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10 Jan 2019

Postharvest Physiology Of Fresh-Cut Tomato Slices

Darwin H. Pangaribuan, 2005
University of Queensland


Fresh-cut products are becoming increasingly popular as an option for processing fruit and vegetable commodities.  Rapid deterioration during storage of tomato slices is the main problem with fresh-cut tomato. Slicing disrupts the plant tissue so the products become more perishable, which leads to a relatively short storage life, tissue softening, and results in tomato slices with poor quality.  The scientific basis for maintaining quality of tomato slices during storage, and postharvest handling techniques to extend storage life, is the focus of this thesis.

The major research objectives of this study focused on the physiological (ethylene and respiration), quality (firmness, colour, soluble solids, titratable acidity, and electrolyte leakage) and nutritional (ascorbic acid and lycopene) changes that occur in fresh- cut tomato slices from cv. ‘Revolution’ during storage.  The specific objectives of the research were:

1. To determine the effects of slicing on the postharvest physiology of tomato slices

2. To study the quality changes in tomato slices taken from fruit at different stages of maturity and stored at different storage temperatures

3. To characterise the involvement of ethylene in the loss of slice quality

4. To determine the efficacy of 1-MCP in maintaining quality of tomato slices

5. To determine the effect of fruit maturity and 1-MCP on the quality of tomato slices

6. To evaluate the effect of applying a brief heat shock to intact tomatoes on the quality of slices.

Study of the physiology of fresh-cut of tomato slices was started with comparisons of ethylene production and respiration between intact tomatoes and sliced tomatoes (arranged stacked or scattered in storage containers).  Ethylene production and respiration initially increased in response to slicing.  The rate of ethylene production and respiration by tomato slices was higher than in intact fruit.  Slices arranged in stacks had lower rates of ethylene production and respiration compared with slices that were scattered.  To reduce ethylene production and respiration rates by tomato slices, regrouping slices into their original shape is desirable during storage.

Tomato fruits at different stages of maturity have different physiological and metabolic activities when stored at different temperature regimes.  Slices taken from fruit at four stages of maturity, characterized by colour as ‘turning’, ‘pink’, ‘light-red’, and ‘red’, were evaluated for quality when stored at 0, 5 or 10 °C.  The slices taken from the ‘turning’ stage of maturity were firmer and had longer storage life compared with those slices taken from the ‘red’ maturity tomatoes.  Tomato slices stored at 0 °C were firmer and had longer storage life compared with those slices stored at 10 °C.  Storage life of tomato slices could be maintained for 12 days at 0 °C, 10 days at 5 °C, or 8 days at 10 °C.  Tomato slices obtained from the ‘pink’ and ‘light-red’ stages of maturity would be acceptable for marketing.

Experiments were conducted to investigate whether ethylene absorbents and ethylene influence the quality of tomato slices. Ethylene absorbent resulted in reduced ethylene, less CO2 accumulation, and firmer slices.  In contrast, ethylene applied 2 days after slicing stimulated the rate of ethylene production, CO2 production, and produced softer slices during storage.  These experiments show that endogenous ethylene produced by slicing of intact tomatoes or application of exogenous ethylene to slices in containers had the undesirable effects of inducing softening during storage.

Changes in firmness are ethylene-mediated in tomatoes and can be prevented by exposure of fruit to 1-methylcyclopropene (1-MCP). When intact tomatoes at the ‘pink’ maturity stage were treated with 0.1, 1.0 or 10.0 µL L-1 1-MCP (20 °C, 12 h), 1-MCP reduced both ethylene production and respiration rate, delayed softening of the pericarp, and inhibited loss in titratable acidity in slices when compared with slices from fruit not treated with 1-MCP.  The storage life of tomato slices was extended by application of 1-MCP to intact tomatoes, but application 1-MCP to slices was of no benefit.  The most effective concentration of 1-MCP for inhibiting the ethylene-induced softening of tomato slices was 1 µL L-1.

A study was carried out to determine whether 1-MCP would be more effective if applied at an early maturity stage or a late maturity stage. 1-MCP (1 µL L–1 at 20 °C) was applied directly to intact tomatoes at ‘turning’ and ‘pink’ (early maturity) and ‘light-red’ (late maturity) stages.  The efficacy of 1-MCP was affected by fruit maturity, as later maturity fruit were usually less responsive to 1-MCP.  This study has shown that application of 1-MCP to intact tomato retarded the progress of ripening and reduced the rate of loss in slice quality if applied at the early stages of maturity (‘turning’ and ‘pink’ stages).

The effect of heat treatment on tomato slice quality was determined when intact ‘pink’ maturity stage tomato fruit were dipped in water at 38 °C, 42 °C or 46 °C for 1 hour or treated with hot air at 38 °C for 24 h, 36 h, or 48 h.  Dipping intact tomatoes in hot water or treating intact tomatoes with hot air prior to slicing did not extend the storage life of tomato slices.

This thesis showed that pre-slicing treatments such as selection of slice portion and arrangement, appropriate fruit maturity and storage temperature, and application of the ethylene inhibitors 1-MCP, as well as post-slicing treatments such as ethylene reduction strategies, can minimise the negative effects of wounding.  The information obtained from this study will provide valuable information for the development of tomato slice production and marketing.

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