- Title
- Effect of halide salts on surface browning of fresh cut apple slices
- Creator
- Li, Yongxin
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2015
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The postharvest life of fresh-cut apples is limited by the development of browning on cut surfaces. The effect of dipping in solution of inorganic salts on surface browning of ‘Granny Smith’ apple slices was examined. This led to a more extensive study on the effect of various halide salts on browning and other biochemical factors associated with the surface browning of apple slices. Dipping in ascorbic acid (AscH) and calcium ascorbate (CaAsc) has long been used to inhibit browning of fresh-cut apple slices but these compounds are comparatively expensive. In order to develop a cost-effective method to inhibit browning, the combined effects of sodium chloride (NaCl) with various forms of ascorbate on the postharvest life of ‘Granny Smith’ apple slices were examined. Results from dipping apple slices in solutions of a range of inorganic salts showed that the relative inhibitory effect on browning was chloride = phosphate > sulfate > nitrate = nitrite with no difference between sodium, potassium and calcium salts. The effectiveness of halide salts on browning was found to be fluoride > chloride = bromide > iodide = control. Polyphenol oxidase (PPO) from ‘Granny Smith’ apples showed a maximum activity at pH 4-5, with activity at pH5 > 4 > 3 > 6 > 7 > 8. The PPO activity of tissue extracted from halides-treated slices was not different to control tissue but when halides were added into the assay solution, both sodium fluoride (NaF) and NaCl significantly decreased PPO activity at pH 3–5. The levels of individual (epicatechin, chlorogenic acid) and total polyphenols in halide treated slices were NaF > NaCl > control. Exogenous application of chlorogenic acid to slices enhanced browning but the addition of NaCl and NaF counteracted this effect. The halide salts showed no effect on respiration, ethylene production, ion leakage or antioxidant activity. It is proposed that the mode of action of NaCl and NaF is thus considered to be through decreasing PPO activity and subsequently reducing the oxidation of polyphenols. The concentration of AscH required to achieve a desired postharvest life was twice that of CaAsc but calcium, sodium and potassium ascorbates were equally effective in inhibiting browning. The inclusion of 0.1 mol/l NaCl into an ascorbate dip reduced by half the concentration of ascorbate needed to maintain the same postharvest life. Since 0.1 mol/l NaCl does not affect the taste of apple slices and is an allowable food additive with a much lower cost, it should be considered as a cost effective partial replacement of ascorbate in commercial dips. There may also be a cost advantage of using sodium ascorbate (NaAsc) over CaAsc.
- Subject
- halide salts; apple browning
- Identifier
- http://hdl.handle.net/1959.13/1310380
- Identifier
- uon:22034
- Rights
- Copyright 2015 Yongxin Li
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT02 | Thesis | 2 MB | Adobe Acrobat PDF | View Details Download |