Research Updates from the 5^th International Postharvest Symposium

The following summaries are a few of the notable oral and poster contributions related to the postharvest handling and storage of apples that were recently presented at the International Postharvest Symposium in Verona, Italy.

Commercialization of SmartFresh^TM (1-MCP) in the South African Apple Export Market - Ian Couch et al., ExperiCo, South Africa

The two most important factors affecting SmartFresh efficacy were percentage of starch breakdown and flesh firmness at treatment. Apples treated with a starch breakdown of less than 40% exhibited the best firmness retention during 4 months of cold storage (> 1 kg, compared to control fruit). Industry recommendations for fruit maturity at the time of SmartFresh treatment are as follows: Royal Gala with 20-60% starch breakdown and 7.7-8.4 kg firmness, Golden Delicious with 20-55% starch breakdown and 7.0-7.8 kg firmness, Granny Smith with 25-50% starch breakdown and 6.8-7.8 kg firmness, Pink Lady with 30-70% starch breakdown and 7.3-8.7 kg firmness, and red cultivars with 20-50% starch breakdown and 7.0-7.5 kg firmness. SmartFresh completely controlled superficial scald development and maintained better fruit firmness than non-treated fruit in all cultivars. A conceptual prediction model that uses fruit maturity variables at the time of treatment (e.g. flesh firmness, skin color, starch content, soluble solids, acidity, and internal ethylene levels) to predict the potential benefit (e.g. firmness and skin color retention, and superficial scald and bitter pit control) of SmartFresh has been developed and is currently being evaluated commercially.

Factors Affecting Efficacy of 1-MCP to Maintain Quality of Apple Fruit after Storage - L.C. Argenta, J.P. Mattheis, and X.F. Fan, Brazil and USDA, Washington

The degree to which ripening processes are inhibited and fruit quality maintained by 1-MCP is dependent on several factors. Responses induced by 1-MCP increase with increased concentrations from 10 ppb to 2 ppm, and saturation responses occur in 12 hours when 1 ppm 1-MCP is applied. In general, fruit temperature during treatment is not critical. Experiments conducted with Delicious and Gala apples harvested over a 4-week period indicated that fruit harvested after optimum maturity for long-term CA can benefit from 1-MCP. However, the potential for long-term storage of late harvested fruit remains low compared to apples harvested earlier. The duration of responses induced by 1-MCP can also be influenced by an interaction between fruit maturity and treatment concentration. Riper fruit may require higher 1-MCP concentration (1 ppm) for maximum duration of induced responses. The length of delay between harvest/cooling and treatment is another critical factor in 1-MCP efficacy. Experiments conducted with Granny Smith and Gala apples indicated that maximum control of fruit softening, superficial scald, and senescent breakdown is achieved by treatment as soon after harvest as possible. Effects of 1-MCP on fruit firmness retention and acidity of Gala apples during 28 weeks of storage were more evident in regular cold air storage than in CA. However, the combination of 1-MCP and CA storage can provide greater benefits then either treatment alone.

Effects of 1-MCP Treatments on Mealiness in Early Red One Apples - Y. Soria et al., Spain

Firmness is the most widely used attribute to describe fruit texture, but apples of similar instrumental firmness may differ considerably in their acceptability to the consumer. This is because they can possess quite different textures in terms of crispness and juiciness, which are related to mealiness. The objective of this study was to determine the effects of 1-MCP on mealiness in Early Red One apples picked at different maturity stages. Immediately after harvest, apples were treated with 625 ppb 1-MCP and then stored in air at 0.5^oC for 6 months. Independent of harvest date, 1-MCP treated fruit exhibited higher values of firmness, crispness, and juiciness. Only slight differences in mealiness were found between the 1-MCP treated and untreated fruit immediately after removal. In contrast, after 7 days shelf-life, 1-MCP treated apples were significantly less mealy when harvested less mature. These results show that 1-MCP may be an interesting tool for reducing mealiness in apples.

Interactions of 1-MCP and Low Oxygen CA Storage on Apple Quality - Jennifer R. DeEll, Dennis P. Murr et al., OMAF and the University of Guelph, Ontario

The objective of this study was to investigate the interactions of 1-MCP and low O₂ CA storage on apple quality. ‘McIntosh’, ‘Empire’, ‘Gala’, and ‘Delicious’ apples harvested at optimum maturity for long-term storage were treated either with 1 ppm 1-MCP or without 1-MCP at 0^oC for 24 hours. After treatment, ‘McIntosh’ and ‘Empire’ apples were placed into standard CA (3% O₂ + 2.5% CO₂ for 30 days then 4.5% CO₂ thereafter and 2.5% O₂ + 2.5% CO₂ for ‘McIntosh’ and ‘Empire’, respectively) at 2.5^oC, and four low O₂ regimes (1% and 0.7% O₂, each with or without 0.7-1% CO₂) at either 2.5^oC or 0^oC. ‘Gala’ and ‘Delicious’ apples were also placed into standard CA (2.5% O₂ + 2.5% CO₂) and the low O₂ regimes, but only at 0^oC. Within a specific CA regime, apples treated with 1-MCP were 0.5 to 1 kg firmer than comparable apples after mid- or long-term storage (120 or 240 days, respectively). Lowering the O₂ and the presence of CO₂ did not consistently improve firmness, as many apples treated with 1-MCP exhibited the highest firmness regardless of gas concentrations during storage. Firmness of certain cultivars in specific CA regimes was influenced by 1-MCP, gas concentrations, and storage temperature. Ethylene, CO₂, and volatile production were generally lower in apples treated with 1-MCP, held at lower temperatures, and in lower O₂ with CO₂, although there were some interactions of these factors. Overall, 1-MCP reduced the incidence of superficial scald, but increased core browning and CO₂ injury, and interacted with the CA regimes to influence internal browning.

ILOS + ULO as a Practical Technology for Apple Scald Prevention - M.P. Fadanelli et al., Fruit Control Equipments, Italy

Intial low oxygen stress (ILOS) followed by ultra-low oxygen (ULO) regimes has been applied for many years on small quantities of red Delicious apples in Italy. In 2001 and 2002, ILOS (15 days at 0.5% O₂) + ULO (0.9-1% O₂, 1-1.2% CO₂, at 0.8-1.2^oC) was applied to commercial CA storage rooms of red Delicious apples. Overall, fruit were generally firmer from the ILOS + ULO treatment than from the standard ULO regime. However, there was slightly more superficial scald development in apples from ILOS + ULO than in those drenched with DPA and held in ULO. The use of ILOS provides good scald control for mid-term storage (23-26 weeks), but difficulties arise with longer storage times (>28 weeks).

Does Acoustic Firmness Relate to Sensory Perception of Apple Texture? - D.S. Johnson and C.J. Dover, United Kingdom

Apple samples covering a wide range in texture were produced by storage in different regimes and by using two varieties (Cox’s Orange Pippin’ and Gala). Acoustic firmness and penetrometer measurements were conducted on the fruit, while a trained panel carried out the sensory assessments. In Cox, the penetrometer measurements showed a general decline with increasing fruit size and with increasing storage O₂ concentration. A decline in acoustic firmness with increasing fruit size and O₂ concentration was observed, although with an apparent reduced sensitivity compared to the penetrometer measure. The sensory assessment of crispness showed a similar overall trend with O₂ concentration, but without a consistent of fruit size. For Gala apples, similar trends with storage atmospheres for sensory crispness and penetrometer measurements were observed, although there was a clear trend of declining values with increasing fruit size for the penetrometer that was not evident for sensory crispness. There appeared to be little effect of storage atmosphere or fruit size on the acoustic firmness index for Gala. When data for the two varieties was combined, there was a good relationship between penetrometer readings and scores for sensory crispness for values below ~ 13 lb, but poorer above 13 lb. The relationship between acoustic firmness and sensory crispness was poor, as was that between acoustic firmness and penetrometer readings particularly between 13-15.5 lb.