Rachel A. Itle1a, Rion T. Mooneyham1 and Savithri U. Nambeesan2
1Department of Horticulture, University of Georgia, 11109 Experiment Street Griffin, GA 30223, 2Department of Horticulture, University of Georgia, 1111 Miller Plant Science Building, Athens, GA 30602. a(ritle@uga.edu)
About this article:
This article, Postharvest Keeping Quality of Southern Highbush, Rabbiteye, and Northern Highbush Blueberry Cultivars in Cold Storage: Taste Traits and Health Benefits, is the second in a series on work comparing fruit quality traits of major commercial cultivars in southern highbush (SHB), rabbiteye (RE), and northern highbush (NHB) cultivars.
In this article:
Introduction and Objective
Georgia’s blueberry industry consists of southern highbush (SHB, Vaccinium corymbosum L. and V. darrowii Camp complex) and rabbiteye (RE, V. virgatum Aiton). There exists a subjective bias in the blueberry industry that SHB has higher fruit quality than RE. Their quality is also compared to northern highbush (NHB, Vaccinium corymbosum L.), which is perceived as superior. This often leads to reduced price points received by growers by third-party distributors and has even resulted in cultivar and/or type exclusion from some commercial purchasers. However, there is limited information that supports this preconceived perception at best. The objective of this study was to examine the physicochemical postharvest keeping quality of major SHB, RE, and NHB cultivars in commercial postharvest cold storage (4°C) and compare how each maintained fruit quality over time.
Fruit Collection and Juice Processing
Fresh fruit was collected from commercial packers from May to August in the 2018 and 2019 blueberry harvest seasons. In 2018, seven SHB (‘Camellia’, ‘Farthing’, ‘Keecrisp’, ‘Meadowlark’, ‘Legacy’ from Georgia and Michigan, ‘Star’, and ‘Suziblue’), five RE (‘Alapaha’, ‘Austin’, ‘Brightwell’, ‘Powderblue’, and ‘Vernon’) and five NHB (‘Bluecrop’, ‘Draper’, ‘Elliott’, ‘Liberty’, and ‘Nelson’), were collected for a total of seventeen cultivars. In 2019, seven SHB (‘Abundance’, ‘Camellia’, ‘Farthing’, ‘Meadowlark’, ‘Legacy’ from Georgia and Michigan, ‘Star’, and ‘Suziblue’), five RE (‘Alapaha’, ‘Brightwell’, ‘Powderblue’,’Premier’, and ‘Vernon’), and three NHB (‘Aurora’, ‘Elliott’, and ‘Liberty’) were collected for a total of fifteen cultivars. SHB and RE cultivars were collected from commercial packers in Georgia during both harvest seasons. NHB cultivars were collected from commercial packers in Michigan and Canada during the 2018 harvest season, and from Michigan and Indiana during the 2019 harvest season. All SHB and RE were placed into half pint clam shells, and coolers with ice and were transported to the UGA Griffin campus for evaluation. All NHB fruit was received via refrigerated truck. All fruit was harvested within a week of the fruit collection. Fruit were kept at 4°C (39°F) and fruit quality attributes were measured over a 30-day period at four timepoints during storage: 1) 3-4 days, 2) 10-11 days, 3) 20-21 days, and 4) 30-31 days after collection.
Fruit were stored in freezer bags and held frozen ( -15°C, 5°F) until processing. A purified juice sample was prepared for each cultivar and storage timepoint. Berry samples were weighed (four replications of a 55.0-56.0g) and were blended for approximately one minute until fruit were puréed (Ninja® Ultima Blender, Model BL810 30, Newton, MA). Fruit purée was then poured into tubes (50 mL Oak Ridge centrifuge tube, Thermo Scientific Nalgene, Waltham, MA) and spun to separate juice from pulp, seed and fruit skins [Centrifuge 5810 R, Eppendorf, Hamburg, Germany) for 20 minutes at 12,100 rpm, at 5° C]. Juice sample were collected and frozen until juice analyses.
Fruit Quality Measurements
The major fruit quality attributes for fresh fruits and vegetables are appearance, texture, taste including aroma and flavor attributes, and nutritional value (Barrett et al., 2010). For this portion of the study, attributes of taste including sugar content (soluble solids, i.e. °brix), acid content [total titratable acids (%TTA)], and sweet tart balance (°brix : %TTA) were measured. Health benefits (total monomeric anthocyanin content) and were also measured.
Sugar content
Soluble solid content is a very easily measured objective estimate of sugar content. It was developed in the 19th century and is a measure of the percentage of sugar, and other solids, present in solution. Often, it is taken as an estimate of sugar concentration due to the assumption that the majority, if not all, of the dissolved solids (soluble solids) present in the fruit juice is sugar.
To measure the concentration of soluble solids in the juice, a refractometer was used. °Brix is used as a quality measurement in numerous fruits (Ball, 2006) and vegetables (Kleinhenz and Bumgarner, 2012), in addition to food products such as wine, maple syrup and honey (Ball, 2006). Blueberry juice collected was thawed on benchtop at room temperature for approximately one hour, vortexed, and kept on ice. A small amount of juice (300 µL juice) sample was placed on a pocket refractometer (Pal-1, Atago, Saitama, Japan) to measure °Brix. For each cultivar at each of the four timepoints, four measurements were done [N=4; 4 reps x 2 subreps/rep].
Acid content
Citric acid occurs naturally in vegetables and in fruits such as citrus fruits, apples pears and peaches (Passam et al., 2011). It influences the tart, or sour, taste. Citric acid is also commercially produced and is used in a variety of industries including pharmaceutical, chemical, textile, beverage, and food. Some of its uses for food items include a preservative for ciders and wines, a flavor for products such as beverages, an emulsifier for products such as ice cream and cheese, and a pH adjuster for products such as jam and jelly (Apelblat, 2014). Citric acid also acts as a protective acid which prevents kidney stone formation and splits up stones as they are starting formation. The higher citric acid concentrations in one’s urine content, the greater protection the body has against the formation of new kidney stones (Ehlenfeldt et al., 1994).
To measure the overall citric acid content, a predominant acid in blueberry fruit (Mitcham et al., 1996), an autotitrator was used. The autotitrator is a machine that automatically processed titration and it measured the acids present in a fruit sample. The autotitrator read the initial pH of the blueberry sample, and added a basic buffer solution to the blueberry sample until the overall sample was at a desired endpoint (pH =8.2 is commonly used for fruit research). The amount of buffer that was used to raise the pH level was used in a formula to calculate the amount of acid present in the sample. The amount of acid in a sample was expressed as percent total titratable acids (%TTA). Blueberry juice collected was thawed on benchtop at room temperature for approximately one hour, vortexed, and kept on ice. Juice was added to distilled water (6mL into 50mL) and a buffer solution (0.1N NaOH) was added until the sample reached the ending point (pH =8.2). For each cultivar at each of the four timepoints, four measurements were done [N=4; 4 reps x 2 subreps/rep].
Sugar acid ratio
Sugar acid ratio, also known as sweet tart balance, is an important indicator of quality in fruit crops. This ratio has an influence on the perception of fruit flavor. Fruit that are higher in sugar content and lower in acid content may have a more desirable taste. Alternatively, fruit that are lower in sugar content and higher in acid content may taste too bitter (Wang et al, 2019).
To estimate the sugar acid ratio, the sugar content (°Brix) was divided by the acid content (%TTA) for each sample. For each cultivar at each of the four timepoints, four measurements were done [N=4; 4 reps x 2 subreps/rep].
Health benefits: Anthocyanin content
Anthocyanins are plant pigments that produce the blue, red, and purple colors. The role of anthocyanins in human health is still being studied. Recent research suggests that anthocyanins may: inhibit obesity from high fat diets; prevent elevation in glucose in the blood which is beneficial in the control of diabetes; reduce the risk of cardiovascular disease; enhance vision
functions including cataract reduction, increase blood flow to the retina in glaucoma, and lessen eye fatigue; and limit degeneration of brain functionality associated with aging (Tsuda, 2012).
To measure anthocyanin content, a spectrophotometer was used. The spectrophotometer passes light at specific wavelengths through a liquid sample and measures how much light was absorbed by the sample. To measure anthocyanin content, blueberry juice was added to two different acidic buffer solutions, each with a different pH level. The blueberry juice mixed with the buffer solutions and caused a color change reaction each solution. When the light beams at different wavelengths were passed through the sample, the spectrophotometer measured how much light was absorbed, and an estimate of total anthocyanin content was calculated. The amount of total anthocyanin content in each sample is expressed as a common anthocyanin pigment (mg/L cyanidin-3-glucoside equivalents), the most commonly occurring anthocyanin in nature (Lee et al., 2005). For each sample, blueberry juice was added to two different acidic buffer solutions, each with a different pH level. Samples were run on the spectrophotometer between 20 to 50 minutes for optimal color change reactions for an accurate anthocyanin calculation. For each cultivar at each of the four timepoints, four measurements were done [N=4; 4 reps x 2 subreps/rep].
For all fruit quality traits, measurements were taken for all cultivars at all four time points throughout 30 days in storage. For simplicity in this article and to review overall trends, results comparing overall blueberry type comparisons over 30 days in storage will be discussed. For this, cultivars within a type were averaged at each timepoint, and the average of a blueberry type (NHB, RE, or SHB) across timepoints were compared using the Tukey HSD test (P≤0.05; SAS v.9.4, SAS Institute, Cary, NC). To quantify the amount of change from beginning to end in cold storage, the percent change of each trait within a blueberry type was also calculated and will be compared below.
Results: How do these fruit quality traits change over time?
Sugar content
For both years, all three blueberry types did not show a significant change in sugar content (°Brix) over time (Figure 1). These results suggest that sugar content remains stable over fresh storage time and that cold storage does not negatively affect blueberry sweetness. In addition, it suggests if there are any changes to taste over time in cold storage, it is not due to changes in sugar for all blueberry types.
Acid content
NHB and RE remained stable over time for acid content (%TTA), with no change observed over 30 days in cold storage, for both years (Figure 2). The acidity of SHB changed over time in year one and showed a reduction over time year by 14%. No change was observed over time in year two. This indicates that fruit acidity, in large part, remains stable over time similar to fruit sugar content. This suggests that the acidity of the fruit that enters the cooler at the start of postharvest storage is the same acidity that leaves the cooler after 30 day, and fruit will not increase in tartness over time.
Sugar acid ratio
The only increase observed for sugar acid ratio (°Brix/%TTA) in blueberry fruit over time was in SHB in year one, with a 20% increase after 30 days in storage (Figure 3). However, in year two SHB did not significantly increase from the beginning to end of cold storage, and no changes over time were observed for NHB and RE for both years. These results suggest that sugar acid ratio, along with sugar content and acid content, doesn’t experience changes over time in the cooler regardless of blueberry type. This suggests that these taste attributes remain stable over fresh storage. In addition, any changes in taste of blueberry fruit are likely not attributed to changes in sugar content, acid content, or sugar acid ratio.
Anthocyanin content
For all blueberry types across both years, there was no significant change in anthocyanin content over 30 days in storage (Figure 4). This indicates that health benefits that may be attributed to anthocyanin content, in addition to fruit coloring, doesn’t change over time and remains stable. This suggests that the health benefits of blueberries may be just as beneficial after 30 days in storage as they are when they enter the cooler after harvest.
Lastly, the variation observed across years for all measured fruit quality traits may be attributed to many things. Differences in quality may be attributed to variations in fruit at harvest maturity (Sams, 1999), harvest timing (Lobos et al., 2014), handling processes (Bower, 2007), flowering time (Suzuki and Kawata, 2001), and amount and composition of fruit wax (bloom) (Lara et al., 2014). Changes in secondary cell wall structures, and enzymatic changes in the fruit cell wall (Chea et al., 2019) and other environmental factors that affect components of fruit texture may also contribute to overall postharvest keeping quality. It would be useful to determine the differences in these other traits among SHB, NHB, and RE blueberry types to further determine underlying structural differences to determine blueberry types best suited to endure long storage times.
Take Home Points
Results suggest:
- Sugar content: All three blueberry types (NHB, RE and SHB) for both years remained stable for sugar content, suggesting that cold storage time has no effect on the sweetness of blueberry fruit.
- Acid content: NHB and RE for both years showed no change in fruit acidity over cold storage. Only SHB showed a small decrease in year one, but remained stable in year two. This trend suggests that fruit acidity is not influenced by cold storage and fruit maintain their acidity over time.
- Sugar acid ratio: NHB and RE for both years did not change in their sweet tart balance over 30 days in storage. Only SHB had a small increase over time in year one. These results suggest that storage time does not influence the blueberry sweet tart balance.
- Anthocyanin content: For all blueberry types across both years, there was no significant change in anthocyanin content over 30 days in storage, which suggests that the health benefits of blueberries may be just as beneficial after 30 days in storage as they are when they enter the cooler after harvest.
- In a big picture summary: After 30 days in postharvest storage, all taste traits (sugar content, acid content, and sugar acid ratio) and health benefits associated with anthocyanin content remain stable over time with only minor changes noticed, if any. These results do not support the subjective bias that NHB has a higher quality than SHB and RE types.
Literature Cited
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Chea, S., D.J. Yu, J. Park, H.D. Oh, S.W. Chung, and H.J. Lee. 2019. Fruit softening correlates with enzymatic and compositional changes in fruit cell wall during ripening in ‘Bluecrop’ highbush blueberries. Sci. Hortic. 245: 163-170.
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Figures
Figure 1. Fruit sugar content(°brix) comparisons of southern highbush (SHB), rabbiteye (RE), and northern highbush (NHB) blueberry cultivars and types (purple overlay) across four timepoints [TP1 (3-4); TP2 (10-11); TP3 (20-21); and TP4 (30-31) days after collection] in fresh postharvest cold storage (4°C) in A) 2018 and in B) 2019. No differences were seen for average of all cultivars within a blueberry type (NHB, RE, or SHB) across timepoints using the Tukey HSD test (P≤0.05; SAS v.9.4, SAS Institute, Cary, NC).

Figure 2. Fruit acid content[% total titratable acids (%TTA)] comparisons of southern highbush (SHB), rabbiteye (RE), and northern highbush (NHB) blueberry cultivars and types (purple overlay) across four timepoints [TP1 (3-4); TP2 (10-11); TP3 (20-21); and TP4 (30-31) days after collection] in fresh postharvest cold storage (4°C) in A) 2018 and in B) 2019. Purple letters compare the average of all cultivars within a blueberry type (NHB, RE, or SHB) across timepoints using the Tukey HSD test (P≤0.05; SAS v.9.4, SAS Institute, Cary, NC).
![Figure 2. Fruit acid content [% total titratable acids (%TTA)] comparisons of southern highbush (SHB), rabbiteye (RE), and northern highbush (NHB) blueberry cultivars and types (purple overlay) across four timepoints [TP1 (3-4); TP2 (10-11); TP3 (20-21); and TP4 (30-31) days after collection] in fresh postharvest cold storage (4°C) in A) 2018 and in B) 2019. Purple letters compare the average of all cultivars within a blueberry type (NHB, RE, or SHB) across timepoints using the Tukey HSD test (P≤0.05; SAS v.9.4, SAS Institute, Cary, NC).](https://smallfruits.org/files/2025/01/blueberry-cold-storage-figure-two-e1737478359840.png)
Figure 3. Fruit sugar acid ratio [°brix / (% total titratable acids)] comparisons of southern highbush (SHB), rabbiteye (RE), and northern highbush (NHB) blueberry cultivars and types (purple overlay) across four timepoints [TP1 (3-4); TP2 (10-11); TP3 (20-21); and TP4 (30-31) days after collection] in fresh postharvest cold storage (4°C) in A) 2018 and in B) 2019. Purple letters compare the average of all cultivars within a blueberry type (NHB, RE, or SHB) across timepoints using the Tukey HSD test (P≤0.05; SAS v.9.4, SAS Institute, Cary, NC).

Figure 4. Fruit anthocyanin content (mg/L cyanidin-3-glucoside equivalents) comparisons of southern highbush (SHB), rabbiteye (RE), and northern highbush (NHB) blueberry cultivars and types (purple overlay) across four timepoints [TP1 (3-4); TP2 (10-11); TP3 (20-21); and TP4 (30-31) days after collection] in fresh postharvest cold storage (4°C) in A) 2018 and in B) 2019. No differences were seen for average of all cultivars within a blueberry type (NHB, RE, or SHB) across timepoints using the Tukey HSD test (P≤0.05; SAS v.9.4, SAS Institute, Cary, NC).
