Bio Lab Report About Food

Practical 2: STARCH

Aim of practical

Starch is the main source of carbohydrates in diet of human body. It is believed that some of the textural properties of starch are important in our diet.

Experiment 1: Starch Gelatinization ?

Introduction

It is believed that temperature affects starch gelatinization. Different temperatures give different texture, visual appearance and viscosity.

Materials and Methods

? Starch

? Tap Water

Methods:

? 15(g) of starch was added to 100ml of tap water and divided to 3 boiling tubes.

? 3 boiling tubes were put into 3 hot water baths of 60?, 75?, 90? respectively and left for 30 minutes.

Results

Temp. of water bath Texture Visual Appearance Viscosity

60? ? Most is liquid-liked

? Sediments at the bottom of boiling tube ? The least viscose among the three

75? ? Gelatinous is smooth ? More viscose than 60?

? less viscose than 90?

90? ? Gelatinous is thicker than 75?

? Gelatinous at the bottom is very thick

? Bubbles in gelatinous ? The most viscose among the three

Table 1: Summary of Results of Experiment 1

Discussion

For 60?, there were sediments at the bottom of the boiling tube. The sediments had not been gelatinized. It was a milk-colored, saturated mixture of hot water and starch. From the result, it is believed that 60? is not enough for starch gelatinization.

For 75?, the gelatinous was smooth. It undergoes gelatinization. At the top part of the boiling tube, there were some half-transparent liquid, which was mixture that had not been gelatinized.

For 90?, the gelatinous was thick, and the bottom part was the thickest. The color of gelatinous was more transparent that the one at 75?. There were bubbles within the gelatinous because of high temperature. It undergoes a more complete gelatinization.

From the experiment, it is believed that 60? is too low for starch gelatinization, where 75? and 90? are enough for gelatinization.

Experiment 2: Starch gelatinization ? Coconut Dessert Gel

Introduction

This experiment is to determine the texture changes of starch after high temperature steaming.

Materials and Methods

? Sucrose

? Coconut Cream

? Maize Starch

? Tap Water

Methods:

? All materials were mixed together and steamed for 30 minutes.

? The gel was left to be cooled down and set for 15 minutes.

Result

Starch percentage of dessert gel mixture

= 50?(45+66+50+80) *100?

= 20.747? w/w

Before steam After steam

Texture ? Liquid-liked

? Less viscose ? Solid-liked

? More viscose

? Harder

Table 2: Summary of Results of Experiment 2

Discussion

The dessert gel mixture became hard and solid-liked after steaming. It is because of starch gelatinization. From experiment 1, it shows that 75? and 90? are enough for starch gelatinization. Steaming is at very high temperature which is above 100?. Therefore, the starch mixture could gelatinize and became hard.

Experiment 3: Light Microscopy of Starch

Introduction

Different starch has different appearance. By using a light microscope, appearance of starch grains can be examined under bright light or dark field illumination.

Material and Methods

? Rice starch

? Potato starch

? Maize starch

? Wheat starch

? Water chestment

? Unknown starch sample

Methods:

? Six samples of starch with very small quantities were put under a light microscope.

Results