The produce industry faces a future with reduced access to postharvest fungicides. It has become increasingly important to reduce commodity susceptibility to decay and to develop non chemical methods for decay control. Heat therapy has been demonstrated to be effective for control of numerous decays and is currently practiced for control of anthracnose in mangoes and papayas and for decay control in oranges. The limitations to heat therapy include the often tine line between effectiveness and commodity injury and the lack of residual protection. Modified atmosphere has been used effectively for many years by the California strawberry and raspberry industry to allow cross-country shipment of a commodity on which no postharvest fungicides are used. It has been shown that CO2 concentrations of 15% and higher inhibit the growth of many fungi, including Botrytis cinerea, the main cause of strawberry decay. Many commodities cannot tolerate 15% CO2 for an extended period of time. However, the short term (1 to 3 weeks) tolerance has not been determined. With the loss of postharvest fungicides, we may find that many commodities could benefit from shipment under high CO2, as have strawberries. The combination of heat therapy and MA will also be discussed.
Peaches and apricots were obtained at harvest. One-half were inoculated with the brown rot organism (Monilinia fructicola) and incubated overnight before immersion in 52C water for 2.5 and 2 minutes, respectively. Fruit were placed in storage at SC in air, 2% O2 and 15% CO2, or 17% O2 and 15% CO2 for 5 or 15 days before ripening at 20C. For peach, controlled atmosphere (CA) had no influence on decay while hot water significantly reduced decay incidence and severity. For apricot, after 15 days cold storage, both hot water and controlled atmosphere storage reduced decay incidence and severity. CA with 2% O2 and 15% CO2 controlled decay better than 17% O2 and 15% CO2. Growth and sporulation of Monilinia fructicola in air and CA was also evaluated in vitro. The combination of heat and CA controlled decay better than either treatment alone. The hot water treatment resulted in minor surface injury on peaches while apricots were not injured. Fruit were evaluated after storage for firmness, soluble solids, and titratable acidity. Accumulation of ethanol and acetaldehyde as a result of CA storage was monitored.
High-temperature, controlled-atmosphere treatments were explored for disinfestation of codling moths from `Bartlett' pear fruit. Fruit were freshly harvested in 1996 and 1997 and sorted for uniformity and absence of defects. Fruit were exposed to forced-heating at 46 °C for 1, 2 and 3 h in either air or a controlled atmosphere of 1% oxygen and 15% carbon dioxide. Fruit were evaluated during ripening at 20 °C immediately after treatment (1997 only) and after 3 weeks of cold storage at -1 °C. Fruit were ripened with and without an exogenous ethylene treatment in 1997. Heat treatments, and particularly heat plus CA treatments, slowed fruit ripening, even after fruit had been stored for 3 weeks. The longer the treatment, the greater the inhibition. Fruit from longer treatments were firmer than untreated fruit after 4 days of ripening, but treatment with exogenous ethylene did not overcome the inhibition in the rate of ripening, although fruit from all treatments softened faster. The mortality of codling moths following exposure to the same treatments was also determined. With the heat plus controlled-atmosphere treatments, 100% mortality was achieved in 2.5 h with the faster heating rate used in our 1996 experiment, while it took 3 h to achieve 100% mortality with the slower heating rate.
Mature green mango (Mangiferaindica L.) fruit were heated (100% RH) at 50C for 120, 180 or 240 min or 46C for 160, 220 or 280 min. The rate of mesocarp color (CIE a*) development was reduced in treated fruit, particularly in inner tissue. Rate of softening of mesocarp tissue was reduced after heat treatment; inner more than outer. Fruit treated at 50C remained more firm than control fruit 9 days after treatment, whereas fruit treated at 46C were more firm than controls 3 days after treatment, but were similar by 9 days. Electrolyte leakage from inner mesocarp tissue disks increased with increasing time at 50C, but was unchanged in fruit treated at 46C. However, after 3 days, electrolyte leakage returned to control levels. Ethylene-forming enzyme (EFE) activity of inner meso-carp tissue was greatly reduced in fruit treated at 50C (all times), and at 46C (220 and 280 min). After 3 days, EFE activity of fruit from most treatments had recovered to levels higher than controls. These data indicate that fruit may be able to recover from heat stress. Mild heat stress may increase postharvest shelf life by reducing the rate of softening.
Controlled atmospheres have been proven an effective postharvest disease deterrent for strawberries both in transport and storage. However, these treatments do not provide residual protection once the commodity is removed from the atmosphere, and the atmospheres can cause off-flavors in the fruit. Elevated oxygen atmospheres are a novel addition to this technology and could potentially provide better decay control without the harmful effects on fruit flavor aspects. Elevated oxygen will potentially discourage microbial growth, as anaerobes grow best under very low oxygen levels and aerobes grow best under atmospheric oxygen. Threshold elevated oxygen levels to prevent Botrytis cinerea growth in vitro and in vivo on strawberry were assessed. Botrytis cultures (mycelial plugs and spores) and fresh strawberry fruit were exposed to 21%, 40%, 60%, and 80% oxygen atmospheres at 5 °C for 5, 7, and 14 d. Growth of cultures from mycelial plugs was evaluated after treatment and during post-treatment incubation by measuring the diameter of the fungus. Spore germination and germ tube elongation were evaluated every 24 h for 3 days after treatment by counting the number of germinated spores and measuring elongation, respectively. Strawberry quality including firmness, color, soluble solids, titratable acidity, ethylene production and respiration rates, and presence of defects were evaluated upon removal from the elevated oxygen atmospheres as well as after 1, 3, and 5 d storage in air at 20 °C simulating market conditions.
`Keitt' and `Tommy Atkins' mango (Mangifera indica L.) fruit were evaluated for selected ripening criteria at six ripening stages, from mature green to overripe. `Tommy Atkins' mangos developed more red and yellow pigmentation (CIE a* and b*) in peel and mesocarp tissues than `Keitt'. The outer mesocarp of `Keitt' remained firm longer than `Tommy Atkins', and the inner mesocarp was softer than the outer at each stage in both cultivars. Cell wall neutral sugars, particularly arabinosyl, rhamnosyl, and galactosyl residues, decreased with ripening in both cultivars. `Keitt' had more loosely associated, chelator-soluble pectin, accumulated more soluble polyuronides, and retained more total pectin at the ripe stage than `Tommy Atkins'. Both cultivars had similar polygalacturonase (EC 18.104.22.168) activity which increased with ripening. The amount and molecular weight of cell wall hemicellulose decreased with ripening in both cultivars. These data indicate that enzymatic and/or nonenzymatic processes, in addition to polygalacturonase activity, are involved in the extensive softening of mango fruit.
Four cultivars of English walnut (Juglans regia) were evaluated by a trained taste panel after 6 and 12 months of storage. English walnuts were stored at 5, 15, or 25 °C, and at 40%, 60%, or 80% relative humidity within each temperature. Principal component analysis was used to compare taste, texture, and aroma attributes evaluated by the taste panel to objective indicators of English walnut quality including water activity, moisture content, free fatty acids, peroxide value, hexanal content, and kernel color. Temperature was found to significantly impact English walnut oxidation and perceived rancidity, whereas storage at high relative humidity affected English walnut texture and accelerated quality loss. Water activity was more strongly correlated to textural changes than moisture content. The effect of relative humidity was more pronounced at lower temperatures, leading to increased hydrolytic rancidity and free fatty acids. Peroxide value had higher and more significant correlation to sensory attributes related to rancidity than hexanal. Free fatty acids were not correlated to the rancid sensory attribute, but were significantly correlated to bitter. English walnuts stored at 5 °C with 40% or 60% relative humidity were associated with the sweet sensory attribute and L* value (light color). Kernel darkening was associated with bitter and rancid, but a causal relationship is unknown. Sensory quality of English walnuts is complex and requires further study to establish thresholds for chemical indices of English walnut quality loss based on organoleptic perception.
Cell wall synthesis during development and ripening of `Rutgers', rin and nor tomato (Lycopersicon esculentum Mill.) fruit was quantified by monitoring incorporation of 14C into outer pericarp cell walls after pedicel injection of (U-14C) - sucrose. Fruit color (Hunter “a” and “b” values) and firmness (Instron) were also monitored. 14C-Incorporation continued throughout development and ripening in `Rutgers' cell walls and exhibited a transient increase from late maturegreen to the turning stage. Incorporation of 14C into cell walls of rin pericarp tissue was similar to `Rutgers' at 20 days pest-anthesls (DPA) (immature-green) but decreased to a level similar to red `Rutgers' fruit by 35 DPA. Incorporation of 14C into nor pericarp cell walls was low throughout the experimental period (20 to 75 DPA). In contrast to previous reports, rin and nor pericarp tissue exhibitad a decrease in firmness of the outer pericarp. However, the rate of softening was slower than in `Rutgers'. Pericarp tissue from rin and nor fruit at 70 and 75 DPA, respectively, resisted compression as much as pink `Rutgers' pericarp tissue.
Blueberry fruit were harvested at commercial maturity from variety trials and shipped overnight to UC Davis. Fruit quality was evaluated upon receipt and after 6 and 20 days of cold storage at 0.5 °C in air shelf life. Firmness, external color, soluble solids, and titratable acidity were measured. Sensory evaluations were conducted by trained tasters to rate the blueberries for crispness, mealiness, sweetness, tartness, blueberry flavor, and off-flavors at harvest and again after 21 days of storage. Many of the blueberries increased in firmness during cold storage. Firmness at harvest tended to be softer in `Santa Fe' and `Jewel' and firmer in `Star'. Sensory data also found `Sharpblue' and `Southmoon' to be more firm; however the objective measurements did not agree. Overall, `Saphire' was low in sugars and acids, and `Jewell' and `Star' were high in acids. `Misty' and `Sharpblue' were consistently high in sugars and acids. Overall objective fruit quality ratings were highest for `Misty', `Sharpblue', and `Southmoon', and lowest for `Santa Fe'. Blueberry flavor was rated highest in `Jewell', `Star', and `Sharpblue', and lowest in `Santa Fe', `Saphire', `Misty', and `Emerald'. These data indicate that blueberry flavor may be closely tied to acid content, as most of the high-flavor varieties had high acid and many of the low-flavor varieties had low acid. Over 3 years, the varieties consistently rated highest for overall objective quality were `Misty' and `Southmoon'. `Star' was rated high for overall quality in 2 years and moderate in 1. `Jewell', `Star', and `Sharpblue' were rated highest in flavor. `Santa Fe' was ranked low in flavor quality in 2 out of 3 years. Selection of variety appears to have a strong influence on the sensory quality of the blueberries marketed.