Gordon E. Anthon

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.

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.

Changes in pectins and product consistency during the concentration of tomato juice to paste.

Concentrating tomato juice to paste during the tomato season allows for preservation and long-term storage, but subsequent dilution for formulation of value-added products is known to result in a loss of consistency. To understand the reasons for this, samples of unconcentrated juice, processing intermediates, and concentrated paste were collected from an industrial processing plant during normal commercial production. All samples were diluted with water to 5 degrees Brix and then analyzed for consistency and pectin content. Whole juice consistency, measured with a Bostwick consistometer, decreased through the course of juice concentration, with the largest change occurring early in the process, as the juice was concentrated from 5 to 10 degrees Brix. This decrease in consistency occurred during the production of paste from both hot- and cold-break juices. The change in Bostwick value was correlated with a decrease in the precipitate weight ratio. The loss of consistency during commercial processing was not the direct result of water removal because a sample of this same 5 degrees Brix juice could be concentrated 2-fold in a vacuum oven and then diluted back to 5 degrees Brix with no change in consistency or precipitate ratio. Total pectin content did not change as the juice was concentrated to paste, but the proportion of the total pectin that was water soluble increased. The greatest increases in pectin solubility occurred during the hot break and late in the process where the evaporator temperature was the highest.

Onion cells after high pressure and thermal processing: comparison of membrane integrity changes using different analytical methods and impact on tissue texture.

UNLABELLED Two different analytical methods were evaluated for their capacity to provide quantitative information on onion cell membrane permeability and integrity after high pressure and thermal processing and to study the impact of these processing treatments on cell compartmentalization and texture quality. To determine changes in cell membrane permeability and/or integrity the methodologies utilized were: (1) measurement of a biochemical product, pyruvate, formed as a result of membrane permeabilization followed by enzymatic activity and (2) leakage of electrolytes into solution. These results were compared to previously determined methods that quantified cell viability and ¹H-NMR T(2) of onions. These methods allowed for the monitoring of changes in the plasma and tonoplast membranes after high pressure or thermal 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. There was strong agreement between the methods in the determination of the ranges of high pressure and temperature that induce changes in the integrity of the plasma and tonoplast membranes. Membrane rupture could clearly be identified at 300 MPa and above in high pressure treatments and at 60 °C and above in the thermal treatments. Membrane destabilization effects could already be visualized following the 200 MPa and 50 °C treatments. The texture of onions was influenced by the state of the membranes and was abruptly modified once membrane integrity was lost. PRACTICAL APPLICATION In this study, we used chemical, biochemical, and histological techniques to obtain information on cell membrane permeability and onion tissue integrity after high pressure and thermal processing. Because there was strong agreement between the various methods used, it is possible to implement something relatively simple, such as ion leakage, into routine quality assurance measurements to determine the severity of preservation methods and the shelf life of processed vegetables.

An integrated approach for flavour quality evaluation in muskmelon (Cucumis melo L. reticulatus group) during ripening

Numerous and diverse physiological changes occur during fruit ripening and maturity at harvest is one of the key factors influencing the flavour quality of fruits. The effect of ripening on chemical composition, physical parameters and sensory perception of three muskmelon (Cucumis melo L. reticulatus group) cultivars was evaluated. Significant correlations emerging from this extensive data set are discussed in the context of identifying potential targets for melon sensory quality improvement. A portable ultra-fast gas-chromatograph coupled with a surface acoustic wave sensor (UFGC-SAW) was also used to monitor aroma volatile concentrations during fruit ripening and evaluated for its ability to predict the sensory perception of melon flavour. UFGC-SAW analysis allowed the discrimination of melon maturity stage based on six measured peaks, whose abundance was positively correlated to maturity-specific sensory attributes. Our findings suggest that this technology shows promise for future applications in rapid flavour quality evaluation.

Rapid Assessment of Quality Parameters in Processing Tomatoes Using Hand-Held and Benchtop Infrared Spectrometers and Multivariate Analysis

Two portable infrared sensors were evaluated for the rapid determination of quality parameters in processing tomatoes. A total of 370 hot-break juices were prepared from ∼40 processing tomato varieties grown in 5 California counties. The levels of sugars, acids, soluble solids, titratable acidity, and pH in these juices were determined using standard reference methods. Juices were processed, filtered, and directly applied to the FT-IR crystal (15-40 μL) to obtain spectra. Partial least-squares regression (PLSR) was used to generate correlation models, both calibration and validation. The PLS validation models showed good ability (Rval > 0.80; <10% SEP) in estimating the sugars, acids, and especially soluble solids in tomato for both the transmission DialPath portable system and benchtop unit using triple-bounce attenuated total reflectance (ATR). The IR portable unit may provide the tomato processing industry with an efficient method for in-plant, high throughput quantification of quality parameters in tomatoes.

Conformational changes in serum pectins during industrial tomato paste production.

It is well-known that an irreversible decrease in serum viscosity occurs when tomato juice is concentrated by evaporation into paste. Several studies have suggested that the loss in serum viscosity is due to pectin depolymerization, caused by the high temperatures used during industrial tomato paste production. This study demonstrates that conformational changes in pectin may play a more important role than pectin depolymerization in the irreversible loss of serum viscosity during industrial tomato paste production. Samples of tomato juice, processing intermediates, and paste were obtained from a commercial producer in California. After dilution to 5 degrees Brix, tomato serum was obtained by centrifugation at 15000 g for 10 min. Weight average molecular weight (M(w)) and root-mean-square (rms) radius of the polymers in the tomato serum were determined using high-performance size-exclusion chromatography with multi-angle laser light scattering and refractive index detectors (HPSEC-MALLS-RI). Serum viscosity decreased throughout the juice concentration process, especially at later stages, where the processing temperature reached a maximum of 90-95 degrees C. In parallel with this decrease in serum viscosity, there was an increase in the soluble pectin concentration. Analysis of the M(w) distribution of the tomato serum showed that solubilization of pectin occurred across the entire polymer distribution range. The M(w) changed from 2.62 x 10(5) g/mol in the juice to 2.61 x 10(5) g/mol in the paste, indicating that minimal depolymerization occurred. However, the rms radius distribution indicated that the pectin conformation became more compact as the juice became more concentrated. Conformational plots revealed that serum pectins in the hot-break tomato juice and at the early stages of concentration behaved as extended coils, having shape factors of about 0.40. In processing intermediates taken from later stages in the process and in the paste, the shape factor changed to about 0.25, indicating a more compact conformation. This conformational change correlated with the observed decrease in serum viscosity in the paste production process. This result is consistent with a Flory-Fox-type relationship between viscosity, rms radius, and M(w). The conformational change may be due to increased polymer-polymer interaction brought about by the concentration process.

Effect of Pectin Methylesterase on Carrot (Daucus carota) Juice Cloud Stability

To determine the effect of residual enzyme activity on carrot juice cloud, 0 to 1 U/g pectin methylesterase (PME) was added to pasteurized carrot juice. Cloud stability and particle diameters were measured to quantify juice cloud stability and clarification for 56 days of storage. All levels of PME addition resulted in clarification; higher amounts had a modest effect in causing more rapid clarification, due to a faster increase in particle size. The cloud initially exhibited a trimodal distribution of particle sizes. For enzyme-containing samples, particles in the smallest-sized mode initially aggregated to merge with the second peak over 5-10 days. This larger population then continued to aggregate more slowly over longer times. This observation of a more rapid destabilization process initially, followed by slower subsequent changes in the cloud, was also manifested in measurements of sedimentation extent and in turbidity tests. Optical microscopy showed that aggregation created elongated, fractal particle structures over time.

The effects of bruising and temperature on enzyme activity and textural qualities of tomato juice.

BACKGROUND During harvest and transportation, processing tomatoes are exposed to elevated temperatures, compression and vibration in the harvester and truck, making them prone to bruising. The objective of this study was to determine how bruising and exposure to high temperatures affect pectin methylesterase (PME) activation and the textural quality of tomato juice. RESULTS Tomatoes were both hand and mechanically harvested using current harvest practices. Mechanically harvested fruits were significantly softer, had greater PME activity and greater juice consistency than hand harvested fruits. In a controlled bruising study, whole tomatoes were exposed to various compressive forces at 21 or 40 °C and held for 0 or 4 h. Greater bruising force and higher temperature resulted in a decrease in firmness and an increase in PME activity. Consistency of tomato juice improved when tomatoes were exposed to 40 °C. Tomatoes subjected to a temperature range from 21 to 65 °C had activated PME at 40 °C and increased activity as temperature increased. Consistency increased at 35 °C but decreased with increasing temperature. CONCLUSION Tomatoes harvested using current mechanical techniques are likely to be less firm and have increased PME activity; however, increased consistency of processed juice is observed. Tomatoes harvested at higher temperatures are also likely to have better consistency when processed.

Changes in consistency of tomato juice during concentration.

Processing tomatoes are typically harvested during a ten to twelve week season in California, and tomato juice is concentrated to stabilize the product for use during the remainder of the year. Manufacturers of value-added products formulated with concentrated tomato paste often note that there is a loss of consistency during the process and storage. To understand the reasons for this, samples of unconcentrated juice, processing intermediates, and concentrated paste were collected from an industrial processing plant during normal commercial production. All samples were diluted with water to 5°Brix then analyzed for consistency and pectin content. Whole juice consistency, measured with a Bostwick consistometer, decreased through the course of juice concentration, with the largest change occurring early in the process, as the juice was concentrated from 5 to 10°Brix. This decrease in consistency occurred during the production of paste from both hot- and cold-break juices. Total pectin content did not change as the juice was concentrated to paste but the proportion of the total pectin that was water soluble increased. The greatest increases in pectin solubility occurred during the hot-break and late in the process where the evaporator temperature was the highest.