Can raspberries be picked pink for fresh markets?

By Penelope Perkins-Veazie, Plants for Human HealthInstitute, North Carolina State University and Gina Fernandez, Department ofHorticultural Science NC State University

Raspberries are the most perishable of the temperate fruitcrops. If you set them on your kitchen counter, you can watch the mold growwithin 24 hours. This fruit’s delicate nature is due to its fragile structure,where drupelets are connected together by only a few trichomes (fruit hairs),no cuticle is present, and gray mold (Botrytis cinerea) can set up spores duringbloom and produce fuzzy gray fruit as the berries are ripening.

While raspberry fruit mostly produce ethylene from the fruitcalyx (the part of the fruit that remains on the plant), there is a smallamount of ethylene, the fruit ripening hormone, present in many varieties. Thisactually can pose an advantage for fruit growers producing raspberries in thewarmer parts of the season. Fruit at the pink or even pink-yellow stage will oftendetach from the calyx with minimal tugging.

We initiated a small test in 2010 to investigate the abilityof raspberries to attain full ripeness if harvested unripe. These fruit wereharvested in August and September from plants grown in high tunnels at theUpper Mountain Research Station, Laurel Springs, NC. Temperatures within thetunnels were above 85°F for approximately four hours per day. Unripe and riperaspberries were picked at weekly intervals for the tests, over a three-weekperiod, and one to two clamshells per cultivar and ripeness were used for thestudy. 

Raspberries were picked into halfpint clamshells and transported at 5°Cin refrigerated ice chests (Kooltron) to Kannapolis, and held at 39 °F for sixdays. Subsamples were removed at day 0 to check firmness, color, sugars, andacidity. Subjective ratings were taken after storage by checking each berry forsoftness, leak, and mold. The overall color of the fruit within the clamshellwas determined subjectively as 0 (light red) to 3 (dark purple red). Percentsaleable fruit was determined by using the relationship of color to percent(where rating of 0 was 100% saleable to 3 was 0% saleable).

Surprisingly, even fruit picked considerably unripe(yellow-pink) achieved full color, soluble solids content, acidity, and flavor(tasted at random) after six days storage (Table 1). The biggest disadvantageof picking unripe berries was a depression in berry size of 4% to 20%,depending on variety and relative ripeness at harvest. What was clear from ratingswas that fruit picked pink was much firmer and less leaky than berries pickedat the normal commercial fresh market ripe stage (Table 2). The amount of moldyberries was slight (less than 10%), due to a rigorous fungicide spray programand the protective effect of the tunnels from moisture and wind.

We hoped that berries varieties known to turn dark red afterstorage, such as Joan J, would be less fully red if picked pink prior tostorage. In fact, we found that color could not be slowed enough, with fruitreaching full color as soon as 2 days at 39° F after harvest. Figure 1illustrates the change in color of ‘Culivar’ in ripe and unripe berries at 0, 5and 10 days after harvest.

Flavonoids are compounds are compounds  that are associated with health benefits,and higher levels in fruit are good. Flavonoids in raspberry include theanthocyanins that give raspberries much of their red color, along with othercolorless phenolic compounds. In raspberries picked before full ripeness, flavonoidcontent was decreased by 5-15% after storage. The slight loss in flavonoids inthe less ripe fruit was madeup in the better appearance and firmness of theraspberries.

Harvesting raspberries at the pink stage is possible. We didnot observe significant problems with composition and flavor, and early pickingimproves the number of marketable fruit. However, harvesting less ripe fruit islikely dependent on air temperature (detaching raspberries is difficult in coolweather), and will require more attention and training of pickers duringharvest than pulling off fully ripe berries. Although we did not determineoptimal temperatures for picking unripe berries in this study, the ability ofraspberries to fully color up and soften may depend greatly on having a productionenvironment where temperatures are at 75° F for at least four hours.

Table 1.  Comparison of raspberry fruit harvested unripe (pink) or ripe (red)
before and after storage at 4C, averaged for Joan J, Nantahala, Caroline
Variant	Days	Unripe	Ripe	Mean
Total phenolics	0	2858	2866	2862
(mg/kg gallic acid equivalents)	6	3090	3144	3117*
Total anthocyanin	0	508	530	519
(mg/kg cyan-3-glucoside equivalents)	6	510	589	550*
FRAP (Ferric reducing antioxidant potential)	0	28.6	26.8	27.7
(umol/g trolox equivalents)	6	28.5	28.8	28.6
Soluble solids content (%)	0	11.2	10.9	11.1
	6	11.9	11.7	11.8
Titratable acidity (%)	0	1.23	1.26	1.24
	6	1.05*	1.19*	1.12*
Means separated within column and days 0,6 using student's t-test, P<5%.

Table 2.  Comparison of raspberries picked unripe (pink) or ripe (red) after storage at 4C for 6 days
	%Leaky berries		%Soft		%Saleable	color
Variety	Unripe	Ripe	Unripe	Ripe	Unripe	Ripe
Autumn Britten	1a	42b	48ab	93a	43b	7b
Caroline	8a	19a	61a	86ab	47b	33ab
Nantahala	2a	37b	38b	75b	67a	47a
Mean	3a	33*	49	82*	52	29*
Means separated within column among cultivars, by letter (P<5%) using REGWQ.

The original version of this article (including photos) appears in Autumn 2011 issue of "The Bramble."  To access this article, you must be a member of the North American Raspberry and Blackberry Association. To become a member to: http://www.raspberryblackberry.com/index.cfm and click on Membership in the left purple panel. 

New Publication

Dr. Ramón Molina-Bravo, was a PhD student that worked with myself and Dr. Bryon Sosinski at NCSU. Dr. Molina-Bravo just published an article that details a study that he conducted as part of his research. In a nutshell, he was able to identify several plants in a population of seedlings that had higher chlorophyll fluorescence, a trait that is associated with heat tolerance. We are using those individuals in our breeding program to see if they will survive the heat in additional locations and we will be using them in crosses in the near future.  Congrats Ramon! Here is a link to that article. doi:10.1016/j.scienta.2011.07.022

Heat stress in raspberries, part 2

So, many of you are probably thinking "Why would anyone try to grow raspberries in a hot, humid environment like North Carolina?" Well, you are not the only one that has had that thought. There are several points that I want to make in regard to this idea.

First, North Carolina has multiple environments. The three primary regions are the Coastal Plain, Piedmont and the Mountains.  So, within the state we have a range of elevations from sea level to over 3000 ft (ca 1000 m). This allows us to grow our plants in a wide range of environments.  In the summer, all regions are hot, some are just not as hot, with high temperatures only in the 80's. However, this range of climates allows some growers to produce fruit earlier in the season and some can go later in the season. We are not trying to produce raspberries in the coastal plain in mid July. That is just too hot for this delicate fruit.

Second, in warm conditions, fruit set is often a problem. However, in our screening process, we find that some of our test plants that are able to survive the heat and have flowers that can produce fruit.  And it is this last group that we choose to select and propagate for further observations. 

Third, even if a raspberry variety can survive in the hotter areas, we find that fruit size improves when we move it to our more moderate locations (see example of fruit size above). The two pictures are fruit from the same selection planted in two different places. The hotter location is SH (the Sandhills) and Sal (Salisbury) is only 90 miles away. 

Lastly, we are finding, thanks to Dr. Penny Perkins-Veazie, that even though some of the newer varieties look good at harvest, once we pick them they go downhill rapidly. Amazingly, the test plants from our program always seem to do better. 

The role of the environment on the performance of a variety is huge. In fact plant breeders spend alot of time evaluating GXE (Genotype X Environment) interactions. We know that the environmental influence on raspberry performance is significant and that our hot and humid climate enables us to screen in an environment that is not ideal for most raspberry varieties. But we are trying and think we are making good progress.

Heat stress in raspberries, part 1

Severe leaf cupping

Moderate leaf cupping

Today in North Carolina, the temperatures are expected to reach 99F (37C). This type of heat is extremely stressful for raspberry plants and very often they will not live for more than a year or two under these conditions. However, we have found that by screening plants in this type of environment, we are able to find some plants that are somewhat tolerant of heat.

Above are pictures of 2 plants in a seedling population taken on the same day last week when it was hot like it is today. The plants are from the same parents, and are in fact, adjacent to one in another in the field at the Sandhills Research Station in Jackson Springs, NC.  The leaves on the first plant are cupped upward, a classic sign of heat stress, while the second plant has leaves that are only moderately cupped. Most of the plants in this population had severely cupped leaves. But a few did not and those are the ones that we will keep, and test in future trials.

Award Winning Student!

Christine Bradish, a MS candidate just returned from the Berry Health Symposium #berryhealth. She won 1st place in the poster competition.  Christine is working with Drs. Penny Perkins, Wei Jei and myself and is in the final stages of her MS degree at NC State University.


Christine looked for flavonoids in red raspberry that are known to be good for you.  She used metabolite-profiling to qualify, quantify, and compare major flavonoid compounds in primocane-fruiting red raspberry cultivars grown at three locations with varying elevation and average temperatures in North Carolina. 


She found:
 •There was significant qualitative and quantitative differences in the metabolite profiles, due to variation in cultivar, location, and environmental factors. (=not all raspberries are the same in terms of health benefits)

•Plants exposed to longer durations of heat stress (over 85°F) had higher total phenolics measurements and antioxidant capacity due to greater production of flavonoid secondary metabolites. (=stress may increase the good compounds in berries)

Implications: 

•Utilization of metabolite profiles, such as the ones in this study, could help breeding programs identify key metabolites contributing to antioxidant properties, and define the genotype-by-environment interactions on them. 

•This technology may be useful for the development of nutritionally enhanced varieties, and further tailoring for functional foods.

The link to the proceedings is below. Her abstract is on page 61.
http://www.berryhealth.org/Information/2011_preproceedings_sm.pdf