1. Rye grain fractions show different sensory and chemical stability
C & E Spring meeting – Texture, flavour and taste
11-13 April 2011, Freising, Germany
Raija-Liisa Heiniö VTT Technical Research Centre of Finland

2. Introduction

3. "To eat healthy and to eat tasty?" - facing the challenge
How to introduce healthy components without compromising sensory quality and production costs?  
White wheat bread
Whole grain wheat
with added bran

4. Sensory quality and consumption of wholegrain foods Barriers between dietary recommendations and actual consumption
Lack of understanding health benefits
Difficulties in identifying whole grain foods
Dietary recommendations not felt to be personally relevant
Taste and texture perception most obvious reason for consumers
Price
Adams and Engström, 2000; Lang and Jebb, 2003; Seal et al., 2006; Lappalainen et al., 1998
'Wholegrain consumption will increase with better taste' Richard Shepherd (Healthgrain), C&E in May 2007 Montpellier, France

5. Sensory evaluation is based on multimodal perception using all senses Brains analyse perceptions
Seeing and smelling
Feeling and hearing
Retronasal smelling
Tasting
Overall perception
Chemoreception

6. PERCEIVED CEREAL FLAVOUR
Chemistry of cereal flavour
Volatile compounds (odour) as such
Non-volatile compounds (flavour) as such or as flavour precursors
Phenolic
compounds
Amino acids,
small peptides
PERCEIVED
CEREAL FLAVOUR
Fatty acids,
lipids
Volatile
compounds
Acids
Sugars

7. Factors having impact on cereal flavour
Location and amount of potential flavour-active compounds in matrix
Processing
Potential reactions
Non-enzymatic reactions
Oxidation
Enzymatic reactions (Endogenic and/or added enzymes), such as
Release from matrix
Hydrolysis

8. Distribution of flavour (e.g. bitterness) and bioactivity in rye grain
In mechanical milling fractionation rye kernel is separated into fractions, each of them having their characteristic flavour and phytochemicals
Heiniö R-L et al. LWT 2003, JCS 2008
Endosperm: Mild flavour
Bran:Strong,bitter flavour
Bitterness-Pinoresinol & syringic acid; Germ-like flavour-Sinapic & ferulic acids, alkylresorcinols, except AlkrC23:0, syringaresinol
Shorts: Rye-like flavour without bitterness
Cereal flavour-Vanillic & veratric acids, alkylresorcinol C23:0, lignans except pinoresinol
Ferulic acid (main phenolic acid in rye) not important to bitterness
Small peptides may cause bitterness
Heat treatment decreases perceived bitterness Heiniö R-L et al. 2005

9. Phenolic acids and lignans
Bioactive compounds located in outer grain layers and related to flavour attributes -
0.6
0.4
0.2
0.8
1.0
0.1
0.3
0.5
Sinapic acid
Syringic acid
Vanillic acid
Ferulic acid p OH
Benzoic acid
Veratric acid
CEREAL FLAVOUR
FRESHNESS
SWEETNESS
BITTERNESS
GERM
LIKE FL.
FLAVOUR INTENSITY
AFTERTASTE
PC1
PC2
Enriched bran
Bran
C Flour
Shorts
B Flour - 2 1 3 4
0.2
0.1
0.3
0.4
0.5
Secoisolariresinol
Matairesinol
Isolariresinol
Lariresinol
Pinoresinol
Syringaresinol
CEREAL FLAVOUR
FRESHNESS
SWEETNESS
BITTERNESS
GERM
LIKE FL.
FLAVOUR INT.
AFTERTASTE
PC1
PC2
C Flour
B Flour
Shorts
Bran
Enriched bran
Phenolic acids and lignans
Heiniö R-L et al. LWT 2003, JCS 2008

10. Objectives To study sensory quality and storage stability of different rye grain fractions in relation to their chemical composition
Sensory analysis by descriptive profiling to measure sensory characteristics of products
Analysis of volatile and non-volatile compounds
Relation of perceived flavour and chemical, flavour-active compounds by using statistical multivariate techniques (PLS regression)

11. Methods

12. Mechanical processing of rye kernels for fractionation of rye
(A) Consecutive milling and air classification process of rye flour R1 to produce rye fractions R3 and R4
(B) Progressive milling and sieving of rye kernels to produce rye bran R7

13. Analysis of the rye fractions
Sensory profiles and chemical composition of the rye samples: wholegrain R1 and fractions R3 (endosperm), R4 (air-classified bran) and R7 (sieved bran)
Sensory perception (n=2x10) of rye fractions in two forms
“raw” water extracts, i.e. supernatants prepared of the rye fractions
baked flour-water suspensions, i.e. ‘rye crackers’
Chemical composition of the rye fractions (water extracts)
Dietary fibre, ash, phenolic compounds, fat, protein, starch, LOX activity, antioxidativity

14. Rye crackers (baked flour-water suspensions) made of flour-water suspensions of R1 (wholegrain), R3 (endosperm), R4 (bran) and R7 (bran)

15. Results

16. Sensory profiles of baked flour-water suspensions, ‘rye crackers’ wholegrain R1, endosperm R3, and brans R4 (air-classified) and R7 (sieved) (n=2x10)
Bran fractions more bitter than WG or endosperm

17. Sensory analysis of the fractions
Sensory profiling of the rye crackers of R1, R3, R4 and R7
Bran fractions R4 and R7 more bitter than WG or mild-tasting endosperm
Endosperm R3 significantly mildest with respect to all assessed attributes except for sweetness (p<0.05)
Crackers made of bran materials R4 and R7
Darkest in colour, most rough in texture, most rye-like, bitter and intense in their flavour and aftertaste
R7 crackers slightly more bitter and intense in flavour than those of R4 crackers, but not statistically significantly

18. Chemical composition of the fractions
Component R1 R3 R4 R7
Protein
12.9±0.1
9.2±0.0
15.8±0.1
19.0±0.1
Crude fat
2.4±0.0
1.3±0.0
3.7±0.0
Ash
1.4±0.0
0.7±0.0
2.6±0.0
2.5±0.0
Carbohydrates
76.3±1.9
93.1±3.7
50.6±2.6
51.0±0.2
Soluble dietary fiber
4.7±0.0
2.9±0.0
7.9±0.1
6.5±0.0
Insoluble dietary fiber
11.7±0.0
4.3±0.2
27.6±0.9
23.4±0.0
Water soluble pentosan
1.5±0.0
1.0±0.0
1.7±0.1
Total pentosan
7.9±0.2
4.2±0.1
14.8±0.0
14.0±0.4
β-Glucan
2.4±0.1
0.9±0.0
5.0±0.1
3.6±0.1
Reducing sugars
2.3±0.1
1.9±0.0
3.2±0.0
Free glucose
0.15±0.00
0.09±0.00
0.18±0.00
0.21±0.00
Free amino nitrogen, FAN
0.25±0.00
0.16±0.00
0.35±0.02
0.40±0.02
Total phenolic compounds (F-C)
0.17±0.00
0.08±0.00
0.37±0.00
0.35±0.00
Free phenolic compounds (F-C)
0.04±0.00
0.13±0.01
Total phenolic compounds
0.41±0.02
0.36±0.01
Lipoxygenase (LOX)
41.8±2.6
10.5±1.1
109.0±3.9
110±4.0
Spontaneus oxygen consumption
2.50.3
1.11.0
4.50.2
2.30.4

19. Chemical composition of the fractions
Different chemical composition in coarse and fine fractions of rye
Dietary fibre, ash, phenolic compounds, fat and protein concentrated in coarse fractions R4 and R7
Starch located mainly in fine fractions R3 (and R5)
LOX activity concentrated in bran fractions R4 and R7
Antioxidant activity (DPPH) highest in WG R1 and bran R4, lowest in endosperm R3
Similar chemical composition in bran fractions R4 (air-classified) and R7 (sieved), except
More dietary fibre (ß-glucans) and phenolic compounds in R4 than in R7
Protein, amino acid, peptide and sugar contents lower in R4 than in R7
Different amount of lipids, but similar lipid class composition in all fractions
Neutral triacylglycerols being the major lipid class

20. Characteristics of the rye fractions
Rye fractions with distinctive chemical composition had differences in their sensory profiles
Intensive, bitter flavour of rye previously related to certain phenolic compounds and small peptides present in rye
What about impact of fats?
The rye bran fractions R4 (air-classification) or R7 (sieving) not significantly different in their flavour profiles
The bran fractions had rather similar chemical composition
Only difference between sensory profiles of bran samples was higher viscosity of air-classified bran suspension; it had smaller particle size → better water absorption capability & arabinoxylan extractability

21. Storage-related changes in sensory and chemical properties
Bitterness and rancidity of the fractions increased during storage, but fractions showed clearly different changes in their flavour profiles
Rancidity increased mostly in endosperm R3, whereas bitterness increased in bran fraction R4 and aftertaste intensity in wholegrain R1
Sensory attributes of air-classified R4 and sieved R7 brans changed at different rates
Development rate of rancidity, bitterness and flavour intensity faster in R4 than in R7
Rancidity of R4 increased at 6 months, whereas in R7 the increase in rancidity was rather small
Composition of lipids changed during storage → action of endogenous lipase
Amount of triacylglycerols decreased, amount of free fatty acids increased, and overall content of lipids decreased with storage time
Oxidation of unsaturated fatty acids (decrease in DUS) more pronounced in endosperm than in other fractions
No major difference in behaviour of lipids between the bran samples R4 and R7

22. Relative amounts of polar lipids, triglycerides, diglycerides and free fatty acids during 12 months storage
Wholegrain (R1)
Endosperm (R3)
Bran (R4) R1 R3 R4

23. Relation between lipids and perceived flavour of the rye fractions during 12 months storage period
Bitterness vs. triglycerols
Rancidity vs. FFAs
PLS regression model explained 100% of variation of lipid data and 36% of variation of sensory results between the rye fractions

24. Relation between sensory profiles and lipid composition of the fractions during storage
Perceived rancid flavour strongly related to free fatty acids, which are thus a feasible reason for rancidity
Rancidity appeared especially in endosperm already after 6 months and also in wholegrain after 12 months storage
Bitterness related to triglycerols, which were noticed in high amounts in bran fractions after 6 and 9 month storage and in wholegrain after 3 and 6 months storage
Diglycerols related to endosperm stored for 3 months
Deterioration of cereal flavour during storage is related to oxidation and hydrolysis of lipids → Rancid flavour
Inhibition of formation of rancid flavour by phenolic compounds

25. Conclusions
Wholegrain rye, endosperm and differently processed bran fractions had different chemical properties and sensory profiles, but also different storage stability
Endosperm had mildest flavour, but its storage stability was poorest
Bran was highest in nutritional quality and had intense, bitter flavour, which enhanced during storage, whereas no increase in rancidity was detected
High phenolic content of bran reduced formation of flavour active lipid-derived oxidation products through high antioxidant activity
Increase in flavour intensity and bitterness in bran due to reactions related either to lipid, protein or phenolic compounds
No significant differences in flavour profiles of air-classified (R4) and sieved (R7) bran fractions, but their storage stability differed
Changes in development rate of rancidity and intensity of flavour faster in air-classified bran than in sieved bran - Due to different susceptibility of bran fractions to oxidation reactions, caused by different microstructure, particle size and different surface areas

26. Thank you raija-liisa.heinio@vtt.fi Raija-Liisa Heiniö1
Emilia Nordlund1
Juha-Matti Pihlava2
Pekka Lehtinen1
Kaisa Poutanen1, 3
Thank you
1VTT Technical Research Centre of Finland, 2MTT Agrifood Research Finland, 3University of Eastern Finland