooking, and calgon-soluble fraction about threefold. Little change was observed in either fraction due to subsequent granule processing steps. There was no indication that pectic substances present in the extracellular matrix could have influenced the processing steps in granule production. Total starch comprised 68.4%/dry wt of raw potato, decreasing slightly after cooking, increasing up to the pre-drying step and stabilizing at a level of 83.7%. In contrast, free water-soluble starch, depended on the processing steps, being lower in cooked unmashed potatoes than in conditioned raw potatoes. Mashing slightly increased starch content while pre-cooling to 5.5°and freezing to −20°C with subsequent thawing to room temperature substantially decreased starch content. Mechanical forces applied in subsequent steps brought about some increase while in the final product the content was related to particle size of the granules. The percentage of broken cells in cooked potatoes mashed at various temperatures appears to be dependent on the free extracellular starch present in cell binding matrix. Broken cell counts were substantially decreased when mashing was performed immediately after cooking at high temperature or when the mash was frozen and thawed. In the latter case determination of Blue Value Index suggested that a decrease in cell binding strength of the matrix occurred due to soluble starch retrogradation.     

PECTIC SUBSTANCES OF FABA BEANS AND THEIR RELATION TO TEXTURE OF COOKED BEANS

Twenty samples of faba beans which showed wide variations in texture after cooking were analyzed for total pectin and pectin fractions (i.e., H2O-, EDTA-, and NaOH-soluble fractions) contents of decoated seeds and seed coats. Total pectin ranged between 0.9 and 1.6% of the cotyledons and between 0.5 to 1.0% of the seed coats. Water-soluble pectin was the highest fraction with a mean value about 50% and 40% of the total pectin for the decoated seeds and the seed coats, respectively. No consistent significant correlation was found between the pectic substances fractions and the texture of cooked faba beans for both 1980 and 1981 samples except for the water-soluble pectin as a percentage of the total pectin content of decoated seeds (r = 0.77, P< 0.01 for penetrometer and r =−0.76, P<0.01 for Kramer maximum shear force for 1980 and 1981, respectively).     

INSTRUMENTAL TEXTURE STUDIES ON CHOCOLATE II. COMPOSITIONAL FACTORS INFLUENCING TEXTURE

Instrumental studies of chocolate are used to investigate the influence of composition, fat content and type of fat on the texture of different plain chocolates and milk chocolates. The quality of the replacement fat influences the texture more than the fat content. As a result of the chocolate's after-crystallization and recrystallization during storage, the composition's influence are increasingly intensified.     

POSTHARVEST CHANGES OF PECTIC SUBSTANCES IN CHILLED PEACHES

ABSTRACT Red Globe peaches were harvested at the threshold-mature stage and either stored at OC after preripening at 20C for 48 h or stored directly at 2C. Total pectin increased from 7.49 mg/g fresh weight in the threshold-mature sample to 10.21 mg/g in pre-ripened fruit stored at OC and 12.83 mg/g in fruits stored directly at 2C. Depending on extraction and storage protocol, between 26% and 73% of total pectin was solubilized. Chelator-soluble fractions had a low degree of esterification (DE ca. 20%), whereas other fractions were highly methylated (DE ca. 56% to 74%). Average DE did not vary between samples. DEAE-cellulose chromatography revealed an uneven distribution of methoxyl groups. Two prominent peaks were observed in chromatograms of chelator-soluble extracts from threshold-mature fruit and fruit stored directly at 2C. One peak was observed in chelator-soluble pectin from preripened fruit stored at OC.     

PECTIC ENZYMES OF ASPERGILLUS ACULEATUS ASSOCIATED WITH POST-HARVEST DETERIORATION OF CITRUS SINENSIS FRUIT

The host-mold relationship between the fruit of orange and Aspergillus aculeatus was investigated. The mold was also grown on wheat offal, sodium polypectate and apple pectin cultures. The cells of orange fruit tissue infected with A. aculeatus showed a more rapid cell separation and maceration than filtrates obtained from mold infected fruits and inoculated wheat offal cultures. Higher activities of pectin methyl-transeliminase and polymethylgalacturonase were recorded in rotted fruit filtrates than in culture filtrates. The detection of an exopolygalacturonase in culture filtrate was also found. Cellulolytic enzymes were found to be higher in infected fruit tissues than in culture filtrate.     

VIRULENCE FACTORS ASSOCIATED WITH PATHOGENICITY OF AEROMONAS ISOLATES

Aeromonas species have been associated with diarrhea, and disseminating infections. Diarrhea is either "cholera-like" or "dysentery-like". Both types of diarrhea are normally mild. However, either type can be severe enough to cause hospitalization. The sources of Aeromonas in these infections are foods and water. Two virulence factors associated with Aeromonas diarrhea are a relatively heat-stable cholera-like enterotoxin and a heat-labile cytotoxic enterotoxin. Researchers who observed either of these enterotoxins rarely saw evidence of the other. These differences are probably due to the rare occurrence of the cholera-like toxin and to differences in purification methods. Human feeding studies showed that enterotoxin production is not sufficient for causation of diarrhea. The Aeromonas must also be able to colonize the intestine or invade the intestinal lining. Virulence factors associated with colonization or invasion have not been identified.     

PRECISE STUDY OF COOKED POTATO TEXTURE

Cylindrical specimens from potato tubers were cooked at constant temperatures (75, 80, 85, 90, 95C) in a special heating cell located on the table of an Universal Testing Machine and arranged in such a manner that a cooked specimen could be tested repeatedly in nondestructive compression test during the whole cooking process. The decrease of Young's modulus during cooking form the basis for the calculation of the Cooking Depression Coefficients and activation energies of the process. The whole cooking time could be divided into two parts for varieties 'Nicola' and 'Panda'. The first part represents a modulus decrease of at least 50% and can be well described by a first order kinetic equation. The second part is kinetically very complicated and represents only a 10–15% further decrease of the original modulus value. Temperature dependence of mean Cooking Depression Coefficients (CDC) for both parts of the cooking curve, as well as Cooking Time Limits (CTL—time limit between both parts) fit the Arrhenius model. Cooking differences between both tested varieties are briefly discussed.     

FACTORS ASSOCIATED WITH FRESH MEAT COLOR: A REVIEW

The color of fresh meat is important to every aspect of the meat industry. The basic explanations for various colors and intensities of color need to be understood in order to minimize off-colors which ultimately result in product loss. This review discusses the various color forms of myoglobin in muscle and their relationship to species, atmospheric conditions, antemortem factors and storage characteristics.     

THE INFLUENCE ON BREAD TEXTURE OF PARTIALLY REPLACING WHEAT WITH POTATO PRODUCTS*

The use of potato products in wheat bread manufacture is reviewed with particular reference to their effect on the textural characteristics of bakers' dough and fresh bread, and the changes associated with bread staling. Possible interactions between the proteins in wheat and potato are discussed. Recent developments relating to the partial replacement of wheat by potato flakes are reviewed. Their effectiveness is discussed in terms of the chemical nature of potato starch, the physical state of starch in potato flakes and the influence exerted by additives such as glyceryl monostearate and fats.     

BETWEEN-SPECIES DIFFERENCES IN FRACTURABILITY LOSS: COMPARISON OF THE THERMAL BEHAVIOR OF PECTIC AND CELL WALL SUBSTANCES IN POTATO AND CHINESE WATERCHESTNUT1

This study was undertaken to determine how the mode of chemical changes taking place during the cooking of two chemically similar vegetables (potato and waterchestnut) might explain the tremendous between-species differences in cooked tissue fractura bility as determined by Instron Texture Profile Analysis. Although pectin breakdown and depolymerization by heat weakens the cell wall structure, loss of cell wall physical strength does not necessarily coincide with pectin depolymerization. Potato phosphate-soluble pectin (PSP) showed a more rapid rate of depolymerization than waterchestnut PSP as proven by both chemical and gel chromatographic studies. The unique composition (e.g., neutral sugar content) of the cell wall microstructure of a given vegetable species is the major determinant of the resistance of that plant tissue to fracturability loss during cooking. Based on GLC analyses of cell wall components, cell wall models have been proposed to illustrate the possible structural differences between potato and waterchestnut tissue. It appears that the cell wall character of edible plant tissue for a given species is determined genetically.     

INSTRUMENTAL TEXTURE STUDIES ON CHOCOLATE III. PROCESSING CONDITIONED FACTORS INFLUENCING THE TEXTURE

The texture characteristics of chocolate are greatly influenced by processing conditions. By means of instrumental texture studies the effect of variations in the conching process parameters, of precrystallization and after-crystallization during storage is illustrated. In order to compare the results, the exact precrystallization of the chocolate masses before moulding is of special importance.     

INSTRUMENTAL AND SENSORY CHARACTERIZATION OF COOKED POTATO TEXTURE

Uniaxial compression, Texture Profile Analysis (TPA) and chemical measurements were related to sensory texture evaluation of potato quality during storage. Principal component analysis grouped the varieties into three types of variation: mealiness versus firmness and springiness (PC1), moistness versus adhesiveness (PC2) and hardness versus adhesiveness and moistness (PC3). In uniaxial compression the variable 'stress', 'work up to fracture' and 'total work during compression' described the same type of information in the data. These uniaxial data and most of the TPA data were highly correlated. Uniaxial compression data (stress, strain, modulus of deformability), starch structural data (area, roundness, aspect ratio), specific gravity and pectin methyl esterase activity discriminated between the varieties and harvest times. Partial Least Squares Regression showed stress, strain, modulus of deformability and specific gravity to be the most important variables in distinguishing between two groups of sensory texture attributes explaining 65% of the total variance in the sensory data. Coefficients of correlation between predicted and measured sensory attributes were in the range 0.36–0.79. The TPA data were not found to be relevant substitutions for the sensory attributes.     

COLOR AND TEXTURE DEVELOPMENT OF POTATO CYLINDERS WITH LIQUID SMOKE DURING BAKING, FRYING AND MICROWAVING

The rate of color and texture development in partially fried before freezing potato cylinders processed by deep fat frying, microwaving and baking was determined. The effect of 0, 1, 3 or 5% wt/wt solution containing 30% liquid smoke was measured at intervals during thermal processing and the reaction order and rate determined. Also, five different wood and dextrose‐derived browning agents were compared at 1% wt/wt addition. The processing method had a significant effect on the reaction rates of color and texture development during processing. Microwaving was faster than frying, which was faster than baking. The addition of liquid smoke led to a significant increase in the rate of color production but had no statistically significant effect on texture. The addition of 1% liquid smoke increased the reaction rate by adding carbonyls, which limit the reaction rate in potatoes. Higher levels of liquid smoke did not change the reaction rate because the carbonyls were no longer limiting the reaction. The processing method and the addition of the browning agent had no effect on the reaction order which remained a pseudo zero‐order reaction. Thus, liquid smoke could be used to reduce processing times, potentially saving money and decreasing acrylamide formation.     

MICROBIOLOGICAL RISK FACTORS ASSOCIATED WITH FOOD HANDLERS IN ELEMENTARY SCHOOLS FROM BRAZIL

A total of 44 food handlers who work in elementary schools from Governador Valadares, Minas Gerais, Brazil, were subjected to the examination of the nasal carriers of Staphylococcus aureus and of hand carriers of Enterobacteriaceae and Pseudomonas aeruginosa. A simple method using the eosine-methilene-blue media to isolate enterobacteria from the hands was performed. Among the total number of food handlers, 29.5% were S. aureus nasal carriers . The following percentages were obtained for enterobacteria isolation from the hand carriers: Enterobacter spp. (54.5%), Serratia spp. (9.0%), Shigella spp. (9.0%), E. coli (6.8%), Salmonella spp. (2.3%) and Yersinia spp. (2.3%). Pseudomonas aeruginosa was isolated from the hands of 2.3% food handlers. Our results demonstrated the necessity of performing evaluation of S. aureus and Enterobacteriaceae in food handlers from elementary schools and also indicated that the method is useful to identify sources of food poisoning in epidemiological studies and in investigations of food contamination sources. Our data also showed that authorities may allot more attention to alerting the community about food problems.

PRACTICAL APPLICATIONS

The methods used in this work could be a valuable and low-cost tool to verify the microbiological risk factors associated with food handlers, including Staphylococcus aureus and enterobacteriaceae.