Physicochemical Properties, Image Textures, and Relationships between Parameters of Red-Fleshed Apples Collected on Different Harvest Dates

Round 1

Reviewer 1 Report

2.2.4. Internal ethylene concentration

Usually, we put the fruit inside a glass tight chamber and take gas sample from the upper part using a gas syringe. Ethylene is a gas phytohormone therefore we need to measure the amount of ethylene in the chamber which will represent the climacteric ethylene production by the fruit. The unit reported is ppm which corresponds to the number of gaseous ethylene molecules per million gaseous molecules. Please perform the experiment again.

 

For color analysis, it would be great to calculate the color difference as follows:

 

 

 

Generally, Total phenolic content (TPC) is measured by the Folin-Ciocalteu's method following a previously described procedure (Swain and Hillis, 1959). How did you measure it using HPLC? Isn’t HPLC used for targeted quantification?

 

How did different harvest dates affect the sensory characteristics of the apples? And how was this effect different among the cultivars? Authors are encouraged to touch the molecular mechanisms in the “Discussion” as well.

 

 

 

 

 

Moderate editing of English language required. 

Author Response

Reviewer 1

- 2.2.4. Internal ethylene concentration

Usually, we put the fruit inside a glass tight chamber and take gas sample from the upper part using a gas syringe. Ethylene is a gas phytohormone therefore we need to measure the amount of ethylene in the chamber which will represent the climacteric ethylene production by the fruit. The unit reported is ppm which corresponds to the number of gaseous ethylene molecules per million gaseous molecules. Please perform the experiment again.

Response: There are at least two methods to determine the climacteric rise of ethylene. One is the measurement of internal ethylene concentration in the apple core (which was used in our research), another is the measurement of ethylene production rate (method described by Reviewer). Both methods are used for the research and commercial (limited by availability of equipment) purposes. The methods were described among others Authors by Łysiak, 2014 (rate of production) and Jung S-K and Watkins C., 2014 (internal ethylene production). The internal ethylene concentration is expressed as ppm or µl/L. The rate of ethylene production is expressed as µl*L*^-1*kg^-1*hr^-1 or ppm*kg^-1*hr^-1.

 

Łysiak, G. Measurement of ethylene production as a method for determining the optimum harvest date of ‘Jonagored’ apples. Folia Hort 2014, 26/2, 117-124.

Jung, S-K., Watkins, C. Internal ethylene concentrations in apple fruit at harvest affect persistence of inhibition of ethylene production after1-methylcyclopropene treatment.

Postharvest Biology and Technology. 2014. 96: 1-6

 

 

- For color analysis, it would be great to calculate the color difference as follows:

Response: It has been added. Subsection 2.6. Statistical Analysis has been supplemented with the following sentence and equation:

“The Color Difference (ΔE) was computed using the following equation (1):

                          (1)

 

The Color Difference was determined for color parameters of skin and flesh of apples. The results are presented in Tables 2 and 3.

 

 

- Generally, Total phenolic content (TPC) is measured by the Folin-Ciocalteu's method following a previously described procedure (Swain and Hillis, 1959). How did you measure it using HPLC? Isn’t HPLC used for targeted quantification?

Response: In the experiment, we determined the content of phenolic compounds divided into individual classes (which was included in the publication). After summing up all groups of phenolic compounds, we obtain the total phenol content. The Hplc method is more sensitive than the spectrophotometric method (Folin-Ciocalteu's method) and allows for a more accurate determination of these compounds.

 

 

- How did different harvest dates affect the sensory characteristics of the apples? And how was this effect different among the cultivars? Authors are encouraged to touch the molecular mechanisms in the “Discussion” as well.

Response: The red-fleshed apple cultivars used in the experiment were treated as cooking apples, not eating (dessert) apples. They were not suitable for eating raw mainly due to their sour taste. Therefore, sensory analysis for raw apples was not performed.

The information about molecular aspects is included in the manuscript, as follows:

“During red-fleshed apple maturation, there is a strong relationship between the overexpression of the MdMYB10 gene and the expression of anthocyanin levels, which induce the red color of apple flesh [10].”

“The regulation of anthocyanin biosynthesis is dependent on the transcription factor MdMYB10. Whereas genotypes belonging to type 2 are less intensely colored. The red coloration occurs late in fruit development, and shoots and leaves are not red. The regulation of anthocyanin biosynthesis is related to the transcription factor MdMYB110a [16]. Anthocyanins are color-presenting substances. They have highly hydrophilic properties. Thus, these substances have a protective role in pathophysiological conditions [17].”

 “In the research of Lemmens et al. [41], it was found that the content of L-ascorbic acid in the apple peel and flesh does not depend on the harvest date but is closely related to the variety and genetic basis. According to Mahmood, et al. [51], the level of acids in apples depends on the balance between the biosynthesis of organic acids, their degradation and their vacuolar storage.”

 

Moderate editing of English language required. 

Response: English language has been checked and corrected.

 

Reviewer 2 Report

This paper contains a great number of data for apples, but the major limitation is that it lack deep analysis and comparison with other literature. It seems more like a testing report. There are many statistical results in R&D, but data mining is relatively not adequate. I suggest the authors to conduct more research on modeling and prediction, such as harvest date based on apple properties, or discrimination.

 

Specific comments:

1.      Page 2, lines 76-79. Can you provide references for "The relationships between physicochemical properties and spectral data or image parameters allowing for the prediction of the apple quality in a robust, objective, and non-destructive manner were revealed" ?

2.      Page 2, lines 79-80. Can you provide references for” Red fleshed apple cultivars may vary in color intensity which may be related to the content of anthocyanins.”

3.      Page 3, lines 109-110. Can you specify at what stage of its growth the apple collected on August 31, 2021 and September 6, 2021, respectively?

4.      Page 4, lines 121-122. Can you add the third row of slices in the picture to the legend?

5.      Page 4, lines 132-133. Can you use image processing to objectively calculate the blush area?

6.      Page 7, lines 258-259. There is a difference in the size of the apples between the two collections, and there is no scientific basis for comparing the weights to conclude that "delayed harvesting resulted in an increase in fruit weight".

7.      Page 7, lines 263-265. The growth cycle, internal ethylene concentration and starch at maturity of apples of different varieties are inherently different and not comparable, and "The fruits of ‘Roxana’ cultivars were more advanced in maturity (even on the first harvest date) compared to other cultivars." This conclusion lacks reasonableness.

8.      Page 12, lines 459-466. Can you briefly describe the correlation results of the linear relationship between the fleshiness parameter b* and the image features and color parameters?

9.      Page 14, lines 512-516. In the previous section, you talked about the hardness of post-harvest apples, but here the conclusion that "Apples harvested too early can be more prone to bruise damage" is presented, can you explain this in detail?

10.  It would be better to merge the third-level tile in section 2.2, because there are only 1-2 sentences in each of them.

11.  The axes in figures 2-4 are not readable. Giving the full name of abbreviation in the figure captions would be better.

Author Response

Reviewer 2

This paper contains a great number of data for apples, but the major limitation is that it lack deep analysis and comparison with other literature. It seems more like a testing report. There are many statistical results in R&D, but data mining is relatively not adequate. I suggest the authors to conduct more research on modeling and prediction, such as harvest date based on apple properties, or discrimination.

Response: Data mining has been improved. The discrimination analysis has been performed and results have been added, as follows:

“2.7. Discrimination of red-fleshed apples in terms of harvest date

The red-fleshed apples belonging to individual cultivars were discriminated in terms of harvest date based on selected texture parameters of the flesh images using WEKA machine learning software (Machine Learning Group, University of Waikato) [27-29]. The textures from images in color channels L, a, b, R, G, B, X, Y, Z, U, V, and S with the highest discriminative power were selected using the Best First algorithm. The discrimination was performed with the use of a 10-fold cross-validation and Multilayer Perceptron algorithm from the group of Functions. The correctly and incorrectly classified instances, average accuracies, and the values of True Positive Rate (TPR), False Positive Rate (FPR), Precision, Recall, F-Measure, Matthews Correlation Coefficient (MCC), Receiver Operating Characteristic Area (ROC Area), and Precision-Recall Area (PRC Area) were determined [30-33].”

 

“3.6. Discrimination of red-fleshed apples in terms of harvest date based on selected texture parameters of the flesh images

The red-fleshed apples were correctly discriminated in terms of harvest date based on selected texture parameters of the flesh images in the case of each cultivar (Table 7). Apples ‘Alex Red’ harvested on the I and II dates were distinguished from each other in 95.5%. The average accuracy of the discrimination of red-fleshed apples ‘Trinity’ collected on both dates was equal to 93.0%. Whereas apples belonging to ‘Roxana’ sampled on two dates were characterized by the lowest average discrimination accuracy of 90%. The values of TPR, Precision, Recall, F-Measure, and MCC were the highest and the values of FPR were the lowest for apples ‘Alex Red’.

 

Table 7. The discrimination of red-fleshed apples in terms of harvest date based on selected texture parameters of the flesh images using Multilayer Perceptron

Predicted class (%)		Sample	Average accuracy (%)	TPR	FPR	Precision	Recall	F-Measure	MCC	ROC Area	PRC Area
‘Alex Red’ - I harvest date	Alex Red’ - II harvest date
97	3	‘Alex Red’ - I harvest date	95.5	0.970	0.060	0.942	0.970	0.956	0.910	0.946	0.852
6	94	‘Alex Red’ - II harvest date		0.940	0.030	0.969	0.940	0.954	0.910	0.946	0.970
‘Trinity’ - I harvest date	‘Trinity’ - II harvest date
93	7	‘Trinity’ - I harvest date	93.0	0.930	0.070	0.930	0.930	0.930	0.860	0.981	0.981
7	93	‘Trinity’ - II harvest date		0.930	0.070	0.930	0.930	0.930	0.860	0.981	0.981
‘Roxana’ - I harvest date	‘Roxana’ - II harvest date
88	12	‘Roxana’ - I harvest date	90.0	0.880	0.080	0.917	0.880	0.898	0.801	0.966	0.974
8	92	‘Roxana’ - II harvest date		0.920	0.120	0.885	0.920	0.902	0.801	0.966	0.946

TPR - True Positive Rate, FPR - False Positive Rate, MCC - Matthews Correlation Coefficient, ROC Area - Receiver Operating Characteristic Area, PRC Area - Precision-Recall Area”

 

 

Specific comments:

1. Page 2, lines 76-79. Can you provide references for "The relationships between physicochemical properties and spectral data or image parameters allowing for the prediction of the apple quality in a robust, objective, and non-destructive manner were revealed" ?

Response: It has been provided as “[18, 20, 21]”.

 

2. Page 2, lines 79-80. Can you provide references for” Red fleshed apple cultivars may vary in color intensity which may be related to the content of anthocyanins.”

Response: It has been provided as “[18]”.

 

3. Page 3, lines 109-110. Can you specify at what stage of its growth the apple collected on August 31, 2021 and September 6, 2021, respectively?

Response: The characteristics of examined red-fleshed apples in terms of fruit size, percentage of blush, maturity, and fruit firmness at two harvest dates are given in Chapter 3.1.

 

 

4. Page 4, lines 121-122. Can you add the third row of slices in the picture to the legend?

Response:  It has been corrected as follows:

“Figure 1. The images of whole fruit, half of an apple and a slice of red-fleshed apples ‘Alex Red’, ‘Trinity’, and ‘Roxana’ harvested on the I (August 31) and II (September 06) dates.”

 

5. Page 4, lines 132-133. Can you use image processing to objectively calculate the blush area?

Response: Within the experiment, the subjective method for assessing the percentage of blush area was chosen. It is a simple, fast, and robust method with reasonable accuracy. So far, we do not have a system for using image processing to objectively calculate the blush area of examined apple cultivars. A lack of software to calculate the blush area for examined apple cultivars is the main problem. The recognition of the color and raw calculation of its area does not guarantee the real estimation of the blush area. The raw calculation of the area of colored skin in the case of different apple cultivars (type blush – solid, stripe, etc.) could give completely different results.

 

6. Page 7, lines 258-259. There is a difference in the size of the apples between the two collections, and there is no scientific basis for comparing the weights to conclude that "delayed harvesting resulted in an increase in fruit weight".

Response: Apple fruits are enlarging to the end of the growing season (until harvest). There are several theories concerning the rate of growth, and factors affecting the rate of enlarging the size and weight of the individual fruits. More often, Authors suggest that the apple growth curve has a simple sigmoid pattern with an exponential initial phase, then linear growth, and finally logarithmic part. Some Authors suggest some modification of this pattern. Although, all of them agree that the fruit size and weight are increasing until harvest.

 

Lakso, A. N., Corelli Grappadelli L., Barnard, J., Goffinet M. C. An expolinear model of the growth pattern of the apple fruit, Journal of Horticultural Science, 1995, 70:3, 389-394, DOI: 10.1080/14620316.1995.11515308

Zadravec, P., Veberic, R., Stampar, F., Schmitzer V., Eler, K. Fruit Growth Patterns of Four Apple Cultivars Using Nonlinear Growth Models. Europ.J.Hort.Sci., 2014, 79 (2), 52–59.

Tijero, V., Girardi, F., Botton, A. Fruit Development and Primary Metabolism in Apple. Agronomy 2021, 11, 1160. https:// doi.org/10.3390/agronomy11061160.

 

 

7. Page 7, lines 263-265. The growth cycle, internal ethylene concentration and starch at maturity of apples of different varieties are inherently different and not comparable, and "The fruits of ‘Roxana’ cultivars were more advanced in maturity (even on the first harvest date) compared to other cultivars." This conclusion lacks reasonableness.

Response: Taking into account internal ethylene concentration (IEC) and starch index as indicators of maturity stage ‘Roxana’ apples were less mature compared to ‘Alex Red’ and ‘Trinity’. The fruits of ‘Trinity’ cultivar were more advanced in maturity (even on the first harvest date) compared to other cultivars. The IEC indicates that both harvest dates for 'Alex Red' and 'Trinity' were provided when the climacteric increase in ethylene production had already begun. In the case of 'Alex Red' it was single ppm, and in the case of 'Trinity' the IEC was already several ppm. In the case of the 'Roxana' variety, the harvest was provided in the initial phase of climatic growth. During the first harvest date, the IEC was approximately 0.1 ppm, which is often taken as the beginning of the climacteric stage [Blanpied 1989]. For ‘Roxana’ apples the delay in harvest resulted in a significant increase in IEC, so it indicated the beginning of climacteric phase. The measuring of IEC or rate of ethylene production is a good method for determining the harvest date for apples [26, Jung and Watkins, 2014]. However, relationships between ethylene production or internal ethylene concentration and optimum harvest dates are not always strong. Several factors, such as a growing region, orchard location, cultivar mutants, conditions during the growing season, and nutrition may be significantly affected even within a cultivar (Watkins 2003). With the delay of harvest, for all examined cultivars, the firmness of the flesh decreased.

 

Blanpied, G.D. Measurements of internal ethylene concentration and studies of its efficacy as a predictor of Empire apple storage life. Acta Horticultrae, 1989, 258, 429-436.

Watkins, C.B. Principles and practices of postharvest handling and stress. In D. Feree and I.J. Warrington, eds., Apples: Crop Physiology, Production and Uses, 2003, 585-614. CAB Intl., Wallingford, U.K.

 

 

8. Page 12, lines 459-466. Can you briefly describe the correlation results of the linear relationship between the fleshiness parameter b* and the image features and color parameters?

Response: It has been supplemented using the following statements:

“Whereas the strongest correlation of the parameter b* (-0.909) was found with the texture RHSkewness. For the parameter L*, the highest correlation with image textures was positive, and for the parameters a* and b* - negative”.

Additionally, a scatter plot for color parameter b* are shown in Figure 2c.

 

9. Page 14, lines 512-516. In the previous section, you talked about the hardness of post-harvest apples, but here the conclusion that "Apples harvested too early can be more prone to bruise damage" is presented, can you explain this in detail?

Response: Generally, apples harvested too early or too late are easily damaged and are susceptible to fungal diseases and physiological disorders. Over-mature fruits lose their flesh structure (softening) which causes their vulnerability to mechanical damage [Walkowiak-Tomczak et al. 2021]. The susceptibility of apples on bruising depend on cultivars, storage conditions and postharvest treatment. The shape of the apple fruits is also important factor, because fruit of regular shape are less susceptibly on bruising [Lipa et al, 2019]

 

Lipa, T., Szot, I., Dobrzański Jr, B., Kapłan M. The assesment of ten apple cultivars and their susceptibility on bruising after storage and shelf-life of fruit treated with 1-MCP. Acta Sci. Pol. Hortorum Cultus, 2019, 18(6), 129-140.

Walkowiak-Tomczak, D.; Idaszewska, N.; Łysiak, G.P.; Bieńczak, K. The Effect of Mechanical Vibration during Transport under Model Conditions on the Shelf-Life, Quality and Physico-Chemical Parameters of Four Apple Cultivars. Agronomy 2021, 11, 81.

 

10. It would be better to merge the third-level tile in section 2.2, because there are only 1-2 sentences in each of them.

Response:  It has been corrected.

 

11. The axes in figures 2-4 are not readable. Giving the full name of abbreviation in the figure captions would be better.

Response: The abbreviations have been explained in the figure captions.

 

Reviewer 3 Report

These studies are undoubtedly relevant. The authors studied the effect of the harvest date on the weight of fruits, starch index, ethylene concentration, chemical composition of apple varieties with red pulp. The authors determined the correlation between the physicochemical properties and texture parameters of images of apples with red pulp.

However, there are a few minor comments. Specify the maturation dates of the experimental varieties. Explain whether the average weight of the fetus or the maximum was determined.

Author Response

These studies are undoubtedly relevant. The authors studied the effect of the harvest date on the weight of fruits, starch index, ethylene concentration, chemical composition of apple varieties with red pulp. The authors determined the correlation between the physicochemical properties and texture parameters of images of apples with red pulp.

However, there are a few minor comments. Specify the maturation dates of the experimental varieties. Explain whether the average weight of the fetus or the maximum was determined.

Response: It has been corrected, as follows:

"The apples belonging to three red-fleshed cultivars of ‘Alex Red’, ‘Trinity’, and ‘Roxana’ were harvested on two dates, August 31, 2021, and September 06, 2021."

"2.2. Maturity and quality of apples at harvest

To assess the fruit weight, apples were weighed individually on a laboratory balance (Radwag, Radom, Poland). Fruit weight was expressed in grams (g), and in Table 1 the mean values are given.

Table 1. The influence of harvest date on fruit weight, percentage of blush, internal ethylene concentration, starch index and fruit firmness (mean value of 30 fruits)."

Round 2

Reviewer 1 Report

Revision is accepted. 

Author Response

We are grateful for this comment

Reviewer 2 Report

Thanks for the authors considering my comments or suggestions. The article has been improved. However, it still lacks the comparison between the results of this paper and other published literature. It is important to show the novelty or significance of this study by comparing with other results.

Author Response

The Discussion section has been added, which indicates the novelty of own research against the background of available literature and compares the obtained results with literature data, as follows: "

4. Discussion

The novelty of the performed study is related to the determination of the impact of the harvest date on the physicochemical properties including fruit weight, percentage of blush, starch index, internal ethylene concentration, fruit firmness, color parameters L*, a*, and b* of the skin and flesh, dry mass, chemical properties (the content of sugars, sorbitol, acids, total pectins, and phenolic compounds), and image texture parameters of red-fleshed apples. This is the first report on the comparison of so many physicochemical properties and image features of red-fleshed apples collected on different dates. An innovative approach also concerns determining correlations between selected physicochemical properties and flesh image textures of red-fleshed apples harvested on two dates.

In our research, the delay in the harvest date caused the increase in fruit weight. This confirms the theory that fruits increase in diameter and weight until harvest [34-36]. During the first harvest date, the IEC was approximately 0.1 ppm, which is often taken as the beginning of the climacteric stage [37]. The measuring of IEC or rate of ethylene production is a good method for determining the harvest date for apples [22,38]. Several factors, such as a growing region, orchard location, cultivar mutants, conditions during the growing season, and nutrition may be significantly affected even within a cultivar [39].

It was found that the color of apple samples differed statistically significantly depending on the harvest date. Wang et al. [40] reported that also red-fleshed apple cultivars can be differed in skin and flesh color. Color is an important characteristic considered in breeding programs [41]. Furthermore, color is a widely used ripening index [14,42-43]. For determining the apple quality, color is an important maturity index [15]. Pigments that are responsible for color are synthesized during fruit ripening [44]. In our study, decreasing the values of parameter L* along with delaying the harvest date revealed that the apples became darker. Higher positive values of color parameter a* indicated that the apples harvested on the later date were redder. Whereas higher positive b* values showed that the color was also more yellow. Wani et al. [15] confirmed an increase in redness (a*) observed with harvest delay. Due to consumer acceptance, red color can be preferred and apples with higher redness can be more appealing. Additionally, the red color may indicate anthocyanin accumulation [11]. It may have health benefits.

The involving image parameters allowed for an objective assessment of the impact of harvest date on the quality of red-fleshed apples. The application of image analysis resulted in a reduction in the labor intensity, time, and costs of analysis [45]. Determining the impact of harvest date on fruit quality based on image textures may be beneficial. Image textures are a function of the spatial variation of the intensity of pixel brightness. Texture parameters provide information about the structure and quantitative analyses of these features give insights into product quality [23-25]. Therefore, image features can be very useful for non-destructive sample evaluation alongside destructive chemical analyses or can be used to estimate the physicochemical properties of samples without the need for more expensive, time-consuming, and labor-intensive measurements.

Only for one cultivar, a statistically significant impact of the harvest delay on the dry matter content was determined. The content of dry matter in apples depends not only on the variety but also on the degree of maturity, climatic and agrotechnical conditions, as well as on the position of the fruit in the crown of the tree. Vieria et al. [46] found that the dry matter content of 'Fuji' apples is not an indicator to estimate fruit maturity stage and, therefore, does not complement information obtained by fruit maturity indicators such as flesh firmness, traditionally used by apple growers to determine the harvest date. In our study, also the impact of the harvest date on the selected sugars and acids was confirmed. The taste and aroma of apples are determined by the level of acids and sugars in them, which affect the overall organoleptic quality and stability of the fruit [47]. The quantitative and qualitative composition of sugars and acids was determined in the performed research. Bhat et al. [48] and Wani et al. [15] also found an increase in total sugars, which can be attributed to the hydrolysis of polysaccharides to monosaccharides and an increase in juice content by moisture loss due to transpiration. In the flesh of many fruits, such as grapes, cherries, and some soft fruits, the malate and citrate (mg∙g^-1 f.m.) content increases at the beginning of ripening and then decreases because stored organic acids can be metabolized [44,49-50]. In the research of Lemmens et al. [41], it was found that the content of L-ascorbic acid in the apple peel and flesh does not depend on the harvest date but is closely related to the variety and genetic basis. According to Mahmood, et al. [51], the level of acids in apples depends on the balance between the biosynthesis of organic acids, their degradation and their vacuolar storage.

In our study, 'Trinity' and 'Roxana' apple cultivars, for which an increase in pectin content was observed, may not have reached the appropriate degree of maturity yet. In the study of Wani et al. [15], a decrease in the content of pectin substances in apples was also noted along with the delay in the harvest date, which can be attributed to the loss of fruit firmness. It has been suggested that this may also be related to the depolymerization of pectins that occurs during ripening. Also in the study by Ornelas-Paz et al. [43], it was found that the pectin content in 'Golden Delicious' apples varies depending on the date of harvest and the degree of ripeness of the fruit.

Furthermore, the red-fleshed apples are a rich source of anthocyanins and other phenolic compounds that are considered to have health-promoting properties [Wang et al. 40]. In the conducted research, the influence of the harvest date was marked in the content of these compounds. In the studies of Zhang et al. [52], a decrease in the content of anthocyanins in red-fleshed apples was also observed along with the delay in their harvest and their constant level, regardless of the variety. In turn, Wani et al. [15] found the highest level of these compounds in apples on the last harvest date. Research by Juhart et al. [10] confirmed the strong influence of the ripening process on the content of anthocyanins the red-fleshed apples. Wagner et al. [19] reported that the anthocyanin content in the red-fleshed apples was up to 381 mg·kg^-1 in the flesh and 1203 mg·kg^-1 in the peel.

Our study confirmed the relationship between image features and physicochemical properties of red-fleshed apples. Wani et al. [15] reported the correlations of color parameters of apples estimated by the machine vision system with the colorimetric index values, which can be used as standards. Also, the texture parameters of images can be correlated with the physicochemical properties of fruit [53-54]. Therefore determining the relationship between image features and color and chemical parameters can be important for the assessment of apple quality.

It is very important to determine the optimal date for the apple harvest. Apples harvested too early can be characterized by greater susceptibility to physiological disorders that can result in inferior surface color, less sugar content, poor production of aroma compounds and poor flavor, smaller fruit weight, poor eating qualities, and stored fruit can be more prone to bruise damage. Whereas harvesting too late can result in higher susceptibility to mechanical damage, rot, CO₂ injury, minimum storage life, and senescence. Such fruits harvested too late are less juicy and crispy with a high sugar/acidity ratio. It caused poor sensory quality [15]. Generally, apples harvested too early or too late are easily damaged and are susceptible to fungal diseases and physiological disorders. Over-mature fruits lose their flesh structure (softening) which causes their vulnerability to mechanical damage [55]. The susceptibility of apples to bruising depends on cultivars, storage conditions and postharvest treatment. The shape of the apple fruit is also an important factor because apples of regular shape are less susceptible to bruising [56].

"