WO2002028201A1

WO2002028201A1 - Method for producing an oat product and an oat cereal and a snack product produced with said method

Info

Publication number: WO2002028201A1
Application number: PCT/FI2001/000865
Authority: WO
Inventors: Olavi Myllymäki; Kaisa Poutanen; Kirsi-Marja Oksman-Caldentey; Arja Laitila; Raija-Liisa HEINIÖ
Original assignee: Valtion Teknillinen Tutkimuskeskus
Priority date: 2000-10-06
Filing date: 2001-10-05
Publication date: 2002-04-11
Also published as: FI20002205A; FI114380B; JP2004510419A; AU2001293901A1; FI20002205A0; WO2002028201B1

Abstract

The invention is directed to a method for producing an oat product wherein the tastiness and the sensory texture of oats are improved, and the contents of functional components are increased. In this method, the oat grains are melted using steeping and germination in a liquid phase, followed by drying and extrusion thereof. Steeping and germination temperatures are low, and a short malting procedure gives grains having a good microbiological quality, higher sterol and phenol contents, and a higher antioxidative capacity, without a significant reduction of the β-glucan content thereof.

Description

Method for producing an oat product and an oat cereal and a snack product produced with said method

The present invention relates to a method for producing an oat product, and an oat ce- real and a snack product obtained with this method.

In contrast to the malting of other cereals, the malting of oat has been studied relatively little. Studies have mainly been directed to brewing of beer, the object being then to decompose β-glucans. Malting times in these studies have been long, even 8 days. Increasing malting times often cause deterioration of the microbiological quality of the germinating material. In malting, no attention has earlier been directed to the functional components of oats.

Malting means a process consisting of three steps, that is, the steeping, germination, and drying of grains .

During germination, several complex chemical changes take place such as decomposition of the nutrient reserves, bioactive mass transfer within the grains, and synthesis of new products from these decomposition products.

At lower steeping temperatures, reactions resembling the germination process may affect - for instance in the form of activated enzymes -the components of grains and flavor factors. With the exception of some endoglucanase enzymes, the enzymes of oats are inactivated at higher temperatures.

Patent DE 1 907 830 discloses a method for producing malt from grits cereal more economically and efficiently.

In DE 3 212 390, barley or wheat is malted in a conventional manner, dried in un- comminuted form, roughly ground and extruded. This extruded product may be used for the preparation of wort.

Document DE 3 211 332 presents a method for malting cereal wherein the starch contained in grains is converted to water soluble sugars and the dissolved sugars are separated from the malt by crystallization. Malt is further treated by rolling, crushing or grinding. Patent US 4 613 507 discloses a method for producing a food composition having a malt-like flavor. In this method, grains are germinated and further incubated to obtain real roots. These roots are roasted to endow them with a malt-like flavor. These roasted roots may be used in food products or drinks as a source of malt-like flavor.

In patent EP 319 726, the invention is directed to a drinkable extract made from germs of grain. In this method, the germination is carried out at a temperature higher than 25 °C to improve the vitamin synthesis.

Patent SE 505 893 presents a method to improve the bioavailability of minerals contained in products based on whole oat grains. In this publication, a method for malting uncomminuted oats is disclosed. The object is to decrease the phytate content considerably. Malted and dried oat grains are ground to oatmeal.

Patent FR 271 6774 discloses the preparation of corn flakes from corn flour using extrusion. Dough prepared from corn flour may also be mixed with some malt.

The article "Malting oats: effects on chemical composition of hull-less and hulled genotypes" [Peterson D., Cereal Chem. (2000) 75 (2): 230 - 234] teaches that during malting of oats nearly all β-glucans were decomposed.

The object of the present invention was to improve and increase the content and quality of the functional components of oats and simultaneously improve the sensory properties thereof thus allowing for the preparation of a tasty wholesome product such as a snack product from oats.

The object is attained with the shortened malting procedure according to the present invention. The malting procedure of the invention is substantially shorter than the prior art malting procedures. The level of β-glucans of the oat grains remains high in contrast to β-glucan levels in the conventional malting. Surprisingly it was found that the wholesome components are not destroyed as the oat malt prepared with this shortened malting procedure is extruded. In addition, the microbiological quality is good.

As in the conventional malting, also in the shortened malting the aroma of oats is changed. With extrusion, a tasty product is obtained having a high content of wholesome components, such as β-glucans. Oats processed with the method of the inven- tion may be used as a functional food product, a raw material for, or a component in a functional food product.

The invention is directed to a method for producing an oat product. The method is characterized in that oat grains are submitted to a shortened steeping, germination and drying, and then the dried grains are ground and processed with extrusion to a cereal product.

Malting

An optimal malting procedure was developed by carrying out small scale malting tests with hulless Lisbeth oats and unhulled Veli oats. The determination of the malting procedure was based on the α-amylase and β-glucan contents of oat malt. The process parameters used were the desired moisture content of 38 %, germination temperature of +15 °C, and germination time of 2 to 3 days. The object of germina- tion and drying accompanying it was to increase the tastiness of oats, to improve the sensory texture of the grain and increase the contents of known functional components due to biotechnological processes during germination.

Assay method for sensory quality

Optimal malting procedure (steeping, germination and drying operations) is based on the sensory evaluation of the malt after the malting. The sensory quality of processed or unprocessed oat grains was evaluated with the quantitative descriptive analysis (QDA) by a panel of trained experts (N = 6 - 17) with tested senses and experienced in sensory evaluation. Part of the evaluations was carried out as repeated tests.

The oat samples were presented to the assessors in coded form and in randomized order of presentation. Mouth was rinsed with water between the samples. The results of the sensory evaluation of the grains of different oat varieties processed in a different way (germinated, dried or extruded) were analyzed with statistical methods. Variance analysis was used to determine the significance of the difference between the samples with respect to a given evaluated characteristic in general, and Tukey's test was used for the significance of the difference with respect to a given evaluated characteristic between individual samples. Optimization of the steeping and germination method

The best germination procedure suitable for oats was the shortened malting procedure wherein the critical moisture content of the oat grain was between 33 and 35 %, that of barley being 45 %, for example. In this shortened malting procedure, oats are wet steeped, that is soaked in water for 2 hours, thereafter dry steeped for 8 to 10 hours by draining off the free water. Dry steeping is followed by wet steeping for 2 hours, draining of the water and finally dry steeping to attain a total germination time of 3 days.

The β-glucan contents of Lisbeth oats malted with this shortened malting procedure were measured with a method described by McCleary and Mugford [Journal of AOAC International, 80 (1997) 3:580-583]. β-glucan contents remained relatively high, that is at 3.2 %, β-glucan contents of the starting material, i.e. native Lisbeth oats being 4.8 %. β-glucan contents of 4.7 % of the Veli oat variety also decreased to 3.2 % during malting.

Plant sterol contents increase from 48.9 mg/100 g of native Lisbeth oats to 64.4 mg/100 g of malted Lisbeth oats. The plant sterol contents of the Veli oat variety in- crease less during malting, from 47.2 mg/100 g of native oats to 52.6 mg/100 g. Assayed plant sterols include campesterol, stigmasterol, sitosterol, sitostanol, d5- avenasterol, d7-avenasterol.and 24-methylsylcoartenol. The main component is sitosterol.

Optimization of the drying method

To optimize the drying method with respect to the sensory quality, germinated oats were dried for different periods of time at different temperatures to provide drying temperature and time profiles differing from each other. In addition to low temperature drying the following drying procedures were tested.

In the drying program from 30 to 50 °C, the oat malt was kept for 8 hours at 30 °C, thereafter the temperature was raised in 2 hours to 50 °C keeping the malt in this temperature for 15 hours.

In the drying program from 40 to 85 °C, the malted oat was kept for 3 hours at 40 °C, then for 7 hours at 50 °C, for 6 hours at 60 °C and finally for 3 hours at 85 °C. The drying program from 65 to 85 °C comprised the following successive steps: for 5 h at 65 °C, then for 4 h at each of the following temperatures: 70 °C, 75 °C, 80 °C and finally 85 °C.

The drying program from 65 to 93 °C comprised the following successive steps: for 5 h at 65 °C, thereafter the temperature was raised in 6 hours to 75 °C with the residence time of 2 hours, then the temperature was raised in 4 hours from 75 °C to 85 °C, the residence time at that temperature being 1 hour. As the final step, the temperature was raised in 1 hour from 85 °C to 93 °C.

In the drying program from 65 to 100 °C, the following temperatures and residence times were used: at 65 °C for 10 minutes, raise to 100 °C in 30 minutes, at 100 °C for 4 hours.

Total phenol content and antioxidative capacity (radical capturing activity) of the hulless Lisbeth oat variety were considerably increased by the malting process. The total phenol content of the native grain measured with the Folin-Ciocalteu method described below was about 400 mg/kg of dry matter expressed as gallic acid equivalents (GAE). After malting and drying with the drying program from 30 to 50 °C, the total phenol content was as high as 1250 mg GAE / kg of dry matter. Higher drying temperatures still gave somewhat higher phenol results: drying temperature of 65 - 85 °C gave about 1300 mg GAE / kg of dry matter, and drying temperature of 65 - 83 °C gave about 1370 mg GAE / kg of dry matter. The DPPH radical capturing activity of the methanol extract (0.1 g/ml) of the Lisbeth variety measured with the method described below was 27 to 52 % of the value assayed for the pyrogallol reference compound (125 mg/1). The lowest activities were measured for the native grain, without any clear differences between different drying temperatures.

The influence of the malting process to the total phenol content and radical capturing activity of the unhulled Veli oat variety was not so strong as in the case of Lisbeth variety. The total phenol content of hulled Veli variety was 300 to 500 GAE / kg of dry matter. However, the native grain had the lowest total phenol content and the total phenol content of malted grain seemed to increase slightly with rising drying temperatures. In the measurement of the radical capturing activity, a higher concentration was used for the Veli variety (0,5 g/ml) due to lower activity than that of the Lisbeth variety. Radical capturing activity of 33 to 39 % was measured. Slightly lower activities were measured for native grains. Sensory quality of malted oats

With respect to several properties, different drying procedures cause significant differences in the sensory profile of oats. Sensory quality of oats processed at higher temperatures is more promising for several sensory properties as for oats dried at a low, or a very low temperature. Roasted odour was observed for samples dried at a high temperature (65 to 100 °C, 65 to 93 °C, and 65 to 85 °C), the taste and aftertaste thereof were evaluated as more intensive and sweeter, and the texture thereof was firmer and crisper than for other samples.

With respect to the firmness of the texture, differences could be observed between oat varieties (hulless Lisbeth and unhulled Veli). Both varieties were submitted to sensory evaluation as a native product and as products germinated in different ways and either undried or dried with different methods. Also the sensory profiles of na- tive, germinated and undried, or germinated and dried oats were found to differ clearly from each other with respect to several sensory properties (roasted character, moisture content, staleness, earthiness, and intensity of the odour, cereal-like character, roasted character and sweetness of the taste, the intensity of the after-taste, and the firmness, toughness, moisture content, crispness, and friability of the texture).

By means of processing, oats are endowed with a pleasant, roasted, nut-like flavor and crisp texture that are well preserved also during storage. The temperature of 93 °C attained in the drying process of the malted product was sufficient for the formation of flavor. In addition it was found that said sensory properties were most in- tensive when heating was carried out in 30 minutes from 65 °C to 100 °C, the total drying time being 4.5 hours.

Bitter taste naturally occurring in unprocessed oats is clearly weaker for the malted oats than for the native (unmalted) oats. Moreover, the bitterness of malted oats be- comes still weaker during the first three months of storage, whereas the bitterness of native oats increases during storage. After six months of storage, slightly more bitterness may be observed also for malted oats. During storage, the taste of native oats becomes increasingly rancid with time. For oats undergone such malting treatment, this increasingly rancid character develops clearly more slowly than for native oats. Determination of radical capturing activity and total phenol content of oat samples

Preparation of extracts

1.5 grams of ground oat sample were extracted with 10 ml of HPLC grade methanol (using magnetic stirring for 60 minutes and ultrasonic bath for 20 minutes). The sample was centrifuged and the supernatant was pipetted into a round bottom flask. The extraction was repeated with 10 ml of methanol and the supernatants were pooled. The pooled supernatants were evaporated to dryness with a rotary evaporator with a water bath, at the temperature of +35 °C. The soluble evaporation residues were dissolved in 1.5 ml of HPLC grade methanol. The solution was pipetted into glass vials having a volume of 1.5 ml. The samples were stored in a freezer at -20 °C. Before the assay the samples were filtered.

Total phenol content

The total phenol contents of the oat extracts were determined with the Folin- Ciocalteu method. The principle of the method and working instructions are presented by Singleton & Rossi in Am. J. Enol. Vitic. (1965) 16: 144 - 158, this basic method being modified by several research teams for the particular application. In connection with this invention, the changes made to the basic method were the use of methanol instead of water as the extracting solvent, and the use of smaller solvent volumes. The total phenol content is given as gallic acid equivalents (GAE), in mg/kg of dry matter (residual moisture is ignored in the calculations of the results).

100 μl of the sample, or standard in methanol, or 100 μl of methanol as blank were pipetted in Eppendorf tubes. 100 μl of methanol was added in all tubes. 100 μl of Fo- lin-Ciocalteu phenolic reagent and immediately thereafter 700 μl of 20 % Na₂C0₃ solution were pipetted into the tubes. The tubes were mixed thoroughly by vortexing. The tubes were centrifuged for 3 minutes at 14 000 rpm and allowed to stand in the dark for 20 minutes. The absorbance was measured at 735 nm. With gallic acid, a standard curve was made using concentrations of 5, 10, 20, 30, 40, 50, and 60 mg/1. The equation of the straight line was established using the mean of six parallel measurements. Radical capturing activity

The radical capturing activity was determined with the slightly modified Malterud method [Malterud et al, Pharmacol. Toxicol. (1996) 78: 111 - 116]. In this method, the methanol extract of the oats under examination is reacted with DPPH^* radicals. As the reaction proceeds, the reduction of these DPPH" (l,l-diphenyl-2- picrylhydrazyl) radicals is detected spectrophotometrically at the wavelength between 515 and 517 nm on the bases of the decreasing absorbance. In this determination, pyrogallol (1,2,3-trihydroxybenzene) was used as the reference compound hav- ing a high radical capturing activity, as is generally known. The absorbance value obtained for pyrogallol now corresponds to a radical capturing activity of 100 %.

2.8 ml of DPPH solution (concentration of 4.5 mg/ 100 ml of methanol) was pipetted into a disposable cuvette and the absorbance was measured (= absorbance at zero moment). 200 μl of pyrogallol solution (reference solution) (concentration of 12.5 mg/100 ml of methanol) was pipetted in said cuvette and the measurement was started. The spectrophotometer was programmed to read the absorbance value every 15 seconds for 5 minutes. The measurement with pyrogallol was carried out 6 times. For each sample, three parallel measurements were made.

Determination of sterol content

The sterol content was determined with a method described by Piironen et al. in Natural Sources of Dietary Plant Sterols, J. Food Comp. Anal. (2000) (in print).

Extrusion

Germinated and dried oat grains having a high sensory quality may be ground and then extruded to obtain a crisp snack-like product having the desired sensory properties. The extruder may be a single screw extruder, or preferably a double screw extruder. Before extrusion the malted, crisp grains are ground with a suitable mill, for instance with a Wiley mill equipped with a 1 mm screen, hammer mill or a disc mill. The texture such as the firmness or the friability of the extrudate may be influenced by varying the moisture content of the oat malt feed, feed amount as well as by changing the screw configuration of the extruder. Sensory quality of malted, extruded oats

By comparing the sensory profiles of native extruded oats, and germinated, dried, and extruded oats, it was found that malting has a particularly favourable effect on the desired sensory properties such as the roasted character and intensity of the odour and taste, the nut-like taste, and the crispness of the texture. These properties were significantly weaker for the native extruded oats than for germinated, dried, and extruded oats. Also the oat variety has an influence on the sensory quality of extruded snack products, that is, the intensities of the desired sensory properties are in general weaker for hulless Lisbeth oats than for unhulled Veli oats.

Grains obtained with a suitable germinating/drying process that improves the taste and sensory quality may be used as such as components in different snack products. After the extrusion process, the friable extrudate may be roasted or coated with suit- able coating materials such as chocolate, yoghurt powder, cheese powder, or sugar. Lactic acid bacteria that are for instance encapsulated into coated potato starch may be added to this oat extrudate before coating, or to the coating material. Lactic acid bacteria encapsulated into potato starch are resistant to the gastric pH.

Example 1

The aroma composition of oats was modified by malting 25 kg batches of hulless Lisbeth oats and unhulled Veli oats in a pilot-scale malting apparatus using a shortened malting procedure for 2 + 10 + 2 hours at the temperature of 15 °C. The total germination time was 3 days. In both malting procedures, the following four different drying programs were tested: 65 - 85 °C, 65 - 93 °C, 65 - 100 °C, 30 - 50 °C.

With respect to sensory properties, best results were obtained with the drying program of 65 - 93 °C wherein the temperature was raised as follows: at 65 °C for 5 hours, raise to the temperature of 75 °C in 6 hours, at 75 °C for 2 hours, raise to the temperature of 85 °C in 4 hours, at 85 °C for 1 hour, raise to the temperature of 93 °C in 1 hour.

The strongest sensory properties were observed in oats treated with the drying program of 65 - 100 °C using the following temperatures: at 65 °C for 10 minutes, raise to the temperature of 100 °C in 30 minutes, at 100 °C for 4 hours. After malting, the β-glucan content of Lisbeth oats was lowered from that (4.8 %) of native oats, being however 3.2 %. Respectively, the β-glucan content of the malted Veli oats was lowered from 4.7 % to 3.2 %.

Example 2

Friable and crisp mouth feel is provided by extruding malted (total malting time being 3 days, drying program of 65 - 93 °C) ground Lisbeth oats with a Clextral BC-45 double screw extruder having 50 mm counter screw elements as the last screw pair upstream of the dies. In this double screw extruder, the water content of the feed was between 16 and 18 % at 135 to 140 °C.

Compared to this, a more solid and firmer texture was obtained by extruding ground malt having a water content of 19 to 25 % using a forward screw structure.

The β-glucan, plant sterol, antioxidant, and phenol contents of the malted oats remained nearly unchanged in the extrusion.

Example 3

Oat malt extrudate having the size of 2 to 20 mm obtained with the counter screw extrusion was coated in a coating drum with a molten yoghurt powder. The powder was pulverized at 40 °C on the extrudate being mixed on the bottom of the drum by the rotative movement thereof. After coating, the extrudate was cooled immediately using cold air cooling to the temperature of 5 °C. The yoghurt based mixture solidified on the extrudate comprised between 20 and 80 % of the total weight of the cereal.

Claims

1. Method for producing an oat product, characterized in that oat grains are submitted to a shortened malting comprising steeping, germination, and drying steps, fol- lowed by grinding of the dried grains and processing thereof using extrusion to obtain a cereal type product.

2. Method according to claim 1, characterized in that the germination of the oat grains is carried out in a liquid phase at a temperature below 20 °C for a period of time sufficient to allow the sterol and phenol contents, and the antioxidative capacity of the grains to be increased without a significant reduction of the β-glucan content thereof.

3. Method according to claim 2, characterized in that unhulled oats are malted.

4. Method according to claim 2, characterized in that hulless oats are malted.

5. Method according to any of the claims 2 - 4, characterized in that the steeping and germination temperature is about 15 °C.

6. Method according to any of the above claims, characterized in that the germination is allowed to proceed so as to attain a three-fold increase in the total sterol and phenol contents, and a higher antioxidative capacity.

7. Method according to any of the above claims, characterized in that the β-glucan content after malting is at least 3 %, preferably 3 to 5 %.

8. Method according to any of the above claims, characterized in that the steeping and germination time is no more than 3 days, preferably 2 to 3 days.

9. Method according to any of the above claims, characterized in that the steeping and germination are carried out using alternating shorter wet steeping cycles and longer dry steeping cycles, the total steeping and germination time being no more than 3 days.

10. Method according to any of the above claims, characterized in that the moisture content of the grains after germination is no more than about 35 %.

11. Method according to any of the above claims, characterized in that the drying is carried out to improve the sensory properties, preferably the roasted character and intensity of the odour and taste, the nut-like taste, and the crispness of the texture.

12. Method according to any of the above claims, characterized in that the drying is carried out at a temperature ranging from 65 to 100 °C, preferably at 93 °C.

13. Method according to any of the above claims, characterized in that the extrusion temperature is between 100 and 150 °C.

14. Method according to any of the above claims, characterized in that the moisture content of the oat malt in extrusion is 15 to 25 %.

15. Method according to any of the above claims, characterized in that the extruded oat cereal is coated with a tasty coating.

16. Oat cereal, characterized in that it is produced with a method comprising the following steps: shortened malting of oats comprising steeping, germination and drying steps, grinding, and extrusion.

17. Oat cereal according to claim 16, characterized in that it is produced with the method according to any of the claims 1 - 15.

18. Snack product, characterized in that it is produced from the oat cereal of claim 16 or 17 by coating with a yoghurt, cheese, chocolate, sugar or like food coating.