Peach Harvest Maturity Indices for Better Yield

• Crop chronology and fruit physical and chemical parameters are useful as peach harvest maturity indices.
• Firmness, size, color, sugar, and acidity content are objective and quantifiable indices.
• External colors estimated with charts are subjective.
• None of the peach harvest maturity indices can be used alone, and additional indices are needed to estimate maturity accurately and fix harvest time.

As with other fruits, peach maturity at harvest significantly influences ripening potential, flavor development, storage time, susceptibility to physiological deterioration, mechanical damage, moisture loss, and diseases. Hence, ideal harvesting maturity indices are crucial to delivering peaches that satisfy consumer preference and have an extended storage life. Find out what quality and crop parameters are used by peach suppliers for manual as well as mechanized harvesting.

Peach Harvest Maturity

Harvest maturity indices are fruit quality or other crop parameters that help growers decide when to pick fruits to maximize yields, meet consumer satisfaction, and have a long storage life.

Peaches are climacteric fruits harvested when mature and can be ripened postharvest. Fruit harvested when immature will not develop sweetness, flavor, and softness. Over-mature fruits will soften rapidly, shortening their shelf-life.

The target market is essential when choosing the value of harvest indices. Peaches for wholesale or retail markets are harvested earlier than those meant for the farmers’ market or pick-your-own practice.

Peach is also a cold-sensitive fruit and suffers freezing damage during long, cold storage. The sensitivity to cold depends on the harvest’s maturity. The more mature the peach, the less sensitivity it has to cold. So, for optimum quality, fruits stored at near-freezing point temperature (NFTS) must be harvested at 80% maturity. Harvesting at this maturity level ensures optimum flavor, taste, firmness, and water content development and lowers ethylene and respiration rates to slow ripening.

Peach Fruit Maturity Indices

Several harvest maturity indices exist for peaches, such as color changes, fruit size, texture, and internal chemical composition. The best practice is to use multiple indices, as no single parameter can accurately determine peach harvest maturity.

When to start monitoring maturity?

Peach maturity will differ based on cultivars/rootstock, orchard blocks, and position on a tree. Hence, a grower should sample each cultivar and block separately to determine the harvest maturity index. Sampling should start four weeks before the estimated harvest time. Fruits must be analyzed once a week in the beginning and on alternate days close to the estimated harvest date.

Chronological Peach Harvest Maturity Indices

The simplest index uses crop chronology. The standard chronological index for peaches is days after full bloom (DAFB). For more precise indices, growers can estimate the DAFB for each block based on previous years’ recorded harvest maturity.

In the USA, the general DAFB recommended is 150-180 days, depending on cultivars. The DAFB can vary by 5-20 days based on environmental conditions.

In Korea, a DAFB of 74 to 77 is ideal for harvesting peach cultivar ‘Mihong.’

In India, the suggested harvest dates for three varieties are

• Last week of April for Florida Prince and Early Grande
• The second week of May for Shan-e-Punjab

Physical Peach Harvest Maturity Indices

The physical quality parameters used as the harvest maturity index for peaches are color, size, and firmness.

Color changes

Figure 1: “Side selection for color measurements, Jayasooriya et al. 2023. (Image credits: https://doi.org/10.3390/horticulturae9070730).

Peach color changes in peel and pulp are used as markers of maturity. The site of color measurement is essential, and color is checked at the fruit apex. Depending on the cultivar, the peel color changes from green to yellow or red. Changes in background and pulp color do not rely on exposure to sun and are more reliable indices than surface color.

Since color can vary from season to season, firmness must also be used as a maturity index. Peaches for distant markets are harvested when they have the targetted color but are still hard. For local consumption, growers wait till fruits are soft. Peel color estimation is nondestructive.

Surface color

The red surface color increases with exposure to sunlight and location on the canopy but reduces with higher temperatures and lack or excessive nutrient supply. Variations exist in cultivars, so surface peel color is not regarded as a reliable harvest maturity index in the USA, even though it is vital for marketing.

In the USA, peaches for wholesale must be firm and yellow to have extended storage time. For farmers’ markets, peaches are harvested when they have a red blush.

Background color

The ground or background color is not used alone as a maturity index, even though it is a common harvest maturity index for peaches in the USA. Color charts are the standard tools for this index.

Growers look for a background change from green to yellow for yellow flesh peaches and cream for white flesh peaches, as harvest index. (Dark yellow indicates ripeness, while orange peaches are over-ripe).

The background color is unsuitable for cultivars with solid red as it can mask the background color, as in  ‘Sunhigh.’

Chlorophyll content

Another harvest maturity index is precision instruments that nondestructively measure the reduction in chlorophyll during ripening. The DA meter estimates the Index of Absorbance Difference (IAD) by measuring chlorophyll-a in peels to give quantifiable objective data. However, the IAD cannot be used in isolation.

• Peaches ready for wholesale market must have an IAD of 0.4 and 0.9.
• For farmers’ markets, an IAD between 0 and 0.4 is good.

Size and shape

Fruit shape and cheek fullness in fully developed fruits are objective harvest maturity indices. However, it is unreliable as fruit size can differ by cultivars, rootstocks, nutrient status, crop load, and position in the canopy. Growers measure the diameter of a peach at its widest with hand-held calipers. It can be non-destructive if fruits are measured without picking.

In the USA, peaches >2.5 inches are needed for the farmers market.

Size and shape are used in addition to color as the peach harvest maturity index.

Flesh firmness

Firmness is peaches’ most popular physical harvest maturity index and gives objective data. However, it is a destructive method that involves judging the force needed to pierce the fruit on the equatorial sides with a  5/16-inch (8mm) wide plunger. The fruit has varying firmness, with the tip, suture, and shoulders being the weak points. Firmness is estimated on the fruit tip. Firmness varies according to varieties, fruit size, climatic conditions, and orchard management, so it cannot be used alone.

In the USA, flesh firmness recommended are as follows:

• Early season peaches are harvested at 9-10 lbs
• Late season peaches at firmness of 11-14 lbs
• 10-16 Ib for wholesale markets and long storage
• 2-4 Ib for ready-to-eat fruits for local farmers’ market

Table 1 shows more detailed firmness requirements at harvest, depending on the markets and transport distance in the USA.

Table 1: “Peach firmness range suggestions depending on marketing destination,” Extension UGA. (Credits: University of Georgia).

Physical parameters are traditional harvest maturity indices. Nowadays, internal chemical parameters are also used.

Chemical Peach Harvest Maturity Indices

The internal composition of fruits is used to determine harvest maturity. The parameters used are soluble solid contents (SSC), titrable acidity (TA), and taste. Water makes up 80-90% of the weight of stone fruits like peaches. The remaining 10-20% is dry matter, mainly made of soluble sugars, some insoluble sugars, cellulose, and lignin. Starch is absent in peaches at maturity. Since soluble sugars are the main components of dry matter in peaches, the two parameters are nearly identical at harvest, and only one is used as a harvest index, regardless of the measuring method.

Soluble solid contents (SSC)

The SSC increases as the peaches mature and ripen, and it is widely used as a harvest maturity index globally. However, SSC cannot be used alone as the harvest index, as it varies with cultivar, region, season, and position on the canopy.

Peaches with an SSC higher than 12% are required in the USA to meet consumer acceptance. Peach varieties are divided into three groups—low, medium, and high—depending on their SSC levels, as shown in Table 2. Low SSC fruits have 9-12%, medium fruits have 12-15%, and high SCC fruits have >15%.

Early-maturing peaches have a higher SSC than late-maturing fruits in Pakistan.

Table 2: “Peach titrable acidity (TA) and soluble solid content (SSC) groups,” Extension UGA. (Credits: University of Georgia).

Tritrable acidity

As peaches mature, titrable acidity (TA) reduces. Peaches are grouped into three groups based on TA levels —low, medium, and high, as shown in Table 2. TA will vary depending on the cultivar but not the season. However, TA is still not used as a harvest index by itself as it varies between 0.2% and over 1%, depending on cultivars.

Taste

Taste is estimated as the ratio of sugar to acidity, or SSC: TA. A balance is better than a high SSC for good taste. Due to increasing SSC levels, the ratio increases as fruits mature and ripen, and a higher ratio is optimum for consumer acceptance. The ratio varies with cultivars and years.

Near Infrared Spectroscopy

Nondestructive harvest maturity indices allow for sampling many fruits without reducing yield, gaining popularity among growers. Near-infrared spectroscopy (NIRs) is the standard technology among the non-destructive methods. It can measure SSC, TA, firmness, and internal and external color. The F-750 Produce Quality Meter from Felix Instruments Applied Food Sciences is one of the portable devices that can be used on farms. The instrument supports customizing the chemometric model for specific cultivars. The F-750 is easy to use and gives accurate results in real time. It can take the guesswork out of fixing harvest time to improve peach yield quality and ROI.

Sources

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Cai, Y. (2021, July 20). Determining Peach Fruit Maturity. Retrieved from https://extension.umd.edu/resource/determining-peach-fruit-maturity/

Jayasooriya, L.S.H., Shin, M.H., Wijethunga, W.M.U.D. …… Kim, J.G. Selection of a Proper Maturity Index for the Mechanical Harvesting of ‘Mihong’ Peach Fruit. Horticulturae, 9, 730. https://doi.org/10.3390/horticulturae9070730

Khan, A. S., Hussain, K., Shah, H. M. S., Malik, A. U., Anwar, R., Rehman, R. N. U., & Bakhsh, A. (2018). Cold storage influences postharvest chilling injury and quality of peach fruits. J. Hortic. Sci. Technol, 1, 28-34.

Mani, A., & Sarkar, T. (2018). Maturity indices of temperate fruits. Retrieved from https://www.researchgate.net/ profile/Arghya-Mani/publication/ 329266897_Maturity_indices_of_temperate_fruit_crops/links/60911be0458515d315f5ca6e/Maturity-indices-of-temperate-fruit-crops.pdf

Scalisi, A., & O’Connell, M.G. (2021). Relationships between Soluble Solids and Dry Matter in the Flesh of Stone Fruit at Harvest. Analytica, 2, 14-24. https://doi.org/10.3390/analytica2010002

UGA Extension. (n.d.). Peaches: Appropriate Harvest and Postharvest Handling. Retrieved from https://extension.uga.edu/publications/detail.html?number=B1555&title=peaches-appropriate-harvest-and-postharvest-handling

Zhang, B., Chen, X., Wang, N., Guo, S., Jiang, W., Yu, M., & Ma, R. (2022). Effects of Harvest Maturity on the Fruit Quality of Different Flesh-Type Peach Stored at Near-Freezing Point Temperature. Foods (Basel, Switzerland), 11(15), 2200. https://doi.org/10.3390/foods11152200