Dr. Marlee Trandel-Hayse, Auburn University

Postharvest physiology is key to maintaining the shelf-life of small fruits and reducing food loss. Typically, research deals with the plant and fruit’s response to different technologies and applications that increase quality and delay senescence (decomposition). Fruit quality is a major component of postharvest physiology as it relates to consumer acceptance. Appearance, aroma, color, flavor, texture, and nutritional composition typically define fruit quality. Due to the healthful benefits, consumption of small fruits like strawberry, blueberry (Figure 1), blackberry and raspberry continues to steadily increase, placing pressure to deliver high-quality fruit with a longer shelf-life. As the Assistant Professor in Postharvest Physiology at Auburn University, it is my job to understand the quality issues of small fruits grown in Alabama and deliver high-quality fruits to our consumers.

Figure 1. Blueberry bushes cultivated for fruit production
Figure 1. Harvested blueberries for postharvest quality research

Postharvest physiology is all-encompassing as there are many preharvest factors that can impact postharvest quality, including plant genetics, cultivar selection, production techniques, maturity, harvest conditions, and packaging. Strategies for fruit after harvest include removal of field heat, storage temperatures and atmosphere, edible films/coating, and other techniques to reduce respiration or ethylene (e.g., the plant ripening hormone). A key issue with many of the small fruits grown in Alabama is their short shelf-life, exacerbated by generally warm to hot conditions during the harvest season. Blackberry and raspberry shelf-life can range from 2 to 10 days. If mishandled during postharvest, the fruit can have a 100% loss of salability within 48 hours of harvest. Part of my program will focus on these pertinent issues by teaming with growers and other university professors to preserve shelf-life.

The overarching goal of my program is to understand the impact of preharvest production, breeding and cultivation techniques on the postharvest quality of Alabama small fruits. My research will focus on shelf-life and texture to understand variability among cultivars and guide grower techniques to extend shelf-life. Fruit texture/firmness and variability of firmness can greatly affect fruit shelf-life. Typically, fruit with lower firmness have a higher rate of decomposition and shorter shelf-life. My program will focus on these firmness differences by addressing inner pulp quality. Microscopy work (example of micro-scan in Figure 2) can deliver important information regarding the type and size of cells laid within the fruit. Other aspects of inner quality include middle lamella separation and fiber, lignin and cell wall polysaccharide composition through shelf-life and storage. All of these can elucidate when and how fruit degradation is occurring.

Example of confocal microscopy work on internal flesh quality

Figure 2. Example of confocal microscopy work on internal flesh quality. Microscopy on small fruits can further elucidate cell structure, size and density which can relate to fruit texture and ripening events.  

General quality assessments of color (L*, a*, b*, C* and hue angle), soluble solids content (Brix), pH, titratable acidity, weight loss and tissue firmness will be conducted on small fruits. Postharvest instruments such as handheld brix meters and automatic titrimeters will be used to assess general quality changes in fruit (Figure 3). Performing these assessments in large variety trials will provide useful information regarding cultivar selections with increased postharvest quality and shelf-life. Other research includes determining the optimal storage conditions and application of postharvest treatments, such as ethylene oxidizers or blockers.

Hand-held Brix meter
Figure 3A. Postharvest equipment such as the hand-held Brix meter is important for quality data collection on small fruits.   
Automatic titrator which measures titratable acidity is important for quality data collection on small fruits
Figure 3B. Postharvest equipment such as the automatic titrator measures titratable acidity on small fruits. 

Another aspect of my program will address nutritional and bioactive content of small fruits. High nutritional quality and flavor are critically important for the acceptance of our consumers. Nutritional quality encompasses vitamins, minerals, fiber, as well as bioactive phytonutrients such as carotenoids, anthocyanin, flavonoids, non-flavonoids, and other secondary metabolites. Flavor is another critical component of postharvest quality and volatile analysis offers the ability to characterize flavor compounds.

Currently, two important postharvest projects focusing on small fruits are in the pipeline. I am eager to tackle the rabbiteye blueberry quality issues our Alabama growers are facing and I will be working with Dr. Sushan Ru, the rabbiteye blueberry breeder. I am also teaming with Drs. Jay Spiers and Edgar Vinson to address blackberry shelf-life and delay crop loss. My program will report data on these projects in a timely fashion to address grower needs on postharvest quality. In the interim, please feel free to reach out to me via email (mat0141@auburn.edu) or cell phone (334-734-6838) to ask any questions about my program. 

Marlee Trandel-Hayse
Auburn University