Comparison of calcium lactate with chlorine as a washing treatment for fresh‐cut lettuce and carrots: quality and nutritional parameters

The efficacies of calcium lactate and chlorine washing treatments of fresh‐cut lettuce and carrots were compared during storage at 4 °C over 10 days. The gas composition of packages, colour, enzyme activity, texture, sensory attributes, microflora and levels of ascorbic acid and carotenoids were evaluated at 1, 3, 7 and 10 days. Calcium lactate treatment was not significantly different to chlorine treatment (p < 0.05) in terms of maintaining colour, texture and acceptability of fresh‐cut lettuce and carrots during the entire storage period. The washing treatments did not affect levels of ascorbic acid of fresh‐cut lettuce or carrots. Carotenoid levels were higher in calcium lactate‐treated carrots than chlorine‐treated samples at the end of storage. Mesophilic, psychrotrophic and lactic acid bacteria counts were not significantly different between treatments for both vegetables. Copyright © 2005 Society of Chemical Industry     

Microbiological hazards involved in fresh‐cut lettuce processing

BACKGROUND: The increasing consumption of produce all over the world has resulted in increasing concern by the regulatory agencies with respect to the level of safety performed by the processors. The objective of the present study was to investigate the hazards involved in the various steps of fresh‐cut lettuce processing (reception/selection of raw material, washing, rinsing, sanitisation and final product) by means of microbiological analyses of microbial groups used as indicators of hygienic conditions and of pathogens. RESULTS: High microbial loads of mesophilic and psychrotrophic bacteria and Pseudomonas spp. were found in the ram reception (～6 log colony‐forming units (CFU) g^?1), which were reduced by a single logarithmic cycle for the last two microbial groups after the sanitisation step (P < 0.05), the latter being ineffective against the first microbial group (P > 0.05). Lower counts of yeasts and moulds, total coliforms (35 °C) and faecal coliforms (44 °C) were observed in the initial step (3.49–4.53 log CFU g^?1, 0.65–1.55 log most probable number (MPN) g^?1 and 0.50–0.90 log MPN g^?1 respectively), these values increasing significantly after the sanitisation step for yeasts and moulds (～5 log CFU g^?1) but remaining unaltered for coliforms (P > 0.05). Salmonella spp. were not found in any of the experiments carried out, while the presence of Escherichia coli was observed in the final product. CONCLUSIONS : Practices compromising the hygienic quality of the final product during commercial storage were observed and corrective measures suggested. To the best of the authors' knowledge, these are the first data on microbiological safety in Brazilian fresh‐cut processing plants. Copyright © 2008 Society of Chemical Industry     

Effectiveness of organic acid,ozonated water and chlorine dippings on microbial reduction and storage quality of fresh‐cut iceberg lettuce

BACKGROUND: The comparative effects of organic (citric and lactic) acids, ozone and chlorine on the microbiological population and quality parameters of fresh-cut lettuce during storage were evaluated. RESULTS: Dipping of lettuce in 100 mg L⁻¹ chlorine solution reduced the numbers of mesophilic and psychrotrophic bacteria and Enterobacteriaceae by 1.7, 2.0 and 1.6 log₁₀ colony-forming units (CFU) g⁻¹ respectively. Treatment of lettuce with citric (5 g L⁻¹) and lactic (5 mL L⁻¹) acid solutions and ozonated water (4 mg L⁻¹) reduced the populations of mesophilic and psychrotrophic bacteria by 1.7 and 1.5 log₁₀ CFU g⁻¹ respectively. Organic acid dippings resulted in lower mesophilic and psychrotrophic counts than ozonated water and chlorine dippings during 12 days of storage. Lactic acid dipping effectively reduced (by 2.2 log₁₀ CFU g⁻¹) and maintained low populations of Enterobacteriaceae on lettuce for the first 6 days of storage. No significant (P > 0.05) changes were observed in the texture and moisture content of lettuce samples dipped in chlorine, organic acids and ozonated water during storage. Colour, β-carotene and vitamin C values of fresh-cut iceberg lettuce did not change significantly (P > 0.05) until day 8. CONCLUSION: Lactic and citric acid and ozonated water dippings could be alternative treatments to chlorine dipping to prolong the shelf life of fresh-cut iceberg lettuce. Copyright © 2007 Society of Chemical Industry     

Effects of aqueous ozone treatments on microbial load reduction and shelf life extension of fresh‐cut apple

Aqueous ozone was first used to take the place of chlorine as fresh‐cut apples sanitiser. Aqueous ozone (1.4 mg L^?1) treatments were evaluated for their effectiveness on microbial growth, quality attributes and shelf life of fresh‐cut apples. The results indicated that aqueous ozone treatments for 5 and 10 min achieved accepted microbial quality and, respectively, reduced total bacteria counts by 1.83 and 2.13 log₁₀CFU g^?1 compared with the control samples on the 12th day. The ethylene production, polyphenol oxidase and peroxidase activities, and total phenol and malondialdehyde contents were reduced by aqueous ozone treatments. In addition, this sanitiser also delayed the quality deterioration of fresh‐cut apples and enhanced their antioxidant capacity. Therefore, it was recommended to sanitise fresh‐cut apples with aqueous ozone (1.4 mg L^?1) for 5 min, which applied to industrial production requirement for both efficiency and costs and could extend the shelf life up to 10 days.     

Screening quality and browning susceptibility of five artichoke cultivars for fresh‐cut processing

BACKGROUND: Artichoke is a rich source of bioactive compounds, mainly phenols, in the Mediterranean diet, but its consumption is limited by the complexity of time‐consuming trimming operations. Fresh‐cut processing would therefore add convenience to its consumption, even though the severity of post‐cutting browning of artichoke pieces is still a major problem. Since susceptibility to browning may vary widely among genotypes, the choice of the cultivar is a very critical step in the fresh‐cut process. In this study, five different Italian cultivars (C3, Catanese, Tema, Violetto Foggiano and Violetto Sardo) were screened for their initial quality and composition, and their post‐cutting performance during storage at 5 °C and 20 °C. RESULTS: C3 showed the highest phenol content (3.4 g GA kg^?1) and antioxidant activity (24.5 mmol L^?1 kg^?1), but the worst quality in terms of appearance and colour changes, also due to its high PPO activity (62.2 U g^?1). Catanese showed the highest vitamin C content (117.7 mg kg^?1), the lowest phenol content (1.8 g GA kg^?1), and the best post‐cutting quality. Tema, Violetto Foggiano and Violetto Sardo showed an intermediate phenol content, the latter showing the lowest appearance score after C3. CONCLUSION: These results confirmed the role of phenols in browning processes of fresh‐cut artichokes, giving the first available information on artichoke cultivar suitability to be processed as a fresh‐cut product. Copyright © 2009 Society of Chemical Industry     

Surface treatments and coatings to maintain fresh‐cut mango quality in storage

BACKGROUND: Edible coatings may extend fresh‐cut fruit storage by preventing moisture loss and decreasing gas exchange. This study evaluated the effect of an antibrowning dip (calcium ascorbate, citric acid and N‐acetyl‐L ‐cysteine), followed or not with carboxymethylcellulose (CMC) or carrageenan coatings on quality of fresh‐cut mangoes stored at 5 °C for up to 20 days. A fourth treatment, only used in one of four experiments, consisted of chitosan. Treatments were applied on ‘Tommy Atkins’, ‘Kent’ and ‘Keitt’ mangoes harvested from Homestead (FL), and on imported store‐bought mangoes. RESULTS: The antibrowning dips maintained the best visual quality during storage for all cultivars, as indicated by higher b*, hue and L*. The CMC coating maintained similar visual quality, but carrageenan or chitosan decreased L* and b*. The antibrowning dip containing calcium ascorbate reduced firmness loss on cut pieces of ‘Keitt’, ‘Kent’ and store‐bought mangoes. The antibrowning treatment maintained higher titratable acidity for ‘Kent’ and ‘Keitt’, resulting in lower sensory sweetness. CONCLUSION: This study with repeated experiments showed that calcium ascorbate with citric acid and N‐acetyl‐L ‐cysteine maintained cut mango slices attractiveness in storage by keeping light color in both varieties. The addition of a polysaccharide coating did not consistently improve quality. Published in 2010 by John Wiley & Sons, Ltd.     

Effect of initial oxygen concentration and film oxygen transmission rate on the quality of fresh‐cut romaine lettuce

Modified atmosphere packaging (MAP) is widely used to maintain the quality of fresh‐cut produce by matching the oxygen transmission rate (OTR) of the packaging film to the respiration rate of the packaged product. The effect of the interaction between film OTR and the initial headspace O₂ on quality of fresh‐cut vegetables has not previously been reported. Romaine lettuce leaves were sliced, washed, dried and packaged with film OTRs of 8.0 and 16.6 pmol s^?1 m^?2 Pa^?1, and with initial headspace O₂ of 0, 1, 2.5, 10 and 21 kPa. Packages were hermetically sealed and stored at 5 °C for up to 14 days. For samples packaged in 16.6 OTR film, increasing the initial headspace O₂ concentration delayed O₂ depletion within the packages, hastened the onset and increased the intensity of discoloration, and inhibited the development of CO₂ injury, acetaldehyde and ethanol accumulation, off‐odors and electrolyte leakage. With 8.0 OTR‐packaged lettuce pieces, ≤1 kPa initial headspace O₂ treatments induced an essentially anaerobic environment within the packages and increased acetaldehyde and ethanol accumulation and off‐odor development. Increasing the initial O₂ concentration above 1 kPa in 8.0 OTR packages transiently increased O₂ concentrations and reduced fermentative volatile production, off‐odors, electrolyte leakage and CO₂ injury. Regardless of initial headspace O₂ concentration, all 16.6 OTR‐packaged samples had severe discoloration after 14 days of storage. Quality was better maintained in 8.0 OTR‐packaged lettuce pieces as the initial headspace O₂ concentration was increased. A 21 kPa initial O₂ treatment of 8.0 OTR‐packaged lettuce maintained good quality throughout storage and had the best overall quality score. Copyright © 2005 Society of Chemical Industry     

Optimization of processing of fresh‐cut pear

BACKGROUND: Successful processing of pears to render fresh‐cut fruits requires a thorough knowledge of their sensitivity to browning reactions, their respiratory metabolism, and their behaviour under modified atmosphere packaging. RESULTS: First, three different varieties of pear (Williams, Conference, Passacrassana) that had reached their commercial ripening stage were evaluated for suitability for minimal processing. Two antioxidant treatments were tested (treatment 1: 2% ascorbic acid + 1% citric acid + 1% CaCl₂; treatment 2: 2% ascorbic acid + 0.01% 4‐hexylresorcinol + 1% CaCl₂) to decide which one was the most effective against enzymatic browning. Finally, a modified atmosphere packaging was designed after two previous tests: measurement of respiratory activity of the peeled and cut pear at three temperatures (4, 15 and 25 °C); and evaluation of fruit tolerance to three different atmospheric compositions (21% O₂ + 10% CO₂; 2% O₂ + 0% CO₂; 2% O₂ + 10% CO₂). CONCLUSIONS: Conference pear was found to be the most suitable variety. Among the antioxidant treatments the one consisting of ascorbic acid, 4‐hexylresorcinol and CaCl₂ was proven to be the most effective against browning. The samples were packaged in a modified atmosphere with a composition of 10% O₂ + 10% CO₂ + 80% N₂. Copyright © 2008 Society of Chemical Industry     

Effects of ozone and chlorine postharvest treatments on quality of fresh‐cut red bell peppers

The effects of chlorine (200 μL L^?1), ozonated water (1 μL L^?1) and gaseous ozone (0.7 μL L^?1) on physicochemical attributes and microbial quality of minimally processed red bell peppers were studied. In all the experiments, O₂ continuously decreased and CO₂ concentration increased, the pH augmented and a significant softening was observed in all the fruits. By day 14, L* values decreased in all the fruits, with the greatest changes found in the chlorinated samples (approximately 12 units). Peppers treated with the aqueous solutions showed greater changes in the quality attributes with increasing washing times and especially when chlorine was used. The exposure for three min to gaseous O₃ reduced the mesophiles, psychrotrophes and fungal populations of the fresh‐cut peppers in 2.5, 3.3 and 1.8 log units, respectively. Combined with modified atmosphere, this could be an appropriate method to maintain the quality and extend the storage period of minimally processed red bell peppers.     

Effect of sodium gluconate on the solubility of calcium lactate

Calcium and lactate are present in excess of their solubility in Cheddar cheese. Consequently, calcium lactate crystals (CLC) are a common defect in Cheddar cheese. A novel approach for preventing CLC is the addition of sodium gluconate. Sodium gluconate has the potential to increase the solubility of calcium and lactate by forming soluble complexes with calcium and lactate ions, and preventing them from being available for the formation of CLC. The objective of this study was to determine if sodium gluconate could increase the solubility of calcium lactate (CaL₂). Seven CaL₂ solutions (5.31% wt/wt) with 7 levels of sodium gluconate (0, 0.5, 1, 1.5, 2, 3, and 4% wt/wt) were made in triplicate. Solutions were stored at 7°C for 21 d, and were visually inspected for CLC formation. Subsequently, they were filtered to remove CLC and the supernatant was analyzed for lactic acid and gluconic acid by HPLC and for calcium by atomic absorption spectroscopy. The visual inspection demonstrated that CLC were formed in the solution with 0% gluconate after the first day of storage and CLC continued to accumulate over time. A minute amount of CLC was also visible in the solution with 0.5% gluconate after 21 d of storage, whereas CLC were not visible in the other solutions. The HPLC results indicated a higher concentration of calcium and lactic acid in the filtrate from the solutions containing added gluconate. Thus, sodium gluconate can increase the solubility of CaL₂.     

Antioxidant capacity of fresh‐cut vegetables exposed to ionizing radiation

The effect of ionizing radiation on antioxidant capacity, phenolic content and tissue browning of three vegetables was studied. Midrib and non‐midrib leaf tissues of Romaine and Iceberg lettuce and endive were irradiated with gamma‐rays at 0, 0.5, 1 and 2 kGy, and then stored at 7–8 °C for 8 days. Antioxidant capacity and phenolic content of tissues as well as tissue browning were analyzed at 1, 4 and 8 days of storage. In general, irradiation increased the phenolic content and antioxidant capacity of both tissue types of all vegetables at day 4 and day 8. The rates of the increase were higher in midrib tissues than in non‐midribs, and increased with storage time. Irradiation, however, increased tissue browning of midrib tissues of Romaine and Iceberg lettuce. Our results suggest that irradiation increased nutritional quality of leafy vegetables, but some adverse visual quality changes were encountered. Published in 2005 for SCI by John Wiley & Sons, Ltd.     

Effect of calcium lactate and heat-shock on texture in fresh-cut lettuce during storage

Textural and microstructural changes in fresh-cut lettuce were analysed over 12 days storage. The vegetable was treated with 120 ppm chlorine and with 15 g/L calcium lactate at room temperature (∼18–20 °C) and at 50 °C (heat-shock). Texturometer analysis showed that samples washed with calcium lactate had significantly (p > 0.05) higher crispness values than samples washed with chlorine. However the use of 50 °C treatment (heat-shock) gave better textural properties at the end of storage and significantly retarded the softening process, being in agreement with the sensorial results. Cryo-SEM micrographs showed a loss of turgor (shrinkage) of the tissue cells in the samples washed with chlorine, effect not so evident in calcium lactate treated samples. The use of heat-shock in combination with calcium lactate reduced this phenomenon better than the other two treatments. Pectin methyl esterase (PME), enzyme related to textural changes, showed higher activity in samples treated with calcium lactate at 50 °C. The combination of calcium lactate and 50 °C washing temperature maintained objective and sensorial textural properties of fresh-cut lettuce better than the calcium lactate or chlorine washing treatments at room temperature.     

Physiological properties of fresh‐cut watermelon (Citrullus lanatus) in response to 1‐methylcyclopropene and post‐processing calcium application

Seedless watermelon (Citrullus lanatus Thunb. Mansfeld, cv. Millionaire) fruit were exposed to 10 µL L⁻¹ 1‐methylcyclopropene (1‐MCP) or air for 18 h. Afterward, the fruit were processed into placental‐tissue pieces, treated with calcium dips (20 g kg⁻¹ CaCl₂) or deionized water, and stored in vented containers for 7 days at 10 °C. At intervals during storage, fresh‐cut placental tissue was monitored for respiration, ethylene production, firmness, electrolyte leakage, total soluble solids, titratable acidity and microbial growth. Ethylene production was below detection in fresh‐cut placental tissue, consistent with the low ethylene production in intact watermelon fruit. Respiration rates were significantly enhanced in response to tissue processing, and continued to increase throughout the 7 days of storage. Tissue derived from 1‐MCP‐treated fruit showed enhanced 1‐aminocyclopropane‐1‐carboxylate synthase (ACS, EC 4.4.1.14) activity, suppressed respiratory rates and undetectable levels of 1‐aminocyclopropane‐1‐carboxylate oxidase (ACO) activity during storage. Post‐processing calcium dips (CaCl₂) had little influence on ACS activity relative to tissue not receiving calcium, but significantly enhanced ACO activity and maintained firmness of fresh‐cut tissue throughout storage. The data collectively support the conclusion that 1‐methylcyclopropene treatment of intact watermelon fruit is alone unlikely to benefit the storage duration of fresh‐cut watermelon. Copyright © 2005 Society of Chemical Industry