Thermal pasteurization of ready-to-eat foods and vegetables: Critical factors for process design and effects on quality.

Increasing consumer desire for high quality ready-to-eat foods makes thermal pasteurization important to both food producers and researchers. To be in compliance with the Food Safety Modernization Act (FSMA), food companies seek regulatory and scientific guidelines to ensure that their products are safe. Clearly understanding the regulations for chilled or frozen foods is of fundamental importance to the design of thermal pasteurization processes for vegetables that meet food safety requirements. This article provides an overview of the current regulations and guidelines for pasteurization in the U.S. and in Europe for control of bacterial pathogens. Poorly understood viral pathogens, in terms of their survival in thermal treatments, are an increasing concern for both food safety regulators and scientists. New data on heat resistance of viruses in different foods are summarized. Food quality attributes are sensitive to thermal degradation. A review of thermal kinetics of inactivation of quality-related enzymes in vegetables and the effects of thermal pasteurization on vegetable quality is presented. The review also discusses shelf-life of thermally pasteurized vegetables.

Spatial variance of physicochemical properties within mangos and the effect of initial ripeness stage on the quality of fresh-cut mangos.

BACKGROUND: This study aimed to assess the spatial variation in physicochemical properties within individual mangos, as well as to investigate the influence of initial ripeness level on physicochemical characteristics of fresh-cut mangos. Individual mangos were evaluated at 12 specific flesh positions in the inner and outer sides. Mango cubes of 1.5 cm prepared from three firmness stages were monitored for changes during 9 days of storage at 5 °C. RESULTS: Mango fruit varied significantly in firmness and color based on spatial position, with the ripening direction from the inner flesh outward and from the stem end to blossom end. Limitations to fresh-cut mango quality were 'desiccation' (dried cut surface) and 'edge or tissue damage' (cut edge damage or brown and bruise-like appearance). Firmer texture and paler yellow of inner flesh were found in less mature mango fruit (P < 0.001). The optimal ripeness stage for fresh-cut mango products was 45 N, based on ease of handling, fresh appearance at the time of purchase and intermediate physicochemical properties (firmness, color and SSC/TA ratio). CONCLUSION: Spatial variance and initial ripeness stage affect fresh-cut mango quality. Therefore, they must be considered by fresh-cut mango processors in order to attain optimal product quality. © 2015 Society of Chemical Industry.

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.

Advanced preservation methods and nutrient retention in fruits and vegetables.

Despite the recommendations of international health organizations and scientific research carried out around the world, consumers do not take in sufficient quantities of healthy fruit and vegetable products. The use of new, 'advanced' preservation methods creates a unique opportunity for food manufacturers to retain nutrient content similar to that found in fresh fruits and vegetables. This review presents a summary of the published literature regarding the potential of high-pressure and microwave preservation, the most studied of the 'advanced' processes, to retain the natural vitamin A, B, C, phenolic, mineral and fiber content in fruits and vegetables at the time of harvest. Comparisons are made with more traditional preservation methods that utilize thermal processing. Case studies on specific commodities which have received the most attention are highlighted; these include apples, carrots, oranges, tomatoes and spinach. In addition to summarizing the literature, the review includes a discussion of postharvest losses in general and factors affecting nutrient losses in fruits and vegetables. Recommendations are made for future research required to evaluate these advanced process methods.

Texture improvement of fresh and frozen mangoes with pectin methylesterase and calcium infusion.

BACKGROUND: A major problem of mango products is texture loss. The effect of commercial pectin methylesterase (PME) and calcium infusion on improvement of the texture of both fresh and frozen-thawed mango cubes was investigated in the present study. RESULTS: The weight gain and moisture content of mango samples were greater at relatively high vacuum level (10 kPa). The PME activity of samples infused with PME and calcium at 10 kPa increased fourfold in comparison with that of control and water-infused samples. The combined effect of PME and calcium was found to improve the texture and microstructure of both fresh and frozen-thawed mangoes. Fresh mangoes infused with PME and calcium at 10 kPa showed significantly higher firmness than control fresh samples. Frozen-thawed mangoes infused with PME and calcium at 50 kPa and atmospheric pressure had superior texture and microstructure in comparison with control frozen-thawed samples. CONCLUSION: The results of the present analysis allow for a better appreciation of the role of PME, calcium and appropriate infusion conditions in improving the texture of both fresh and frozen-thawed mangoes.

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.

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.

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.

Nonenzymatic degradation of citrus pectin and pectate during prolonged heating: effects of pH, temperature, and degree of methyl esterification.

The underlying mechanisms governing nonenzymatic pectin and pectate degradation during thermal treatment have not yet been fully elucidated. This study determined the extent of nonenzymatic degradation due to beta-elimination, acid hydrolysis, and demethylation during prolonged heating of citrus pectins and its influence on physicochemical properties. Solutions of citrus pectins, buffered from pH 4.0 to 8.5, were heated at 75, 85, 95, and 110 degrees C for 0-300 min. Evolution of methanol and formation of reducing groups and unsaturated uronides were monitored during heating. Molecular weight and viscosity changes were determined through size exclusion chromatography and capillary viscometry, respectively. Results showed that at pH 4.5, the activation energies of acid hydrolysis, beta-elimination, and demethylation are 95, 136, and 98 kJ/mol, respectively. This means that at this pH, acid hydrolysis occurs more rapidly than beta-elimination. Furthermore, the rate of acid hydrolysis is diminished by higher levels of methyl esterification. Also, citrus pectin (93% esterified) degrades primarily via beta-elimination even under acidic conditions. Acid hydrolysis and beta-elimination caused significant reduction in relative viscosity and molecular weight.

Reactivation of broccoli peroxidases: structural changes of partially denatured isoenzymes.

UNLABELLED: Structural changes involved in the reactivation of peroxidases (PODs) from broccoli and horseradish (HRP) following heat denaturation were investigated by using circular dichroism and absorption spectroscopy. Cooling heat-treated enzymes resulted in rapid refolding of the secondary structure into an inactive structural species, similar in conformation to the native enzyme. Reassociation of heme to the refolded peroxidase, as well as molecular rearrangement of the structure around the heme, occurs during incubation at approximately 25 degrees C and results in the return of biological activity. The secondary structure of neutral broccoli POD (N) is relatively heat labile, resulting in a rapid loss of activity, but the level of reactivation is high because the structure at the heme pocket is relatively stable. Acidic broccoli POD and HRP are more heat stable than N, but have a low degree of reactivation. Loss of activity is due primarily to alteration of the structure at the heme pocket. Effects of bovine serum albumin and pH on reactivation of PODs are also discussed. KEYWORDS: Peroxidase; reactivation; horseradish; broccoli; circular dichroism; absorption spectroscopy.

Ten-year comparison of the influence of organic and conventional crop management practices on the content of flavonoids in tomatoes.

Understanding how environment, crop management, and other factors, particularly soil fertility, influence the composition and quality of food crops is necessary for the production of high-quality nutritious foods. The flavonoid aglycones quercetin and kaempferol were measured in dried tomato samples (Lycopersicon esculentum L. cv. Halley 3155) that had been archived over the period from 1994 to 2004 from the Long-Term Research on Agricultural Systems project (LTRAS) at the University of California-Davis, which began in 1993. Conventional and organic processing tomato production systems are part of the set of systems compared at LTRAS. Comparisons of analyses of archived samples from conventional and organic production systems demonstrated statistically higher levels (P < 0.05) of quercetin and kaempferol aglycones in organic tomatoes. Ten-year mean levels of quercetin and kaempferol in organic tomatoes [115.5 and 63.3 mg g(-1) of dry matter (DM)] were 79 and 97% higher than those in conventional tomatoes (64.6 and 32.06 mg g(-1) of DM), respectively. The levels of flavonoids increased over time in samples from organic treatments, whereas the levels of flavonoids did not vary significantly in conventional treatments. This increase corresponds not only with increasing amounts of soil organic matter accumulating in organic plots but also with reduced manure application rates once soils in the organic systems had reached equilibrium levels of organic matter. Well-quantified changes in tomato nutrients over years in organic farming systems have not been reported previously.

Characterization of the temperature activation of pectin methylesterase in green beans and tomatoes.

Low-temperature blanching of vegetables activates the enzyme pectin methylesterase (PME), which demethylates cell wall pectins and improves tissue firmness. This temperature activation of PME has been investigated by measuring the formation of methanol in intact tissue of green beans and tomatoes. Rates of methanol formation at temperatures of 35-65 degrees C were obtained by measuring the release of methanol from thin slices of tomato pericarp or green bean pod material. Activation energies of 112 and 97 kJ mol(-1) were calculated for PME activity in green beans and tomatoes, respectively. These activation energies indicate that the rate of pectin demethylation at 65 degrees C will be nearly 100 times that at 25 degrees C. PME activity was also determined titrimetrically using a solubilized form of the enzyme and purified pectin at temperatures from 30 to 60 degrees C. Under these conditions, much lower activation energies of 37 and 35 kJ mol(-1) were obtained for green beans and tomatoes, respectively. Methanol accumulation during heating of whole intact green beans was also determined and yielded an activation energy similar to that obtained with sliced beans. Whole green beans held at room temperature did not accumulate any methanol, but sliced or homogenized beans did. If whole beans were first heated to 45 degrees C and then cooled, methanol accumulation was observed at room temperature. These results indicate that two factors contribute to the observed high rate of pectin de-esterification during low-temperature blanching: (1) An irreversible change, causing PME to become active, occurs by heating to > or = 45 degrees C. (2) The high activation energy for pectin de-esterification means that the rate of de-esterification increases substantially with increasing temperature.

Effects of Peach Cultivar on Enzymatic Browning Following Cell Damage from High-Pressure Processing.

Peach cultivars contribute to unique product characteristics and may affect the degree of browning after high-pressure processing (HPP). Nine peach cultivars were subjected to HPP at 0, 100, and 400 MPa for 10 min. Proton nuclear magnetic resonance (1H NMR) relaxometry, light microscopy, color, polyphenol oxidase (PPO) activity, and total phenols were evaluated. The development of enzymatic browning during refrigerated storage occurred because of damage during HPP that triggered loss of cell integrity, allowing substrates to interact with enzymes. Increasing pressure levels resulted in greater damage, as determined by shifts in transverse relaxation time (T2) and by light micrographs. Discoloration was triggered by membrane decompartmentalization but limited by PPO activity, which was found to correlate to cultivar harvest time (early, mid, and late season). Outcomes from the microstructure, 1H NMR ,and PPO activity evaluation were an effective means of determining membrane decompartmentalization and allowed for prediction of browning scenarios.

The Impact of Maturity Stage on Cell Membrane Integrity and Enzymatic Browning Reactions in High Pressure Processed Peaches (Prunus persica).

Fruit maturity is an important factor associated with final product quality, and it may have an effect on the level of browning in peaches that are high pressure processed (HPP). Peaches from three different maturities, as determined by firmness (M1 = 50-55 N, M2 = 35-40 N, and M3 = 15-20 N), were subjected to pressure levels at 0.1, 200, and 400 MPa for 10 min. The damage from HPP treatment results in loss of fruit integrity and the development of browning during storage. Increasing pressure levels of HPP treatment resulted in greater damage, particularly in the more mature peaches, as determined by shifts in transverse relaxation time (T2) of the vacuolar component and by light microscopy. The discoloration of peach slices of different maturities processed at the same pressure was comparable, indicating that the effect of pressure level is greater than that of maturity in the development of browning.

High hydrostatic pressure as a method to preserve fresh-cut Hachiya persimmons: A structural approach.

The "Hachiya" persimmon is the most common astringent cultivar grown in California and it is rich in tannins and carotenoids. Changes in the microstructure and some physicochemical properties during high hydrostatic pressure processing (200-400 MPa, 3 min, 25 ℃) and subsequent refrigerated storage were analyzed in this study in order to evaluate the suitability of this non-thermal technology for preservation of fresh-cut Hachiya persimmons. The effects of high-hydrostatic pressure treatment on the integrity and location of carotenoids and tannins during storage were also analyzed. Significant changes, in particular diffusion of soluble compounds which were released as a result of cell wall and membrane damage, were followed using confocal microscopy. The high-hydrostatic pressure process also induced changes in physicochemical properties, e.g. electrolyte leakage, texture, total soluble solids, pH and color, which were a function of the amount of applied hydrostatic pressure and may affect the consumer acceptance of the product. Nevertheless, the results indicate that the application of 200 MPa could be a suitable preservation treatment for Hachiya persimmon. This treatment seems to improve carotenoid extractability and tannin polymerization, which could improve functionality and remove astringency of the fruit, respectively.

Purification and partial characterization of broccoli (Brassica oleracea Var. Italica) peroxidases.

Three peroxidase (POD) isoenzymes were purified from a soluble extract of broccoli stems. The acidic and neutral PODs were purified to homogeneity by using ion exchange and hydrophobic chromatography. The basic POD was purified by cation exchange and gel filtration chromatography. The neutral and basic PODs had molecular masses of approximately 43 kDa, and the acidic POD had a molecular mass of 48 kDa by SDS-PAGE. pI was approximately 4, 5, and 8 for acidic, neutral, and basic PODs, respectively. Optimum activity using guaiacol as the H donor was obtained at pH approximately 6 for both neutral and basic PODs and at pH approximately 4 for acidic POD. All three of the purified isoenzymes are glycosylated. Reaction rates with various substrates including guaiacol, guaiacol/MBTH, DMAB/MBTH, and ferulic acid/MBTH were different among the isoenzymes. K(m) and amino acid composition were also determined.

Heat inactivation and reactivation of broccoli peroxidase.

Heat inactivation characteristics differed for acidic (A), neutral (N), and basic (B) broccoli peroxidase. At 65 degrees C, A was the most heat stable followed by N and B. The activation energies for denaturation were 388, 189, and 269 kJ/mol for A, N, and B, respectively. Reactivation of N occurred rapidly, within 10 min after the heated enzyme was cooled and incubated at room temperature. The extent of reactivation varied from 0 to 50% depending on the isoenzyme and heating conditions (temperature and time). The denaturation temperature allowing the maximum reactivation was 90 degrees C for A and horseradish peroxidase (HRP) and 70 and 80 degrees C for B and N, respectively. In all cases, heat treatment at low temperatures for long times prevented reactivation of the heated enzymes. Calcium (5 mM) increased the thermal stability of N and B but had no effect on reactivation. The presence of 0.05% bovine serum albumin decreased thermal stability but increased the extent of reactivation of A..

Mineral, fiber, and total phenolic retention in eight fruits and vegetables: a comparison of refrigerated and frozen storage.

Minerals, total phenolics, and fiber were analyzed in several fruit and vegetable commodities to evaluate the differences between fresh and frozen produce. Magnesium, calcium, iron, zinc, and copper were evaluated in corn, carrots, broccoli, spinach, peas, green beans, strawberries, and blueberries. Each commodity was harvested fresh and split into two batches. Half of each commodity was kept fresh, and the other half was frozen. The nutrient content was analyzed over three storage times per treatment. The retention of nutrients was highly dependent on the commodity, but the majority of the commodities showed no significant difference between fresh and frozen for all analytes (p ≤ 0.05).

Vitamin retention in eight fruits and vegetables: a comparison of refrigerated and frozen storage.

Four vitamins were analyzed in several fruit and vegetable commodities to evaluate the differences between fresh and frozen produce. Ascorbic acid, riboflavin, α-tocopherol, and ß-carotene were evaluated in corn, carrots, broccoli, spinach, peas, green beans, strawberries, and blueberries. Samples of each commodity were harvested, processed, and analyzed for nutrient content at three storage times per treatment. Ascorbic acid showed no significant difference for five of the eight commodities and was higher in frozen samples than fresh for the remaining three commodities. Apart from broccoli and peas, which were higher and lower in frozen vs fresh samples, respectively, none of the commodities showed significant differences with respect to riboflavin content. Three commodities had higher levels of α-tocopherol in the frozen samples, while the remaining commodities showed no significant difference between fresh and frozen. ß-Carotene was not found in significant amounts in blueberries, strawberries, and corn. Peas, carrots, and spinach were lower in ß-carotene in the frozen samples, while green beans and spinach showed no significant difference between the two storage methods. Overall, the vitamin content of the frozen commodities was comparable to and occasionally higher than that of their fresh counterparts. ß-Carotene, however, was found to decrease drastically in some commodities.

Comparison of three colorimetric reagents in the determination of methanol with alcohol oxidase. Application to the assay of pectin methylesterase.

Three colorimetric reagents for the determination of formaldehyde, the Nash reagent (ammonia plus acetylacetone), Purpald (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole), and N-methylbenzothiazolinone-2-hydrazone (MBTH), were compared for the determination of methanol when used in conjunction with alcohol oxidase. The combination of alcohol oxidase plus the commonly used Nash reagent was specific for methanol versus ethanol, but had the lowest sensitivity of the three reagents tested. Substituting Purpald for the Nash reagent increased the sensitivity 3-fold while still maintaining a high (59-fold) selectivity for methanol versus ethanol. Using MBTH increased the sensitivity still further, but with a loss of the selectivity toward methanol. Since MBTH reacted with aldehydes under neutral conditions, it could be included along with the alcohol oxidase to act as an aldehyde trap. This prevented further oxidation reactions by alcohol oxidase and allowed for extended incubations. A procedure for assaying low levels of pectin methylesterase activity that relies on this trapping ability is described. In addition, alcohol oxidase plus Purpald is shown to be a simple and sensitive way to measure the methanol released from plant material following the thermal activation of endogenous pectin methylesterase.