Blanching and Browning of Apples

Essay by elizanesiaUniversity, Bachelor'sA, October 2009

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QuestionsFor the rapid peroxidase test on the potato. Was there a difference between the uncut, cut, and scratched flesh? Please explain the reasons for any differences observed.

The results of the rapid peroxidise test were; the uncut potato took 10 seconds to brown, the cut potato took 5 seconds to brown, while the scratched and cut potato took 2 seconds to brown. Both cut potatoes went a convincing brown colour, but the uncut potato did not. The uncut potato had only little bits of brown compared to large patches on the other samples.

The outer layers of the potato are tougher and act as a barrier to outside influences that could brown the potato. The further in to the potato you get, the more vulnerable it is to oxidative damage. The scratched potato exposed the most layers (larger surface area to volume ratio) and cut deeper in, so therefore it was more at risk of oxidative damage.

It is therefore better to only cut potatoes when you are about to use them.

QuestionsWhich treatments deactivated the polyphenol oxidase enzymes in the apple most effectively according to the rapid Peroxidase test? Which apple treatments had the least colour formation (browning) after standing 30-60mins?The most effective treatments for deactivating the polyphenol oxidase enzymes in the apple were: 0.2% L-ascorbic acid for 3 minutes (v); 0.3% Na metabisulphite for 3 minutes (vi); 1% Citric Acid for 3 minutes (vii); 0.3% MBS then 1% Citric acid for 3minutes (viii); and the steam tunnel for185 seconds, at 100 oC.(ix) The longer it takes for the rapid Peroxidase test to turn a treatment sample brown, the more effective the treatment is. Standing the apple treatments for an hour (60 minutes) after they are treated, and then observing brown colour formation is also a good test of how good a treatment is.

Treatment (ix) was the most effective because the Rapid Peroxidase test took 10 minutes, and even then there only very, very slight colour. Blanching inactivates enzymes and kills bacteria. The steam tunnel treatment didn’t have any colour formation after standing for an hour.

The next best treatment number was (viii). It took 2 minutes 10 seconds for the rapid Peroxidase test to turn this treatment sample brown. It also wasn’t affected by standing for an hour.

Treatments (v), (vi), and (vii) were quite equally effective, and won the prize of the third best treatments. They all went brown in the Peroxidase test at around 1 ½ minutes. Treatment five went slightly brown after standing for an hour, so it failed that test, but the other 2 treatments had no colour formation.

No treatment is perfect, and the fruit will eventually undergo enzymatic browning no matter which treatment you use. Fruit has to go bad eventually. These treatments can however, stall the enzymatic browning from occurring.

QuestionsUsing literature briefly describe how each of the 9 treatments controlled the browning of the apple slices, relate this information to your observations for the peroxidase test, pH and colour formation upon standing.

i.Control no treatmentThe colour development time of this treatment was 40 sec in the Rapid Peroxidase test. The ph of this treatment was 7. There was brown colour formation in the treatment sample after being left for 60 minutes. The apple had Rapid enzymatic browning without its skin, its natural protection and preserver. (Mc Gee, 2009)ii.80oC water, 30sec –The colour development time of this treatment was 78 seconds in the Rapid Peroxidase test. The ph of the water was 7. There was light brown colour formation in the treatment sample after being left for 60 minutes. This treatment had double the resistance to browning than the control treatment. A small amount of enzymes must have been deactivated by this short amount of heating. Literature findings (Almeida and Nogueira, 1995), have found that heating deactivates enzymes.

iii.80oC water, 60sec –The colour development time of this treatment was 60 seconds in the Rapid Peroxidase test. The ph of water was 7. There was light brown colour formation in the treatment sample after being left for 60 minutes. This had 50% more resistance to enzymatic browning than the control. It must have been subjected to more oxygen in the air before the Peroxidase test than treatment (ii), explaining the shorter time taken to turn brown. A small amount of enzymes must have been deactivated by this short amount of heating. Literature findings (Almeida and Nogueira, 1995), have found that heating deactivates enzymes.

iv.80oC water, 90sec –The colour development time of this treatment was 35 seconds in the Rapid Peroxidase test. This was less than the control treatment, indicating a flaw in the experimental method. It must have been subjected to more oxygen in the air before the Peroxidase test than all other treatments, explaining the shorter time taken to turn brown. The ph of water was 7. There was light brown colour formation in the treatment sample after being left for 60 minutes. Literature findings (Almeida and Nogueira, 1995), have found that heating deactivates enzymes, but this treatment didn’t actually go as smoothly as that. It seems like no enzymes were affected, though they probably were, but other enzymes had already starting working their enzymatic browning.

v.0.2% L-ascorbic acid, 3 mins –The colour development time of this treatment was 1 minutes and 30 seconds in the Rapid Peroxidase test. The ph of L-ascorbic acid was 6.5. There was pale brown colour formation in the treatment sample after being left for 60 minutes. This had much improved resistance to browning. Acids have been proven to improve the resistance of fruits to enzymatic browning. Enzymes have an optimal ph, without that they can’t work as well; adding acid lowers the pH, and so makes the enzymes less efficient at what they want to do. (Garcia and Barrett, 2002)vi.0.3% MBS, 3 mins –The colour development time of this treatment was 1 minute and 35 seconds in the Rapid Peroxidase test. The ph of the MBS was 6.5. There was no colour formation in the treatment sample after being left for 60 minutes. This had much improved resistance to browning. Acids have been proven to improve the resistance of fruits to enzymatic browning. Enzymes have an optimal ph, without that they can’t work as well; adding acid lowers the pH, and so makes the enzymes less efficient at what they want to do. (Garcia and Barrett, 2002)vii.1% citric acid, 3 mins –The colour development time of this treatment was 1 minute and 45 seconds in the Rapid Peroxidase test. The ph of the citric acid was 2.59. There was no colour formation in the treatment sample after being left for 60 minutes. This had much improved resistance to browning. Acids have been proven to improve the resistance of fruits to enzymatic browning. Enzymes have an optimal ph, without that they can’t work as well; adding acid lowers the pH, and so makes the enzymes less efficient at what they want to do. (Garcia and Barrett, 2002)viii.0.3% MBS then 1% Citric acid, 3min-The colour development time of this treatment was 2 minutes and 10 seconds in the Rapid Peroxidase test. The ph of MBS was 6.5 and the ph of the citric acid was 2.59. This treatment had very impressive resistance to enzymatic browning.

There was no colour formation in the treatment sample after being left for 60 minutes. Literature findings (Almeida and Nogueira, 1995), have found that using a mixture of substances to control the activity of polyphenol oxidase (PPO) is much more effective then using just one. This treatment was the second best, aside from the steam tunnel, so the experiment supported prior literature evidence.

ix.Steam Tunnel, 185 sec at 100 oC –The colour development time of this treatment was 10 minutes in the Rapid Peroxidase test, but the colour was only a very slight bit of brown, hardly noticable. The ph of the steam tunnel was 7.There was no colour formation in the treatment sample after being left for 60 minutes. Basically blanching inactivates enzymes and kills bacteria, giving the apple a much longer time before it browns. (Almeida and Nogueira, 1995)References•Almeida M.E.M., Nogueira J.N. 1995. The control of polyphenol oxidase activity in fruits and vegetables - A study of the interactions between the chemical compounds used and heat treatment. Plant Foods for Human Nutrition 47: 245-256.

•Garcia E., Barrett D. M. 2002. Preservative treatments for fresh-cut fruits and vegetables, Chapter 9. Lamikanra O, (editor). Fresh-cut fruits and vegetables, science technology and market. CRC Press, Boca Raton.

•McGee, H. (2004) On Food and Cooking: The Science and Lore of the Kitchen, Scribner, New York.