Background

Apple (Malus domestica Borkh.) is one of the most important temperate fruits of Nepal. A total of 54 districts are growing apple in Nepal, however, there are only 12 major apple producing districts mainly from high mountainous regions. Out of these, five districts of Karnali province are the major apple growing districts with a production of 14,556 mt from the productive area 2,160 ha. Jumla ranks the first among the apple producing districts of Nepal in terms of productive area (960 ha) and total production (6,799 mt) (MOALD, 2020).

Early harvesting of apple is one of the major causes of lower quality fruit and weight loss during the postharvest handling and storage. Determining optimum harvesting time plays a crucial role in maintaining the postharvest quality as well as prolonging the storage period of apple fruits. The quality of fruits cannot be improved after the harvest since it is determined at the harvesting time in the tree. In addition, the harvesting time also influences important characteristics that define the commercial value of fruits such as size and peel color (Plotto et al., 1995). The quality of fruits depends on the optimum harvesting date and appropriate storage condition during the postharvest period (Streif, 1996; Vielma et al., 2008). To ensure the highest quality at the end of long-term storage, apples fruits must be harvested when mature but not yet fully ripe stage (De Long et al., 1999; Rutkowskie et al., 2008). When apples are harvested immaturely, they do not develop their full ripeness after storage, which leads to a small size, poor fruit color, sour and starchy flavor and a weak aroma. They are also more susceptible to scald, bitter-pit and internal breakdown. Mass reduction by water loss is also greater in apples picked earlier because the cuticle is not completely formed at this moment (Juan et al., 1999; Zerbini et al., 2003). All these physiological processes take place even under optimum conditions, which complicates storage (Braun et al., 1995; Ingle et al., 2000). The harvest of fruits after the optimum maturity stage also favors the occurrence of low sensorial quality due to the loss of crispness and juiciness and excessively high sugar/acidity ratio (Watkins et al., 2005).

This study was carried out with an objective of assessing the quality of ‘Golden Delicious’ apple fruit harvested at different dates and determining the optimum harvesting time of ‘Golden Delicious’ apple as it is a major delicious apple at Jumla after ‘Red Delicious’ which is cultivated as pollinizer variety for ‘Red Delicious’ apple. It is hoped that finding of this study will be highly supportive to the apple growers of Jumla as well as other areas having the similar climatic tract of Nepal. Fruits picked at optimum date and stored them in cold storage with minimum losses both in weight and quality will help increasing economic status of the growers by fetching higher price of the quality fruits.

1 Material and Methods

1.1 Study site

The studies were conducted at the fruit laboratory of Horticultural Research Station, Rajikot, Jumla. Samples were collected from ‘Golden Delicious’ apple tree of 40 years old planted in Gairagaun farm which is located at 29.26^oNorth latitude to 82.17^oEast longitude with 2,406 meter altitude above mean sea level. The mean pH, organic matter (%), nitrogen (%, N), phosphorous (mg/kg soil, P₂O₅) and potassium (mg/kg soil, K₂O) content of the soil was 5.64, 5.0, 0.18, 28.93, and 195 respectively. The climatic data of the study site is given in Table 1.

Table 1 Mean monthly climatic data of the study site in 2016 Source: Meteorological Office, Jumla, 2016

1.2 Treatments and experimental design

Treatments were arranged in randomized complete block design (RCBD) where four trees were considered as four replications (single tree as a single replication). In each replication each date of harvest was considered as single plot. The total number of plots i.e. date of harvest in each replication (single tree) was six.

1.3 Plant materials

Samples were taken from ‘Golden Delicious’ apple tree of 40 years old grafted onto crab apple (Malus baccata Borkh.) rootstocks receiving the optimum amount of chemical fertilizers and manures. Cultural practices like mulching, weeding, control of insect pest and diseases were done as per the recommendations.

1.4 Sampling and fruit analysis

During 2015 and 2016, fruit samples were taken from four trees as a replication and a total of eight fruit per tree were picked from the branches located at east, west, north and south directions (two fruit per branch). Fruit were harvested at weekly intervals started from 19^th August and continued till 23^rd September for 36 days.

1.5 Parameters taken for observation

1.5.1 Total soluble solid (%)

Fruit juice was extracted with apple juicer. After extracting and straining the juice, TSS was observed by placing a single drop of juice in prism of the analog hand refractometer.

1.5.2 Titratable acidity (%)

TA was measured with the help of titration method using standardized 0.1 N NaOH solution and phenolphthalein indicator (2-3 drops) and calculated as percent malic acid. Percent titratable acidity was calculated by using the formula as suggested by Saini (2001).

TitratableAcidity (%) =(Volume of titrant*x Normaility of titrant x Miliequivalent weight of malic acid **/Volume of sample)*100

Where, *Volume of titrant and sample is in milliliter; **Milliequivalent weight of malic acid is 0.067

1.5.3 TSS/TA (ripening ratio)

TSS/TA was calculated with the formula TSS/TA.

1.5.4 Starch Index (SI)

Starch index were prepared by dipping half part of the fruit for 30 seconds into a solution of 1 g potassium iodide plus 0.25 g iodine in 100 mL distilled water (Beattie and Wild, 1973). The starch index which indicated the relative amount of starch and sugar scored on a scale of 0-6 (Smith et al., 1979).

1.6 Statistical analysis

The recorded data for different parameters were subjected to analysis of variation (ANOVA) with date of harvesting as the source of variation. The observed data were analyzed using MS-Excel and MSTATC package. Means were separated with Duncan’s Multiple Range Test (DMRT).

2 Results

‘Golden Delicious’ apple fruit were analyzed for TSS, TA and TSS/TA ratio on each picking dates from 19^th August to 23^rd September at each 7 days intervals. Results showed highly significant difference on these parameters.

2.1 Total soluble solids (TSS)

Significantly the highest TSS (15.5%) was recorded on 23^rd September harvesting whereas, the lowest value (12.0%) was observed on 19^th August harvesting (Figure 1). Regarding TSS, it can be observed in the Figure 1 that during the ripening process, the TSS increased from 12.0% to 15.5% i.e. total increment was 3.5% during 36 days period.

Figure 1 Total soluble solids, titratable acidity and ripening ratio of 'Golden Delicious' apple harvested on different date in 2015 and 2016 at HRS, Rajikot, Jumla

2.2 Titratable acidity (TA)

Unlike sugars, the concentrations of organic acids decreased with the advancement of ripening resulting decreased TA in ripe fruit. TA content of late harvested fruit was lower than those harvested at an earlier date. Significantly the highest acidity (0.56%) was observed on the 19^th August harvesting followed by 26^th August harvesting (0.42%). The lowest acidity was recorded on 16^th and 23^rd September harvesting (0.37%) which was statistically at par with 9^th September and 2^nd September harvesting (Figure 1).

2.3 TSS/TA ratio (ripening ratio)

Ripening ratio was statistically highly significant on different harvesting dates. Significantly the highest ratio (42.69) was recorded on 23^rd September harvesting which was statistically at par with 16^th September harvesting (40.1). The lowest ratio (21.6) was observed on 19^th August harvesting (Figure 1).

2.4 Starch index

‘Golden Delicious’ apple fruits were analyzed for starch index on each picking dates from 19^th August to 23^rd September at each 7 days intervals. The study done for two years revealed that the starch index was highly significant in different dates of harvesting. Statistically, the highest starch index (6.0) was recorded on 23^rd September harvesting which was followed by 16^th September harvesting (5.5). The lowest starch index (3.0) was observed on 19^th August harvesting (Figure 2).

Figure 2 Average Starch Index of ‘Golden Delicious’ apple harvested on different dates in 2015 and 2016 at HRS, Rajikot, Jumla

3 Discussions

The preference of consumers for apples was positively correlated with the soluble solid content, with rejection of apple fruits with its level below 12% (Harker et al., 2008). Since, TSS percentage was a function of total dissolved solids and moisture content of the fruit, the increase in TSS could be due to the concentration of soluble solids in moisture loss (Farooq and Khan, 2012). In a study made by Baumann (1994) reported that soluble solid showed little difference just before optimum harvesting date in ‘Janagold’ apple during 1989, 1990 and 1992, respectively. Similar results have been reported by Argenta (1995) who observed at optimum harvesting date, there were variations in the internal indices among orchards and seasons and found that the TSS increased to a greater extent in apples as the picking time delayed. In the present study TSS content of ‘Golden Delicious’ apple fruit showed the increasing trend. During 36 days period the TSS was increased from 12.00% to 15.50% i.e. total increment was 3.50% (Figure 1) due to the breakdown of insoluble polysaccharides into a more soluble form by the enzymatic activity (Ng et al., 2013).

The contribution of acid (mainly citric, malic and oxalic) of citrus in the TSS is 10% whereas 80% contribution is of sugar (mainly glucose, fructose and sucrose), the remaining 10% contribution is from nitrogenous compounds (amino acids) (Lado et al., 2014). The acidity of the fruit may not determine the harvesting time of apple fruit however, acidic fruit is not preferred by the consumer. The ratio of TSS/TA determines the taste of fruit and is the indicator for determination of the harvesting time.

The TSS of apples and other fruits is an important quality factor which determines the fruit taste (TSS/TA ratio) (Weibel et al., 2004). With the advancement of ripening, the ripening ratio showed ever increasing trend. Icka and Damo (2014) reported that during the harvest time the ratio TSS/TA should be between 15 and 20. In the present study, the TSS/TA ratio was 21.60 on 19^th August. However, at that time other ripening indicators were below the prescribed level indicating the inappropriate time of harvesting (Figure 1).

Similarly, starch index (SI) is another important parameter for determining the harvesting time. According to Luton (1994) starch iodine test gives a less reliable guide to the maturity of fruit which is used for classifying local orchards in order of their probable maturity time. According to Blanpied (1974), starch content in the core of ‘Red Delicious’ apple fruit was a useful indicator of immaturity of the fruit. Smith et al. (1979) noted uniformity of starch index readings at the pre-climacteric minimum for three apple varieties is the good indicator of the maturity of the fruit. Thus there is evidence that a relationship exists between starch hydrolysis and the physiological age of the fruit. In the present study, the harvesting time of ‘Golden Delicious’ apple was suitable on 16^th September since the starch index reading was 5.50 on that date (Figure 2).

4 Conclusions

Jumla is the most important apple producing district of Karnali province of Nepal. Apple is the most important cash generating crop of Jumli people. Higher price during the beginning of important festivals of Nepal, like Haritalika Teej, Vijaya Dashami and Deepawali, is the major reason for early harvesting of apple fruits. Additionally, due to the problem of theft, the growers also compelled to harvest apple before the optimum harvesting time. Harvesting apples at the optimum time enhance and preserve the flavor and quality of the fruit. Fruit harvested too early is small in size with hard flesh and taste starchy. In contrast to this, over mature fruit have a dark dull color with greasy peel and taste starchy or have off flavors. The early harvesting also results the higher loss of fruit weight due higher transpiration loss from the fruit as at that time there is poor development of cuticle layer and wax in the fruit surface. The study results revealed that fruit of ‘Golden Delicious’ apple can be harvested from, 16^th September in Jumla since at that time TSS, TA, TSS/TA, and Starch Index (SI) were 14.80%, 0.37%, 40.11, and 5.5 respectively. Therefore, the optimum date for ‘Golden Delicious’ apple harvest is 16^th September and onwards. Harvesting time should be adjusted for some days in warmer or cooler growing years.

Authors’ contributions

BC carried out trial designing, data recording, data analysis, literature review and manuscript preparation. GD designed trial and manuscript preparation. RK carried out trial designing, conducted laboratory analysis of fruit sample and manuscript preparation. SK reviewed literatures and prepared manuscript. LB conducted laboratory analysis of fruit sample. All authors read and approved the final manuscript.

Acknowledgements

Authors would like to extend their sincere thanks to all the staffs of Horticultural Research Station, Rajikot, Jumla for their cordial help during sampling and laboratory analysis. Authors would also like to thanks Nepal Agricultural Research Council for providing fund support (project no. 60970290).

References

Argenta L.C., Bender R.J., Kreuz C.L., and Mondardo M., 1995, Maturity patterns and harvesting indices of apple cultivars ‘Gala’, ‘Golden Delicious’ and ‘Fuji’ apples, Pesuisa Agr. Brasileira, 10: 1259-1266

Baumann H., 1994, Optimum harvest date of some apple varieties in the Rhine land from 1989-1992, Proc. of the Meeting of Working Group on Optimum Harvest, Jun. 9-10, Lotus, Norway, pp. 33-38

Beattie B.B., and Wild B.L., 1973, Assessing harvest maturity of ‘Granny Smith’ apples for export, The Agricultural Gazette of New South Wales, 84: 30-33

Blanpied G.D., 1974, A study of indices for earliest acceptable harvest of Delicious apples, J. Am. Soc. of Hort. Sci., 99: 537-539

Braun H., Brosh B., Ecker P., and Krumbock K., 1995, Changes in quality of apples before, during and after CA-cold storage, Obstau Fruchteverwert, 45(5):143-206

De Long J.M., Prange R.K., Harrison P.A., Shofield R.A., and DeEll J.R., 1999, Using the Streif index as a final harvest window for controlled-atmosphere storage of apples, Hort Science, 34(7): 1251-1257

https://doi.org/10.21273/HORTSCI.34.7.1251

Farooq R.A., and Khan I., 2012, Physico-chemical quality of apple cv. ‘Gala’ fruit stored at low temperature, Fuuast J. Biol., 2: 103-107

Harker F.R., Kupferman E.M., Marin A.B., Gunson F.A., and Triggs C.M., 2008, Eating quality standards for apples based on consumer preferences, Postharvest Biology and Technology, Amsterdam, 50(1): 70-78

https://doi.org/10.1016/j.postharvbio.2008.03.020

Icka P., and Damo R., 2014, Assessment of harvest time for ‘Red Delicious’ cv. through harvest indexes in Albania, Bulg. J. Agric. Sci., 20(3): 628-632

Ingle M., D’Souza M.C., and Townsend E.C., 2000, Fruit characteristics of York apples during development and after storage, Hort Science, 35(1): 95-98

https://doi.org/10.21273/HORTSCI.35.1.95

Juan J.L., Frances J., Montesinos E., Camps F., and Bonany J., 1999, Effect of harvest date on quality and decay losses after cold storage of ‘Golden Delicious’ apples in Girona, Acta Horticulture, 485:195-201

https://doi.org/10.17660/ActaHortic.1999.485.26

Lado J., Rodirgo M., J., and Zacaris L., 2014, Maturity indicators and citrus fruit quality. Stewart Postharvest Review, 2(2): 1-7

Luton M.T., 1994, The year of optimum harvest date: Data for the variety ‘Cox’s Orange Pippin’. Proc. of a Meeting of the Working Group on Optimum Harvest, Jun. 9-10, Lofthus, Norway, pp. 39-48

MOALD, 2020, Statistical Information on Nepalese Agriculture 2018/19. Ministry of Agriculture and Livestock Development, Planning and Development Cooperation Coordination Division, Statistics and Analysis Section, Singha Durbar, Kathmandu, Nepal, pp. 435

Ng J.K., Schroder R., Sutherland P.W., Hallett I.C., Hall M.I., and Prakash R., 2013, Cell wall structures leading to cultivar differences in softening rates develop early during apple (Malus domestica) fruit growth, Pl. Biol., 13(1): 183

https://doi.org/10.1186/1471-2229-13-183

PMid:24252512 PMCid: PMC4225529

Plotto A., Azarenko A.N., Mattheis J.P., and Mcdaniel M.R., 1995, ‘Gala’, ‘Braeburn’ and ‘Fuji’ apples: maturity indices and quality after storage, Fruit Varieties J., 49(3): 133-142

Rutkowski K.P., Michalczuk B., and Konopacki P., 2008, Nondestructive determination of ‘Golden Delicious’ apple quality and harvest maturity, J. Fruit Ornam Plant Res, 16:39-52

Saini R.S., Sharma K.D., Dhankhar O.P., and Kaudishk R.A., 2001, Laboratory manual of analytical techniques in Horticulture, Agrobios, Jodhpur, India, 136p.

Smith R.B., Lougheed E.C., and Franklin E.W., 1979, The starch iodine test for determining stage of maturation in apples, Canadian J. of plant sci., 59(3): 725-735

https://doi.org/10.4141/cjps79-113

Streif J., 1996, Optimum harvest date for different apple cultivar in the ‘Bodensee’ area. Proc. of the Working Group on Optimum Harvest Date COST 94; Lofthus, Norway, pp. 15-20

Vielma M.S., Matta F.B., and Silval J.L., 2008, Optimal harvest time of various apple cultivars grown in Northern Mississippi, J. Am. Pomol. Soc., 62(1):13-20

Watkins C.B., Erkan M., Nock J.F., Iungerman K.A., Beaubry R.M., and Moran R.E., 2005, Harvest date effects on maturity, quality, and storage disorders of ‘Honey Crisp’ apples, Hort Science, 40(1): 164-169

https://doi.org/10.21273/HORTSCI.40.1.164

Weibel F., Widmer F., and Husistein A., 2004, Comparison of production systems: integrated and organic apple production. Part III: Inner quality: composition and sensory, The Swiss Journal of Pomology and Viticulture, 140: 10-13

Zerbini P.E., Grassi M., Cubeddu R., Pifferi A., and Torricelli A., 2003, Time-resolved reflectance spectroscopy can detect internal defects in pears, Acta Horticulture, 599:359-365

https://doi.org/10.17660/ActaHortic.2003.599.44