Antibrowning and antimicrobial properties of sodium acid sulfate in apple slices

Authors: Fan, Xuetong; Sokorai, Kimberly; Liao, Ching Hsing; Cooke, Peter; Zhang, Howard

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2009
Publication Date: 10/15/2009
Citation: Fan, X., Sokorai, K.J., Liao, C., Cooke, P.H., Zhang, H.Q. 2009. Antibrowning and antimicrobial properties of sodium acid sulfate in apple slices. Journal of Food Science. 74(9):M485-M492.

Interpretive Summary: Fresh-cut apples have emerged as one of the popular products in restaurants, schools, and food service establishments as more consumers demand fresh, convenient and nutritious foods. Processing of fresh-cut apples induces mechanical damage to the fruit and exposes apple tissue to air, resulting in the development of undesirable tissue browning. The fresh-cut industry currently uses antibrowning agents to prevent discoloration. However, the antibrowning solutions can become contaminated with human pathogens such as Listeria monocytogenes, and washing of apple slices with the contaminated solutions can result in the transfer of pathogens to the product. It would be ideal if an antibrowning compound prevents the proliferation of human pathogens in solutions and minimizes the growth of pathogens during storage. The study was conducted to investigate antibrowning and antimicrobial properties of sodium acid sulfate (SAS) in comparison with other common antibrowning agents on Granny Smith apples. Results showed that among the antimicrobial agents we tested, SAS was the most effective in inhibiting browning and microbial growth for 14 days at 4 C. However, SAS caused some skin discoloration of apple slices. Overall, SAS can potentially be used to inhibit tissue browning while reducing the microbial growth on apple slices. The information is useful for the fresh-cut produce industry to enhance microbial safety of fresh-cut apples while minimizing browning, thus increasing the consumption of the health benefiting fresh fruit.

Technical Abstract: Microbial safety and tissue browning are the two major challenges in the processing of many fresh-cut fruits. There are few available compounds that can both control browning and enhance microbial safety of fresh-cut fruits. In the present study, the antibrowning and antimicrobial properties of sodium acid sulfate (SAS) were evaluated. The antibrowning ability of SAS on “Granny Smith” apple slices was investigated in terms of optimum concentration and treatment time. In a separate experiment, the apple slices were treated with water or 3% of SAS, calcium ascorbate, citric acid, or acidified calcium sulfate for 2 min. Total plate count, color, firmness, and tissue damage were assessed during a 21-day storage at 4 C. Results showed that the efficacy of SAS in inhibiting browning of apple slices increased with increasing concentration. A minimum 3% of SAS was needed to achieve 14 days of shelf-life. Firmness was not significantly affected by SAS at 3% or lower concentrations. Treatment time between 2 to 10 min had little effect on the antibrowning ability of SAS. However, SAS caused some skin discoloration of apple slices. When the cut surface of apple slices was stained with a fluorescein diacetate solution, tissue damage could be observed under a microscope even though visual damage was not evident. Among the antibrowning agents we tested, SAS was the most effective in inhibiting browning and microbial growth for the first 14 days. Total plate count of samples treated with 3% SAS was significantly lower than those treated with calcium ascorbate, a commonly used antibrowning agent. Our results suggested that it is possible to use SAS to control browning while inhibiting the growth of microorganisms on the apple slices if the skin damage can be minimized.