Lab report: food dehydration. This experiment focuses on the follow four questions: 1, to calculate the moisture contents on the dry basis of carrot and potato samples; 2, to assess the possible influence of pre-dehydration such as blanching on the qua
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Lab report: food dehydration 1. Introduction In food preservation, dehydration is a common used approach. It is one of the oldest but also a simple and safe way to preserve food. It is process to remove moisture or water away from food. In a low moisture environment, yeast, bacteria and mold cannot grow (Andress and Harrison, 2006). Therefore, dehydration is helpful to minimize the growth of microorganism that is a major reason of food deterioration. At the meantime, drying also reduces the activity of enzymes that cause degradation of some nutrients. For fruit and vegetables that contain high level of water, they can go bad easily if inappropriate storage approach is applied. It was estimated 25-30% of total fruits and vegetable produced is wasted due to spoilage (Ramaswamy and Marcotte, 2006). Furthermore, dehydrated food is usually smaller and lighter and thus is convenient to transfer or store. There are several ways to achieve dehydration in industrial production, such as heat, dry air, air movement, in the sun, in the oven and using a food dehydrator (Ramaswamy and Marcotte, 2006). For some kinds of food, pretreatment such as blanching is required. Blanching which is a process of briefly precooking of food in steam or boiling water is helpful to reduce activity of enzymes, to skill spoilage organisms and to shorten drying time. However, beside the time of storage, color, nutrient, taste and texture are also important points that should be considered in preservation (Salunkhe and Kadam, 1998).
6.14 6.04 5.76 5.47 5.11 4.85 4.68 4.38 4.00 3.59 Blanched (i) 6.42 6.27 5.95 5.61 5.24 5.08 4.78 4.37 3.87 3.33 Over blanched (i) 9.02 8.74 8.36 8.18 7.79 7.44 7.04 6.46 5.90 5.57 Table 7 Moisture content on the dry basis of potato samples Graph 2 Moisture content on the dry basis of potato samples 5.4 Temperature, Dehydration and Rehydration Data Time (min) Temperature (?) 0 10 20 30 40 50 60 Dry bulb 68 61 68 66 67 66 66 Wet bulb 46 43 45 51 58 42 51 Table 8 The temperature of dehydrator at different time by two thermometers *Dry bulb=air temp Wet bulb=surface of food Treatment Carrot (g) Potato (g) Unblanched 28.6 55.0 Blanched 30.8 46.6 Over blanched N/A 38.6 Table 9 Weight carrot and potato sample after dehydration under 102?,overnight Products Carrot (g) Potato (g) Items Out from dehydrator After hydration 10mins Out from dehydrator After hydration 10mins Commercial 10g 144.4g 10g 16g Raw 10g 20.6g 10g 15.2g Blanched 10g 14.4g 10g 14.2g Over blanched 10g 13.6g 10g 15.4g Table 10 Rehydration of the two food products 5.5 Water activity Item aw Temperature (?) Raw carrot 0.979 23.4 Raw potato 0.896 23.4 Dehydration carrot 0.313 23.4 Dehydration potato 0.400 23.4 Table 11 the water activities of different samples under different temperature 5.6 Color code Colours of Samples L* a* b* Blanched Carrot 58.17 25.78 54.51 Over Blanched Carrot 58.29 24.06 59.02 Blanched Potato 74.76 -4.36 9.00 Over Blanched Potato 77.91 -3.71 6.75 L*: Lightness, a*: Redness/hue, b*: Yellowness/chroma Table 12 Color value of food before dehydration Colors of Samples Dehydration Color Measurement Raw Color Measurement Carrot Potato Carrot Potato (Average of 5 readings)
The structure change, which directly resulted in change of wavelength of reflected light of the carrot and potato sample, is the root source of color change after blanching. Besides, carrot and potato contain some pigments that contribute to their color. Blanching may change or damage the structure of these pigments can thus change the wavelength of reflected light. Minolta Chroma Meter System involves three elements, including L* a* b* to define a color, L* refers to Value, which represents the saturation of a color, a* refers to Hue, which defines the basic color in the color wheel, while b* is means chroma, which shows the level of light (Pattee, Giesbrecht and Young, 1991). The unbleached pieces of potato are creamy. When the pieces were blanched, the pectin of potato cells degrades and the cells loss its turgidity. Therefore, it is brighter and has lower opacity. Further blanch contribute to the translucent appearance. The level of carotenoid determines the color of carrot pieces. Blanch leads to gradual loss of this pigment has thus the pieces became lighter. Since carrot do not have much starch as potato, opacity is not an appropriate indicator of color. 7. Conclusion In conclusion, dehydration is an effective approach to preserve food. However, in some cases, pretreatment such as blanching is required to support better effect of dehydration. Although the pretreatment has some negative effect to the texture, flavor, and nutrients of the food, it directly contributes to better decline of moisture content and water activity of the food. This is helpful to improve shelf time. The appropriate time of blanching should be identified based on test in advance. Over blanching makes the food tasteless.
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