JFS: Food Chemistry and Toxicology High Oxygen and High Carbon Dioxide Modified Atmospheres for Shelf-life Extension of Minimally Processed Carrots ABSTRACT: The impact of high O2 + high CO2 modified atmospheres (MA), on the preservation of minimally processed carrots was studied. A combination of 50% O2 + 30% CO2 prolonged the shelf life of sliced carrots compared to storage in air by 2 to 3 d. When the carrots received a pre-treatment with a 0.1% citric acid dip and a sodium alginate edible coating prior to packaging, shelf life was extended by 5 to 7 d. Advantages and disadvantages of the proposed MA over previously recommended MA (1% O2 + 10% CO2), related to a range of physicochemical and microbiological characteristics of carrots are discussed. Key Words: minimal processing, carrots, modified atmospheres, disinfection, edible coating, spoilage Introduction M INIMALLY PROCESSED (MP) CARROTS (washed, sliced, trimmed, cut, or peeled) are used as ready-to-eat snacks or salad vegetables. MP carrots are sold within 7 to 8 d after preparation but poor quality may limit shelf life to 4 to 5 d (Carlin and others 1990a). Deterioration occurs due to the development of off flavors, acidification, loss of firmness, and discoloration (Andersson 1984; Carlin and others 1989; Bolin and Huxsoll 1991; Howard and Griffin 1993). In general, the use of CA/MA (controlled/modified atmospheres) is beneficial for minimally processed products. Typically, a concentration of 5% to 10% CO2 and 2% to 5% O2 is applied to extend shelf life of these products (Kader and others 1989). For carrots, the reports on MA storage are contradictory. Bruemmer (1988) claimed that harvested carrots are physiologically too mature for senescence control, and thus MA storage is not beneficial. At 2% to 10% O2 and 10% to 40% CO2, sugar content may be retained to a greater extent than in air-stored samples, but spoilage can occur due to excessive growth of lactic acid bacteria (Carlin and others 1990b). Kato-Noguchi and Watada (1996, 1997a) reported that glycolysis is accelerated and that the ethanol and acetaldehyde levels are increased at O2 concentration below 2% as compared to air storage. In a few cases, MP carrots responded well under anoxic conditions (i.e. 0.5% O 2; Izumi and others 1996; Kakiomenou and others 1996), although the risk due to growth of anaerobic pathogenic microorganisms may be increased under these conditions. © 2000 Institute of Food Technologists Oxygen-enriched atmospheres (> 30%) have been tested for packaging of iceberg lettuce, oranges, and potato tubers (Aharoni and Houck 1982; Heimdal and others 1995). Sprouting of whole carrots was increased and mold growth was inhibited at 40% O 2 (Abdel-Rahman and Isenberg 1974). Day (1996) suggested that high O2 concentrations inhibit enzymatic activity, prevent moisture losses and microbial contamination during wet handling of carrots. Combinations of elevated O2 and CO2 may, however, delay growth of aerobic and anaerobic microorganisms, as was observed in an in vitro study, previously (Amanatidou and others 1999). The objective of this study was to investigate a range of quality indices (color, texture, sugar, phenols, thiobarbituric acid values, off-odor, and microbial spoilage) in order to identify possible benefits of the storage of MP carrots under high levels of O2 + CO2 in comparison to air and previously used MA storage. Carrots were exposed to controlled gas mixtures at 8 °C, a temperature generally used at retail storage. Since disinfection is commonly applied to slow down deterioration processes (Eytan and others 1992; Sapers and others 1995), the effect of dipping in chlorine and alternative disinfectants (citric acid, H2O2, and so forth) in combination with MA storage was studied. A sodium alginate edible coating was used as a barrier to white discoloration (Nussinovitch and Hersko 1996; Cisneros-Zevallos and others 1997). Results and Discussion Disinfection of carrots Effect on total quality. Washing with distilled water resulted in spoilage of MP carrots after 4 d at 8 °C (data not shown). After 8 d, softening and browning of the surface was clearly observed. Browning is probably related to oxidation of phenols (Chubey and Nhlund 1969). Disinfection with chlorine or 5% (v/v) H2O2 enhanced off-flavors or bitter taste, respectively. Sapers and Simmons (1998) recommended removal of residual H 2O2 after treatment but such action was not taken in our study, and this might explain the adverse effect of H2O2 treatment on the quality attributes. Washing in 0.1% and especially 0.5% (w/v) citric acid successfully kept the original appearance of the carrots for 8 d at 8 °C (Table 1). At the highest citric acid concentration (0.5%) a harsh taste was noted, probably as the result of acidification. The use of a protective edible coating retarded moisture losses and bleaching but did not extend shelf life. However, the quality characteristics of MP carrots were maintained for 10 d when 0.1% citric acid was incorporated in the edible coating (data not shown). Effect on color. Increased Whiteness Index (WI) values are related to the visual development of white discoloration (Table 1). White discoloration is an enzyme stimulated reaction related to dehydration of surfaces or formation of the wound barrier lignin (Tatsumi and others 1991; CisnerosZevallos and others 1995). For water-treated samples, increased WI values were recorded between d 1 and 4 of storage. Sapers and others (1995) reported rapid discoloration immediately after treatment with 5% or 10% H2O2, related to the browning of lettuce and carrots and bleaching of strawberries and raspberries. Vol. 65, No. 1, 2000—JOURNAL OF FOOD SCIENCE 61 Food Chemistry and Toxicology A. AMANATIDOU, R.A. SLUMP, L.G.M. GORRIS, AND E.J. SMID O2 and CO2 Effects on Carrots . . Food Chemistry and Toxicology A comparative study between several commercial waxes and coatings identified the hydrocolloid coating sodium alginate S170, with Ca++ as gelling agent, as a suitable coating for carrot slices (data not shown). Orange/red color of carrots was maintained for at least 8 d (Table 1). Alginate coatings allow the control of white discoloration of MP carrots (Li and Barth 1998). Sodium alginate reacts with polyvalent cations such as CaCl2 to form a gel (Kester and Fennema 1986). Nussinovitch and Hershko (1996) reported several applications of alginate coatings on vegetable products as barriers to moisture losses. Citric acid alone or incorporated in the coating allowed color retention and inhibited white discoloration (Table 1). Reyes and others (1996) used an edible coating incorporating an acidulant to inhibit white discoloration for up to 4 wk at 4 °C. Combined application of calcium and citric acid delayed browning of MP Chinese cabbage (Byeong and Klieber 1997). Effect on firmness. Chlorine treatment did not affect firmness of carrots as compared to the water-dipped samples. On the other hand, dipping in 5% H2O2 significantly increased firmness immediately after treatment and during storage (Table 1). The alginate coating gave a glossy appearance to the product and textural characteristics were retained for at least 8 d. Incorporation of 0.1 or 0.5% (w/v) citric acid in the edible coating had a slight effect on firmness even after 8 d (Table 1). Calcium and citric acid have been used to improve firmness of cooked carrots as well as shredded carrots (Stanley and others 1995). Calcium is thought to preserve membrane integrity of carrot shreds by delaying senescence-related membrane lipid changes, but also by augmenting membrane restructuring processes (Picchioni and others 1996). Effect on pH. All treatments resulted in a lowering of the pH from 6.1 (water control) to approximately 5.7 to 5.9 (data not shown). Chlorine treatment did not affect initial pH. Acidification was observed to some extend after 8 d of storage at samples dipped in 0.5% citric acid (pH 5.4). Effect on microbial flora. Microbial growth on MP carrots is favored by the high moisture and numerous cut surfaces (Brocklehurst and others 1987). The initial population of untreated carrots was high (6.4 log CFU/g). Spoilage of MP carrots under air is the result mainly of the action of pectolytic Pseudomonads. Other groups such as lactic acid bacteria and Enterobacteriaceae are also present on the surface of carrots after cutting. Chlorine or H2O2 dipping as well as coating treatment did not affect substantially the initial microbial load but reduced somewhat the level of Table 1—Changes in firmness, whiteness index, and spoilage symptoms after several disinfection treatments of carrots stored at 8 °C, in air, immediately after treatment (day 0) and after 8 d day Firmness (N) Whiteness index Distilled water 0 8 828a 690b 30.4a 37.2 c,d Chlorine 200ppm 0 8 835a,c 790 a,b,c 31.6a 38.7d White blush, off-flavor H2O2 5% 0 8 1189d 1274d 34.4b >42d White blush, slime, texture, bitter taste Citric acid 0.1% 0 8 870a,b 855 a,b,c 32.5a,b 35.4 b,c Citric acid 0.5% 0 8 901a,c 795a 30.4a ND1 Coating (S170 + 2% CaCl2) 0 8 890a,c 774a,b 32.3a,b 35.9 b,c Citric acid 0.1% + coat. 0 8 903a,c 828a,c 29.8a 34.9b 0 8 923b 30.6a 880a,b 35.8b Disinfection method/treatment Citric acid 0.5% + coat. Spoilage symptoms White blush, browning, soft rot ND2 Harsh (acid) taste Slime ND2 ND2 1Not measured 2No spoilage was detected after 8 d of storage abcdMeans with different letters are significantly different (p < 0.05) Table 2—Dynamics of microbial populations (log CFU/g) in carrots as affected by disinfection treatments Population (log CFU/g) Microbial group ctrl HOCl 5% H2O2 coating (S170 + 2% CaCl2) Total viable counts Pseudomonas spp. Lactic acid bacteria Enterobacteriaceae 6.4 6.3 5.6 5.4 6.0 6.1 5.0 4.8 6.0 5.9 5.0 4.7 6.1 6.2 5.3 5.0 Enterobacteria present (Table 2). By contrast, combinations of 0.1% or 0.5% citric acid and 2% CaCl2 significantly reduced initial total flora for at least 1 or 2 log CFU/ g respectively). The combination treatment affected the development of the microbial flora up to 4 d of storage but after 8 d, no differences in the total viable counts were recorded (data not shown). Our results on the effect of citric acid or CaCl2 alone on the microbial flora of minimally processed carrots are in agreement with those obtained by other researchers (Eytan and others 1992; Izumi and Watada 1994). High O2 and high CO2 controlled atmospheres General quality. The poor quality of carrots observed after storage in air for 12 d (Table 3) is related to changes in texture color and increased decay incidence. Samples stored under 1% O2 + 10% CO2 had a minimum shelf life of 12 d, which was further extended to 15 d after a dipping in citric acid and coating (data not shown). Good quality was observed for carrots stored under 50% O2 +30% CO2 for at least 12 d. Although concentrations of CO2 high- 62 JOURNAL OF FOOD SCIENCE—Vol. 65, No. 1, 2000 0.1% 0.1% citric citric acid acid + coating 5.9 5.6 5.0 4.9 5.3 5.1 4.1 4.0 0.5% 0.5% citric citric acid acid + coating 4.9 4.6 4.0 3.6 4.5 4.3 4.2 3.5 er than 20% are not generally recommended for storage of respiring products like carrots, Carlin and others (1989) reported CO2 concentrations as high as 30% to 40% in equilibrium packs. After 12 d of storage, the quality of carrots was poor when O2 concentration was further increased (70% to 90%) combined with 10% to 30% CO2 regardless of the treatment. Effect on color. Increased WI values were apparent after 8 d in untreated (water dipped) samples independent of gas condition applied during storage. Treated (coated and dipped in 0.1% citric acid) carrots kept their characteristics for at least 12 d under 50% O2 + 30% CO2 or 1% O2 + 10% CO2 (Table 3). No obvious correlation existed between the gas concentration and the WI, although the values carrots stored under 90% or 80% O2 combined with 10% or 20% CO2 were high. Good retention of the orange color has been previously reported at high CO2 levels in acidified carrots (Juliot and others 1989). Surface browning occurred due to oxidation of carrot phenols of samples stored in air and occasionally in 1% O2 + 10% CO2 but not when more than 50% O2 was used. According to Day (1998), enzymatic discoloration should not be expected at high O2 MAP due to a substrate inhibition. Heimdal and others (1995) did not find any correlation between browning and high oxygen on packed iceberg lettuce. Effect on firmness. Increased firmness was typically noted with carrots exposed to 70% to 90% O2 for 12 d. On the contrary, carrots stored in air were significantly softer after 12 d of storage (Table 3). Loss of firmness under these conditions may be related to an increased proliferation of pectolytic pseudomonas. Retention of firmness was satisfactory for treated samples stored under 1% or 50% O2. Effect on total phenols. A high concentration of total soluble phenols was observed in carrots stored under air (Fig. 1). Most likely, this increase is related to polymerization of phenols catalyzed by microbial oxidases (Howard and others 1994). Accumulation of phenols is a physiological response to infections or injuries. At 10%, CO2 total phenol-content remained at low level in the presence of 1% O2, whereas an increase was observed in the presence of 90% O2, especially for untreated samples. Storage in the presence of 50% O2 + 30% CO2 strongly reduced the accumulation of total phenols comparing to air. Under all gas atmosphere conditions, the phenolic content of treated samples was lower than that of untreated samples. Howard and Dewi (1996) found that treatment with citric acid, but not coating, slightly reduced the amount of total phenols of peeled carrots. The bitter taste, observed in airstored samples, is related to increased concentrations of isocoumarin, chlorogenic, and hydrobenzoic acid (Sarkar and Phan 1979; Babic and others 1993), as a response of carrots to severe stress. Effect on sugars. D-Sucrose is the main Table 3—Effect of O2 and CO2 concentrations and dipping on firmness, whiteness index, and % of rotten discs of treated and untreated carrots stored for up to 12 d at 8 °C Fig. 1—Changes in total phenol of untreated (water dipped) (black bars) carrot disks or treated (washed in 0.1% citric acid and coated) (white bars) under 6 controlled atmospheres for 12 d at 8 °C. Fig. 2—Changes in D-sucrose content of untreated (water dipped) carrot disks (black bars) or treated (washed in 0.1% citric acid and coated) (white bars) under 6 controlled atmospheres for 12 d at 8 °C. Firmness (N) Untreated carrots 1% O2 + 10% CO2 50% O2 + 30%CO2 70% O2 + 30% CO2 80% O2 + 20%CO2 90% O2 + 10%CO2 Air Coated and dipped 1% O2 + 10% CO2 50% O2 + 30%CO2 70% O2 + 30% CO2 80% O2 + 20%CO2 90% O2 + 10%CO2 Air Whiteness Index %Rot Day 0 Day 12 Day 0 Day 12 Day 12 813a 832a 910b,c 922b,c 903b,c 950b,c 755d 30.3a 36.1c 37.5 c,d 39.6d 38.6 c,d 40.9d 38.1d 30 0 0 0 0 80 865a,b 890a,b 886b 893b 950c 910b,c 730d 29.4 a 32.4a,b 31.6a,b 33.6b 35.8b 36.8 b,c 36.2c 0 0 0 0 0 50 a,b,c,d Means with different letters are significantly different (p < 0.05) Table 4—Ethanol, acetaldehyde, and ethylene accumulation of treated (dipped in 0.1% citric acid and coated) and untreated (water dipped) carrots stored at 8 °C under 3 atmospheres, for 48 h Air 90% O2 + 10% CO2 1% O2 + 10% CO2 50% O2 + 30% CO2 Volatiles Untr. Treated Untr. Treated Untr. Treated Untr. Treated Ethanol (␮mole/g fw) 5.0b 0.75a 0.5a 1.0a 1416e 2712f 38d 20c Acetaldehyde (␮mole/g fw) 0.75a 1.125 a 0.5a 1.25a 56d 95e 7.5 c 3.8b Ethylene (␮mole/g fw) 0.92b 0.32a 0.41a 0.54a 0.30a 0.26a 1.15c 1.63c sugar contributing to the taste of carrots (61 mg/g fresh wt). After 12 d at 8 °C, the sucrose content of carrots stored in air or 90% O2 + 10% CO2 was as low as 21 mg/g fresh wt. In contrast, samples stored under 50% or 70% O2 + 30% CO2 or 1% O2 + 10% CO 2 retained more than 60% of the initial sucrose content (Fig 2). Sensory analysis for bitterness showed that unpeeled carrots stored in 1% O2 were consis- tently sweeter than those stored in air (data not shown). Carlin and others (1990b) found good retention of sucrose in the presence of 10% to 40% CO2 with 2% or 10% O2 and Howard and Dewi (1996) did not find any difference on the sugar content of coated and uncoated carrots stored in air. In this study, D-sucrose content was significantly retarded when coating and citric acid treatment, was combined with 20% or 30% CO2. Effect on ethylene production. Ethylene as high as 1.25 ␮mole/g fresh weight was measured in the headspace of sliced carrots 30 min after cutting. Preliminary experiments indicated a rapid increase in the level of ethylene of cut carrots during the first hours of storage (data not shown). Although carrot is a nonclimacteric crop, ethylene may reduce postharvest quality by promoting senescence, low temperature injuries and microbial decay. In carrots exposed to ethylene level > 0.125 ␮M on the headspace the synthesis of socalled “stress metabolites,” such as the bitter compounds isocoumarin and eugenin, was stimulated (Lafuente and others 1996). Surprisingly, increased accumulation of ethylene (1.63 ␮mole/g fw) by the treated and 1.15 by the untreated carrots was observed at 50% O2 + 30% CO2 but not at 90% O2 + 10% CO2 (Table 4). CO2 is a well Vol. 65, No. 1, 2000—JOURNAL OF FOOD SCIENCE 63 Food Chemistry and Toxicology Treatment O2 and CO2 Effects on Carrots . . Food Chemistry and Toxicology known inhibitor of ethylene synthesis but Pal and Buescher (1993) found that exposure to 30% CO2 indeed accelerated ethylene evolution in carrots possibly due to an early injury response. Li and Barth (1998) found excessively high concentrations of ethylene on MP carrots after use of an edible coating with very low pH (2.7). The pH of the coating used in our study was 7.8, and thus phytotoxicity due to low pH is not likely. After 12 d of storage, traces of ethylene (< 0.06 ␮mole/g fw) were measured under all conditions (data not shown). Effect on volatile accumulation. After 4 d of storage, increased ethanol and acetaldehyde production was detected for samples stored at 1% O2 + 10% CO2 compared to air stored samples both for untreated and treated carrots (Table 4). High ethanol concentrations affected the taste of carrots stored under these conditions. Accumulation of acetaldehyde and ethanol was suppressed in the presence of 50% to 90% O2 despite of the CO2 levels. At low O2 levels, glycolytic flux in carrots is accelerated; ethanol and acetaldehyde levels increase in response to hypoxia (Kato-Noguchi and Watada 1996, 1997b). Increased or decreased response of carrots tissue to low or high O2 respectively is sustained by the concept of the dual role of O2 in regulating respiration (Leshuk and others 1991). Citric acid treatments slow down respiration and glycolytic metabolism of carrot discs (Kato-Noguchi and Watada 1997a). TBA values. Lipid oxidation (measured as % percentage of the highest TBA value observed) appeared to increase during storage especially for water treated samples. Lipid oxidation was not observed at air stored samples (Table 5). This may indicate that the development of off-odors under air is mainly caused by the spoilage microflora, which produces off-flavor volatile. It is unlikely that the increased TBA values recorded at 1% O2 + 10% CO2 after 12 d of storage is due to lipid oxidation. The method used for the determination is not specific for malonaldehyde and interference by other aldehydes is possible. Carrots kept in 90% O2 + 10% CO2 had low TBA values. High O2 did not retard formation of secondary oxidation products in the presence of 30% CO2. Effect on microbial flora. The maximum level of bacterial growth in air was reached for all samples at d 8 to 10, and very little changes occurred after that (data not shown). For untreated carrots stored in air, total counts were 8.8 log CFU/ g after 10 d of storage. Excessive growth and, thus, spoilage due to lactic acid bacteria was never observed in untreated carrots, stored under air. This might be related to accumulation of phenols with anti- Table 5—Thiobarbituric acid (TBAR) values of treated and untreated carrots stored for 12 d at 8 °C, in 6 atmospheres. TBARS are expressed as a percentage of the higher absorbance recorded at 532 nm TBARS (%) max Abs (532nm) of carrots kept in: Untr. carrots Treated carrots 1% O 2 + 10% CO2 70% O2 + 30% CO2 50% O2 + 30%CO2 80% O2 + 20%CO2 90% O2 + 10%CO2 Air 100a 93a 91a,b 82b,c 86b 85b 69d 65d 56e 48f 58.2d,e 50.8f microbial properties under these conditions. After 12 d at 8°C, total viable counts of the water dipped samples exceeded 8.0 log CFU/g with pseudomonads being dominant under all gas atmospheres. For treated samples, the total viable count was as high as 7.5 log CFU/g, mainly due to partial inhibition of pseudomonads (Fig 3). Lactic acid bacteria were dominant in the presence of high O2 + high CO 2 after acid coating treatment. Enterobacteria were inhibited under 50% O2 + 30% CO2 but stimulated under 80% or 90% O2. Microbial spoilage due to extended growth of lactic acid bacteria was observed after 12 d in treated samples stored under 80 or 90% O2 with 20 or 10% CO2, respectively. Conclusions O N THE BASIS OF THE EVALUATION OF A range of quality indices, it is concluded that minimally processed carrots washed with 0.1% citric acid retained fresh product characteristics for at least 8 d, especially when treated with CaCl2 and an alginate coating. The quality of MP carrots stored under 50% O2 + 30% CO2 was similar or better than those stored at 1% O2 + 10% CO2 after 8 to 12 d at 8 °C. Shelf life was further extended from 12 to 15 d, but only when products were disinfected with 0.1% citric acid and coated prior to storage un- Fig. 3—Changes in the microbial populations of treated carrots (dipped in 0.1% citric acid and coated) during storage at 8 °C in air (A) or 50% O2:30% CO2 (B). 䊉 = Total viable counts. 䉬 = Pseudomonas. 䊏 = Lactic acid bacteria. 䊊 = Enterobacteriaceae. Standard errors are presented on the graphs. 64 JOURNAL OF FOOD SCIENCE—Vol. 65, No. 1, 2000 Material and Methods Product preparation and processing Carrots (cultival “Amsterdamse bak”) were obtained from the Dutch Greenery (Utrecht, The Netherlands), within 2 wk of harvest. Each experiment was repeated 3 times in the period of September 1997 to February 1998. Roots of medium size were selected and washed, and all heavily contaminated parts were removed. Carrots were sliced using a Sammic CA300 food processor in discs with an average size of 1 cm × 3 cm. The parts of the processor were regularly disinfected with 70% ethanol during preparation Sliced carrots were washed twice in sterile, distilled water (untreated carrots), a solution of NaOCl containing 200 mg/L active chlorine or 5% H2O2 (v/v) for 2 min. The effect of a citric acid treatment was studied by dipping the sliced carrots twice in a solution of 0.1% or 0.5% (w/v) citric acid. Untreated and treated carrots were dried in air for 15 min at room temperature. Aseptic conditions were kept during preparation, and the processor and surfaces were at time intervals disinfected with 70% ethanol. In order to study the effect of the edible coating, the carrots were dipped in a solution of 2% CaCl2 (w/v) or 2% CaCl2 + 0.1% citric acid. After drying, an alginate based coating Satialginate S170 (SBI BENELUX), pH = 7.8 was sprayedon the surface. Carrots (70 g) from each treatment were transferred to plastic boxes that were disinfected with ethanol prior to use. Boxes with the carrots were placed in a temperature-controlled room maintained at 8 °C, 92% relative humidity in hermetically closed containers connected to a flow-through system and continuously flushed with the desired combinations of gases. Pure N2, O2, and CO2 were mixed using mass flow controllers (Brooks, 5850 TR series) at a flow rate 200 ml/h. The following combinations of gases were used (a) 90% O2 + 10% CO2; (b) 80% O2 + 20% CO2; (c) 50% O2 + 30% CO2; (d) 70% O2 + 30% CO2; (e) 1% O2 + 10% CO2; (f) air control. Equilibrium condition in the chamber were reached after 2 h. At certain time intervals, 2 boxes from each treatment were removed from the containers and used for microbiolog- 30% in the presence of 50% O2. Overall, high-oxygen MA storage can be used as an alternative to low-oxygen MA storage for minimally processed carrots, since it al- ical and physicochemical analysis. Microbiological analysis Total aerobic mesophiles were enumerated on plate count agar (PCA, Oxoid) after 3 d of incubation at 25 °C. Pseudomonads were enumerated on Pseudomonas Agar Base supplemented with Cetrimide-Fucidin-Cephaloridine (CFC agar, Oxoid) after 3 d at 25 °C. Counts of lactic acid bacteria (LAB) were performed on Man–Rogosa–Sharpe agar after incubation for 4 d at 25 °C and Enterobacteriaceae were enumerated on Violet Red Bile Glucose agar (VRBGA, Oxoid) after 24 h at 37 °C. The pour plate technique was used for the enumeration of LAB and Enterobacteriaceae. Duplicate samples were examined on each day of analysis. Quality analysis Color. Color measurements were made using a Minolta chromameter model CR200 (Minolta Camera Co., Japan). The L*, a*, and b* data were transformed to a Whiteness Index score using the equation 100-[(100-L*) 2 + a*2 + b*2]0.5 (Bolin and Huxsoll 1991). Each datapoint is presented as the mean of measurements on both sides of 20 different carrot disks. Texture. In preliminary studies, Texture Profile Analysis of carrots showed that the most comparative parameter between samples was firmness. It was measured with a texture analyzer ( TA.XT2I, Texture Technologies, N.Y., U.S.A.), equipped with a 10-mm cylindrical ebonite probe. A speed of 1 mm/s and a penetration distance 10 mm were used and firmness was expressed as maximum compression force (N). The data are presented as means of 10 independent measurements. pH. Aliquots of 25 g of carrots were homogenized with an equal volume of distilled water. The pH of the homogenate was determined at each sampling time with a glass electrode (Metrohm model 691). Sugars. Sugars (sucrose/D-glucose/ D-Fructose) were quantified by using a test combination kit (Boehringer-Mannheim, Germany). Prior to the determination, samples (25 g) were homogenized with equal amount of water and clarified lows the product to retain fresh, natural characteristics and retards microbial growth during prolonged storage. with 2.5 ml Carrez I and 2.5 ml Carrez II solution. pH was adjusted to 7.2 with 0.1mole/L sodium hydroxide). Homogenates were transferred quantitatively into a 100-ml volumetric flask and rinsed with water. Next, n-Octanol (0.1 ml) was added and the flask was shaken until the foam has disappeared. Finally, the extracts were filtered and immediately used for the assay. Total phenols. Total soluble phenols were extracted in 80% ethanol and measured using the Folin-Ciocalteau reagent (Swain and Hillis 1959). Thiobarbituric acid values. Samples (50 g) were homogenized in 100-ml distilled water. Aliquots of 25 ml of the homogenate were mixed with equal volume of 10% (trichloroacetic acid) TCA and filtered. After extraction the thiobarbituric acid method described by Barry-Ryan and O’Beirne (1998) was used to measure the degree of lipid oxidation. TBA value is defined as the increase in the absorbance due to formation of condensation products after the reaction of the equivalent of 1 mg of sample/mL volume with 2-thibarbituric acid. Absorbance was read at 532 nm. All values were reported as percentages of the highest absorbance obtained. Three independent measurements were performed for each condition. Ethylene, acetaldehyde, and ethanol production. A portion of 120 g of carrots from each treatment was placed in a glass jar (vol. 1 Lt) fitted with a rubber septum, flushed with the desired combination of gases, sealed, and kept at 8 °C. The ethylene concentration inside the jar was measured with a gas chromatograph (GC) equipped with a flame ionization detector (CHROMPACK Model 437A) using an external standard. Acetaldehyde and ethanol were measured with a GC (CHROMPACK Model CP9001), using Helium as a carrier gas. The ethylene, ethanol and acetaldehyde concentrations were expressed as ␮mole of volatile/g fresh weight. Statistical analysis Data were subjected to analysis of variance and the Duncan’s Multiple Range test. Each experiment was performed 3 times with 2 repetitions. 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Hydrogen peroxide disinfection of minimally processed fruits and vegetables. Food Technol. 52(2):48-52 Sarkar SK, Phan CT. 1979. Naturally occuring and ethylene induced phenolic compounds in the carrot root. J. Food Prot. 42:526-534 Stanley DW, Bourne MC, Stone AP, Wismer WV. 1995 Low temperature blanching effects on chemistry, firmness and structure of canned green beans and carrots J. Food Sci. 60:327-333 Swain T, Hillis WE. 1959. The phenolic constituents of Prunus domestica I. The quantitative analysis of phenolic constituents. J. Sci. Food Agric. 10:63 Tatsumi Y, Watada AE, Wergin WP. 1991. Scanning electron microscopy of carrot stick surface determine cause of white translucent appearance. J. Food Sci. 56:1357-1359 MS 19990417 received 4/5/99; revised 8/4/99; accepted 8/ 20/99. This work was funded by the Commission of the European Union through contract FAIR-CT96-5038 to author AA. The authors thank S. Fervel and J. Verschoor for assistance with the measurements of the ethylene and respiration metabolites. H.J.Neerhof is acknowledged for providing the edible coating and for helpful discussions. Finally, the authors are indebted to prof. D. Knorr for critical reading of the manuscript. Authors Amanatidou and Gorris, formerly with the Agrotechnological Research Institute (ATODLO), are now with Unilever Research Laboratorium, Unit Microbiology and Preservation, P.O. Box 114, 3130 AC, Vlaardingen, The Netherlands. Slump and Smid are with ATODLO, P.O. Box 17, 6700 AA, Wageningen, The Netherlands. Send inquiries to A. Amanatidou (E-mail: athina.esveld@unilever.com).