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

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). Whether the pretreat process will influence the quality of final product should be carefully assessed. Besides, dehydrated food requires rehydration before cooking and eating and whether the rehydrated food can maintain the same consistency as the original fresh food should also be considered.

2. Objectives

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 quality of final products;

3, to investigate why rehydrated foods cannot reconstitute to the same consistency as the original fresh food;

4, to study to association between AW and food preservation.

3. Methods

This experiment is to dehydrate carrots and potatoes. And the following processes were performed.

The carrots and Potatoes were peeled and sliced into small pieces about 2mm thick. One tray is prepared a time;

On each tray, 300 ± 5 g of the food pieces was weighed accurately;

Three treatments were performed for both carrots and potatoes, including (1) unblanched; (2), blanched for predetermined term; and (3), over blanched, blanched for 15 min. two trays of food were used in each treatment.

Blanching time for the second treatment was determined by the following steps: (1), place small pieces of vegetables in a test tube, to a depth of 2 cm; (2) add 10 mL of water and keep it for 10 minutes; (3) Add 1 mL of 3% H2O2. Shake, and then add 1 mL of 1% guaicol; (4) if no color shows up after 5 mins, the product is adequately blanched.

The dehydrator was set at the following variables: operating temperature--150°F (65°C); air speed--150 m/min; fan speed setting--8.2; and thermostat setting--4.5.

A multipoint recorder was sued to determine the temperature of: (1) dry bulb; (2) wet bulb; and (3) inside potato and carrot piece;

Re-weigh each tray in a 10 mins interval in the first hour, then in a 15 mins interval in the second hour and in a 30 mins interval during the third and fourth hour. The position of the trays was changed after each weighing.