What Are the Harvest Maturity Indices for Strawberries?

• Strawberries can be harvested at two different maturities to meet marketing needs at varying distances.
• Color is the most critical parameter used as a maturity index for strawberry harvest.
• Other harvest maturity indices are size, sugar content, and taste.
• Non-destructive measurements using portable NIR spectroscopy devices are best suited for establishing harvest maturity indices.

Strawberries are harvested close to full ripeness for flavor. It is a highly perishable fruit with a limited shelf life. Therefore, harvesting at the proper maturity to optimize consumer satisfaction and shelf life is necessary. Various harvest maturity indices can help in this aim. In this article, you can find out which parameters are best suited as the harvest maturity index for strawberries.

Strawberry Characteristics

Strawberries are non-climacteric fruits that do not ripen after harvest. Therefore, strawberries must be harvested when they are ripe and ready for consumption to ensure they have the optimum quality to meet consumer satisfaction. The strawberries are also thin-walled and have a high water content that makes postharvest storage challenging.

To account for varying market types, including those involving long-distance transport, strawberries can be harvested earlier than at full ripeness to extend their storage time. In all these cases, there are fixed maturity points to guide growers in maximizing yield benefits.

It is advisable to have strawberries at a similar maturity level packed in a batch, as mixing fruits at varying ripeness can lead to increased batches being rejected due to the development of mold, discoloration, bruising, and other issues.

Ripe strawberries lose glossiness and firmness in storage, especially in warm temperatures, so the supply chain can use several postharvest measures customized for non-climacteric fruits to capitalize on quality fruits harvested at the right time.

Research on various cultivars in several regions worldwide has identified the best parameters for use as a harvest maturity index, including peel color, size, firmness, bruising, total soluble solids, and taste. The harvest maturity index, as well as specific values of these parameters for various cultivars, are discussed below.

Physical Harvest Maturity Indices

Color, size, firmness, and bruising are the physical parameters of strawberries used as indicators of harvest maturity.

Figure 1: Stages of color development in strawberry variety San Andreas, Sanchez-Sevilla et al. 2021. (Image credits: https://doi.org/10.3389/fpls.2021.688481)

Color

Peel color is crucial in determining the optimal harvest maturity for strawberries worldwide. Strawberry fruits undergo color change as they ripen, as shown in Figure 1, from green to white to red. Ripeness is closely associated with the development of peel color. The changes in color can be measured non-destructively through handheld visible and near-infrared spectrometers to measure chroma color (C*), lightness (L*), and hue (H°). However, it is the red color coverage that is more important as harvest maturity, and usually estimated in strawberries manually and used as indicated below:

• Fully ripe: Ripe fruits have over 75% red or pink color development and are best for fresh consumption. These have the best taste and sweetness, as well as maximum size and weight development. Strawberries harvested at this stage have the longest storage capacity. Ripe fruits suffer only 10% losses after ten days in the postharvest stages.
• Over-ripe: Strawberries are considered over-ripe if they have 100% red or pink color development. Approximately 50% fruit loss is possible ten days postharvest when strawberries are harvested at this stage.
• Half-ripe: Fruits that are half-ripe (50% red or pink color development) have less sugar and low taste scores as the acidity content is high.

Figure 2: Color development in grade 1 and 2 strawberries in the USA, UGA Extension. (Image credits: https://extension.uga.edu/publications/detail.html?number=C1308&title=strawberry-maturity-indices-and-quality)

The exact color requirements can vary in countries and are as follows:

USA: The optimum color for harvest depends on grading. U.S. Grade No. 1 strawberries must have a minimum of 75% red/pink color development. U.S. Grade No. 2 must have a minimum of 50% red/pink coverage; see Figure 2. In states like California, all strawberries must have a 75% color development to meet market standards.

Pakistan: The strawberry variety ‘Chandler’ was harvested when fully ripe at 75% red-colored stage.

Iran: Strawberry varieties ‘Selva’ and ‘Gavita’ need to have 85% and 95 % of red development, respectively, to be harvested in Iran.

Size

Strawberries continue to grow in size even after ripening begins. Hence, fully ripe (75% red) strawberries will be larger than in the early stages of color development. The shape is usually short-conical, although ovate to long-conical forms can exist, depending on the variety.

In the USA, U.S. Grade No. 1 strawberries must be larger than 3/4 inches, and U.S. Grade No. 2 strawberries must be a minimum of 5/8 inches. The USA permits 5% off-sizes.

Firmness and Bruising Susceptibility

As the fruit ripens, it becomes softer. The rate of softening depends on the cultivar, season, and growing conditions and can vary significantly. The process of softening also continues after harvest, but the difference between cultivars narrows in time, as indicated in Figure 3. Ripe strawberries are softer than unripe fruits. Fruits meant for distant markets are, therefore, harvested when less ripe but fully mature. Farmers can also choose to grow strawberry cultivars that have firmer fruits for long-distance markets.

Figure 3: Firmness reduction in cv Selva and Gavita. The term (-b) is for days before harvest, and (-a) stands for days after harvest, Salamaat et al. 2013. (Image credits: https://www.cabidigitallibrary.org/doi/pdf/10.5555/20133272668)

Firm strawberry fruits and some varieties have less bruise susceptibility and store well. For example, firmness and bruising are used in Iran to fix harvest days. Strawberry cultivar ‘Selva’ is firmer and less susceptible to bruising than ‘Gavita’ and is better suited for long-distance transport.

Chemical Harvest Maturity Indices

The chemical parameters used as harvest indices for strawberries are total soluble solids and taste.

Total Soluble Solids

Total soluble solids (TSS), which control sweetness, increase with ripening in strawberries and are associated with changing color. It can be used to fix harvest time and is measured as °Brix. It is a useful quantitative index. Growers can measure TSS through refractometers, a destructive method, or near-infrared spectroscopy, a non-destructive process.

Table 1. “Effect of maturity stages and cultivars on shelf-life, TSS, and taste (sugar to acid ratio) of Bangladeshi strawberry cultivars ‘Festival,’ ‘Sweet Charlie,’ ‘Camarosa,’ ‘FA 008,’ and ‘BARI Strawberry-1,’ Rahman et al. 2016. (Credits: https://doi.org/10.1016/j.jssas.2014.05.002)

The minimum acceptable TSS can vary between 5% and 10% based on region and cultivar.

Bangladesh: In five strawberry cultivars, ‘Festival,’ ‘Sweet Charlie,’ ‘Camarosa,’ ‘FA 008,’ and ‘BARI Strawberry-1,’ the maximum TSS was seen at 75% redness or full maturity in most cases, see Table 1. However, the sugar content varies with cultivars. Camarosa had the most sugar, followed by Festival.

Iran: Fruit ripeness was found to increase even after harvest, which was 5% in Selva and 6% in Gavita.

Slovenia: Thirteen strawberry varieties have varying sweetness, with a minimum TSS ranging between 6.1 and 6.7% at two harvest times, technological ripeness (75% red) and fully ripe (100% red), respectively. For details on each cultivar, see Table 2.

Table 2: “The mean total soluble solids, mean content of total sugars, total organic acids, and sugar/acid ratio in strawberry fruits of 13 cultivars at two maturity stages, (1) technological ripeness (75% red), and (2) fully ripe (100% red),” Strum et al. 2003. (Image credits: https://doi.org/10.1016/S0308-8146(03)00124-9)

Taste

Taste is measured as the ratio of sweetness to sourness or TSS to total acids. A mixture of sweet and sour is usually required to meet consumer demands.

The acid content is measured as total titrable acidity (TA). In strawberries, TA is not used directly as a harvest maturity index, but to calculate taste. In strawberries in Slovenia, TA at harvest can vary between 5 g/kilo to 11.2 g/kilo; see Table 2. The TA content decreases with ripening.

For most fruits, a higher sugar-acid ratio provides the preferred taste and increases with ripeness. An increasing TSS and decreasing TA content ensures the optimum sugar-to-acid ratio as ripening proceeds. In places like Italy, taste is considered the most critical indicator of harvest maturity. It can be measured by handheld NIR spectrometers that can measure TSS and TA in the field.

Italy: The ‘Sabrosa’ cultivar with a TSS: TA ratio of 12.30 is considered fit for harvest.

Bangladesh: Strawberries of five cultivars showed varying TSS: TA ratios at 75% redness or full maturity, ranging from 4.6 to 6.32; see Table 1 for details.

Slovenia: Taste varied among the 13 cultivars grown in Slovenia; a mean of 5.5 was ideal at 75% redness and 6.5% at 100% redness; see Table 2 for details.

The values for the harvest indices must be customized for cultivar and region to optimize strawberry harvests.

Non-Destructive NIR Spectroscopy Measurements

Handheld NIR spectroscopy devices that allow non-destructive measurement of fruit parameters are best suited for establishing the harvest maturity index. Felix Instruments Applied Food Science offers the F-750 Produce Quality Meter. This portable and precise instrument captures visible and near-infrared (vis-NIR) spectral data and analyzes it in real-time to provide valuable insights. It is suitable for measuring internal and peel color, TSS, and TA. The F-750 can be used to construct models customized for strawberries. The device has been a standard tool in fresh produce supply chains for over a decade.

Discover more about Felix Instruments’ quality meters tailored to your harvesting needs.

Sources

Cantwell, M. and T. Suslow. (2002). Lettuce, Crisphead: Recommendations for Maintaining Postharvest Quality. Retrieved from http://ucanr.edu/sites/Postharvest_Technology_Center_/Commodity_Resources/Fact_Sheets/Datastores/Vegetables_English

 

Corvino A., Romaniello R., Palumbo M., Ricci I., Cefola M., Pelosi S., Pace B. (2023). Image analysis to predict the maturity index of strawberries. Adv. Hort. Sci., 37(1): 8387.

 

Kader AA, 1999. Fruit maturity, ripening and quality relationships. Journal of Acta Horticulturae (ISHS). 52: 43-51.

 

Pedrozo, P., Lado, B., Moltini, A. I., Vicente, E., & Lado, J. (2024). Exploration of Strawberry Fruit Quality During Harvest Season Under a Semi-Forcing Culture with Plants Nursed Without Chilling. Plants (Basel, Switzerland), 13(21), 3052. https://doi.org/10.3390/plants13213052

 

Rabasco-Vílchez, L., Jiménez-Jiménez, F., Possas, A., Brunner, M., Fleck, C., & Pérez-Rodríguez, F. (2024). Evaluating the shelf life of strawberries using a portable Vis-NIR spectrophotometer and a Reflectance Quality Index (RQI). Postharvest Biology and Technology, 218, 113189.

 

Rahman, M. (2016). Determination of maturity indices of strawberry in Dhaka, Bangladesh. Bangladesh Journal of Botany, 45(5), 1127-1134.

 

Saeed, M. T., Anwar, R., Khan, A.S.,  et al. (2023). Impact of Maturity Stage on Postharvest Quality of Strawberries Cold Stored for Fresh Consumption. (2023). Plant Bulletin, 2(2), 142-150. https://doi.org/10.55627/pbulletin.002.02.0756

 

Salamat, R., Ghassemzadeh, H. R., Heris, S. S. S., & Hajilou, J. (2013). Determination of appropriate harvesting time for strawberry to enhance its flavor index and reduce bruising susceptibility.

 

Strum K, Koron D, and Stampar F,2003. The composition of fruit of different strawberry varieties depending on maturity stage. Food Chemistry. 83: 417-422

 

UGA. (2024, Feb 02). Strawberry Maturity Indices and Quality. Retrieved from https://extension.uga.edu/publications/detail.html?number=C1308&title=strawberry-maturity-indices-and-quality