Why Dry Matter Matters In Apples

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Apples have long been known for their bright, bold, and beautiful appearance. Sometimes, though, consumers found these beautiful “typey” apples, such as Red Delicious, lacked in flavor and their preference shifted from looks alone to flavor and crunch. The adage “what’s inside matters most” could not be truer. Research is being conducted to help breeders and growers build the perfect apple by understanding its internal chemistry, specifically the dry matter content.

Why Dry Matter Matters
What exactly is dry matter? The simple answer is everything in the apple minus the water.

“Dry matter is the accumulated sugars, cell wall, proteins, and starch that are present in the apple. All of this is derived from the photosynthetic activity in the leaves and enters the fruit as sugar and is subsequently metabolized into storage (starch), enzymes (protein) and/or cell wall material. As the fruit grows and matures it accumulates dry matter,” says Peter Toivonen, a postharvest physiologist with Agriculture and Agri-Food Canada.

Dry matter gives you an insider’s view of what’s going on within the apple. Some researchers say accurate reads of dry matter content, or DMC, can help you gauge the ripening state of your apples, help you see if there is an issue with your crop, and can help you establish when to harvest your fruit. Understanding the nuances of dry matter can give you a leg up on your competition because there is a direct correlation between consumers’ preference and varieties with high DMC.

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“[Dry matter] measures the biological process as it happens on the tree — you can start to see early on if there’s a problem. For growers, they have information they can share with the supply chain,” says Roger Harker, principle scientist with Plant and Food Research in New Zealand. “There are opportunities to use [the information] more so you can understand well before harvest what the fruit is likely to be.”

How You Can Test For Dry Matter
Testing for dry matter content is not a new concept. The standard method has been to cut apples into quarters or thin slices, weigh the quarters and dry them in an oven for approximately 48 hours, or until weight loss is no longer detected. The final weight divided by the original fresh weight is the dry matter reading. This testing for dry matter is referred to as “destructive” methods.

While common, using destructive methods like these to assess dry matter can be time-consuming, and there is a wait to get a reading of the fruit’s maturity. The same is true of the starch pattern index, familiar to many growers, which has traditionally been used to track maturity.

“Apples are now picked on starch degradation. It’s a common index for harvesting. In apples, there is a scale of value that corresponds to starch degradation,” says Stefano Musacchi, associate professor of tree fruit physiology and management with Washington State University.

Both Felix Instruments and T.R. Turoni have handheld meters that use infrared technology to assess fruit in a nondestructive method. Felix Instrument’s F-750 Produce Quality Meter captures the range of Brix, color, acidity, and dry matter. T.R. Turoni’s DA meter measures the chlorophyll content in a fruit immediately below the skin, giving an index of the fruit’s ripening state.

“The DA meter can integrate the information the starch degradation provide to the growers. Something that can be very useful to better define the ripening stage of the fruit,” says Musacchi.

As fruit matures, it loses chlorophyll. The DA Meter “puts a number to this loss of chlorophyll,” says Jon Clements, Extension Educator, University of Massachusetts Amherst.

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A Fine-Tuned Approach To DMC
These handheld meters are relatively new to North America. Some growers and researchers are using the delta absorbance (DA) Meter on a trial basis. However, in Nova Scotia, John DeLong, a research scientist with Agriculture and Agri-Food Canada, has developed a protocol for the use of the DA Meter on Honeycrisp.

DeLong and his research team understood Honeycrisp’s finicky nature, and it’s predisposition to early and late- season storage disorders. If picked too early, Honeycrisp will get bitter pit. If picked too late, senescent breakdown will occur. In storage, the cultivar is prone to soft scald and soggy breakdown, or low temperature breakdown. Honeycrisp is also a multi-pick cultivar, which complicates pack-out. The team sought to identify an optimum harvest window to minimize these disorders by using the DA meter. After several years, they established parameters for its use.

Apples prone to bitter pit had readings higher than 0.59 or 0.6 , whereas apples prone to senescent breakdown had readings of 0.35-0.32 or lower.

“If you pick your fruit between the readings of 0.59 or 0.6 and 0.35, the fruit in that window should be the fruit in the optimum maturity zone, and we recommend those fruit for long-term storage,” DeLong says.

You still need to delay cool your Honeycrisp prior to storage. The DA Meter helps you assess and segregate your fruit, but if you neglect to care for the apples after harvest, the meter is much less useful . If your apples fall below the 0.35-0.32 reading, those over-ripe fruit should be the first to hit the marketplace as they are more likely to develop disorders when stored for longer periods.

DeLong believes the upper and lower harvest window boundaries established for Nova Scotia may be similar for some growing environments, but he stresses researchers need to develop their own models based on a similar method template.

Larry Lutz, tree fruit specialist for Scotian Gold, was one of the first growers in North America to have a DA Meter and use DeLong’s methods to compare results of his starch-iodine tests for maturity with the readings he was getting from the meter itself. The readings helped him establish a curve of numbers related to harvest. This was essential for Honeycrisp, where trying to assess background color was impossible.

“Honeycrisp gets so red that you can’t go on background color because you can’t see the background color. You don’t know what the maturity is. We rely on the DA Meter to tell us where we are because if you don’t pick it mature enough, then the flavor doesn’t develop,” he says.

Lutz also uses the DA Meter on SweeTango (Minneiska). He and Clements have tried the meter on McIntosh and Cortland, with inconsistent results. DeLong says he thinks Gala, Ambrosia, Golden Delicious, Sonya, and other high-value cultivars may make excellent candidates for DA Meter method studies.

Should You Buy A Produce Meter?
Before rushing out to buy one of these meters, keep in mind that you should have enough acres of to justify the purchase. The DA Meter runs around $4,000 (for pricing information on Felix Instrument’s F-750 Produce Quality Meter, visit FelixInstruments.com). Just as you’d consider the return on investment for a higher-density planting or a new piece of equipment, you should be sure this is right for you.

“If you have enough blocks of Honeycrisp or Minneiska, this can be a useful tool to help predict the correct harvest order, especially if some of your apples are going into CA. We have found on a 10-to-20-apple sample that the average reading is helpful to predict harvest timing, and the order to pick blocks. Over the course of the season correlates closely with starch test,” says Rod Farrow, owner of LaMont Fruit Farms in Waterport, NY.

For a packing house, it may provide some quantifiable numbers as fruit is being inspected.

“If a grower brings a lot of Honeycrisp in, and there’s a question of where it should go, [you can use the meter to decide if the apples go in] either in long-term storage or the immediate market. The average reading of 20 or 25 fruit may help them put the fruit in the appropriate storage spaces,” says DeLong.

Ease of use is the biggest selling point for Lutz.

“You can drive up in your pickup truck, stick it out the window, and check a half-dozen apples and never get out of your truck. When time is of the essence, and you’re extremely busy, you can cover a huge amount of ground. You can get a good feel for your different elevations, and different sides of the orchard very quickly,” he says.

However, Farrow cautions that data needs to be collected for several years, instituting a decision program around the meters.

“Verify the DA readings until you have developed the correct parameters for your area. It is not a silver bullet,” he says.

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What Else Impacts The Eating Quality Of An Apple?
Dry matter is directly linked to a consumer’s eating experience; however, dry matter is only part of the apple production equation. Successfully growing an apple requires a conscious approach from bloom to harvest. It’s a “case of getting all the ducks in a row,” says John Palmer of Plant and Food Research in New Zealand.

Light interception in the canopy, for example, can help in the production of dry matter. More light in a canopy means more photosynthesis, Musacchi says and “more photosynthesis means more sugar and soluble solids.”
Clements says, above all, you must manage the trees’ crop loads better if you really want to improve the quality of an apple.

“Honeycrisp in particular is a good example — over-cropped Honeycrisp is just not the same as a properly cropped Honeycrisp in terms of the quality of the fruit. It doesn’t develop the sugars; it doesn’t develop the colors,” he says.
Palmer says a focus on the eating quality of an apple will cause a grower to “think about some of the other techniques he is using, e.g., time of thinning, crop load, and leaf area per fruit, as all of these can influence the flow of carbohydrate into the fruit.”

Chris Willett, quality control and packing manager for Enza in North America, says proper harvest management is also crucial in delivering a high-quality product.

“Dry matter content can be used to determine the ‘potential’ of fruit quality; harvesting fruit at proper maturity is still absolutely critical,” he says.

The Future Of Fruit Production
Fruit size has been the target for growers too long, and dry matter is becoming more important, with its strong ties to eating quality. In the end, this focus on quality will help deliver a consistent product, Palmer says.

“Future fruit growing is going to be all about precision production, growing specific cultivars for specific markets to specific standards of size, visual appeal, and eating experience,” he says.
Musacchi agrees.

“Everything starts in the field and if we are able to provide that real homogeneous quality over the trees, you have a better product,” says Musacchi. “There is a lot of movement around the quality of the apple, and now those tools, the DA meter and the dry matter concentration can be really useful to assess different things, of course, but with a common goal to optimize quality.”

Ultimately, though, focusing on the dry matter of your apples will help ensure you have a place in the industry.

“It is a very crowded marketplace,” Palmer says. “You can lose your place by presenting apples of poor eating quality.”

 

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