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Research was conducted to understand the effect of har-
vesting method and postharvest temperature on fruit quality of ‘Bright-
well’ and ‘Tifblue’ rabbiteye blueberries (Vaccinium ashei
Mass loss, firmness and fruit respiration were measured under refriger-
ated (1°C) and ambient (22°C) conditions for both machine harvested
(MH) and hand harvested (HH) berries of each cultivar. Few differences
were found between cultivars for the various postharvest quality param-
eters. Firmness of MH blueberries was diminished by an overall average
of 36.2% as compared to HH berries. MH berries placed at 22°C had a
mass loss rate of 2.6% per day as compared to 0.2% per day at 1°C dur-
ing the first two days of storage. Respiration rate of MH berries at ambient
temperature was 31.1% higher than HH berries. Refrigeration reduced
Abelardo Nunez-Barrios was a Visiting Scientist, Department of Horticulture, The
University of Georgia, 1109 Experiment Street, Griffin, GA 30223 during this re-search. Currently, he is Research Scientist with INIFAP in Mexico. D. Scott NeSmithis Professor, Department of Horticulture, The University of Georgia, 1109 ExperimentStreet, Griffin, GA 30223. Manjeet Chinnan is Professor, Department of Food Science,The University of Georgia, 1109 Experiment Street, Griffin, GA 30223. Stanley E.
Prussia is Professor, Department of Biological and Agricultural Engineering, The Uni-versity of Georgia, 1109 Experiment Street, Griffin, GA 30223.
Address correspondence to: D. Scott NeSmith at the above address.
2005 by The Haworth Press, Inc. All rights reserved.
Digital Object Identifier: 10.1300/J301v04n02_08
respiration rates by an overall average of 79%. Refrigerated HH blueber-ries had the best overall fruit quality after storage, and firmness mea-sures suggested that HH berries had an extended shelf-life of about oneweek as compared to MH berries. Thus, MH and HH fruit differ in theirpostharvest handling needs. Also, multiple quality measures are valu-able in more clearly assessing fruit storage life. [Article copies availablefor a fee from The Haworth Document Delivery Service: 1-800-HAWORTH.
E-mail address: <[email protected]> Website: HaworthPress.com>
2005 by The Haworth Press, Inc. All rights reserved.]
Fruit firmness, fruit mass loss, fruit respiration, mechan-
ical harvesting, berry quality, blueberry storage, Vaccinium
sp., V. ashei
The quality of fresh market blueberry (Vaccinium
sp.) fruit is a very
important issue for growers, marketers, and consumers. Preharvest fieldconditions, as well as harvesting methods and cultivars may all influ-ence the final product quality. Blueberries are susceptible to mechanicalinjuries and lose mass and firmness during the process of harvesting,handling, and storage (Austin and Williamson, 1977; Brown et al.,1996; Mainland et al., 1975; NeSmith et al., 2002). Miller and Smittle(1987) found differences between two rabbiteye blueberry (V. ashei
Reade) cultivars in response to harvest method. Their study revealedmass of hand-harvested (HH) ‘Climax’ berries decreased by 0.2% perweek, which was about half of the rate of mass loss of HH ‘Woodard’berries during storage at 3°C. Mass loss of machine-harvested (MH)‘Woodard’ berries was about double that of HH berries.
In general, MH berries are softer and have a higher incidence of
postharvest decay than HH berries (Austin and Williamson, 1977). San-ford et al. (1991) showed that mechanical damage of lowbush blueberries(V. angustifolium
) may decrease firmness by 15.3 to 32.1%. Recently,research with MH and HH rabbiteye blueberries has suggested that me-chanical damage during harvesting and grading accounts for a majorportion of the firmness loss of fruit, and immediate cooling followingharvest has only a slight influence on firmness retention (NeSmith et al.,2002). Cell wall weakening and loss of firmness at different tempera-tures are related to an increase in ethylene production, enzymatic activ-ity and higher respiration rates (Trinchero et al., 1999). Hence, themechanical effect of harvesting and higher temperatures may diminish
fruit quality by increasing fruit softening and mass deterioration as aconsequence of bruising, membrane damage and higher respirationrates (Huang and Bourne, 1983; Patten et al., 1988).
The trends and interactions among blueberry harvest methods, cul-
tivars, and temperatures as affecting overall fruit quality still need ex-ploration, especially giving attention to dynamics during storage andutilizing different postharvest quality assessments. The objective of thisresearch was to determine the effect of harvesting methods and post-harvest handling and storage temperature on fruit firmness, mass deteri-oration and fruit respiration of two rabbiteye blueberry cultivars.
MATERIALS AND METHODS
This research was conducted during June 2002 using mature (more
than 10 years old) ‘Tifblue’ and ‘Brightwell’ rabbiteye blueberriesgrown at the University of Georgia’s Blueberry Research Farm nearAlapaha, GA. Plants were grown in the field under non-irrigated condi-tions and experienced homogeneous cultural practices common forrabbiteye blueberries (Krewer et al., 1989). Harvesting was done usingboth machine harvesting (MH) and hand harvesting (HH) methods. Themechanical harvester (provided by B.E.I., Inc., Southaven, MI) was aB.E.I. model LBT pulled by a tractor. The harvester has variable speedbeater bars that were run at a slow to moderate operational speed. Grad-ing and sorting of the fruit was conducted on a packing line (also pro-vided by B.E.I.) having an air blower, a tilt belt, and a 3 m grading table.
HH berries were randomly picked from the bushes and were placed inbulk containers, and MH berries were bulked in containers during theharvesting operation. Following harvest, all berries from the two cultivarsand two harvest methods were graded and allocated to commercial“clamshell” containers, and were placed in a portable cooler for trans-porting to the laboratory. Once at the Postharvest Laboratory in Griffin,GA, blueberries were placed in 24-berry batches in specialized plasticclosed containers for postharvest quality assessment. Two temperatureregimes were established for this experiment using a walk-in refrigera-tor set a 1°C (±0.3°C) and a specialized plexiglass closet set at 22°C(±0.9°C).
Firmness and mass loss readings were taken for two sets of berries
during the 10 d period from 18 to 28 June 2002. Firmness readings weretaken using a Bioworks Firmtech II device (Timm et al., 1996). Berries
were set at room temperature (ca. 22°C) for 1 h prior to Firmtech read-ings. Calibration was done using small rubber balls and a compressionforce minimum of 50 g and a maximum of 150 g. Mass loss was mea-sured with a Mettler Toledo PR 403 balance, accurate to 0.001 g. Fruitrespiration was determined during four consecutive days at the begin-ning of the experiment. A specialized system of glass containers with avolume of 946.4 ml each were prepared for the study. A 750 g sample ofeach of the two blueberry cultivars were weighed and deposited in eachcontainer and were placed either under refrigerated (1°C) or laboratoryambient (22°C) conditions. Bottles with fruit samples inside weresealed and connected to an air-flow system that was shut down 4 hr be-fore taking the readings at ambient temperature and 12 hr before takingthe readings at 1°C. The time lags were determined from previous pre-liminary tests and allowed the CO to accumulate in enough quantity to
be measured in a gas chromatograph (GC). Two samples from eachcontainer were taken in a 20 ml head-space bottle for GC analysis.
Data from all measurements were subjected to statistical analyses to
test cultivar differences. When none were apparent, data were pooledfor overall analyses.
RESULTS AND DISCUSSION
As expected, harvest method overall significantly influenced fruit
firmness of both blueberry cultivars (Table 1). No significant differ-ences were observed between cultivars in firmness losses, althoughthere was a trend for ‘Brightwell’ to perform better. ‘Brightwell’ had adecrease in firmness of 1.6% and 5.7%, and ‘Tifblue’ diminished by4.7% and 15.0% at 1°C and 22°C, respectively. At ambient temperature(22°C), firmness of both HH-cultivars diminished by 32.0% to 35.1%during the 8 to 10 d storage period. Under refrigerated conditions (1°C)the decrease in firmness of HH berries of the cultivars was only 1.5 to4.7% over the same period of time. On average, MH berries had firm-ness readings that were 36.2% less than the HH ones (Figure 1). Themain effect of the MH treatments was observed at the moment of har-vest, and only a slight additional decrease in firmness was observedover the storage period under both refrigerated and ambient conditions.
It took the entire storage period for HH berries kept at ambient tempera-ture to reach the level of firmness of MH fruit kept at 1°C beginning atthe first day of harvest. Hence, hand harvesting of fruit extends shelf lifeby a week or more.
TABLE 1. Initial and postharvest storage firmness values of two rabbiteye blue-berry cultivars in response to harvest method and postharvest storage temper-ature. Harvest methods were hand harvest (HH) and mechanical harvest (MH).
y Mean separation within column by LSD test (P Յ 0.05).
FIGURE 1. Firmness values of machine harvested (MH) and hand harvested(HH) rabbiteye blueberry fruit over time when stored under ambient (22°C) andrefrigerated (1°C ) conditions. Data were taken with a FirmTech II firmnessreading device. Vertical bars represent standard error.
Several studies have shown that mechanical-harvested berries are of-
ten softer than hand harvested fruits (Austin and Williamson, 1977;Mainland et al., 1975; NeSmith et al., 2002). Miller and Smittle (1987)found that the amount of firmness lost due to mechanical-harvesterdamage of berries depended on cultivar, but averaged 32% less thanfirmness of hand-harvested berries. Other factors such as weather con-ditions, degree of ripeness, and even time of day can influence the ex-tent of damage caused by mechanical harvesting (Miller and Smittle,1987; Patten et al., 1988).
As for mass deterioration, no cultivar differences were noted. How-
ever, in a separate experiment, Deepak et al. (2003) showed that duringstorage these two cultivars had a similar pattern of mass deteriorationuntil temperature exceeded 20°C. After that, they found that ‘Tifblue’reached greater values of mass loss when compared to ‘Brightwell’. Forthe current study mass loss values of the two cultivars were averaged(Figure 2). Overall MH-berries under ambient conditions lost 2.6% oftheir mass per day shortly after harvest as compared to only 0.2% perday for MH-berries kept under refrigeration. This difference rapidly de-
FIGURE 2. Rate of mass loss for machine harvested (MH) and hand harvested(HH) rabbiteye blueberry fruit over time when stored under ambient (22°C) andrefrigerated (1°C ) conditions. Vertical bars represent standard error.
creased by 4 d after harvest, with a rate of mass loss of 0.7% per day and0.3% per day observed for the MH-berries at ambient and refrigeratedconditions, respectively. By 6 d after storage, there was little or no dif-ference in the rate of mass loss between harvest methods or storage con-ditions. Jackson et al. (1999) concluded that minimizing delays beforerefrigerated storage is one of the best options for maximizing fresh blue-berry quality. Our studies suggest this is especially important for reduc-ing rate of mass loss for MH berries. Mass loss of MH berries can besubstantially reduced if they are immediately placed under refrigeratedconditions. The urgency for getting HH fruit cooled seems to be lessthan that for MH fruit.
Fruit respiration of MH-berries was higher than HH-berries both un-
der ambient and refrigerated conditions (Figure 3). At 22°C, MH blue-berries reached respiration rates that were 31.1% higher than HHblueberries. Under refrigeration, MH fruits had 29.1% higher respira-tion rates than HH-berries. In general, refrigeration diminished respira-tion by 79.3% and by 78.5% for MH and HH-berries, respectively.
FIGURE 3. Rate of respiration of machine harvested (MH) and hand harvested(HH) rabbiteye blueberry fruit over time when stored under ambient (22°C) andrefrigerated (1°C ) conditions. Vertical bars represent standard error.
Boyette et al. (1993) showed that blueberries left at ambient tempera-ture after harvest rapidly loose fruit quality due to high respiration rates.
Mathooko (1996) suggested that enhancement of respiratory activity infruits may result from either an activation of enzymes at increasing tem-perature or as a response to fruit stresses such as that of bruising and me-chanical damage. Therefore, those berries that were subjected to greatermechanical damage in the current study had accelerated respiration.
In summary, our findings suggest that blueberry fruit quality varies
substantially depending on harvesting method and postharvest handlingtemperature, however, the method used to assess quality needs to beconsidered. Current recommendations to farmers are to cool berries asrapidly as possible after harvest (Thomaston et al., 2002; Boyette et al.,1993) and certainly this will decrease mass loss and respiration rates asshown in the current study, especially for MH fruit. However, refriger-ating MH berries will only give a slight gain of fruit firmness (about9%) as compared to MH berries left at ambient temperature. Likewise,some delay in cooling appears to be possible for HH berries without suf-fering severe quality losses. Therefore, an economic evaluation is sug-gested in terms of the benefit/cost of refrigeration and use of labor asrelated to the changes in fruit quality of MH and HH blueberries. Also,those quality measures that best reflect consumer appeal should be usedin evaluating berry quality.
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