Marita Cantwell

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%.

Wound-induced phenylalanine ammonia lyase activity: factors affecting its induction and correlation with the quality of minimally processed lettuces

Abstract One of the major causes of quality loss in minimally processed lettuce (Lactuca sativa L.) is the browning of the cut pieces. Phenylalanine ammonia lyase (PAL, EC 4.3.1.5) is a key enzyme in phenolic synthesis. PAL activity increased in lettuce midrib tissue with wounding and storage in the presence or absence of ethylene. PAL activity increased 2.5 and 3-fold at 5 and 15 °C, respectively, by reducing midrib size from 2.5 × 15 to 0.5 × 1 cm. Wounding usually induced maximum levels of enzyme activity within 3 days at 5 °C and 1 day at 15 °C. Pre and postharvest factors affected the kinetics of wound-induced PAL (WI-PAL) activity and of subsequent changes in the quality of minimally processed lettuce. The rate at which WI-PAL activity increased and the maximum level attained were influenced by the duration of storage before processing. These parameters were also affected by the cultivar and type of lettuce used. Butterhead and iceberg types had the highest and lowest levels, respectively, of WI-PAL activity; romaine, green leaf and red leaf had intermediate levels. The activity of PAL 1–2 days after processing, and the slope of the induction curve between days 0 and 2, were the enzyme measurements that gave the highest correlations with processed lettuce quality attributes, including overall visual quality, leaf edge browning, and leaf surface browning.

The visual quality of minimally processed lettuces stored in air or controlled atmosphere with emphasis on romaine and iceberg types

Five different types of lettuce (iceberg, romaine, butter, green leaf, and red leaf) were prepared as salad pieces and stored for 16 days at 5°C in air or in a controlled atmosphere (CA) (3% O2 + 10% CO?). Samples were evaluated for overall visual quality, surface and edge browning, and russet spotting. After 8 days, differences in overall visual quality between air and CA-stored samples were observed; after 12 days, air-stored samples were below the limit of salability, whereas visual quality was maintained in CA-stored pieces from all lettuce types except butter lettuce. Transferring lettuce to air for 12 h at 15°C accentuated the differences between storage atmospheres. An analysis of the various components of overall visual quality showed that surface and edge browning were the defects which most contributed to a decrease in quality. Among the lettuce types studied, the CA benefit for overall visual quality was highest for iceberg lettuce, and some differences between cultivars were observed. There was no CA benefit for butter lettuce, but CA induced surface discoloration and tissue softening. Pre-processing storage of lettuce heads at 5°C for 7 and 14 days negatively affected overall visual quality and leaf edge browning of the prepared salad pieces; this intact head storage effect was more evident on romaine than iceberg pieces.

Developmental changes in composition and quality of prickly pear cactus cladodes (nopalitos)

The composition and quality of edible tender stems or cladodes of 3 Prickly Pear Cactus species (Opuntia amyclaea, O. ficus-indica, and O. inermis) were studied at different stages of development. This traditional Mexican vegetable is called “nopalitos” in Spanish and “cactus leaves” in English. Cladodes harvested when 20 cm in length have the following average composition per 100 g: 91.7 g of water, 1.1 g of protein, 0.2 g of lipid, 1.3 g of ash, 1.1 g of crude fiber, 4.6 g of complex carbohydrates and 0.82 g of simple sugars, 12.7 mg of ascorbic acid and 28.9 µg of carotenes. The cladodes juice has an average pH of 4.6, 0.45% titratable acidity and 6.9% soluble solids. The components which varied most during development of the cladodes were: carotenes, acidity and total carbohydrates which increased, and protein and crude fiber (acid-detergent) which decreased. The nutritive value of the tender cladodes in the stages of growth at which they are commonly harvested and consumed (15 to 25 cm long weighing 50 to 80 g per stem), was similar for the 3 species.

Phenolic metabolism and ethanolic fermentation of intact and cut lettuce exposed to CO2-enriched atmospheres

Abstract Intact heads and cut leaf midrib tissue of crisphead lettuce ( Lactuca sativa , L., cv. ‘Salinas’ and ‘Vanguard’) were kept in air or air +5%, 10%, or 20% CO 2 for 10 or 20 days at 2.5°C and then transferred to air at 20°C for 12 hrs to study CO 2 effects on phenolic metabolism and fermentative products. Exposure of cut midribs to 20% CO 2 increased extractable activity of phenylalanine ammonia-lyase (PAL) when assayed at its optimum pH (8.5). However, under the 20% CO 2 treatment PAL activity was reduced as a result of a decrease in cytoplasmic pH. Total phenolic content of cut midribs was reduced under 20% CO 2 -enriched atmosphere probably due to this decrease in PAL activity. The phenolic content rapidly increased after the tissue was transferred from 20% CO 2 at 2.5°C to air at 20°C when cytoplasmic pH returned to its normal value and the PAL activity was restored. Such effects of CO 2 on PAL and phenolics were of lower magnitude in intact heads, probably due to their lower sensitivity to phenolic metabolism. Off-flavor developed in the intact heads exposed to 20% CO 2 , which was associated with increased concentrations of ethanol and acetaldehyde. When exposed to 20% CO 2 , levels of ethanol and acetaldehyde in cut midribs were only about half of those in intact heads.

Phenylalanine ammonia lyase inhibitors control browning of cut lettuce

Inhibitors of the first enzyme in the phenylpropanoid pathway, phenylalanine ammonia lyase (PAL), were used to investigate the role of phenolic metabolism in browning of lettuce tissue. Excised 4 7-cm midrib segments were soaked fo r1ha t20°C in aqueous solutions of the PAL inhibitors, a-aminooxyacetic acid (AOA; 0.1‐10 mM), 2-aminoindan-2-phosphonic acid (AIP; 50‐100 mM), and a-aminooxi-b-phenylpropionic acid (AOPP; 200 mM). Browning of the cut ends and uncut surfaces was measured using a visual score, and CIE color values (L*, a*, b*). Overall browning potential was measured as the absorbance at 340 nm of an aqueous extract of the tissue. The visual scores were more highly correlated with hue angle than with the a* and b* values; there was no correlation with the L* values. Ethylene applied at 5 m ll 1 had no effect upon browning compared with the air treatments. AIP at 50 mM and AOPP at 200 mM effectively inhibited browning; AOA was less effective requiring 3‐10 mM to reduce browning. These results confirm the view that for browning to occur in lettuce PAL activity is required to form phenolics that are subsequently oxidized and polymerized.

Quality changes of minimally processed honeydew melons stored in air or controlled atmosphere

Pieces (1835 mm cylinders) were prepared from sanitized fruits of four honeydew melon varieties (Green Flesh, Morning Ice, Rico, RML 2704) harvested at typical commercial maturity. Pieces were stored in air or controlled atmosphere (CAair15% CO2) at 5°C and evaluated for sensory quality, firmness, color and soluble solids concentration (SSC) after 0, 6 and 12 days. Significant variation was found among varieties in SSC (9.9‐12.2%), firmness (14.0‐19.9 N), and chroma (10.4‐19.0), hue angle (115‐113) and L* (63.7‐66.8) color values of pieces on day 0. Pieces from the four varieties averaged 10 N firmness loss from day 0 to 12 and CA reduced loss significantly in only one variety. During air storage color saturation decreased only in pieces from varieties with high initial chroma (C) values. Average DC between days 0 and 12 was 3.7 for air-stored vs 1.0 for CA-stored pieces. Average DL* was 5.8 and 1.4 for the same conditions, respectively. SSC were maintained during storage in air or CA. Pieces stored in 15% CO2 had higher visual quality scores than those stored in air. In addition, CA storage greatly reduced development of macroscopic decay, translucency and off-odors.

Reduction by gaseous ozone of Salmonella and microbial flora associated with fresh-cut cantaloupe

This research investigates the efficacy of gaseous ozone, applied under partial vacuum in a controlled reaction chamber, for the elimination of Salmonella inoculated on melon rind. The performance of high dose, short duration treatment with gaseous ozone, in this pilot system, on the microbial and sensory quality of fresh-cut cantaloupes was also evaluated. Gaseous ozone (10,000 ppm for 30 min under vacuum) reduced viable, recoverable Salmonella from inoculated physiologically mature non-ripe and ripe melons with a maximum reduction of 4.2 and 2.8 log CFU/rind-disk (12.6 cm(2)), respectively. The efficacy of ozone exposure was influenced by carrier matrix. Salmonella adhering to cantaloupe was more resistant to ozone treatment when suspended in skim-milk powder before aqueous inoculation to the rind. This indicated that organic matter interferes with the contact efficiency and resultant antimicrobial activity of gaseous ozone applied as a surface disinfectant. Conversely, in the absence of an organic carrier, Salmonella viability loss was greater on dry exocarp surfaces than in the wetted surfaces, during ozone treatment, achieving reductions of 2.8 and 1.4 initial log CFU/rind-disk, respectively. Gaseous ozone treatment of 5000 and 20,000 ppm for 30 min reduced total coliforms, Pseudomonas fluorescens, yeast and lactic acid bacteria recovery from fresh-cut cantaloupe. A dose Ct-value (concentration x exposure time) of 600,000 ppm min achieved maximal log CFU/melon-cube reduction, under the test conditions. Finally, fresh-cut cantaloupe treated with gaseous ozone, maintained an acceptable visual quality, aroma and firmness during 7-day storage at 5 degrees C. Conclusions derived from this study illustrate that gaseous ozone is an effective option to risk reduction and spoilage control of fresh and fresh-cut melon. Moreover, depending on the timing of contamination and post-contamination conditions, rapid drying combined with gaseous ozone exposure may be successful as combined or sequential disinfection steps to minimize persistence of Salmonella on the surface of cantaloupe melons and transference during fresh-cut processing of home preparation. Based on these results, greater efficacy would be anticipated with mature but non-ripe melons while ripe tissues reduce the efficacy of these gaseous ozone treatments, potentially by oxidative reaction with soluble refractive solids.

Changes in acetaldehyde, ethanol and amino acid concentrations in broccoli florets during air and controlled atmosphere storage

Abstract Acetaldehyde, ethanol and non-protein bound amino acids were determined in broccoli florets ( Brassica oleracea L. var. Italica cv. Marathon) stored for 7 days at 10°C in air or controlled atmospheres (0.125, 0.25, or 0.5% O 2 alone or in combination with 20% CO 2 , or 20% CO 2 in N 2 ) followed by 2 days aeration. Floret yellowing was visible at days 7 and 9 in air. Low O 2 or low O 2 plus high CO 2 atmospheres delayed yellowing. Acetaldehyde and ethanol concentrations increased as O 2 concentrations decreased with or without 20% CO 2 . Aeration for 2 days generally reduced acetaldehyde and ethanol concentrations. The total free amino acid concentration increased during air-storage from 244 μmol g −1 dry weight at harvest to 573 μmol g −1 dry weight at day 9. Due to severe soft rot development in the broccoli treated with 0.125 and 0.25% O 2 free amino acids were only determined in samples treated with 0.5% O 2 , 0.5% O 2 +20% CO 2 and 20% CO 2 . Amino acid change in samples stored under 0.5% O 2 were similar to those of air-stored broccoli. Storage for 7 days in the CO 2 -containing atmospheres resulted in an increase in non-protein amino acids and a decrease in protein amino acids, although total amino acid content remained the same. Alanine accumulated in 0.5% O 2 or 20% CO 2 in N 2 atmospheres. The non-protein amino acid, γ-aminobutyrate accumulated in 20% CO 2 but its concentration decreased upon aeration, and these changes were associated with similar but opposite changes in glutamate concentrations. Aspartate content also decreased in 20% CO 2 and increased upon aeration. This coincided with the formation of an unidentified amino acid. In broccoli treated with high CO 2 atmospheres, α-decarboxylation seemed to be an important path of metabolic interconversion, however, these reaction pathways were reversible upon aeration.

Use of controlled atmospheres and heat treatment to maintain quality of intact and minimally processed green onions

To maintain high quality and to extend the shelf life of intact and minimally processed (removal of roots and compressed stem) green onions (Allium cepaA. fistulosum), the potential benefits of controlled atmospheres (CA) and heat treatment were evaluated. Atmospheres of 0.1‐0.2% O2 or 0.1‐0.2% O2 containing 7.5‐9% CO2 were the CA conditions that best maintained the visual appearance and prolonged shelf life to more than 2 weeks at 5°C in both intact and cut onions. No CA treatment completely controlled extension, growth or ‘telescoping’ of the inner white leaf bases of the minimally processed onions at 5°C. Heat treatment (55°C water for 2 min) of the white leaf bases effectively controlled ‘telescoping’ of cut onions stored at 5°C. Total soluble sugars generally decreased in intact and minimally processed green onions, but were maintained in heat-treated cut onions. Heat treatment did not affect thiosulfinate concentrations during 14 days at 5°C, except for treated cut onions not stored under CA.