Part 1: Fruit Firmness
Authors: Rion T. Mooneyham, Savithri U. Nambeesan, and Rachel A. Itle
This article is the first of a series from my master’s research. Overall, this work is the examination and comparison of fruit quality traits in southern highbush (SHB), rabbiteye (RE), and northern highbush (NHB) cultivars in commercial postharvest cold storage across two years. Our main objective is to provide objective information about the postharvest keeping quality without the use of postharvest treatments for the cultivars with a large commercial presence in Georgia and in the overall blueberry market. This study is aimed at identifying cultivars that are able to maintain their quality characteristics over fresh storage, and to objectively examine differences between cultivars and blueberry types.
In this article, we discuss the differences and changes in fruit firmness within and between these three blueberry types over two years.
Fruit Collection
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 eighteen 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 was 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 and fruit firmness was 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. To keep this article concise, only the first and last timepoints are shown in the results. These will be referred to as “at harvest” and “30 days in storage”, respectively.
Fruit Firmness Determination
Fresh fruit samples of 50.0-51.0g fruit were used to measure fruit firmness using a TMS-Pro Texture Analyzer. We compared fruit firmness values between cultivars at harvest and after 30 days in storage. This comparison was also performed between SHB, RE, and NHB overall. We also determined the percent change of firmness values between at harvest and after 30 days in storage.
Results
Fruit firmness at harvest and after 30 days in storage
In 2018, fruit firmness across types within a timepoint (at harvest and after 30 days in storage) were compared (Figure 1, Table 1). SHB were the highest for fruit firmness followed by NHB and then by RE for at harvest and after 30 days in storage. These results are contrary to subjective biases that RE have firmer fruit than highbush types. In 2019, RE and NHB were the highest fruit firmness at harvest and after 30 days in storage (Figure 2, Table 2). Overall, these results suggest that fruit firmness across types is variable across years and ranking of blueberry types for firmness. There are likely other factors (pre- and post-harvest) are likely influencing fruit firmness than blueberry type alone.
Fruit firmness changes over time
Overall, in both harvest seasons, the majority of blueberry cultivars experienced significant increases in fruit firmness during the 30-day storage period (Table 1, Table 2). The only exceptions to an increase in fruit firmness over time in storage for both years were in the 2018 season. NHB cultivars (‘Bluecrop’ and ‘Nelson’) decreased in fruit firmness, and ‘Draper’ did not change in firmness over time.
To quantify the amount of change from harvest to 30 days after storage, percent change was calculated. In 2018, when examining blueberry types overall, RE was the only type that was significantly different from harvest to 30 days after storage with a 23% increase in firmness over time. This indicated a loss of fruit quality since the increase in fruit firmness may be due to water loss during storage time in the cooler. However, there was no significant difference for firmness over time for SHB or NHB types overall, indicating that highbush types overall maintained fruit firmness over storage time in the cooler.
In 2019, all three types increased in firmness over time in the cooler. SHB maintained quality in storage the best with the lowest increase in fruit firmness (25%). RE were intermediate in firmness loss over time, with a 31% increase over 30 days in storage. NHB lost the most quality for fruit firmness over time with a 33% increase in fruit firmness over time. The results suggest that SHB maintain their quality in terms of fruit firmness the best over time in the cooler, followed by RE and then by NHB. Overall for both years, these results suggest there is variability for fruit firmness maintenance over storage time across years.
The variation observed across years may be attributed to many things. Differences in texture may be attributed to variations in fruit at harvest maturity (1), harvest timing (2), handling processes (3), flowering time (4), and amount and composition of fruit wax (bloom) (5). Changes in secondary cell wall structures, and enzymatic changes in the fruit cell wall (6) 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
- In 2018, SHB were the highest for fruit firmness followed by NHB and then by RE for at harvest and after 30 days in storage. In 2019, RE and NHB were the highest fruit firmness at harvest and after 30 days in storage. These results are contrary to subjective biases that RE have firmer fruit than highbush types.
- Overall, in both harvest seasons, the majority of blueberry cultivars experienced significant increases in fruit firmness during the 30-day cold storage period.
- In 2018, only RE increased in firmness over time (23%), indicating a likely a loss of fruit quality. SHB or NHB did not increase in fruit firmness over storage time in the cooler, indicating maintenance of fruit quality.
- In 2019, all three types increased in firmness over time in the cooler. SHB maintained quality in storage the best with the lowest increase in fruit firmness (25%). RE were intermediate in firmness loss over time (31%), and NHB lost the most quality for fruit firmness over time (33%). This suggests that SHB maintain their quality in terms of fruit firmness the best over time in the cooler, followed by RE and then by NHB.
- There is variability for fruit firmness maintenance over storage time across years. There are likely other factors (pre- and post-harvest) are likely influencing fruit firmness than blueberry type alone and need to be further investigated.
Literature Cited
- Sams, C.E..1999. Preharvest factors affecting postharvest texture. Post Harv Bio Technol. 15(3): 249-254.
- Lobos, G.A., P. Callow, and J.F. Hancock. 2014. The effect of delaying harvest date on fruit quality and storage of late highbush blueberry cultivars (Vaccinium corymbosum L.). Post Harv Bio Technol. 87:133-139.
- Bower, C., 2007. Postharvest handling, storage, and treatment of fresh market berries. FoodSci Technol. 168: 261.
- Suzuki, A. and N. Kawata. 2001. Relationship between anthesis and harvest date in highbush blueberry. J JPN SOC HORTIC SCI. 70:60-62.
- Lara, I., B. Belge, and L.F. Goulao. 2014. The fruit cuticle as a modulator of postharvest quality. Post Harv Bio Technol. 87: 103-112.
- 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.
