Effect of ultrasound treatment on fruit decay and quality maintenance in strawberry after harvest
Introduction
Strawberry fruit is a commercially important fresh fruit in southeast China. The ripe fruit is highly susceptible to mechanical injury, microbiological decay, and physiological deterioration. Low temperature in combination with carbon dioxide-enriched atmosphere (10–20% CO2) has been used to extend the storage life of strawberries by delaying fruit softening and decay (Gil et al., 1997, Li and Kader, 1989). However, grey mold rot, caused by Botrytis cinerea Pers.: Fr infection, remains a major factor in limiting shelf-life of strawberries and causing up to 50% loss (Garcia, Aguilera, & Jimenez, 1996). The current method of postharvest decay control for strawberry during storage and transport is application of synthetic fungicides, but problems related to development of pathogen resistance to many currently used fungicides and potentially harmful effects on the environment and human health have stimulated research to look for alternative measures for disease control (Ragsdale & Sisler, 1994).
Recently, ultrasound treatment has been reported to be an attractive means in food science and technology because of its promising effects in food processing and preservation. Knorr, Zenker, Heinz, and Lee (2004) reviewed the direct food processing improvements such as cleaning surfaces, enhancement of dewatering, drying and filtration, inactivation of microorganisms and enzymes, extraction of enzymes, proteins and antioxidant compounds, disruption of cells, degassing of liquid food and acceleration of heat transfer. Though a lot of works have been done on the application of ultrasound during food processing and preservation, little information is reword about the effect of ultrasound treatment as a factor that affects decay incidence and quality in vegetables and fruit after harvest. The objective of this study was to evaluate the effects of a postharvest ultrasound treatment on fruit decay and quality of strawberries during storage at 5 °C.
Section snippets
Fruit and treatment
Strawberries (Fragaria × ananassa Duch. cv. Fengxiang) were hand-harvested at commercially ripe stage from a farm at Nanjing in Jiangsu province and transported within 2 h to our laboratory. They were sorted to eliminate damaged or unripe fruit, and selected for uniform size and color, and then randomly divided into five groups. The fruit were immersed in a water bath (20 °C) with dimension of 500 × 300 × 150 mm in the ultrasonic chamber (SB-500DTY, Ningbo Xinzhi Science and Technology Co.) and treated
Effect of ultrasound treatment on decay incidence and microorganisms on strawberry fruit
Strawberry is a highly perishable fruit and the shelf-life usually ends due to microbial infection (Wszelaki & Mitcham, 2003). As shown in Table 1, decay incidence of strawberry fruit increased with storage time. There were no significant differences in decay index between control and 25 or 28 kHz ultrasound treatment. However, treatment with 40 or 59 kHz ultrasound significantly (p < 0.05) inhibited the increase of decay index. The decay index in 40 and 59 kHz ultrasound treatments was 43.7% and
Acknowledgement
This study was supported by the Nanjing Scientific and Technical Supporting Program (200803017).
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