Fresh-cut radish using different cut types and storage temperatures

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1 Postharvest Biology and Technology 40 (2006) Fresh-cut radish using different cut types and storage temperatures Juan Saavedra del Aguila a,,1, Fabiana Fumi Sasaki b,2, Lilia Sichmann Heiffig a,1, Edwin Moisés Marcos Ortega c, Angelo Pedro Jacomino a,1, Ricardo Alfredo Kluge b,1 a Department of Crop Production, Escola Superior de Agricultura Luiz de Queiroz, University of São Paulo, C.P. 9, , Piracicaba, SP, Brazil b Department of Biological Science, Escola Superior de Agricultura Luiz de Queiroz, University of São Paulo, C.P. 9, , Piracicaba, SP, Brazil c Department of Basic Science, Escola Superior de Agricultura Luiz de Queiroz, University of São Paulo, C.P. 9, , Piracicaba, SP, Brazil Received 30 March 2005; accepted 31 December 2005 Abstract This project studied the effects of different types of cuts and storage temperatures on the quality of stored, fresh-cut radish. Two types of cuts (sliced and shredded), and three storage temperatures (1, 5 and 10 C), were studied during 10 d. Whole radish was used as the control. Respiration rate and ethylene production were evaluated daily, while physicochemical parameters (soluble solids, weight loss, titratable acidity, ascorbic acid content, and color) were evaluated every second day. Twelve hours after processing, shredded roots had produced 0.04, 0.11 and 0.17 ng kg 1 s 1 of C 2 H 4 at 1, 5 and 10 C, respectively. On the 10th day, whole roots stored at 1 C showed the lowest respiration rate (1.59 gkg 1 s 1 of CO 2 ) while the highest rate was observed in shredded roots stored at 10 C (7.42 gkg 1 s 1 ). Shredded radishes had lower soluble solids during storage compared to other cut types. Loss of fresh matter increased with storage time and temperature. The content of ascorbic acid decreased in shredded roots stored at 10 C. The value of lightness (L * ) of shredded roots decreased during storage at the three studied temperatures. Temperatures of 1 and 5 C are recommended for maintenance of quality in fresh-cut radishes Elsevier B.V. All rights reserved. Keywords: Raphanus sativus L.; Fresh-cut; Respiration rate; Ethylene; Postharvest; Cold storage 1. Introduction The demand for fresh-cut products is growing rapidly in the foodservice and retail markets. Fresh-cut business has been experiencing exponential increases in many countries, particularly in large metropolitan areas such as São Paulo, one of the biggest cities in Brazil, where supermarkets sell around US$ 4 million of fresh-cut products per month, including both fruit (54%) and vegetables (46%) (Rojo and Saabor, 2002). Minimal processing (fresh-cut) comprises selection, washing, peeling and cutting procedures aimed at producing a product that is fresh and convenient to prepare or consume (Burns, 1995). In general, fresh-cut products have a Corresponding author. Tel.: ; fax: address: jsaguila@esalq.usp.br (J.S. del Aguila). 1 CNPq fellow. 2 FAPESP fellow. shorter shelf life, which is mainly due to mechanical stresses (Watada, 1997). At the cut surface, cells and membranes are damaged leading to alterations in tissue metabolism. Although these alterations are different, many authors have observed increase in carbon dioxide and ethylene evolution, water loss, alterations in flavor and aroma, in volatile profiles, and increase in the activity of enzymes related to enzymatic browning (Rolle and Chism, 1987; Brecht, 1995; Artés et al., 1998; Saltveit, 2003). Temperature control is the most common and important technology to minimize the effects of cutting in fruit and vegetables (Brecht, 1995; Cantwell, 1996; Watada et al., 1996). Whole and sliced carrots kept at 0 and 10 C demonstrate the importance of low temperatures for the reduction of respiration, and consequently metabolism. Whole carrots produced 1.0 and 1.4 gkg 1 s 1 of CO 2 at 0 and 10 C, respectively, which represents an increase of 40.54% in respiration at 10 C, while carrot slices produced 1.7 and 3.0 gkg 1 s /$ see front matter 2006 Elsevier B.V. All rights reserved. doi: /j.postharvbio

2 150 J.S. del Aguila et al. / Postharvest Biology and Technology 40 (2006) of CO 2 at 0 and 10 C, respectively, which represents an increase of 66.67% in respiration at 10 C. Sliced carrots showed an increase of 62.2 and 92.3% in respiration rate compared to whole carrots, at 0 and 10 C, respectively (Cantwell, 1992). Furthermore, Vitti et al. (2004) have observed that respiration rate of fresh-cut beets stored at 15 C was two times higher than that observed at 5 C. Among many fruit and vegetable crops processed in Brazil, radish is increasing in importance, being an important component of many mixed salads, and a relatively good source of vitamin C. Fresh-cut radish has had little study with respect to storage and preparation mode. In this study, different cut types and storage temperatures were investigated in an attempt to maintain the quality and enhance the storage period of radish minimally processed. 2. Materials and methods 2.1. Plant material Bunched radishes (Raphanus sativus L., CV. Crimson Gigante) obtained from a producer in Piracicaba, SP, Brazil, were use for this study. The above-ground foliage was removed from the bunched radishes, thus obtaining topped radishes. The product was sorted for uniform appearance, size and absence of physical and pathological damage Minimal processing Whole, topped radishes were pre-washed in running water to remove impurities, and after drying, were stored at 10 C for 12 h before minimal processing. Radishes were submitted to the following cut types: shred cut (approximately 2 mm for 20 mm), slice cut (2 mm thick) and without cut (whole radish). The radishes were cut with an industrial processor (Robot Coupe CL50 version D). Minimal processing was carried out at 15 C. Treatments were washed in a 200 mg L 1 chlorine solution for 3 min, rinsed for 1 min to remove the excess chlorine and, finally, centrifuged at 800 g for 1 min to remove excess water. Fresh-cut and whole radishes were placed in expanded polystyrene trays (130 g in each 14 cm 20 cm tray), wrapped in 14- m thick polyvinyl chloride (PVC) film and stored in cold chambers at 1 ± 1, 5 ± 1or10± 1 C and 90 ± 5% RH for 10 d Assessments The evaluations of respiration rate and ethylene production were carried out daily, while for the other variables the evaluations were carried out every second day. To determine respiration rate, 130 g of minimally processed or whole radish were placed in 580 ml glass flasks and hermetically sealed for 1 h at different temperatures (1 ± 1, 5 ± 1or10± 1 C and 90 ± 5% RH). A silicone septum was fitted in the flask lids to allow the collection of a 1 ml of internal atmosphere. Gas samples were analyzed in a gas chromatograph (Thermoffinigan, model Trace 2000 GC). Results in % CO 2 were used in the calculation of the respiration rate, which considered the flask volume, the radish mass and the time the flask was closed. The respiration rate was determined within 5 h after minimal processing, by means of four readings, the first of which (time zero) was carried out 1 h after processing. Subsequent readings were conducted daily for 10 d. Results were expressed as the production rate of CO 2 in gkg 1 s 1. The procedures to determine ethylene production were the similar to those used for respiration rate analysis. Internal atmosphere readings were analyzed with a gas chromatograph (Thermoffinigan, model Trace 2000 GC) equipped with flame ionization detector (FID) with column Porapack N, of 2 m of length. The injector, column, and detector temperatures were 100, 100 and 250 C, respectively, and with H 2 carrier gas flow of 0.40 ml s 1. The production rate of C 2 H 4 was expressed in ng kg 1 s 1. The soluble solids concentration (SSC) was determined by direct reading of centrifuged fresh-cut in a digital refractometer (Atago PR-101, Atago Co. Ltd., Tokyo, Japan) with the results expressed in percentage (%). Titratable acidity (TA) was determined from 10 g of puree diluted with 90 ml of water, titrated with 0.1N NaOH to ph 8.1 and expressed in percentage of malic acid (Carvalho et al., 1990), once this acid represents approximately 80% of the total organic acids presents in radish (Wang, 1998). Ascorbic acid content was determined by titration (Carvalho et al., 1990) and the results expressed in mg kg 1. The weight loss was the difference between the initial and the final mass of each replicate and the results were expressed in %. Lightness (L * ), was determined using a colorimeter (Minolta CR-300, Osaka, Japan). A decrease of L * value indicated a loss of whiteness (brightness). Readings were conducted directly on the minimally processed products and on the whole radish just after cutting Data analysis The data were subjected to analysis of variance and the least significant differences were calculated using SAS software for the completely randomized experimental design with five replicates for each day of analysis. Differences between any two treatments greater than the sum of two standard deviations were always significant (P > 0.05). 3. Results and discussion At all temperatures used the maximum respiration rate was observed just 1 h after processing (Fig. 1) with subsequent decrease through the final evaluation (4 h). This initial increase of respiration was due to the stress caused by cutting, which promotes the uncontrolled mixing of cellular components, or through controlled cellular repair mechanism (Saltveit, 2003). The subsequent decrease in the respiration

3 J.S. del Aguila et al. / Postharvest Biology and Technology 40 (2006) Fig. 1. Respiration rate of evolved CO 2 ( gkg 1 s 1 ) in whole, shredded and sliced radish just after processing, during cold storage at 1 C (A), 5 C (B) and 10 C (C). Vertical bars represent ±S.D. (n = 5). rate after 1 h is probably due to the self-regulation of the tissue respiratory activity caused by the great production of ATP (Purvis, 1997). It is also possible that such reduction in the respiration rate happens because respiratory substrates stop reacting with the enzymes of the cells present in the cut surface. Therefore, the respiration rate observed after 1 h, is probably caused by cells injured by the cut lying below the surface. Preliminary tests had verified this statement. Significant differences in respiration rate between shredded and sliced cut were obtained at the temperatures of 1 and 5 C 1 h after processing (Fig. 1A and B). Also, shredded radish showed higher respiration than whole radish throughout the 4-h period. At 10 C whole radish showed lower respiration rate than minimally processed radish throughout the 4-h period of evaluation (Fig. 1C). The response of tis- Fig. 2. Respiration rate of evolved CO 2 ( gkg 1 s 1 ) of whole, shredded and sliced radish during cold storage at 1 C (A), 5 C (B) and 10 C (C). Vertical bars represent ±S.D. (n = 5). sue to processing wounds usually increases as the severity of the injury increases (Brecht, 1995; Saltveit, 2003). This can explain the differences observed in the respiration rate between whole and shredded radish and between shredded and sliced radish. During cold storage the respiration rate of whole radish remained stabile, while oscillations in fresh-cut radishes were observed. Respiration was generally higher in shredded radish (Fig. 2). There was no detectable ethylene production up to 9 h after processing. After 9 h, ethylene production was higher in shredded and sliced radish compared to whole radish (Fig. 3). No ethylene was detected 12 h after processing. Ethylene production is another response of vegetables to wounding (Abeles et al., 1992; Sakr et al., 1997). Thus, the increase

4 152 J.S. del Aguila et al. / Postharvest Biology and Technology 40 (2006) Fig. 3. Ethylene production rate (ng kg 1 s 1 ) in whole, shredded and sliced radish after 9 12 h at 1 C (A), 5 C (B) and 10 C (C). Vertical bars represent ±S.D. (n = 5). in ethylene production may be attributed to the biosynthesis of wound ethylene (Abeles et al., 1992). In radish, the ethylene production response to injury appears to be retarded if compared to other fresh-cut underground storage organs. For example, in shredded beets ethylene (0.22 ng kg 1 s 1 ) was detected after 1 h of processing (Vitti et al., 2004). In relation to storage temperature it was verified that ethylene production was higher with increase of temperature. Freshcut radish produced C 2 H 4 at ng kg 1 s 1 at 1 C, ng kg 1 s 1 at 5 C and ng kg 1 s 1 at 10 C. Weight loss increased as a function of storage time and temperature (Fig. 4), but it did not increase as a function of cut type. At 1 and 5 C, weight loss was 2 3% at the end of 10 d of storage, while at 10 C the weight loss was about 5%. Shredded radish lost more soluble solids than sliced and whole radish (Fig. 5). Shredded radish lost 2.2% during 10 d Fig. 4. Weight loss (%) of whole, shredded and sliced radish during cold storage at 1 C (A), 5 C (B) and 10 C (C). Vertical bars represent ±S.D. (n = 5). of cold storage, while the loss observed in whole and sliced was 0.43 and 1.1%, respectively. This decrease in soluble solids can be attributed, partially, to the consumption of carbohydrates in respiration related to the repair of injury. In addition, the higher injured area of shredded radish may have caused an amplification of the response to the injury. There were no differences in acidity among cut types and storage temperatures. The values of malic acid have varied from 0.05 to 0.06% (data not shown). Ascorbic acid content decreased in shredded radish stored at 10 C(Fig. 6) from to mg kg 1 after 10 d of storage. Whole and sliced radish showed essentially no reduction of ascorbic acid during storage at both temperatures. Ascorbate is the most important antioxidant molecule

5 J.S. del Aguila et al. / Postharvest Biology and Technology 40 (2006) Fig. 5. Soluble solids (SS) of whole, shredded and sliced radish during cold storage at 1 C (A), 5 C (B) and 10 C (C). Vertical bars represent ±S.D. (n = 5). in plants, having a vital role in the removal of H 2 O 2 through the glutathione ascorbate cycle (Noctor and Foyer, 1998). The content of ascorbic acid in most vegetables decreases when bruising, trimming and cutting occurs (Lee and Kader, 2000). In the present study, the severity of injury has contributed to the large decrease of this antioxidant. The content of ascorbic acid in fresh-cut produced during storage is affected by both biosynthesis and degradation reactions. Thus, the decrease in ascorbic acid in the shredded radish does not necessarily mean a lack of ascorbic acid biosynthesis, but concomitant consumption of this antioxidant by browning reactions. The last explanation can be related to the values of L * verified in shredded radish (Fig. 7). At all temperatures there was a decrease of L *, which indicated a loss of whiteness of shredded radish just after 2 d of storage. No difference was observed in the L * value between whole and sliced radish during cold storage at the temperatures studied. Processing injury induces many physical and physiological responses. Most of these changes are unwanted and contribute to decreasing product quality. Temperature is the main Fig. 6. Ascorbic acid of whole, shredded and sliced radish during cold storage at 1 C (A), 5 C (B) and 10 C (C). Vertical bars represent ±S.D. (n = 5). technique postharvest to preserve the quality of fruit and vegetables. In fresh-cut commodities, the use of low temperature from preparation to the marketing is essential, considering that several reactions are triggered by the processing injury and many of these reactions are amplified by an increase in temperature. Temperature of 5 C has been indicated for cold storage of fresh-cut produce. Shredded and sliced are the main forms of commercial fresh-cut radish in Brazil. However, in many cases the product is marketed at temperature of C. In this trial, quality differences were observed between these cut types, mainly when the storage temperature was 10 C. In this study, few quality differences were observed between 1 and 5 C in minimally processed radish, while 10 C contributed to the loss of quality of the product. At this temperature, the loss of ascorbic acid (vitamin C) was high in shredded radish compared to the lowest temperatures. Respiration and ethylene were also higher at 10 C, denoting a higher metabolism and, consequently, higher consumption of reserves. On the other hand lower temperature (1 or 5 C) showed decreases in metabolism, thus preserving fresh-cut radish quality.

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