In modified-atmosphere (MA) packaging of fruits and vegetables, there is a risk of generation of excessively low, injurious O2 levels due to improper package design, temperature abuse, and/or product respiration rate variation. When exposed to injurious O2 levels, product quality deteriorates and off-flavors develop. Also, there is increased production of ethanol and other fermentative volatiles. For blueberries, off-flavors were positively correlated with tissue ethanol level when the product was exposed to a range of O2 partial pressures (0 to 18 kPa) and temperatures (0 to 25C). A biosensor that measures ethanol level in package headspace will be useful for easy identification of the packages containing injured products. Biosensors that measure ethanol in aqueous solutions by a color change reaction are commercially available. We have found a positive correlation between the color (hue) of the sensor and headspace ethanol levels in packages containing cut broccoli at 22C. The utility of the biosensor in quality assurance (QA) based on the identification of low-O2 injury of the packaged products will be discussed.
P. Chowdary Talasila, Arthur C. Cameron, and Randolph M. Beaudry
Gustavo H.A. Teixeira and José F. Durigan
compromising the ripening process or presenting any low O 2 injury symptoms. This conclusion supports the use of these oxygen levels for ‘Pedro Sato’ guava fruits in extended storage. It is noteworthy that these levels are quite similar to the 5-kPa O 2
Tolerance of apples to low levels (0.5%) of O2 was cultivar-dependent. `Spartan' (SP), `Delicious' (RD), and `Golden Delicious' (GD) apples (Malus domestica Borkh.) held for 7 months in 1.0% O2 (with 1.5% CO2) at 0.5C, plus ≈2 months in air at 0C and 7 days in air at 20C, were similar to those held in 1.5% O2. However, incidence of skin injury in fruit held in 0.5% O2 was very high in SP (purple-brown discoloration), low in RD (purple-brown discoloration), but only negligible in GD (lesions). Skin discoloration in SP and RD developed rapidly in air at 20C. Holding in 0.5% O2 improved retention of flesh firmness and juice acidity in GD and, under certain conditions, reduced scald in RD and SP, delayed yellowing in GD, but increased flesh breakdown in SP, flesh browning and alcohol flavor in SP and RD, and core browning in RD.
In the past four years the effects of levels of O2 from 1 % to 100%1 on ripening of Gala apples were studied. It was observed that oxygen concentrations larger than 8% did not delay the onset of the climacteric rise in ethylene evolution and respiration, and had no effect on any parameters of ripening, such as texture, acidity and soluble solids. The timing of the onset in the rise of ethylene evolution differed with the year. Low O2 environments of 1-2% did not induce any rise in ethanol concentration. One hundred percent O2 was highly detrimental in that it induced visible symptoms akin to low O2 injury and enhanced the accumulation of ethanol. Hypoxic environments induced a novel 61 kd polypeptide whose quantity was inversely related to the levels of O2. The data also indicate that the effect of low O2 environments on respiration is a function of the physiological stage of the fruits.
Storage of `McIntosh' apples (Malus domestica Borkh.) in high humidity (94% to 100% RH) or in 0.5% CO2 plus 1.0% O2 at 3C (LO) atmospheres decreased resistance to ethane diffusion relative to fruit stored in low humidity (75% RH) or in 5.0% CO2 plus 3.0% O2 at 3C (SCA), respectively. Loss of fruit firmness of SCA- or LO-stored `McIntosh' apples, determined immediately after storage or after 7 days at 20C, decreased with increased storage humidity in each of three crop years. Storage humidity did not significantly affect (P = 0.05) fruit titratable acids or soluble solids contents. High storage humidity (96% to 100% RH) generally increased the incidence of senescent disorders (consisting of senescent breakdown and senile brown core) in SCA-stored fruit, while humidities of 92% to 100% RH decreased the incidence of low-O2 injuries (epidermal bluing and cortical browning) in LO-stored fruit. Senescent disorders were found in SCA-stored fruit, but not in LO-stored fruit. The incidence of decay was not significantly affected by either storage humidity or atmosphere.
P. Guy Lévesque, Jennifer R. DeEll, and Dennis P. Murr
Sequential decreases or increases in the levels of O2 in controlled atmosphere (CA) were investigated as techniques to improve fruit quality of `McIntosh' apples (Malus ×sylvestris [L.] Mill. var. domestica [Borkh.] Mansf.), a cultivar that tends to soften rapidly in storage. Precooled fruit that were harvested at optimum maturity for long-term storage were placed immediately in different programmed CA regimes. In the first year, CA programs consisted of 1) `standard' CA (SCA; 2.5–3.0% O2 + 2.5% CO2 for the first 30 d, 4.5% CO2 thereafter) at 3 °C for 180 d; 2) low CO2 SCA (2.5–3.0% O2 + 2.5% CO2) at 3 °C for 60 d, transferred to low O2 (LO; 1.5% O2 + 1.5% CO2) at 0 or 3 °C for 60 d, and then to ultralow O2 (ULO; 0.7% O2 + 1.0% CO2) at 0 or 3 °C for 60 d; and 3) ULO at 3 °C for 60 d, transferred to LO at 0 or 3 °C for 60 d, and then to SCA or low CO2 SCA at 0 or 3 °C for 60 d. In the second year, the regimes sequentially decreasing in O2 were compared with continuous ULO and SCA. After removal from storage, apples were held in ambient air at 20 °C for a 1-week ripening period. Fruit firmness was evaluated after 1 and 7 d at 20 °C, whereas the incidence of physiological disorders was assessed only after 7 d. Lowering the temperature while decreasing O2 was the best CA program with significant increased firmness retention during storage and after the 1-week ripening period. Reduced incidence of low O2 injury in decreasing O2 programs and absence of core browning at the lower temperature were also observed.