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

Introduction

"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

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

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

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

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

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

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

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)

Methods

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

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

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

Results

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

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

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

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

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

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

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

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

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

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

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