Vol. 78, No. 6, 2001 707 Effect of Drying Treatment Conditions on Sensory Profile of Germinated Oat R.-L. Heiniö, 1,2 K.-M. Oksman-Caldentey, 1 K. Latva-Kala, 1 P. Lehtinen, 3 and K. Poutanen 1 ABSTRACT Cereal Chem. 78(6):707–714 Germination and subsequent drying of oat produced significantly different sensory profiles depending on processing parameters such as drying speed and temperature profile. The most salient sensory attributes for processed oat were roasted odor and flavor, sweet taste, intense odor, intense aftertaste, and hard, crisp, brittle texture (P < 0.05). High temperatures (>85ºC) were necessary to produce these sensory attributes, and quick drying after germination resulted in higher levels of intensity of favorable sensory attributes. The total amount of volatile compounds was higher in native (ungerminated) oat than in processed oat. During germination, and particularly during the drying treatment, the profile of volatile compounds changed. The most abundant volatile compounds responsible for odor were dimethyl sulfide, hexanal, pentanal, and iso- butanal. The relative amount of dimethyl sulfide increased as a function of temperature in drying, whereas hexanal, pentanal, and isobutanal dis- appeared during heating, as did several other small ketones, alcohols, and esters. The germinated oat dried at high temperatures (65–93°C and 65– 85°C) was perceived as being roasted, sweet, and nutty. Sensory and instrumental profile analyses of selected volatile compounds using partial least squares (PLS) regression techniques showed that these sensory attributes were clearly related to dimethyl sulfides and isobutanol. A moist and earthy odor was related to cymene, limonene, and isobutanal. Phenolic compounds significantly influenced oat flavor, whereas lipids had a negligible effect. Oat is perceived as a tasty cereal with a positive health image, but bitter off-flavor and tendency to rancidity limits its use. Cur- rently, oat is generally used in cereals and flaked products but its use could be extended to entirely new food applications such as convenience foods. Sensory quality is an important criterion in con- sumer food choice; tailoring of sensory attributes improves the acceptability of oat ingredients in different applications. Oat flavor is mainly formed during processing. It is important to know the impact of precursors and enzymes of the native oat on flavor formation. Important volatile compounds identified in native oat include 3-methylbutanal, 2,4-decadienal, and benzaldehyde which are associated with raw oat, weed-hay, and grass-like flavors (Hey- danek and McGorrin 1986). The flavor of processed oat is a complex, precursor- and heat-dependent combination of volatile compounds. The flavor of cooked oat is reportedly more oat-like, nutty, browned, or burnt. The nutty flavor of toasted oat originates mainly from carbonyl compounds and amines (Heydanek and Mc- Gorrin 1986). Maillard reaction products such as heterocyclic pyrazines, pyrroles, furans, and sulfur-containing compounds are abundant in high-temperature, low-moisture extruded oats and pro- duce toasted or roasted flavors (Pfannhauser 1993; Parker et al 2000). Volatile pyrazines and oxidation products of lipids are also important for the flavor of other cereals (Pfannhauser 1993). At lower processing temperatures and higher moisture levels, other types of volatile compounds influence oat flavor. The com- position of volatile compounds responsible for the perceived odor and flavor varies depending on the analysis method used and the type of processing. The major volatile compounds found in moistened, extruded oat flour stored at 32°C were hexanal, decane, 2-pentyl- furan, and nonanal (Sjövall et al 1997). Depending on the drying treatment used, the most important volatile compounds influencing oat flavor were terpenes, alkylbenzenes, aldehydes, alcohols, and heterocyclic compounds (Dimberg et al 1996). In addition, some nonvolatile substances such as phenolic compounds, free fatty acids, reducing sugars, and free amino acids might influence oat flavor. Even very small amounts of phenolic acids, phenolic aldehydes, vanilline, and avenanthramides influence oat flavor. Their release is dependent on humidity, time and temperature during processing, and oat cultivar (Molteberg et al 1996b). Rancid, bitter, intense flavor may be en- hanced by moisture level and phenolic compounds; while fresh oat- like odor and flavor may be decreased. Avenanthramides may be related to low flavor intensity and rancidity; and caffeic acid and fat acidity may be related to less sweetness and aftertaste. The mouthfeel of oat is mainly affected by β-glucan and pentosans which are responsible for its rheological properties. The perceived textural properties of cooked oatmeal from different oat cultivars were significantly different, whereas no differences were found in odor and flavor attributes (Lapveteläinen and Rannikko 2000). Germination is well known to intensify both the color and flavor of grain products. To date, it has been used mostly for barley. Germination of barley has been shown to change its flavor profile significantly from fruity, hay-like (native barley), to burnt, bread-like, malty, and chocolate-like (germinated-dried barley) (Beal and Mot- tram 1993). There is little data in the literature on the effect of germination on oat. We previously studied the microbiological and chemical changes during germination of oat (Wilhelmson et al 2001). In this investigation, we wanted to specify how the sensory profile of oat is altered by the germination process followed by drying treat- ment, and why these changes occur. MATERIALS AND METHODS Oat Samples Two oat cultivars, hulled Veli and hull-less (naked) Lisbeth, har- vested in summer 1997 in Finland, were used in the present study. Germination conditions have been described elsewhere (Wilhelmson et al 2001). Several drying treatments (Table I) were tested. Native (ungerminated) Veli or Lisbeth grains were used as a control. The Veli cultivar was always dehulled before sensory evaluation. To analyze the effect of the germination process, native, ger- minated-undried, and germinated-dried oat grains of both cultivars were profiled by a trained sensory panel. To determine the effect of the drying temperature, four drying treatments were used for the germinated oat: 65–93, 65–85, 30–50°C, and freeze-dried. Also compared were two alternative drying treatments: slow stepwise temperature increase over 17 hr from 65 to 100°C, or raising the temperature quickly over 40 min from 65 to 100°C (Table I). Sensory Analysis The sensory profiles of the oat grains were evaluated by a trained panel (n = 6–17) with proven skills using descriptive analysis (Stone et al 1974; Stone and Sidel 1993, 1998). The vocabulary of 1 VTT Biotechnology, P.O. Box 1500, FIN-02044 VTT Finland. 2 Corresponding author. E-mail: raija-liisa.heinio@vtt.fi Phone: +358 9 456 5178. Fax: +358 9 455 2103. 3 Helsinki University of Technology, P.O. Box 1000, FIN-02015 TKK Finland. Publication no. C-2001-1002-05R. © 2001 American Association of Cereal Chemists, Inc.