Fresh blueberries are very susceptible to mechanical damage, which limits postharvest life and firmness. Softening and susceptibility of cultivars ‘Duke’ and ‘Brigitta’ to developing internal browning (IB) after mechanical impact and subsequent storage was evaluated during a two-year study (2011/12, 2012/13). On each season fruit were carefully hand-picked, segregated into soft (< 1.60 N), medium (1.61–1.80 N) and firm (1.81–2.00 N) categories, and then either were dropped (32 cm) onto a hard plastic surface or remained non-dropped. All fruit were kept under refrigerated storage (0°C and 85 – 88% RH) to assess firmness loss and IB after 7, 14, 21, 28 and 35 d. In general, regardless of cultivar or season, high variability in fruit firmness was observed within each commercial harvest, and significant differences in IB and softening rates were found. ‘Duke’ exhibited high softening rates, as well as high and significant r2 between firmness and IB, but little differences for dropped vs. non-dropped fruit. ‘Brigitta’, having lesser firmness rates, exhibited almost no relationships between firmness and IB (especially for non-dropped fruit), but marked differences between dropping treatments. Firmness loss and IB development were related to firmness at harvest, soft and firm fruit being the most and least damaged, respectively. Soft fruit were characterized by greater IB development during storage along with high soluble solids /acid ratio, which could be used together with firmness to estimate harvest date and storage potential of fruit. Results of this work suggest that the differences in fruit quality traits at harvest could be related to the time that fruit stay on the plant after turning blue, soft fruit being more advanced in maturity. Finally, the observed differences between segregated categories reinforce the importance of analyzing fruit condition for each sorted group separately.

Fresh fruit from northern highbush blueberry ( Vaccinium corymbosum ) and rabbiteye blueberry ( Vaccinium ashei ) are highly perishable, so reaching distant markets while maintaining superior quality and value is a challenge. Although firmness is one of the most critical traits of blueberries ( Vaccinium sp.), most of the industry relies on a subjective-tactile assessment or on the use of low-cost texture analyzers, whereas scientists tend to rely on the FirmTech II instrument. In the present study, the FirmTech II was evaluated as a texture analyzer and compared with tactile estimation, two other FirmTech II devices, and three relatively inexpensive durometers (Penefel, Durofel, and DM1600). Tests were run for fruit previously segregated by tactile (T) measurements into three classes of firmness: Soft-T, Moderate-T, and Firm-T; fruit were classified into instrument-based (I) categories of texture: Soft-I, Moderate-I, and Firm-I using the FirmTech II instrument. The level of coincidence between T and I assessments were higher in the soft (90.7% to 92.6%) and moderate (69.6% to 78.2%) classes compared with the firm class (51.6% to 61.4%). Among firmness categories, T and I assessments tended to agree; none of the Soft-T fruit were classed as Firm-I. In comparisons between equivalently calibrated FirmTech II devices, concordance always decreased as fruit firmness increased, indicating that more reproducible readings for a given instrument could be expected from softer fruit. Dual measurements on a single fruit for FirmTech II and a second device yielded variable, but significant correlation coefficients (Penefel: r ² = 0.61 to 0.67; Durofel: r ² = 0.48 to 0.61; DM1600: r ² = 0.08 to 0.49). The highest correlation existed between two FirmTech II devices ( r ² = 0.94 to 0.95). However, correlations between the FirmTech II and second devices among the three firmness classes yielded very low correlation coefficients (Penefel: r ² = 0.09 to 0.40; Durofel: r ² = 0.05 to 0.32; DM1600: r ² = 0.00 to 0.25; FirmTech II: 0.03 to 0.33), suggesting that although all instruments were suitable for evaluating across broad ranges of fruit firmness, they were all similarly unsuitable within a narrow firmness range (e.g., for all soft or all firm fruit). Given the subjectivity of the tactile measurement and the range of variability between the evaluated alternatives, both FirmTech II and Penefel performed better in soft fruit but not as well in moderate or firm fruit. Therefore, among the more economical durometer devices, Penefel could be used by the industry to discriminate soft fruit from moderately firm or firm fruit. The results highlight the relevance of studying the predictive capacity of a particular instrument and to understand the performance of that instrument within a particular range of firmness values.

Fresh blueberries are prone to softening and dehydration during postharvest, which limits their competitiveness when reaching the final markets. Commercial cultivars ‘Duke’ and ‘Brigitta’ exhibit contrasting softening patterns. Although ‘Duke’ berries usually show higher firmness levels at harvest as compared to ‘Brigitta’, they display higher softening and weight loss rates after cold storage. The aim of this study was to evaluate the physicochemical changes and modifications in cuticle composition of ‘Duke’ and ‘Brigitta’ blueberries across five developmental stages: green (G), 25 and 50% pink (25P, 50P), and 75 and 100% blue (75B, 100B), to determine those characters with the most influence on their postharvest behavior. For each developmental stage, maturity parameters, respiration, and ethylene production rates were assessed, and cuticular wax and cutin were analyzed. Principal component analysis (PCA) revealed that ‘Duke’ berries were characterized by higher respiration and ethylene production rates, while ‘Brigitta’ showed higher contents of oleanolic acid and α-amyrin over total waxes. The results suggest that larger surface/volume ratios and higher amounts of ursolic acid and lupeol in ripe fruit may underlie higher weight and firmness loss rates of ‘Duke’ berries as compared to ‘Brigitta’.