CHANGES IN CHEMICAL COMPOSITION OF 'CAVENDISH' BANANA (MUSA ACUMINATA) DURING RIPENING

Green 'Cavendish' bananas were exposed to ethylene for 16 h and the subsequent development of ripening at 20°C was followed in terms of skin color, respiration and ethylene production. At six stages of ripeness, as determined by skin color, pulp tissue was analysed for firmness and for water, protein, fat, individual sugars, starch, dietary fibre, organic acids, ash, soluble solids, pH, vitamin C, thiamin, riboflavin, niacin, carotenes, sodium, potassium, calcium, magnesium, iron and zinc; energy content and edible weight were calculated.     

STARCH MOBILIZATION AND SUCROSE ACCUMULATION IN THE PULP OF KEITT MANGOES DURING POSTHARVEST RIPENING

Sugar is a determinant for the quality of mangoes, but information about its accumulation is scarce. Although starch can contribute to sugar production during ripening, not much is known about the enzymes involved. This work presents the changes in carbohydrate and enzymes during the development and ripening of Keitt mangoes. Starch disappearance was concomitant to a fivefold increase of sucrose, the most abundant sugar of the ripe fruits. The activities of α-amylase, β-amylase, phosphorylase and isoamylase were detected in the pulp, and while α-amylase increased parallel to the starch content, β-amylase presented a 20-fold increase during ripening. On the other hand, high phosphorylase activity was observed when fruits were still accumulating starch, and lowered during ripening. Isoamylase was detected during development and increased slightly during ripening, which would be in agreement to the expected role for isoamylases as acting on both subproduct of starch synthesis and degradation.

PRACTICAL APPLICATIONS

The present work reinforces our previous works that Keitt mangoes do not ripen when attached to the tree. This fact allowed us to study all the starch degradation after mango harvesting which does not occur with the other cultivars. Data obtained in this work reinforce the role of α-amylase, β-amylase and isoamylase rather than the starch phosphorylases on starch granule degradation in mangoes, and the subsequent soluble sugar accumulation.     

干酪成熟过程发酵剂的作用及快速成熟的研究进展

干酪的成熟过程,是在添加酶及各种微生物的协同作用下完成的.干酪中的微生物作用也包括人为添加发酵剂的作用.本文综述了干酪生产过程中发酵剂的使用和成熟过程所起的作用,主要有酸化、改善质构、形成风味物质.此外,本文也讨论了干酪的成熟机制,综述了目前用于促进干酪成熟所使用的一些方法和技术以及对它们的最新研究进展.     

CHANGES IN VISCOELASTIC PROPERTIES DURING THE RIPENING OF ARZÚA-ULLOA CHEESE. EFFECT OF PROTEOLYSIS

Changes in viscoelastic properties during the ripening of three different batches of Arzúa-Ulloa cheese, a traditional Spanish variety, were studied. Proteolysis changes were determined in terms of the typical nitrogen fractions, these fractions were significantly correlated with the measured viscoelastic properties. Substantial changes in stress amplitude over the linear viscoelastic range were observed at 20C, as were significant differences in storage modulus (G') and viscous modulus (G") throughout the ripening period. Both moduli decreased markedly over the first two weeks, but exhibited an opposite trend from the third week. Mechanical spectra were recorded at 20, 25, 30 and 35C throughout the ripening period. The viscous component significantly increased compared to the elastic one as function of temperature and ripening time.     

MODELING THE BEHAVIOR OF LISTERIA MONOCYTOGENES IN pH-MODIFIED CHICKEN SALAD DURING COLD STORAGE AND TEMPERATURE ABUSE CONDITIONS

Listeria monocytogenes grows at refrigeration temperatures (5C or below) and tolerates various environmental stressors. The Food and Drug Administration specifies a zero tolerance for this pathogen in certain ready‐to‐eat processed foods. Modeling its dynamic behavior to fluctuation in temperature at various pH levels is critical to the safety of food. This study presents linear and nonlinear models to predict the behavior of L. monocytogenes in pH‐modified chicken salad at various cold storage and temperature abuse conditions. A linear model of the kinetics accounting for simple and interactive effects of storage time, temperature and pH was developed. Predictions of the linear model were inconsistent with laboratory observations. The limitations of the linear model were reflected in the poor correlation of model predictions to the observed values (r² = 0.58). A proposed nonlinear model was therefore used to model the observed data. The four model parameters (N(0), C_c(0), k_max and N_res ) were optimized for each of the nine treatments. Correlation coefficient (r²) values ranged from 0.70 (pH 5.2, 7.2C) to 0.99 (pH 4.0, 21.1C), indicating an improved accuracy. Developing a functional and validated microbial predictive model for chicken salad requires further analyses and collection of data at additional pH and temperature values to determine a single set of parameter values that would represent the microbial behavior at the full range of pH and temperatures observed under storage conditions. Future experiments should address the adaptive nature of L. monocytogenes, as the response to environmental stressors affects the survival of the organism in food systems.     

CHANGES IN EQUILIBRIUM MODULUS AND αsl-CASEIN BREAKDOWN DURING THE RIPENING OF PORT SALUT ARGENTINO CHEESE AS AFFECTED BY FROZEN STORAGE

The effect of the freezing, frozen storage and thawing on textural parameters and α_sl-casein breakdown during the ripening of Port Salut Argentino cheese was studied. Moisture content, salt concentration, casein profiles and asymptotic equilibrium modulus were monitored in control cheeses ripened at 5C and in cheeses, stored at -22C for 30 days, thawed and ripened at 5C, for different ripening times (1, 6, 13, 27 and 56 days) and two sampling zones (central and external). The freezing process significantly increased the rate of α_sl-casein and α_sl-I-casein hydrolysis. This process may affect the susceptibility of α_sl-casein to chymosin attack and also the availability of hydrolytic enzymes released by damaged microorganisms, which may contribute to the faster hydrolysis of α_sl-I-casein. The freezing process did not significantly affect the decay rates of asymptotic equilibrium modulus. First order kinetics constants for decay of the asymptotic equilibrium modulus were 3.71 10^-2day^-1 (control cheeses, central zone), 8.48 10^-2 day^-1 (control cheeses, external zone), 4.52 10^-2 day^-1 (frozen cheeses, central zone), and 11.43 10^-2 day^-1 (frozen cheeses, external zone). Significant differences in the decay rates of asymptotic equilibrium modulus were found between central and external zones in control and frozen cheeses primarily due to differences in moisture contents of the sampling zones.     

A REVIEW OF TEXTURAL DEFECTS IN COOKED RECONSTITUTED LEGUMES —THE INFLUENCE OF STRUCTURE AND COMPOSITION

Legumes provide an important part of the world's protein requirements, as well as other nutrients, but they are underutilized as food. A major factor limiting expanded consumption is storage induced textural defects that prolong cooking time and demand correspondingly higher energy requirements for preparation. These defects, including the hard-to-cook phenomenon and hardshell, are initiated by structural and compositional factors but can be at least partially controlled by storage and processing conditions. Structural components implicated include seed coat, cell walls, middle lamella, starch granules and membranes while, compositionally, proteins, carbohydrates, phytate, polyphenols and lignin may also be important. Methods of texture measurement of legumes, including mechanical, physical and sensory properties are reviewed. The most commonly held hypothesis for the mechanism of the hard-to-cook defect states that beans fail to soften after exposure to high temperature and humidity storage because the increased water activity potentiates phytase which hydrolyzes phytate, rendering it no longer capable of chelating the Ca⁺⁺ and Mg⁺⁺ ions of the middle lamella and, hence, undissoluble. More recent evidence, however, provides potential roles for lignification, starch gelatinization and perhaps other mechanisms depending upon conditions. The possibility of a nonenzymatic as well as an enzymatic route is raised and thoughts presented on a course of action for future research.     

CHANGES IN THE CATIONIC ISOENZYMES OF PEROXIDASE DURING THE MALTING OF BARLEY. I: TISSUE LOCATION STUDIES

Sixteen cationic isoenzymes of peroxidase were detected in barley grain (variety: Chariot) and twenty in green malt, falling to fifteen after kilning. The distribution of these among the different seed tissues was examined with a view to determining which isoenzymes were likely to survive mashing and be active during brewing. In isolated barley tissues, the aleurone layer contained one major band (Rm 0.77), and the endosperm only the four fastest running bands (Rm values 0.84–0.97). In green malt the growing embryo tip contained fifteen isoenzyme bands (Rm values 0.04–0.70), with an absence of only the faster running bands. In kiln-dried malt, isoenzymes with Rm values 0.04–0.10 increased in activity, two extra light bands appeared (Rm 0.26 and 0.61) and three other bands present in barley were lost (Rm values 0.63, 0.70 and 1.0). Much of the activity in the aleurone layer was lost. Seven of the fifteen isoenzymes in finished malt accounted for over 75% of the cationic peroxidase activity. Variation in aleurone and endosperm isoforms between different cultivars was observed, whereas the embryo showed little variation. The endosperm isoforms seem to be the ones most likely to cause oxidation problems during brewing.     

CHANGES IN APPARENT VISCOSITY AND VITAMIN C RETENTION DURING THERMAL TREATMENT OF BUTTERNUT SQUASH (CUCURBITA MOSCHATA DUCH) PULP: EFFECT OF RIPENING STAGE

ABSTRACT

The effects that ripening stage have on the apparent viscosity and ascorbic acid retention in squash pulp exposed at cooking process were analyzed. Total soluble solids contents were taken as indicative of ripening degree. In the raw material, water contents ranged from 79 to 96%, but no significant differences were observed among samples grouped as unripe, ripe and overripe. The ascorbic acid contents of pulp increase with increases in soluble solids contents. Pulp from unripe and ripe squash had similar apparent viscosity values; however, lower viscosity values were obtained in pulp from overripe squash. During heat treatment, significant changes in the apparent viscosity values of pulp from unripe and ripe squash were observed. Heat penetration properties of squash pulp indicate correlation between the inverse slope of the straight portion in the heat penetration curves on a semilog plot (fh) and thermal diffusivity values (α) with dry matter content, but no correlation was found with squash maturity degree. High ascorbic acid retention (82%) in pulp held for 30 min at 95C was found independently of squash maturation degree.

PRACTICAL APPLICATIONS

Knowing the rheological behaviour and the ascorbic acid retention of butternut squash pulp during cooking process could be used as a valuable information previously to make decisions for use this crop as a food supply.

     

CHOICE OF MALE AND FEMALE PARENTS OF SEEDLING POPULATIONS OF HOPS IN RELATION TO THE α-ACID CONTENT AND THE TIME OF RIPENING OF THE FEMALE PROGENY

The transmission of α-acid content and time of ripening in female hop seedlings was studied over periods of 3 and 4 years respectively. The inheritance of α-acid content in seedling populations having female parents with a low α-acid content was determined by the α-acid content of the male parent, while the average α-acid content of populations with “high” female parents was shown to be inversely proportionate to the α-acid contents of those parents. There were indications, however, that α-acid content of the female parent of males also played a role in determining the α-acid content of the female progeny in the second generation. Between-population variations in time of ripening were relatively small. It was found that the time of ripening was predominantly determined by the female parents of the populations.     

THE COMPOSITION OF TWO SPANISH PEPPER VARIETIES (FRESNO DE LA VEGA AND BENAVENTE‐LOS VALLES) IN DIFFERENT RIPENING STAGES

ABSTRACT

The chemical composition of two traditional varieties of Spanish peppers, “Fresno de la Vega” and “Benavente‐Los Valles” harvested in the provinces of León and Zamora, respectively, at different ripening stages (green mature, breaker and red) were evaluated. Herein we report the global composition, mineral and trace element contents, and the most relevant physicochemical parameters of each variety of pepper collected in 2 consecutive years. Both pepper varieties showed a similar chemical composition, except in vitamin C content, which resulted to be about 70% higher in Fresno de la Vega peppers. Red ripe fruits were high in total carbohydrates, fructose, glucose, sucrose, fat (64.5, 29.14, 25.57, 2.94, 1.79/100 g dry weight, respectively) and total soluble solids (6.83°Brix). Ascorbic acid content also increased progressively during ripening, reaching a mean value of 1.81 mg/100 g dry weight for Fresno de la Vega peppers. Potassium was the most abundant of the analyzed elements in the all samples, followed by phosphorus, magnesium, calcium and sodium. The order of the levels of the trace elements was iron > manganese > zinc > copper.

PRACTICAL APPLICATIONS

This report underscores the potential value of two traditional varieties of Spanish peppers and provides information on their composition during ripening to decide the proper harvesting time, which can be useful in the food industry.     

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.     

CHANGES IN THE CATIONIC ISOENZYMES OF PEROXIDASE DURING THE MALTING OF BARLEY II: THE EFFECT OF GIBBERELLIC AND ABSCISIC ACIDS

During germination, alpna-amylase activity in barley (variety: Chariot) increased 29-fold, while peroxidase activity increased 4.2-fold. Increasing concentrations of GA₃ increased the rate of development of alpha-amylase activity while the rate of increase of peroxidase activity remained unchanged, but there was an overall increase in the amount of peroxidase synthesized. ABA caused a concentration-dependent suppression of activity and a decrease in the rate of expression of both enzymes. Three different types of response of individual peroxidase isoenzymes occurred during germination. Six isoenzymes increased in activity during malting, four decreased in activity and nine showed a rise at the beginning of germination followed by a significant fall. The majority of the isoenzymes were positively GA₃-sensitive, ie increased in activity or were synthesized earlier in the presence of GA₃, and negatively ABA-sensitive. Only four isoenzymes were negatively GA₃-sensitive, and only three were positively ABA-sensitive. Detailed data for the synthesis during germination of the six major peroxidase isoenzymes that survive into the finished malt is presented .     

KINETIC BEHAVIOR OF SOYBEAN LIPOXYGENASE: A COMPARATIVE STUDY OF THE FREE ENZYME AND THE ENZYME IMMOBILIZED IN AN ALGINATE SILICA SOL‐GEL MATRIX1

Lipoxygenase (LOX) is an enzyme that regioselectively introduces a hydroperoxide into polyunsaturated fatty acids (PUFA). We recently reported a procedure that immobilizes soybean LOX within an alginate sol‐gel matrix. In this study, the kinetic profile of free LOX was compared with that of the sol‐gel immobilized LOX. The temperature dependent activity profile of free LOX was optimal at 25C whereas immobilized LOX had optimal activity over the temperature range of 25–35C. Enzyme activity, measured in aqueous buffer, for both the free and immobilized LOX preparations had K_m values of 2.5 and 1.40 mmoles/L, respectively, and V_max values of 0.056 and 0.02 μmol/min, respectively. The relative rates of oxidation of linoleic acid and acylgfycerols containing linoleoyl residues catalyzed by free and immobilized LOX also were determined The results showed that both free and immobilized LOX favor linoleic acid as a substrate. Relative substrate preference for free LOX was linoleic acid >1‐monolinolein > 1,3‐dilinolein >trilinolein, and for immobilized LOX was linoleic acid >l, 3‐dilinolein >1‐monolinolein >trilinolein. In general, LOX immobilized in alginate silica sol‐gel matrix retained the physical and chemical characteristics of free LOX.