NIR Spectroscopy for Persimmons

Visible and Near-infrared spectroscopy can improve the monitoring and control of persimmon quality at several stages of fruit production. Persimmon is a soft-fleshed fruit that can be easily damaged during transport and storage. The quality of the fruit at harvest, along with management during storage and transport, will determine its condition at retailing. Therefore, some of the critical points for use are setting harvest time, monitoring quality during storage, supply, and retailing.

Persimmon

There are two types of persimmon. The first type is Diospyros kaki, or the Asian persimmon, which is the variety that is commonly available commercially. This can be either astringent or non-astringent.

The other type, Diospyros virginiana, or the American persimmon, is always astringent and is not common.

Persimmon can be dried or eaten as fresh fruits, or they can be processed into wine, vinegar, or pulp. It is used to make baked products, custard, ice creams, puddings, and preserves.

Though persimmon is a climacteric fruit, it has higher levels of ethylene in the early maturity stages, so harvesting has to be done with extra care.

VIS-NIR Spectroscopy

The interaction of light with matter results in its reflection, absorption, and transmission based on the chemical composition of the compounds. This interaction, which is called spectroscopy, is widely used in food science to identify and quantify compounds.

The wavelength of light that any matter reacts with also depends on its compounds. Most biocompounds respond to wavelengths lying in the visible (VIS) and near-infrared (NIR) range. NIR specifically reacts with the bonds that hold compounds together.

Research is needed to check whether reflectance or absorption of light is important for each compound in each species of fruit.

Fruits are perishable and a substantial proportion is lost from farm to shelf. Therefore, scientists have focused a lot of research on the application of VIS-NIR spectroscopy to optimize their supply chain.

The Felix F-750 Produce Quality Meter is one of the tools on the market that is used to test the quality parameters of a lot of fruits and vegetables. The handheld tool, which is manufactured by Felix Instruments Applied Food Science, has a starter model for testing total soluble sugar or BRIX0 in persimmon. The measurements are based on VIS-NIR and are non-destructive. Each individual reading can be made within a few seconds. The device can also measure color, titrable acidity, and dry matter. Being portable, the tool can be used in all stages of the supply chain.

The parameters used for persimmon are total soluble solids (TSS), titrable acidity (TA), tannin contents, color, and firmness.

The following are some recommendations, based on scientific findings, where this technology can be used for persimmon: managing preharvest orchard, setting harvest time, controlling quality, and indentifying varieties.

Preharvest Orchard Management

Persimmon trees can suffer from chloride toxicity due to accumulation from irrigation water.

Even slight chloride stress can reduce the weight of fruits. Moreover, the accumulation of chloride in slight or moderate amounts in the calyx of the developing fruit accelerates the time of ethylene release and increases their quantities; as a result, fruits mature faster and lose firmness. When the toxicity is high, maturity happens very quickly and it is hard to maintain fruit firmness during storage.

Thus, chloride toxicity causes a reduction in yield, quality, and storage time.

It is necessary to inspect trees non-destructively to check if they are suffering from chloride stress. When portable NIR tools are used, chloride levels can quickly be detected in real time without waiting for laboratory tests, so farmers can alter their practices as needed.

Setting Harvest Time

Harvesting persimmons at the correct stage of maturity is the best way to ensure that it can be stored for longer periods. Since they are climacteric fruits, farmers can harvest them when they are fully mature but not ripe and soft. Harvesting early yields greener fruits, which can be stored longer but have low quality, taste, flavor, and sweetness. Therefore, getting the harvest time right is essential. This is best done by the analysis of internal attributes.

Traditionally, color charts have been used to categorize fruits based on maturity. However, an investigation with NIR spectrometers has proven that color alone is unreliable as a maturity index or indicator of other quality attributes except for firmness. Moreover, color depends on the area of production and temperature, and it varies within a single variety

Quality at maturity determines the post-harvest quality of TSS and TA after storage and shelf life. So, the recommended levels at harvest for the various parameters are as follows:

• Total soluble solids: TSS is the harvest indicator used worldwide for persimmon.
  • New Zealand requires a minimum of 12% and an average of 14% (page 8)
  • South Africa requires 14⁰ Brix for ‘Triumph’ persimmon (page 8)
• Color: Harvest is recommended when fruits reach values of 4 to 5 on the color chart to improve storage time and maintain quality later.

Fruits harvested at the right maturity can be stored up to two months without loss of quality, decay, or browning. Fruits harvested too early can develop peel browning disorder due to chill injury during storage.

Quality control

Figure 1: Estimation of TSS/SSC and firmness with hyperspectral images for online use in sorting fruits, Wie et al. 2020. (Image credits: https://www.sciencedirect.com/science/article/abs/pii/S1350449519307601)

Persimmon is a fruit that is often exported and imported. The quality of the fruit is measured by set standards for objective internal parameters. Sugar and tannin levels determine the taste and quality of fruits. In general, the fruits should have the following:

• A firmness equivalent to penetration force of 2.3 kg
• TSS that ranges between 18-23% depending on the variety. For example, TSS of 21-23 % in ‘Hachiya’ and 18-20 % in ‘Fuyu’ (page 8). As the fruit ripens post-harvest, its sugar content increases making the fruit sweeter.
• No astringency or tannins in fruits meant for eating. In non-astringent varieties, the tannins that are present in the early stages of development are reduced, especially under high temperatures. If temperatures are lower there could be some tannins left; therefore, this parameter has to be estimated.

TSS and color are the parameters that can be easily followed throughout the storage and transport period using NIR tools. The technology can also be used for measuring acidity and firmness.

Astringency can be detected best by using VIS-NIR spectroscopy.

NIR hyperspectral imaging can be used to visually identify SSC and firmness, and it is recommended as a method for developing online classification using multiple parameters.

Quality of persimmon is monitored during transport, storage, and retailing.

Identification of Varieties by VIS╱NIRS Spectroscopy

Persimmon is eaten not just for its taste and nutritional value, but also for its medicinal properties. The fruit is rich in vitamin C, carotene, calcium, phosphorus, iron, and other minerals; it is also a rich source of sugars, like glucose and fructose.

Since this is a fruit that is often imported, it is important to be able to find the variety at the port of arrival. This is best done by using a non-destructive analysis of the whole fruit so that packaging is not spoiled and fruits are not wasted. It is possible to identify the varieties of persimmon with an accuracy of 100% by absorbance of VIS-NIR spectroscopy.

Farm to Shop Quality Control

Besides the VIS-NIR checks on quality during harvest, storage, and retailing, persimmon has to be monitored even before harvest. It is not just the fruits, but also the general management of farms that can be checked using NIR tools. The quality of persimmon post-harvest and during storage depends on preharvest growth and development, which can be influenced by nutrition or toxicity stress. Therefore, NIR spectroscopy can be used starting from the farm, before harvest, and during harvest.

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Vijayalaxmi Kinhal
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture

Feature image courtesy of Mike Licht

Sources

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Cortés, V., Rodríguez, A., Blasco, J., Rey, B., Besada, C., Cubero, S., . . . Aleixos, N. (2017). Prediction of the level of astringency in persimmon using visible and near-infrared spectroscopy. Journal of Food Engineering, 204, 27-37. doi:10.1016/j.jfoodeng.2017.02.017

de Paz, J. M., Visconti, F., Chiaravalle, M., & Quiñones, A. (2016). Determination of persimmon leaf chloride contents using near-infrared spectroscopy (NIRS). Analytical and bioanalytical chemistry, 408(13), 3537–3545. https://doi.org/10.1007/s00216-016-9430-2

Besada, C., Gil, R., Bonet, L., Quiñones, A., Intrigliolo, D., & Salvador, A. (2016). Chloride stress triggers maturation and negatively affects the postharvest quality of persimmon fruit. Involvement of calyx ethylene production. Plant physiology and biochemistry: PPB, 100, 105–112. https://doi.org/10.1016/j.plaphy.2016.01.006

Marzolo, G. (2016, June). Persimmon. Retrieved from https://www.agmrc.org/commodities-products/fruits/persimmon

Nakano, R., Ogura, E., Kubo, Y., & Inaba, A. (2003). Ethylene biosynthesis in detached young persimmon fruit is initiated in calyx and modulated by water loss from the fruit. Plant physiology, 131(1), 276–286. https://doi.org/10.1104/pp.010462

Wei, X., He, J., Zheng, S., & Ye, D. (2020). Modeling for SSC and firmness detection of persimmon based on NIR hyperspectral imaging by sample partitioning and variables selection. Infrared Physics & Technology, 105, 103099. doi:10.1016/j.infrared.2019.103099

Zanamwe. P. (2014). The role of harvest time and maturity, orchard and simulated wind on postharvest quality of ‘Triumph’ persimmon fruit, and potential of NIR as non-destructive sorting tool. MS. Thesis (Horticultural Science), Stellenbosch University, South Africa. Retrieved from https://core.ac.uk/download/pdf/37436774.pdf

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