Structure of Potato Starch

Academic Press is an imprint of Elsevier 30 Corporate Drive, Suite 400 Burlington, MA 0183, USA 525 B Street, Suite 1900, San Diego, CA 92101-4495, USA 32 Jamestown Road, London, NW1 7BY, UK 360 Park Avenue South, New York, NY 10010-1710, USA First edition 2009 Copyright © 2009, Elsevier Inc. All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email; [email protected]. Alternatively visit the Science and Technology Books website at www.elsevierdirect.com/rights for further information Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verifi cation of diagnoses and drug dosages should be made Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-374349-7 For information on all Academic Press publications visit our website at www.elsevierdirect.com Typeset by Thomson Digital, Noida, India Printed and bound in the United States of America 09 10 11 12 13 9 8 7 6 5 4 3 2 1 Preface The potato (Solanum tuberosum L.) which is grown in over 100 countries throughout the world is one of the staples of the human diet. Potato is an important raw material for the industry as well. Growing conditions, genetic origin and aging during post-harvest storage can affect potato quality. The chemical composition of potato is of utmost importance during processing at industrial scale. The potato components such as starch, non starch polysaccharides and minerals affect the quality of potatoes and their products to a significant extent. An understanding of the chemical structure of potato components is also important for the development of unique or novel potato products. Potatoes are among the most efficient sources of energy and other nutrients including vitamins and minerals. With potatoes having such great importance, it is perhaps surprising that very few books about them have been written. Considerable progress has been made by potato chemists and technologists over the years, which is available through a scattered scientific literature. The aim of this book is to provide a consistent set of our advanced knowledge on potato chemistry and technology in one volume. The first chapter provides a brief introduction about the potato tuber and forms the basis for the next chapters on the potato origin, breeding, potato composition including cell wall components, starch, proteins, lipids and minerals. Potatoes are either stored under controlled conditions or processed for consumption long after harvest. Storage conditions can promote extensive changes in the chemical composition of potato tubers, thereby altering the quality characteristics of the final product. A detailed chapter on the post-harvest storage of potatoes and its impact on potato quality cover the main components affected by post-harvest metabolism in potato tubers. The chapter on the analysis of glycoalkaloids, phenolic compounds and anthocyanins describes their analysis, toxicity and health benefits. Various modern and sophisticated analytical techniques such as differential scanning calorimetry, rapid visco-analysis, infrared spectroscopy, optical, electron and atomic force microscopy, nuclear magnetic resonance spectroscopy, X-ray diffraction, high performance size exclusion chromatography, and high performance anion exchange chromatography for the quality evaluation of potato and their products are dis- cussed in the next chapter. The chapters on textural and rheological characteristics of raw and cooked potatoes, and fried and dehydrated potato products emphasize the technological and processing aspects; while the chapter on the potato starch modification deals with the various factors that may affect the extent of physical, chemical and enzymatic modification of potato vii Preface starch. The alteration in the physic-chemical, morphological and functional properties of potato starch which occur due to modification has been described in detail. The detailed nutritional aspects of potatoes have been presented in the form of two chapters. The chapters on the non- food uses of potatoes are a novel feature of this book and provide information on the industrial scale non-food use of potato and their products. The last chapter deals with the use of potatoes for human life support in space. We hope that this book will serve as a valuable reference for academics, potato scientists, chemists, industry professionals, and graduate students. Jaspreet Singh Lovedeep Kaur viii Introduction The potato (Solanum tuberosum L.) has an annual world production of 322 million metric tonnes, China being the major producer (FAOSTAT, 2007). Potato production has increased over the past years in both developed and developing countries much faster than other tuber or root crops because of its high yield per unit area and nutritive value (Karim et al., 1997). Potato plant is a perennial herb belonging to the family Solanaceae. The plant bears white to purple flowers with yellow stamens and some cultivars bear small green fruits each containing up to 300 seeds (Figure 1). Potato tuber develops as an underground stem (swollen part of a subterranean rhizome or stolon) bearing auxillary buds and scars of scale leaves and is rich in starch and storage proteins (Figure 2). Potatoes can be grown from the botanical seeds or propagated vegetatively by planting pieces of tubers. The eyes on the potato tuber surface, which are actually dormant buds, give rise to new shoots (sprouts) when grown under suitable conditions. A sprouted potato is not acceptable for consumption and processing. But optimum sprouting is a desired attribute when the tubers are used for propagation. New cultivars of potatoes with better yield, disease resistance, and desirable end-use are being developed with the help of breeding techniques. In recent years, many potato cultivars with desired cooking texture (such as waxy, floury), flesh color, and disease resistance have been developed with the help of breeding. Following the rational development of genetic engineering, many genetically modified varieties of potatoes have been produced. However these transgenic varieties of potatoes are not permitted for food use in many countries because of the concerns related with the safety of the consumer and environment. Genetically modified potato varieties having very high amylose/amylopectin content of starch, antioxidants levels, and tuber yield are developed. Morphologically, a potato tuber is usually oval to round in shape with white flesh and a pale brown skin, although variations in size, shape, and flesh color are also frequently encountered, depending on genetics of the cultivar. The color, size, and texture of potatoes are the main quality attributes assessed by the consumer for acceptability. Good-quality potatoes are considered to be relatively smooth, firm, and free from sprouts or any other disorders. In a potato tuber, about 20% is dry matter and the rest is water. The yield, dry matter, and composition of dry matter vary among different potato cultivars; soil type and temperature; location; cultural practices; maturity; post-harvest storage conditions and other factors (Burton, 1989). Starch is the major component of the dry matter accounting for approximately 70% of the total solids. Major part ix Introduction Figure 1: A potato farmer. Figure 2: Potato plants in the field. of the fresh potato tuber is comprised of storage parenchyma in which the starch granules are stored as a reserve material. Potatoes are a rich source of high-value protein, essential vitamins, minerals, and trace elements. The average range of raw material composition of a potato tuber is as follows: starch (10–18%) having 22–30% amylose content, total sugars (1–7%), protein (1–2%), fiber (0.5%), lipids (0.1–0.5%), vitamin A (trace/100 g fresh weight, FW), vitamin C (30 mg/100 g FW), minerals (trace), and glycoalkaloids (1–3 mg/100 g FW). The average composition of a potato tuber is presented in Table 1. The less well-known constituents of potato tuber are carotenoids and phenolics, which are potent antioxidants. Carotenoid content of potatoes ranges from 50 to 100 ␮g per 100 g FW in white-fleshed cultivars to 2000 ␮g per 100 g FW Table 1: An average composition of potato tuber, per 100 g, after boiling in skin and peeling before consumption (Source: USDA, National Nutrient Database) Potato Water 77 g Carbohydrates 20.13 g Energy 87 kcal Protein 1.87 g Fat 0.1 g Calcium 5mg Potassium 379 mg Phosphorus 44 mg Iron 0.31 mg Niacin 1.44 mg Thiamin 0.106 mg Riboflavin 0.02 mg Photographs by Jaswinder Gill. x Introduction in deeply yellow to orange-fleshed cultivars. Potatoes also contain phenolic compounds, predominantly chlorogenic acid, and up to 30 ␮g per 100 g FW of flavonoids in white-fleshed potatoes and roughly 60 ␮g per 100 g FW in red- and purple-fleshed potatoes. The total antho- cyanin content of whole unpeeled red- and purple-fleshed potatoes may be around 40 mg per 100 g FW (Brown, 2005). The influence of potato chemical composition during industrial processing is of high significance to maintain the quality of the potato products. As an example, the texture of potato crisps is dependent mainly on starch content of the raw potato tubers.

Load more