How to Use Mango Harvest Maturity Indices to Improve Fruit Quality and Yield

• The mango harvest maturity indices can be physical, computational, physiological, and biochemical attributes.
• Physical indices are simple but subjective and unreliable.
• Biochemical harvest maturity indices are the most reliable, and standard NIR spectroscopy-based non-destructive estimation methods are the best.

Mango fruits must be harvested at optimum maturity to continue developing internal and external quality attributes to meet consumer acceptance and extend storage life. Many mango harvest maturity indices are available based on external and internal attributes and cultivation practices. This article covers the types of indices available for mangos and examples from around the world.

Mango Maturity

Mangos are climacteric fruits and can be harvested before ripening at physiological maturity. Depending on the cultivar, mangoes have varying shapes, sizes, colors, flavors, and tastes. So, the maturity index used at harvest is not the same for all mangos. Moreover, there are many quality parameters used as harvest maturity indices.

These harvest maturity indices are crucial in determining harvest date, sorting, grading, and compliance.

• Harvest: Immature fruits are susceptible to postharvest problems like mechanical damage, chilling injury, uneven color development, and poor quality when ripe. Keeping fruits longer on trees leads to better aroma development but reduces storage potential. Over-maturation at harvest also causes postharvest physiological disorders. The storage period is crucial, and optimum harvest maturity will depend on the target market and intended use.
• Sorting: Fruits are sorted according to harvest maturity indices so that fruits in a batch have the same ripening levels in a box and load.
• Grading: Following sorting, growers and suppliers can decide how to use fruits based on quality and maturity.
• Compliance: Several national and regional regulations require that mangoes meet a specific harvest maturity index before they are accepted into the market.

Types of Harvest Maturity Indices

The choice of harvest maturity indices is crucial. Unreliable harvest maturity indices are partly responsible for high postharvest losses of 40-50% of fruits in the mango supply chain.

Many types of indices for mangos exist to determine optimum maturity for harvesting:

• Morphological or physical features
• Chemical attributes
• Physiological processes
• Computational methods

The choice of harvest indices will vary based on farm economics, region, and target market.

1. Physical Harvest Maturity Indices

Physical quality parameters are the most common harvest maturity indices used for mangoes. They include morphological features like fruit shape, length, width, size, peel, and pulp color. Morphological indices methods involve non-destructive visual observation, but the process is subjective. Physical attributes like firmness, specific gravity, and weight can also be used but involve destructive sampling.

Physical harvest maturity indices do not account for differences in quality due to orchard management, region, year, weather, and soil conditions.

Shape, Size, & Weight

Figure 1: “Fullness of cheeks, flat shoulder at stem end (a) and presence of bloom as indices of maturity (b)” FAO 2018. (Image credits: FAO).

Shape parameters measured are the development of a flat shoulder, full cheek, and grooves around the stylar scar (See Figures 1 and 2). To measure size, length and width are used.

In Ghana, the values for optimum harvest indices for four cultivars, Haden, Kent, Keitt, and Palmer, were as follows:

Haden: Weight is 640 g, length is 16.31cm, width is 30.97 cm, and density is 1.147 g/cm³. The intensity of grooves at the stylar-scar end is 0.075 mls.

Kent: Weight is 836 g, length is 16.19 cm, width is 33.47 cm, and density is 1.076 g/cm3. The intensity of grooves at the stylar-scar end is 0.150 mls.

Keitt: Weight is 1104 g, length is 19 cm, width is 35.91 cm, and density is 1.189 g/cm3. The intensity of grooves at the stylar-scar end is 0.116 mls.

Palmer: Weight is 837 g, length is 21.22 cm, width is 30.86 cm, and density is 1.084 g/cm3. The intensity of grooves at the stylar-scar end is 0.425 mls.

Ghana uses these harvest maturity indices also for mangos grown for export to the European Union.

Figure 2: “Changes in ridge/groove formation around the stylar-scar end of Palmer mango fruit by stage of fruit development,” Abu et al. 2021. (Image credits: DOI: 10.4236/as.2021.1210071)

In Kenya, physiological maturity was seen in stage 1, and the following physical harvest maturity indices are applicable for the cultivars- Tommy Atkins, Van dyke, and Kent.

Tommy Atkins: Size or length is 31.53-32.70 cm, and specific gravity is 1.214 to 1.298 g/cm3.

Van dyke: Length is 28.27-29.17 cm, and specific gravity is 1.162 to 1.205 g/cm3.

Kent: Size is 35.03-35.03 cm, and specific gravity is 1.214 to 1.298 g/cm3.

Size is widely used as a harvest maturity index but is unreliable, as small fruits can have advanced maturity. Neither is shape an objective index; large mangoes with developed shoulders can be mature or immature.

Color

Internal pulp and peel color are essential for mangoes since the peel color remains green in many cultivars, even in ripe fruits. Color development starts at the seed and progresses to the peel.

The formation of white bloom is also a harvest index, see Figure 1.

Color charts for cultivars are available in each country. In the US, 90% of mangos must reach stage 2 or higher to meet a maturity index. Figure 3 shows the optimum colors for Tommy Atkins, Honey, Kent, Keitt, Haden, and Francis.

Figure 3: Internal pulp color used as a harvest maturity index for the cultivars Tommy Atkins, Honey, Kent, Keitt, Haden, and Francis, according to Mango.org. (Image credits: Mango.org)

Firmness

Firmness is a consistent harvest maturity index. As the fruit matures and ripens, firmness reduces. However, the required method is destructive. Growers use a fruit penetrometer with a 5/16″ or 8mm tip to measure firmness on the cheek after removing the peel. The force used is recorded as Newton (N).

The various firmness harvest maturity indices based on cultivar and region are as follows:

As shown in Figure 3, in the USA, the optimum maturity is reached at stage 2, and the corresponding firmness required as harvest index is as follows:

Tommy Atkins-35-15 N

Honey– 29-12 N

Kent– 29-14 N

Keitt– 47-18 N

Haden– 35-16 N

Francis– 19-12 N or less.

In Kenya, the firmness indices are:

Van dyke– 50.19 to 33.92 N

Tommy Atkins– 47.33 to 34.77 N

Kent– 60.58 to 40.54 N

If physical harvest maturity indices are used, using more than one feature may be necessary. Size or shoulder development is not enough. Farmers can avoid losses by using additional information from computational, physiological, and biochemical indices.

2. Computational Harvest Maturity Indices

Computational methods used as a harvest maturity index for mangos are days from full bloom (DFFB) or fruit onset to physiological maturity. These indices are fixed for cultivars depending on environmental conditions. Examples are as follows:

• In Kenya, the DFFB for mangos is 90 to 160 days.
• In India, mangos are harvested 120 to 140 days after fruit set.

This method is reliable but provides broad recommendations and not fruit-specific information.

3. Physiological Harvest Maturity Indices

The physiological parameters used as mango harvest maturity indices are ethylene production and respiration rate, as the fruit is climacteric. The indices are sensitive to cultivars. As maturity increases, respiration and ethylene evolution rates increase.

In Kenya, the physiological maturity indices needed at stage 1 are as follows: 

Van dyke– ethylene evolution should be 0.114 μl/kg/hr and respiration rate17.97 ml/kg/hr.

Tommy Atkins—ethylene evolution should be 0.115 μl/kg/hr and the respiration rate 21.40 ml/kg/hr.

Kent—ethylene evolution should be 0.1123 μl/kg/hr and a respiration rate of 22.69 ml/kg/hr (stage 2).

Estimating the physiological process requires picking fruits, keeping them in a container, and measuring the gases in the headspace.

4. Biochemical Harvest Maturity Indices

Biochemical harvest indices are the most reliable as the estimations are objective and accurate. The quality parameters measured are sugar or soluble solids content (SSC), dry matter (DM), total titrable acidity, and SSC: TTA ratio for taste. As maturity increases, the SSC, DM, and SSC: TTA ratio increases. During ripening, the SSC and SSC: TTA ratio rises. These internal biochemical parameters are sensitive to cultivar, weather, region, and cultivation practices.

In Kenya, the optimum values of biochemical indices to harvest mangos at stage 1 are:

Van dyke– the SSC should be 7-8.097 ^oBrix and TTA 0.299 %.

Tommy Atkins– the desired SSC is 7.793 ^oBrix, and TTA is 0.2360 %

Kent– the SSC must be 7-8.097 ^oBrix and TTA 0.297 %.

In the USA, Tommy Atkins should have an SSC >13.5% to achieve 80% consumer acceptance. The SSC for Tommy Atkins, Honey, Kent, Keitt, Haden, and Francis at stage 2 ranges between 6 and 13; see Figure 3.

In Australia, dry matter is the standard for the Australian Mango Industry Association, which recommends a minimum of 15 % DM for most mango cultivars grown in the country. This DM gives the desired SSC at ripeness.

Dry matter harvest indices for various cultivars in other parts of the world can vary between 14.0 and 16.9%.

Figure 4: Preparing a model for mango cultivars using NIR spectroscopy devices like Felix 750 Fruit Quality Meter, Neto et al. 2017. (Image credits: https://doi.org/10.1016/j.postharvbio.2017.03.009)

Non-Destructive Near Infrared Spectroscopy

Estimations for biochemical harvest maturity indices are possible through destructive and non-destructive methods. Dry matter estimation is done in laboratories. Refractometer is the destructive SSC method for Brix measurement in the field, where juice from the cheek or close to the seed is used.

Non-destructive estimation is usually done through near-infrared (NIR) spectroscopy for all three parameters simultaneously—DM, SSC, and TTA. The analysis results are ready in real-time, and the devices can be used in the field. An example is the F-751 Mango Quality Meter manufactured by Felix Instruments Applied Food Science. The tool is helpful for many cultivars globally.

As shown in Figure 4, the F-751 Mango Quality Meter and F-750 Produce Quality Meter can be used to produce new models for other cultivars.

NIR spectroscopy-based devices have become the standard tool to monitor mangos for harvest maturity indices in many parts of the world.

Sources

Abu, M., Olympio, N. and Darko, J. (2021) Determination of Harvest Maturity for Mango (Mangifera indica L.) Fruit by Non-Destructive Criteria. Agricultural Sciences, 12, 1103-1118. doi: 10.4236/as.2021.1210071.

Anderson, N. T., Walsh, K. B., Subedi, P. P., & Hayes, C. H. (2020). Achieving robustness across season, location and cultivar for a NIRS model for intact mango fruit dry matter content. Postharvest Biology and Technology, 168, 111202.

dos Santos Neto, J. P., de Assis, M. W. D., Casagrande, I. P., Júnior, L. C. C., & de Almeida Teixeira, G. H. (2017). Determination of ‘Palmer’ mango maturity indices using portable near-infrared (VIS-NIR) spectrometer. Postharvest Biology and Technology, 130, 75-80.

FAO. (2018). Post-harvest management of mango for quality and safety assurance. Retrieved from https://openknowledge.fao.org/server/api/core/bitstreams/f6bf4e89-275b-42a2-a402-b53255feaa04/content

Mango.org. (n.d.). Mango maturity and ripeness guide. Retrieved from https://www.mango.org/wp-content/uploads/2017/10/Maturity-poster_hi.pdf

Muiruri, J., Ambuko, J., Nyankanga, R., & Owino, W. O. (2022). Maturity indices of specific mango varieties produced at medium altitude agro-ecological zone in Kenya. African Journal of Food, Agriculture, Nutrition and Development, 22(6), 20572-20774.

(n.d.). Mango Post-Harvest Management Protocols. Retrieved from https://www.face-cii.in/cclrc/fruits-vegetables/Mango.pdf

Shah, S. S. A., Zeb, A., Qureshi, W. S., Malik, A. U., Tiwana, M., Walsh, K., … & Alanazi, E. (2021). Mango maturity classification instead of maturity index estimation: A new approach towards handheld NIR spectroscopy. Infrared Physics & Technology, 115, 103639.