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Under the Microscope In Your Food Sabrina Crewe Consultant: Professor Anne K. Camper, Montana State University Copyright © 2010 by Infobase Publishing All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Chelsea Clubhouse An imprint of Chelsea House 132 West 31st Street New York NY 10001 Library of Congress Cataloging-in-Publication Data Crewe, Sabrina. In your food / Sabrina Crewe ; consultant, Anne K. Camper. p. cm. -- (Under the microscope) Includes index. ISBN 978-1-60413-824-5 (hardcover) ISBN 978-1-4381-3318-8 (e-book) 1. Food--Microbiology--Juvenile literature. I. Title. QR115.C74 2010 664.001’579--dc22 2009043207 Chelsea Clubhouse books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please call our Special Sales Department in New York at (212) 967-8800 or (800) 322-8755. You can find Chelsea Clubhouse on the World Wide Web at http://www.chelseahouse.com Text design by Sabine Beaupré Illustrations by Stefan Chabluk Originated by Discovery Books Composition by Discovery Books Cover printed by Bang Printing, Brainerd, MN Book printed and bound by Bang Printing, Brainerd, MN Date printed: May 2010 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 This book is printed on acid-free paper. All links and Web addresses were checked and verified to be correct at the time of publication. Because of the dynamic nature of the Web, some addresses and links may have changed since publication and may no longer be valid. Acknowledgments We would like to thank the following for permission to reproduce photographs: Centers for Disease Control and Prevention, US Department of Health and Human Services: p. 22; Sabrina Crewe: p. 29; Dennis Kunkel Microscopy, Inc.: pp. 6, 19, 20, 23, 26; Science Photo Library: pp. 5 (Clouds Hill Imaging Ltd.), 7 right (David Scharf), 10 (Scimat), 13 (Andrew Syred), 15 (Biophoto Associates), 18 (Scimat); Shutterstock Images: pp. 4 (Jacek Chabraszewskiin), 7 left (Optimarc), 9 (Julián Rovagnatin), 11 (Alexey Chernitevich), 12 (Georgy Markov), 16 (Mayer Kleinostheim), 17 (Carolina K. Smith), 21 (Alena Brozova), 24 (Razumovskaya Marina Nikolaevna), 25 (Nice_pictures); US Department of Agriculture: pp. 14, 27. Contents What Are You Eating? 4 Bread and Microfungi 6 Milk and Bacteria 8 Yogurt and Cheese 10 Fruit 12 Vegetables and Grains 14 Magnified Meat 16 Meat Microbes 18 Pantry Pests 20 What’s in the Water? 22 Keeping Food Safe 24 Inside Food Cells 26 Size and Scale 28 About Microscopes 28 Micro-Detective 29 Glossary 30 Explore These Web Sites 31 Index 32 Some words are bold the first time they appear in the text. These words are explained in the glossary at the back of this book. Yogurt is a healthy food partly because of the microbes that live in it. We will find out more about these microbes. What Are You Eating? You probably think you know what is in the food you are eating. You may be surprised, however, when you see your food under a microscope. Microscopes allow us to see things up close and look at them in a different way. Under the microscope, we can see the tiny parts that foods are made of. We can learn why foods change when we cook them or when they spoil. Sharing your food The microscope also shows us that you may not be the only one eating your food! In the refrigerator or on the kitchen counter, tiny organisms (living things) may also be munching away. 4 Microorganisms and microbes Organisms too small to see are called microorganisms. They range from tiny animals that you could find with a magnifying glass to living things so small you could fit thousands of them on a grain of salt. Microorganisms that are not animals are often called microbes. Some of these make our food rot. Others make us sick if we eat them. Other microbes actually make food healthy or give it a good taste. Food up close Let’s take a look at your food under the microscope and discover what you are really eating. By looking first at two everyday foods—bread and milk—we’re going to learn about two important kinds of microorganisms with which we share our food and our world. Micro-Monster The flour mite could live in your kitchen cabinet in a package of flour. In real life, this mite is 0.3 to 0.5 of a millimeter long, so you could see it with a magnifying glass. This is what it looks like when it is magnified 200 times.  Bread and Microfungi Fungi are a type of organism that includes the mushrooms we eat. But there are much tinier fungi that are part of some foods. These microscopic forms of fungi are known as microfungi. Food invaders First, let’s look at some microfungi that are invaders. Fungi spread through their food source with threads called hyphae. And their food source may well be your food source! Fungi feed on living things and organic matter (things that were once alive or come from living things). As they do so, they break down their food by releasing chemicals into it. Moldy bread Mold is a type of fungus that invades food and breaks it down, causing it to spoil. If you look at a slice of bread and see a patch of mold, you are actually seeing a fungus feeding on the bread. The mold is a network of hyphae called a mycelium. These are spores of Mucor, a microfungus that spreads through bread and makes it moldy. 6 As the mycelium spreads, the hyphae grow fruiting bodies that hold spores, which are like tiny seeds. When the fruiting bodies release the spores, they travel in the air to find new food to grow on. Making bread How Small Is Small? An average yeast cell is about 4 micrometers across. There are 1,000 micrometers in a millimeter, so you could line up 250 yeast cells alongside just 1 millimeter on your ruler. You could fit more than 6,000 alongside 1 inch. Yeasts are different from regular fungi. They only have one cell. Carbohydrates—sugar and starch—are the yeast cell’s favorite food. When yeast is mixed with flour and water to make bread, the yeast cells begin to feed on the starch in the flour. This process, called fermentation, releases carbon dioxide bubbles. The bubbles make the bread swell up, or rise. After the bread is These yeast cells are budding to cooked, the bubbles reproduce themselves. appear as holes. The bud comes off to make a new yeast cell. These cells have been magnified 4,000 times. You can see the holes in this bread made by the yeast releasing gas bubbles. 7 Milk and Bacteria The smallest and most plentiful microorganisms in our food—and in the world—are bacteria. Even though you can’t see them without a microscope, bacteria are everywhere. What are bacteria? So what are these microscopic life-forms? Unlike plants and animals, bacteria are made of a single cell. You can see a typical bacterium below and take a look inside its cell. Bacteria often live in large clumps called colonies. They multiply constantly by dividing their cells. Most bacteria are shaped like rods, but many are round. Others are Whatever shape bent or shaped like spirals. bacteria are, the insides Bacteria also vary in size, but of their cells hold the same most measure between 1 and basic parts. On the outside, some bacteria have pili 4 micrometers across. to hold onto the cells of their food source. The larger hairs are flagella, which many bacteria use to move around. Pili are used to attach to other cells. The nucleoid contains the bacterium's DNA. DNA tells a cell how to develop and function. The cell wall gives the bacterium its shape. Cytoplasm is the fluid that fills a cell. The ribosomes make protein. The plasma membrane carries things around, into, and out of the cell. Flagella are used to move around. 8 Hungry bacteria Bacteria need food to survive. Mostly they live on organic matter—food that comes from living things—just like we do. As bacteria digest food, they change the food they are eating. Living in milk Milk contains bacteria called lactobacilli that live on lactose, the sugar in milk. When milk goes sour, it’s because lactobacilli are producing a sour substance called lactic acid as they feed. Nobody wants to drink sour milk, but we can use the bacteria in milk to make food we do like. Next you will see how bacteria and fungi together help make some of our favorite foods! Bacterial Names Scientists use the term bacilli to describe rodshaped bacteria and cocci for bacteria shaped like spheres. These bacteria shapes are common in milk. Lacto means milk, so some milk bacteria are named lactobacilli and others are lactococci.