EXPERIMENT 9:
THE EFFECT OF DIFFERENT PEELING METHODS ON PRODUCT LOSS AND QUALITY OF ONIONS AND POTATOES
INTRODUCTION:
Peeling is used in the processing of many fruits and vegetables to remove unwanted or inedible material, and to improve the appearance of the final product. The main consideration is to minimize costs by removing as little of the underlying food as possible and reducing energy, labour and material costs to a minimum. The peeled surface should be clean and undamaged.
OBJECTIVE:
1. To peel the potato and onion by using chemical, heat and manual methods.
MATERIALS: 1. Onions 2. Potato
3. Saturated sodium chloride solution 4. 5 % natrium hydroxide (NaOH)
APPARATUS: 1. Knife 2. Peeler 3. Gloves 4. Beakers 5. Weighing balance PROCEDURES:
A.
Preparation and observation of samples
1. For each method, use at least 3 potatoes with similar sizes.
2. For each method, the weight of the potato with skin and without skin (after peeling process) was recorded.
3. The percentage of weight loss is calculated.
4. The potatoes were cut and ‘heat ring’ was observed.
B.
Lye (NaOH) peeling
1. The potatoes were soaked in boiling 5 % NaOH solution for 5 minutes.
2. Then, it was sieve for 1 minute. The potatoes were rinsed under running water until the skin peels off.
3. Phenolphthalein or litmus paper was used to test the remainining alkali. (If alkali remains on the surface of potato, blue colour will apperar).
C.
NaCl solution peeling
1. Potatoes were soaked in boiling saturated NaCl solution for 6 to 15 minutes. 2. The potatoes were rinsed under running water until the skin peels off.
D.
Steam peeling
1. A potato was retort at temperature 121 ˚C for 5 minutes in autoclave or even steamer. 2. The potato was washed under running water until the skin peels off.
E.
Direct heet peeling
1. The potatoes were burned directly under fire until all the skin was burned. 2. The skin of the potatoes was removed manually under running water.
F.
Knife peeling
1. The skin of potatoes was removed manually by using peeler (knife) or knife. RESULT:
A. Product losses
Peeling Potatoes Onions
Before (g) After (g) Before (g) After (g)
Lye (NaOH) 179.32 159.34 118.16 113.54
NaCl 166.75 159.65 101.3756 94.07
Steam 198.64 182.91 122.5393 120.75
Direct heat 96.06 71.56 49.7468 34.75
Knife 85.57 64.5 47.5714 35.27
Table 9.1: Weight of samples after and before peeling
Peeling Potatoes Onions
Weight loss % loss Weight loss % loss
Lye (NaOH) 19.98 11.1421 4.62 3.9099
NaCl 9.106 5.4608 7.3027 7.2036
Steam 15.7331 7.9202 1.7847 1.4564
Direct heat 24.503 25.508 14.9968 30.1463
Knife 21.066 24.6196 12.3034 25.863
Table 9.2: Loss percentage of samples after peeling
B. Finished product observation (Heat ring and finish cost)
Peeling
Remark (s)
Potatoes Onions
Lye (NaOH) 0.8 cm heat ring form 0.5 cm heat ring form
NaCl 0.9 cm heat ring form 1.1 cm heat ring form
Steam No heat ring form No heat ring form
Direct heat 2 cm heat ring form No heat ring form
Knife No heat ring form No heat ring form Table 9.3: Observation data for skinless potatoes and onions
Weight loss of potatoes during peeling (g)
= weight of potatoes before peeling (g) – weight of potatoes after peeling (g)
% weight of potatoes before peeling = weight loss × 100 Weight before peeling
Lye (NaOH)
Weight loss of potatoes during peeling (g) = 179.32 – 159.34 = 19.98 g
% weight of potatoes before peeling = 19.98 × 100
179.32
= 11.1421 % NaCL
Weight loss of potatoes during peeling (g) = 166.75 – 159.65
= 9.106 g
% weight of potatoes before peeling = 9.106 × 100
166.75
= 5.4608 % Steam
Weight loss of potatoes during peeling (g) = 198.64 – 182.91 = 15.7331 g
% weight of potatoes before peeling = 15.7331 × 100
198.64
= 7.9202 % Direct heat
Weight loss of potatoes during peeling (g) = 96.06 – 71.56 = 24.503 g
% weight of potatoes before peeling = 24.503 × 100
96.06
= 25.508 % Knife
Weight loss of potatoes during peeling (g) = 85.57 – 64.50
= 21.066 g
% weight of potatoes before peeling = 21.066 × 100
85.57
DISCUSSION:
Through this experiment, peeling is the best method to remove unwanted or inedible material from vegetable or fruits materials. This method to improve the appearance and the taste of the product. During peeling, peeling losses need to be minimized by removing as little of the underlying food as possible but still achieving a clean peeled surface. In this experiment, potato and onions are used to determine the effect of peeling methods on product loss and quality of them. There are five types of peeling method that was used which are Lye (NaOH) peeling, NaCl solution peeling, steam peeling, direct heat peeling and knife peeling.
Based on the result obtained, the range of weight loss of potatoes by using various of peeling method in descending order form, direct heat is 24.503 g, knife is 21.066, Lye (NaOH) is 19.98 g, steam is 15.7331 g and NaCl is 9.106 g. While for onions, the range of weight loss from descending order, by direct heat is 14.9968 g, knife is 12.3034 g, NaCl is 7.3027 g, Lye (NaOH) is 4.62 g and steam is 1.7847 g. From the observation, by using direct heat peeling on the potatoes and onions the percentage of weight loss is the highest which is 25.508 % for potato and 30.1463 % for onions. Then, 2 cm of heat ring form when potato was peeled with direct heat which is the biggest heat ring form among the others method. While, no heat ring is form when potato was peeled by using steam and knife method.
In addition, when onions is peeled with NaCl method, 1.1 cm of heat ring is form and no heat ring form when it was using steam, direct heat and knife peeling method. NaCl peeling method is the most suitable for onions and potatoes because weight loss only in small amounts compared to other peeling method so it can retain the quality of onions and potatoes. Other than that, it is only requires small amount of cost when using NaCl as peeling method.
Abrasion peeling method is the method where the material to be peeled is fed onto abrasive rollers or fed into a rotating bowl which is lined with an abrasive. The abrasive surface removes the skin, which is then washed away with water. The process is normally carried out a ambient temperature. Advantages of the method include low energy costs as the process operates at room temperature, low capital costs and a good surface appearance of food. Irregular product surfaces (for example ‘eyes’ on potatoes) may spoil the appearance of peeled product and require hand finishing.
CONCLUSION:
As conclusion, after conducting this experiment we would able to determine the effect of different peeling methods on product loss and quality of onions and potatoes. Then, the peeling method which only loss small amount of weight loss is NaCl.
REFERENCES:
Peeling. (n.d.). Retrieved March 10, 2013 from
http://www.hyfoma.com/en/content/processing-technology/raw-materials-reception-preparation/peeling/
Sudheer, P. K. , & Indira, V. , (2007). Post Harvest Technology of Horticultural Crops. New Delhi: New India Publishing Agency.
