Diane M. Barrett

Comparison of calcium chloride and calcium lactate effectiveness in maintaining shelf stability and quality of fresh-cut cantaloupes.

Fresh-cut cantaloupe cylinders were dipped for 1 min in 2.5% solutions of either calcium chloride (CaCl2 )a t 25°C or calcium lactate at 25 and 60°C. Firmness, microbiological (total plate count, yeast and mold, and microaerophilic bacteria) and sensory characteristics, respiration (CO2) and ethylene (C2H4) production were evaluated during 12 days storage at 5°C and 95% relative humidity air. Both calcium salts maintained melon firmness throughout cold storage. CaCl2, but not calcium lactate, imparted undesirable bitterness to the fruit pieces. No significant differences were observed in the physiological behavior of the treated fresh-cut compared to just-cut samples.

Fresh-cut cantaloupe: effects of CaCl2 dips and heat treatments on firmness and metabolic activity

Abstract Calcium chloride (1–5%) dips were applied to melon cylinders taken from commercially ripe (3/4 to full slip) cantaloupe melons for 1–5 min. A wound response was observed after cutting, and CO 2 production was higher in untreated samples than in calcium treated and intact fruit. Dip time did not significantly effect respiration rate. Application of calcium dips at any temperature resulted in unchanged ethylene production throughout storage, and inhibited respiration. Calcium chloride dips improved firmness of fresh-cut cantaloupe during storage at 5°C, with 1 min dips showing the same effect as 5 min dips. When dipped for 1 min in 2.5% calcium chloride solutions at 20, 40 or 60°C, firmness was maintained or improved, especially at higher dip temperatures while total calcium concentration in the melon tissue was increased on average by 300%.

Color, Flavor, Texture, and Nutritional Quality of Fresh-Cut Fruits and Vegetables: Desirable Levels, Instrumental and Sensory Measurement, and the Effects of Processing

The color, flavor, texture, and the nutritional value of fresh-cut fruit and vegetable products are factors critical to consumer acceptance and the success of these products. In this chapter, desirable and undesirable quality attributes of fresh-cut fruit and vegetable products are reviewed. Both instrumental and sensory measurements for determining these critical quality attributes are discussed. The advantages and disadvantages of sensory and instrumental quality measurements are described. A review of typical unit operations involved in the production of fresh-cut products is presented. The effects of fresh-cut processing techniques and treatments on sensory quality, including the appearance, texture, flavor (taste and aroma) of vegetables, and fruits are detailed.

Textural modification of processing tomatoes.

Knowledge of the textural properties of processing tomatoes is crucial to ensuing product acceptability; measurement, control, and optimization of these properties through judicious selection of varieties and control of unit operations results in products that the consumer prefers. It is important to first define the terms texture, rheology, consistency, and viscosity prior to discussing principles of their measurement. The textural properties of processing tomatoes may be measured using both sensory and objective tests, and the latter may be either destructive or nondestructive in nature. The unique anatomy of tomato fruit (peel, pericarp, columella, and locules) in part dictates the method of texture measurement. Numerous factors, including variety, maturity, genetic modification, cultural particles, and environmental conditions, processing conditions, and calcium addition affect the textural integrity of tomatoes. Textural properties of raw tomatoes and most processed tomato products are reviewed in this article.

Changes in pH, acids, sugars and other quality parameters during extended vine holding of ripe processing tomatoes

BACKGROUND Two important quality attributes of processing tomatoes are pH and titratable acidity. These and other quality attributes can be affected by tomato fruit maturity and over-maturity. We have determined the magnitude of these maturity effects in four processing tomato cultivars commonly grown in California. RESULTS Allowing tomatoes to remain on the vine for up to 4 weeks after ripening resulted in an increase in fruit pH of between 0.01 and 0.02 unit per day for the four cultivars examined. The increase in pH was paralleled by a decrease in titratable acidity, due to a loss of citric acid. Glucose and fructose concentrations also declined with increasing maturity after ripening. Other quality parameters (color, lycopene, total pectin, pectin solubility, and Bostwick consistency) all showed little change. CONCLUSION Vine holding of ripe fruit adversely affects quality, especially pH and titratable acidity. Recent problems with high tomato juice pH encountered by tomato processors in California could be the result of increased average fruit maturity at harvest.

Thermal, High Pressure, and Electric Field Processing Effects on Plant Cell Membrane Integrity and Relevance to Fruit and Vegetable Quality

Advanced food processing methods that accomplish inactivation of microorganisms but minimize adverse thermal exposure are of great interest to the food industry. High pressure (HP) and pulsed electric field (PEF) processing are commercially applied to produce high quality fruit and vegetable products in the United States, Europe, and Japan. Both microbial and plant cell membranes are significantly altered following exposure to heat, HP, or PEF. Our research group sought to quantify the degree of damage to plant cell membranes that occurs as a result of exposure to heat, HP, or PEF, using the same analytical methods. In order to evaluate whether new advanced processing methods are superior to traditional thermal processing methods, it is necessary to compare them. In this review, we describe the existing state of knowledge related to effects of heat, HP, and PEF on both microbial and plant cells. The importance and relevance of compartmentalization in plant cells as it relates to fruit and vegetable quality is described and various methods for quantification of plant cell membrane integrity are discussed. These include electrolyte leakage, cell viability, and proton nuclear magnetic resonance (¹H-NMR).Advanced food processing methods that accomplish inactivation of microorganisms but minimize adverse thermal exposure are of great interest to the food industry. High pressure (HP) and pulsed electric field (PEF) processing are commercially applied to produce high quality fruit and vegetable products in the United States, Europe, and Japan. Both microbial and plant cell membranes are significantly altered following exposure to heat, HP, or PEF. Our research group sought to quantify the degree of damage to plant cell membranes that occurs as a result of exposure to heat, HP, or PEF, using the same analytical methods. In order to evaluate whether new advanced processing methods are superior to traditional thermal processing methods, it is necessary to compare them. In this review, we describe the existing state of knowledge related to effects of heat, HP, and PEF on both microbial and plant cells. The importance and relevance of compartmentalization in plant cells as it relates to fruit and vegetable quality is described and various methods for quantification of plant cell membrane integrity are discussed. These include electrolyte leakage, cell viability, and proton nuclear magnetic resonance (1H-NMR).

Critical Electric Field Strengths of Onion Tissues Treated by Pulsed Electric Fields

The impact of pulsed electric fields (PEF) on cellular integrity and texture of Ranchero and Sabroso onions (Allium cepa L.) was investigated. Electrical properties, ion leakage rate, texture, and amount of enzymatically formed pyruvate were measured before and after PEF treatment for a range of applied field strengths and number of pulses. Critical electric field strengths or thresholds (E(c)) necessary to initiate membrane rupture were different because dissimilar properties were measured. Measurement of electrical characteristics was the most sensitive method and was used to detect the early stage of plasma membrane breakdown, while pyruvate formation by the enzyme alliinase was used to identify tonoplast membrane breakdown. Our results for 100-μs pulses indicate that breakdown of the plasma membrane occurs above E(c)= 67 V/cm for 10 pulses, but breakdown of the tonoplast membrane is above either E(c)= 200 V/cm for 10 pulses or 133 V/cm for 100 pulses. This disparity in field strength suggests there may be 2 critical electrical field strengths: a lower field strength for plasma membrane breakdown and a higher field strength for tonoplast membrane breakdown. Both critical electric field strengths depended on the number of pulses applied. Application of a single pulse at an electric field up to 333 V/cm had no observable effect on any measured properties, while significant differences were observed for n≥10. The minimum electric field strength required to cause a measurable property change decreased with the number of pulses. The results also suggest that PEF treatment may be more efficient if a higher electric field strength is applied for a fewer pulses.

Relating descriptive analysis and instrumental texture data of processed diced tomatoes

The textural properties of two varieties of tomatoes processed in duplicate by three methods (aseptic, cold-fill and hot-fill) were assessed by descriptive analysis and instrumental measurements [Kramer shear press, back extrusion and texture profile analysis (TPA)]. Sensory and instrumental data were compared and correlated using correlation analysis, principal component analysis (PCA), cluster analysis (CA) and partial least squares (PLS) regression analysis. The biplot of PLS2 with all the samples and variables explained 89% of the X variables (instrumental measurements) and 58% of the Y variables (sensory attributes). Sensory firmness was mostly explained by the instrumental firmness measurements such as the area under the curve for the Kramer and back extrusion tests. Samples were separated according to the processing method, with cold-filled samples clustered in the region where firmness variables (sensory and instrumental) were located; and hot-filled and aseptic samples grouped in the region of cohesiveness (TPA measurement), chewy (sensory) and metallic variables. These were consistent with the results from the PCA of the matrix of mean sensory texture ratings and instrumental variables across samples, run on the correlation matrix. Cluster analysis of the sensory matrix clearly classified the samples according to the processing method, whereas cluster analysis of the instrumental matrix did not. We conclude that descriptive analysis provided a more accurate account of the textural properties of diced tomatoes than the instrumental measurements we used and that PLS is the technique of choice for relating sensory and instrumental variables. # 1999 Elsevier Science Ltd. All rights reserved.

Combined enzymatic and colorimetric method for determining the uronic acid and methylester content of pectin: Application to tomato products

A simple procedure for determining the galacturonic acid and methanol contents of soluble and insoluble pectins, relying on enzymatic pectin hydrolysis and colorimetric quantification, is described. Pectin samples are incubated with a commercial pectinase preparation, Viscozyme, then the galacturonic acid content of the hydrolyzed pectin is quantified colorimetrically using a modification of the Cu reduction procedure originally described by Avigad and Milner. This modification, substituting the commonly used Folin-Ciocalteau reagent for the arsenic containing Nelson reagent, gives a response that is linear, sensitive, and selective for uronic acids over neutral sugars. This method also avoids the use of concentrated acids needed for the commonly used m-phenylphenol method. Methanol, released by the action of the pectin methylesterase found in the Viscozyme, is quantified using alcohol oxidase and Purpald. This combined enzymatic and colorimetric procedure correctly determined the galacturonic acid and methanol content of purified, soluble citrus pectin. Application of the procedure to water insoluble pectins was evaluated with water insoluble material from apples and oranges. In both cases good agreement was obtained between this method and commonly used methods based on chemical pectin hydrolysis. Good agreement between these procedures was also found in the analysis of both soluble and insoluble pectins from several tomato products.

Influence of Cell Integrity on Textural Properties of Raw, High Pressure, and Thermally Processed Onions

UNLABELLED The integrity of onion cells and its impact on tissue texture after high pressure and thermal processing was studied. The contribution of cell membranes and the pectic component of cell walls on the texture properties of onion tissue were analyzed. Neutral red (NR) staining of onion parenchyma cell vacuoles was used for the evaluation of cell membrane integrity and microscopic image analysis was used for its quantification. The content of methanol in tissue as a result of pectin methylesterase activity was used to evaluate the pectin component of the middle lamella and cell walls and the hardening effect on the tissue after processing. High pressure treatments consisted of 5-min holding times at 50, 100, 200, 300, or 600 MPa. Thermal treatments consisted of 30-min water bath exposure to 40, 50, 60, 70, or 90 °C. In the high pressure treatments, loss of membrane integrity commenced at 200 MPa and total loss of membrane integrity occurred at 300 MPa and above. In the thermal treatments, membrane integrity was lost between 50 and 60 °C. The texture of onions was influenced by the state of the membranes and texture profiles were abruptly modified once membrane integrity was lost. Hardening of the tissue corresponded with pressure and temperature PME activation and occurred after membrane integrity loss. PRACTICAL APPLICATION The texture of vegetables is an important quality attribute that affects consumer preference. Loss of textural integrity also indicates that other biochemical reactions that affect color, flavor, and nutrient content may occur more rapidly. In this study, we analyzed changes in the texture of onions after preservation with heat and high pressure.