Graduated Controlled Atmosphere: A Novel Approach to Increase "Duke" Blueberry Storage Life

Effect of Short-Term High-CO2 Treatments on the Quality of Highbush and Rabbiteye Blueberries During Cold Storage

The global demand for blueberries has increased due to their health benefits, but postharvest losses, particularly firmness loss and decay, present significant challenges. This study evaluated the effects of high CO2 concentrations (15% and 20%) applied for 3 d at 1.0 °C on highbush (cv. 'Duke') and rabbiteye (cv. 'Ochlockonee') blueberries, with a focus on quality maintenance during cold storage. The quality parameters evaluated included titratable acidity, pH, total soluble solids, weight loss, and decay. The effect of gaseous treatments on firmness was analyzed using mechanical parameters and the expression of genes related to cell wall integrity (XTH23, PL8, PG, PM3, EXP4, and VcGH5). Treatment efficacy varied between species. High CO2 levels reduced decay in both cultivars, but only the highbush cultivar ('Duke') showed improvements in firmness. In 'Duke', CO2 treatments affected the expression of XTH23, PL8, and GH5, while the role of PG and PME in maintaining firmness was minimal, with no significant differences between treatments. In 'Ochlockonee', CO2 effectively reduced weight loss but did not improve firmness. In conclusion, these results highlight the need for tailored postharvest strategies for different blueberry cultivars and suggest that short-term high CO2 treatments may effectively prolong the postharvest life of highbush blueberries.

Virtual Cold Chain Method with Comprehensive Evaluation to Reveal the Effects of Temperature Abuse on Blueberry Quality

Blueberry is one of the most perishable fruits, and the postharvest supply chain environment temperature has great effects on fruit quality. In order to determine the critical steps referring to non-optimal conditions and the key quality indexes in response to temperature along the cold chain, 15 time-temperature scenarios were conducted simultaneously for the storage of blueberry fruits and 17 quality attributes were determined. The results indicated that different cold chain steps under abusing temperatures significantly affected blueberry qualities. Based on the comprehensive evaluation analysis, storage in farm at 8 °C and a 10 h delay in precooling were found to be the critical steps that had strong impacts on the qualities of blueberries, affecting 33 and 31 total qualities during shelf life, respectively. Furthermore, seven effective indexes, including the sensory scores, weight loss, decay rate, content of titratable acid, malondialdehyde, respiratory rate and antioxidant activities, were confirmed to be the key quality attributes influenced by the cold chain temperature. It is necessary to circulate postharvest blueberry fruits under relatively isothermal and optimum temperatures throughout the cold chain to maintain the preferred quality, especially at the initial stage of the supply chain.

Use of Heat-Shock and Edible Coating to Improve the Postharvest Preservation of Blueberries

The quality of blueberry fruit is easily altered after harvest. We investigated the regulatory mechanism of heat-shock (postharvest treatment) and edible coating (preharvest treatment) on the post-harvest physiological quality of blueberry from the perspective of physiological, biochemical and organoleptic characteristics. In our research, the optimal TKL concentration and the appropriate range of heat-shock temperatures were first screened based on actual application results, and then a combination of heat-shock temperature and TKL coating with significant differences in preservation effects was selected to investigate the effects of different heat-shock temperatures and TKL60 composite coating on post-harvest quality and volatile compound concentration of blueberries under refrigerated conditions. Our results showed that TKL with 60 mg/L thymol can retard the development of the degree of membrane lipid peroxidation and effectively reduce the incidence of fruit decay and the severity of blueberries infected with major pathogens at 25 °C. Meanwhile, heat-shock treatments were effective in maintaining the quality of blueberries, with a certain advantage from 45 °C to 65 °C after 8 d of storage at ambient temperature, but these treated groups were slightly inferior to TKL60 groups for fresh-keeping effect. Remarkably, the combination of heat-shock treatment and edible coating application could extend the shelf life of blueberries by 7-14 d compared to the results obtained with coating alone under low temperature storage. Specifically, heat treatment at 45 °C for 60 min after TKL60 coating (HT2) retarded the decrease in the levels of ascorbic acid, total anthocyanin, total acid and soluble solids. Gas chromatography-mass spectrometry hierarchical clustering analysis showed that this treatment also improved the aroma of the fruit, which maintained a certain similarity with that of fresh blueberries after 14 d. Principal component analysis (PCA) of the results of the evaluations carried out using an electronic nose (E-nose) and electronic tongue (E-tongue) showed that blueberries of the HT2 treated group did not show a large placement change of the PC1 distribution area from that of the fresh and blank control group. Accordingly, the combination of coating with heat-shock treatment can effectively improve the post-harvest quality and aroma compound concentration of blueberries, showing good application potential in storage and preservation of fresh fruits such as blueberries.

High CO2 Reduces Spoilage Caused by Botrytis cinerea in Strawberry Without Impairing Fruit Quality

High CO₂ (> 20 kPa) conditions are beneficial for suppressing spoilage caused by Botrytis cinerea in strawberry fruit; however, these conditions are often accompanied by discoloration, off-flavors, and faster softening. Stepwise increments of CO₂ concentrations have been proposed to alleviate injuries in fruits caused by high CO₂. In this study, we investigated whether stepwise increments of CO₂, up to 30 kPa and under a reduced O₂ concentration, are beneficial for reducing fungal spoilage without inducing CO₂ injury symptoms in strawberry fruit. Based on recommended settings (5-10 kPa O₂ with 15-20 kPa CO₂), we first selected optimal O₂ and CO₂ concentrations that best-reduced spoilage caused by B. cinerea in red ripe "Sonsation" strawberry fruit. We found that higher O₂ (10 kPa) and CO₂ (20 kPa) concentrations were most beneficial for prolonging strawberry fruit shelf life. Subsequently, we studied the performance of red ripe "Arabella" strawberry fruit stored at 5°C under different controlled atmosphere (CA) conditions (10 kPa O₂ with either 0, 20, or 30 kPa CO₂). The CO₂ concentrations were achieved either within 8 h or in a stepwise manner within the first 4 days of storage. As a control, 21 kPa O₂ and 0 kPa CO₂ were used. Following storage for up to 11 days, the spoilage incidence was assessed at 12°C for 5 days. The application of high CO₂ (20 and 30 kPa) combined with 10 kPa O₂ greatly suppressed fruit spoilage during storage and subsequent shelf life. High CO₂ suppressed respiration as well as maintained a higher pH and firmness in treated fruit. The level of total sugars did not change, but during storage, a substantial part of sucrose was converted into glucose and fructose, especially under high CO₂ conditions. High CO₂ did not affect ascorbic acid and anthocyanin levels. The stepwise increments of CO₂ did not result in beneficial effects compared to the static application of high CO₂. Our results show that "Arabella" strawberry fruit are highly tolerant to elevated CO₂ and can be stored under 30 kPa CO₂ to prolong the shelf life.

Effect of Chitosan/Nano-TiO2 Composite Coating on the Postharvest Quality of Blueberry Fruit

Blueberries are a rich source of health-promoting compounds such as vitamins and anthocyanins and show a high antioxidant capacity. Thus, considerable commercial and scientific interest exists in prolonging its postharvest life to meet the year-round demand for this fruit. In this investigation, the effect of a chitosan-based edible coating, as well as a chitosan-based edible coating containing nanosized titanium dioxide particles (CTS-TiO2), on the postharvest quality of blueberry fruit quality was evaluated during storage at 0 °C. The blueberries were treated with a chitosan coating (CTS) and a CTS-TiO2 composite, respectively. The most suitable chitosan and nano-TiO2 fraction concentrations to be incorporated in the coating formulation were prepared based on the wettability of the corresponding coating solutions. Changes in firmness, total soluble solids (TSS), titratable acidity (TA), ascorbic acid (VC), malondialdehyde (MDA), polyphenol oxidase (PPO), and peroxidase (POD) activities, anthocyanins, flavonoids, total phenolic content, and microbiological analysis were measured and compared. This combined treatment prevented product corruption. Compared with CTS, the CTS-TiO2 composite coating application effectively slowed down the decrease in firmness, TSS, VC, and TA in the blueberries. Additionally, changes in the total polyphenol, anthocyanin, and flavonoid contents and the antioxidant capacity of CTS-TiO2 composite coating blueberry fruits were delayed. Therefore, these results indicated that the chitosan/nano-TiO2 composite coating could maintain the nutrient composition of blueberries while playing a significant role in preserving the quality of fruit at 0 °C.

Effect of Different Modified Atmosphere Packaging on the Quality of Mulberry Fruit (Morus alba L. cv Kokuso 21)

The control of temperature and gas composition is essential to maintain the fresh flavor and quality of perishable fruits like mulberry. This study presented a modified atmosphere experiment (MAP) for fresh fruit showing the potential benefits of innovative gas mixing with argon. The effects of MAP were studied on the physicochemical and qualitative attributes of mulberry preserved at 4 ± 1°C and 90 ± 5% R.H. Fresh mulberries were packaged with different gas combinations: MAP1 (4%O₂+6%CO₂+90%N₂), MAP2 (10%O₂+5%CO₂+85%Ar), CTR1 (20.9%O₂+0.04%CO₂), and CTR2 (10%O₂+5%CO₂+85%N₂). Changes in quality parameters were evaluated after 0, 4, 8, and 12 days of storage. Mulberries packaged with MAP had a lower weight loss than CTR samples which lost more than 80% of their initial weight. Furthermore, the results showed that the argon treatment was the best in keeping the fruit juice content, preserving its structure. Despite not showing great differences with MAP1 treatment, Ar allowed to maintain high TSS up to 8 storage days, slowed CO₂ production. The sensory profile of mulberry fruit was not significantly affected by storage in modified atmospheres, and the production of potential unpleasant odors in MAP2 could not be perceived. The results of this study confirm that this innovative approach, using MAP technology, has a potential use in maintaining mulberry fruit quality for a longer time.