Effects of Frozen Storage and Harvest Time on the Textural and Sensory Properties of Rabbiteye Blueberries (Vaccinium virgatum Aiton)

Abstract

Rabbiteye blueberries (V. virgatum Aiton), while praised for small stem scars, improved firmness over highbush cultivars, ease of mechanical harvesting, and superior keeping quality in storage, have also been reported to be have tougher skins after extended frozen. Growers and processors alike fear that significant increases in blueberry skin toughness following extended frozen storage could lead to a decrease in demand for the species. Furthermore, industry representative have been of the opinion that later harvests produce the toughest berries. The objectives of this study were to objectively determine by mechanical textural analysis if there is a change in the toughness of rabbiteye blueberry skins over time when frozen, and also if later harvests resulted in fruit with tougher skins before, and especially after frozen storage. In addition, the objective data were compared to sensory panel data to determine whether consumers could detect any changes in firmness and/or toughness, and if they found them to be unpalatable. In the first year four rabbiteye cultivars; Premier, Tifblue, Powderblue, and Ira, one highbush cultivar; Beaufort, and one rabbiteye - highbush hybrid variety NC 3465 were picked, individually quick frozen (IQF) and stored at -14ï‚° F for a total of 13 months. A second harvest of Premier, Powderblue and Tifblue were picked two weeks after the first, frozen and stored in the same manner. In the second year, cultivars Powderblue, Tifblue, Premier, and Beaufort were picked again, as well as Brightwell, another rabbiteye cultivar. Three harvests were picked of Powderblue, Tifblue, Beaufort and Brightwell, and two harvests of Premier were collected. All harvests and cultivars were simultaneously tested every three months by puncture and compression tests on a TA-XT Plus Texture Analyzer to measure skin toughness and berry firmness. Large, untrained sensory panels of approximately 75 persons each evaluated skin firmness and firmness liking every three months. Also in the second year, small samples from each harvest were separated at six months and stored for an additional seven months at 6ï‚° F to evaluate toughness at temperatures closer to consumer freezers. Results over two years did not reflect increased toughness over time, except in the small test for treatments at 6ï‚°F, which confirmed past research, and indicated a storage temperature threshold at which toughness increased significantly. In both years, most cultivars tested as being much firmer and as having tougher skins while fresh than after freezing. Results did not indicate later harvests result in increased toughness among rabbiteye cultivars. Mechanical textural analysis and sensory results both indicate cultivar effect to be much more significant than time. Furthermore, year-to-year differences due to environmental conditions, location and ripeness all had impact. In both years, Beaufort was found to have the least tough skins both by mechanical testing and sensory panels. In the first year, Powderblue had significantly tougher skins than all other cultivars, and in the second year, Brightwell was the toughest by a significant margin, whereas Powderblue was average in skin toughness.