Bruising Reduction: Effect Of Storage Humidity and Post-Storage Handling on Compression Bruising of CA Stored Apples
Bruising can be a major problem in marketing apples and pears from controlled atmosphere (CA) storage. Although any apple cultivar can have bruising, 'McIntosh' fruit tend to be more prone to visible bruising, compared with other CA-stored apple cultivars. The bruising results from impact damage and/or compression damage (Bollen et al., 1995). Temperature and storage humidity just before handling are very important in reducing impact bruising of both 'Red Delicious' and 'Golden Delicious' apples (Zhang and Hyde, 1992). Impact bruising is reduced in these two cultivars if the fruit were in low humidity (50% RH) or above 60 °F before receiving an impact force. However, no studies have been done to indicate if compression - induced bruising is similarly affected and if the relative humidity effect can be related to moisture loss in the fruit.
Materials and Methods
In a 2-year study, pre-climacteric 'McIntosh' apples were stored in a CA regime of 4.5% CO2 + 2.5% O2. Within the CA cabinets there were three humidity levels: >75% RH (CaCl2 supersaturated salt solutions in the chamber), >90% RH (ambient), or >95% RH (distilled water in the chamber).
A sample of fruit (20 kg) was removed from each humidity treatment after 4 and 8 months and immediately weighed to determine the weight loss. Subsamples of 10-fruit were warmed to handling temperatures of 0°C, 10°C, or 20°C. After 24 hours they were subjected to three levels of compression pressure of 0, 45, or 90 N with a penetrometer (Ballauf) equipped with a 1.5 x 1.5-cm tip. Each fruit received 4 compressions: 1 on the red side, 1 on the green side and the other 2 were in between the red and green side. The sub-samples were then held for 48 hours at 20°C in a sample chamber receiving 1.2 L/hr of CO2 - free air, then assessed for O2 uptake and CO2 evolution using a gas chromatograph (Varian 3400) equipped with CRT 1 column (Alltech Assoc., Mandel Scientific, Guelph, Ontario) and a thermal conductivity detector. Ethylene production was measured using a gas chromatograph (Carle AGC-211) equipped with an Alumina packed column (122 cm x 0.32 cm) and a flame ionization detector.
Fruit firmness was determined using a penetrometer (Ballauf) equipped with a 11.1-mm-diameter tip on opposite pared sides of the fruit. The resulting juice was used to determine total soluble solids using a hand-held, temperature-compensated refractometer (Atago, model N1, Japan). Titratable acid content was measured by titrating a 2-mL juice sample with 0.1 N NaOH using a semiautomatic titrator (Multi-Dosimat E-415, Metrohm AG, Herisau, Switzerland) to an endpoint of pH 8.1 as indicated by phenolphthalein.
Visible damage to the bruised site was recorded using a 0 to 3 rating, (0=absent, 1=slight, 2=moderate, 3=severe). The remainder of the sample of fruit was evaluated after seven days at 20 °C for storage disorders (%), decay (%), and shrivelled skin (%).
The results were analyzed statistically using the ANOVA procedure of Genstat 5 (Genstat Committee, 1993). Only sources of variation that were significant at P<0.05 are discussed, unless otherwise noted.
The amount of visible bruising tended to be higher on the green side, compared with the red side of the fruit. It is not clear whether this was due to green background color making the bruise more visible or the possibility that the green side was less firm.
The level of compression pressure was important. The bruising damage increased from 45 to 90 N. The beneficial effects of low-humidity storage and post-storage handling temperature were more obvious on apples receiving 90 N compression pressure than on apples receiving 45 N compression pressure.
The results showed that low-humidity CA storage decreased visible bruising, especially if the compression pressure was 90 N. Although only slight amounts of visible shrivel were observed in the low-humidity storage treatment, the low-humidity storage had the greatest moisture loss and the possibility exists that low-humidity storage would increase the occurrence of visible shrivel to the point where it reduced market value.
Respiration, measured as O2 uptake or CO2 evolution, was lowest in fruit from the low-humidity CA storage and highest in the ambient humidity CA storage. The humidity treatments did not affect firmness, soluble solids, titratable acids, or ethylene production.
If the compression pressure was 45 N, increasing the temperature during post-storage handling had no effect on visible bruising or any other variates. However, if the compression pressure was 90 N, increasing the temperature during post-storage handling decreased the amount of visible bruising without affecting other variates such as firmness, soluble solids, titratable acids, respiration or ethylene production.
The implementation of low-humidity CA storage to maintain post-storage quality of apples and pears is routine in Europe (R. Prange, pers obs.). CA storages in Europe are monitored for moisture loss by running the water condensed from the evaporator coils into a large container outside the CA room where its volume can be monitored throughout the storage season. In this manner the benefits of moisture loss are maximized and the risk of excess fruit shrivel is minimized.
The results from this study on 'McIntosh' enhance the conclusions from other impact and compression bruising studies on apples, namely:
Bruising due to compression appears to be influenced in a manner similar to bruising due to impact.
Compression-induced bruising can be reduced by increasing moisture loss during CA storage and increasing the handling temperature, especially if the compression pressure is 90 N.
In addition, we have observed some previously unreported effects, namely:
The green side of 'McIntosh' fruit tends to show bruising damage more than the red side.
Moisture loss during storage results in lower respiration after storage, suggesting improved shelf life in apples stored in low-humidity CA storage.
Bollen, A.F., I.M. Woodhead and B.T. Dela Rue. 1995. Compression forces and damage in the postharvest handling system, p. 168-175. In: L. Kushwaha, R. Serwatokowski, and R. Brook (eds.) Proc. Intl. Conf. - Harvest and postharvest technologies for fresh fruits and vegetables. ASAE, 2950 Niles Rd., St. Joseph, Mich.
Genstat Committee. 1993. Genstat 5 release 3 reference Manual. Clarendon Press, Oxford, U.K.
Zhang, W. and G.M. Hyde. 1992. Apple bruising research update: Effects of moisture, temperature, cultivar. Wash. State Univ. Tree Fruit Postharvest J. 3(3):10-11.
Dr. Robert K. Prange and Dr. John M. Delong, Postharvest Physiologists
Agriculture and Agri-Food Canada, Atlantic Food and Horticulture Research Centre
14th Annual Postharvest Conference,
March 10-11, 1998