Preface

In recent years, high-intensity sweeteners have become more and more important as they are intended to face the worldwide problem with excessive sugar consumption which is known to be directly related to metabolic disorders, obesity, diabetes and other diseases. Therefore, intensive sweeteners are nowadays widely spread in foodstuffs with growing demand in beverages. But the use of sweeteners as food additives is controversially discussed and there are concerns mainly about the safety of synthetic sweeteners. For example, the safety of aspartame, a widely used sweetener especially in beverages, is permanently discussed despite of global approvals and recent reevaluations, e.g. by the European Food Safety Authority (EFSA) in 2017. Therefore, a sweetener like steviol glycosides colloquially called “stevia”, which is of natural origin and very stable during food production is of rising interest. It derives from the plant Stevia rebaudiana Bertoni and is applied in food, feeds and cosmetics as a white powder with a purity of more than 95%.

Due to their natural origin steviol glycosides have a lot of interesting aspects being worthy to be elucidated. Steviol glycosides represent a class of diterpenes with more than 40 different single components. The steviol glycosides rebaudioside A and stevioside are most abundant in the plant. Obviously, the composition of the different sweet compounds in the plant can vary significantly depending on several influences like genotype, climate, soil composition etc. The taste of the sweet mixture is also varying decisively depending on its steviol glycoside composition. It is obvious that a lot of aspects have to be taken into consideration for gaining a well tasting and safe high-purity sweetener.

In this book, we try to reflect these aspects by discussing acceleration and improvement of the traditional breeding of the stevia plant, traditional and new strategies to enrich, isolate and purify the interesting sweet ingredients in commercial scaled-up processes, novel trends in the analysis of steviol glycosides, further constituents in the plant and strategies for their analysis and the potential antioxidant capacity of the stevia extracts. A precondition for improvements in breeding is profound knowledge of the biosynthetic pathways for the synthesis of the sweeteners in the plant. Furthermore, it is essential to reflect upon potential adverse health effects which have to be considered together with metabolic functions of the steviol glycosides in the human body. An example for non-food application of steviol glycosides is their use in dentistry, which is discussed. Last but not least, we put a special emphasis on the most important aspect deciding the economic success of the sweetener: we look at its taste. After an introduction about taste perception in general, hints were given that and how steviol glycosides can influence both taste perception and insulin secretion.

I would like to thank the esteemed chapter authors for being part of this book and the publisher Royal Society of Chemistry, namely Nicki Dennis for the idea and Katie Morrey for speeding up the completion of the project. Special thanks are extended to Benno Zimmermann who offered numerous helpful suggestions and corrections.

We hope that this book will be a gain for students, teachers and researchers with interests in stevia as a sweetener of natural origin.

Ursula Wölwer-Rieck