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Shelf-life estimation of ‘Fuji’ apples
Postharvest Biology and Technology 50 (2008) 64–69
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Shelf-life estimation of ‘Fuji’ apples II. The behavior of recently harvested fruit during storage at ambient conditions P. Varela, A. Salvador, S. Fiszman ∗ Instituto de Agroquímica y Tecnología de Alimentos (CSIC), Apartado de Correos 73, 46100 Burjassot, Valencia, Spain
a r t i c l e
i n f o
Article history: Received 19 December 2007 Accepted 31 March 2008 Keywords: ‘Fuji’ apples Shelf-life Consumer acceptability Descriptive analysis Rheology Texture
a b s t r a c t Variations in the eating quality of recently harvested ‘Fuji’ apples during long-term storage at ambient temperature were analyzed from different approaches: sensory (consumers and trained descriptive panel), instrumental (texture and dynamic rheology), and physicochemical (acidity, soluble solids, and pectin content). In particular, the application of dynamic rheological tests is a new tool which proved to be successful to characterize the whole apple tissue. The percentage of consumers rejecting the apples did not increase with storage time, even at 61 d of storage and the overall acceptability was not significantly different between the sampling dates over all the storage period, and most quality parameters remained stable up to more than 61 d storage (20 ◦ C, no controlled atmosphere (CA)). From day 70, the apples became shriveled as a result of the non-controlled atmosphere storage; this physiological deterioration would cause rejection of the fruit before consumption, this being the major determinant of their shelf-life. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Depending on the cultivar, apples can currently be stored for up to 1 year in controlled atmosphere (CA) storage. This is why fruit from both hemispheres are sometimes sold in the market at the same time, and consumers have to choose (consciously or not) between recently harvested and long-term stored apples. Time and conditions of storage has been the subject of many studies; the main objective being to extend keepability while maintaining consumer acceptability (Hoehn et al., 2003; Lund et al., 2006). Consumer preference for apples is generally associated with firmness, juiciness and sweetness; they perceive mealiness as a negative quality attribute and associate it with long-term stored, not-fresh apples (Jaeger et al., 1998). Sometimes the consumers rate freshness of fruit not only for their sensory characteristics, but also for the time from harvest (if known), considering that fresh products should have been recently picked, although in some cases consumer expectations based on the knowledge of storage duration may not match the real sensory characteristics of the apples (Lund et al., 2006). Another consumer concern is that “old”, stored apples get “mealy” if kept in the home, which in many cases is true, as apple texture can deteriorate during cold storage, resulting in softness and mealiness (Fillion and Kilcast, 2001).
∗ Corresponding author. Tel.: +34 963 90 0022; fax: +34 963 63 6301. E-mail address: sfi[email protected] (S. Fiszman). 0925-5214/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2008.03.016
‘Fuji’ apples (Malus domestica Borkh. cv. Fuji) have become very popular in Europe in recent years, taking some of the market from more traditional varieties; this bi-colored apple variety has distinctive sensory characteristics, particularly regarding flavor and a crunchy texture, and is well suited to storage (Jaeger et al., 1998; Echeverría et al., 2004; Varela et al., 2005). Fruit are commonly kept at ambient temperatures for daily home consumption and also by small-scale distributors and retailers. Varela et al. (2005), in previous work, raised some points. How long apples would remain fit to eat after having undergone a prolonged period of CA-storage? At ambient conditions, what are the sensory quality and consumer acceptability criteria with respect to the shelf-life of apples? They studied the behavior of ‘Fuji’ apples kept at 20 ◦ C in a normal atmosphere until consumption following 7 months’ refrigerated storage (1 ◦ C) in a CA (2% O2 , 2% CO2 ) and estimated the apples’ shelf-life. Consumer acceptability and descriptive sensory analyses for storage periods of up to 28 d at 20 ◦ C indicated that the greatest quality loss in stored ‘Fuji’ apples was associated with increased mealiness, and appearance of an over-ripe taste, and alcoholic taste and odor. Following that first study on 7 months CA-stored apples, the objective of the present work was to follow this up by studying the behavior of recently harvested ‘Fuji’ apples, without CA storage, and analyzing the variations in quality when kept at ambient temperature. Further tools for the study of apple quality are applied.
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2. Materials and methods 2.1. Plant material and storage conditions
Table 1 Sensory attributes and their associated descriptors used in the descriptive analysis of ‘Fuji’ apples Attribute
‘Fuji’ apples (M. domestica Borkh. cv. Fuji) were harvested at commercial maturity. Flesh firmness was determined on 10 fruit randomly taken from the orchard. Whole apple firmness (penetration force) was determined with a TA-XT2 Texture Analyzer (Stable Micro Systems Ltd., Surrey, U.K.) by measuring the force required for a 4-mm diameter probe to penetrate the flesh of a whole apple; fruit were considered “commercially mature” when the fruit had values of 50.5 ± 3.2 N. The fruit (350 apples) came from a Spanish orchard (Lleida, Spain) in October 2004. Immediately after harvest they were selected for uniformity and absence of defects, and placed in cold storage at 1 ◦ C. Sub-batches of 32 apples were subsequently transferred to storage at 20 ◦ C without atmosphere control, where they remained for 0, 9, 20, 30, 41, 51, 61, 70, 78 and 91 d to provide 10 samples with different storage times at the same time. They were sampled as follows: the apples to be stored for 91 d were placed in a 20 ◦ C room, followed 13 d later by the apples to be stored for 78 d, and so on, until the last day (day 91) when apples to be stored 0 d were placed in the 20 ◦ C room. This last day is the sensory assessment day. In this way, on the same day all the apples had been stored at 20 ◦ C for the planned times; this logically supposed that during the time that they were not at 20 ◦ C, they were previously at 1 ◦ C, a price to pay for the shelf-life sampling, and with the assumption that at this temperature the ripening rate was minimum. Prior to storage at 20 ◦ C the apples were sanitized with a 200 ppm chlorine solution for 10 min, rinsed and individually dried. 2.2. Sensory analysis Testing was carried out in a sensory laboratory equipped with individual booths (ISO 8589, 1988). The samples were peeled and cut into 1.5 cm sided cubes for evaluation. Cutting took place at the most 1 h before evaluation. Data acquisition was performed using Compusense® five release 4.6 software (Compusense Inc., Guelph, Ont., Canada). 2.2.1. Consumer testing Consumers were recruited among non-scientific workers and students from the Instituto de Agroquímica y Tecnología de Alimentos, Valencia, Spain. Fifty persons, 25–65 years old, approximately half female, half male, who consumed apples on a regular basis, participated in the study. They received one cube from each different storage time following a balanced complete block experimental design. For each sample they scored global acceptability using a 9-box scale labeled on the left with “dislike very much”, in the middle with “neither like nor dislike” and on the right with “like very much”. To estimate sensory shelf-life they also answered the question “Would you normally consume this product?” with a yes or a no (Hough et al., 2003; Varela et al., 2005). 2.2.2. Descriptive analysis A panel of 11 assessors previously trained in the description of ‘Fuji’ apples was used for the analysis. The selection of the terminology (Table 1) and the training procedure is described elsewhere (Varela et al., 2005). Formal assessment of the samples was carried out following a balanced complete block experimental design. For scoring, 10 cm unstructured scales labeled “nil” and “high” were used. Six cubes taken from different apples of each of the seven samples (0, 9, 20, 30, 41, 51, and 61 d at 20 ◦ C), were served at 10 ◦ C in closed, odor-
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Associated descriptor
Appearance
Roughness (of the surface)
Odor
Ripe Alcoholic Aged
Oral texture
Hardness Crunchiness Sound produced Mealiness Granularity Juiciness
Taste
Fresh Sweet Acid Ripe Alcoholic
Aftertaste
Astringent Alcoholic
less plastic containers identified with three digit random codes. All the samples of different storage times were evaluated on the same session. Water was used for rinsing between samples. 2.3. Physical and chemical determinations 2.3.1. Acidity and soluble solids Titrable acidity, expressed as malic acid, and soluble solids, were quantified by AOAC standard techniques, methods 942.15 and 932.12 (AOAC, 2000). The Thiault index was calculated as follows: index = [10 × acidity (g/L) + sugar content (g/L)] (Harker et al., 2002). Four apples of each sample (different storage times at 20 ◦ C) were processed homogenized and measured. 2.3.2. Protopectin/total pectin ratio The total pectin content and the water-soluble pectin fraction were determined by the m-hydroxydiphenyl method (Kintner and Van Buren, 1982; Varela et al., 2007a). Assuming protopectin as the non water-soluble fraction, the protopectin/total pectin ratio was calculated as: (total pectin − water-soluble pectin)/(total pectin). Four apples of each sample (different storage times at 20 ◦ C) were processed homogenized and measured. 2.3.3. Instrumental texture A TA-XTplus Texture Analiser (Stable Micro Systems, Godalming, UK) was used to evaluate the texture of the apple cubes. Immediately before measuring, the samples were peeled and cut into 1.5 cm-sided cubes with a sharp cutter, avoiding vascular tissue. All tests on the cubes were performed with the same orientation because of the fibrous non-isotropic properties of apple flesh (Khan and Vincent, 1993). Five cubes taken from different apples corresponding to each sample (different storage time at 20 ◦ C), were measured. Penetrometer tests were conducted with the Volodkevich tooth geometry (VB) penetrating 12 mm into the apple cube (Varela et al., 2007b). Test parameters were: test speed of 1 mm/s, a trigger force of 5 g, and force in compression mode. Force vs. time was plotted and the following parameters were extracted: the area under the complete penetration curve, the number of peaks and the gradient of the initial linear slope of the curve. 2.3.4. Rheological measurements Dynamic rheological behavior was characterized using a controlled stress rheometer (rheostress RS100) equipped with a
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Phoenix II P1 C2 5-P circulation bath (Haake, Karlsruhe, Germany), at 10 ◦ C, using plate and plate geometry, 35 mm in diameter, serrated plates to prevent slippage, with a 9.9 mm gap between plates, 1% compression and 5 min of equilibration time. The samples were measured in disks of whole tissue 35 mm in diameter and 10 mm in height. The detailed sampling and measuring procedure is explained in Varela et al. (2007b). All experiments were conducted on apple cylinders with the same orientation (top–bottom) because of the fibrous non-isotropic properties of apple flesh. The linear viscoelastic range (LVR) was determined through shear stress sweeps from 1 to 1000 Pa. A constant stress of 50 Pa was then chosen (common to the LVR of all samples) to obtain the mechanical spectra as frequency sweeps from 0.01 to 10 Hz. Tg␦ (G /G ) were calculated and the storage modulus (G ) was plotted to characterize the viscoelastic behavior. Four discs taken from different apples corresponding to each sample (different storage time at 20 ◦ C) were measured. 2.4. Statistical analyses Analyses of variance (ANOVA) were performed on the physical and chemical data and the acceptability scores using storage time as the variation factor and on the trained sensory panel data using storage time, assessor and their interaction as variation factors. In order to study the differences among samples, least significant differences were calculated by Tukey’s test. These analyses were performed with the use of the SPSS 12 package (SPSS Inc., Chicago). Survival analysis methodology (SAM) was used to estimate the shelf-life of ‘Fuji’ apples using the results obtained from consumers when asked if they would normally consume the samples with different storage times (Hough et al., 2003; Varela et al., 2005). 3. Results and discussion 3.1. Sensory characteristics 3.1.1. Consumer test and shelf-life considerations Recently harvested ‘Fuji’ apples were kept at 20 ◦ C in a normal atmosphere for 91 d until consumption; from day 70 of the storage, the apples showed external skin damage as a result of the noncontrolled atmosphere storage. Excess or too low relative humidity can have a detrimental effect on fruit during storage; if the humidity is too low it causes dehydration of the tissues leading to shriveling. Shriveling in apples is an obvious signal of an unfresh product (Lund et al., 2006), and most probably would be rejected before consumption. It was then decided to perform the sensory analysis on samples with storage periods up to 61 d. In previous work, Varela et al. (2005) estimated the shelf-life of ‘Fuji’ apples kept at 20 ◦ C in a normal atmosphere until consumption; these apples had been stored for 7 months under CA refrigeration. Survival analysis methodology was successfully used
Table 2 Mean values for consumer acceptability (9-point box scale) and percentage of rejection over the storage of ‘Fuji’ apples at 20 ◦ C Sample
Consumer acceptability a
0D 9D 20 D 30 D 41 D 51 D 61 D
Consumer percentage of rejection 27a 23a 28.5a 26.6a 29a 22a 30a
6.6 6.8a 5.9a 5.7a 6.2a 6.0a 5.9a
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
for the estimation by using the results obtained from consumers when asked if they would normally consume the samples with different storage times. This method’s key concept is to focus the shelf-life hazard on the consumer rejecting the product rather than on the product deteriorating (Hough et al., 2003), as is particularly suited to products where shelf-life is determined for sensory reasons rather according to microbiological or chemical deterioration. In the work mentioned above (Varela et al., 2005), the estimated shelf-life of ‘Fuji’ apples was of 23 d at a 50% rejection probability. Consumer acceptability and descriptive sensory analyses indicated that the greatest quality loss was associated with increased mealiness, ripe taste and alcoholic taste and odor; at the same time, the acceptability dropped from a score of 6 at day 0 of storage to 4.2 at day 28. In the present study, the percentage of consumers rejecting the apples did not increase with storage time (Table 2), not surpassing 30% even at 61 d storage. As a result, the survival analysis procedure could not be applied to the acceptance/rejection data in this case. Furthermore, the overall acceptability evaluated by the consumers did not present significant differences between the different times of storage in all the storage period (Table 2). Therefore, sensory rejection of the edible part of the apple because of the eating quality loss would not be the reason of the end of shelf-life in this case. Instead, physiological deterioration leading to the rejection of the entire fruit before consumption would be the determinant of shelflife. 3.1.2. Descriptive analysis The descriptors roughness, ripe odor, granularity, juiciness, sweetness, alcoholic taste and astringent and alcoholic aftertaste, did not present significant differences between days 0 and 61 of storage (Tukey’s test). The descriptors’ values that did show significant differences over the storage time are shown in Table 3. The texture parameters hardness, crunchiness and sound, had higher values for the fresher samples, fell at the start of storage and then remained constant throughout the period. The ripe taste values also showed a change on the first days of storage and then remained constant. The rest of the descriptors’ values only showed significant changes on the last days of storage.
Table 3 Mean values for the sensory descriptive analysis parameters (trained panel, 10-cm unstructured scales) that showed significant differences during storage of ‘Fuji’ apples at 20 ◦ C Sample
Alcoholic odor
Aged odor
Hardness
Crunchiness
Sound
Mealiness
Fresh taste
Acidity
Ripe taste
0D 9D 20 D 30 D 41 D 51 D 61 D
1.4a 3.2a 2.1a 2.5a 2.0a 5.0b 4.8b
1.8a 2.1a 3.1a,b 3.2a,b 2.8a,b 4.2a,b 5.3b
6.2b 5.4a 4.7a 3.5a 4.0a 4.5a 5.4a
6.1b 4.0b 4.6a 3.8a 4.9a 4.3a 4.3a
6.0b 4.2a 4.2a 3.4a 4.8a 4.5a 4.2a
1.7a 1.7a 3.8a,b 2.5a,b 3.8a,b 4.9b 4.3b
6.0c 3.6a,b,c 5.7b,c 4.2a,b,c 5.0a,b,c 2.8a 2.8a
4.7b 3.0a,b 4.2a,b 4.0a,b 2.0a 1.9a 2.3a
1.7a 3.8a,b 5.1b 4.1b 5.2b 6.1b 4.7b
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
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Table 4 Mean values (four determinations) of the chemical parameters (protopectin/total pectin, acidity and soluble solids) during storage of ‘Fuji’ apples (0–91 d at 20 ◦ C) Sample
Protopectin/ total pectin
Acidity (% of malic acid)
Soluble solids (g/L)
0D 9D 20 D 30 D 41 D 51 D 61 D 70 D 78 D 91 D
0.46b 0.43b 0.53b 0.60b 0.51b 0.40b 0.44b 0.23a 0.26a 0.21a
0.24d 0.25d 0.19c 0.20c 0.13b 0.15b 0.20c 0.09a 0.10a 0.10a
170a 182a 165a 165a 168a 175a 169a 169a 169a 170a
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
However, it is worth pointing out, that the variation of the measured sensory characteristics during storage was lower than that obtained in our previous work on refrigerated, CA-stored apples (Varela et al., 2005). Apples in both studies were from the same variety, from the same orchard, and were harvested at the same stage, but from two different harvests. Some of the differences between both studies could then be attributed to that fact. However, it is likely that most of the differences found in the changes that took place in the apples over the 20 ◦ C storage were due to the postharvest cold-storage conditions used in the previous work. Furthermore, weather conditions in Lleida were quite stable and were particularly similar during both harvests, and because of being an experimental orchard, conditions were closely controlled. With regard to the sensory data obtained, both with consumers and the trained panel, the stored apples did not vary in acceptability during 61 d at room temperature and only some of the sensory attributes assessed varied significantly with time of storage. That is quite a long storage time without any particular means of conservation. Consequently, not all harvested ‘Fuji’ apples would have to be refrigerated/CA-stored to be available for consumption in the following couple of months. It would be interesting to study the possibility of storing the harvested fruit differently into batches depending on the expected date of retail and consumption, not just divide into “fresh consumption” and “cold storage”, having in mind that cold storage could accelerate quality damage. It seems that ambient storage with humidity control might be more advantageous than CA storage if the expected retail date is, for example, 1 or 2 months after harvest. 3.2. Physical and chemical characteristics 3.2.1. Pectins, acidity and soluble solids Table 4 shows the mean values of the measured chemical parameters. Acidity values significantly dropped with storage time, but soluble solid contents did not vary. Because the soluble solids carry more weight in the Thiault index calculation, this did not present significant differences throughout the storage period (91 d), having an average value of 174. This suggested that chemical deterioration of the sugars, because of ripening, took place on the first stages. Growers use this index as an indicator of optimum ripeness for harvesting and consumption; values over 170 are considered acceptable for some apple varieties (Porro et al., 2002). The results were then in agreement with those obtained in the acceptability test by consumers. Until 61 d storage, apples were “equally” accepted. In our previous work (Varela et al., 2005), significant falls in the Thiault index were observed over the storage period at 20 ◦ C, dropping to 141 in the sample stored for 28 d (with a previous period at 1 ◦ C/CA-storage during 210 d) with a concomitant
Fig. 1. Penetration plots obtained with a Volodkevich jig: force (N) vs. distance (mm) of apples stored at 20 ◦ C for 0, 9, 41, 61 and 91 d.
drop in acceptability, a much lower value than those obtained in the present work up to 91 d. The protopectin/total pectin ratio significantly decreased from day 70 of storage. The value of the ratio obtained between days 0 and 61 was consistent with the one measured for fresh ‘Fuji’ apples in previous work (Varela et al., 2007a). 3.2.2. Instrumental texture A Volodkevich jig simulates the action of an incisor tooth biting through the sample, where the probe penetrates into the apple cube and the force necessary to achieve a certain penetration depth is measured, both compressive and shear forces being involved. As discussed in our previous work on apple textural characteristics (Varela et al., 2005, 2007a), apart from extracting numerical values, it is interesting to observe the differences in the complete profiles of instrumental texture curves. Fig. 1 shows the changes in the penetration profiles over storage at 20 ◦ C. A highly jagged penetration curve with many peaks due to numerous fracture events is often produced by products that are perceived as crispy or crunchy (Vincent, 1998; Varela et al., 2006a). That was the case for the samples in the first days of storage, and as the time of storage increased, the curves became smoother, although many fracture peaks were present, even until day 61. On day 91 very few fracture events could be observed. The area under the curve decreased with storage time. This parameter can be associated with the work of penetration and can be related to apple stiffness, hardness or rigidity. Table 5 shows the numerical values of the parameters extracted from the curves and their statistical differences. The gradient of the first linear part of the curve where compression takes place (and before penetration begins) and related to the elasticity of the sample, presented a similar change, where the sample became more elastic and less Table 5 Mean values (five determinations) of the textural parameters (area, gradient, number of force peaks) during storage of ‘Fuji’ apples (0–91 d at 20 ◦ C) Sample
Area (N/s)
Gradient (N s)
Number of force peaks
0D 9D 20 D 30 D 41 D 51 D 61 D 70 D 78 D 91 D
150c 146b,c 140b,c 112a,b,c 102a,b,c 142b,c 118b,c 106a,b,c 101a,b,c 68a
8.8d 8.4d 5.3c 5.7c 4.3b,c 2.7a,b 2.7a,b 2.7a,b 1.0a 0.6a
56d 44c,d 34b,c 33b,c 32b,c 31b,c 31b,c 29b 23a,b 13a
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
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Fig. 2. Determination of the linear dynamic viscoelastic range in a 41-d stored sample at 20 ◦ C. Stress sweep at 1 Hz: G and G (Pa) vs. shear stress (Pa).
rigid with storage time. The three parameters presented significant differences and reflected the quality loss at the end of storage, the textural parameters being quite stable until more than 70 d. 3.2.3. Rheological measurements Dynamic mechanical analysis is an effective method because it applies very small strains on the samples over a very short time. The properties of solid foods can then be studied with minimal physical changes, and study of the rheological properties of materials at different frequencies can be undertaken, providing valuable information for discrimination between samples. However, it is a technique rarely used for the study of fresh fruit. Varela et al. (2006b, 2007b) successfully applied this tool for the characterization of apple varieties and for the study of small changes in apple texture through storage. LVR was determined for all samples by dynamic stress sweeps; Fig. 2 shows an example for one of the samples. LVR was found to be between 10 and 500 Pa for most samples. To ensure the subsequent frequency sweeps were performed within the LVR, a constant stress of 50 Pa was chosen. Frequency sweeps showed that all samples behaved as viscoelastic materials, having clearly dominant solid characteristics with G values much higher than G . The replicates of each curve were run with good reproducibility since the differences between them were less than 5%. Tg␦ represents the ratio between the energy lost and stored per cycle, and thus, a relation between the viscous and elastic portions of the sample. No significant differences were found in the values of Tg␦ throughout storage (Table 6), showing no changes in the contribution of the two moduli in the viscoelastic behavior of the samples. G was then plotted to evaluate the mechanical characteristics in each day of storage. When subjected to oscillatory strain, all samples showed a slight linear decrease in G as frequency diminished. Fig. 3 shows the frequency dependence (mechanical spectrum) of the samples with storage. G decreases as the time of storage at 20 ◦ C increases, indicating some Table 6 Mean values (four determinations) of the rheological parameters (G (Pa) and Tg␦) at 1 Hz, during storage of ‘Fuji’ apples (0–91 d at 20 ◦ C) Sample 0D 9D 20 D 30 D 41 D 51 D 61 D 91 D
G (at 1 Hz) (Pa) d
1,430,000 465,500c 344,500c 342,000c 204,500b,c 189,210b,c 123,900b 68,460a
Tg␦(at 1 Hz) 0.10a 0.10a 0.11a 0.12a 0.13a 0.12a 0.12a 0.11a
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
Fig. 3. Frequency dependence (Hz) of the storage modulus, G (Pa), of apples with different times of storage (0, 9, 20, 41, 61 and 91 d) at 20 ◦ C.
loss in the structural integrity of the apple flesh. An important drop can be observed from the fresh sample (day 0) to day 9. The mechanical characteristics then became stable and started to decrease again from day 61. In order to quantify this variation, G at 1 Hz was compared (Table 6). A statistically significant decrease in G was confirmed. G is related to the rigidity of the tissues, the first drop observed (fresh to 9 days) agreed with the differences found by the trained panel in the attributes hardness, crunchiness, and sound, and also with the number of force peaks of the texture plot. Presumably, this first drop was not detected by the consumers, or else, they noticed a different texture but liked it all the same. The second drop in G , from day 61 of storage is attributed to the consequences of shriveling and long-term storage deterioration with softening occurring due to loss in structure. This second decrease in G is in agreement with the textural measurements. A drop in the work of penetration and a considerable loss in crispness shown by the less numbers of peaks, was also reflected in the profile of the texture curves. The values of G (1 Hz) obtained for fresh ‘Fuji’ apples are consistent with those obtained in previous work for ‘Fuji’ apples at commercial maturity (Varela et al., 2006b). In that work, where the application of dynamic rheological techniques for the characterization of apple tissue was presented, G (1 Hz) values for ‘Fuji’ apples with 14 d storage at 20 ◦ C of the same order of those found in the present work until 61 d were obtained. That also confirms the good quality levels maintained by the recently harvested ‘Fuji’ apples in the present study, at least until 61 d storage at ambient conditions. 4. Conclusions In the present work, we have shown that the changes that ‘Fuji’ apples undergo at ambient conditions, as in the home or with small retailers, are totally different whether they were previously cold/CA-stored for some months or had been recently harvested. No matter what the eating quality parameters, soluble solids, acidity, pectins, firmness, were at the time of harvest or out of storage, those parameters were not representative of the subsequent changes under ambient conditions. The previous history of the apples and the eating quality parameters as well as consumer appreciation all throughout shelf-life must be studied to obtain a complete picture. However, to construct a robust recommendation with “industry-wide” validity, extended research should be done. Acknowledgements The authors are indebted to the Comisión Interministerial de Ciencia y Tecnología for financial support (Project AGL 2006-11653-
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Shelf-life estimation of ‘Fuji’ apples II. The behavior of recently harvested fruit during storage at ambient conditions P. Varela, A. Salvador, S. Fiszman ∗ Instituto de Agroquímica y Tecnología de Alimentos (CSIC), Apartado de Correos 73, 46100 Burjassot, Valencia, Spain
a r t i c l e
i n f o
Article history: Received 19 December 2007 Accepted 31 March 2008 Keywords: ‘Fuji’ apples Shelf-life Consumer acceptability Descriptive analysis Rheology Texture
a b s t r a c t Variations in the eating quality of recently harvested ‘Fuji’ apples during long-term storage at ambient temperature were analyzed from different approaches: sensory (consumers and trained descriptive panel), instrumental (texture and dynamic rheology), and physicochemical (acidity, soluble solids, and pectin content). In particular, the application of dynamic rheological tests is a new tool which proved to be successful to characterize the whole apple tissue. The percentage of consumers rejecting the apples did not increase with storage time, even at 61 d of storage and the overall acceptability was not significantly different between the sampling dates over all the storage period, and most quality parameters remained stable up to more than 61 d storage (20 ◦ C, no controlled atmosphere (CA)). From day 70, the apples became shriveled as a result of the non-controlled atmosphere storage; this physiological deterioration would cause rejection of the fruit before consumption, this being the major determinant of their shelf-life. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Depending on the cultivar, apples can currently be stored for up to 1 year in controlled atmosphere (CA) storage. This is why fruit from both hemispheres are sometimes sold in the market at the same time, and consumers have to choose (consciously or not) between recently harvested and long-term stored apples. Time and conditions of storage has been the subject of many studies; the main objective being to extend keepability while maintaining consumer acceptability (Hoehn et al., 2003; Lund et al., 2006). Consumer preference for apples is generally associated with firmness, juiciness and sweetness; they perceive mealiness as a negative quality attribute and associate it with long-term stored, not-fresh apples (Jaeger et al., 1998). Sometimes the consumers rate freshness of fruit not only for their sensory characteristics, but also for the time from harvest (if known), considering that fresh products should have been recently picked, although in some cases consumer expectations based on the knowledge of storage duration may not match the real sensory characteristics of the apples (Lund et al., 2006). Another consumer concern is that “old”, stored apples get “mealy” if kept in the home, which in many cases is true, as apple texture can deteriorate during cold storage, resulting in softness and mealiness (Fillion and Kilcast, 2001).
∗ Corresponding author. Tel.: +34 963 90 0022; fax: +34 963 63 6301. E-mail address: sfi[email protected] (S. Fiszman). 0925-5214/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2008.03.016
‘Fuji’ apples (Malus domestica Borkh. cv. Fuji) have become very popular in Europe in recent years, taking some of the market from more traditional varieties; this bi-colored apple variety has distinctive sensory characteristics, particularly regarding flavor and a crunchy texture, and is well suited to storage (Jaeger et al., 1998; Echeverría et al., 2004; Varela et al., 2005). Fruit are commonly kept at ambient temperatures for daily home consumption and also by small-scale distributors and retailers. Varela et al. (2005), in previous work, raised some points. How long apples would remain fit to eat after having undergone a prolonged period of CA-storage? At ambient conditions, what are the sensory quality and consumer acceptability criteria with respect to the shelf-life of apples? They studied the behavior of ‘Fuji’ apples kept at 20 ◦ C in a normal atmosphere until consumption following 7 months’ refrigerated storage (1 ◦ C) in a CA (2% O2 , 2% CO2 ) and estimated the apples’ shelf-life. Consumer acceptability and descriptive sensory analyses for storage periods of up to 28 d at 20 ◦ C indicated that the greatest quality loss in stored ‘Fuji’ apples was associated with increased mealiness, and appearance of an over-ripe taste, and alcoholic taste and odor. Following that first study on 7 months CA-stored apples, the objective of the present work was to follow this up by studying the behavior of recently harvested ‘Fuji’ apples, without CA storage, and analyzing the variations in quality when kept at ambient temperature. Further tools for the study of apple quality are applied.
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2. Materials and methods 2.1. Plant material and storage conditions
Table 1 Sensory attributes and their associated descriptors used in the descriptive analysis of ‘Fuji’ apples Attribute
‘Fuji’ apples (M. domestica Borkh. cv. Fuji) were harvested at commercial maturity. Flesh firmness was determined on 10 fruit randomly taken from the orchard. Whole apple firmness (penetration force) was determined with a TA-XT2 Texture Analyzer (Stable Micro Systems Ltd., Surrey, U.K.) by measuring the force required for a 4-mm diameter probe to penetrate the flesh of a whole apple; fruit were considered “commercially mature” when the fruit had values of 50.5 ± 3.2 N. The fruit (350 apples) came from a Spanish orchard (Lleida, Spain) in October 2004. Immediately after harvest they were selected for uniformity and absence of defects, and placed in cold storage at 1 ◦ C. Sub-batches of 32 apples were subsequently transferred to storage at 20 ◦ C without atmosphere control, where they remained for 0, 9, 20, 30, 41, 51, 61, 70, 78 and 91 d to provide 10 samples with different storage times at the same time. They were sampled as follows: the apples to be stored for 91 d were placed in a 20 ◦ C room, followed 13 d later by the apples to be stored for 78 d, and so on, until the last day (day 91) when apples to be stored 0 d were placed in the 20 ◦ C room. This last day is the sensory assessment day. In this way, on the same day all the apples had been stored at 20 ◦ C for the planned times; this logically supposed that during the time that they were not at 20 ◦ C, they were previously at 1 ◦ C, a price to pay for the shelf-life sampling, and with the assumption that at this temperature the ripening rate was minimum. Prior to storage at 20 ◦ C the apples were sanitized with a 200 ppm chlorine solution for 10 min, rinsed and individually dried. 2.2. Sensory analysis Testing was carried out in a sensory laboratory equipped with individual booths (ISO 8589, 1988). The samples were peeled and cut into 1.5 cm sided cubes for evaluation. Cutting took place at the most 1 h before evaluation. Data acquisition was performed using Compusense® five release 4.6 software (Compusense Inc., Guelph, Ont., Canada). 2.2.1. Consumer testing Consumers were recruited among non-scientific workers and students from the Instituto de Agroquímica y Tecnología de Alimentos, Valencia, Spain. Fifty persons, 25–65 years old, approximately half female, half male, who consumed apples on a regular basis, participated in the study. They received one cube from each different storage time following a balanced complete block experimental design. For each sample they scored global acceptability using a 9-box scale labeled on the left with “dislike very much”, in the middle with “neither like nor dislike” and on the right with “like very much”. To estimate sensory shelf-life they also answered the question “Would you normally consume this product?” with a yes or a no (Hough et al., 2003; Varela et al., 2005). 2.2.2. Descriptive analysis A panel of 11 assessors previously trained in the description of ‘Fuji’ apples was used for the analysis. The selection of the terminology (Table 1) and the training procedure is described elsewhere (Varela et al., 2005). Formal assessment of the samples was carried out following a balanced complete block experimental design. For scoring, 10 cm unstructured scales labeled “nil” and “high” were used. Six cubes taken from different apples of each of the seven samples (0, 9, 20, 30, 41, 51, and 61 d at 20 ◦ C), were served at 10 ◦ C in closed, odor-
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Associated descriptor
Appearance
Roughness (of the surface)
Odor
Ripe Alcoholic Aged
Oral texture
Hardness Crunchiness Sound produced Mealiness Granularity Juiciness
Taste
Fresh Sweet Acid Ripe Alcoholic
Aftertaste
Astringent Alcoholic
less plastic containers identified with three digit random codes. All the samples of different storage times were evaluated on the same session. Water was used for rinsing between samples. 2.3. Physical and chemical determinations 2.3.1. Acidity and soluble solids Titrable acidity, expressed as malic acid, and soluble solids, were quantified by AOAC standard techniques, methods 942.15 and 932.12 (AOAC, 2000). The Thiault index was calculated as follows: index = [10 × acidity (g/L) + sugar content (g/L)] (Harker et al., 2002). Four apples of each sample (different storage times at 20 ◦ C) were processed homogenized and measured. 2.3.2. Protopectin/total pectin ratio The total pectin content and the water-soluble pectin fraction were determined by the m-hydroxydiphenyl method (Kintner and Van Buren, 1982; Varela et al., 2007a). Assuming protopectin as the non water-soluble fraction, the protopectin/total pectin ratio was calculated as: (total pectin − water-soluble pectin)/(total pectin). Four apples of each sample (different storage times at 20 ◦ C) were processed homogenized and measured. 2.3.3. Instrumental texture A TA-XTplus Texture Analiser (Stable Micro Systems, Godalming, UK) was used to evaluate the texture of the apple cubes. Immediately before measuring, the samples were peeled and cut into 1.5 cm-sided cubes with a sharp cutter, avoiding vascular tissue. All tests on the cubes were performed with the same orientation because of the fibrous non-isotropic properties of apple flesh (Khan and Vincent, 1993). Five cubes taken from different apples corresponding to each sample (different storage time at 20 ◦ C), were measured. Penetrometer tests were conducted with the Volodkevich tooth geometry (VB) penetrating 12 mm into the apple cube (Varela et al., 2007b). Test parameters were: test speed of 1 mm/s, a trigger force of 5 g, and force in compression mode. Force vs. time was plotted and the following parameters were extracted: the area under the complete penetration curve, the number of peaks and the gradient of the initial linear slope of the curve. 2.3.4. Rheological measurements Dynamic rheological behavior was characterized using a controlled stress rheometer (rheostress RS100) equipped with a
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Phoenix II P1 C2 5-P circulation bath (Haake, Karlsruhe, Germany), at 10 ◦ C, using plate and plate geometry, 35 mm in diameter, serrated plates to prevent slippage, with a 9.9 mm gap between plates, 1% compression and 5 min of equilibration time. The samples were measured in disks of whole tissue 35 mm in diameter and 10 mm in height. The detailed sampling and measuring procedure is explained in Varela et al. (2007b). All experiments were conducted on apple cylinders with the same orientation (top–bottom) because of the fibrous non-isotropic properties of apple flesh. The linear viscoelastic range (LVR) was determined through shear stress sweeps from 1 to 1000 Pa. A constant stress of 50 Pa was then chosen (common to the LVR of all samples) to obtain the mechanical spectra as frequency sweeps from 0.01 to 10 Hz. Tg␦ (G /G ) were calculated and the storage modulus (G ) was plotted to characterize the viscoelastic behavior. Four discs taken from different apples corresponding to each sample (different storage time at 20 ◦ C) were measured. 2.4. Statistical analyses Analyses of variance (ANOVA) were performed on the physical and chemical data and the acceptability scores using storage time as the variation factor and on the trained sensory panel data using storage time, assessor and their interaction as variation factors. In order to study the differences among samples, least significant differences were calculated by Tukey’s test. These analyses were performed with the use of the SPSS 12 package (SPSS Inc., Chicago). Survival analysis methodology (SAM) was used to estimate the shelf-life of ‘Fuji’ apples using the results obtained from consumers when asked if they would normally consume the samples with different storage times (Hough et al., 2003; Varela et al., 2005). 3. Results and discussion 3.1. Sensory characteristics 3.1.1. Consumer test and shelf-life considerations Recently harvested ‘Fuji’ apples were kept at 20 ◦ C in a normal atmosphere for 91 d until consumption; from day 70 of the storage, the apples showed external skin damage as a result of the noncontrolled atmosphere storage. Excess or too low relative humidity can have a detrimental effect on fruit during storage; if the humidity is too low it causes dehydration of the tissues leading to shriveling. Shriveling in apples is an obvious signal of an unfresh product (Lund et al., 2006), and most probably would be rejected before consumption. It was then decided to perform the sensory analysis on samples with storage periods up to 61 d. In previous work, Varela et al. (2005) estimated the shelf-life of ‘Fuji’ apples kept at 20 ◦ C in a normal atmosphere until consumption; these apples had been stored for 7 months under CA refrigeration. Survival analysis methodology was successfully used
Table 2 Mean values for consumer acceptability (9-point box scale) and percentage of rejection over the storage of ‘Fuji’ apples at 20 ◦ C Sample
Consumer acceptability a
0D 9D 20 D 30 D 41 D 51 D 61 D
Consumer percentage of rejection 27a 23a 28.5a 26.6a 29a 22a 30a
6.6 6.8a 5.9a 5.7a 6.2a 6.0a 5.9a
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
for the estimation by using the results obtained from consumers when asked if they would normally consume the samples with different storage times. This method’s key concept is to focus the shelf-life hazard on the consumer rejecting the product rather than on the product deteriorating (Hough et al., 2003), as is particularly suited to products where shelf-life is determined for sensory reasons rather according to microbiological or chemical deterioration. In the work mentioned above (Varela et al., 2005), the estimated shelf-life of ‘Fuji’ apples was of 23 d at a 50% rejection probability. Consumer acceptability and descriptive sensory analyses indicated that the greatest quality loss was associated with increased mealiness, ripe taste and alcoholic taste and odor; at the same time, the acceptability dropped from a score of 6 at day 0 of storage to 4.2 at day 28. In the present study, the percentage of consumers rejecting the apples did not increase with storage time (Table 2), not surpassing 30% even at 61 d storage. As a result, the survival analysis procedure could not be applied to the acceptance/rejection data in this case. Furthermore, the overall acceptability evaluated by the consumers did not present significant differences between the different times of storage in all the storage period (Table 2). Therefore, sensory rejection of the edible part of the apple because of the eating quality loss would not be the reason of the end of shelf-life in this case. Instead, physiological deterioration leading to the rejection of the entire fruit before consumption would be the determinant of shelflife. 3.1.2. Descriptive analysis The descriptors roughness, ripe odor, granularity, juiciness, sweetness, alcoholic taste and astringent and alcoholic aftertaste, did not present significant differences between days 0 and 61 of storage (Tukey’s test). The descriptors’ values that did show significant differences over the storage time are shown in Table 3. The texture parameters hardness, crunchiness and sound, had higher values for the fresher samples, fell at the start of storage and then remained constant throughout the period. The ripe taste values also showed a change on the first days of storage and then remained constant. The rest of the descriptors’ values only showed significant changes on the last days of storage.
Table 3 Mean values for the sensory descriptive analysis parameters (trained panel, 10-cm unstructured scales) that showed significant differences during storage of ‘Fuji’ apples at 20 ◦ C Sample
Alcoholic odor
Aged odor
Hardness
Crunchiness
Sound
Mealiness
Fresh taste
Acidity
Ripe taste
0D 9D 20 D 30 D 41 D 51 D 61 D
1.4a 3.2a 2.1a 2.5a 2.0a 5.0b 4.8b
1.8a 2.1a 3.1a,b 3.2a,b 2.8a,b 4.2a,b 5.3b
6.2b 5.4a 4.7a 3.5a 4.0a 4.5a 5.4a
6.1b 4.0b 4.6a 3.8a 4.9a 4.3a 4.3a
6.0b 4.2a 4.2a 3.4a 4.8a 4.5a 4.2a
1.7a 1.7a 3.8a,b 2.5a,b 3.8a,b 4.9b 4.3b
6.0c 3.6a,b,c 5.7b,c 4.2a,b,c 5.0a,b,c 2.8a 2.8a
4.7b 3.0a,b 4.2a,b 4.0a,b 2.0a 1.9a 2.3a
1.7a 3.8a,b 5.1b 4.1b 5.2b 6.1b 4.7b
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
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Table 4 Mean values (four determinations) of the chemical parameters (protopectin/total pectin, acidity and soluble solids) during storage of ‘Fuji’ apples (0–91 d at 20 ◦ C) Sample
Protopectin/ total pectin
Acidity (% of malic acid)
Soluble solids (g/L)
0D 9D 20 D 30 D 41 D 51 D 61 D 70 D 78 D 91 D
0.46b 0.43b 0.53b 0.60b 0.51b 0.40b 0.44b 0.23a 0.26a 0.21a
0.24d 0.25d 0.19c 0.20c 0.13b 0.15b 0.20c 0.09a 0.10a 0.10a
170a 182a 165a 165a 168a 175a 169a 169a 169a 170a
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
However, it is worth pointing out, that the variation of the measured sensory characteristics during storage was lower than that obtained in our previous work on refrigerated, CA-stored apples (Varela et al., 2005). Apples in both studies were from the same variety, from the same orchard, and were harvested at the same stage, but from two different harvests. Some of the differences between both studies could then be attributed to that fact. However, it is likely that most of the differences found in the changes that took place in the apples over the 20 ◦ C storage were due to the postharvest cold-storage conditions used in the previous work. Furthermore, weather conditions in Lleida were quite stable and were particularly similar during both harvests, and because of being an experimental orchard, conditions were closely controlled. With regard to the sensory data obtained, both with consumers and the trained panel, the stored apples did not vary in acceptability during 61 d at room temperature and only some of the sensory attributes assessed varied significantly with time of storage. That is quite a long storage time without any particular means of conservation. Consequently, not all harvested ‘Fuji’ apples would have to be refrigerated/CA-stored to be available for consumption in the following couple of months. It would be interesting to study the possibility of storing the harvested fruit differently into batches depending on the expected date of retail and consumption, not just divide into “fresh consumption” and “cold storage”, having in mind that cold storage could accelerate quality damage. It seems that ambient storage with humidity control might be more advantageous than CA storage if the expected retail date is, for example, 1 or 2 months after harvest. 3.2. Physical and chemical characteristics 3.2.1. Pectins, acidity and soluble solids Table 4 shows the mean values of the measured chemical parameters. Acidity values significantly dropped with storage time, but soluble solid contents did not vary. Because the soluble solids carry more weight in the Thiault index calculation, this did not present significant differences throughout the storage period (91 d), having an average value of 174. This suggested that chemical deterioration of the sugars, because of ripening, took place on the first stages. Growers use this index as an indicator of optimum ripeness for harvesting and consumption; values over 170 are considered acceptable for some apple varieties (Porro et al., 2002). The results were then in agreement with those obtained in the acceptability test by consumers. Until 61 d storage, apples were “equally” accepted. In our previous work (Varela et al., 2005), significant falls in the Thiault index were observed over the storage period at 20 ◦ C, dropping to 141 in the sample stored for 28 d (with a previous period at 1 ◦ C/CA-storage during 210 d) with a concomitant
Fig. 1. Penetration plots obtained with a Volodkevich jig: force (N) vs. distance (mm) of apples stored at 20 ◦ C for 0, 9, 41, 61 and 91 d.
drop in acceptability, a much lower value than those obtained in the present work up to 91 d. The protopectin/total pectin ratio significantly decreased from day 70 of storage. The value of the ratio obtained between days 0 and 61 was consistent with the one measured for fresh ‘Fuji’ apples in previous work (Varela et al., 2007a). 3.2.2. Instrumental texture A Volodkevich jig simulates the action of an incisor tooth biting through the sample, where the probe penetrates into the apple cube and the force necessary to achieve a certain penetration depth is measured, both compressive and shear forces being involved. As discussed in our previous work on apple textural characteristics (Varela et al., 2005, 2007a), apart from extracting numerical values, it is interesting to observe the differences in the complete profiles of instrumental texture curves. Fig. 1 shows the changes in the penetration profiles over storage at 20 ◦ C. A highly jagged penetration curve with many peaks due to numerous fracture events is often produced by products that are perceived as crispy or crunchy (Vincent, 1998; Varela et al., 2006a). That was the case for the samples in the first days of storage, and as the time of storage increased, the curves became smoother, although many fracture peaks were present, even until day 61. On day 91 very few fracture events could be observed. The area under the curve decreased with storage time. This parameter can be associated with the work of penetration and can be related to apple stiffness, hardness or rigidity. Table 5 shows the numerical values of the parameters extracted from the curves and their statistical differences. The gradient of the first linear part of the curve where compression takes place (and before penetration begins) and related to the elasticity of the sample, presented a similar change, where the sample became more elastic and less Table 5 Mean values (five determinations) of the textural parameters (area, gradient, number of force peaks) during storage of ‘Fuji’ apples (0–91 d at 20 ◦ C) Sample
Area (N/s)
Gradient (N s)
Number of force peaks
0D 9D 20 D 30 D 41 D 51 D 61 D 70 D 78 D 91 D
150c 146b,c 140b,c 112a,b,c 102a,b,c 142b,c 118b,c 106a,b,c 101a,b,c 68a
8.8d 8.4d 5.3c 5.7c 4.3b,c 2.7a,b 2.7a,b 2.7a,b 1.0a 0.6a
56d 44c,d 34b,c 33b,c 32b,c 31b,c 31b,c 29b 23a,b 13a
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
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Fig. 2. Determination of the linear dynamic viscoelastic range in a 41-d stored sample at 20 ◦ C. Stress sweep at 1 Hz: G and G (Pa) vs. shear stress (Pa).
rigid with storage time. The three parameters presented significant differences and reflected the quality loss at the end of storage, the textural parameters being quite stable until more than 70 d. 3.2.3. Rheological measurements Dynamic mechanical analysis is an effective method because it applies very small strains on the samples over a very short time. The properties of solid foods can then be studied with minimal physical changes, and study of the rheological properties of materials at different frequencies can be undertaken, providing valuable information for discrimination between samples. However, it is a technique rarely used for the study of fresh fruit. Varela et al. (2006b, 2007b) successfully applied this tool for the characterization of apple varieties and for the study of small changes in apple texture through storage. LVR was determined for all samples by dynamic stress sweeps; Fig. 2 shows an example for one of the samples. LVR was found to be between 10 and 500 Pa for most samples. To ensure the subsequent frequency sweeps were performed within the LVR, a constant stress of 50 Pa was chosen. Frequency sweeps showed that all samples behaved as viscoelastic materials, having clearly dominant solid characteristics with G values much higher than G . The replicates of each curve were run with good reproducibility since the differences between them were less than 5%. Tg␦ represents the ratio between the energy lost and stored per cycle, and thus, a relation between the viscous and elastic portions of the sample. No significant differences were found in the values of Tg␦ throughout storage (Table 6), showing no changes in the contribution of the two moduli in the viscoelastic behavior of the samples. G was then plotted to evaluate the mechanical characteristics in each day of storage. When subjected to oscillatory strain, all samples showed a slight linear decrease in G as frequency diminished. Fig. 3 shows the frequency dependence (mechanical spectrum) of the samples with storage. G decreases as the time of storage at 20 ◦ C increases, indicating some Table 6 Mean values (four determinations) of the rheological parameters (G (Pa) and Tg␦) at 1 Hz, during storage of ‘Fuji’ apples (0–91 d at 20 ◦ C) Sample 0D 9D 20 D 30 D 41 D 51 D 61 D 91 D
G (at 1 Hz) (Pa) d
1,430,000 465,500c 344,500c 342,000c 204,500b,c 189,210b,c 123,900b 68,460a
Tg␦(at 1 Hz) 0.10a 0.10a 0.11a 0.12a 0.13a 0.12a 0.12a 0.11a
Different letters indicate that there is significant difference at p ≤ 0.05 (Tukey’s test).
Fig. 3. Frequency dependence (Hz) of the storage modulus, G (Pa), of apples with different times of storage (0, 9, 20, 41, 61 and 91 d) at 20 ◦ C.
loss in the structural integrity of the apple flesh. An important drop can be observed from the fresh sample (day 0) to day 9. The mechanical characteristics then became stable and started to decrease again from day 61. In order to quantify this variation, G at 1 Hz was compared (Table 6). A statistically significant decrease in G was confirmed. G is related to the rigidity of the tissues, the first drop observed (fresh to 9 days) agreed with the differences found by the trained panel in the attributes hardness, crunchiness, and sound, and also with the number of force peaks of the texture plot. Presumably, this first drop was not detected by the consumers, or else, they noticed a different texture but liked it all the same. The second drop in G , from day 61 of storage is attributed to the consequences of shriveling and long-term storage deterioration with softening occurring due to loss in structure. This second decrease in G is in agreement with the textural measurements. A drop in the work of penetration and a considerable loss in crispness shown by the less numbers of peaks, was also reflected in the profile of the texture curves. The values of G (1 Hz) obtained for fresh ‘Fuji’ apples are consistent with those obtained in previous work for ‘Fuji’ apples at commercial maturity (Varela et al., 2006b). In that work, where the application of dynamic rheological techniques for the characterization of apple tissue was presented, G (1 Hz) values for ‘Fuji’ apples with 14 d storage at 20 ◦ C of the same order of those found in the present work until 61 d were obtained. That also confirms the good quality levels maintained by the recently harvested ‘Fuji’ apples in the present study, at least until 61 d storage at ambient conditions. 4. Conclusions In the present work, we have shown that the changes that ‘Fuji’ apples undergo at ambient conditions, as in the home or with small retailers, are totally different whether they were previously cold/CA-stored for some months or had been recently harvested. No matter what the eating quality parameters, soluble solids, acidity, pectins, firmness, were at the time of harvest or out of storage, those parameters were not representative of the subsequent changes under ambient conditions. The previous history of the apples and the eating quality parameters as well as consumer appreciation all throughout shelf-life must be studied to obtain a complete picture. However, to construct a robust recommendation with “industry-wide” validity, extended research should be done. Acknowledgements The authors are indebted to the Comisión Interministerial de Ciencia y Tecnología for financial support (Project AGL 2006-11653-
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