Sensory quality and chemical composition of culinary preparations

76 Pages·2012·1.99 MB·English

S
ENSORY QUALITY AND CHEMICAL COMPOSITION

OF CULINARY PREPARATIONS OF ROOT CROPS

PhD thesis by
Vibe Bach
October 2012

Department of Food Science
Aarhus University
Research Centre Aarslev
Faculty of Science and Technology
Kirstinebjergvej 10
5792 Aarslev
Denmark
Main supervisor
Associate professor Merete Edelenbos
Department of Food Science, Aarhus University

Co-supervisors
Associate professor Ulla Kidmose
Department of Food Science, Aarhus University

Senior scientist Erik Larsen
Department of Food Science, Aarhus University

Assessment Committee
Senior scientist Marianne G. Bertelsen (chairman)
Department of Food Science, Aarhus Universtity

Head of Department, Professor Lars Porskjær Christensen
Institute of Chemical Engineering, Biotechnology and Environmental Technology,
University of Southern Denmark

Senior Researcher Randi Seljåsen
Bioforsk, Norwegian Institute for Agricultural and Environmental Research

ii
PREFACE
The work described in this Phd thesis was performed at the Department of Food
Science, Aarhus University in the research group Food, Metabolomics and Sensory Science
from October 2009 to September 2012. The PhD-project was part of the Gourmet roots
project, financed by the Danish Minestry of Food, Agriculture and Fisheries in the Food
Research Programme 2008 (RUFF, project No. 3304-FVFP-08-K-04-01).
First of all, I would like to acknowledge my supervisors Merete Edelenbos, Ulla
Kidmose and Erik Larsen. I would like to thank Merete Edelenbos for her support and
guidance throughout this PhD, and for helping me in the process of identifying my own
scientific interests. My gratitude goes to Ulla Kidmose for assisting me in all sensory
related questions I might have had during these three years, and Erik Larsen for the same
in regards to natural product chemistry.
The partners of the Gourmet root project (www.gourmetroots.dk) are thanked for
practical support and the contribution of raw material of Jerusalem artichoke tubers,
beetroots and carrots for laboratory studies.
A very special thanks goes to Birgitte Foged for her excellent technical help in regards
to the laboratory work performed. But most of all I would like to thank Birgitte for being a
great “buddy”, not only in the beginning of my time in Årslev, but also during the entire
duration of this PhD project.
I would also like to thank Caroline Nebel and Camilla Bjerg Kristensen for
introducing me to SPME analysis, and for helping me with my experiments when I was in
Foulum, and I would like to thank Jens M. Madsen for taking some great pictures.
A special thanks goes to my reviewers Sidsel Jensen and Sandie Mejer Møller for
constructive criticism, encouraging comments and helpful advice, and for quick feedback
when it was needed. I would also like to thank Aase Karin Sørensen for thorough
proofreading of this thesis.
I would like to thank all of my colleagues in the Department of Food Science for
making Årslev a very cheerful and pleasant workplace. A special thanks goes to every one
of you, who got up early in the morning and helped me cutting Jerusalem artichoke tubers.
Finally, I would like to send my love and gratitude to my family and friends, who have
supported me through both easy and tough times in this three-year period. Especially, I
thank Anders for scientific challenging discussions and for his enormous help the last
months of this PhD.
Vibe Bach, Odense, September 2012

iii
ABSTRACT
Root crops exist in many different varieties, colours and shapes, but consumers are
unaware of how to handle and prepare these varieties. This project has focused on the root
crops Jerusalem artichoke tubers and beetroots. Both root crops are available in many
varieties with many different qualities, and both are underutilised among Danish
consumers. Increased knowledge of the qualities of the different varieties can be used to
guide consumers and industry in the choice of the right product for their individual needs.
The main aim of the present PhD project was to provide a chemical approach to
understand the sensory variation in root crops as an effect of raw material diversity and
culinary preparation. This included an investigation of the aroma, flavour, taste, texture
and colour of root crops. These parameters were analysed by sensory and instrumental
analyses, by analysis of the chemical composition and by a consumer study on the
appropriateness of root crops for culinary preparation.
Overall there were only few differences in sensory quality between varieties of
Jerusalem artichoke tubers and beetroots regardless of culinary preparation. When
differences were found, they were related to texture and taste. Larger differences were
found for raw than for boiled, baked and pan-fried root crops. The appropriateness of
Jerusalem artichoke tubers and beetroots in all culinary preparations were related to
crispness, juiciness, sweetness and colour intensity.
The volatile profiles of raw, boiled and baked Jerusalem artichoke tubers and
beetroots consisted mainly of terpenes, but lipid oxidation and Maillard products were also
produced during heat treatment. The sweetness and carbohydrate content of Jerusalem
artichoke tubers were determined by the maturity of the tuber at the time of harvest.
Beetroots were evaluated as sweet and bitter, and large differences between raw varieties
were found in the sensory attribute sweetness. These differences were not reflected in the
content of sugars and may be influenced by the content of bitter compounds. Jerusalem
artichoke tubers softened during heat treatment and in some cases developed mealy
characteristics. The inulin content of Jerusalem artichoke tubers probably affected the
texture development of the tubers during boiling and baking, as inulin was thermally
degraded by heat treatment. In Jerusalem artichoke tubers, enzymatic browning of raw
tubers and after-cooking darkening of boiled tubers were identified and associated with
low appropriateness. However, it was not possible to identify the chemical background for
these colour changes.
The results of this thesis clearly show that texture, taste and colour are the most
important parameters of root crop quality. This novel information can be used by
producers and retailers when growing and promoting root crops, and by consumers when
they are preparing and handling root crops in the kitchen.

iv
RESUMÉ
Rodfrugter findes i mange forskellige sorter, farver og former, dog er forbrugerne
uvidende om hvordan disse nye varianter skal tilberedes. Fokus i dette projekt har været
på rodfrugterne jordskok og rødbede. Begge findes i mange sorter med forskellige
kvaliteter, som ikke udnyttes til fulde blandt danske forbrugere. Øget kendskab til
kvaliteterne af de enkelte sorter, kan bruges til at vejlede forbrugere og producenter i
valget af det rigtige produkt til deres behov.
Hovedformålet med dette Ph.d. projekt var at udvikle en kemisk tilgang til
forståelsen af sensorisk variation og kulinarisk tilberedning. Dette inkluderede en
undersøgelse af aroma, flavour, smag, tekstur og farve af rodfrugter. Disse parametre blev
analyseret ved sensoriske og instrumentelle analyser, ved analyser af kemisk
sammensætning og ved forbrugeranalyse af egnetheden af rodfrugter i kulinariske
tilberedninger.
Der var gennemgående kun få forskelle på sensorisk kvalitet mellem sorterne af
jordskokker og rødbeder, uanset hvordan de var tilberedt. Når forskelle fandtes, var de
relateret til tekstur og smag. Der blev fundet større forskelle mellem sorter i de rå end i de
kogte, bagte og stegte rodfrugter. Egnetheden af jordskokker og rødbeder i alle
tilberedninger var relateret til sprødhed, saftighed, sødhed og farveintensitet.
Indholdet af flygtige forbindelser i rå, kogte og bagte jordskokker og rødbeder bestod
hovedsageligt af terpener, men oxidationsprodukter af lipider og Maillard produkter blev
dannet ved varmebehandling. Sødheden og kulhydratindholdet i jordskokker afhang af
hvor modenheden på høsttidspunktet. Rødbeder blev bedømt til at være både søde og
bitre, og der blev fundet stor variation i den sensorisk egenskab sødhed, mellem de
forskellige rå sorter. Disse variationer kunne dog ikke forklares af indholdet af
sukkerstoffer og kan være påvirket af indholdet af bitterstoffer. Jordskokker blev bløde
under varmebehandling, og i nogle tilfælde, udviklede de en melet konsistens.
Udviklingen af teksturen i jordskokker ved kogning og bagning er sandsynligvis
påvirket af indholdet af inulin, da inulin blev termisk nedbrudt ved varmebehandling.
Enzymatisk brunfarvning af rå jordskokker, og mørkfarvning efter tilberedning af kogte,
blev identificeret og associeret med lav egnethed. Dog var det ikke muligt at identificere
det kemiske grundlag for disse misfarvninger. Resultaterne i denne afhandling
demonstrerer tydeligt at tekstur, smag og farve er de vigtigste parametre for kvaliteten af
rodfrugter. Disse nye informationer kan bruges af producenter og forhandlere når
rodfrugter skal dyrkes eller promoveres, og af forbrugere når rodfrugter skal håndteres og
tilberedes i køkkenet.

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LIST OF PUBLICATIONS

Paper 1 Effects of harvest time and variety on sensory quality and chemical
composition of Jerusalem artichoke (Helianthus tuberosus L.) tubers.
Vibe Bach, Ulla Kidmose, Gitte K. Bjørn and Merete Edelenbos.
Food Chemistry (2012) 133, 82-89.

Paper 2 Metabolomics reveals drastic compositional changes during overwintering
of Jerusalem artichoke (Helianthus tuberosus) tubers.
Morten R. Clausen, Vibe Bach, Merete Edelenbos and Hanne C. Bertram.
Journal of Agricultural and Food Chemistry (2012) 60, 9495-9501.

Paper 3 The effect of culinary preparation on chemical composition and sensory
quality of Jerusalem artichoke tubers (Helianthus tuberosus L.).
Vibe Bach, Sidsel Jensen, Ulla Kidmose, Jørn N. Sørensen and Merete
Edelenbos.
LWT – Food Science and Technology, submitted September 2012.

Paper 4 Characterization of enzymatic browning and after-cooking darkening of
Jerusalem artichoke (Helianthus tuberosus L.) tubers.
Vibe Bach, Sidsel Jensen, Morten R. Clausen and Merete Edelenbos.
Food Chemistry, submitted September 2012.

Paper 5 Sensory quality and appropriateness of raw and boiled Jerusalem
artichoke tubers (Helianthus tuberosus L.).
Vibe Bach, Ulla Kidmose, Anette K. Thybo and Merete Edelenbos.
Journal of the Science of Food and Agriculture, accepted, DOI
10.1003/jsfa.5878.

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ABBREVIATIONS
CAR/PDMS Carboxen/polydimethylsiloxane
DH Dynamic headspace
DM Dry matter
DMAPP Dimethylallyl diphosphate
FAO Food and Agriculture Organization of the United Nations
FC Folin-Ciocalteu
FOS Fructooligosaccharides
FW Fresh weight
GC Gas chromatography
GC-MS GC-mass spectrometry
GC-O GC-Olfactometry
HPAEC High performance anion exchange chromatography
HPLC High performance liquid chromatography
HSPME Headspace SPME
IPP Isopentenyl diphosphate
LRI Linear retention index
MEP Methylerythtritol phosphate
NMR Nuclear magnetic resonance
NNF New Nordic food
PAL Phenylalanine ammonia-lyase
PCA Principal component analysis
PLS Partial least square
POD Peroxidase
PPO Polyphenol oxidase
QDA Quantitative descriptive analysis
Rt Retention time
SPME Solid phase micro extraction
TPA Texture profile analysis

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TABLE OF CONTENTS
Preface ........................................................................................................................... iii
Abstract........................................................................................................................... iv
Resumé ............................................................................................................................ v
List of publications ......................................................................................................... vi
Abbreviations ................................................................................................................ vii
1. Introduction ................................................................................................................. 1
2. Root crop ..................................................................................................................... 5
2.1 The plant root ......................................................................................................... 5
2.2 Root crop production............................................................................................ 6
2.3 Constituents in root crop ..................................................................................... 10
2.4 Raw material diversity ......................................................................................... 11
3. Sensory quality .......................................................................................................... 12
3.1 Perception ............................................................................................................ 12
3.2 Evaluating sensory quality .................................................................................. 13
3.3 Descriptive sensory analysis of root crops .......................................................... 14
3.4 Consumer evaluations of root crops .................................................................... 17
4. Aroma and flavour .................................................................................................... 22
4.1 Aroma and flavour compounds .......................................................................... 22
4.2 Isolation of volatile compounds ......................................................................... 24
4.3. relating volatile compounds and sensory analysis ............................................ 29
4.4 Volatile compounds in culinary preparations of root crops .............................. 30
5. Taste .......................................................................................................................... 36
5.1 Taste Compounds ................................................................................................ 36
5.1 Taste compounds in root crops ........................................................................... 36
6. Texture ...................................................................................................................... 42
6.1 Texture properties ............................................................................................... 42
6.2 Measuring root crop texture ............................................................................... 43
6.3 Texture of culinary prepared root crops ............................................................ 44
7. Colour ........................................................................................................................ 47
7.1 Pigments in root crops ......................................................................................... 47
7.2 Enzymatic browning ........................................................................................... 48
7.3 After-cooking darkening ..................................................................................... 50
7.4 Discolouration of Jerusalem artichoke tubers .................................................... 51
8. Conclusions and perspectives ................................................................................... 55

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1. INTRODUCTION
Root crops have several positive qualities, which make them ideal constituents of a
healthy diet, but their potential, as a food source is not fully exploited. In this thesis root
crops are defined as any underground part of a plant e.g. root or tuber, which can be eaten
cooked as part of a main meal. There are several advantages in increasing the intake of root
crops in the Danish population. First of all, root crops have great nutritional and health
beneficial qualities such as high fibre and mineral content, and they are rich sources of
secondary metabolites with possible biological activities (Saxholt et al. 2008; Brandt et al.
2004). Secondly, many root crops are suitable for growth in the temperate climate of
Northern Europe, and when used as a part of a locally produced diet, root crops can reduce
the carbon footprint. Furthermore, an increased intake will be an economical advantage
for the local producers, while root crops remains a cheap vegetable product for the
consumers.
Carrot and potatoes are the most prevalent root crops eaten in Denmark. The average
Danish consumption of root crops is 882 g/week of which 658 g/week are potatoes (Meyer
et al. 2010). Root crops have been an important part of the Northern diet for centuries, as
they could be eaten fresh in the summer and autumn, or stored and eaten over the winter
to provide nutrients and contribute to a varied diet all year (Haastrup 2003). During the
1970’s meat became the dominant part of the dinner, and although potatoes were still
important, they were gradually partially replaced by rice and pasta. During this period,
lettuces, tomatoes, cucumbers and other vegetables with high water and low fibre content,
which became available in the supermarkets all year round (Haastrup 2003), replaced
coarse vegetables like cabbage and root crops. In the last decade, the consumption of the
coarse vegetables including root crops has increased, with a simultaneous small decline in
the use of salad-vegetables (Fagt et al. 2008). This increase can probably be ascribed to the
focus on the concept New Nordic Food (NNF), which was introduced in 2004 by a group of
Danish chefs (Meyer et al. 2010). Root crops fit well in the context of NNF as the manifest
focuses on the use of products, which are suited for growth in the Nordic climate, and
which reflect the changing seasons. NNF recommends that the consumption of root crops
is increased to 1050 g/week for root vegetables and to 980 g/week for potatoes (Meyer et
al. 2010).
A large genetic diversity is found between and within the individual species of root
crops expressed as differences in colour, shape, aroma, taste, flavour and texture. The

1
influence of this variation on the eating quality is well understood in raw carrots
(Kreutzmann et al. 2008b; Kreutzmann et al. 2007; Szymczak et al. 2007; Surles et al.
2004; Alasalvar et al. 2001) and in raw and cooked potatoes (Seefeldt et al. 2011a), but
information on other Nordic root crops is lacking. The culinary possibilities arising from
product diversity is not exploited to its full extent. Consumers do often not know how to
handle unfamiliar and culinary diverse root crops, and the liking or preference of well-
known products is often higher than for new unknown products (Szymczak et al. 2007;
Surles et al. 2004; Sangketkit et al. 2000; Busch et al. 2000). Appearance is the key
attractant for consumers to buy novel products, but re-purchase is determined by the
actual experience of aroma, flavour, taste and texture (Barrett et al. 2010). The relationship
between expected and experienced quality is considered to be deciding for consumer
satisfaction, and the probability of repeated purchase (Espejel et al. 2008; Oliver 1993,
1980). An understanding of the sensory quality and of the chemical composition behind
quality differences, can be used to guide consumers and industry to choose the most
suitable raw material for a specific culinary preparation. This will increase the probability
of consumer satisfaction and eventually lead to a higher consumption of root crops.
Sensory analysis is the best descriptor of food quality perception (Martens & Martens
2001), but chemical analysis can provide an understanding of the underlying factors, and
an explanation for the sensory observation.
The work in this PhD project has focused on Jerusalem artichoke tubers and
beetroots. These two root crops have a large potential to expand their utilization in
Denmark. The Jerusalem artichoke tubers have increased in popularity within the last
decade, but the consumption is still limited outside restaurant settings. Knowledge on the
eating quality of Jerusalem artichoke tubers is sparse. Denmark is maintaining a gene
bank of 18 Jerusalem artichoke varieties placed at Aarhus University Aarslev, which
constitutes a solid basis for an investigation of their quality for culinary preparations.
Beetroots are traditionally eaten pickled, but have great potential for use in a range of
culinary preparations. Besides this, mainly the dark red varieties are employed at the
present, although beetroots exists in a large variation of colours, sizes and shapes, which
can add to the diversity of the Danish diet.
The overall objective of this PhD project is to investigate the aroma, flavour, taste,
texture and colour of root crops in relation to harvest time, variety and culinary
preparation. The quality parameters were chosen on the basis of sensory evaluation and

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